Micropaleontology [m.y. Ali, M.n. El-sabrouty, A.s. El-sorogy, 2015] (ksupress) @geo Pedia

IN THE NAME OF ALLAH, MOST GRACIOUS, MOST MERCIFUL

MICROPALEONTOLOGY

Dr. Mohamed Youssef Ali Associate Professor of Micropaleontology & Stratigraphy Department of Geology and Geophysics, College of Science King Saud University, Riyadh, Saudi Arabia South Valley University, Qena, Egypt

Dr. Mohamed N. El-Sabrouty Associate Professor of Palynology Department of Geology and Geophysics, College of Science King Saud University, Riyadh, Saudi Arabia

Prof. Abdelbaset S. El-Sorogy Professor of Paleontology and Stratigraphy Department of Geology and Geophysics, College of Science King Saud University, Riyadh, Saudi Arabia Zagazig University, Zagazig, Egypt

© King Saud University Press, 2015 King Fahd National Library Cataloging-in-Publication Data Ali, Mohamed Youseff Micropaleontology. / Mohamed Youseff Ali ; Mohamed N El-Sabrouty ; Abdelbaset S El-Sorogy .- Riyadh, 2015 134 p., 21 x 28 cm ISBN: 978-603-507-366-0 1- Paleontology I-Mohamed N El-Sabrouty (co. author) III-Title 564.80 dc

2- Fossils - Saudi Arabia II-Abdelbaset S El-Sorogy (co. auhtor)

1436/3659

L.D. No. 1436/3659 ISBN: 978-603-507-366-0

This book has been published based on the approval of the Academic Council of the University in its 16th session of the academic year 1434/1435 H., which was convened on 9-5-1435 H. (10-3-2014), after meeting the terms of scientific refereeing.

All publishing rights are reserved. No part of the book may be republished or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or via any storage or retrieval system, without written permission from King Saud University Press.

PREFACE

Micropaleontology is designed to be a primary textbook for college courses in the marine microfossils for students in the Arab countries. This book will deal with an introductory survey of the major groups of microfossils, including calcareous, siliceous, phosphatic and organic-walled types (Foraminifera, Ostracodes, Calcareous Nannofossils, Radiolaria, and Conodonts). The skeletal anatomy, biology, mode of life, and geologic history of these benthic and planktic, marine and nonmarine organisms will be reviewed. Applications of micropaleontology to interdisciplinary research in biostratigraphy, paleoecology, paleoceanography, paleoclimatology and environmental science will be featured. The specific goals of the Micropaleontology are:        

To identify the geologic range of the different fossil groups. To understand the general features of different group. To analyze the components of tests. To explain the basis of classification of the different fossil group. To identify the stratigraphic importance of the different fossil group. To understand the ecology and mode of life of the different group. To provide adequate principles for a foundation for graduate training in micropaleontology. To provide a sufficient base for graduates entering industry to apply micropaleontology to the solution of geologic problems.

In this book, we will deal with five major groups of microfossils that are important not only for biostratigraphy and paleoenvironments constructions, but also are applied in the hydrocarbon exploration in six chapters, each chapter followed by a series of questions that are added for the different chapters and in different styles to train the students for the micropaleontology exams. These groups of microfossils are:     

Foraminifera (small foraminifera and larger foraminifera). Ostracodes. Calcareous nannofossils. Radiolaria. Conodonts.

Chapter I gives an introduction to micropaleontology. Micropaleontology is the study of large numbers of taxonomically unrelated groups united solely by the fact that they must be examined with a microscope. Most marine microfossils are protists (unicellular plants and animals), but others are multicellular or microscopic parts of macroscopic forms. Thus, their grouping into one discipline remains essentially practical and utilitarian. Chapter II deals with the most important group of microfossils, foraminifera which are a diverse group of protists. 220 foraminiferal families and 25,000 species have been recognized. They range in size from microforaminiferans as small as 0.02 mm to giant forms which can be 110 mm or more. Chapter III is organized to explain larger foraminifera. Larger foraminifera are species from foraminifera that attain a large size more than 3 mm. They have complex internal morphologies. The numbers of large foraminifera include 40 families (Loeblish & Tappan, 1982). They are found both as fossils and in modern seas. The most abundant genus of larger foraminifera is Nummulites which is abundant in the limestone used by Egyptians to build the pyramids. v

Preface

Chapter IV is devoted to ostracods which are the most complex organisms studied within the field of micropalaeontology. They are Metazoa and belong to the Phylum Arthropoda, Class Crustacea. They are found today in almost all aquatic environments including hot springs, caves, within the water table, semi-terrestrial environments, in both fresh and marine waters, within the water column as well as on (and in) the substrate. Chapter V deals with calcareous nannofossils, which include the coccoliths and coccospheres of haptophyte algae and the associated nannoliths which are of unknown provenance. The organism which creates the coccosphere is called a coccolithophore, and they are phytoplankton (autotrophs that contain chloroplasts and photosynthesise). In Chapter VI, we try to give brief information about Radiolarian and Conodonts. Radiolaria are holoplanktonic protozoa and form part of the zooplankton. Conodont elements are phosphatic tooth-like structures whose affinity and function is now believed to be part of the feeding apparatus of an extinct early vertebrate. Chapter VII deals with the application of micropaleontology. One of the aims of micropaleontological studies is to resolve the geological history of the surface of the earth in a state that can be achieved, in relatively quick time and at the same time be economically being reasonable. The appendixes to the book include a glossary of the scientific terms used in the book chapters. The authors would like to thank many colleagues who have contributed to the emergence of this book, even by moral support. A special word of thanks goes to Dr. Hisham Ahmed Hussein, South Valley University, Egypt. We would like also to thank Mr. Khaled Mohamed, E-learning Center, South Valley University, Egypt for his help in the modification of some figures. Further Readings Bown, P.R. 1998. Calcareous Nannofossil Biostratigraphy. Kluwer Academic Publishers, 314 pp. Haq, B., and Boersma, A. (Eds.) 1977. Introduction to Marine Micropaleontology, Elsevier, Amsterdam, 376 pp. Lee, J.J & Anderson, O.R., (eds), 1991. Biology of foraminifera. Academic Press, London. Lipps, J.H. (ed.) 1993. Fossil Prokaryotes and Protists. Blackwell Scientific Publication, 342 pp. Loeblich, A. R. & Tappan, H., 1964. Part C. Protista 2. Chiefly “Thecamoebians and Foraminiferida. In: Moore, R.C. (ED.), Treatise on Invertebrate Paleontology. The Geological Society of America and the University of Kansas. Lawrence Kansas, 900 pp. Loeblich, A. R. & Tappan, H., 1987. Foraminiferal genera and their Classification. Van Nostrand Reinhold. 970 pp + 847 Pl. Loeblich, A. R. & Tappan, H., 1992. Present Status of Foraminiferal classification. In: Takayanagi, Y., & Saito, T. (eds) Studies in Benthic Foraminifera, Proceedings of the Fourth Intentional Symposium on benthic Foraminfera, Sendai, 1990. Tokai Univ. Press, 93-101. Murray, J. W., 1991. Ecology and Paleoecology of benthic foraminifera. Longman Scientific. 397 pp.

vi

Preface

Micropaleontological Journals 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Contributions from the Cuhman Laboratory for Foraminiferal Research (1925-1950). Contributions from the Cuhman Laboratory for Foraminiferal Research (1951-1973). Journal of Foraminiferal Research, Cushman Foundation (1973- present). Journal of Micropaleontology, the Micropaleontology Society (1982- present). Marine Micropaleontology, Elsevier, Netherlands (1976-present). Micropaleontology, Micropaleontology Press, N.Y. (1955- present). Revista Espanola de Micropaleontologia, Spain. Revue de Micropaleontologie, Elsevier, Netherlands. Revue de paleobiologie, Switzerland. British Micropaleontology Society Special Publications (chapman & Hall, Kluwer Acad Press). Cushman Foundation Special Publications (Washington, D.C.). Grzybowski Foundation Special Publications (Krakow, Poland). Internet Sites Related to Micropaleontology

             

http://www.ucl.ac.uk/GeolSci/micropal/welcome.html http://ead.univ-angers.fr/~geologie/atlas/Taxo.htm http://www.ucmp.berkeley.edu/alllife/eukaryotasy.html http://www.nhm.ac.uk/hosted_sites/ina/ http://services.chronos.org/foramatlas/pages/home.htm http://www.ucmp.berkeley.edu/foram/foramintro.html http://www.foraminifera.eu/ http://foraminifera.net/ http://www.ucmp.berkeley.edu/arthropoda/crustacea/maxillopoda/ostracoda.html http://www.gaultammonite.co.uk/pages/Ostracoda/Albian_Ostracoda.htm http://www.ucl.ac.uk/GeolSci/micropal/ostracod.html http://www.ucl.ac.uk/GeolSci/micropal/foram.html http://www.ucl.ac.uk/GeolSci/micropal/calcnanno.html http://userpage.fu-berlin.de/~palaeont/irgo/irgohome.html

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CONTENTS

Page Preface........................................................................................................................................................... v Chapter I: Introduction ............................................................................................................................... 1 Chapter II: Small Foraminifera ................................................................................................................. Introduction ........................................................................................................................................ History of the Study ............................................................................................................................ Application ......................................................................................................................................... Preparation Techniques....................................................................................................................... Observation Techniques ..................................................................................................................... Range .................................................................................................................................................. Living Foraminifera ............................................................................................................................ Biology ............................................................................................................................................... Life Cycle ........................................................................................................................................... Classification ...................................................................................................................................... Test Morphology ................................................................................................................................ Taxonomy ........................................................................................................................................... Ecology ............................................................................................................................................... Distribution of Recent Foraminifera ................................................................................................... Questions ............................................................................................................................................

7 9 9 9 10 11 12 12 13 13 14 15 21 24 27 30

Chapter III: Larger Foraminifera .............................................................................................................. Introduction ........................................................................................................................................ Classification ...................................................................................................................................... Questions ............................................................................................................................................

35 37 38 50

Chapter IV: Ostracoda ................................................................................................................................ Introduction ........................................................................................................................................ Classification ...................................................................................................................................... Description of Ostracoda .................................................................................................................... Ecology ............................................................................................................................................... Distribution of Marine Ostracodes...................................................................................................... Paleoecology ....................................................................................................................................... Questions ............................................................................................................................................

51 53 55 57 73 73 74 76

Chapter V: Calcareous NannoFossils......................................................................................................... 79 Introduction ........................................................................................................................................ 81

ix

Contents

History of the Nannoplankton Research ............................................................................................. Biology of the Organisms ................................................................................................................... Coccolith Shape Classification ........................................................................................................... Life Cycle (Reproduction, Nutrition and Growth) .............................................................................. Mineralogy of Coccolith ..................................................................................................................... Morphology of Coccolith.................................................................................................................... Function of Coccolith ......................................................................................................................... Major Morphologic Groups ................................................................................................................ Ecology ............................................................................................................................................... Biogeography...................................................................................................................................... Questions ............................................................................................................................................

82 82 84 86 87 87 89 91 100 100 101

Chapter VI: Radiolaria and Conodonts ..................................................................................................... Radiolaria............................................................................................................................................ Conodont ............................................................................................................................................ Questions ............................................................................................................................................

103 105 109 113

Chapter VII: Application of Micropaleontology ....................................................................................... Introduction ........................................................................................................................................ Different Microfossils Groups ............................................................................................................ Biostratigraphy ................................................................................................................................... Kinds of Biostratigraphic Units ..........................................................................................................

115 117 117 120 120

References ..................................................................................................................................................... 125 Glossary ........................................................................................................................................................ 127 Subject Index ................................................................................................................................................ 133

x

LIST OF FIGURES

Page Fig. 1. Stratigraphic distribution of the major marine microfossil groups ..................................................... Fig. 2. Division of the marine environment ................................................................................................... Fig. 3. Material necessary for dealing with Foraminifera .............................................................................. Fig. 4. Binocular zoom stereomicroscope ...................................................................................................... Fig. 5. Geologic time scale based on Harland et al. (1989) ........................................................................... Fig. 6. A living planktonic foraminifera ........................................................................................................ Fig. 7. Life cycle of foraminifera (simplified) ............................................................................................... Fig. 8. Foraminiferal suborders and their envisaged phylogeny .................................................................... Fig. 9. Agglutinated wall structure ................................................................................................................. Fig. 10. Examples of agglutinated wall structure ........................................................................................... Fig. 11. Calcareous hyaline wall structure ..................................................................................................... Fig. 12. Examples of calcareous hyaline wall structure ................................................................................. Fig. 13. The optical axis orientation in porcelaneous test .............................................................................. Fig. 14. Examples of calcareous poreclenaeous wall structure ...................................................................... Fig. 15. Chamber shape and arrangement in foraminifera ............................................................................. Fig. 16. Principle type of chamber arrangement ............................................................................................ Fig. 17. Some chamber arrangements in foraminifera ................................................................................... Fig. 18. Principle types of aperture ................................................................................................................ Fig. 19. Some types of sculpture in foraminifera ........................................................................................... Fig. 20. Habitats of foraminifera .................................................................................................................... Fig. 21. Depth distribution of recent benthic foraminifera ............................................................................. Fig. 22. Distribution of larger benthic foraminifera ....................................................................................... Fig. 23. Zoogeographical planktonic foraminiferal provinces ....................................................................... Fig. 24. Trends in bathymetry and fossil content of sediments from the shelf to the abyssal environments ....................................................................................................................... Fig. 25. Distribution of foraminifera from the shelf to the abyssal environments ......................................... Fig. 26. Fusulinellid wall ............................................................................................................................... Fig. 27. Schwagrinid wall .............................................................................................................................. Fig. 28. Types of septa ................................................................................................................................... Fig. 29. Types of sections in Fusulina and Schwagerina ............................................................................... Fig. 30. Genus Fusulina ................................................................................................................................. Fig. 31. Genus Schwagerina .......................................................................................................................... Fig. 32. Family Neoschwageriniodae............................................................................................................. Fig. 33. Wall structure in Alveolonidae ......................................................................................................... Fig. 34. Praealveolina..................................................................................................................................... Fig. 35. Septa, septum in the Nummulitidae .................................................................................................. Fig. 36. Septal filaments in Nummulitidae .................................................................................................... Fig. 37. Granules in Nummulitidae ................................................................................................................ xi

3 4 11 11 12 13 14 14 15 16 16 16 17 17 18 18 19 20 20 24 25 25 26 28 29 38 38 39 40 41 41 42 42 43 43 44 44

List of Figures

Fig. 38. Equatorial section in Nummulitidae ................................................................................................. Fig. 39. Tight and lax spire coiling in Nummulitidae .................................................................................... Fig. 40. Axial section in Nummulitidae ......................................................................................................... Fig. 41. Two types of sections in Nummulitidae ........................................................................................... Fig. 42. Shapes of the equatorial chamber in Orbitoididae ............................................................................ Fig. 43. Axial section of Orbitoididae ............................................................................................................ Fig. 44. Orbitoides ......................................................................................................................................... Fig. 45. Axial section in Orbitoides ............................................................................................................... Fig. 46. Genus: Lepidocyclina ....................................................................................................................... Fig. 47. Axial section in Lepidocyclina.......................................................................................................... Fig. 48. Axial section of Discocyclina ........................................................................................................... Fig. 49. Type of hinges in Ostracoda ............................................................................................................. Fig. 50. Types of muscles in Ostracoda ......................................................................................................... Fig. 51. Orientation of the carapace ............................................................................................................... Fig. 52. Maximum length, height and width of ostracoda.............................................................................. Fig. 53. Outline of the carapace in the lateral view ........................................................................................ Fig. 54. Outline of the carapace in the lateral view (continued) .................................................................... Fig. 55. Outline of the carapace in the lateral view (continued) .................................................................... Fig. 56. Outline of the carapace in the lateral view (continued) .................................................................... Fig. 57. Maximum height of the carapace ...................................................................................................... Fig. 58. Maximum length of the carapace ...................................................................................................... Fig. 59. Dorsal margin ................................................................................................................................... Fig. 60. Ventral margin .................................................................................................................................. Fig. 61. Overhanging valves .......................................................................................................................... Fig. 62. Anterior margin end of the carapace ................................................................................................. Fig. 63. Posterior margin end ......................................................................................................................... Fig. 64. Outline of the carapace in “dorsal view” .......................................................................................... Fig. 65. Outline of the carapace in “dorsal view” (continued) ....................................................................... Fig. 66. Outline of the carapace in “dorsal view” (continued) ....................................................................... Fig. 67. Thickness of the carapace in dorsal view.......................................................................................... Fig. 68. Outline of the carapace in “dorsal view” (continued) ....................................................................... Fig. 69. Types of ribs according to their development ................................................................................... Fig. 70. Types of ridges ................................................................................................................................. Fig. 71. Types of inflation according to its position ...................................................................................... Fig. 72. Types of inflation according to its position ...................................................................................... Fig. 73. Shape of opening .............................................................................................................................. Fig. 74. Size of opening ................................................................................................................................. Fig. 75. Arrangement of opening ................................................................................................................... Fig. 76. Diagram illustrating the ecological distribution of recent ostracoda ................................................ Fig. 77. Coccosphere...................................................................................................................................... Fig. 78. Living cell ......................................................................................................................................... Fig. 79. Component of the living cell............................................................................................................. Fig. 80. Early stage of coccolith formation in E. huxleyi ............................................................................... Fig. 81. Shape of coccolith............................................................................................................................. Fig. 82. Shape of coccolith (continued) ......................................................................................................... Fig. 83. Coccolithophorid life cycle ............................................................................................................... Fig. 84. Mineralogy of coccolith .................................................................................................................... xii

45 45 45 46 46 46 47 47 47 48 48 54 55 58 59 60 60 61 61 62 62 62 63 63 63 64 65 66 67 67 68 69 70 71 71 72 72 73 75 81 83 83 84 85 86 86 87

List of Figures

Fig. 85. Heterococcolith ................................................................................................................................. Fig. 86. Holococcolith .................................................................................................................................... Fig. 87. Protection-related functions of coccolith .......................................................................................... Fig. 88. Biochemical functions of coccolith .................................................................................................. Fig. 89. Flotation-related functions of coccolith ............................................................................................ Fig. 90. Light regulation functions of coccolith ............................................................................................. Fig. 91. Morphology of coccolith .................................................................................................................. Fig. 92. Morphology of Discoaster ................................................................................................................ Fig. 93. Arkangelskiella ................................................................................................................................. Fig. 94. Genus: Broinsonia ............................................................................................................................ Fig. 95. Genus: Watznauria ........................................................................................................................... Fig. 96. Coccolithaceae (Cruciplacolithus, Chiasmolithus, and Coccolithus) ............................................... Fig. 97. Genus: Prinsius ................................................................................................................................. Fig. 98. Genus: Toweius ................................................................................................................................. Fig. 99. Genus: Gephyrocapsa ....................................................................................................................... Fig. 100. Genus: Emiliana ............................................................................................................................. Fig. 101. Pontosphaera, Transversopoints, Lophodolithus, and scyphosphaera ........................................... Fig. 102. Genus: Braarudosphaera ................................................................................................................ Fig. 103. Genus: Ceratolithus ........................................................................................................................ Fig. 104. Discoaster multiradiatus................................................................................................................. Fig. 105. Discoaster mirus ............................................................................................................................. Fig. 106. Discoaster lodoensis ....................................................................................................................... Fig. 107. Tribrachitus orthostylus .................................................................................................................. Fig. 108. Genus: Fasciculthus........................................................................................................................ Fig. 109. Heliolithus....................................................................................................................................... Fig. 110. Sphenolithus.................................................................................................................................... Fig. 111. Thoracosphaera .............................................................................................................................. Fig. 112. Genus: Microrhabdulus .................................................................................................................. Fig. 113. Genus: Micula ................................................................................................................................. Fig. 114. Genus: Nannoconus ........................................................................................................................ Fig. 115. Radiolaria (cross-sections) .............................................................................................................. Fig. 116. Basic morphological features of radiolarian (nassellarian) ............................................................. Fig. 117. Some images of Radiolaraia ........................................................................................................... Fig. 118. The morphological terminology of conodont ................................................................................. Fig. 119. Some images of Conodont .............................................................................................................. Fig. 120. Biosteering in a horizontal well ...................................................................................................... Fig. 121. Benthic foraminiferal species ......................................................................................................... Fig. 122. Planktonic foraminiferal species ..................................................................................................... Fig. 123. Calcareous nannofossils species ..................................................................................................... Fig. 124. Palynomorphs: Oligosphaeridium (left) and Chlamydophorella nyei (right) ................................. Fig. 125. Taxon-range zone ........................................................................................................................... Fig. 126. Concurrent-range zone .................................................................................................................... Fig. 127. Interval zone ................................................................................................................................... Fig. 128. Interval (highest-occurrence zone) zone ......................................................................................... Fig. 129. Examples of lineage zones .............................................................................................................. Fig. 130. Assemblage zone ............................................................................................................................ Fig. 131. Abundance zone.............................................................................................................................. xiii

88 88 89 90 90 91 92 92 93 93 94 94 95 95 95 95 96 96 96 97 97 97 98 98 98 98 99 99 99 100 107 107 108 110 112 118 118 119 119 120 121 121 122 122 123 124 124

CHAPTER I INTRODUCTION

CHAPTER I

INTRODUCTION

Micropaleontology is the study of microscopic fossils, which includes the study of large numbers of taxonomically unrelated groups that only unite by the fact that they must be examined with a microscope. Most marine microfossils are protists (unicellular plants and animals), but others are multicellular or microscopic parts of macroscopic forms. The practical value of marine microfossils in various fields of historical geology is enhanced by their minute size, abundant occurrence and wide geographic distribution in sediments of all ages and in almost all marine environments. Micro-organisms at the base of the food chain make up nearly 90% of the biomass in oceans and lakes. Due to their small size and large numerical abundance, relatively small sediment samples can usually yield enough data for the application of more rigorous quantitative methods of analysis. Moreover, most planktonic and many benthic microfossils have wide geographic distributions that make them indispensable for regional correlations and comparisons, and paleooceanographic reconstructions. The limestone of the plateau, from which the Sphinx and Pyramids are carved, is actually a mass of foraminifera (Nummulites), preserved in a vast offshore formation that, 40 million years ago. Marine microfossils occur in sediments of Precambrian to Recent ages (Fig. 1), and in every part of the stratigraphic column one or more groups can always be found useful for biostratigraphic and paleoecologic interpretations.

