Geologic Time Scale 2020

By Felix Gradstein, James G. Ogg and Gabi M. Ogg

Geologic Time Scale 2020 (2 volume set) contains contributions from 80+ leading scientists who present syntheses in an easy-to-understand format that includes numerous color charts, maps and photographs. In addition to detailed overviews of chronostratigraphy, evolution, geochemistry, sequence stratigraphy and planetary geology, the GTS2020 volumes have separate chapters on each geologic period with compilations of the history of divisions, the current GSSPs (global boundary stratotypes), detailed bio-geochem-sequence correlation charts, and derivation of the age models.

The authors are on the forefront of chronostratigraphic research and initiatives surrounding the creation of an international geologic time scale. The included charts display the most up-to-date, international standard as ratified by the International Commission on Stratigraphy and the International Union of Geological Sciences.

As the framework for deciphering the history of our planet Earth, this book is essential for practicing Earth Scientists and academics.

• Completely updated geologic time scale
• Provides the most detailed integrated geologic time scale available that compiles and synthesize information in one reference
• Gives insights on the construction, strengths and limitations of the geological time scale that greatly enhances its function and its utility

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 30, 2020
• ISBN: 9780128243619

Book preview

Geologic Time Scale 2020

Edited by

Felix M. Gradstein

James G. Ogg

Mark D. Schmitz

Gabi M. Ogg

Table of Contents

Cover image

Title page

Copyright

Quotes

Contributors

Editors’ Biographies

Preface

Abbreviations and acronyms

Organizations

Time Scale Publications

Geoscientific Concepts

Symbols

Part I: Introduction

Chapter 1. Introduction

Abstract

Chapter outline

1.1 The Geologic Time Scale

1.2 A Geologic Time Scale GTS2020

1.3 How this book is arranged?

1.4 Historical overview of geologic time scales

1.5 The World Geologic Time Scale

Bibliography

Chapter 2. The Chronostratigraphic Scale

Abstract

Chapter outline

2.1 History of geologic stratigraphic standardization

2.2 Stage unit stratotypes

2.3 Global Boundary Stratotype Section and Point (GSSP)

2.4 Global Standard Stratigraphic Age (GSSA)

2.5 Other considerations for choosing a GSSP

References

Part II: Concepts and Methods

Chapter 3. Evolution and Biostratigraphy

Abstract

Chapter outline

Subchapter 3A. Trilobites

3A.1 Earliest trilobites

3A.2 Trilobite phylogeny

3A.3 Trilobite biostratigraphy

Subchapter 3B. Graptolites

3B.1 Graptolite construction and relationships

3B.2 Paleogeography, paleoecology, and sedimentology

3B.3 Practicalities and history of study

3B.4 Biostratigraphy

3B.5 Ordovician graptolite evolution and succession

3B.6 Silurian graptolite evolution and succession

Subchapter 3C. Chitinozoans

3C.1 Introduction

3C.2 Phylogeny and taxonomy

3C.3 Origin and diversification

3C.4 Applications

Subchapter 3D. Conodonts

3D.1 Introduction

3D.2 Biologic affinity

3D.3 Paleoecology and biofacies

3D.4 Biostratigraphy and evolution

3D.5 Cambrian

3D.6 Ordovician

3D.7 Silurian

3D.8 Devonian

3D.9 Carboniferous

3D.10 Permian

3D.11 Triassic

Subchapter 3E. Ammonoidea

3E.1 Paleozoic Ammonoidea

3E.2 Triassic Ammonoidea

3E.3 Orders/Suborders

3E.4 Jurassic Ammonoidea

3E.5 Cretaceous Ammonoidea

Subchapter 3F. Calcareous nannofossils

3F.1 Introduction

3F.2 Evolution

3F.3 Biostratigraphy—Mesozoic

3F.4 Biostratigraphy—Cenozoic

Subchapter 3G. Planktonic foraminifera

3G.1 Introduction

3G.2 Jurassic

3G.3 Cretaceous

3G.4 Cenozoic

Subchapter 3H. Larger benthic foraminifera

3H.1 Introduction

3H.2 Key groups of larger benthic foraminifera

3H.3 Late Paleozoic LBF Biostratigraphy

3H.4 Triassic LBF Biostratigraphy

3H.5 Jurassic LBF Biostratigraphy

3H.6 Cretaceous LBF Biostratigraphy

3H.7 Cenozoic LBF Biostratigraphy

Acknowledgments

Subchapter 3I. Dinoflagellates

3I.1 Dinoflagellates as organisms

3I.2 Dinoflagellates as fossils

3I.3 Evolution of dinoflagellates

Acknowledgments

Subchapter 3J. Plants, spores, and pollen

3J.1 The Precambrian

3J.2 Paleozoic

3J.3 Mesozoic

3J.4 Cenozoic

3J.5 Final remarks

Subchapter 3K. Cretaceous microcrinoids

Subchapter 3L. Three major mass extinctions and evolutionary radiations in their aftermath

