Microfossils - Armstrong Brasier, 2005

Microfossils - Armstrong Brasier, 2005

(Parte 1 de 8)

Wonder is the first of all passions René Descartes, 1645

Howard A. Armstrong Senior Lecturer in Micropalaeontology, Department of Earth Sciences, University of Durham, UK

Martin D. Brasier Professor of Palaeobiology, Department of Earth Sciences, University of Oxford, UK

© 2005 Howard A. Armstrong and Martin D. Brasier

BLACKWELL PUBLISHING 350 Main Street, Malden, MA 02148-5020, USA 108 Cowley Road, Oxford OX4 1JF, UK 550 Swanston Street, Carlton, Victoria 3053, Australia

The right of Howard A. Armstrong and Martin D. Brasier to be identified as the Authors of this Work has been asserted in accordance with the UK Copyright, Designs, and Patents Act 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs, and Patents Act 1988, without the prior permission of the publisher.

First edition published 1980 by George Allen & Unwin, © M.D. Brasier 1980 Second edition published 2005 by Blackwell Publishing Ltd

Library of Congress Cataloging-in-Publication Data

Armstrong, Howard, 1957–

Microfossils. – 2nd ed./Howard A. Armstrong and Martin D. Brasier. p. cm.

Rev. ed. of: Microfossils / M.D. Brasier. 1980. Includes bibliographical references and index. ISBN 0-632-05279-1 (pbk. : alk. paper) 1. Micropaleontology. I. Brasier, M.D. Microfossils. I. Title.

A catalogue record for this title is available from the British Library.

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Contents

Preface vii

Part 1Applied micropalaeontology1

Chapter 1 Introduction 3 Chapter 2Micropalaeontology, evolution and biodiversity8 Chapter 3Microfossils in stratigraphy16 Chapter 4Microfossils, stable isotopes and ocean-atmosphere history25 Chapter 5Microfossils as thermal metamorphic indicators35

Part 2The rise of the biosphere37

Chapter 6The origin of life and the early biosphere39 Chapter 7Emergence of eukaryotes to the Cambrian explosion48 Chapter 8Bacterial ecosystems and microbial sediments59

Part 3Organic-walled microfossils69

Chapter 9Acritarchs and prasinophytes71 Chapter 10Dinoflagellates and ebridians80 Chapter 1 Chitinozoa 96 Chapter 12 Scolecodonts 101 Chapter 13Spores and pollen104

Part 4Inorganic-walled microfossils127

Chapter 14Calcareous nannoplankton: coccolithophores and discoasters129 Chapter 15 Foraminifera 142 Chapter 16Radiozoa (Acantharia, Phaeodaria and Radiolaria) and Heliozoa188 Chapter 17 Diatoms 200 Chapter 18Silicoflagellates and chrysophytes210 vi Contents

Chapter 19Ciliophora: tintinnids and calpionellids215 Chapter 20 Ostracods 219 Chapter 21 Conodonts 249

Appendix – Extraction methods273 Systematic Index280 General Index287

In the 25 years since the first, highly successful, edition of Microfossilswas published there have been significant advances in all the areas of understanding of microscopic life and their fossil counterparts. Our new knowledge has led to major changes in the classification, applications and in some cases the biological affinities, of the major groups covered in this book. Greater understanding of species concepts, stratigraphical ranges and the completeness of the microfossil record means all of the Phanerozoic and parts of the Proterozoic can now be dated using microfossils. The high fidelity of the microfossil record provides the best test bed for numerous evolutionary studies. Microfossils remain an indispensable part of any sedimentary basin study, providing the biostratigraphical and palaeoecological framework and, increasingly, a measure of maturity of hydrocarbonprone rocks. The rise of palaeoclimatology has given micropalaeontology a new impetus too, with calcareouswalled groups providing stable isotope and geochemical proxies for oceanographic, palaeoenvironmental and palaeo-climatic change. Indeed it is now widely accepted that some microscopic groups are responsible for maintaining the Earth as a habitable planet and have been doing so since the early Proterozoic and perhaps before. Micropalaeontology therefore now occupies a central role in the modern Earth and environmental sciences and increasingly a much wider group of Earth scientists are likely to come across the work of micropalaeontologists. We hope this second edition provides an inexpensive introductory textbook that will be of use to students, teachers and non-specialists alike.