Fig. 1. Stratigraphic distribution of the major marine microfossil groups (after Haq & Boersma, 1998).

3

4

Micropaleontology

Fossil marine organisms have lived in almost all marine areas; Neritic (littoral) province (inner, middle and outer) up to 200 m, Bathyal (Oceanic) province (upper, middle and lower) up to 2000 m, and Abyssal (Oceanic) province up to 5000 m (Fig. 2). The marine microfossils are invaluable in the study of changes in the paleoenvironments. For instance, radiolaria, silicoflagellates, calcareous nannoplankton, pteropods, and some foraminifera and diatoms are planktonic (i.e., free floating) and live in abundance from 0 to 200 m in the open ocean, but diminish rapidly near the continents. These forms are useful in monitoring past changes in the oceanic environments, particularly changes in temperature. Other groups such as the ostracodes, bryozoa, and some foraminifera and diatoms are benthic (i.e., adapted to living on the bottom of the sea), as either mobile or sessile organisms.

Fig. 2. Division of the marine environment.

Microfossils are indispensable to oil exploration. Because of their minute size and great abundance, they occur completely in the rock fragments brought up by drilling into the deeply buried ocean formations and lake beds where oil is found. By comparing the characteristic fossils from each formation as they are penetrated by the exploratory drills, geologists can unravel the geometry of the strata far beneath the surface and locate the domes and traps that may hold oil. The condition of the fossils, as well, indicates whether the petroleum source rocks have been buried and heated sufficiently to generate oil from trapped organic matter. Most importantly of all, the organic matter itself is almost entirely from ancient micro-organisms that make up the ocean’s biomass. (Diatoms, as at left, are important trace fossils as well as the primary source of oil.). Most of the principal microfossil groups are Protista. These are single-celled or colonial Eukaryotes (i.e., organisms with cell nuclei and chromosomes), that are more advanced than Prokaryotes (archaea and bacteria), while being ancestral to higher eukaryotes such as fungus, plants and animals. The foraminifera and radiolaria are two orders of predatory (i.e., non-vegetative) protists, related to amoeba in the Sarcodina, that secrete multichambered limy and siliceous shells, respectively. Vegetative (photosynthesizing) protists with fossilizing hard parts include coccoliths, with complex structures (as in the coccolith at the right, and on our splash panel) that break down into submicroscopic but readily identifiable limy disks and stars, and the diatoms, with singlechambered circular or ovoid valves of silica that fit together like pillboxes. The dinoflagellates and their extinct relative’s acritarchs, with whip-like propulsive flagella and chitinous body casing, are both predatory and

Introduction

5

photosynthesizing; they are represented in the fossil record by the cysts that they make during one part of their life cycle. Important groups of microfossils are also found among animals and plants, for instance the ostracodes, tiny free-swimming crustaceans in the same family as barnacles. Spores and pollen from fungi and plants give important paleonvironmental data. In ancient strata conodonts, the teeth of an extinct group of soft-bodied invertebrates are important stratigraphical guides, and icthyoliths, or fish teeth, are used for deep-sea dating.

CHAPTER II SMALL FORAMINIFERA

      

Kingdom: Protista Subkingdom: Protozoa Phylum: Sarcomastigophora Subphylum: Sarcodina Superclass: Rhizopoda Class: Granuloreticulosea Order: Foraminiferida (foraminifera)

CHAPTER II

SMALL FORAMINIFERA

Introduction The order foraminiferida (or foraminifera as they are informally called) form the most important group of microfossils for two reasons: first, they are abundant in rocks and there are numerous species; second they provide valuable information about the dating of strata and the reconstruction of sedimentary environments. Foraminifera are an order of single-celled protists that live either on the sea floor or amongst the marine plankton. The soft tissue (protoplasm) of the foraminifera cell is largely enclosed within a shell (test) variously composed of secreted minerals (calcite, aragonite or silica) or of agglutinated particles. This test consists of a single chamber or several chambers mostly less than 1 mm across and each is interconnected by an opening (foramen) or several openings (foramina). Foraminifera are known from early Cambrian times through to Recent times, however the molecular biology and recent fossil discoveries place their origin in the Late Precambrian. Foraminifera are found in all marine environments, and they may be planktonic or benthic in mode of life. The generally accepted classification of the foraminifera is based on that of Loeblich and Tappan (1964, 1992). Unpicking this nomenclature tells us that foraminifera are testate (that is possessing a shell), protozoa, (single celled organisms characterized by the absence of tissues and organs), which possess granuloreticulose pseudopodia (these are thread-like extensions of the ectoplasm often including grains or tiny particles of various materials). History of the Study The study of foraminifera has a long history; their first recorded “mention” is in Herodotus (fifth century BC) who noted that the limestone of the Egyptian pyramids contained small lentil-like objects turn out to be the large benthic foraminifer Nummulites. In 1835, Dujardin recognized foraminifera as protozoa and shortly afterwards d’Orbigny produced the first classification. The famous 1872 HMS Challenger cruise, the first scientific oceanographic research expedition to sample the ocean floor, collected so many samples that several scientists, including foraminiferologists such as H.B. Brady were still working on the material well into the 1880s. Work on foraminifera continued throughout the 20th century, and workers such as Cushman in the USA and Subbotina in the Soviet Union developed the use of foraminifera as biostratigraphic tools. Later in the 20th century, Loeblich, Tappan and Bolli carried out much pioneering work. The books by Loeblish & Tappan (1986, 1987) are the most useful for taxonomy and nomenclature. Applications As previously mentioned, foraminifera have been utilized for biostratigraphy for many years, and they have also proven invaluable in palaeoenvironmental reconstructions, most recently for palaeoceanographical and palaeoclimatological purposes (e.g., palaeobathymetry, where assemblage composition is used, and palaeotemperature, where isotope analysis of foraminifer tests is a standard procedure). In terms of 9

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Micropaleontology

biostratigraphy, foraminifera have become extremely useful, different forms have shown evolutionary bursts at different periods, and generally if one form is not available to be utilized for biostratigraphy, another is. For example, the preservation of calcareous walled foraminifera is dependent on the depth of the water column and Carbonate Compensation Depth (CCD) (the depth below which dissolution of calcium carbonate exceeds the rate of its deposition), and if calcareous walled foraminifera are therefore not preserved, agglutinated forms may be. The oldest rocks for which foraminifera have been biostratigraphically useful are Upper Carboniferous to Permian strata, which have been zoned using the larger benthic fusulinids. Planktonic foraminifera have become increasingly important biostratigraphic tools, especially as petroleum exploration has extended to offshore environments of increasing depths. The first and last occurrence of distinctive “marker species” from the Cretaceous to Recent (particularly during the Upper Cretaceous) has allowed the development of a well established fine scale biozonation. Benthic foraminifera have been used for palaeobathymetry since the 1930s and modern studies utilize a variety of techniques to reconstruct palaeodepths. For studies of relatively recent deposits, a simple comparison to the known depth distribution of modern extant species is used. For older material changes in species diversity, planktonic to benthic ratios, shell-type ratios and test morphology have all been utilized. Variations in the water temperature inferred from oxygen isotopes from the test calcite can be used to reconstruct palaeoceanographic conditions by careful comparison of changes in oxygen isotope values as seen in benthic forms (for bottom waters) and planktonic forms (for mid to upper waters). This type of study has allowed the reconstruction of oceanic conditions for the whole Cenozoic (Zachos et al., 2001). Benthic foraminifera have been divided into morphogroups based on the test shape and these groups used to infer palaeo-habitats and substrates (Corliss & Chen, 1988); infaunal species tending to be elongate and streamlined in order to burrow into the substrate, and epifaunal species tending to be more globular with one relatively flatter side in order to facilitate movement on top of the substrate. It should be remembered, however, that a large variety of morphologies and possible habitats have been recognized making such generalizations of only limited use. Studies of modern foraminifera have recognized correlations between test wall type (for instance porcelaneous, hyaline, agglutinated), palaeodepths and salinity by plotting them onto triangular diagrams (Murray, 1973). Preparation Techniques Foraminifera range in size from several millimeters to a few tens of microns and are preserved in a variety of rock types. The preparation techniques used depend on the rock type and the “predicted” type of foraminifera one expects to find. Very hard rocks such as many limestones are best thin sectioned as in normal petrological studies, except instead of grinding to a set thickness (commonly 30 microns) the sample is ground very carefully by hand until the optimum thickness is obtained for each individual sample. This is a skilled job and requires expensive equipment but provides excellent results and is particularly used in the study of larger benthic foraminifera from reef type settings. Planktonic and smaller benthic foraminifera are prepared by crushing the sample into roughly fivemillimeter fragments. The crushed sample is then placed on a strong glass beaker or similar vessel and water and washing soda or 6% hydrogen peroxide added, left to stand and then heated and allowed to simmer. The length of time the sample is left to simmer depends on the rock type involved and if peroxide is used the sample should not be left immersed in the solution for more than about half an hour. Next, the material is washed through a 63micron sieve until the liquid coming through the sieve is clean (i.e., the clay fraction has been removed). The sample can then be dried and sieved into fractions (generally 63-125 microns, 125-250 microns, 250-500 microns and greater than 500 microns) using a “nest” of dry sieves. Care must be taken to clean all sieves and materials used between the preparations of each sample to prevent contamination (Fig. 3).

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Fig. 3. Material necessary for dealing with Foraminifera.

Observation Techniques

Fig. 4. Binocular zoom stereomicroscope.

Thin sections are viewed using transmitted-light petrological type microscopes (Fig. 4). Washed, dried fossil samples can be picked from any remaining sediment using a fine brush and a reflected light, binocular microscope. The best method is to scatter a fine dusting of sieved sediment on to a black tray divided into squares, and this can then be scanned under the microscope and any foraminifera preserved in the sediment can be picked out with a fine brush (preferably a 000 sable-haired brush). The picked specimens can then be mounted on card slides divided into numbered squares with sliding glass covers. Gum tragocanth was traditionally used to attach the specimens to the slides, but modern office-type paper adhesives are now used.

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Fig. 5. Geologic time scale based on Harland et al. (1989).

Range Foraminifera have a geological range from the latest Precambrian to the present day. The earliest forms which appear in the fossil record (the allogromiine) had organic test walls or are simple agglutinated tubes. The term “agglutinated” refers to the tests formed from foreign particles “glued” together with a variety of cements. Foraminifera with biomineralized tests are scarce until the Devonian, during which period the fusulinids began to flourish culminating in the complex fusulinid tests of the late Carboniferous and Permian times; the fusulinids died out at the end of the Palaeozoic. The miliolids first appeared in the early Carboniferous, followed in the Mesozoic by the appearance and radiation of the rotaliids and other calcareous groups. The earliest forms are all agglutinated benthic. Planktonic forms do not appear in the fossil record until the Early Jurassic in the strata of the northern margin of Tethys and epicontinental basins of Europe. They were probably meroplanktonic (planktonic only during late stages of their life cycle). The high sea levels and “greenhouse” conditions of the Cretaceous saw a diversification of the planktonic foraminifera, and the major extinctions at the end of the Cretaceous included many planktonic foraminifera forms. A rapid evolutionary burst occurred during the Palaeocene with the appearance of the planktonic globigerinids and globorotalids and also in the Eocene with the large benthic foraminifera belonging to the nummulites, alveolinids and orbitoids. The orbitoids died out in the Miocene, since which time the large foraminifera have dwindled. The diversity of planktonic forms has also generally declined since the end of the Cretaceous with brief increases during the warm climatic periods of the Eocene and Miocene (Fig. 5). Living Foraminifera Foraminifera are unicellular organisms belonging to the rhizopod protozoa (protista). Their protoplasm, differentiated into endoplasm and ectoplasm, is emitted in the form of retractile pseudopodia, which are granular, anatomizing filaments. These are used in catching prey (Fig. 6).

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Fig. 6. A living planktonic foraminifera (from Stanley, 1993).

Biology Studies of living foraminifera, in controlled laboratory environments, have provided limited information regarding trophic strategies, but much has been inferred by relating test morphology to habitat. Foraminifera utilize a huge variety of feeding mechanisms, as evidenced by the great variety of test morphologies that they exhibit. From the variety of trophic habits and test morphologies, a few generalizations may be made. Branching benthic foraminifera such as Notodendrodes antarctikos, which resembles a microscopic tree, absorbs dissolved organic matter via a “root” system. Other sessile benthic foraminifera exhibit test morphologies dependent on the substrate on or in which they live, many are omnivorous opportunistic feeders and have been observed to consume autotrophic and heterotrophic protists (including other foraminifera), metazoans and detritus. Some suspension feeding foraminifera utilize their pseudopodia to capture food from the water column, or interstitial pore waters, Elphidium crispum forms a “spider’s web” between the stipes of coralline algae. Infaunal forms are probably detritivores and commonly have elongate tests to facilitate movement through the substrate. Benthic and planktonic foraminifera that inhabit the photic zone often live symbiotically with photosynthesising algae such as dinoflagellates, diatoms and chlorophytes. It is thought the large benthic, discoidal and fusiform foraminifera attained their large size in part because of such associations. Foraminifera are preyed upon by many different organisms including worms, crustacea, gastropods, echinoderms, and fish. It should be remembered that the biocoenosis (life assemblage) will be distorted by selective destruction by predators. Life Cycle Of the approximately 4000 living species of foraminifera, the life cycles of only 20 or so are known. There is a great variety of reproductive, growth and feeding strategies. However, the alternation of sexual and asexual generations is common throughout the group and this feature differentiates the foraminifera from other members of the Granuloreticulosea. An asexually produced haploid generation commonly forms a large proloculus (initial chamber) and are therefore termed megalospheric (Fig. 7). Sexually produced diploid generations tend to produce a smaller proloculus and are therefore termed microspheric. Importantly in terms of the fossil record, many foraminiferal tests are either partially dissolved or partially disintegrate during the reproductive process. The planktonic foraminifera Hastigerina pelagica reproduces by gametogenesis at depth, the spines, septa and apertural region are resorbed leaving a tell-tale partially dissolved test. Globigerinoides sacculifer produces a sac-like final chamber and additional calcification of later chambers before dissolution of spines occurs, this again produces a distinctive test, which once gametogenesis is complete the test sinks to the sea bed.

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Fig. 7. Life cycle of foraminifera (simplified).

Classification In the widely used scheme of Loeblish & Tappan (1992) Foraminifera are classified primarily on the composition and morphology of the test. Three basic wall compositions are recognised, organic (protinaceous mucopolysaccharide i.e. the allogromina), agglutinated and secreted calcium carbonate (or more rarely silica). Agglutinated forms, i.e the Textulariina, may be composed of randomly accumulated grains or grains selected on the basis of specific gravity, shape or size; some forms arrange particular grains in specific parts of the test. Secreted test foraminifera are again subdivided into three major groups, microgranular (i.e. Fusulinina), porcelaneous (i.e. Miliolina) and hyaline (i.e. Rotalina, Lagenina, Globigerinina). Microgranular walled forms (commonly found in the late Palaeozoic) are composed of equidimensional subspherical grains of crystalline calcite. Porcelaneous forms have a wall composed of thin inner and outer veneers enclosing a thick middle layer of crystal laths, hey made from high magnesium calcite (Fig. 8).

Fig. 8. Foraminiferal suborders and their envisaged phylogeny (redrawn from Tappan and Loeblich, 1988). Among the suborders shown only the Fusulinina are extinct.

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The hyaline foraminifera add a new lamella to the entire test each time a new chamber is formed; various types of lamellar wall structure have been recognized, and the wall is penetrated by fine pores and hence termed perforate. A few “oddities” are also worth mentioning. The Suborder Spirillinina has a test constructed of an optically single crystal of calcite, the Suborder Silicoloculinina as the name suggests has a test composed of silica. Another group (the Suborder Involutina) have a two-chambered test composed of aragonite. The Robertinina also have a test composed of aragonite and the Suborder Carterina is believed to secrete spicules of calcite which are then weakly cemented together to form the test, although this group is placed in the agglutinated textulariina in the updated classification of Kaminski (2004). Test Morphology Foraminifera are animals which build a shell; and for paleontologists the characteristics of the shell are the primary features which can be used to distinguish one species from another. Wall structure The most readily obvious feature distinguishing one foraminifer from another is its wall type. Whether the foraminifer builds its test wall by cementing together exogenous grains, by carbonate mineralization, or by some combination of these two processes separates the three primary foraminiferal groups, the agglutinated, the calcareous, and the microgranular foraminifera. Agglutinated wall structure (Fig. 10) In these, organic and mineral matter from the sea floor is bound together by an organic, calcareous or ferric oxide cement. The grains are commonly selected for size, texture or composition (e.g., coccoliths, sponge, spicules and heavy minerals). Other agglutinated forms are non-selective and will employ any particle from a substrate as long as it lies in the appropriate size range (Fig. 9).

Fig. 9. (1) Agglutinated test with compact wall: agg = agglutinated; c = cement; cb = chitinoid basal layer. (2) Agglutinated test with alveolar wall: ramified and unramified alveoli opening towards the interior of the test.

Microgranular walls Microgranular walls evolved during the Paleozoic and are considered the link between the agglutinated and the precipitated tests in foraminifera. Microgranular particles of calcite cemented by a calcareous cement characterize this wall type and give it a sugary appearance.

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Fig. 10. Examples of agglutinated wall structure.

Calcareous walls, hyaline type (Fig. 12) Calcareous wall may be composed of either low or high Mg calcite, or aragonite which is confined to only two foraminiferal families. Hyaline calcareous tests are characterized by the possession of minute perforations in the test wall. The calcareous hyaline is generally glassy (hyaline) when viewed with reflected light and grey to clear in transmitted light (Fig. 11).

Fig. 11. Calcareous hyaline wall structure.

Fig. 12. Examples of calcareous hyaline wall structure.

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Calcareous walls, porcelaneous type (Fig. 14) The term porcelaneous derives from the shiny, smooth appearance of the tests and is the result of the orientation of submicroscopic crystalline elements that may be randomly arranged or organized in brick-like patterns, but both patterns give the test a smooth, opaque appearance (milky white) in polarized light. Both in shallow-marine and in deeper environments porcelaneous tests are often composed of calcite with high proportion of Mg (Fig. 13).

Fig. 13. The optical axis orientation in porcelaneous test.

Fig. 14. Examples of calcareous poreclenaeous wall structure.

Chamber shape and chamber arrangement Foraminiferal tests may possess one or more chambers. The initial chamber is most often spherical or oblate with an aperture. Later chambers range in shape from tubular, spherical, ovate to several others. Additional chambers are added in a variety of patterns termed chamber arrangements (Figs. 15 and 16): 1. 2. 3. 4. 5. 6.

Uniserial: The chamber is arranged in a single row; if it forms a curved row, it is termed arcute; if a straight series, it is termed rectilinear. Biserial: The chambers arranged in a double row. Triserial: Chambers are added every 120° in a spiral fashion. Polyserial: The chambers are arranged in a multiple row. Planispiral: The chamber is arranged spirally around an axis of coiling and the spiral lies in a single plane. Trochospiral: When the spiral does not lie in one plane, but progresses up the axis of coiling, and the chamber arrangement becomes helicoidal.

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Fig. 15. Chamber shape and arrangement in foraminifera.

Fig. 16. Principle type of chamber arrangement. (1) Single chambered. (2) Uniserial. (3) Biserial. (4) Triserial. (5) Planispiral to biserial. (6) Milioline. (7) Planispiral evolute. (8) Planispiral involute. (9) Streptospiral. (10-12) Trochospiral (10, dorsal view; 11, edge view; 12, ventral view). Redrawn from Loeblich and Tappan (1964).

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7.

19

The Miliolidae have a streptospiral arrangement. The arched chambers, tangential at their two extremities with the extension axis, are arranged in cycles of five, three or two planes of coiling, or may be planispiral or single chambered. Each new chamber has its aperture facing the aperture of the preceding chamber.

Fig. 17. Some chamber arrangements in foraminifera.

When a series of chambers is arranged spirally or coiled about an axis, the chambers involved in one complete revolution are termed a whorl or coil. The degree to which one whorl covers, or hides a previous one, is known as the degree of involution. Where the majority of the previous coils are hidden, a species is termed involute, while it is evolute if the majority of the previous coils are visible. On a coiled test the side of the foraminifer showing the trace of the coil, or spiral, is termed the spiral side. The opposite side is termed the umbilical side. The umbilicus, the axial space between the inner wall margins of the chambers belonging to the same coil, may not necessarily be present. The area where one chamber meets another is the suture area and represents the line of junction projected to the surface of the test (Fig. 17). Apertures and openings The aperture is the primary opening of the test to the outside environment. Apertures vary in size and shape and the shape is most often a function of the shape of the chamber on which they are located. The aperture is found in the wall of the final chamber and serves to connect the external pseudopodia with the internal endoplasm, allowing passage of food and contractile vacuoles, nuclei and release of the daughter cells. Aperture may be single or multiple in number and terminal, areal, basal extraumbilical, umbilical or sutural in position. Their shape varies widely (e.g., rounded, bottle-necked (phialine), radiate, dendritic, sieve-like (cribrate), circular form, slit- or loop-shaped) (Fig. 18). Sculpture The external surface of the test may bear spines (termed spinose), keels (carinate), rugae (rugose), fine striae (striate), coarser costae (costate), granules (granulate), Nodose, Reticulate (Fig. 19).

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Fig. 18. Principle types of aperture. (1) Open end of tube. (2) Terminal radiate. (3) Terminal slit; umbilical. (5) Loop shaped. (6) Interiomarginal. (7) Interiomarginal multiple. (8) Areal cribrate. (9) With phialine lip. (10) With bifid tooth. (11) With umbilical teeth. (12) With umbilical bulla. Redrawn from Loeblich and Tappan (1964).

Fig. 19. Some types of sculpture in foraminifera. (A) Costate. (B) Spinose. (C) Nodose. (D) Carinate. (E) Reticulate.