3L.1 Introduction

3L.2 The Late Ordovician mass extinction

3L.3 End-Permian mass extinction

3L.4 End-Cretaceous mass extinction

3L.5 Concluding remarks

Chapter 4. Astrochronology

Abstract

Chapter outline

4.1 Introduction

4.2 Eccentricity

4.3 Chaos in the solar system

4.4 Inclination and obliquity

4.5 Chaotic diffusion and secular resonances

4.6 Discussion

Acknowledgments

References

Chapter 5. Geomagnetic Polarity Time Scale

Abstract

Chapter outline

5.1 Principles

5.2 Late Cretaceous through Cenozoic geomagnetic polarity time scale

5.3 Middle Jurassic through Early Cretaceous geomagnetic polarity time scale

5.4 Geomagnetic polarity time scale for Early Jurassic and older rocks

5.5 Summary

Bibliography

Chapter 6. Radioisotope Geochronology

Abstract

Chapter outline

6.1 Introduction

6.2 U–Pb geochronology

6.3 ⁴⁰Ar/³⁹Ar geochronology

6.4 Re–Os geochronology

6.5 Application of radioisotope geochronology in the stratigraphic record

6.6 Conclusion

Bibliography

Chapter 7. Strontium Isotope Stratigraphy

Abstract

Chapter outline

7.1 Introduction

7.2 Methodologies for Sr-isotope stratigraphy

7.3 The databases used in this volume

7.4 Numerical ages

7.5 Fitting the LOESS database

7.6 The quality of the fit

7.7 Comments on the LOESS fit

7.8 Sr-isotope stratigraphy for pre-Ordovician time

Bibliography

Chapter 8. Osmium Isotope Stratigraphy

Abstract

Chapter outline

8.1 Introduction

8.2 Untapped potential

8.3 Hydrogenic Fe–Mn crusts

8.4 Organic-rich mudrock

8.5 Re–Os isochrons and (¹⁸⁷Os/¹⁸⁸Os)0 profiles

8.6 Pre-Phanerozoic changes in seawater ¹⁸⁷Os/¹⁸⁸Os

8.7 Higher resolution ¹⁸⁷Os/¹⁸⁸Os Phanerozoic records

8.8 Integrating organic-rich mudrock and oxic pelagic sediment ¹⁸⁷Os/¹⁸⁸Os records

Bibliography

Chapter 9. Sulfur Isotope Stratigraphy

Abstract

Chapter outline

9.1 Introduction

9.2 Mechanisms driving the variation in the S isotope record

9.3 Isotopic fractionation of sulfur

9.4 Measurement and materials for sulfur isotope stratigraphy

9.5 A Geologic time scale database

9.6 A database of S isotope values and their ages for the past 130 Myr using LOWESS regression

9.7 Use of S isotopes for correlation

Bibliography

Chapter 10. Oxygen Isotope Stratigraphy

Abstract

Chapter outline

10.1 Introduction

10.2 Methodology

10.3 Application principles and considerations

10.4 Oxygen isotope stratigraphy

10.5 Summation

Acknowledgments

Bibliography

Appendices

Chapter 11. Carbon Isotope Stratigraphy

Abstract

Chapter outline

11.1 Introduction

11.2 Methodology

11.3 Application principles and considerations

11.4 Materials and methods

11.5 Chronostratigraphic correlation and excursions

11.6 Causes of carbon isotope excursions

11.7 Conclusion

Acknowledgments

References

Chapter 12. Influence of Large Igneous Provinces

Abstract

Chapter outline

12.1 Large Igneous Provinces

12.2 Influence on environment

12.3 Correlation with Phanerozoic time scale boundaries

12.4 Implications for natural boundaries in the Precambrian

12.5 Additional important Proterozoic Large Igneous Provinces

12.6 Large Igneous Provinces volume and extent of environmental effects

12.7 Future work

Acknowledgments

Bibliography

Chapter 13. Phanerozoic Eustasy

Abstract

Chapter outline

13.1 Introduction

13.2 The sequence stratigraphy paradigm and eustasy

13.3 Anatomy of eustatic variations

13.4 Phanerozoic eustasy: a review

13.5 Summary

Acknowledgments

Bibliography

Chapter 14. Geomathematics

Chapter outline

SubChapter 14A. Geomathematical and Statistical Procedures

14A.1 History

14A.2 Spline fitting in GTS2004

14A.3 Modifications in GTS2012

14A.4 Statistical distribution of age determinations along the geologic time scale

14A.5 Modifications in GTS2020

SubChapter 14B. Global Composite Sections and Constrained Optimization

14B.1 The geologic time scale challenge

14B.2 Constrained optimization of a composite section

14B.3 Projecting the composite sequence onto a time scale

14B.4 Slotting composite sections

14B.5 Technical information

Part III: Geologic Periods: Planetary and Precambrian

Chapter 15. The Planetary Time Scale

Abstract

Chapter outline

15.1 Introduction and methodologies

15.2 Time scales

Bibliography

Chapter 16. Precambrian (4.56–1 Ga)

Abstract

Chapter outline

16.1 International subdivisions

16.2 Hadean

16.3 Archean Eon

16.4 Proterozoic Eon

16.5 Isotopic and geochemical tracers of Precambrian evolution

16.6 Implications of recent findings for subdivision of the Precambrian time scale

Acknowledgement

References

Chapter 17. The Tonian and Cryogenian Periods

Abstract

Chapter outline

17.1 Introduction

17.2 Historical background

17.3 Geochronological constraints on the Tonian and Cryogenian Periods

17.4 Biostratigraphy

17.5 Chemostratigraphy

17.6 Paleogeographic context

17.7 Tonian–Cryogenian Earth system evolution

17.8 Formalization and potential subdivision of the Tonian and Cryogenian Periods

Bibliography

Chapter 18. The Ediacaran Period

Abstract

Chapter outline

18.1 Historical background

18.2 Cap dolostones and the base of the Ediacaran System

18.3 The biostratigraphic basis for the Ediacaran System

18.4 Toward an Ediacaran chronostratigraphy

Acknowledgments

References

Part IV: Geologic Periods: Phanerozoic

Chapter 19. The Cambrian Period

Abstract

Chapter outline

19.1 History and subdivisions

19.2 Cambrian Stratigraphy

19.3 Cambrian Time Scale

Acknowledgments

Bibliography

Chapter 20. The Ordovician Period

Abstract

Chapter outline

20.1 History and subdivisions

20.2 Regional subdivisions

20.3 Ordovician stratigraphy

20.4 Ordovician time scale

Acknowledgments

Bibliography

Chapter 21. The Silurian Period

Abstract

Chapter outline

21.1 History and subdivisions

21.2 Silurian Stratigraphy

21.3 Silurian time scale

Acknowledgments

Bibliography

Chapter 22. The Devonian Period

Abstract

Chapter outline

22.1 History and chronostratigraphic subdivisions

22.2 Devonian stratigraphy

22.3 Devonian time scale

Bibliography

Chapter 23. The Carboniferous Period

Abstract

Chapter outline

23.1 History and subdivisions

23.2 Carboniferous stratigraphy

23.3 Carboniferous time scale

Bibliography

Chapter 24. The Permian Period

Abstract

Chapter outline

24.1 History and subdivisions

24.2 Regional correlations

24.3 Permian stratigraphy

24.4 Permian time scale

Bibliography

Chapter 25. The Triassic Period

Abstract

Chapter outline

25.1 History and subdivisions

25.2 Triassic stratigraphy

25.3 Triassic time scale

25.4 Summary

Acknowledgments

Bibliography

Chapter 26. The Jurassic Period

Abstract

Chapter outline

26.1 History and subdivisions

26.2 Jurassic stratigraphy

26.3 Jurassic time scale

Acknowledgments

Bibliography

Chapter 27. The Cretaceous Period

Abstract

Chapter outline

27.1 History and subdivisions

27.2 Cretaceous stratigraphy

27.3 Cretaceous time scale

Bibliography

Chapter 28. The Paleogene Period

Abstract

Chapter outline

28.1 History and subdivisions

28.2 Paleogene Biostratigraphy

28.3 Paleogene time scale

Acknowledgments

Bibliography

Chapter 29. The Neogene Period

Abstract

Chapter outline

29.1 History and subdivisions

29.2 Neogene stratigraphy

29.3 Neogene astronomically tuned time scale

29.4 Summary

Acknowledgments

Bibliography

Chapter 30. The Quaternary Period

Abstract

Chapter outline

30.1 This chapter

30.2 Evolution of terminology

30.3 The Plio–Pleistocene boundary and definition of the Quaternary

30.4 Subdivision of the Pleistocene

30.5 Pleistocene/Holocene boundary

30.6 Holocene Series

30.7 Subdivision of the Holocene

30.8 Anthropocene Series

30.9 Terrestrial records

30.10 Ocean–sediment records

30.11 Land–sea correlation

30.12 Quaternary dating methods

Bibliography

Chapter 31. The Anthropocene

Abstract

Chapter outline

31.1 Origin of the term and history of research as a stratigraphic unit

31.2 Lithostratigraphic evidence for the Anthropocene

31.3 Chemostratigraphic indicators of the Anthropocene

31.4 Biostratigraphic indicators of the Anthropocene

31.5 Climatic signals of the Anthropocene

31.6 Anthropocene GSSP possibilities

31.7 Summary

Bibliography

Appendix 1. Recommended color coding of stages

Appendix 2. Radioisotopic ages used in GTS2020

Index

Copyright

Elsevier

Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands

The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom

50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States

Copyright © 2020, Felix M. Gradstein, James G. Ogg, Mark D. Schmitz and Gabi M. Ogg. Published by Elsevier BV. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

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A catalog record for this book is available from the Library of Congress

This Volume (1) ISBN: 978-0-12-824362-6

Volume 2 ISBN: 978-0-12-824363-3

Set ISBN: 978-0-12-824360-2

For Information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Front cover of Volume 1: Toarcian boundary stratotype section, Peniche, Portugal. Photograph by F.M. Gradstein.

Publisher: Candice Janco

Acquisitions Editor: Amy Shapiro

Editorial Project Manager: Susan Ikeda

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Quotes

To place all the scattered pages of Earth history in their proper chronological order is by no means an easy task.