We have not changed the main motivation of this book, which is to provide a manual for somebody with little micropalaeontological background working at the microscope. Morphology and classification lie at the core of the book, supported by more derivative information on geological history, palaeoecology and applications, with supporting references. An addition to this book are selected photomicrographs, which are not intended to give a comprehensive coverage of the taxa discussed but to supplement the line drawings.

Conscious of the adage that for every expert there is a different classification we have favoured the use of those schemes published in the Fossil Record I (Renton, M. (ed.), 1993, Chapman & Hall, London), a volume compiled by experts in the respective groups and a statement of the familial level classification at the time of publication. Students will therefore have access to a much more detailed treatment of family level stratigraphical ranges than can be provided by this text. Mindful also of the value of collecting and processing microfossil material, the section on preparatory methods has been retained. This focuses on techniques that are simple, safe and possible with a minimum of sophisticated equipment.

In order to compile this book we have relied on the work and advice freely given by our many colleagues past and present. We are particularly indebted to those who have commented on the various parts of the manuscript: Professor R.J. Aldridge, Professor D.J. Batten, Dr D.J. Horne, Professor A.R. Lord, Dr G. Miller, Dr S.J. Molyneau, Dr H.E. Presig, Dr J.B. Riding and Dr J. Remane. Mrs K.L. Atkinson prepared the diagrams and new line drawings. In addition, a special thankyou is offered to all these authors and publishers who have kindly allowed the use of their illustrations and photomicrographs; formal acknowledgement is provided throughout the text. Without all these people this project would never have been completed and we are most grateful for their help.

Preface vii

Blackwell Publishing and the Natural History MuseumLondon are the publishers of PaleoBase: Microfossils, a powerful illustrated database of microfossils designed for student use. Please see w.paleobase.comfor ordering details, or email ian.francis@oxon.blackwellpublishing.com

PART 1 Applied micropalaeontology

Microfossils – what are they?

A thin blanket of soft white to buff-coloured ooze covers one-sixth of the Earth’s surface. Seen under the microscope this sediment can be a truly impressive sight. It contains countless numbers of tiny shells variously resembling miniature flügelhorns, shuttlecocks, water wheels, hip flasks, footballs, garden sieves, space ships and chinese lanterns. Some of these gleam with a hard glassy lustre, others are sugary white or strawberry coloured. This aesthetically pleasing world of microscopic fossils or microfossils is a very ancient one and, at the biological level, a very important one.

Any dead organism that is vulnerable to the natural processes of sedimentation and erosion may be called a fossil, irrespective of the way it is preserved or of how recently it died. It is common to divide this fossil world into larger macrofossilsand smaller microfossils, each kind with its own methods of collection, preparation and study. This distinction is, in practice, rather arbitrary and we shall largely confine the term ‘microfossil’ to those discrete remains whose study requires the use of a microscope throughout. Hence bivalve shells or dinosaur bones seen down a microscope do not constitute microfossils. The study of microfossils usually requires bulk collecting and processing to concentrate remains prior to study.

The study of microfossils is properly called micropalaeontology. There has, however, been a tendency to restrict this term to studies of mineral-walled microfossils (such as foraminifera and ostracods), as distinct from palynologythe study of organic-walled microfossils (such as pollen grains, dinoflagellates and acritarchs). This division, which arises largely from differences in bulk processing techniques, is again rather arbitrary. It must be emphasized that macropalaeontology, micropalaeontology and palynology share identical aims: to unravel the history of life and the external surface of the planet. These are achieved more speedily and with greater reward when they proceed together.

Why study microfossils?