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Taxonomy Suborder: Allogromiina Loeblich and Tappan, 1961 Suborder: Textulariina Delage & Herouard, 1896 Superfamily: Hormosinacea Haeckel, 1894 Family: Hormosinidae Haeckel, 1894 Subfamily: Reophacinae Cushman, 1919 Superfamily: Lituolacea de Blainville, 1827 Family: Haplophragmoididae Maync, 1952 Suborder: Fusulinina Wedekind 1937 Superfamily: Parathuramminacea Bykova, 1955 Superfamily: Earlandiacea Cummings, 1955 Superfamily: Archaediscacea Cushman 1928 Superfamily: Moravamminacea Pokorny, 1951 Superfamily: Nodosinellacea Rhumbler, 1895 Superfamily: Ptychocladiacea Elias, 1950 Superfamily: Endothyracea Brady, 1884 Superfamily: Tetrataxacea Galloway, 1933 Superfamily: Fusulinacea von Moeller, 1878 Suborder: Involutinina Hohenegger & Piller, 1977 Suborder: Spirillinina Hoheneger & Piller, 1975 Family: Spirillinidae Reuss & Fritsch, 1861 Suborder: Miliolina Delage & Hérouard, 1896 Superfamily: Cornuspiracea Schultze, 1854 Family: Cornuspiridae Schultze, 1854 Subfamily: Cornuspirinae Schultze, 1854 Superfamily: Miliolacea Ehrenberg, 1839 Family: Spiroloculinidae Wiesner, 1920

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22 Family: Hauerinidae Schwager, 1876 Subfamily: Siphonapertinae Saidova, 1975 Subfamily: Hauerininae Schwager, 1876 Subfamily: Miliolinellinae Vella, 1957

Suborder: Lagenina Delage & Hérouard, 1896 Superfamily: Nodasariacea Ehrenberg, 1838 Family: Vaginulinidae Reuss, 1860 Subfamily: Lenticulininae Chapman, Parr & Collins, 1934 Subfamily: Marginulininae Wedekind, 1937 Family: Lagenidae Reuss, 1862 Family: Polymorphinidae d’Orbigny, 1839 Subfamily: Polymorphininae d’Orbigny, 1839 Family: Ellipsolagenidae Silvestri, 1923 Subfamily: Oolininae Loeblich & Tappan, 1961 Subfamily: Ellipsolageninae Silvestri, 1923 Subfamily: Parafissurininae Jones, 1984 Suborder: Robertinina Loeblich & Tappan, 1984 Superfamily: Ceratobuliminidae Cushman, 1927 Family: Ceratobuliminidae Cushman, 1927 Subfamily: Ceratobulimininae Cushman, 1927 Suborder: Rotaliina Delage & Hérouard, 1896 Superfamily: Bolivinacea Glaessner, 1937 Family: Bolivinidae Glaessner, 1937 Superfamily: Cassidulinacea d’Orbigny, 1839 Family: Cassidulinidae d’Orbigny, 1839 Subfamily: Cassidulininae d’Orbigny, 1839 Superfamily: Eouvigerinacea Cushman, 1927

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Family: Lacosteinidae Sigal, 1952 Superfamily: Turrilinacea Cushman, 1927 Family: Stainforthiidae Reiss, 1963 Superfamily: Buliminacea Jones, 1875 Family: Buliminidae Jones, 1875 Family: Buliminellidae Hofker, 1951 Family: Uvigerinidae Haeckel, 1894 Subfamily: Angulogerininae Galloway, 1933 Superfamily: Fursenkoinacea Loeblich & Tappan, 1961 Family: Virgulinelidae Loeblich & Tappan, 1984 Superfamily: Discorbacea Ehrenberg, 1838 Family: Rosalinidae Reiss, 1963 Family: Rotaliellidae Loeblich & Tappan, 1964 Superfamily: Planorbulinacea Schwager, 1877 Family: Cibicidae Cushman, 1927 Subfamily: Cibicidinae Cushman, 1927 Family: Planorbulinidae Schwager, 1877 Subfamily: Planorbulininae Schwager, 1877 Superfamily: Asterigerinacea d’Orbigny, 1839 Family: Asterigerinatidae Reiss, 1963 Superfamily: Nonionacea Schultze, 1854 Family: Nonionidae Schultze, 1854 Subfamily: Nonioninae Schultze, 1854 Superfamily: Chilistomellacea Brady, 1881 Family: Trichohylidae Saidova, 1981 Superfamily: Rotaliacea Ehrenberg, 1839 Family: Rotaliidae Ehrenberg, 1939

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24 Subfamily: AMMONIINAE Saidova, 1981 Family: Elphidiidae Galloway, 1933 Subfamily: Elphidiinae Galloway, 1933

Suborder: Globigerinina Délage & Herouard, 1896 Family: Globigerinidae Family: Globotruncanidae Family: Globorotaliidae Ecology During life, forams are either benthic of planktonic, relying on their pseudopodia for both locomotion and creating water currents for food gathering. Benthic forms inhabiting shallow to deep water environments can be recognized by their large size, thick heavily ornamented walls, and less “globular” shape. Planktonic forams are recognized by their thin, and often perforated, tests and globular inflated chambers. You should be able to recognize the difference between the two main types of foraminifera (Fig. 20).

Fig. 20. Habitats of foraminifera.

Numerous foraminifera inhabit the benthic environment. Some move freely over the sea-bed or in the first few millimeters of sediment. Others use their pseudopodia or calcareous secretions to attach themselves to supports such as rocks, shells and seaweed. Most are marine and stenohaline (they can tolerate only very small variations in the salinity of the water). Certain groups, however, having a porcelaneous test (e.g. the milolines) can live equally well in hyper saline environments (lagoons with a salinity ›35 Parts per thosuand (‰). Certain types such as the agglutinates (e.g., Eggerella) and hyalines (Nonion) prefer water with a low salinity (e.g., brackish lagoons and estuaries). Still others (e.g., Trochammina and Eliphidium) can adjust to considerable variations in salinity and may be found in all environments with the exception of fresh water lakes. Foraminifera are used to interpret past water depth, and since depth- and space-related parameters are of great significance, the foraminifera occupy different levels according to local values for temperature, oxygen content, light, etc. As a general role, species with a hyaline test occur everywhere but in the deepest areas. Species with agglutinated testes are similarly ubiquitous, but they alone survive at depths below the CCD (2500 to 4500 m). The physical environment of the ocean basins, the chemical constitution and dynamics of sea water, and all of the organisms dwelling in the ocean comprise the marine ecosystem. Indicator faunas have become one of the several indices that can be used to characterize a particular environment. Other indices now used include the planktonic to benthic (P/B) ratio, the ostraacode to foraminifera ratio, the calcareous to agglutinated ratio, the percentage of various families present, diversity indices (Fig. 21).

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Physical variables There is a combination of variables that controls the distribution of individual foram (water depth, temperature, etc.). Temperature is one of the most important and easily determined variables affecting benthics. Foraminifera are found living at temperatures from 1° to over 30°C. Some variables affect foraminiferal distribution indirectly like hydrostatic pressure, light intensity.

Fig. 21. Depth distribution of recent benthic foraminifera. After Bolstovsky & Wright (1976).

Numerous foraminifera inhabit the benthic environment. Some move freely over the sea-bed or in the first few millimeters of sediment. Others use their pseudopdia or calcareous secretions to attach themselves to supports such as rocks, shells and seaweed. Most are marine and stenohaline (Fig. 22). Certain groups, however, having a porcelaneous test (milioline) can live equally well in hyperhaline environments (lagoons with salinity > 35 parts per mile (‰)).

Fig. 22. Distribution of larger benthic foraminifera (SEPM stratigraphy web).

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Chemical variables 1. Salinity Foraminifera inhabit environments with salinities ranging from a typical open ocean value of 35‰ to as high as 45‰. The genus Discorbinopsis was found to tolerate salinities up to 57‰. At the other extreme, a river and its estuary may have salinities varying from as low as 15‰ to 0.05‰ and still contain foraminifera. The lower the salinity of the environments, the lower the diversity of the faunas there (Fig. 23).

Fig. 23. Zoogeographical planktonic foraminiferal provinces (after Darling et al., 2000).

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2. Alkalinity As a function of the concentration of CO2 in the water, alkalinity is governed chiefly by temperature, pressure, and biological respiration. The top 500 m of sea water are said to be saturated with respect to calcium carbonate which reflects the high alkalinity in this region. Below 500 m water is considered under saturated with respect to calcium carbonate. Below this depth the lower alkalinities tend to cause calcium carbonate to dissolve. Biotic variables The study of foraminifera as members of marine communities falls into the realm of autecology. Such an approach seeks to relate the foraminifera to the food chain of which it is a part, as well as to understand the types of relations foraminifera have among themselves and with other members of the marine communities. Figures for the density of living benthic foraminifera vary from 1,000 to 2,000,000 individuals per square meter of sea bottom. When the density of individuals becomes great, foraminifera have been observed to migrate away from the crowded areas. Planktonic foraminiferal ecology The distribution and ecology of recent planktonic foraminifera is essentially similar to that of other zooplankton and is primarily governed by the temperature, oceanic current systems and availability of food. Planktonics live in the water column from the surface zone down to depths of over 1000 m. The distribution of taxa through the water column may change seasonally. In cooler seasons or at high latitudes, a species may live near the surface than it does in warmer waters or at lower latitudes. Geographically there are close parallels between the distribution of planktonic foraminifera in modern oceans and in the past. In general, smaller species are found in cold water masses or at high latitudes and larger species in warm water or at low latitudes. Diversity is lower at high latitudes and increases toward the subtropics. Distribution of Recent Foraminifera Foraminifera have been reported from marine environments extending from tide pools in a marsh to the abyssal plains. Each environment is characterized by its particular species, their diversity and densities. We consider that past environments may have contained many analogous components and hence modern environmental indicator faunas are carefully applied to the understanding of both recent and past environments (Fig. 24). Carbonate platforms, reefs and back reefs Foraminifera occur in coral reefs environments either as adherent forms (Homotrema) or as epifauna in niches developed within the reef framework (Calcarina, Amphistigina, Marginopora). Smaller benthic foraminifera are one of the primary contributors to the sediments of shallow carbonate platforms. They attach to sea weeds and grasses, algal and coral fragments. Larger foraminifera inhabit these shallow waters in association with the macroflora which foraminifera use for protection, and the microflora which the foraminifera use for food. Brackish environments Historically foraminifera have been considered predominantly marine organisms, with primitive or aberrant types inhabiting freshwater ecosystems. There is a group of foraminifera that occurs in brackish environments and this brackish-water fauna is geographically very uniform. Brackish environments are typified by finer-sized sediments containing abundant plant detritus. The critical controlling factor in this environment is apparently the low salinity.

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Marshes Foraminifera live from the deepest tidal channels to shallow ephermal tide pools in the marsh grass. Marshes and bays are characteristically areas of high daily and seasonal fluctuations in temperature, salinity, water depth, turbidity, and water chemistry. In addition, high in organic matter and nutrients are found in marshes and thus support large biomasses low in diversity. There is a marked difference between living faunas and faunas recovered from fossil march sediments. Hyaline, agglutinated and a few porcelaneous genera characteristically form the living fauna. The test walls of the calcareous and porcelaneous genera are frequently thin. The number of calcareous genera in the sediments, however, is significantly lower or they are altogether absent, while the number of agglutinated forms is generally the same in both sediment and living populations. Continental shelf and open marine The shallow shelf is characterized by a small fauna dominated by a few species, very few of which are agglutinated and none of which are pelagic. The inner shelf is characterized by coarse-grained clean, well sorted sands containing abundant rounded shell fragments. The benthic faunas are usually highly dominated by a few species. Tests are small and not strongly ornamented. A few pelagic species, usually of the genus Globigerina, may be present. It brought from upper water by currents. The deep inner shelf contains fine- to medium-grained sand, silt, clay with common glauconite and mollusk and echinoid remains. There is an increase in the number of specimens. Pelagic types are more numerous and agglutinated foraminifera increase in abundance, but still have simple interiors. Middle shelf sediments are composed of clay, silt, poorly sorted sands, and abundant glauconite. Species are often highly ornamented, with pelagic types comprising from 15-30% of the total microfauna. Species dominance is low and the number of species is high. Agglutinated forms have more complex interior structures (Fig. 25). The outer shelf is characterized by fine grained sediments such as clays and some glauconite. Species number is high and ornamentation is strong. Planktonics constitute approximately 50% of the faunas. Some agglutinated foraminifera have complex interiors. The upper continental slope strongly resembles the outer shelf. Planktonic foraminfera comprise from 50-85% of the microfaunas. The number of benthic species is large on the abyssal plain, though there is a dilution effect from dead planktonic tests. Planktonic foraminifera may comprise more than 99% of the microfaunan in areas where “Globigerina ooze” is deposited. The deepst-dwelling, abyssal agglutinated foraminifera are simple tube-like structures, surrounded by detrital particles held together by organic cement. The lack of carbonate in their tests reflects the absence of carbonate particles in the abyssal “red clay” environment.

Fig. 24. Trends in bathymetry and fossil content of sediments from the shelf to the abyssal environments.

Small Foraminifera

Fig. 25. Distribution of foraminifera from the shelf to the abyssal environments.

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30

Questions (A) Multi-choice questions: 1.

Foraminifera live: (a) on the sea floor

(b) amongst the marine plankton

(c) in both

2.

The soft tissue (protoplasm) of the foraminiferida cell is largely enclosed within a shell composed of: (a) calcite agglutinated particles (b) organic matter (c) Silica

3.

Benthic foraminifera have been divided into morphogroups as: (a) Epifauna and infauna (b) globular and subglobular

(c) elongate and tabular

To observe foraminifera we use: (a) transmitted-light microscope only (b) stereomicroscope only

(c) both microscopes

The term “agglutinated” refers to the tests formed from: (a) foreign particles (b) organic matter

(c) same particles

Secreted test foraminifera are again subdivided into three major groups: (a) Microgranular, porcelaneous, and hyaline (b) Agglutinated

(c) Organic

Calcareous wall may be composed of: (a) low or high mg calcite (b) Silica

(c) Microcline

In the porcelaneous wall, the calcite crystal is arranged: (a) randomly (b) symmetrically

(c) does not matter

In the uniserial arrangement, the chamber is arranged in: (a) double rows (b) single row

(c) multiple rows

4. 5. 6. 7. 8. 9.

10. In the Polyserial arrangement, the chambers are arranged in a: (a) multiple row (b) around an axis

(c) single row

11. In the Trochospiral coiling, the spiral lie in: (a) one-plane (b) two-plane

(c) horizontally

12. Aperture is found in the wall of: (a) the final chamber

(b) last chamber

(c) mid of the test

13. Sutural aperture characterize the: (a) uniserail shell

(b) polyserial shell

(c) biserial shell

14. The physical parameters that control the distribution of foraminifera include: (a) temperature, salinity (b) pH

(c) light

15. The salinity of the Euhaline water is: (a) >30 g/Kg

(c) 5-15 g/kg

(b) < 0.5 g/Kg

16. The carbonates compensation depth is: (a) ~600 m (b) ~2000 m

(c) ~4500 m

Small Foraminifera

17. The oxic environment contain: (a) 8.0—2.0 ml/l O2

(b) 0.2—0.0 ml/l O2

31

(c) 0.0 ml/l O2

18. Marine plants can tolerate or exist in environments with pH ranging between: (a) 5.0 and 10.0 (b) 5 and 7

(c) 8 and 10

19. Hematite is indicative of …………… environment: (a) oxidizing (b) reducing

(c) intermediate

20. The mineralogy of diatoms is: (a) opaline silica

(c) phosphate

(b) calcite

21. The mineralogy of benthic foraminifera is: (a) carbonates (b) Silica

(c) both

22. In the Qunquiloculina the chambers added in: (a) 180° (b) 120°

(c) 72°

23. Warm populations can be distinguished by: (a) dextral coiling (b) sinistral coiling

(c) both

24. Warm populations can be distinguished by: (a) dextraly coiling (b) sinisterly coiling

(c) both

25. The solubility of CaCO3 is less in: (a) cool water

(b) warm water

(c) hypersaline water

26. The solubility of CaCO3 is less in: (a) cool water

(b) warm water

(c) hypersaline water

(B) True and false questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

Foraminifera are an order of single-celled protests. The foraminiferal test consists of a single chamber or several chambers. Foraminifera are known from early Cambrian-Recent times. Foraminifera are found in the planktic mode of life only. Benthic foraminifera have been used for palaeobathymetry. Foraminifera range in size from several millimeters to a few tens of microns. The Miliolids first appeared in the early Devonian. Foraminifera which inhabit the photic zone live symbiotically with photosynthesising algae. Number of living foraminifera have reached 2000 species. Some agglutinated forms are non-selective and use any particle from a substrate. The term porcelaneous derives from the shiny appearance of the tests. The calcareous hyaline is glassy when viewed with transmitted light. In Triserial chambers are added every 120° in a spiral fashion. In planispiral coiling the chambers arranged spirally around two axis of coiling. The area where one chamber meets another is the suture area. The external surface of the foraminiferal test is only smooth. Marine animals do not contain gases. CaCO3 is much more soluble in cold than in warm water. Sodium is the most common salt in sea water. The currents in the sea are harmful to marine life. The CaCo3 is highly soluble in deep, cold waters.

Micropaleontology

32 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50.

Oxygen is the most abundant dissolved gas in seawater. The solubility of oxygen varies negatively with salinity. The solubility of oxygen varies positively with temperature. Carbonates will not be a deposited alkaline environment. Silica dissolves in the acidic medium. Marcasite is indicative of acidification. Kaoline requires an acidic medium for its formation. The absence of normal benthonic fauna is an indication of low oxygen. There is little problem among the floaters as for crowding in the sea. Most marine microfossils are protists. Most benthonic microfossils have wide geographic distributions. Planktonic are used as good index fossils. Marine microfossils occur in sediments of Precambrian to Recent ages. Dinoflagellates are known to contain both planktonic and benthic phases. Spores and pollen are strongly climate-dependent. The occurrence of Foraminifera is an indication of marine conditions. Scavenger’s foraminifera are feeding on dead organic particles. The depth of the photic zone is not more than 100 m. Anaerobic assemblages are typically living with free oxygen. Infauna lives in the sediments of the sea floor. In the hayaline wall structure, the calcite crystals are randomly distributed. Numerous foraminifera inhabit the benthic environment. Some foraminifera benefit from endosymbiotic algae. Low diversity foraminiferia suggest a wide range of food resources. The majority of foraminifera are adapted to abnormal marine salinities. The high CaCO3 concentrations of hypersaline waters favor Milioline. CaCO3 solubility increases with depth. Foraminifera have low diversity in lakes. The majority of foraminifera are feeding within the top 10 mm of substrates.

(C) Complete 1.

Marine environments have been classified on the basis of: (a) ………………………………… (b) ………………………………… (c) ………………………………… (d) ………………………………… (e) ………………………………… (f) …………………………………

2.

The sea floor consists of the ………………, the ………………, the ……………… and the ……………… Region.

3.

The vertical classifications of organisms by environment are: (a) ………………………………… (b) ………………………………… (c) ………………………………… (d) …………………………………

4.

Based on the Eh, the chemical environment is subdivided into: (a) ………………………………… (b) ………………………………… (c) …………………………………

Small Foraminifera

33

(d) ………………………………… (e) ………………………………… (f) ………………………………… 5.

The depth of light penetration in water depends on: (a) ………………………………… (b) ………………………………… (c) ………………………………… (d) …………………………………

6.

The value of marine microfossils is enhanced by their: (a) ………………………………… (b) ………………………………… (c) ………………………………… (d) …………………………………

7.

There are types of reproduction in foraminifera, which are: (a) ………………………………… (b) …………………………………

8.

The young gamonts with the larger proloculus are termed the ………………

9.

The individuals with smaller proloculi are called the ………………………………

10. The non-coiled chamber arrangements in foraminifera include: (a) ………………………………… (b) ………………………………… (c) ………………………………… (D) Define the following scientific terms Aerobic, Anaerobic, Epifauna, Infauna, Scavengers organisms, Anoxic, Dysoxic, Salinity, oxygen minimum zone, carnivore’s organisms. (E) General questions 1. 2. 3. 4. 5. 6. 7.

What is the difference between epifauna and infauna? Why are marine microfossils useful? What are the applications of foraminifera? What are the bases for the subdivision of foraminifera? Discuss using illustrations the different kinds of wall structure in foraminifera. Discuss using illustrations the chamber arrangements in foraminifera. Discuss the physical parameters control the Marine environments.

CHAPTER III LARGER FORAMINIFERA

CHAPTER III

LARGER FORAMINIFERA

Introduction Larger foraminifera are unicellular protists housed within a hardened shell or test that is at least 3 mm3 in volume, as opposed to the other foraminifera that do not exceed 1-2 mm3 (Lee and Hallock, 1987; Ross, 1974). Eichwald (1830) named the order Foraminiferida for the numerous, tiny foramen (pores) in the test. The tests are made primarily of calcium carbonate, but occasionally silica, organic compounds or particles are cemented together (agglutinated). Their intricately designed interior is the taxonomical base used to describe the order. Larger foraminifera have complex and variable life cycles (Leutenegger, 1977). Most larger foraminifera reproduce by an alternation of generations through haploid-diploid life cycles. The haploid process involves the union of opposite sex gamonts resulting in the megalospheric type (A-form), whereas the diploid route entails asexual division into agamonts that produce the microspheric type (B-form). The A-forms usually have a bigger test than the B-forms; however, the embryons of the A-forms are much bigger than the B-forms. Larger benthic foraminifera are highly specialized protists that secrete a skeleton. The extant species host photosynthetic algae as symbionts. This form of symbiosis is only profitable in warm, oligotrophic seas within the photic zone (Renema & Hart, 2012). In modern seas, symbiont-bearing foraminifera are restricted to areas with a minimum sea surface temperature of 16° C in the coldest month (Langer & Hottinger, 2000). This group includes representatives of all foraminiferal groups: agglutinated, porcelaneous, and hyline calcareous. The following groups are generally included: Agglutinated

Fusulinida

Loftusida

Miliolid

Rotallida

Alveolinoidea

Nummulitoidea

Soritoidea

Asterigerinoidea Planorobulinoidea

Orders of Larger Foraminifera: 1. 2. 3. 4. 5. 6. 7.

Fusulinidae. Neoschwagerinidae. Alveolinidae. Nummulitodae. Orbitoididae. Miogypsinidae. Discocyclinidae.

37

38

Micropaleontology

Classification 1. Suborder: Fusulinida Order Fusulinida is the distinct group of foraminifera of late Paleozoic age. They appeared at the beginning of the Pennsylvanian and went extinct at the end of the Permian.  

The shell: It is coiled involutes planispiral with an elongate axis. The shell is fusiform, subcylindirical, subangular in shape. The shell wall: Among the Fusulinida there are two types of wall structures: 1. The Fusulinellid wall. 2. The Schwagerinid wall (alveolar).