Arthur Holmes

The fascination in creating a new geologic time scale is that it evokes images of creating a beautiful carpet by many skilled hands. All stitches must conform to a pre-determined pattern, in this case the pattern of physical, chemical and biological events on Earth aligned along the arrow of time.

This book—Foreword

Contributors

Senior authors

Felix M. Gradstein,     Geological Museum, University of Oslo, P.O. Box 1172 Blindern, N-0318 Oslo, Norway

James G. Ogg,     State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, 610059, China

Mark D. Schmitz,     Department of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho, 83725-1535, USA

Gabi M. Ogg,     Geologic TimeScale Foundation, 1224 N. Salisbury St., West Lafayette, Indiana, 47906, USA

Frits P. Agterberg,     Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A OE8, Canada

Markus Aretz,     Laboratoire Géosciences Environnement, Université de Toulouse, CNRS, IRD, UPS, 31400 Toulouse, France

Thomas R. Becker,     Geologisch-Paläeontogisches Institut, Westfalische Wilhelm-Universität, Correnstrasse 24, D-48149 Münster, Germany

Anthony Butcher,     School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, PO1 3QL, UK

Bradley D. Cramer,     Earth and Environmental Sciences, University of Iowa, Iowa City, Iowa, 52242, USA

Richard E. Ernst,     Department of Earth Sciences, Carleton University, Ottawa, Ontario, K1S 5B6, Canada

Selen Esmeray-Senlet,     Chevron Energy and Technology Company, 1500 Louisiana St., Houston, Texas, 77002, USA

Rob A. Fensome,     Geological Survey of Canada (Atlantic), Natural Resources Canada, Dartmouth, Nova Scotia, B2Y 4A2, Canada

Andrew S. Gale,     School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, PO1 3QL, UK

Philip L. Gibbard,     Department of Geography, University of Cambridge, Cambridge, CB2 3EN, UK

Daniel Goldman,     Department of Geology, University of Dayton, Dayton, Ohio, 45469, USA

Ethan L. Grossman,     Department of Geology & Geophysics, Texas A&M University, College Station, Texas, 77843-3115, USA

Galen P. Halverson,     Department of Earth and Planetary Sciences, McGill University, Montréal, Québec, H3A 0E8, Canada

Charles M. Henderson,     Department of Geoscience, University of Calgary, Calgary, Alberta, T2N 1N4, Canada

Stephen P. Hesselbo,     Camborne School of Mines, University of Exeter, Penryn, TR10 9FE, UK

Harald Hiesinger,     Institut für Planetologie, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany

Hans Kerp,     Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität, D-48143 Münster, Germany

Jacques Laskar,     IMCCE, Observatoire de Paris, 77 Av. Denfert-Rochereau, 75014 Paris, France

John M. McArthur, [Chemostratigraphy coordinator for GTS2020],     Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK

Michael J. Melchin,     Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, B2G 2W5, Canada

Adina Paytan,     Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High St, Santa Cruz, California, 95064, USA

Shanchi Peng,     Nanjing Institute of Geology and Palaeontology, The Chinese Academy of Sciences, 39 East Beijing Road, Nanjing, 210008, China

Maria Rose Petrizzo,     Department of Earth Sciences Ardito Desio, Universitá degli Studi di Milano, Via Mangiagalli, 34 20133 Milano, Italy

Bernhard Peucker-Ehrenbrink,     Woods Hole Oceano-graphic Institution, Woods Hole, Massachusetts, 02543-1541, USA

Isabella Raffi,     Dipartimento di Ingegneria e Geologia, Università G. d’Annunzio di Chieti-Pescara, I-66013 Chieti Scalo, Italy

Peter M. Sadler,     Department of Earth Sciences, University of California, Riverside, Riverside, California, 92521, USA

Matthew R. Saltzman,     School of Earth Sciences, Ohio State University, Columbus, Ohio, 43210-1398, USA

Graham A. Shields,     Department of Earth Sciences, University College London, London, WC1E 6BT, UK

Michael D. Simmons,     Halliburton, 97 Milton Park, Abingdon, OX14 4RY, UK

Robert P. Speijer,     Department of Earth and Environmental Sciences, K.U. Leuven, B-3001 Leuven, Belgium

Rob Strachan,     School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, PO1 3QL, UK

David K. Watkins,     Department of Earth & Atmospheric Sciences, University of Nebraska, Lincoln, Nebraska, 68588-0340, USA

Shuhai Xiao,     Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, Virginia, 24061-0420, USA

Jan Zalasiewicz,     Department of Geology, University of Leicester, Leicester, LE1 7RH, UK

Co-authors

Per Ahlberg,     Department of Geology, Sölvegatan 12, SE-223 62 Lund, Sweden

Loren E. Babcock,     School of Earth Sciences, Ohio State University, Columbus, Ohio, 43210, USA

Sietske J. Batenburg,     Geosciences Rennes, Université de Rennes, UMR 6118, 35000 Rennes, France

David P.G. Bond,     Department of Geography, Environment and Earth Sciences, University of Hull, Hull, HU6 7RX, UK

Zhong-Qiang Chen,     State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan, 430074, China

John Cope,     Department of Natural Sciences, National Museum Wales, Cardiff CF10 3NP, UK

Anne-Christine Da Silva,     Pétrologie sédimentaire, B20, Géologie, Université de Liège, B-4000 Liège, Belgium

James Darling,     School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth PO1 3QL, UK

Andrew Davies,     Halliburton, Milton Park, Abingdon, OX14 4RW, UK

Kristina L. Faul,     Chemistry Department, Mills College, 5000 MacArthur Blvd, Oakland, California, 94613, USA

Stephan R. Gradstein,     Muséum National d’Histoire Naturelle, Department Systématique et Evolution, 57 rue Cuvier, 75231 Paris cedex 05, France

Ellen T. Gray,     Earth and Planetary Science, University of California Santa Cruz, Santa Cruz, California, 95064, USA

Benjamin Gréselle,     Halliburton, Milton Park, Abingdon, OX14 4RW, UK

Martin J. Head,     Department of Earth Sciences, Brock University, St. Catharines, Ontario L2S 3A1, Canada

Hans-Georg Herbig,     Universität zu Köln, Institut für Geologie und Mineralogie, 50674 Köln, Germany

Andrew C. Hill,     Centro de Astrobiología (INTA-CSIC), Instituto Nacional de Técnica Aeroespacial, 28850 Torrejón de Ardoz, Madrid, Spain

Christopher J. Hollis,     GNS Science, Lower Hutt, 5040, New Zealand

Jerry J. Hooker,     Department of Palaeontology, Natural History Museum, London, SW7 5BD, UK

Richard J. Howarth,     Department of Earth Sciences, University College London, London, WC1E 6BT, UK

Christina Ifrim,     Institut für Geowissenschaften, Ruprecht-Karls-Universität Heidelberg, Im Nuenheimer Feld 234, 69120 Heidelberg, Germany

Ian Jarvis,     Department of Geography, Geology and the Environment, Kingston University London, Kingston upon Thames KT1 2EE, UK

Michael M. Joachimski,     GeoZentrum Nordbayern, Lithosphere Dynamics, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany

Clark M. Johnson,     Department of Geoscience, University of Wisconsin-Madison, 1215 W Dayton St., Madison, Wisconsin, 53706, USA

Dieter Korn,     Leibniz Institute for Research on Evolution and Biodiversity, Humboldt University Berlin, 10115 Berlin, Germany

Stephen A. Leslie,     Department of Geology and Environmental Science, James Madison University, MSC 6903, Harrisonburg, Virginia, 22807, USA

Breandán A. MacGabhann,     Earth and Ocean Sciences, National University of Ireland, Galway, Galway, Ireland