Most sediments contain microfossils, the kind depending largely on the original age, environment of deposition and burial history of the sediment. At their most abundant, as for example in back-reef sands, 10cm3of sediment can yield over 10,0 individual specimens and over 300 species. By implication, the number of ecological niches and biological generations represented can extend into the hundreds and the sample may represent thousands if not hundreds of thousands of years of accumulation of specimens. By contrast, macrofossils from such a small sample are unlikely to exceed a few tens of specimens or generations. Because microfossils are so small and abundant (mostly less then 1mm) they can be recovered from small samples. Hence when a geologist wishes to know the age of a rock or the salinity and depth of water under which it was laid down, it is to microfossils that they will turn for a quick and reliable answer. Geological surveys, deep sea drilling programmes, oil and mining companies working with the small samples available from borehole cores and drill cuttings have all therefore employed micropalaeontologists to learn more about the rocks they are handling. This commercial side to micropalaeontology has undoubtedly been a major stimulus to its growth. There are some

CHAPTER 1 Introduction

4Part 1: Applied micropalaeontology philosophical and sociological sides to the subject, however. Our understanding of the development and stability of the present global ecosystem has much to learn from the microfossil record, especially since many microfossil groups have occupied a place at or near to the base of the food web. Studies into the nature of evolution cannot afford to overlook the microfossil record either, for it contains a wealth of examples. The importance of understanding microfossils is further augmented by discoveries in Precambrian rocks; microfossils now provide the main evidence for organic evolution through more than three-quarters of the history of life on Earth. It is also to microfossils that science will turn in the search for life on other planets such as Mars.

The cell

A great many microfossils are the product of singlecelled (unicellular) organisms. A little knowledge of these cells can therefore help us to understand their way of life and, from this, their potential value to Earth scientists. Unicells are usually provided with a relatively elastic outer cell membrane(Fig. 1.1) that binds and protects the softer cell material within, called the cytoplasm(or protoplasm). Small ‘bubbles’ within the cytoplasm, called vacuoles, are filled with food, excretory products or water and serve to nourish the cell or to regulate the salt and water balance. A darker, membrane-bound body, termed the nucleus, helps to control both vegetative and sexual division of the cell and the manufacture of proteins. Other small bodies concerned with vital functions within the cell are known as organelles. The whip-like thread that protrudes from some cells, called a flagellum, is a locomotory organelle. Some unicells bear many short flagella, collectively called cilia, whilst others get about by means of foot-like extensions of the cell wall and cytoplasm, known as pseudopodia. Other organelles that can occur in abundance are the chromoplasts(or chloroplasts). These small structures contain chlorophyll or similar pigments for the process of photosynthesis.

Nutrition

There are two basic ways by which an organism can build up its body: by heterotrophy or by autotrophy. In heterotrophy, the creature captures and consumes living or dead organic matter, as we do ourselves. In autotrophy, the organism synthesizes organic matter from inorganic CO2, for example, by utilizing the effect of sunlight in the presence of chlorophyll- like pigments, a process known as photosynthesis. Quite a number of microfossil groups employ these two strategies together and are therefore known as mixotrophic.

Reproduction

Asexual(or vegetative) and sexualreproduction are the two basic modes of cellular increase. The simple division of the cell found in asexual reproduction results in the production of two or more daughter cells with nuclear contents similar in proportion to those of the parent. In sexual reproduction, the aim is to halve these normal nuclear proportions so that sexual fusion with another ‘halved’ cell can eventually take place. Information contained in each cell can then be passed around to the advantage of the species. This halving

Fig. 1.1The living cell. (a) Eukaryotic cell structure showing organelles. (b) Cross-section through a flagellum showing paired 9+2 structure of the microfibrils. (Reproduced with permission from Clarkson 2000.)

Chapter 1: Introduction5 process is achieved by a fourfold division of the cell, called meiosis, which results in four daughter cells rather than two.

The empires of life

Living individuals all belong to naturally isolated units called species. Ideally, these species are freely interbreeding populations that share a common ecological niche. Even those lowly organisms that disdain sexual reproduction (such as the silicoflagellates) or do not have the organization for it (such as the cyanobacteria), occur in discrete morphological and ecological species. Obviously it is impossible to prove that a population of microfossils was freely interbreeding but, if specimens are sufficiently plentiful, it is possible to recognize both morphological and ecological discontinuities. These can serve as the basis for distinguishing one fossil species from another.

(Parte 1 de 8)

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