The Fusulinellid wall The wall consists of the primary wall (Protheca) and the secondary wall or (Epitheca). The Protheca constitute a layer of clear transparent calcite “Diaphanotheca” covered by thin dark and rind like film “Tectum”. The Epitheca consists of two thin layers which are translucent grey layers (Fig. 26).

Fig. 26. Fusulinellid wall.

These two layers cover the roof and floor of the earlier chambers and termed “Tectorium”. In the thin section, the wall of the inner whorls appears to have four layers differing in opacity: The Tectum is appears as a dark line, Diaphanotheca as a clear transparent layer and the both inner and outer Tectorium as translucent layers. The Schwagerinid wall This wall consists of only two layers: the outer layer is a thin dark rim, this layer is termed the “Tectum”. The inner layer is thick and perforate and have been reduced to “sieve-like” structure termed the “keriotheca” (Fig. 27).

Fig. 27. Schwagrinid wall.

Larger Foraminifera

39

The septa In axial section the septa are perfectly planer, gently folded or in some genera are complex folded. The septa are folded from pole to pole with the same depth and regularity, so that; the longitudinal meridional chambers are subdivided into a series of chamberlets (Fig. 28).

Fig. 28. Types of septa.

In equatorial section the successive chambers are in communication by means of a low equatorial tunnel formed by the reception of the basal margin of the septa near the equator. The tunnel is bordered by massive chomata “choma”. Choma is a dense, textureless deposit on previous whorl constituting the chamber floor, forming a pair of parallel ridges, each extending from a tunnel margin to the previous one, in fusulinids. May extend progressively polewards over the entire chamber floor in staffellids much like a basal layer in fusiform porcelaneous shells. In tangential section, it is nearly parallel to the equatorial section, but near the surface of the test and not passing through the center of the test. (A) Genus: Fusulina (Fig. 29) The test is fusiform to subcylindrical, and the size of the test is 3 mm to 1.5 cm. The wall structure “Fusulinellid wall” consists of four layers. The septa are deeply and fully folded. The tunnel is bordered by massive chomata (Fig. 30).  Age: Lower-middle Pennsylvanian. (B) Genus: Schwagerina The test is fusiform to subcylindrical or subglobular. The wall structure “Schwagerinid wall” is formed from two layers. The septa are regularly and very deeply folded, so that the lower part of opposed folds in adjacent septa meet. Subdividing the meridonal chambers into a series of cell-like hamberlets, chomata are lacking (Fig. 31).  Age: Early Permian.

40

Micropaleontology

Fig. 29. Types of sections in Fusulina and Schwagerina.

Larger Foraminifera

41

Fig. 30. Genus Fusulina.

Fig. 31. Genus Schwagerina.

2. Family: Neoschwagerinidae The Neoschwagerinidae first appeared in the Permain. They resemble the fusulines only in their planispiral growth, normally about an elongate axis. The wall structure is Schwagerinid wall consisting of two layers tectum (T) and Keriotheca (K). In the Neoschwagerinidae the primary septa are perfectly planer. There are no folds, but there are secondary septa (Septula). The longitudinal meridional chambers are subdivided by secondary septa into a series of chamberlets. The communication between chamberlets of the chamber are by a row of rounded formation along the base of each septum. The secondary deposits take the form of slender, hoop-like ridges on the floor of the volution alternating in position with the foramina (Fig. 32). 3. Family:Alveolinidae The alveolinidae appeared firstly in the Cretaceous and still alive today. Test large free fusiform, ellipsoidal or spherical. The shell is coiled in an involute planispiral with an elongate axis. The wall structure is porcellaneous imperforate, and this wall consists of crystals of calcite having a horizontal position with the “c” axis of the crystal that is parallel to the surface. Therefore, the light does not pass through this wall (Fig. 33).

42

Micropaleontology

Fig. 32. Family Neoschwageriniodae.

Fig. 33. Wall structure in Alveolonidae.

The aperture consists of rows of single circular apertures (rounded pores) in the apertural face of the last chamber, which corresponds to each of the chamberlets. These apertures appear in several rows. Internal structures Alveolines are studied in oriented sections and there are two types of sections as follows: (a) Axial section (longitudinal): this section is parallel to the long axis and passing through the center. (b) Equatorial section (Sagittal): this section perpendicular to the long axis. Septa (primary septa) and Septula (secondary septa) They are whorls divided by the primary septa into longitudinal meridional chambers and these are subdivided by the secondary septa (Septula) into the chamberlets. The communication between the chamberlets of the longitudinal chamber that is maintained by means of transversal passages are termed “stolon” and there are two types of stolon that appear in the equatorial section:  

The pre-septal stolon or (pre-septal passage). The post-septal stolon or (post-septal passage).

Larger Foraminifera

43

Genus: Praealveolina The test in this genus is fusiform, with the secondary septa being in continuous alignment, and no postseptal stolon. The genus Praealveolina appeared in the upper Cretaceous (Fig. 34). Genus: Alveolina The test in this genus is fusiform, with the secondary septa being in alternating alignment with post-septal stolon. The age of Alveolina range from Paleocene to Eocene. Alveolina was recorded from the Egyptian deposits in two main forms: the small form (A. ovulum) in the Paleocene deposits, and the spherical form (A. decipiens) in the lower Eocene rocks.

Fig. 34. Praealveolina.

4. Family: Nummulitidae The Nummulitidae appeared in the Paleocene and range in Age to the Oligocene, and they are found in large numbers in Egypt in the Eocene. The different species of Nummulitidae are considered as index fossils for the Paleogene. Shell: Lenticular, varying from flat to globes, the size of the shell varies from 1 mm to 15 cm. The coiling is involute planispiral and the test is bilaterally symmetrical. There are septal filaments on the surface of the test, and the wall structure is calcareous perforate (Fig. 35).

Fig. 35. Septa, septum in the Nummulitidae.

44

1. 2. 3. 4. 5.

Micropaleontology

Septal filaments Nummulitidae can be classified on the basis of septal filaments into different species (Fig. 36): Simple “Radial”: Septal filaments have radial orientation (e.g., N. deserti …… Paleocene). Sigmoidal “S-shape”: Septal filaments are radial having an S-shape (e.g N. atacicus …… E. Eocene). Meanderine: Grouped in bundles, running in a faint straight course and more complex than sigmoidal (N. gizahensis). Subreticulate: Irregularly radial, frequently branching or uniting with other filaments. Reticulate: The filaments unite with other filaments in a reticulated pattern (e.g., N. fabianis).

Fig. 36. Septal filaments in Nummulitidae.

Granules Some species of Nummulites have a surface spotted over with rounded spots. Usually lighter in color than the rest of the test and varying greatly in size and number in different species termed granules (Fig. 37).

Fig. 37. Granules in Nummulitidae.

Internal structure Nummulitdea are studied in oriented sections and there are two type of sections as follows: (a) Equatorial section: A section along the plane of symmetry termed equatorial section or horizontal section. (b) Axial section: A section in a plane perpendicular to the equatorial one and passing through the center and also named radial or vertical section. (a) Equatorial section The test is formed from spiral whorls. The spiral whorls is termed spiral lamina, enclosed between the successive whorls of the spiral lamina a spiral cavity. The spiral cavity is divided by septa into chambers. The successive chambers are communicated by foramina at the base of the septa (Fig. 38). If the height of the chamber is greater than their length, the coiling will be “lax spired”. If the length of the chamber is greater than the height, the coiling will be “tight spired” (Fig. 39).

Larger Foraminifera

45

Fig. 38. Equatorial section in Nummulitidae.

Fig. 39. Tight and lax spire coiling in Nummulitidae.

II) Axial section The spiral lamina appears in the V-shape form and the secondary skeleton appears with complex canal system or “canalicular skeleton” along the equatorial part. It is termed “the marginal cord” and the granules on the surface seem to be the outer ends of the cylindrical or conical “pillars” which extend perpendicular to the surface. The pillars are united with other pillars and form the “Polar pustule” in the center of the shell (Figs. 40 and 41).

Fig. 40. Axial section in Nummulitidae.

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Micropaleontology

Fig. 41. Two types of sections in Nummulitidae.

5. Family: Orbitoididae Test is large, lenticular, subcircular, or circular. The ornamentation is granulate or reticulate, or papillate. The high part in the center of the test is termed the nephionic “stage” (Fig. 42). In equatorial section, the proloculum will appear bilocular if consisting of two chambers, quadrilocular if consisting of four embryonic chambers, and multilocular if consisting of more than four chambers. The equatorial chambers communicated by tubular foramina “Stolons”. The proloculum is surrounded by an equatorial chamber, and the shape of the equatorial chamber are shown in Fig. 43.

Fig. 42. Shapes of the equatorial chamber in Orbitoididae.

Fig. 43. Axial section of Orbitoididae.

Larger Foraminifera

47

Genus: Orbitoides  Age: Upper Cretaceous.  Shell: Circular, ornamented by granulate.  Type of coiling: Annular discoid to complex. In the equatorial section, the proloculum consists of four embryonic chambers “quadrilocular”. The equatorial chambers are “Arcuate” (Figs. 44 and 45).

Fig. 44. Orbitoides.

Fig. 45. Axial section in Orbitoides.

Genus: Lepidocyclina (Fig. 46)  Age: Eocene-U. Miocene.  Shell: Test lenticular, granulate ornamentation.  Type of coiling: Annular discoidal to complex. In the equatorial section, the proloculeum consists of two embryonic chambers “bilocular”. The proloculum is termed “Polylepidine” if the second chamber is smaller than the first one. The proloculum is named “nephrolepidine” if the second chamber is larger than the first. If the first chamber is equal or subequal to the second, one the proloculum is termed “isolepidine”. The equatorial chambers have many forms: arcuate, hexagonal, rhombic, or spatulate. The equatorial chambers are communicated by stolons (Fig. 47).

Fig. 46. Genus: Lepidocyclina.

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Micropaleontology

Fig. 47. Axial section in Lepidocyclina.

Family: Discocyclinidae  Genus: Discocyclina  Age: Middle to Upper Eocene  Wall structure: calcareous  Shell: Test discoidal, the ornamentation by radial ridges  Type of coiling: annular complex. In the equatorial section, the proloculum consisting of two embryonic chambers is termed “bilocular”. The first chamber protoconch is partly or almost completely embraced by the 2nd chamber “Deutroconch”. The shape of equatorial chambers are only elongate.  Proloculus: initial chamber of foraminiferal test in all generations.  Protoconch: first chamber of test in which a deuteroconch is differentiated.  Deuteroconch: chamber following immediately the proloculus and differing in shape and often in size from subsequently formed chambers (Fig. 48).

Fig. 48. Axial section of Discocyclina.

Larger Foraminifera

49

7. Family: Miogypsinidae  Genus: Miogypsina.  Age: Oligocene-Middle Miocene.  Shell: Test large, triangular or lenticular to subcircular.  Type of coiling: Subannular complex. In the equatorial section, the proloculum that usually consists of two embryonic chambers is termed “bilocular”. The first chamber is usually equal to the second chamber, so the proloculum is termed “Isolepidine”. The equatorial chambers are only Rhombical.

Micropaleontology

50

Questions (A) Multi-choice questions 1. 2. 3. 4. 5.

The shell in fuslunidae is coiled involutes planispiral with a: (a) horizontal axis (b) elongate axis

(c) no axis

The secondary wall in fusulinidae is: (a) Protheca

(c) Tectum

(b) Epitheca

The inner layer of the Schwagerinid wall is: (a) Tectum (b) keriotheca

(c) epitheca

In Genus Fusulina, the test is: (a) elongate

(c) fusiform

(b) globular

The family Neoschwagerinidae first appeared in: (a) Permain (b) Carboniferous

(c) Jurassic

6.

The different species of Nummulitidae are considered as index fossils for: (a) Cretaceous (b) Paleocene (c) Paleogene

7.

The shell in Nummulitidae is: (a) Fusiform

(b) lenticular

(c) subglobular

8.

If the height of the chamber is greater than their length in Nummulitidae, the coiling will be: (a) lax spired (b) tight spired (c) free spired

9.

The type of coiling in Orbitoides is: (a) Planispiral

10. The test in Discocyclina is: (a) discoidal

(b) Trochospiral

(c) annular discoid to complex

(b) fusiform

(c) lenticular

(B) True and false questions 1. 2. 3. 4. 5. 6. 7. 8.

Family Fusulinidae is the distinct group of foraminifera late Mesozoic. The primary wall in fusulinidae is termed Protheca. The shell in Alveolinidae is coiled involute trochospiral. The age of Alveolina range from Paleocene to Eocene. Genus Orbitoides appeared in lower Cretaceous. Genus Orbitoides is circular and ornamented by granulate. The age of Genus Discocyclina is Middle to Upper Eocene. The Miogypsina appear in Oligocene.

CHAPTER IV OSTRACODA

CHAPTER IV

OSTRACODA

Introduction The ostracodes are the most useful group of crustacean in geological sciences especially for stratigraphers or paleontologists. The remains of these small, mostly microscopic, crustaceans are widely distributed in the rocks of all the periods of the phanerozoic era, beginning in the Camberian to Recent. The taxonomic position is:   

Phylum: Arthropoda Class: Crustacea Subclass: Ostracoda

This subclass is one of the best documented groups within the whole animal kingdom due to the most characteristic features of their bodies, a bivalve well calcified shell which fossilizes easily. The majority of Ostracoda have a length between 0.15-2 mm , the recent marine swimming forms attain up to about 25 mm in length, and the largest Paleozoic species are up to 80 mm. Ostracodes live in fresh, brackish, saline and hypersaline waters and rarely in extra-aquatic environments. In the sea, they are found from the shoreline down to hyperabyssal depths. The greatest number of fossil marine ostracodes are benthic forms. The planktonic species, due to their weakly calcified shells, are generally rare in fossil assemblages and play a minor role in paleontology. The ostracode lineages are extremely useful as markers in cases where foraminifera are absent, such as in fresh water deposits. The carapace The ostracode body is wholly covered by a continuous cuticle secreted by the epidermis. When first formed, the cuticle in all crustaceans is soft but becomes largely hardened by a complex tanning process called sclerotization, the deposition of mineral salts. However, parts of cuticle called joints remain permanently soft so that movement is possible. The ostracode carapace is an integral part of the cuticle. It develops as a single cuticular fold originating on the head region and completely enveloping the body. The two valves arise through the mineralization of its left and right sides and are united in their dorsal part by a narrow strip of soft cuticle called ligament. The left and right valves are connected by an adductor muscle which traverses the soft body in its median region, and an articulation of the valves called the hinge is also developed in the dorsal margin of the two valves in many ostracodes. The hinge In some ostracodes, as in the extinct archeocopids or in many myodocopins, no hinge structure exists. It is believed that this unhinged state is primitive and that hinges later evolved in several ostracode groups. Hinges may be composed of variously shaped bars, grooves (Fig. 49), teeth and sockets affecting the articulation of the two valves. There are three main categories of hinges are:

53

Micropaleontology

54 1.

Unipartite hinges: This category includes all the hinge types in which no subdivision into terminal and median elements developed (rectodont, prionodont). 2.

Merodont hinges: This category comprises all the hinges which possess terminal teeth in one valve only (lophodont, hemimerodont). 3.

Amphidont hinges: Have teeth and sockets in both valves (archidont, hemiamphidont, schizodont).

Fig. 49. Type of hinges in Ostracoda (from Haq and Boersma, 1983).

Muscle scars On the internal surface of a well preserved ostracode valve there are small spots of a somewhat different shell structure. They are confined to two areas which according to their position on the valve are (Fig. 50): 1. 2.

Central muscle scar field. Dorsal muscle scar field. 1. Central muscle scar field This central muscle scar field includes three groups of scars as follows:

(a) The adductor muscle scar group: which represents the imprints of closing adductor muscles? (b) The mandibular group: lies in the front of the ventral part of the adductor muscle scars group, its scars are not due to muscles but to chitinous support rods. (c) The frontal group: situated above the mandibular scars due to the mandibular muscle.

Ostracoda

55

2. The dorsal group: The dorsal group is studied only in few species. The most distinctive group of muscle scars which is also most resistant to fossilization is the adductor group.

Fig. 50. Types of muscles in Ostracoda.

Orientation of the carapace For descriptive purposes, the following views of the carapace are recognized:    

The lateral or side view normal to the contact sagittal plane of the valves. The dorsal view: The view on the hinge margin. The ventral view: The appearance of the carapace in line of the sagittal plane seen from below. The frontal view: View the carapace seen from the anterior end in the line of the sagittal plane.

Carapace length is not uniformly conceived in straight-backed ostracodes. It is defined as the maximum dimension of the carapace in the direction parallel to the hinge line. In specimens with an (arched dorsum), the length is understood as the maximum distance of the end points of the carapace measured parallel to the basal line. The height is measured as the maximum distance perpendicular to the length. The width is the maximum distance of the carapace outline perpendicular to the sagittal plane. Frontal and mandibular scars, if present, definitely mark the position of the anterior end. Classification The classification of Recent ostracodes is based primarily on the morphology of the soft body, chiefly on appendages, but also on other features, such as shape and position of the gonads, and presence or absence of eyes and heart. Since the Second World War, neontologists who were influenced by intensive systematic paleontological studies began to attribute more importance to the features of the carapace as taxonomic criteria, especially at the generic and specific level. For the definition of a (genus), the shape of the carapace, basic pattern of gross sculpture, character of the hinge, presence or absence of the eye spots, details of muscle scars, the course of the line of concrescence, the shape, position and number of pore canals, and the structure and width of the marginal zone are among the most frequently used features.

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For species recognition, the modification of the carapace shape, hinge, number and position of pore canals, development of vestibule, presence or absence of opaque spots in the valve walls, their shapes, as well as other minor features are employed. Major morphological groups The following summarizes the classification of ostracodes. The diagnoses of the ordinal groups are given in the table; subordinal and subrafamilial levels are briefly described in the text. The more common or typical genera are illustrated. Suprageneric classification of ostracode 1.

Order: Archeocopida  Diagnosis: Carapace equivalved or nearly so, with long straight dorsal margin and strongly convex ventral margin.  Range: Lower to upper Cambrian: lower Ordovician.  Classification: Suborder: 1) Bradoriids. 2) Phosphatocopins.  Principal families: Badoriidae, Hipponichariiidoe.

2.

Order: Leperditicopida  Diagnosis: Includes the largest ostracodes, ranging up to 80 mm in length, carapace heavily calcified, slightly to strongly unequivalved with long straight hinge margin.  Range: Ordivician to Devonian.  Classification: Suborder: Leperditipina  Principal family: Leperditidae.

3.

Order: Myodocopida  Diagnosis: It is impossible to give a detailed diagnosis for this order because of the great morphological variety of its members. Carapace mostly with a convex ventral margin and a [peripheral calcification] of the inner lamella.  Range: Ordivician to Recent.  Classification: (a) Suborder: Myodopina, Superfamily: Cypridinoidea, Family: Cypridinidae. (b) Suborder: Halocypriformes, Superfamily: Halocypridaoidea, Family: Halocyprididae. (c) Suborder: Cladocopina, Family: Polycopidae.

4.

Order: Beyrichicopida  Diagnosis: Carapace well calcified, in both larval and adult specimens typically with a more or less straight usually long cardinal margin and convex extracaridinal margin.  Range: Known since Ordivician, most of them are restricted to the Paleozoic, few in Trassic.  Classification: (a) Suborder: Hollinonorpha, Superfamily: Hollinacea i. Family: Hollinellidea ii. Superfamily: Eurychilinaoidea, Family: Eurychilinidae iii. Superfamily: Primitiopsaoideaa, Family: Primitiopsidiae (b) Suborder: Beyrichiomorpha Superfamily: Beyrichiaoidea, Family: Beyrichiidae (c) Suborder: Binoodicopina Superfamily: Drepanellacea  Principal families: Drepanellidae, Aechminidae, Bolliidae.

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57

5.

Order: Podocopida  Diagnosis: Calcified carapace which never bears rostral incisures. Larval valves with a more or less straight ventral margin.  Range: Ordivician to Recnt.  Classification: (a) Suborder: Podo copina Superfamily: Cytheraoidea Families: Cytheuridae, Cytheridae, Cytherettidae, etc. Superfamily: Bairdiidae Family: Bairdiiae Superfamily: Darwinulacea Family: Darwinulidae Superfamily: Cypridacea Family: Cyprididae, etc. (b) Metacopina: Superfamily: Healdiaeoa Family: Healdiidae Superfamily: Thlipsuraea Family: Thlipsuridae, etc. (c) Platycopina Superfamily: Kloedenellacea Family: Kloedenellidae Superfamily: Cytherellacea Family: Cytherellidae

6.

Uncertain Order Suborder: Kirkbyocopina. Superfamily: Kirkbyacea, Family: Kirkbyidae, Amphissilidae, Arcyzonidae. Description of Ostracoda We can describe the ostracodes among both “external surface” and “internal surface” features.

External surface features The description of the external surface features includes the following: (a) Lateral view 1. Outline of the carapace in “lateral view” with maximum length and maximum height. 2. Dorsal margin. 3. Ventral margin. 4. Anterior margin (end). 5. Posterior margin (end). (b) Dorsal view 1. Outline of the carapace in “dorsal view” with maximum width. (c)

Sculpture: “Ornamentation” One of the most important features in the description of ostracodes is sculptures, which are used in recognizing the different species, including the structures which are not reflected on the inner surface except for the sulcus eye spot. The sculpture includes the following:

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58 1. 2. 3. 4. 5. 6. 7. 8.

Ribs and Riblets. Ridges. Inflation. Eye spot “tubercle”. Reticulation. Muscle region. Sulcation lobation. Alate “wings”.

There are other features such as smooth surface, punctation, denticles, nodes, depression and elevation, tubercles and spines. Internal surface features In some forms we can observe and describe the internal features, and in other forms the internal features cannot be observed “accessible” and described. The internal features include the following: 1. 2. 3. 4. 5. 6.

Marginal zone with the shape, position and number of pore canals. Hinge “teeth, sockets and bars, grooves”. Muscle scars. Inner lamina and line of concrescence. Vestibule. Selvage.

(I) External surface: Orientation of the carapace (Fig. 51)

Fig. 51. Orientation of the carapace.

  

Maximum length: Maximum dimension of the carapace in the direction parallel to the hinge line. Maximum height is measured as the maximum distance perpendicular to the length. Maximum width is the maximum distance of the carapace outline perpendicular to the sagittal plane (Fig. 52).

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Fig. 52. Maximum length, height and width of ostracoda.