Gunn Mangerud,     Department of Earth Science, University of Bergen, N-5020 Bergen, Norway

John E. Marshall,     National Oceanography Centre Southampton, Southampton SO14 3ZH, UK

Alistair J. McGowan,     BioGeoD, 23 Glendinning Crescent, Edinburgh, Scotland, EH16 6DR, UK

Ken G. Miller,     Department of Earth & Planetary Sciences, Rutgers University, Piscataway, New Jersey, 08854, USA

Dirk K. Munsterman,     T.N.O. Princetonlaan 6, 3508 TA Utrecht, The Netherlands

Brendan J. Murphy,     Department of Earth Sciences, St Francis Xavier University, Antigonish, Nova Scotia, B2G 2W5, Canada

Joerg Mutterlose,     Institut fuer Geologie, Mineralogie und Geophysik, 44801 Bochum, Germany

Guy M. Narbonne,     Department of Geological Sciences & Geological Engineering, Queen’s University, Kingston, Ontario, K7L 3N6, Canada

Heiko Pälike,     MARUM Center for Marine Environmental Science, Universität Bremen, D-28359 Bremen, Germany

Susannah M. Porter,     Department of Earth Science, University of California Santa Barbara, Santa Barbara, California, 93106-9630, USA

Gregory E. Ravizza,     Department of Geology & Geophysics, University of Hawaii at Manoa, Honolulu, Hawaii, 96822, USA

David C. Ray,     Halliburton, 97 Milton Park, Abingdon, OX14 4RY, UK

Alan D. Rooney,     Department of Geology and Geophysics, Yale University, New Haven, Connecticut, 06520-8109, USA

Micha Ruhl,     Department of Geology, Trinity College, Dublin 2, Ireland

Adrian Rushton,     Department of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK

Shu-Zhong Shen,     Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing, 210008, China

Brad S. Singer,     The Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, 53706-1692, USA

Craig Storey,     School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth PO1 3QL, UK

Ken Tanaka,     4214 N Fanning Dr., Flagstaff, Arizona, 86004, USA

Frans S. Van Buchem,     Halliburton, Milton Park, Abingdon, OX14 4RW, UK

Bridget S. Wade,     Department of Earth Sciences, University College London, London, WC1E 6BT, UK

Xiangdong Wang,     Nanjing University, School of Earth Sciences and Engineering, Nanjing, 210023, China

Colin N. Waters,     Department of Geology, University of Leicester, Leicester, LE1 7RH, UK

Mark Williams,     School of Geography, Geology and the Environment, University of Leicester, Leicester, LE1 7RH, UK

Weiqi Yao,     Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada

Shuan-Hong Zhang,     Institute of Geomechanics, Chinese Academy of Geological Sciences, No. 11 South Minzudaxue Road, Beijing, 100081, China

Ying Zhou,     London Geochemistry and Isotope Centre, Institute of Earth and Planetary Sciences, University College London and Birkbeck, Gower Street, London, WC1E 6BT, UK

With contributions by:

Alan G. Beu,     GNS Science, Lower Hutt 5040, New Zealand

Martin Crundwell,     GNS Science, Lower Hutt 5040, New Zealand

Linda A. Hinnov,     Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University, Fairfax, Virginia, 22030, USA

Chunju Huang,     School of Earth Sciences, China University of Geosciences, Wuhan, 430074, China

Haishui Jiang,     State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan, 430074, China

Wouter Krijgsman,     Department of Earth Sciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands

Theodore Moore,     Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan, 48109, USA

Michael Orchard,     Geological Survey of Canada, 101-605 Robson Street, Vancouver, British Columbia, V6B 5J3, Canada

J. Ian Raine,     GNS Science, Lower Hutt, 5040, New Zealand

Raffaele Sardella,     Dipartimento di Scienze della Terra, la Sapienza Università di Roma, 00185 Roma, Italy

Yuliia Vernyhorova,     Institute of Geological Sciences, National Academy of Sciences of Ukraine, Kyiv 01601, Ukraine

Editors’ Biographies

Felix M. Gradstein is Professor Emeritus at Oslo University, Norway, and visiting Research Fellow at the University of Portsmouth, United Kingdom. From 2000 to 2008, he was chair of the International Commission on Stratigraphy. Under his leadership, major progress was made with the formal definition of chronostratigraphic units from Precambrian through Quaternary. For his fundamental work concerning the Geologic Time Scale, geochronology in general, quantitative stratigraphy, and micropaleontology, the European Geosciences Union awarded him the Jean Baptiste Lamarck Medal in 2010. He is Chair of the Geologic TimeScale Foundation and teaches courses in quantitative stratigraphy and the geologic time scale. Now that he has free time again, after completing this book with his outstanding coeditors and coauthors, he studies the early evolution of planktonic foraminifera.

James G. Ogg is Professor at Purdue University, Indiana, United States, now retired/adjunct. He is also currently a visiting distinguished professor at Chengdu University of Technology and at China University of Geoscience (Wuhan). He served as Secretary General of the International Commission on Stratigraphy (2000–08) and currently is executive director of the Geologic TimeScale Foundation and coordinator of TimeScale Creator service (https://timescalecreator.org/). His Mesozoic Stratigraphy Lab group has worked on aspects of climate cycles, magnetic polarity correlations, and integration of stratigraphic information. Their TimeScale Creator array of visualization tools and extensive databases in global and regional Earth history was used to generate many of the diagrams in this book.

Mark D. Schmitz is Professor of Geochemistry at Boise State University, Idaho, United States. He has extensive research interests in the development and application of radiogenic isotope geochemistry and high-precision U–Pb geochronology to problems of Earth systems evolution. He has been an active member of the Earth Time community and was coeditor and author for the Geologic Time Scale 2012. He seeks to enrich the radioisotopic calibration of the time scale through targeted dating of stratigraphically important volcanic event beds and the construction of robust chronostratigraphic models through geologic time. His extensive database with over 300 standardized radiogenic isotope ages (mainly U/Pb and Ar/Ar) is vital to this book.

Gabi M. Ogg applied micropaleontology to Jurassic–Cretaceous correlations before concentrating on public outreach in geosciences. She coordinated the extensive array of graphics in this book and is the webmaster for the Geologic TimeScale Foundation (https://timescalefoundation.org) and for the TimeScale Creator visualization and database suites (https://timescalecreator.org). In addition to coauthoring the Concise Geologic Time Scale (GTS2016) and The Geologic Time Scale (GTS2012) books, she has produced numerous posters and time scale cards for public audiences.

Preface

This study presents the academic science community, industry, and schools with the new geologic time scale for c. 4 billion years of Earth history. A chapter also is devoted to time scales for our Moon and neighboring planets. This book details many recent advances in stratigraphy, the science of the layering of strata and its content, in evolution and biostratigraphy, in astrochronology, in geomagnetics, in radiogenic and stable isotope chronology, and in age and duration calculations using orbital tuning and geostatistics. The new scale closely links radioisotopic and orbitally tuned age dates and tries to provide comprehensive error analysis on the ages of a majority of boundaries for the geologic divisions of time. Much benefit is derived from the steady increase in formal definition of geologic stage boundaries such that we have more stability in their definition than in 2012. This book thus presents Geologic Time Scale 2020 (GTS2020), as the successor of GTS2012.

Besides being utilized as a scholarly and convenient standard, GTS2012 also provided fruit and gave impetus to a large body of new research in the fields of radiometrics, chronostratigraphy, orbital tuning, and other Earth Science specialties. One of the most rewarding aspects of science is always to see result becoming the springboard for exciting new developments, and unexpected new answers.

As a fruit of these intense developments, we now proudly present The Geologic Time Scale 2020 building on a tremendous amount of new information, much of it generously assembled and contributed by the large team of specialists.

The fascination in creating a new geologic time scale is that it evokes images of creating a beautiful carpet by many skilled hands. All stitches must conform to a predetermined pattern, in this case the pattern of physical, chemical, and biological events on the Earth aligned along the arrow of time. It is thus, that this, new scale is a tribute to the truly close cooperation achieved by this new slate of outstanding coauthors. We also consider the new time scale a tribute to the scientific competence harbored and fostered by the global geoscience community.

We are deeply grateful to all coauthors and contributors, who without reservation accepted the challenge to be part of this dedicated team, slowly (!) stitching and weaving this carpet of time and its events that portray Earth’s unique and splendid history.

The Norwegian Arctic explorer, scientist, and statesman Fridtjof Nansen is quoted as once saying The difficult is what takes a little time; the impossible is what takes a little longer. To be frank, there were times when we encountered seemingly impossible obstacles in what otherwise seemed to be fairly smooth long-distance sailing from one specialty island to the next one, and staying in touch through a dense network of emails. To says it simple: the challenge with the construction of a detailed geologic time scale spanning almost 4 billion years of Earth history is that it should not have glaring gaps in time coverage.

Looking back at the 8 years it took to complete GTS2020, it is almost funny to consider that chapters of this book covering the oldest rocks and some time before, that is, Precambrian and Planetary were completed first, followed by Late Proterozoic and Precambrian, whereas Mesozoic and particularly Paleogene and Neogene book chapters were last. We might consider that the younger record on the Earth is more complete, more easily accessible, and more easily decipherable but also creates high-resolution data swamping.

Whatever the timing and delays in bringing some chapters to market, we are grateful that all authors, without exception, have strived to keep to the final deadline agreed upon by Elsevier Publishing. To achieve clarity and uniformity in scientific and artistic presentation, Gabi M. Ogg drafted most of the figures. Christopher Scotese kindly provided paleogeographic map reconstructions with the chapters. The Elsevier Production Manager, Kiruthika Govindaraju, was very patient in shepherding the new GTS book through a seemingly endless type-setting and proofing process.

Felix M. Gradstein, James G. Ogg, Mark D. Schmitz and Gabi M. Ogg

Oslo, Norway; W. Lafayette, IN, USA; and Boise, ID, USA. 8 September 2020

Abbreviations and acronyms

Organizations

CGMW Commission for the Geological Map of the World

DNAG Decade of North American Geology

DSDP Deep Sea Drilling Project

GSC Geological Survey of Canada

ICS International Commission of Stratigraphy

IODP International Ocean Drilling Project

IGC International Geological Congress

IGCP International Geological Correlation Project

INQUA International Quaternary Association

IUGS International Union of Geological Sciences

IUPAC International Union of Pure and Applied Chemistry

ODP Ocean Drilling Project

SNS Subcommission (of ICS) on Neogene Stratigraphy

PGS Subcommission (of ICS) on Paleogene Stratigraphy

SQS Subcommission (of ICS) on Quaternary Stratigraphy

STS Subcommission (of ICS) on Triassic Stratigraphy

SOS Subcommission (of ICS) on Ordovician Stratigraphy

SCS Subcommission (of ICS) on Cambrian Stratigraphy

UNESCO United Nations Education, Scientific, and Cultural Organization

USGS United States Geological Survey

Time Scale Publications

NDS82 Numerical Dating in Stratigraphy (Odin et al., 1982)

GTS82 A Geologic Time Scale (Harland et al., 1982)

DNAG83 Geologic Time Scale, Decade of North American Geology (Palmer, 1983)

KG85 Kent and Gradstein (1985)

EX88 Exxon 1988 (Haq et al., 1988)

GTS89 A Geologic Time Scale 1989 (Harland et al., 1990)

OB93 Obradovich (1993)

JGR94 Journal of Geophysical Research 1994 (Gradstein et al., 1994)

SEPM95 Society for Sedimentary Geology 1995 (Gradstein et al., 1995)

GO96 Gradstein and Ogg (1996)

GTS2004 Gradstein, Ogg and Smith (2004)

GTS2008 Ogg, Ogg and Gradstein (2008)

GTS2012 Gradstein, Ogg, Schmitz and Ogg (2012)

GTS2016 Ogg, Ogg and Gradstein (2016)

Geoscientific Concepts

CA-TIMS Chemical abrasion—thermal ionization mass spectrometry (in U–Pb dating)

FAD First appearance datum

FOD First occurrence datum

FCT (FCs) Fish Canyon Tuff sanidine monitor standard (in Ar–Ar dating)

GPTS Geomagnetic polarity time scale

GSSP Global Boundary Stratotype Section and Point

GSSA Global Standard Stratigraphic Age (in Precambrian)

HO Highest occurrence level

HR–SIMS High-resolution secondary ion mass spectrometry (in U–Pb dating)

ID-TIMS Isotope dilution thermal ionization mass spectrometry (in U–Pb dating)

LAD Last appearance datum

LA-ICPMS Laser ablation-inductively coupled plasma-mass Spectrometry (in U–Pb dating)

LO Lowest occurrence level

LOD Last occurrence datum

LA2004 Laskar 2004 numerical solution of orbital periodicities

LA2010 Laskar 2010 numerical solution of orbital periodicities (Laskar et al., 2011)

MMhb-1 McClure Mountain hornblende monitor standard (in Ar–Ar dating)

SL13 Sri Lanka 13 monitor zircon standard (in HR–SIMS dating)

TCs Taylor Creek Rhyolite sanidine monitor standard (in Ar–Ar dating)

Symbols

ka 10³ years ago (kilo annum)

kyr 10³ years duration

Ma 10⁶ years ago (mega annum)

Myr 10⁶ years duration

Ga 10⁹ years ago (giga annum)

Gyr 10⁹ years duration

SI Le Système Internationale d’Unités

a annus (year)

s second

Volume 1

Outline

Part I Introduction

Part II Concepts and Methods

Part III Geologic Periods: Planetary and Precambrian

Part I

Introduction

Outline

Chapter 1 Introduction

Chapter 2 The Chronostratigraphic Scale

Chapter 1

Introduction

F.M. Gradstein

Abstract

The Geologic Time Scale (GTS) is the framework for deciphering and understanding the history of our planet. The steady increase in data, development of better methods and new procedures for actual dating and scaling of the rocks on Earth, and a refined relative scale with more defined units are stimulating the need for a comprehensive review of the GTS. This review is called GTS2020, of which GTS2012 is the ancestor. Relative to its ancestor, the scope of the GTS2020 study is considerably expanded, and stratigraphic resolution has further improved.

GTS2020 is laid out in two volumes. Volume 1 deals with principles and methods and Volume 2 with the stratigraphy and time scale units itself, for a total of 31 chapters, 14 Subchapters, and 2 Appendices. All information is clearly visualized in over 500 figures and tables.