(A) Lateral View The outline of the carapace in the lateral view with maximum length and height is as follows (Figs. 53, 54, 55 and 56): 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Sub rectangular: Rounded end margins and almost parallel to subparallel longitudinal margins. Bairdied outline: Posterior margin is composed of three parts bluntly to smoothly joined to each other, with the dorsal margin being more convex. Bean-like: Bean like outline with arched convex dorsum and straight ventral margin with slightly mouth in curvature. Elongated carapace: Elongated carapace with posterior end acute and rounded anterior end. Sub trapezoidal outline: With rounded anterior end and acuminate (tapering) posterior end, steeply dipping. Oval. Sub oval. Quadrangular. Sub quadrangular. Sub circular. Pear-shaped. Sub triangular: Ventral margin strongly rising. Rhomboidal: Centrally inflated carapace with sub angular posterior margin. Sub rectangular outline, with broadly rounded anterior end and more pointed posterior end (margin) [with strongly concave above the middle of height of the carapace].



Maximum height (Fig. 57) a) Maximum height at the eye tubercle “eye spot”. b) Maximum height at the anterior margin “anteriorly”. c) Maximum height at the center of the carapace “at the mid length”. d) Maximum height at about one-third of the length. e) Maximum height at about one-fourth of the length.



Maximum length (Figs. 58, 59 and 60) a) Maximum length at the mid height “median height”. b) Maximum length dorsal “sub dorsal”. c) Maximum length ventral “sub ventral”.

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Fig. 53. Outline of the carapace in the lateral view.

Fig. 54. Outline of the carapace in the lateral view (continued).

Ostracoda

Fig. 55. Outline of the carapace in the lateral view (continued).

Fig. 56. Outline of the carapace in the lateral view (continued).

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Fig. 57. Maximum height of the carapace.

Fig. 58. Maximum length of the carapace.

(II) Doral margin: “Dorsum”

Fig. 59. Dorsal margin.

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63

(III) Ventral margin

Fig. 60. Ventral margin.

If the two valves of the carapace are unequal or one valve overhanging the other valve.  

R.V. overlapping (over reaches) L.V. L.V. overlapping (over reaches) R.V. (Fig. 61).

Fig. 61. Overhanging valves.

We will describe the dorsum and ventral margin for each valve (e.g., the right valve overlapping the left valve). (IV) Anterior margin “end” (Fig. 62)

Fig. 62. Anterior margin end of the carapace.

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64 (V) Posterior margin “end”

Fig. 63. Posterior margin end.

(B) Dorsal view Outline of the carapace in “dorsal view” (Figs. 64, 65 and 66): 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18)

Oval with anterior and posterior ends not compressed “oval without compressed ends margins”. Sub oval, with sides gently slope anteriorly and steep slope posteriorly to tapering. Elongated sub oval with tapering “posterior end” or “anterior end” or wedged towards posterior end or towards anterior end. Oval with compressed end margins slightly compressed strongly compressed. Sub oval with rugged outline. Oval, tumid with compressed end “extremities”. Sub oval outline with tapering end and acutely, triangular-alate. Arrow head-shaped. Hexagonal outline. Hexagonal with compressed ends. Hexagonal with compressed tapering ends. Six-sides compressed carapace in D.V. “irregular outline”. Carapace in dorsal view with “gradual lateral slope anterioly” trancat posteriorly, with compressed ends. Carapace in dorsal view has “parallel longitudinal sides” with tapering in one side and truncate in the other side. Triangular outline with “acute anterior” and “slightly extended posterior end”. The outline with “median deeply sulcus” divides the carapace into “slightly smaller nodose anterior” and “humped posterior” port. Pear-shaped. Rhomboidal outline.

Ostracoda

Fig. 64. Outline of the carapace in “dorsal view”.

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Fig. 65. Outline of the carapace in “dorsal view” (continued).

Maximum width “thickness” Is the maximum distance of the carapace outline perpendicular to the sagiital plane? The maximum width is measured through dorsal view (Fig. 67): 1) 2) 3) 4) 5) 6) 7)

Maximum width at the center of the carapace. Maximum width behind the center. Maximum width front the center. Maximum width at the anterior end. Maximum width at the posterior end. Maximum width at the alate. Maximum width behind the sulcus.

Note that in some species which have sexual dimorphisum, the males are longer and less width “thickness” than females, and these are clearly shown in dorsal view.

Ostracoda

Fig. 66. Outline of the carapace in “dorsal view” (continued).

Fig. 67. Thickness of the carapace in dorsal view.

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68 (C) Sculpture “ornamentation”

(i) Ribs and riblets (Figs. 68 and 69) The following are the types of ribs according to their positions in the carapace:      

Ventral ribs. Dorsal ribs. Marginal ribs. Parallel to anterior margin. Parallel to posterior margin. Median longitudinal ribs.

Fig. 68. Outline of the carapace in “dorsal view” (continued).

The following are the types of ribs according to their shapes:         

Straight. Inclined → towards posterior. Curved towards anterior. Not bifurcate. Bifurcate. Lamellar ribs “thin sharp”. Sinuous ribs. Irregular ribs. Fine striae.

The following are the types of ribs according to their developments: 

Weakly developed.

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 

69

Moderately developed. Strongly developed “prominent”.

If the carapace of the outer surface contains more than one rib, we must determine the number of ribs with their positions, shapes and their developments. (ii) Riblets Riblets are smaller than ribs.

Fig. 69. Types of ribs according to their development.

(iii) Ridges Ridges are similar to ribs but larger in size. The following are the types of ridges (Fig. 70):       

Ventral ridge. Alate ventral ridge. Dorsal ridge. Ventral ridge at one valve. Spiny ventral ridge. Ventral ridge at each valve. Spiny dorsal ridge with alamellar lateral wing-like projection.

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Fig. 70. Types of ridges.

The following are the developments of ridges:   

Weakly “slightly” developed. Moderately developed. Strongly developed.

Over hanging “outreaching” Ventral ridge and dorsal ridge may be outreached on ventral margin and dorsal margin respectively. There are three degrees of the overhanging of ridges:   

Slightly overhanging. Moderately overhanging. Strongly overhanging.

(iv) Inflation (Figs. 71 and 72)  At the center of the carapace.  At the anterior end (margin).  At the posterior end (margin).  Two inflations, anterior and posterior, separated by unisulcus.  Ventro lateral inflation (outreaching the ventral margin).

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Fig. 71. Types of inflation according to its position.

(v) Eye spot and “eye tubercle” The eyes are one of the few soft organs which leave traces on the carapace. Their position on the anterodorsal part of the valve is marked by a hyaline circular area on the wall by subglobular elevation, sometimes an elongated area. It may be reflected or not reflected on the internal surface. The shape of eye spot is usually a glassy circular area, but sometimes it is an elongated area. The following are the degrees of development of the eye spot:     

Absent (not developed) “blind”. Small size (slightly developed). Medium size (moderately developed) “moderately elevated”. Large size (strongly developed) “prominent” clear. Very prominent, stalked projecting eye spot.

Fig. 72. Types of inflation according to its position.

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(vi) Reticulation The most important features on the external surface of the carapace are as follows:   

Shape of reticules “opening of reticulets”. Size of opening. Arrangement “orientation of opening”.

1. Shape of opening (Fig. 73)

Fig. 73. Shape of opening.

2. Size of opening (Fig. 74)  Fine reticulates (weakly).  Medium reticulates (moderately).  Coarse reticulates (strongly).

Fig. 74. Size of opening.

3. Arrangement “orientation of opening” (Fig. 75)  Irregular.  Concentric “parallel to the margin” [more or less concentric].  In vertical rows.  Elongated “longitudinal”.  Curved rows.

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73

Fig. 75. Arrangement of opening.

Ecology Ostracodes probably originated in a marine environment, and the largest number of species still inhabit the pelagic and benthic realms of the ocean from the shoreline down to several thousand meters, and from the equator to polar seas. Some species flourish in brackish waters and some are found even in hypersaline environments. Some species occur in fresh-water environments from which they are known since the Carboniferous, and some lineages of both fresh-water and marine ostracodes have even invaded terrestrial niches. Ostracodes have evolved a wide variety of nutritional system including filter-feeding and deposit-feeding. Numerous species feed on marine plants and small living animals such as annelids or small crustaceans. Some eat detritus from decaying vegetal or animal tissues, while others are (limnivorous) eating bottom sediments without any selection, some have (oral apparatus) transformed into piercing and sucking organs which are used for the intake of plant juices. Some are known as commensals, clinging to the appendages or gillcavities of other crustaceans and to the body surface of echinoderms. Some ostracodes are parasitic in the gills and nostrils of fishes. Others have glands along the valve margins which secrete a sticky substance to which the food adheres. Distribution of Marine Ostracodes A comparatively small number of marine ostracodes inhabit the pelagic realm, some are living in surficial waters, others are distributed through the water column. The greatest number of ostracode species are benthic and their distribution is controlled by a large number of physical, chemical and biological factors (Fig. 76). 1. Salinity Salinity is the most fundamental factor determining the distribution of ostracodes, as it has a decisive influence on the physiology of the organism.  

Fresh-water assemblages are taxonomically distinct from marine faunas and few species can thrive in both marine and fresh-water environments. With decreasing salinity, foraminifera and other marine groups gradually disappear and the dominate position in the microfaunal assemblage is assumed by the ostracodes.

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2. Temperature Some species of ostracodes are widely eurythermal, while others are bound to a narrow temperature range.   

The cold-living deep-sea species are termed psychrospheric. The cold-living marine shallow-water species are termed cryophilic. The warm-loving are termed thermophilic.

Shallow marine ostracode assemblages of the low latitudes are considerably more taxonomically diverse than those of high latitudes. 3. Substrate The nature of the substrate has a pronounced effect on the composition of ostracode communities. They either live on the bottom or live on marine plants or animals. The sediment-inhabiting species live either at the surface of the sediment, or within the sediment, thus forming a part of the infauna. Coarse-grained sediments, like clean sands, support only a small ostracode population, whereas mud-mixed sands sediments usually have larger and much more diversified ostrarode fauna. The size and shape of the sedimentary particles as well as the degree of their compaction are factors which control the distribution of the ostracodes. 4. Depth It is difficult to assess the influence of depth, as other decisive factors change in close correlation with depth. With increasing depth, the stability of the environment generally increases, whereas the energy level of the environment causes decreasing the grain size of the sediment, decreasing light penetration and vegetation cover. Below the photic zone, the food supply also decreases. Observations suggest that the depth-correlated factors are of greater importance for the ostracode distribution than the depth itself. In high-energy shallow waters, both diversity and density of ostracodes are lower than deeper and more stable offshore environments. Pressure may be a physical barrier to the distribution of species which are adapted to specific depth conditions (stenobathic). Many ostracodes are adapted to a considerable depth range (eurybathic). 5. Food supply A high organic content of the sediment has been considered to be a factor controlling ostracode distribution. For example, the deep-sea ostracode fauna of the Mediterranean sea seems to be controlled by the amount of nutrients according to Buri et al. (1969). Paleoecology Paleoecological analysis using ostracodes is based on several methods as follows: 1) 2) 3) 4) 5) 6) 7)

Actualistic comparison, or comparison to the mode of life of living species. Functional morphology of carapace characters and their changes in time and space. Population structure of species (mode of reproduction, sex ratio, and patterns of distribution). Structure of ostracode communities, diversity, dominace, and pattern of distribution in space and time. Analysis of accompanying fossil groups. Biostratonomic study (ratio valves/carapaces, larvae/adults, general made of preservation, and study of post-mortem distribution). Analysis of accompanying sediment.

Ostracoda

Fig. 76. Diagram illustrating the ecological distribution of recent ostracoda, with some typical forms represented.

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76

Questions (A) Multi-choice questions 1. 2.

The recent marine swimming ostracodes attain a length up to about: (a) 15 mm (b) 25 mm

(c) 50 mm

The greatest number of fossil marine ostracodes are: (a) benthic forms (b) nektonic form

(c) planktonic form

3.

The Merodont hinges in ostracodes include: (a) no teeth (b) terminal teeth in both valve (c) terminal teeth in one valve only

4.

The Amphidont hinges in ostracodes include: (a) teeth and sockets in both valves (b) teeth in both valves

(c) no teeth and sockets

The adductor muscle scars in ostracodes represent the imprints of: (a) closing adductor muscles (b) opening adductor muscles

(c) mandibular scars

5. 6.

Carapace length in ostracodes is the maximum dimension of the carapace in the direction: (a) parallel to the hinge line (b) perpendicular to the hinge line (c) cut the hinge line

7.

Frontal and mandibular scars, if present, definitely mark the position of the: (a) posterior end (b) anterior end (c) adductor muscle scars

8.

Ostracodes probably originated in: (a) marine environment

9.

(b) fresh water

The cold-living marine shallow-water ostracodes species are: (a) psychrospheric (b) cryophilic

10. One of the important internal features in ostracodes include: (a) muscle scars (b) sculpture

(c) both (c) thermophilic (c) sulcus

11. The centrally inflated carapace in ostracode with sub angular posterior margin is: (a) subtriangular (b) rhomboidal (c) circular 12. One of the types of ribs according to their positions the carapace is: (a) marginal ribs (b) lateral ribs

(c) posterior ribs

13. One of the types of ribs according to their shapes is: (a) sinuous ribs (b) coastal ribs

(c) side ribs

14. One of the types of ribs according to their developments is: (a) depressed (b) prominent

(c) flashed

15. Muscle region on the external surface of the carapace of ostracode is: (a) ventral (b) dorsal

(c) sub central or central

16. The sulci in ostracode are designated from: (a) dorsal to ventral (b) anterior to posterior

(c) posterior to anterior

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77

17. We can describe the number and places of the teeth in the hinge in ostracode as: (a) lateral teeth (b) dorsal teeth (c) anterior tooth 18. One of the shapes of teeth in ostracode is: (a) lateral (b) circular

(c) kidney

19. Merodont hinges comprises all the hinges which possess: (a) terminal teeth in one valve only (b) terminal teeth in both valves

(c) terminal teeth and sockets

20. Ostracodes feed by: (a) filter-feeding

(c) both

(b) deposit-feeding

21. From the types of ribs according to their positions in the carapace: (a) ventral ribs (b) dorsal ribs

(c) straight ribs

22. From the types of ribs according to their shape: (a) curved (b) bifurcate

(c) median longitudinal ribs

23. From the types of ribs according to their developments: (a) weakly developed (b) parallel to anterior margin

(c) irregular ribs

24. For the definition of a (genus) in ostracoda, we use: (a) presence or absence of opaque spots in the valve (c) character of the hinge

(b) the sharpness of the carapace

25. One of the criteria to recognize a species in ostracoda is: (a) number and position of pore canals (c) details of muscle scars

(b) the sharpness of the carapace

(B) True and false questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Ostracodes live in fresh, brackish, saline and hypersaline waters. The most resistant to the fossilization group of muscles in ostracodes is the adductor group. The height of ostracode is measured as the maximum distance parallel to the length. Some species of ostracodes occur in fresh-water environments. Fresh-water ostracodes are taxonomically distinct. The eyes are one of the few soft organs which leave traces on the carapace of ostracode. In some forms, we cannot observe and describe the internal features. Muscle scars can be observed in poor preserved carapaces. The greatest numbers of fossil marine ostracodes are benthic forms. The left and right valves are connected by an adductor muscle. The mandibular muscle scars group is closing muscles. The ventral view of the carapace, which is the view on the hinge margin, is measured as the maximum distance parallel to the length. The males are shorter than females in ostracoda. The females are thicker than males in ostracoda. The ridges are similar to ribs but smaller in size. The greatest numbers of ostracode species are benthic. Few ostracoda can thrive in both marine and fresh-water environments. Coarse-grained sediments have much more diversified ostrarode fauna. The classification of recent ostracodes is based primarily on the morphology of the soft body.

CHAPTER V CALCAREOUS NANNOFOSSILS

CHAPTER V

CALCAREOUS NANNOFOSSILS

Introduction When fine particles of a marine sediment rich in carbonate are observed under a high magnification of x500 to x1000, one is struck by the “great diversity” and the “quantitative prominence” of tiny arrays of calcite crystallites known informally as coccoliths and formally as calcareous nannoplankton. Nanno (Greek) = dwarf Over 150 known species of these minute unicellular, autotrophic, marine algae “Coccolithophores” are living in the present-day oceans (Fig. 77).

Fig. 77. Coccosphere.

The fossil coccolithophores and related groups of nannofossils (collectively known as nannoliths) have been important constituents of marine carbonate sediments since early Jurassic time. Age: Latest Jurassic-Recent In the coccolithophores, the cell secretes a skeleton of minute calcareous shields, which may envelop the cell completely or partially (coccosphere). The elliptical to circular coccolith range in size from 1-15 micron (in some references 1-25 micron).

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Other related, but morphologically dissimilar groups of organisms traditionally included under the calcareous nannoplankton, comprise a wide array of elaborate designs. The Tertiary lineage of steroliths (discoasters) are more important because of their higher diversity, relative quantitative prominence in the tropical and subtropical sedimentary provinces and their great value to the biostratigrapher. History of the Nannoplankton Research 1836: First reference to the nannoplankton was made by the German biologist C. G. Ehernberg. He has been called the “founder of micropaleontology”. He reported the occurrence of small flat elliptical discs of “agaric-mineral” in the chalk from the island of Rügen. He also figured the first discoasters and called them “calcareous crystal-discs” and considered both these and coccolith to be of inorganic origin. 1858: T. H. Huxley reported the presence of Ehrenberg’s “crystalloids” in deep sea oozes recovered prior to the laying of the first trans-atlantic telegraphic cable and referred to them as “coccolith”. He also regarded them as of inorganic origin. 1861: G. C. Wallich and H. C. Sorby came to the conclusion that coccolith were parts of larger spherical objects to which the former gave the name of “coccosphere”. Wallich compared the coccospheres to the juvenile stage of foraminifera “Globigerina”, but Sorby considered them as separate organisms. 1865: Wallich reported the discovery of living coccosphere from the tropical waters of the Indian and Atlantic oceans. 1891: John Murray and R. F. Renard recorded a wide variety of microfauna and flora, including nannoplankton. 1931: Jossef Schiller presented a complete account of all known species of extant coccolithophores, and this work persisted as one of the standard references on the subject to this day. 1954: This year marked the beginning use of nannoplankton as biostratigraphic indicator. Bramlette and Riedel pointed out the distinctiveness of the Mesozoic and Tertiary assemblages, and suggested their usefulness, particularly that of discoasters in worldwide correlation of pelagic sediments. 1960: Hay and Bramlette used the biostratigraphic zonation of nannoplankton in tropical-subtropical and temperate regions for worldwide correlation of pelagic sediments. Biology of the Organisms Most living coccolithophores are known to possess the flagellar apparatus, haptonema, and organic surface scales characteristic of the unicellular class: haptophyceae (Fig. 78). The ability of the coccolithophore to secrete calcareous plates “coccolith” on these organic scales distinguishes them from other members of haptophyceae and all other algae. Organization at the cellular level The components of the cell of Emiliana huxleyi are shown in Fig. 79. The cell is bound by two double membranes that enclose the protoplasm, containing a prominent nucleus, two chloroplasts, mitocondria, the dictyosome or the Golgi apparatus, and a vacuolar body referred to as “body-x”.

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Fig. 78. Living cell.

Fig. 79. Component of the living cell.

  

Chloroplasts contain the chlorophyll responsible for photosynthesis (a process by which light energy is converted into chemical energy with the help of photosynthetic pigments). The chemical energy is used in the reduction of carbon dioxide to form carbohydrates and liberate oxygen. Mitiochondria: They contain the oxidative enzyme systems which produce energy for the various cell functions. Golgi-apparatus is well developed in E. huxleyi. The function of it is not well understood, but it is believed to participate in the secretion of cell wall material.

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Strains of E. huxleyi normally secrete coccoliths, in which the body-x or vacuolar body is not present and is replaced by another body (reticular structure). The function of these reticular structures is not well understood, but it is intimately connected with the formation of coccoliths. Formation of coccoliths (Fig. 80) In their study of the cross-section of the various stages of development of E. huxleyi under the electron microscope, Wilbur and Watable (1963) noticed that the mineralization of the coccoliths occurs within the protoplasm immediately next to the reticular body. Between this body and the nucleus, a non-granular matrix material is differentiated and first assumes the general shape of coccolith.

Fig. 80. Early stage of coccolith formation in E. huxleyi. The coccolith begins to form between the (N) and reticular body.

Precipitation of the mineral calcite starts from central points in this matrix, advancing from the base of the coccolith upwards and then to the periphery of the shields. After the calcification, the coccoliths are evidently pushed to the surface of the cell where they form into an interlocking spherical envelope around the cell. This coccolith envelope may become multi-layered as more coccoliths are produced. The process of calcification in all species of coccolithophres is evidently not identical. Mantan and Leedale (1969) have observed that in Coccolithus pelagicus and Circosphaera carterae the coccolith are attached to underlying unmeneralized organic scales and both of these originate within the cisternae of the Golgi apparatus. Most coccolithophores have a definite range in the number of coccoliths around the cell (from about 10 to 30 in Gephyocapsa oceanica), but these ranges vary considerably in different species. Coccolith Shape Classification A number of terms have been introduced to describe the overall shapes which coccoliths may take. The following is a list of the more common shape terms used for the coccolith of living coccolithophores. The terms used for fossil forms may be found in Hay (1979), Tappan (1980), and Gartner (1981), the commonest of which is a near-spherical shape. Oblong and spindle shaped tests and other intermediate varieties are also seen in some extant species (Figs. 81 and 82):

Calcareous Nannofossils

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Calyptroliths: Basket-shaped, open proximally. Caneolith: Disc- or bowl-shaped, lath field central area. Ceratolith: Horse shoe or wishbone shaped. Cribrilith: Disc-shaped, numerous central area perforations. Cyrtolith: Disc-shaped, convex outward, often with a projecting central process. Discolith: Disc-shaped, thickened, raised rim. May or may not have central area perforations. Helicolith: Spiraling, overlapping marginal flange. Lopadolith: Basket, cup, or vase-shaped, with high rim opening distally. Pentalith: Five four-sided crystals joined to form a pentagon. Placolith: Two shields joined by a central column. Prismotolith: Solid or perforate polygonal prism. Rhabdolith: Single shield, surmounted by a club-shaped central process. Scapholith: Rhombohedral shape, with parallel laths joining in the central area.

Fig. 81. Shape of coccolith.

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86

Fig. 82. Shape of coccolith (continued).