Keywords

Geologic Time Scale; GTS2020; Time Scale Methods; Paleozoic Scales; Mesozoic Scales; Cenozoic Scales; World Geologic Time Scale

Chapter outline

Outline

1.1 The Geologic Time Scale 3

1.2 A Geologic Time Scale GTS2020 4

1.2.1 Recent developments 4

1.2.2 Methods and ages 10

1.3 How this book is arranged? 11

1.3.1 Conventions and standards 11

1.4 Historical overview of geologic time scales 12

1.4.1 Paleozoic scales 12

1.4.2 Mesozoic scales 14

1.4.3 Cenozoic scales 16

1.5 The World Geologic Time Scale 18

Bibliography 19

1.1 The Geologic Time Scale

The Geologic Time Scale (GTS) is the framework for deciphering and understanding the long and complex history of our planet, Earth, the third planet in the constellation around the Sun and the fifth largest after Jupiter, Saturn, Uranus, and Neptune. As Arthur Holmes, the Father of the GTS once wrote (Holmes, 1965) To place all the scattered pages of Earth history in their proper chronological order is by no means an easy task. Ordering these pages, and understanding the physical, chemical and biological processes that acted on them since Earth appeared and solidified, requires a detailed and accurate time scale. The time scale is the tool par excellence of the geological trade, and insight in its construction, strength, and limitations greatly enhances its function and its utility. All Earth scientists should understand how the time scale is constructed and how the myriad of physical and numerical data in it are calibrated, rather than merely using the numbers in them, plucked from a convenient wall chart or laminated wallet card. This calibration to linear time of the succession of events recorded in the rocks on Earth has three components:

1. the international stratigraphic divisions and their correlation in the global rock record,

2. the means of measuring linear time or elapsed durations from the rock record, and

3. the methods of joining the two scales, the stratigraphic one and the linear one.

For clarity and precision in international communication the rock record of Earth’s history is subdivided into a chronostratigraphic scale of standardized global stratigraphic units, such as Carboniferous, Eocene, "Zigzagiceras zigzag ammonite zone, or polarity Chron M19r. Unlike the continuous ticking clock of the chronometric scale (measured in years before the year CE 2000), the chronostratigraphic scale is based on relative time units in which global reference points at boundary stratotypes define the limits of the main formalized units, such as Permian." The chronostratigraphic scale is an agreed convention, whereas its calibration to linear time is a matter for discovery or estimation (Fig. 1.1).

Figure 1.1 The construction of a geologic time scale is the merger of a chronometric scale (measured in years) and a chronostratigraphic scale (formalized definitions of geologic stages, biostratigraphic zonation units, magnetic polarity zones, and other subdivisions of the rock record).

In contrast to the Phanerozoic that has an agreed-upon chronostratigraphic scale with formal stage boundary stratotypes, Precambrian stratigraphy is formally classified chronometrically, that is, the base of each Precambrian eon, era, and period is assigned a numerical age (Table 1.1). In Chapter 16, Precambrian (4.56 Ga to 1 Ga), this Precambrian scale is outlined in some detail.

Table 1.1

Current framework for subdividing Earth stratigraphy.

Moon, Earth’s only satellite, the Sun, and the universe surrounding the Sun system play crucially important roles in geology (think of tidal movements, global climatic change, and Milankowić cyclicity, and meteorite impacts). Earth GTS is a component of a much broader and longer scale, the Astronomic Geologic Scale. Hence, this book also devotes an important planetary chapter to GTSs for our satellite Moon, our neighboring planets Venus and Mars, and the more distant planets. In the last decade, geologic research on these fascinating celestial bodies has much expanded and improved.

1.2 A Geologic Time Scale GTS2020

1.2.1 Recent developments

For the last few years, there have been several major developments that directly bear and have considerable impact on the international GTS.

1. Stratigraphic standardization through the work of the International Commission on Stratigraphy (ICS) is steadily refining the international chronostratigraphic scale. Of the 100 stage or series units in the Phanerozoic Eonothem a majority (75) now have ratified boundary definitions, versus fewer than 45 in 2004 and just over 30 in the year 2000. Details on the new and existing stage boundary definitions are presented in Chapter 2, The Chronostratigraphic Scale.

2. In many cases traditional European-based geologic stages have been replaced with new subdivisions that allow global correlation. The Tonian, Cryogenian, and Ediacaran Periods are filling up with stratigraphic information and the latter has a formal lower boundary definition (see Chapter 18: The Ediacaran Period). New stages have been introduced in Cambrian and Ordovician that allow global correlations, in contrast to British, American, Chinese, Russian, or Australian regional stages. Long ratified stage definitions in Silurian and Devonian are undergoing long overdue revision to better reflect the actually observed fossil and rock record. The Cretaceous, for a long time the only period in the Phanerozoic without a formal definition for its base, has a realistic and practical biomagnetostratigraphic proposal for its lower boundary (see Chapter 27: The Cretaceous Period). Curiously, the largest formal stratigraphic knowledge gap is from Callovian to Aptian for which only one Global Boundary Stratotype Section and Point (GSSP) has been defined (Hauterivian). A similar, albeit slightly shorter GSSP gap exists in Pennsylvanian (Late Carboniferous) through Early Permian.

All Paleocene (Danian, Selandian, Thanetian), three Eocene (Ypresian, Lutetian, and Priabonian) and all Oligocene (Rupelian, Chattian) stages are now defined in the Cenozoic, and all but two Neogene Stages (Langhian and Burdigalian) have been defined and ratified. The Pleistocene and Holocene each are formally divided into several units, and the Anthropocene is eagerly working towards potential formal chronostratigraphic recognition.

3. New or enhanced methods of extracting linear time from the rock record have enabled age assignments with a precision of 0.1% or better, leading to improved age assignments of key geologic stage boundaries, and intrastage levels. A good protocol exists to assign uncertainty to age dates (see Chapter 6: Radioisotope Geochronology), and calibrate the two principal radiogenic isotope techniques using potassium–argon and uranium–lead isotopes. Improved analytical procedures for obtaining uranium–lead ages from single zircons have shifted published ages for some stratigraphic levels to older ages by more than 1 Myr (e.g., at the Permian/Triassic boundary). Similarly, an astronomically assigned age for the neutron irradiation monitor for the ⁴⁰Ar–³⁹Ar dating method makes earlier reported ages older by 0.64%. Also, the rhenium–osmium (¹⁸⁷Re–¹⁸⁷Os) shale geochronometer has a role to play for organic-rich strata with limited or no potential for ash bed dating with the uranium–lead isotopes. Details on the improved radiogenic isotope methods are in Chapter 6, Radioisotope Geochronology.

4. A welcome practice is that, instead of micro- and macrofossil events, also global geochemical excursions are defining criteria for chronostratigraphic boundaries, like the Corg positive anomaly at the Paleocene/Eocene boundary. Carbon isotope excursions are close proxies for base Cambrian, base Triassic, base Jurassic, base Aptian, and base Turonian. The famous iridium anomaly is at the Cretaceous/Paleogene boundary. More GSSPs should use global geochemical events.

5. Milankowić orbital climate cyclicity tunes the Neogene GTS, scaling it in over 50 405-kyr Astrochrono Zones (see Chapter 29: The Neogene Period). For the first time the classical seafloor spreading and magnetochronology methods play only a minor role in scaling the Paleogene. It is now almost completely orbitally tuned (see Chapter 28: The Paleogene Period). Hence, magneto- and biochronology are refined and stage boundary ages strengthened. Parts of Jurassic and Cretaceous benefit from cycle scaling for sets of floating stages, providing detailed estimates of stage duration. Chapter 4, Astrochronology, provides an in-depth review of Astrochronology for the construction of an orbitally tuned GTS.

6. Improved scaling of stages is feasible with composite standard techniques on fossil zones, as a means of estimating relative zone durations. A good example is the Ordovician–Silurian interval with a refined graptolite composite standard with more and better age dates. Since radioisotopic dates often are now more accurate than zonal or fossil event assignments, the uneven spacing and fluctuating accuracy and precision of both radioisotopic dates and zonal composite scales demands special statistical and mathematical techniques to calculate the GTS. This is outlined in-depth in the important Chapter 14, Geomathematics, on time scale geomathematics and geostatistics.

7. The assignment of error bars to ages of stage boundaries, first advocated by Gradstein et al. (1994) attempts to combine the most up-to-date estimate of uncertainty in radioisotopic dating and in stratigraphic scaling into one number. Although stratigraphic reasoning to arrive at uncertainties plays a role, geosciences are no less than physics and chemistry when it comes to assigning realistic error bars to its vital numbers. The geomathematical and geostatistical methods employed to construct GTS2020 are outlined in Chapter 14, Geomathematics.

Continual improvements in data coverage, methodology, and standardization of chronostratigraphic units imply that no GTS can be final. The new GTS2020 provides detailed insight in the most up-to-date GTS and is the successor to GTS2012 (Gradstein et al., 2012), GTS2004 (Gradstein et al., 2004) and GTS1989 (Harland et al., 1990).

The set of chronostratigraphic units (stages, eras) and their computed ages that constitute the main framework for GTS2020 is shown in Fig. 1.2, with detailed descriptions and stratigraphic scales in appropriate chapters. About 30% of Phanerozoic stage boundary ages have a change of their lower boundary by more than 0.5 Myr, and in some cases much more (shown in red) (see Table 1.2).

Figure 1.2 The new Geologic Time Scale.

Table 1.2

The time scale project leading to GTS2020 commenced in 2016, and in total involved over 99 scientists. The project includes contributions by past and present chairs and other officers of different subcommissions of ICS, geochemists, and physicists working with radiogenic and stable isotopes, stratigraphers using diverse tools from traditional animal and plant fossils to sequence stratigraphy to astronomical cycles to data programing, an astronomer and a geomathematician. GTS2020 is available both as two volumes paper book and in digital format.

1.2.2 Methods and ages

The methods used for the construction of GTS2020 integrate different techniques depending on the quality of data and methods available for different intervals and are shown schematically in Fig. 1.3.

Figure 1.3 Methods used to construct GTS2020 integrate different techniques depending on the quality of data available within different intervals.

GTS2020 construction may be summarized in five steps:

Step 1. Construct an updated global chronostratigraphic scale for the Earth’s rock record.

Step 2. Scale the updated chronostratigraphic scale with magnetochronology (the mid-km C-and M-sequences tabled in Chapter 5: Geomagnetic Polarity Time Scale), or a composite standard technique. The latter commonly takes average zone thickness from many sections as directly proportional to zone duration. It is applied for Paleozoic periods.

Step 3. Identify key linear-age calibration levels for the chronostratigraphic scale using radioisotopic dates, and/or apply astronomical tuning to cyclic sediment, or scale and interpolate (near) linear segments of stable isotope sequences.

Step 4. Interpolate the combined chronostratigraphic and chronometric scale, for example with a cubic spline that fits closest to data points with the lowest possible error. Such splines effectively bridge gaps in data along the linear scale or along the chronostratigraphic scale.

Step 5. Calculate or estimate error bars on the combined chronostratigraphic and chronometric information to obtain a GTS with estimates of uncertainty on stage boundary ages.

The first step, integrating multiple types of stratigraphic information in order to construct the chronostratigraphic scale is the most time-consuming; it summarizes and synthesizes centuries of detailed geological research, while reconciling it with the most up-to-date information. The second step has progress wanting, with periods such as Cambrian, Devonian, Triassic, and part of Jurassic not yet having a composite standard of bio- and other events. The third step, identifying which radiogenic isotope and cycle-stratigraphic studies are to be used as the primary constraints for assigning linear ages, is the one that is evolving most rapidly since the last decade. Historically, time scale building went from an exercise with few and relatively inaccurate radioisotopic dates, as used by Holmes (1947, 1960), to one with many dates with greatly varying analytical precision (like GTS1989), to one with a majority of accurate and often precise dates (like GTS2020). The new philosophy, which was started with GTS2004 and GTS2012, is to select analytical precise radioisotopic dates with high stratigraphic resolution. More than 330 radioisotopic dates were thus selected for their reliability and stratigraphic importance to calibrate the geologic record in linear time.

The uncertainty on older stage boundaries systematically increases owing to potential systematic errors in the different radiogenic isotope methods, rather than to the analytical precision of the laboratory measurements. In this connection, it is good to remember that biostratigraphic error is fossil event and fossil zone dependent, rather than age dependent.

Ages and durations of Cenozoic stages derived from orbital tuning are considered to be accurate to within a precession cycle (~20 kyr) assuming that all cycles are correctly identified, and that the theoretical astronomical tuning for progressively older deposits is precise.

Table 1.2 lists the age of stage boundaries in this book relative to the GTS2012, published 8 years ago. Comments are provided why these ages changed by 0.5 million years or more. There are minor age changes in Cenozoic and Late Cretaceous and substantial changes of 1 Myr or more in the age of stage boundaries for the Early Cretaceous, Jurassic, late Triassic, lower half of Permian, part of Devonian, part of Silurian and part of Ordovician. Base Phanerozoic is estimated to be about 3-Myr younger than in GTS2012. The large change in age for base Aptian from 126.3 to 121.4 Ma has an effect on stage boundary ages down into Jurassic, all becoming slightly younger. Uncertainties in age for several Early Cretaceous, Jurassic, and Devonian through Ordovician stages changed by more than 0.5 Myr. Details are in the relevant chapters on the geologic periods and in Chapter 14, Geomathematics.

1.3 How this book is arranged?

The foundation of the GTS is the standardized system of international stratigraphic units. In Chapter 2, The Chronostratigraphic Scale, the construction of this international standard, the definition of stage boundaries, and the origin of the main divisions of eons and eras are outlined.

Part I of the book contains chapters detailing astrochronology, magnetostratigraphy with the M and C marine magnetic sequences; radiogenic isotope geochronology; strontium-, osmium-, sulfur-, oxygen-, and carbon isotope stratigraphy; Phanerozoic sea-level changes; and geomathematical and statistical procedures. The evolution and biostratigraphy in Chapter 3 contains (mostly short) chapters on micro– and macro–fossil groups of importance for biostratigraphy and paleoecology and another important mini chapter on major mass extinction events and subsequent evolutionary radiations. The erudite chapter on larger benthic foraminifera is a bit larger for reason that this stratigraphically important group of Late Paleozoic, Mesozoic, and Cenozoic microfossils is not easy to grasp from the literature. Another important mini chapter (in Chapter 12: Influence of Large Igneous Provinces) deals with the influence of large igneous provinces. None of the contents in these short chapters received attention in GTS2004 or in GTS2012 and may be welcomed by teachers and students.

Part II of the book deals with the detailed stratigraphy and the new time scale for the Precambrian, Tonian–Cryogenian, Ediacaran, and all Phanerozoic periods plus the Anthropocene. Part II starts with a fascinating overview of the Planetary Time Scale and its stratigraphic underpinning.

Appendix 1 summarizes recommended color coding of stages and in Appendix 2 is the listing of radioisotopic dates, of which the majority were employed for GTS2020.

1.3.1 Conventions and standards

Ages are given in years before Present (BP). To avoid a constantly changing datum, Present was fixed as CE 1950 (as in ¹⁴C determinations), the date of the beginning of modern isotope dating research in laboratories around the world. For most geologists, this offset of official Present from today is not important. However, for archeologists and researchers into events during the Holocene (the past 11,500 years), the offset between the BP convention from radiogenic isotope laboratories and actual total elapsed calendar years becomes significant. The offset between the current year and Present has led many Holocene specialists to use a BP2000, which is relative to the year CE 2000. This practice is used in GTS2020 also.