Life Cycle (Reproduction, Nutrition and Growth) Reproduction (Fig. 83) Some coccolithophores pass through two phases in their life cycle. A motile phase during which they possess the flagellar apparatus (the haptonema) alternating with a non-motile phase. The cell in the non-motile phase normally secretes coccoliths, but in the motile phase it is either naked or bears a coccolith of a different type than those in the non-motile phase. The only known living example of non-motile phase is Coccolithus pelagicus. The motile phase of C. pelagicus was described as a different species namely crystallolithus hyalinus characterized by coccoliths called crystalloliths consisting of loosely bound, unmodified rhombohedral microcrystals contained in the outer hyaline layer of the cell wall. The cell reproduces by fission to two daughter cells, then emerging as naked cells and forming their own crystallolith. Motile phase Haploid stage

5-8 weeks

Non-motile phase Diploid stage

Fig. 83. Coccolithophorid life cycle.

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87

Nutrition Coccolithophores are mostly photoautotrophic. They manufacture organic materials for their sustenance from water, CO2, nitrates and other inorganic salts with photosynthesis of sunlight as the source of energy. The motile cells of Coccolithus pelagicus have been observed to ingest bacteria and small algae. Some species are believed to be heterotrophic utilizing both organic and inorganic substance from the surroundings. Growth The growth rates of coccolithophores are relatively high, as some species multiply more than twice in one day (e.g., Emiliana huxleyi in nature). The cell division rate of this species varies from a low of 1.2 divisions per day in Atlantic to a high rate of 4.8 divisions per day recorded in the Black Sea. Most coccolithophore species exist within a relatively narrow temperature range. The optimum growth of E. huxleyi occurs only between a temperature range of 18-24C°. At the optimum growth temperature of 18C°, the number of normal coccoliths occur more frequently at other temperatures. Other features such as number and shape of crystal elements of the coccolith and their dimensions also varied at different temperatures. Mineralogy of Coccolith The calcium carbonate CaCo3 in coccolith normally crystallizes as calcite and to a lesser degree as aragonite. In laboratory cultures of minor traces of a third polymorph of lime, vaterite have also been found. For example, in E. huxleyi all three polymorphs have been detected, but aragonite and vaterite are present only in very small amounts. Due to the relatively unstable nature of aragonite and vaterite, it is not surprising that these polymorphs have not been found in fossil coccolith. The calcite produced by coccolithphores is the “low-Mg” variety (high Mg-calcite contains >4% MgCo3, low-Mg calcite contains <4% MgCo3). The planktonic calcareous organisms build skeletons of low-Mg calcite, and this may be because planktonic organisms prefer the lighter calcite phase (low-Mg) to the heavier phase (high-Mg) for flotation purposes (Fig. 84).

Fig. 84. Mineralogy of coccolith.

Morphology of Coccolith There are two different types of crystallization that can be distinguished amongst coccolithophores as follows:

88 



Micropaleontology

Heterococcolith: The majority of the coccoliths of living and fossil species are made up of crystallites of varied shapes and size in which the basic rhombohedral shape of the calcite has been modified by the cell to fit into specialized morphologies. These coccoliths are informally known as the heterococcolith (or coccoliths formed of crystallites of different shapes and sizes (Fig. 85). Holococcoliths: A smaller group of species produce coccoliths composed of crystals which are minute, usually equidimensional and more or less, maintain their original rhombohedral or hexagonal prism habits. These coccoliths are known collectively as “holococcoliths” (or coccoliths formed of similar types of crystals). Holococcoliths may consist of unmodified or slightly modified rhombohedral or hexagonal crystals or a combination of both. Coccolithus pelagicus have both types of coccolith: Holo (in motile phase), and Hetero (in non-motile phase). It is a unique example of its kind. No other coccolithophores is known to produce coccoliths of both types during its life cycle and species restricted to the coccoliths of one type or the other (Fig. 86).

In the motile phase, most species or perhaps all of species produce holococcolith or less modified coccolith that, due to most of the cell energy, is used in flagella motion, and little or none is available for chemical reorganization within the cell and for crystal modification. On the other hand, in the non-motile phase flagellar motion being discarded, this energy can be utilized for chemical changes and modifying crystal shape and dimensions.

Fig. 85. Heterococcolith (from the International Nannoplankton Association).

Fig. 86. Holococcolith (Knappertsbusch, 2000).

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89

Function of Coccoliths Coccoliths are beautiful and elaborate structures; their production is an important feature of coccolithophore biochemistry, and coccoliths must greatly affect the physiological ecology of the organism. The two most widely suggested types of function are protection and flotation-regulation. Protection against predation has often been assumed to be the function of phytoplankton cell-covering. Nonetheless, cell-coverings may protect the cells from osmotic, chemical, or physical shocks, or from ultraviolet light flotation which is important since all phytoplankton need to stay within the photic zone. More specialized possible functions include light concentration, which is possible for cell-covering which increases the area over which light is collected. Finally, since coccoliths, unlike the cell-covering of most other phytoplankton, are formed of calcite, it is possible that the chemical process of coccolith formation may aid photosynthesis. Coccoliths as cell-covering components Phytoplanktonic organisms are composed of two parts, the protoplasm and the cell covering. The components of protoplasm interact as a complex biochemical system. The cell-covering separates this system from the environment, providing physical protection and moderating an interchange of material between the cell and the environment. The cell-covering of most coccolithophores consist of two components: Resistant organic scales and calcareous coccoliths. There are also a number of prymnesiophytes which don’t calcify. Most of these are not naked but have an extracellular cover of resistant organic scales. These scales are strong and similar to coccoliths. First, coccolith and organic scales are homologous that are formed by the same process. Both coccolith and organic scales are formed in intracellular vesicles associated with the Golgi body. Second, coccolith and organic scales appear in many cases to be analogous that carry out similar functions. The idea that coccoliths function as cell-covering components is supported by the observation that coccoliths are arranged as a continuous cover on the cell-surface and are often modified in form so as to achieve this efficiently. There are two main coccolith arrangement patterns, directly a butting, and overlapping. Protection-related functions Grazing is one of the main controls on phytoplankton. Coccosphoeres do not, however, appear very effective at stopping predation. Coccospheres are common in the guts and fecal pellets of slaps, copepods, and other zooplanktons. Most zooplanktons seem to be rather unselective grazers ingesting all particles within a given size range—the lowest size range represented by coccolithophores. Calcification does not prevent grazing; it may make grazing more difficult and less efficient. There are various ways in which a protective function may operate. First, an armoring effect may render the “coccosphore” indigestible or cause them to be rejected as food particles. Second, increasing the coccosphores size may thus lower the grazing pressure achieved by spines. Third, a low ratio of cell size to coccosphore size might reduce the feeding efficiency of the zooplankton, particularly if there is a large volume of calcite in the coccosphore (Fig. 87).

Fig. 87. Protection-related functions of coccolith.

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Biochemical functions of coccolith formation (Fig. 88) Coccolith and organic scales are both homologous and analogous, so the difference between them may not be very significant. “CaCo3” may be a more convenient material than organic macromolecules. An elegant biochemical explanation for the occurrence of calcification is that it is linked to photosynthesis. The basic equations for calcification and photosynthesis are: Calcification: Ca+++2HCO3Photosynthesis: 6CO2 + 6H2O

CaCo3+Co2+ H2O C6H12O6 + 6O2

Since carbon dioxide (CO2) is produced by calcification and used by photosynthesis, it is possible for the two reactions to be linked. It is further possible that there is a direct linkage between photosynthesis and calcification and that calcification acts as a source of carbon dioxide for photosynthesis, or as a sinke for hydroxyl ions (OH)-. In this way, calcification would reduce the energy cost of photosynthesis.

Fig. 88. Biochemical functions of coccolith.

Flotation-related functions of coccolith (Fig. 89) The bulk of Oceanic phytoplankton occurs in the surface mixed-layer above the thermocline (about 10150 m). Within this layer, the particularly non-motile forms are essentially randomly distributed by turbulence and show minimal depth zonation. All phytoplankton cells need a flotation strategy in order to remain within the mixed layer and shelf seas to stay above the sediment bottom. There are main flotation strategies that are available to phytoplankton. For coccolithophore, the possible mechanisms include increasing the weight of the calcification of individual coccoliths, increasing the number of coccolith layers in the coccosphore, and the aggregation of cells. Some non-motile coccolithophores do show such adaptations. Spines with flaring ends may increase cell diameter without greatly increasing weight and so may reduce excess density and settling rate. Rhabdosphaera clavigera is a prominent example of this morphotype.

Fig. 89. Flotation-related functions of coccolith.

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91

Light regulation (Fig. 90) Since phytoplankton is dependent on photosynthesis, light regulation is an attractive possible function for cell coverings. Two separate light regulatory functions have been proposed. Braarud et al. (1952) suggested that coccoliths could reflect ultraviolet light, thus enabling them to live higher in the water column than other phytoplankton. Possible support for this comes from remote-sensing work which has identified oceanic patches with high light reflectance caused by blooms of Emilina huxleyi. Gartner and Bukry (1969) noted that coccoliths would tend to reflect light into the cell, since calcite has a higher refractive index than water, so they suggested the reverse role that coccoliths may act as light gathers, enabling coccolithophores to live deeper than other phytoplankton in water column.

Fig. 90. Light regulation functions of coccolith.

Taxonomic Position    

Kingdom: Protista Phylum: Prymnesiophyta Class: Prymnesiophyceae Order: Coccolithophorales (a) Heterococcolithophores. (b) Holococcolithophores.

(Haeckel, 1866). (Hibberd, 1976). (Hibberd, 1976). (Schiller, 1926).

Major Morphologic Groups Calcareous nannoplankton constitutes a diverse group of morphological forms, many of which are either clearly related or show similarity to the extant coccolithophores (forms with coccolith like shield). Other forms with no clear morphologic relationship to coccolithophores (e.g., discoaster) occur as calcareous microfossil within the same size fraction as coccolith and may form a substantial part of nannofossil assemblages. Thus, both the coccolithophores and the associated non-coccolithophores nannolith are traditionally studied together by the nannopaleontologists. Because of the dual, plant and animal characteristics of nannoplankton, they are claimed by both the botanists and zoologists, and a complicated double system has developed over the years (Figs. 91 and 92). Most present-day nannopaleontologists, however, favor the plant origin. Botanists usually include coccolithophores in:    

Kingdom: plant. Division: Chrysophyta. Class: Coccolithophyceae. Order: Heliolithae.

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Fig. 91. Morphology of coccolith.

Fig. 92. Morphology of Discoaster.

The groups are arranged into three categories (see Table 1): (a) Those that show clear relationship to coccolithophores. (b) Non-coccolithophores, but common nannolith. (c) Common incertae sedies genera. With the exception of four groups (Coccolithides, Zygodiscids, Braarudosphaerids, Thoracosphaerids) that occur in both Mesozoic and Cenozoic sediments, all other morphologic groups are either restricted to the Mesozoic or the Cenozoic. (a) Coccolithphores and related nannoliths Under this division, we include those groups that show some similarity to the basic coccolith-like shield construction. (1) Arkangelskillids (Figs. 93 and 94) This group includes the Mesozoic Family: Arkangelskiellaceae, as elliptical coccoliths are composed of complex shields of two to four cycles of joined elements. The common genera in this group are: Arkangelskiella, Broinsonia, Gartnerago and Kamptnerius.    

Genus: Arkangelskiella: The genera in this group are distinguished by the difference in construction of the coccolith rim. Arkangelskiella has a three-tiered rim in the proximal view. Genus: Broinsonia: Has additional inner rim cycle in distal view and distinctive perforation. Genus: Gartnerago: It has a multi-tiered rim in proximal view. Genus: Kamptnerius: Asymmetrical outer rim cycle.

Calcareous Nannofossils Table 1. Key to major morphologic groups of calcareous nannoplankton A) Coccolithophores and related Nannoliths 1) Arkhangeelskiellides Family: Arkanglskiellacea 2) Coccolithids Family: Coccolithaceae Family: Prinsiaceae Family: Heloicosphaeraceae 3) Podorhabdids Family: Podorhabdaceae 4) Pontosphaerids Family: Pontosphaeraceae 5) Rhabdospaerids Family: Rhabdosphaeraceae 6) Stphanolithids Family: Stephanolithionaceae 7) Syracosphaerids Family: Syracosphaeraceae 8) Zygodiscids Family: Eiffellithaceae Family: Zygodiscaceae B) Non-Coccolithophores Nannoliths 1) Braarudosphaerids Family: Braarudsphaeraceae 2) Ceratoslithids Family: Ceratolithaceae 3) Discoasterids Family: Discoasteraceae 4) Fasciculithids Family: Fasciculithaceae 5) Heliolithids Family: Helolithaceae 6) Lithastrinids Family: Lithastrinaceae 7) Lithstromationids Family: Lithostromationaceae 8) Sphenolithids Family: Sphenolithaceae 9) Thoracospherids Family: Thoracospharaceae C) Genra Incertae seids 1) Isthmolithus 2) Microrhabdulus 3) Micula 4) Nannoconus 5) Triquetrorhabdulus

Fig. 93. Arkangelskiella.

Fig. 94. Genus: Broinsonia.

93

Mesozoic Mesozoic, Cenozoic Cenozoic Cenozoic Mesozoic Cenozoic Cenozoic Mesozoic Cenozoic Mesozoic Cenozoic Mesozoic Cenozoic Cenozoic Cenozoic Cenozoic Mesozoic Cenozoic Cenozoic Mesozoic Cenozoic Mesozoic Mesozoic Mesozoic Cenozoic

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(2) Coccolithids group (Figs. 95, 96, 97, 98, 99 and 100) This is one of the four groups that occur in both Mesozoic and Cenozoic strata. The group is characterized by two-shield coccoliths. Each shield is composed of one or more cycles of crystal elements connected at their inner margins. There are three families in this group: (i)

Family: Coccolithaceae (Mesozoic-Cenozoic)

Common Mesozoic genera are: Biscutum and Watznauria. Common Cenozoic genera are: Coccolithus, Chiasmolithus, Ciruciplacolithus. 



Mesozoic Coccolithids: They are characterized by shape of the coccolith elliptical or circular and number of cycles in two shields and central area. - Genus: Biscutum: Consists of two single cycle elliptical shields. - Genus: Watznauria: Has two or three cycles of elements in distal shield. Cenozoic Coccolithids: - Family: Coccolithaceae: Has the shape of the coccolith and the characteristics of the central area. o Genus: Coccolithus: Is oval with a central pore. o Genus: Cruciplacolithus: Has a + shaped central structure. o Genus: Chiasmolithus: An X-shaped central structure. - Family: Prinsiacea: Is restricted to the Cenozoic. The basic construction of the elliptical to subcircular coccolithus of the Prinsiaceae is similar to that of the family coccolithaceae and differentiated from them only under light microscope where the former shows bright proximal shields and dextrogyre "clock-wise coiling" extinction lines under crossed-polarized light. Common genera include: Prinsius, Toweius, Gephyrocapsa and Emiliania. o Genus: Prinsius: Has a multi-cycle distal shield but a single non-distinct central opening. o Genus: Toweius: Has a multi-cycle distal shield and multiple openings. o Genus:Gephyrocapsa: Has a central cross-bar. o Genus: Emilania: Has a distinctive rim of I-shaped elements and a central grid.

Fig. 95. Genus: Watznauria.

Fig. 96. Coccolithaceae: (A) Cruciplacolithus. (B) Chiasmolithus. (C) Coccolithus.

Calcareous Nannofossils

Fig. 97. Genus: Prinsius.

Fig. 98. Genus: Toweius.

Fig. 99. Genus: Gephyrocapsa.

Fig. 100. Genus: Emiliana.

95

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(3) Pontosphaerids group (Fig. 101) The family Pontosphaeraceae is characterized by the following: 1. 2. 3.

Elliptical coccolithus with two shields closely appressed. The distal shield that may have distally enlarged walls to give it a basket-shaped appearance. The central area is either closed, perforated or spanned by a bridge. Common genera are: Pontosphaera, Transversopoints, Lophodolithus and scyphosphaera.

Fig. 101. (A) Pontosphaera, (B) Transversopoints, (C) Lophodolithus, and (D) scyphosphaera.

(b) Non-coccolithophore nannolithus This division includes groups with no clear relationship to extant coccolithophores, but which occur commonly in the nannofossil assemblages. (1) Braarudosphaerids group (Mesozoic-Cenozoic) This is the third group that is common to both Mesozoic and Cenozoic. Braarudosphaerids are pentaliths composed of five crystal units belonging to the family Braarudosphaeraceae. 

Family: Braarudosphaeraceae: Common genera in this family are Braarudosphaera and Micrantholithus that are encountered in both the Mesozoic and Cenozoic, but Genus Pemma is found only in the Cenozoic (Fig. 102).

Fig. 102. Genus: Braarudosphaera.

(2) Ceratolithids group (Late Cenozoic) These horse-shoe shaped nannoliths occur in the late Cenozoic only. 

Family: Ceratolthacea: This family includes two genera: Ceratolithus and Amaurolithus. - Genus: Ceratolithus: With an elongated projected part (Fig. 103). - Genus: Amaurolithus: Horse-shoe shaped nannolith without elongated projected part.

Fig. 103. Genus: Ceratolithus.

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97

(3) Discoasterids group (Cenozoic) This is a numerically important group of asteroliths. Some of them are disc-shaped (Rosette-shape), and others are star-shaped (stellat shape) with or without stems on one side of the asterolith. 

Family: Discoasteraceae: The common genera in this family are: Discoaster and tribrachiatus. - Genus: Discoaster: o Discoaster multiradiatus: Rosette-like asteroliths consisting of 18-28 rays or segments of equal size, radiating from a focal point and are joined throughout the their whole lengths. The central area has a small knob in shallow depression (Fig. 104). o Discoaster mirus: Specimens of this species are characterized by 6-9, rarely 10-12 heavy rays, with two terminal and two lateral nodes (Fig. 105). o Discoaster lodoensis: Stellate asteroliths consisting of 6, rarely 5 or 7 long slender rays joined together for about a third of their length. The rays are slightly curved in one direction, tapering gradually to a sharp point and extending upwards in the center forming a solid stem (Fig. 106). - Genus: Tribrachiatus: Tribrachitus orthostylus: Three rayed asterolithus are radiating from an undifferentiated center, and their tips may be rounded or nodded; the width of their rays may be parallel-edged or tapering. This species shows a great variation in the curvature of rays as can be seen in side view (Fig. 107).

Fig. 104. Discoaster multiradiatus.

Fig. 105. Discoaster mirus.

Fig. 106. Discoaster lodoensis.

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Fig. 107. Tribrachitus orthostylus.



(4) Fasciculithids group (Cenozoic) Family: Fasciculthaceae: - Genus: Fasciculthus: There are subcylindrical boundless of wedge-shaped crystals whose thin edges meet along the center. One end of the cylinder is concave and the other is pointed or flat, and its surface may be ornamented (Fig. 108).

Fig. 108. Genus: Fasciculthus.



(5) Heliolithids group (Cenozoic) Family: Heliolithaceae: - Genus: Heliolithus: There are two abutting unequal shields lacking a connecting tube and one shield with subradial sutures (Fig. 109).

Fig. 109. Heliolithus.



(6) Sphenolithids group Family: Sphenolithaceae - Genus: Sphenolithus: This genus has a rounded to polygonal base surmounted by an elongated rib-cone with one or more spines radiating from the center (Fig. 110).

Fig. 110. Sphenolithus.

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

99

(7) Thoracosphaerids Family: Thoracosphaeraceae: Members of this family are found in both the Mesozoic and Cenozoic. They are spherical shells composed of a mosaic of interlocking crystal units. The shells may be with or without an opening which may have a lid cover (Fig. 111).

Fig. 111. Thoracosphaera.

(c) Genera incertae sedis Common genera are Isthmolithus, Triquetrorhabdulus (Cenozoic), Microrhabdulus, Micula, and Nannoconus. (1) Genus: Microrhabdulus (Mesozoic) This genus has long, cylindrical (rod-like nannoliths), either truncate or tapering at the ends and showing checkered extinction patterns under cross polarized light (Fig. 112).

Fig. 112. Genus: Microrhabdulus.

(2) Genus: Micula (Mesozoic) It is rectangular to subcubical with concave sides and constructed of two or more units of different calcite orientations (Fig. 113).

Fig. 113. Genus: Micula.

(3) Genus: Nannoconus (Mesozoic) It has cone-shaped nannoliths, composed of minute wedge-shaped crystal units arranged radially around and perpendicular to the long axis which is occupied by a canal opening at both ends of the test (Fig. 114).

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Fig. 114. Genus: Nannoconus.

Ecology Coccolithophores are exclusively planktonic marine organisms and are distributed from the open ocean, pelagic environment to near shore littoral and in shore lagoonal environment. The occurrence of coccolithphores in littoral, lagoonal and estuarine areas where salinities are either much higher or lower than the average salinity of the open ocean (35%) demonstrates their tolerance of a wide range of salinities. Coccolithophores being photosynthetic live in the upper 100-150 m of the oceans, or the photic zone where sunlight can easily penetrate. Although coccolithophores are found throughout the photic zone, they are most abundant a few meters to about 50 m below the surface of the water and their concentration decreases rapidly at a greater depth. Biogeography Although over 150 species of coccolithophores have been recorded living in the oceans, quantitatively coccolithophores show greater concentrations in the zones of high organic productivity where more nutrients are available because of the upwelling of bottom waters or the convergence of currents. Significant contributions to our knowledge of the biogeography of coccolithophores have been made by Andrew McIntyre, who have mapped the occurrence of selected species in the Atlantic ocean. By studying both plankton samples and surface sediments from the ocean bottom, MacIntyre and Bé (1976) were able to group the coccolithophores of the Atlantic ocean into five discrete latitudinal climatic assemblages: Tropical, subtropical, transitional, subarctic and subantarctic. Tropical and subtropical assemblages contain over three times more species than the subarctic and subantarctic assemblages and thus conform to present ideas on latitudinal changes in diversity. The warming of the ocean since the end of the last glacial age was approximately 12 ky ago. That rapid warming lead to a poleward migration of the surface isotherms and warm water species will thus show a broad latitudinal distribution, while the distribution of cold water species becomes narrower. There is another example on the pacific ocean that shows a vertical distribution of coccolithophores along the north south transect in the north pacific, where we note the wide variations in the number of individuals at various depth and high concentrations at (50 N°) and around equator (0°).

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Questions (A) Multi-choice questions 1.

Living coccolithophores belong to: (a) haptophyceae

(b) crysophycea

(c) haptonema

2.

Most coccolithophores have a definite range in the number of coccoliths around the cell which is: (a) 5-15 (b) 10-30 (c) 20-40

3.

The coccolith is formed between: (a) reticular body and the nucleus

4. 5. 6.

(b) nucleus and mitochondria

(c) nucleus and chloroplast

Pentalith coccolith is five four-sided crystals joined to form: (a) rectangle (b) pentagon

(c) circle

Coccolithophores are mostly: (a) eutrophic

(c) photoautotrophic

(b) heterotrophic

In heterococcolith, the coccolith is made up of crystallites of: (a) equal shape and size (b) varied shapes and size

(c) equal shape and varied size

7.

The two most widely suggested types of the function of coccoliths are protection and: (a) flotation-regulation (b) decoration (c) biochemical

8.

Coccoliths could reflect ultraviolet light thus enabling them to live: (a) higher in the water (b) deeper in the water

(c) median in the water

Arkhangeelskiellides appear only in: (a) Paleozoic

(c) Cenozoic

9.

(b) Mesozoic

10. Braarudosphaerids are pentaliths composed of: (a) four crystals (b) five crystal

(c) six crystal

11. Discoaster multiradiatus are Rosette-like asteroliths consisting of: (a) 18-28 rays (b) 10-15 rays

(c) 20-30 rays

12. Genus: Microrhabdulus showing checkered extinction patterns: (a) under normal light (b) under phase contrast

(c) under cross polarized light

13. Coccolithus pelagicus have: (a) hetreococolith

(c) both forms

(b) holococolith

(B) True and false questions 1. 2. 3. 4. 5. 6. 7.

The age range of calcareous nannofossil is latest Jurassic-Recent. Wallich first reported the discovery of living coccospheres from the tropical waters in 1865. The components of the cell of coocolithophores include one chloroplasts. Ceratolithcoccolith is horse-shoe or wishbone shaped. The calcite produced by coccolithphores is the “low-Mg” variety. The bulk of Oceanic phytoplankton occurs in the surface mixed-layer above the thermocline. Coccolithophores are exclusively planktonic marine organisms.

102 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

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The coccolithophores adapt a wide range of salinities. Family: Prinsiacea is restricted to the Mesozoic. Thoracosphaeraceae are composed of a mosaic of interlocking crystal units. Coccolithophores are living in the present-day oceans and they are heterotrophic. Coccolithophores are distinguished from the other algae by secreting “coccolith”. Mitiochondria contain chlorophyll responsible for photosynthesis. The calcareous nannofossils are the fossil of coccolithophores only. Coccolithophores are exclusively planktonic marine organisms. Coccolithophores tolerate a narrow range of salinities. Heterococcolith is composed of equidimensional crystals. Holococcolith is composed of crystallites of varied shapes and size. Calcification in coccolithophores can prevent grazing. Coccolithophores show greater concentrations in the zones of high organic productivity. Spines with flaring ends reduce the sinking of coccolithophores.

CHAPTER VI RADIOLARIA AND CONODONTS

CHAPTER VI

RADIOLARIA AND CONODONTS

Radiolaria Introduction Radiolaria are holoplanktonic protozoa and form a part of the zooplankton. They are non-motile (except when flagella-bearing reproductive swarmer’s are produced) but contain buoyancy enhancing structures; they may be solitary or colonial. Formally they belong to the:    

Phylum: Protista Subphylum: Sarcodina Class: Actinopoda Subclass: Radiolaria

The sister Subclass Acantharia have skeletons composed of strontium sulphate which is easily dissolved in seawater and are not preserved in the fossil record. Within the Subclass Radiolaria, there are two important super-orders. The Tripylea which includes the Phaedaria that have skeletons composed of hollow silica bars joined by organic material, which are not commonly preserved, and the Polycystina that form skeletons of pure opal and are therefore more resistant to dissolution in seawater and hence more commonly preserved in the fossil record. The Polycystina may be divided into two suborders: the Spumellaria and the Nassellaria. They are wholly marine, the most relatively commonly preserved and therefore studied members of the formal Subclass Radiolaria. It must be remembered, however, that seawater is under saturated with respect to silica, and the degree of the preservation of Radiolaria depends on the robustness of the skeleton, depositional and burial conditions and diagenesis. History of the study The name Radiolaria was first used by Meyer in the early 19th century. Haeckel’s book of 1862 is full of fabulous illustrations which are available online in Hamburg University (see http://www.biologie.unihamburg.de/b-online/radio/). The Challenger expedition of 1873-76 was a milestone in Radiolaria, but the study did not last because of the huge amount of material collected and the subsequent large monograph by Haeckel. The 1970s with the advent of the Deep Sea Drilling Program saw another burst of research. During the 1950s, W. Riedel showed how Radiolaria evolved rapidly and could therefore be utilized as biostratigraphic tools. Range The first recorded occurrences of Radiolaria are from the latest Pre-Cambrian; they are generally thought to have been restricted to shallow water habitats. By the Silurian deep water, forms are believed to have evolved. All early Radiolaria are spumellarians, and the first possible nassellarians appear in the Carboniferous and definite true nassellarians do not appear until the Triassic. During the late Palaeozoic, Radiolaria show a gradual decline until the end of the Jurassic when there is a rapid diversification, and this coincides with the diversification of the dinoflagellates which may have represented an increased source of food for the Radiolaria.

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It is thought that the evolution of diatoms in the Cretaceous may have had a significant effect on radiolarian evolution due to the competition for silica (diatoms also use silica to build their skeleton); it is commonly accepted that radiolarian skeletons have become finer and less robust from this time. Classification Extant radiolaria are classified using features of both the preservable skeleton and the soft parts, which make the classification of fossil forms extremely difficult. Most workers in this field today use classification schemes based on Nigrini and Moore’s and Nigrini and Lombari’s works on modern and Miocene radiolarians. A major problem with radiolarian classification is that separate classifications have been established for the Palaeozoic, Mesozoic and Cenozoic, and little has been done to integrate them. The two suborders, the spumellarians and the nassellarians, are subdivided into informal groups which equate to family level. Application Radiolarian assemblages often contain 200-400 species, so they can potentially be very useful biostratigraphic and palaeoenvironmental tools. They have an unusually long geological range, from latest PreCambrian to Recent. Because Radiolaria have a skeleton composed of silica and have an extremely long geological range, they have become useful in the study of sediments which lack calcareous fossils, either because of deposition below the CCD (Carbonate Compensation Depth) or because the strata being examined are too old. Cherts and particularly nodules within chert bands are often good sources for Radiolaria. Ophiolites and accretionary terrains often include chert bands, and Radiolaria may be the only palaeontological aid available in these situations and as such have proved invaluable in the study of these geological settings. Biology Despite being single-celled protozoans, Radiolaria are quite complex and sophisticated organisms. The body is divided into a central capsule which contains the endoplasm and nucleus (or nuclei), and the extracapsulum which contains peripheral cytoplasm is composed of a frothy bubble-like envelope of alveoli and a corona of ray-like axopodia and rhizopodia. They feed on other zooplankton, phytoplankton and detritus using their axopodia and rhizopodia in a similar fashion to foraminifera, except that Radiolaria seldom possess pseudopodia and their rhizopodia are not as branching or anatomizing as in foraminifera. Symbiotic algae (including dinoflagellates) often occur in the extracapsulum. The central capsulum is separated from the extracapsulum by the central capsular wall, cytoplasmic strands called fusules link the central capsulum and extracapsulum via pores in this wall. Fusules are unique to Radiolaria and their close relatives the Acantharia. Because Radiolaria are heterotrophic, they are not limited to the photic zone and have been found at water depths as great as 4000 m. However, because many living Radiolaria contain symbiotic photosynthesising algae, they must spend at least daylight hours within the photic zone. Skeletal elements of radiolaria are covered with a layer of cytoplasm which is rapidly withdrawn if the organism is disturbed. It is suggested that new skeletal material is formed within this sheath (called the cytokalyamma) and that it acts somehow like a dynamic mould (Figs. 115 and 116). Life cycle Simple asexual fission of radiolarian cells has been observed. Sexual reproduction has not been confirmed but is assumed to occur; possible gametogenesis has been observed in the form of “swarmers” being expelled from swellings in the cell. Swarmers are formed from the central capsule after the ectoplasm has been discarded. The central capsule sinks through the water column to the depths of hundreds of meters greater than the normal habitat and swells, eventually rupturing and releasing the flagellated cells. Recombination of these cells, which are assumed to be haploid to produce diploid “adults”, has not been observed however and is only inferred to occur. Comparisons of standing crops within the water column and sediment trap samples have ascertained that the average life span of radiolarians is about two weeks, ranging from a few days to a few weeks.

Radiolaria and Conodonts

Fig. 115. Radiolaria (cross-sections).

Fig. 116. Basic morphological features of radiolarian (nassellarian).

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Preparation technique Radiolaria are often found in standard micropalaeontological preparations (i.e., those aimed at recovering foraminifera). However, for the best results, samples are washed using a weak (10%) concentration of hydrofluoric acid. It is also possible to differentially etch Radiolaria from cherts using hydrofluoric acid. This is extremely dangerous and must only be carried out in a fume cupboard with full protective clothing and as such should be left to trained personnel only. Observation technique Radiolaria are often smaller than foraminifera, but they may be viewed using the same techniques as those described for foraminifera, and they can be picked and mounted in the same way. They can also be prepared in strew mounts on glass slides. Images Figure 117 shows a representative selection of Radiolaria aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and, if possible, a species name followed by its age range: LM (Light Microscope) SEM (Scanning Electron Microscope). Typical and selected marker species are illustrated from each main period of the geological column in which Radiolaria occur. The images are divided into Cenozoic, Mesozoic and Palaeozoic forms (Fig. 117).

Fig. 117. Some images of Radiolaraia.

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Conodont Introduction Conodont elements are phosphatic tooth-like structures whose affinity and function are now believed to be part of the feeding apparatus of an extinct early vertebrate. Early ideas concluded that the conodontophorid was a soft bodied, bilaterally symmetrical nektonic organism, although there is still much debate concerning possible benthic, nektonic or combined mode of life. Conodont elements are composed of calcium carbonate fluorapatite with additional organic matter. They are found in marine deposits, commonly in black shales associated with graptolites, radiolarians, fish remains, brachiopods, cephalopods, trilobites and palaeocopid ostracods. History of the study The name “conodont” was coined by C. H. Pander (a Russian) in 1856, who worked on Silurian fish fossils of Eastern Europe. Ulrich and Bassler (1926) described many new species from North America and were the first to recognize their biostratigraphic usefulness. In 1934, Schmidt and Scott discovered groups of individual elements preserved together on the same bedding plain. This importantly led to the theory that the individual elements were in life held in pairs (termed an apparatus) often likened to mouth parts. From the 1960s onwards, conodonts have developed into one of the most important biostratigraphic tools available in Palaeozoic and Triassic rocks. Range The very earliest conodonts are known from the rocks of probable Precambrian age in Siberia. They are found more commonly in Cambrian deposits, and diversity increased in the Ordovician and again during the Devonian. The conodont-bearing organism clearly survived the Permo-Triassic boundary extinctions, but became extinct during the late Triassic. It has been noted that the extinction of the conodonts coincides with the diversification of dinoflagellates and the first appearance of calcareous nannofosils. The most primitive conodonts are single cones, which dominate early Ordovician assemblages and reach a peak in the Arenigian (late Early Ordovician). The first platform type conodonts occur around this time as well. Conodont diversity and abundance declined in the Silurian. During the early and mid Devonian, diversity gradually increased reaching an acme in the late Devonian. In the early Carboniferous, conodonts remained abundant and widespread, but diversity decreased during the late Carboniferous. In the Permian, the conodonts almost became extinct; however, they made a recovery in the early to middle Triassic only to disappear in the late Triassic. Classification Conodonts have been assigned to their own Phylum, Conodonta, divided into two Orders based on chemical and ultrastructural differences. Eleven superfamilies have been recognized by reconstructing associations of individual elements into apparatuses, and morphological and element compositional differences further divide these into 47 families. One hundred and eighty genera have been recognized. It must be remembered that any classification of conodonts is an un-natural one, as it is based on morphology only. Morphologically, four main groups of conodonts can be distinguished (Fig. 118).    

Simple cones: Formed by a single tooth, or denticle. Blade-type: Elongate, laterally compressed units formed by a row of denticles which are fused except at their tips. Bar-type: Thin bars with or without a bent shaft which is commonly branched. Platform: It is thought that these forms evolved from bar and blade-type conodonts by the development of broad flanges into plates.

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Fig. 118. The morphological terminology of conodont (Muller, 1978).

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Application The fact that conodonts are relatively common in the rocks of the Palaeozoic age, a period when other microfossil groups are either not present or scarce has made them extremely useful stratigraphic tools. Together with acritarchs, chitinozoa and spores, conodonts are the primary microfossils available to palaeontologists working on Ordovician to Permo-Triassic strata. Biology Isolated conodonts are widespread and abundant. Until the 1980s, their biological affinities were still not known. Two enlightening fossil finds provided a few clues to the affinity of conodonts. The first, a chordate animal with conodonts scattered within what is interpreted as its gut from the fish bears Namurian (Carboniferous) Bear Gulch limestone of Montana. The second, from the famous Cambrian Burgess Shale of British Columbia, is a flattened worm-like animal 60 mm long with a distinct head bearing a U-shaped structure interpreted as a lophophore (a circular or horse-shoe shaped fleshy ridge surrounding the mouth, bearing tentacles found in Bryozoans and Brachiopods). At the base of each of the 20-25 tentacles is a compressed cone closely resembling some contemporaneous conodonts. However, the discovery of a Carboniferous fossil near Edinburgh (and subsequent finds in South Africa) has finally solved the mystery of what the conodont elements are. It is now believed that they are the tooth-like feeding apparatus of a hagfish-like vertebrate. The cooccurrence of conodont elements in symmetrical pairs has allowed certain inferences to be made: The host animal probably exhibited bilateral symmetry. Several pairs of one sort can be associated with one or more pairs of another sort. The shape and arrangement of conodont elements in the apparatuses suggest that they were tooth-like feeding tools. The use of scanning electron microscopy has revealed signs of wear on conodont elements and it is thought that the host organism probably produced only one set in its life time. Life cycle Clearly very little can be stated about possible life cycles since the host organism of conodonts (conodontophorid) is extinct. Preparation technique Since conodonts are resistant to mechanical and chemical attacks, preparation techniques can utilize acids such as acetic, formic, or monochloric to release the elements from their host rocks, which are commonly carbonates. Conodonts are commonly between 200 microns and 5 millimeters in size and can be sieved from finer materials and further concentrated by heavy liquid or ultrasonic techniques. Observation technique The cleaned specimens can then be viewed using a reflected light microscope, then manipulated and mounted in slides in the same manner as foraminifera. Conodonts can also be observed in thin sections. Some images Figure 119 shows a representative selection of conodonts aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and if possible a species name. SEM images in all cases are courtesy of Leicester University (Fig. 119).

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Fig. 119. Some images of Conodont.

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Questions (A) Multi-choice questions 1. 2. 3.

The conodonts are common in: (a) black shale

(b) sand

(c) limestone

The conodonts extinct during: (a) the late Triassic

(b) late Jurassic

(c) late Permian

The conodontophora are feeding by: (a) filter feeding

(b) herbivorous

(c) carnivorous

(B) True and false questions 1. 2. 3. 4. 5. 6. 7. 8. 9.

Radiolaria always live in solitary form. The Phaeodarians radiolaria are rarely preserved in sediments. The deep water forms of radiolaria have evolved Silurian. Radiolaria are rarely found below the CCD. Radiolaria are heterotrophic organisms. Radiolaria diversity declines as latitude increases. Conodont elements are calcareous tooth-like structures. Conodonts are found in marine deposits. Conodont elements are also used as paleothermometers.

CHAPTER VII APPLICATION OF MICROPALEONTOLOGY

CHAPTER VII

APPLICATION OF MICROPALEONTOLOGY

Introduction Together with their high preservation potential, the wide range of environments in which foraminifera occur makes them ideal tools for biostratigraphy and paleoenvironmental studies. In general, the benthic group is more suitable for reconstructing depositional environments, as the occurrence of certain species is restricted to welldefined habitats. The planktic group is highly suitable for detailed biostratigraphical age-dating and correlation due to its cosmopolitan distribution and high evolutionary rates. The small dimensions and the relatively easy and safe preparation methodology make foraminifera highly suitable for projects using cuttings and cores from boreholes. In oil and gas exploration, biostratigraphy and paleoenvironmental reconstructions are the most common applications of microfossils. Whereas biostratigraphy provides the temporal constraint of rock units based on the fossil content, paleoenvironmental reconstruction provides the interpretation of the depositional environment in which the rock was formed. The main advantage of the microfossils is represented by the small dimension of such organisms which allow interpretation using cuttings and cores from boreholes. Since the increase need for detailed stratigraphy, the classical biostratigraphy does not provide sufficient information. Therefore, paleoenvironmental interpretation is more and more required. Quantitative and semi-quantitative micropaleontological analyses provide information on the paleoenvironmental changes, such as paleobathymetric variation and also paleoproductivity. Paloebathymetry is mainly determinate by the integration of depth marker species, and the ratio between the number of planktic and the benthic foraminifera. In order to have a more reliable picture, the combination with other microfossils (e.g., ostracods, pyritized diatoms and radiolaria) is also used (Fig. 120). Different Microfossils Groups Microfossils, particularly from deep-sea sediments, also provide some of the most important records of global environmental change on long, medium or short timescales. Across vast areas of the ocean floor, the shells of planktonic micro-organisms sinking from surface waters provide the dominant source of sediment, and they continuously accumulate (typically at rates of 20-50 million per million years). The study of changes in the assemblages of microfossils and of changes in their shell chemistry (e.g., oxygen isotope composition) are fundamental to research on climate change in the geological past. The two most common uses of microfossils are: biostratigraphy and paleoenvironmental analyses. Biostratigraphy is the differentiation of rock units based upon the fossils which they contain. Paleoenvironmental analysis is the interpretation of the depositional environment in which the rock unit formed, based upon the fossils found within the unit. There are many other uses of fossils besides these, including: paleoclimatology, biogeography, and thermal maturation. There are a great number of different types of microfossils available for use. There are three groups which are of particular importance to hydrocarbon exploration. Micropaleontology is also a tool of Geoarchaeology used in archaeological reconstruction of human habitation sites and environments. Changes in the microfossil population abundance in the stratigraphy of current and former water bodies reflect 117

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changes in environmental conditions. Naturally occurring Ostracods in freshwater bodies are impacted by changes in salinity and pH due to human activities. When correlated with other dating techniques, prehistoric environments can be reconstructed.

Fig. 120. Biosteering in a horizontal well using microfossils in order to confine the drilling in the reservoir target.

Benthic foraminifera tend to be restricted to particular environments and as such provide information to the paleontologist about what the environment was like where the rock containing the fossils formed. For example, certain species of foraminifera prefer the turbid waters near the mouths of rivers while others live only in areas of very clear water. These preferences are recognized by two methods: (1) studies of the distribution of modern foraminifera, and (2) analysis of the sediments containing ancient microfossils. In the first case, if the modern species has a fossil record, one can reasonably assume that the fossil ancestors had similar modes of life as the living organism. However, if the species in question is extinct, then one examines modern forms, inferring that the fossil forms had similar environmental preferences. In the latter case, studies of the rock containing the fossils (sandstone, shale, limestone, etc.) give further clues to the environment of deposition. If a given species is always found in sandstones deposited in river deltas, it is not too much of a guess to suggest that this species preferred to live in or near ancient river deltas. If a company is drilling for oil in deltaic reservoirs, then such information can be very useful by helping to locate ancient deltas both in time and space (Fig. 121).

Fig. 121. Benthic foraminiferal species.

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Planktonic foraminifera provide less information concerning the environment of deposition, since they lived floating in the water column; but they have other advantages. Whereas benthic foraminifera are restricted to certain environments, planktonic foraminifera are dispersed over a much broader part of the world oceans and are often found in large numbers. On a geologic time-scale, events such as the first appearance of a given species or its extinction can happen very quickly (Fig. 122).

Fig. 122. Planktonic foraminiferal species.

Nannofossils first appeared during the Mesozoic Era and have persisted and evolved through time. The function of the calcareous “plates”, even in living forms, is uncertain. One extant group that produces “nannofossils” is the Coccolithophorans, planktonic golden-brown algae that are very abundant in the world’s oceans. The calcareous plates accumulate on the ocean floor, become buried beneath later layers, and are preserved as nannofossils. Some chalks, such as those comprising the White Cliffs of Dover, are composed almost entirely of nannofossils. Like the planktonic foraminifera, the planktonic mode of life and the tremendous abundance of calcareous nannofossils makes them very useful tools for biostratigraphy (Fig. 123).

Fig. 123. Calcareous nannofossils species.

Palynomorphs, which are organic walled fossils, include fossil pollen and spores, as well as certain marine organisms such as dinoflagellates (the red algae which make up the “red tides” in modern oceans). Pollen and spores are transported by wind and water and can travel long distances before the final deposition. They are surprisingly resistant to decay and are common as fossils. Because of the long transport before deposition, they usually tell us little about the environment of deposition, but they can be used for biostratigraphy. Fossil pollen and spores can also give us information about ancient climates. Additionally, the organic chemicals which comprise palynomorphs get darker with increased heat. Because of this color change, they can be used to assess the temperature to which a rock sequence was heated during burial. This is useful in predicting whether oil or gas may have been formed in the area under study, because it is heat from burial in the Earth that makes oil and gas from original organic rich deposits (Fig. 124).

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Fig. 124. Palynomorphs: Oligosphaeridium (left) and Chlamydophorella nyei (right).