For clarity, the linear age in years is abbreviated as "a" (for annum), and ages are measured in ka, Ma, or Ga for thousands, millions, or billions of years before present. Elapsed time or duration is abbreviated as "yr." (for year), and longer durations in kyr or Myr. Therefore the Cenozoic began at 66 Ma and spans 66 Myr (to the present day, defined as the year CE 2000).

The Ma and Myr practice is confusing and inconsistent both internally and with respect to SI (Le Système international d’unités). As Holden et al. (2011) elegantly clarify (on behalf of IUPAC and IUGS), the same unit is used for absolute and relative measurements. This is in compliance with quantity calculus, and its unit assignment for continuous and interval scales. Hence, elapsed time or duration would also be abbreviated as in ka or Ma. Therefore the Cenozoic began at 66 Ma and spans or lasted 66 Ma. This is similar to the use of m (meter) for both absolute depth/distance and a depth/distance difference, and the use of °C for both temperature and temperature difference. For example, we say that interval between two logmarkers in a borehole is 450 m thick and starts 900 m below ground level. Despite this solution to an often fuzzy and confusing debate with respect to the notation of age and duration units in Earth science, we (for now) stick to the same format as used in GTS2004 and in GTS2012, with both Ma and ka, and Myr and kyr units.

The uncertainties in computed ages or durations are expressed as standard deviation (1-sigma or 68% confidence) or 2-sigma (95% confidence). The uncertainty is indicated by ± and will have implied units of thousands or millions of years as appropriate to the magnitude of the age. Therefore an age cited as 124.6±0.3 Ma implies a 0.3 Myr uncertainty (2-sigma, unless specified as 1-sigma) on the 124.6 Ma date. We present the uncertainties (±) on summary graphics of the GTS as 2-sigma (95% confidence) values.

Geologic time is measured in years, but the standard unit for time is the second s. Because the Earth’s rotation is not uniform, this second is not defined as a fraction (1/86,400) of a solar day, but as the atomic second. The basic principle of the atomic clock is that electromagnetic waves of a particular frequency are emitted when an atomic transition occurs. In 1967 the 13th General Conference on Weights and Measures defined the atomic second as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of cesium-133. This value was established to agree as closely as possible with the solar-day second. The frequency of 9,192,631,770 Hz, which the definition assigns to cesium radiation was carefully chosen to make it impossible, by any existing experimental evidence, to distinguish the atomic second from the ephemeris second based on the Earth’s motion. The advantage of having the atomic second as the unit of time in the International System of Units is the relative ease, in theory, for anyone to build and calibrate an atomic clock with a precision of 1 part per 10¹¹ (or better). In practice, clocks are calibrated against broadcast time signals, with the frequency oscillations in hertz being the pendulum of the atomic time-keeping device.

1 year is approximately 31.56 mega seconds (1 a=~31.56 Ms).

The Système International d’Unités (SI) conventions at 10³ intervals that are relevant for spans of geologic time through sizes of microfossils are:

Although dates assigned in the GTS are measured in multiples of the atomic second as unit of time (year), there are two other types of seconds: mean solar second and ephemeris second.

Universal time is utilized in the application of astronomy to navigation. Measurement of universal time is made directly from observing the times of transits of stars; since the Earth’s rotation is not uniform, corrections are applied to obtain a more uniform time system. In essence, universal time is the mean solar time on the Greenwich meridian, reckoned in days of 24 mean solar hours beginning with zero hour at midnight, and derives from the average rate of the daily motion of the Sun relative to the Greenwich meridian. The mean solar second is 1/86,400 of the mean solar day, but because of nonuniformity this unit is no longer the standard of international time.

Ephemeris time (ET) is uniform and obtained from observation by directly comparing positions of the Sun, Moon, and the planets with calculated ephemerides of their coordinates. Webster’s dictionary defines ephemeris as any tabular statement of the assigned places of a celestial body for regular intervals. ET is based on the ephemeris second defined as 1/31,556,925.9447 of the tropical year for 1900 January 0 day 12-hour ET. The ephemeris day is 86400 ephemeris seconds, which unit in 1957 was adopted by the International Astronomical Union as the fundamental invariable unit of time.

1.4 Historical overview of geologic time scales

1.4.1 Paleozoic scales

The Paleozoic spans 286.9 Myr between 538.8 and 251.9 Ma. Its estimated duration has decreased about 60 Myr since the scales of Holmes (1960) and Kulp (1961). Selected key Paleozoic time scales are compared to GTS2020 in Fig. 1.4. Differences in relative estimated durations of component period and stages from 1960 through today are substantial (e.g., for the Ludlow Stage in the Silurian, or for the Emsian Stage in the Devonian). Whereas most of the Cenozoic and Mesozoic have had relatively stable stage nomenclature for some decades, the historical lack of an agreed nomenclature for the Cambrian, Ordovician, Carboniferous, and Permian Periods complicates comparison of time scales.

Figure 1.4 Comparison of selected Paleozoic time scales with GTS2020. In some columns epochs and stages are stacked together; scales of Holmes (1937, 1960) and Kulp (1961) are more detailed than shown.

The 570–245 Ma Paleozoic time scale in GTS89 derived from the marriage of the chronogram method with the chron concept. The chron concept in GTS89 assumed equal duration of zones in prominent biozonal schemes, such as a conodont scheme for the Devonian. The two-way graphs for each period in the Paleozoic were interpolated by hand, weighting tie points subjectively. Error bars on stage boundaries calculated with the chronogram method were lost in the process of drawing the best-fit line. The fact that the Paleozoic suffered both from a lack of data points and relatively large uncertainties led to poorly constrained age estimates for stages; this uncertainty is readily noticeable in the chronogram/chron figures of GTS89.

The 545–248 Ma Paleozoic part of the Phanerozoic time scale of Gradstein and Ogg (1996) is a composite from various sources, including the well-known scales by McKerrow et al. (1985), Harland et al. (1990), Roberts et al. (1995), and Tucker and McKerrow (1995).

The International Stratigraphic Chart (Remane, 2000) rather odd provided two different sets of ages for part of the Paleozoic stage boundaries. The column that has ages for most stages slightly updated Odin and Odin (1990) and Odin (1994) and is shown here.

Stability in methodology and a highly systematic approach involving a large slate of key experts, not only in many aspects of stratigraphy, but also in astronomy, geochemistry, geophysics and geomathematics, is the hallmark of GTS2004, GTS2012 and now again GTS2020. This broad and multidisciplinary approach has created a relatively stable platform to utilize and present the diverse data underlying each GTS.

1.4.2 Mesozoic scales

The Mesozoic time scale spans an interval of 185.9 Myr, from 251.9 to 66 Ma, which is a decrease of ~60 Myr since Holmes (1937) and ~35 Myr compared to the scales of Holmes (1960) and Kulp (1961). Selected key Mesozoic time scales are compared to GTS2020 in Fig. 1.5. The GTS for the Mesozoic has undergone major improvements during the last two decades, although weak spots remain, for example, the Norian and Rhaetian Stages still lack ratified definitions and have few age dates. For the base of the Rhaetian Stage, the use of its promoted candidate GSSP and marker in Italy, rather than the older candidate and marker in Austria as used in GTS2012, resulted in a 4-Myr shortening of that stage relative to GTS2012. This shortening and a revised correlation to the Newark cycle scale magnetostratigraphy resulted in a 21.6 Myr duration for the Norian, making it the longest Phanerozoic stage.

Figure 1.5 Comparison of selected Mesozoic time scales with GTS2020.

The Jurassic scales of KG85, EX88, Westermann (1988) and SEPM95 in part relied on biochronology to interpolate the duration of stages. As a first approximation, it was assumed that the numerous ammonite zones and/or subzones of the