Biostratigraphy Biostratigraphy plays a critical role in the building of geologic models for hydrocarbon exploration and in the drilling operations that test those models. The fundamental principal in stratigraphy is that the sedimentary rocks in the Earth’s surface are accumulated in layers, with the oldest on the bottom and the youngest on the top. The history of life on Earth has been one of creatures appearing, evolving, and becoming extinct. Putting these two concepts together, we observe that different layers of sedimentary rocks contain different fossils. When drilling a well into the Earth’s crust in search of hydrocarbons, we encounter different fossils in a predictable sequence below the point in time where the organism became extinct. By studying the fossils in many wells, a geologic model for the area can be built up. Kinds of Biostratigraphic Units Five kinds of biozones are in common use: range zones, interval zones, assemblage zones, abundance zones, and lineage zones. These types of biozones have no hierarchical significance, and are not based on mutually exclusive criteria. A single stratigraphic interval may, therefore, be divided independently into range zones, interval zones, etc., depending on the biostratigraphic features chosen. 1. Range zone It is the body of strata representing the known stratigraphic and geographic range of occurrence of a particular taxon or combination of two taxa of any rank. There are two principal types of range zones: taxonrange zones and concurrent-range zone. (A) Taxon-range zone The body of strata represens the known range of stratigraphic and geographic occurrence of specimens of a particular taxon. It is the sum of the documented occurrences in all individual sections and localities from which the particular taxon has been identified. The boundaries of a taxon-range zone are biohorizons marking the outermost limits of a known occurrence in every local section of specimens whose range is to be represented by the zone. The boundaries of a taxon-range zone in any one section are the horizons of the lowest stratigraphic occurrence and the highest stratigraphic occurrence of the specified taxon in that section. The taxon-range zone is named from the taxon whose range it expresses. The local range of a taxon may be specified in some local sections, areas, or regions as long as the context is clear (Fig. 125).

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Fig. 125. Taxon-range zone.

(B) Concurrent-range zone The body of strata includes the overlapping parts of the range zones of two specified taxa. This type of zone may include taxa that are additional to those specified as characterizing elements of the zone, but only the two specified taxa are used to define the boundaries of the zone. The boundaries of a concurrent-range zone are defined in any particular stratigraphic section by the lowest stratigraphic occurrence of the higherranging of the two defining taxa and the highest stratigraphic occurrence of the lower-ranging of the two defining taxa. A concurrent-range zone is named from both the taxa that define and characterize the biozone by their concurrence (Fig. 126).

Fig. 126. Concurrent-range zone.

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2. Interval zone The body of fossiliferous strata is located between two specified biohorizons. Such a zone is not itself necessarily the range zone of a taxon or a concurrence of taxa; it is defined and identified only on the basis of its bounding biohorizons (Fig. 127).

Fig. 127. Interval zone.

In subsurface stratigraphic work, where the section is penetrated from top to bottom and paleontological identification is generally made from drill cuttings, often contaminated by the recirculation of previously drilled sediments and material sloughed from the walls of the drill hole, interval zones defined as the stratigraphic section comprised between the highest known occurrence (first occurrence downward) of two specified taxa are particularly useful (Fig. 128).

Fig. 128. Interval (highest-occurrence zone) zone.

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This type of interval zone has been called “last-occurrence zone” but should preferably be called “highest-occurrence zone”. Interval zones defined as the stratigraphic section comprised between the lowest occurrence of two specified taxa (“lowest-occurrence zone”) are also useful, preferably in surface work. The boundaries of an interval zone are defined by the occurrence of the biohorizons selected for its definition. The names given to interval zones may be derived from the names of the boundary horizons, the name of the basal boundary preceding that of the upper boundary; e.g., Globigerinoides sicanus-Orbulina suturalis Interval Zone. In the definition of an interval zone, it is desirable to specify the criteria for the selection of the bounding biohorizons (e.g., lowest occurrence, highest occurrence, etc.). An alternative method of naming uses a single taxon name for the name of the zone. The taxon should be a usual component of the zone, although not necessarily confined to it. 3. Lineage zone Lineage zones are discussed as a separate category because they are required for their definition and recognition not only in the identification of specific taxa, but also in the assurance that the taxa chosen for their definition represent successive segments of an evolutionary lineage (Fig. 129).

Fig. 129. Examples of lineage zones.

The body of strata contains specimens representing a specific segment of an evolutionary lineage. It may represent the entire range of a taxon within a lineage or only that part of the range of the taxon below the appearance of a descendant taxon. The boundaries of lineage zones approach the boundaries of chronostratigraphic units. However, a lineage zone differs from a chronostratigraphic unit in being restricted, as all biostratigraphic units are, to the actual spatial distribution of the fossils. Lineage zones are the most reliable means of correlation of relative time by the use of the biostratigraphic method. The boundaries of a lineage zone are determined by the biohorizons representing the lowest occurrence of successive elements of the evolutionary lineage under consideration. A lineage zone is named for the taxon in the lineage whose range or partial range it represents. 4. Assemblage zone The body of strata is characterized by an assemblage of three or more fossil taxa that, taken together, distinguishes it in biostratigraphic characters from adjacent strata. The boundaries of an assemblage zone are drawn at biohorizons marking the limits of the occurrence of the specified assemblage that is a characteristic of the unit. Not all

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members of the assemblage need to occur in order for a section to be assigned to an assemblage zone, and the total range of any of its constituents may extend beyond the boundaries of the zone. The name of an assemblage zone is derived from the name of one of the prominent and diagnostic constituents of the fossil assemblage (Fig. 130).

Fig. 130. Assemblage zone.

5. Abundance zone The body of strata, in which the abundance of a particular taxon or specified group of taxa, is significantly greater than usual in the adjacent parts of the section. An unusual abundance of a taxon or taxa in the stratigraphic record may result from a number of processes that are of local extent, but may be repeated in different places at different times. For this reason, the only sure way to identify an abundance zone is to trace it laterally. The boundaries of an abundance zone are defined by the biohorizons across which there is a notable change in the abundance of the specified taxon or taxa that characterize the zone. The abundance zone takes its name from the taxon or taxa whose significantly greater abundance it represents (Fig. 131).

Fig. 131. Abundance zone.

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Bassiouni, M.A.A., Luger, P., 1990: Maastrichtian to Early Eocene ostracoda from southern Egypt: paleontology, paleoecology, paleobiogeography and biostratigraphy. Berliner Geowissenschaftlischen Abhandlungen A 120, 755–928. Bolli, H. M. Saunders, J. B. and Perch Nielsen, K. 1985: Plankton stratigraphy (planktonic foraminifera, calcareous nannofossils and calpionellids), 573 pages. Cambridge. Boltovskoy, E . and Wright, R. 1976. Recent foraminifera. Dr W. Junk b.v., The Hague, the Netherlands: 515pp. Bown, P. R. 1998: Calcareous Nannofossil Biostratigraphy. Chapman & Hall, 1998. ISBN: 0412789701, 9780412789700. Bramlette, M. N & Sullivan, F. R. 1961: Coccolithophorids and related nannoplankton of the Early Tertiary in California. Micropaleont., 7: 129-174.Hay and Bramlette 1960. Corliss, B . H . and C. Chen. 1988. Morphotypepattern of Norwegian Sea, deep sea benthic foraminifera and ecological implications: Geology, 16: 716-719. Darlina, K., Wade, M., Stewart, I., Kroon, O., Dingle, R., & Brown, A. 2000: Molecular evidence for genetic mixing of Arctic and Antarctic subpolar populations of planktonic foraminifers. Nature, 405, pp. 43-47. Gartner, S. Jr. 1977: Nannofossils and biostarigraphy: an overview. Earth sci. Rev. 13, 227-250. Gartner, S. Jr. 1981: Calcareous nannofossils from Neogene of Trinidad, Jamaica and Gulf of Mexico. - Kansas Univ. ... Micropal., 6, 553-579, Amsterdam 1981. MARTINI, E.: Standard Tertiary and Quaternary calcareous nannoplankton zonation. Haq, B. U. & Boersma, A. 1983: Introduction to marine micropaleontology. 376 pages. El Sevier Science. Haynes, J., R. 1981: Foraminifera. - With 15 plates, 94 figs., 433 pp. - London-: Macmillan Publ. Ltd. 1981. ISBN 0 333 28681 2. Hottinger, L., 1982: Larger Foraminifera, giant cells with a historical background: Naturwissenschaften, v. 69, p. 361–371. Hottinger, L., 1983: Processes determining the distribution of larger foraminifera in space and time: Utrecht Micropaleontological Bulletins, v. 30, p. 239–253. Hottinger, L., 1998: Shallow benthic foraminifera at the Paleocene-Eocene boundary: Strata, ser. 1, v. 9, p. 61– 64. Kaminski, M.A. 2004a. The new and revised genera of agglutinated foraminifera published between 1996 and 2000. In: Bubík, M. & Kaminski, M.A. (eds), Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 8, 257-271.

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Knappertsbusch, M. 2000. Morphologic evolution of the coccolithophorid Calcidiscus leptoporus from the upper Oligocene to Recent. Journal of Paleontology, 74(3):712-730. Langer, M.R. & Hottinger, L. 2000. Biogeography of selected “larger” foraminifera. Micropaleontology, 46 (1): 105-127. (supplement 1): 105-127. Loeblich A., R. and Tappan H. 1964: foraminiferida In: R. C. Moore (ed), Treatire on invertebrate paleontology C. Protista, vols 1 and 2, pp. 1-868. The geological society of America and the university of Kansas press. Loeblich, A., R. & Tappan, H. 1987. Foraminiferal Genera and their Classification (2 vols). xi + 970 pp.; ix + 213 pp. + 847 plates. New York: Van Nostrant Reinhold; London: Chapman & Hall. ISBN: 0 442 25937 9. Loeblich, A., R. & Tappan, H. 1992. Present status of foraminiferal classification, in Takayanagi, Y., and Saito, T. (eds.), Studies in Benthic Foraminifera, Proceedings of the Fourth International Symposium on Benthic Foraminifera, Sendai, 1990: Tokai University Press, Tokyo, Japan, p. 93–102. Mcintyre, A., Bé, A.W.H., 1967. Modern Coccolithophoridae of the Atlantic Ocean — I. Placoliths and crytoliths. Deep-Sea Res. 14, 561–597. Murray, J. W. 1973. Distribution and Ecology of Living Benthic Foraminiferids. Heinemann Educational Books, London. Renema, W. & Hart, M.B. 2012. Larger benthic Foraminifera of the type Maastrichtian. Scripta Geol., Spec. Issue 8 (2012). Stanley, D. J.. "Sea Level and Initiation of Predynastic Culture in the Nile Delta." Nature 363 (6428)(1993): 435-438. Wilbur, K., M. & Watable, N. 1963: experimental studies on classification of the alga coccolithus huxleyi. Ann. N. Y. Accad. Sci., 109: 82-112. Winter, A. & Siesser, W. G. 2006: Coccolithophores, 256 pages, Publisher: Cambridge University Press, ISBN10: 0521031699. Zachos , J., Pagani, M., Sloan, L., Thomas, E., and Billups, K. 2001. Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present. Science, 292: 686-693.

GLOSSARY

Acute: a shape with acute or sharp angles. Agglutinated: a shell texture characterized by components gathered in the ambient environment and bound by organic or biomineralized cements produced by the cell. Alveolar layer: a layer of alveoles in lateral chamber walls. Annular arrangement: an arrangement of concentric annular chambers. Annular chamber: ring-shaped. May be subdivided. Anterior: directed to or positioned near or on the frontal part of a chamber, usually enclosing main aperture, distal in respect to direction of growth. Apertural face: surface of chamber-wall comprising the main cameral aperture. Apertural flange: see Lip. Apertural lip: see Lip. Apertural tooth: see Milioline tooth/teeth and Valvular tooth. Aperture: a primary opening within the test or between test elements, putting it into communication intrathalamous with extrathalamous cytoplam. Apex: an initial portion of trochospiral or conical test. Apical: referring to the initial part of trochospiral or conical test. Areal: aperture and/or intercameral foramen: position of aperture(s) and/or foramina within apertural face, not at its base nor at the shell margin. Areal aperture: a cameral aperture in the distal wall, not at suture. May be single or multiple. Arenaceous: see Agglutinated. Axial section: slice bisecting test in plane coinciding with the axis of coiling and intersecting proloculus. Axis of coiling: an imaginary line around which spiral test is coiled. Biconcave: a test having both sides concave (in coiled forms). Biconvex: test having both sides convex (in coiled forms). Bifid: divided into two branches.

127

128

Glossary

Bilateral: having two equal sides, as reflected by a plane surface. Bilocular: said of an embryonic apparatus having two chambers differing in size and shape from following ones. Biloculine: see Milioline coiling. Biserial: trochospiral chamber arrangement with about 180° between consecutive chambers producing two rows of chambers. Biumbilicate: a spiral test having umbilici on both sides. Biumbonate: having an umbo on both sides of the test. See also Umbo. Bulla: a blister-like test element covering primary, main or supplementary apertures. May have marginal accessory apertures. Present on ultimate chamber of planktic foraminifers only. Cancellate: having honeycomb-like surface ridges. Chamber [loculus]: space(s) comprised between skeletal elements of the test and produced at an instar, i.e. during a single growth step. See also Cyclical chamberlets, Foliar chamberlets, Stellar chamberlets, Subsidiary chamberlets. Chamber arrangement: a disposition pattern of chambers. Chamberlets: segments or subdivisions of a chamber. See also Cyclical chamberlets, Foliar chamberlet, Stellar chamberlet, subsidiary chamberlets. Choma (pl. chomata): dense, textureless deposit on previous whorl constituting the chamber floor, forming a pair of parallel ridges, each extending from a tunnel margin to the previous one, in fusulinids. Coil: see Whorl. Cosmopolitan: occurring all over the world wherever there is a suitable habitat. Costae: raised ribs or ridges on test surface. See also Blades, Striae. Costate: having costae. Cribrate: perforated by multiple holes. Should be used exclusively for numerous and small multiple apertures. Cytoplasm: protoplasm, excluding nucleus. Deuteroconch: chamber following immediately the proloculus and differing in shape and often in size from subsequently formed chambers. Dextral coiling: a clockwise direction of coiling as seen from the spiral side. Diaphanotheca: a light-colored or translucent wall layer immediately below tectum in fusulinids. Dimorphism: the coexistence of two distinct morphotypes corresponding to different generations in the life cycle of a single species, concerning adult growth stages and/or protoconch and following nepionic chambers. Dorsal: the side of a flattened organism turned away from its substrate, as opposed to ventral. See also Spiral side, Umbilical side.

Glossary

129

Embryonic: the earliest growth stage in foraminiferal ontogeny, usually distinguished from later stages by an abrupt change in the shell architecture, commonly with thickened walls indicating a longer period of standstill in growth (embryonic apparatus) as frequent in the megalospheric generation of larger K-strategists. Endoplasm: a central part of protoplasm containing nucleus or nuclei and in which the major metabolic processes take place. Epitheca: biomineralized deposits on the inner chamber surface in fusulinids, comprising tectorium and chomata. Equator(ial): a peripheral line in a median plane, perpendicular to the axis of planispiral coiling or radial symmetry in chamber arrangement. Equatorial chambers or chamberlets: see Main equatorial chamberlets. Equatorial section: a slice of test in an equatorial plane. Evolute chamber arrangement: in spirally coiled foraminifera where, due to the chamber shape, the chamber lumina in a coil do not laterally cover those of the preceding coil. Extraumbilical aperture: an interiomarginal primary chamber aperture in enrolled species unconnected with umbilicus. Extraumbilical-umbilical aperture: an interiomarginal primary chamber aperture extending in enrolled species from umbilicus towards the periphery. Foramen, foramina [intercameral]: an opening or openings putting in communication consecutive main chamber lumina and providing passage for functional endoplasm. Fusiform: a shell shape in the form of a spindle produced by planispiral-involute growth where the axial diameter is larger than the equatorial diameter and where the polar ends of the shell are tapered. Hispid: covered with minute pustules or pseudospines. Imperforate: lacking pores or parapores. Interiomarginal aperture: an aperture situated at the suture between the distal wall and the preceding coil. Involute chamber arrangement: in spirally coiled forms where, due to the chamber shape, the chamber lumina in a coil cover laterally those of the preceding coil. Keriotheca: an alveolar, honeycomb-like structure of the spiral wall in advanced fusulinids, may consist of an upper (outer) and a lower (inner) “layer” produced by a split of the alveoli into narrower subunits below the tectum. May be combined in highly specialized forms with additional exoskeletal structures. Knob: see Boss. Life cycle: most eucariotic, free-living cells reproduce asexually but shift from time to time to sexual reproduction in order to avoid degeneration. Limbate: referring to the thickened border of chamber-edge at suture; may be elevated. Lip [apertural lip]: an averted extension of the chamber wall along a cameral aperture. May be narrow or broad (flange), small or large. See also Phialine lip, Rim. Compare with Folium.

130

Glossary

Loculus: chamber. Microspheric: in dimorphic species; a test having a small proloculus or microsphere; commonly a schizont. Milioline: referring to taxa or their characters of the suborder Miliolina. Milioline coiling: in porcelaneous foraminifera: each chamber added in, for example, 72° (quinqueloculine), 120° (triloculine), or 180° (spiroloculine or biloculine). Milioline tooth/teeth: one or more inward projections of the inner portion of the chamber wall into the aperture of milioline species. Monothalamous (unilocular): a shell consisting of a single chamber. Ornamentation: patterns of an external modification of a wall thickness and/or texture. Perforate: referring usually to a wall possessing true pores, but the term is also applied to a wall possessing parapores. Planispiral chamber arrangement: an arrangement in whorls where the rate of translation is zero. Spiral and umbilical sides of the test are identical and symmetrical with regards to the plane of bilateral symmetry. Polythalamous (multithalamous, multilocular): a shell consisting of numerous chambers. Porcelaneous test wall: composed of optically cryptocrystalline lathes and rods or needles of calcite. Rods arranged randomly, lathes arranged in a tile-roof pattern and forming the outer wall-layer. Wall imperforate, but may possess pits. Primary aperture: see Accessory aperture, Main cameral aperture, Stolon, Supplementary aperture. Proloculus: the initial chamber of the foraminiferal test in all generations. Protheca: a free chamber wall of fusulinids composed of tectum and diaphanotheca. Protoconch: the first chamber of test in which a deuteroconch is differentiated. See Proloculus. Protoplasm: a living matter comprising a cell-body. Proximal: nearer to the proloculus, opposite to the direction of growth. Pseudopodia: semi-permanent or temporary extrathalamous ectoplasmic projections. Pustule [tubercle; papilla]: hemispherical to subconical inflational protuberance of the outer lamella. See also Pseudospine. Quinqueloculine: see Milioline coiling. Radial: a direction from a pole or axis to any part of the circumference of the test. Radiate aperture: a single aperture, in terminal or margino-terminal position, with radially directed, slit-like or pointed extensions. The radial aperture margins may fuse and thereby subdivide the aperture, as in some nodosariaceans. Reticulate: having ornamental features arranged in a network. See Cancellate.

Glossary

131

Rhizopodia: bifurcating and anatomizing pseudopodia. Sagittal section: a slice through a test normal to the axis of coiling and passing through proloculus. Sessile: permanently attached, usually with an attachment surface on the dorsal (spiral) side of trochospiral shells. Designates also sedentary life habit. Sinistral coiling: a counterclockwise direction of coiling as viewed from the spiral side. Spinose: possessing true, acicular spines (in planktic foraminifera). See also Pseudospinose. Spiral aperture: an interiomarginal aperture along the spiral suture. Usually supplementary, not converted into a foramen. Striae: thin costae. Striate: having striae. Sulcus: a peripheral infold of primary chamber-wall, always imperforate. May or may not have radial passages between underlying sulcus canal and chamber-lumen. May or may not be covered by marginal structures, like, for example, a marginal cord. Suture: a line of the adherence of the chamber wall(s) to a previously formed test. Symbiosis: in foraminifera; algal cells living (as symbionts) within the foraminiferal cytoplasm in a mutualistic relationship with their host. Tectorium: in fusulinids; a slightly transparent internal shell layer lining the chamber walls and covered by the opaque tectum in the external, spiral wall. May be combined with a diaphanotheca. Tectum: a thin, dense outer layer of the spirotheca (spiral outer wall) in fusulinids. Homologous in position to an epiderm but may be produced by different shell building processes. See also Marginal prolongation. Terminal: positioned at the distal end of a linear structure or of an elongate chamber. Test: a shell or skeletal component of a foraminifer. May be composed of a variety of material secreted, agglutinated or both. Triserial: a chamber arrangement in a trochospire with three chambers per coil, hence with about 120° between the median planes of consecutive chambers. Trochospiral arrangement: a chamber arrangement in whorls or coils where the rate of translation is more than zero. Spiral and umbilical sides dissimilar. May be involute or evolute on either the spiral or umbilical side. Umbilical [intraumbilical] aperture: the primary aperture of a chamber leading into umbilicus. Umbilical side: in trochospiral tests the side opposite to the spiral one. See also Ventral. Umbo (central pillar, pars auct.): an expanding pile of thickened lamellae in the axial position of involute or orbitoidal foraminifera (never associated with an open umbilicus or with canals). See also Pile, Plug. Unilocular (monolocular, monothalamous): single-chambered. Uniserial: chambers arranged in a single row. Compare with Biserial, Triserial.

132

Glossary

Whorl [coil]: a single turn or volution of the spiral test through 360°. Zygote: a diploid cell resulting from the fusion of two (haploid) gametes in a sexual reproduction. The biomineralized envelope of the zygote is called microsphere. See also Life cycle.

SUBJECT INDEX

H

A Actinopoda 103 Agglutinated 10 Abyssal 4 Amphidont 52 Assemblage 121

Heterococcolith 86 Holococcolith 86 Hyaline 16

I Inflation 68

B Bathyal 4 Benthic 10, 24 Biostratigraphy 115 Brackish 27

L Lineage 121 Lopadolith 83 Lophophore 109

C Capsule 104 Carbonate platforms 27 Carapace 51, 53, 55, 56, 61 Choma 37 Coccolith 82, 85, 87 Coccolithophores 90, 98 Conodonta 107

M Mandibular 52 Marches 27 Merodont 52 Microfossils 4

N Nanno 79 Nummulites 3, 42 Neritic 4

D Deuteroconch 46 Diatoms 13 Dimorphism 64 Dinoflagellates 13

P

E

Palaeobathymetry 9, 10 Paleoecology 72 Paleontologists 15 Palynomorph 117 Photosynthesizing 5 Planktonic 10, 24 Porcelaneous 15 Protoconch 46 Protista 12

Eukaryotes 4 Eye spot 69 Estuary 26

F Fusulinellid 36, 37

G

R

Gamonts 35 Green house 12

Rhizopoda 12

133

Subject Index

134

S Scapolith 83, 84 Schwagerinid 36, 37 Sculpture 19, 66 Stenohaline 24 Substrate 72

T Taxon 118 Tectorium 36 Terminal 19 Textulariina 14 Triserial 17 Trochospiral 17

U Umbilical 19 Unipartite 52 Uniserial 17

Z Zone 117, 118, 120 Zygote 14