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Le présent ouvrage édité par Gilles S. Odin est le bienvenu.
La géochronologie absolue occupe dans les sciences de la Terre une place de plus en plus grande sans que chacun ne mesure toujours exactement quels sont ses rapports avec la chronologie stratigraphique traditionnelle. Il en résulte une certaine incertitude quant à l'usage qui en est fait, voire un certain malaise. Il était donc essentiel de revoir la calibration de l'échelle des temps, en fonction des stratotypes de l'échelle stratigraphique communément admise. Celle-ci étant essentiellement européenne, il était important que, après une première partie consacrée au rappel, à la discussion et à l'établissement des fondements, en particulier pour ce qui regarde l'utilisation des minéraux des sédiments en tant que géochronomètres, l'ouvrage édité par M. Odin comporte une analyse exhaustive des temps phanérozoïques par une confrontation des données de la Géochronologie avec celles de la Stratigraphie des gisements fossilifères sur lesquels est fondée la Chronologie stratigraphique classique. Car il y a toujours quelque chose de paradoxal à définir, par exemple, l'âge nuérique de l'Éocène sur des gisements dont on ne soit pas sûr qu'ils sont bien éocènes lorsqu'on s'adresse à des roches volcaniques d'Amérique du Nord ou celui des subdivisions du Trias d'après des gisements du continent du Gondwana si éloigné des formations types des Alpes occidentales. S'il était utile de connaître l'âge des formations géologiques il ne l'était pas moins de savoir dans quelle mesure cette connaissance était approchée. Tout en réévaluant clairement ces âges, ce qui constitue un nécessaire progrès, ce travail analyse et précise les limites de confiance de ces estimations ce qui est plus nouveau et explique bien des imprécisions, parfois des conflits entre les différentes chronologies géologiques. Voilà donc une lacune comblée par un ouvrage qui devrait réconcilier les stratigraphes et les géochronologistes et redonner à ces deux approches de la mesure du temps un élan nouveau.

JEAN AUBOUIN
Membre de l'Institut

AVANT PROPOS

During the period 1968 to 1980, a group of French sedimentologists have accumulated data on the geology of formations yielding glaucony, a geochronometer which is widespread in the well studied sequences of Western Europe. As a member of that group, the editor of this book has applied these data to construct a numerical time-scale for the Mesozoic and Cenozoic eras. Between 1975 and 1980, this research, which is still ongoing, has been undertaken as part of a project in the International Geological Correlation Programme, which has studied both methodological and practical problems. About 20 laboratories all over the world have been involved in the research, either as part of IGCP Project 133 or independently. Bentonites, glauconies, lavas and plutons have been analysed using potassium-argon, rubidium-strontium, uranium-lead and fission-track methods.

In this book, the data now available from the research for Cambrian to Palaeogene times are presented and compared with earlier data, with many of which they disagree. As far as possible, those geochronologists actually working with the dating techniques were invited to contribute their results. Most were able to accept and have provided contributions based on their published data, in many cases supplemented by more recent information and interpretations. Gaps in existing knowledge were identified and research was initiated, giving the editor an opportunity to undertake isotopic studies on specific problems in various host laboratories including Paris, Bern, Strasbourg, Nancy, Orsay, Leeds, and Hanover over the past eight years. This book provides a synthesis of this research into many geological horizons and includes much new information which is placed into context with classic geochronological data.

The book is divided into 2 volumes for ease of reference and handling. Volume I comprises 34 chapters on methodology and calibrating the time scale. Under "Methodology" (Sections I to IV) are gathered the methodological results which form the basis for the principles used in selecting age data discussed in the chapters on calibrating the time scale. It gives an up-to-date review of current opinion relating to the evaluation of the uncertainties involved when calibrating the time scale. There is an examination of stratigraphical correlation, analytical errors, and geochemical problems, with emphasis on the last ones, as this is probably the most complex question of the three and the one least understood by geologists. A particular attempt has been made to explain that an apparent age or a series of apparent ages obtained by means of a chronometer (a whole-rock, a mineral or a mixture) can only be used as a calibration point on the time scale after thorough analysis and proper interpretation of a sufficient amount of stratigraphical, geochemical, and analytical information. At the end of each chapter on methodology there is a short résumé in French of the most important points, for the benefit of readers.

Under the heading "Calibrating the Time Scale" (Sections V and VI) are gathered chapters discussing the time scale itself on the basis of the criteria set out in the chapters on methodology. Reference is also made to data used for the time scale proposed by Harland et al. (1964) and revised by Harland & Francis (1971). These data are referred to using the abbreviation PTS. Many of Harland's data have now been superseded due to the development of more reliable measuring techniques for the same samples or to the use of samples whose biostratigraphical relations are better established. The more recent and more accurate age data are presented in volume II and referred to by the abbreviation NDS. All relevant data are considered in the discussions proposing a new time scale. Each stratigraphical boundary is in fact defined by the time interval in which it may be located with some degree of accuracy, so long as its geological definition is not modified. The results are presented in the form of tables and summary diagrams, which it is hoped will make the information clear even to non-English-speaking readers.

Volume II, comprises mainly the collection of 251 abstracts… Each of the 251 Abstracts was written after a discussion between stratigrapher and geochronologist and attempts to summarise all available data in a common format. The data are then used to support (or else to discredit) the formation in question as a reference point for calibrating the time scale. Very often, the conclusions arrived at in the Abstracts are quite different from those appearing in earlier publications, which they therefore should supersede. It should be pointed out that the techniques for isotope analysis were not really developed until after 1960 and that considerable progress has been made since 1971.

Finally, it is hoped that the time scale proposed in this book, being more precise and better founded than the previous ones, will serve as a good instrument to geologist for evaluating the duration measured in years of geological phenomena such as biological, geochemical or sedimentological changes as well as the date duration and speed of tectonic or magmatic events.

GILLES S. ODIN

1-	Uncertainties in evaluationg the numerical time scale G.S. Odin	3
*Section I: Methods of correlation*
2-	Biochronology - Biological events in time resolution, their potential and limitations B. U. Haq & T.R. Worsley	19
3-	Geochemical events as a means of correlation G. S. Odin, M. Renard & C. Vergnaud Grazzini	37
4-	The marine strontium geochronometer G. Faure	73
5-	Palaeomagnetic stratigraphy as a correlation technique J. E. T. Channel	81
*Section II: Isotopic dating*
6-	The physical decay constants N. Gale	107
7-	Interlaboratory standards for dating purposes G. S. Odin and 35 collaborators	123
	Appendix: An example of interlaboratory reproductibility for Glauconite GL-O W. Harre & H. Kreuzer	149
8-	Potassium-argon analysis M. Flisch	151
9-	Range and effectiveness of unspiked potassium-argon dating C. Cassignol & P.-Y. Gillot	159
10-	The `39`Ar/`40`Ar technique of dating F. Albarède	181
11-	The application of fission track dating to stratigraphy: critical review D. Storzer & G. Wagner	199
*Section III: Utilization of sediments as geochronometers*
12-	A comparison of rubidium-strontium and potassium-argon apparent ages of glauconies E. Keppens & P Pasteels	225
	Appendix: Analytical feasibility of rubidium-strontium dating of young glauconies E. Keppens	240
13-	The rubidium-strintium method applied to sediments: certitudes and uncertainties N. Clauer	245
14-	Zero isotopic age of glauconies G. S. Odin & M. Dodson	277
15-	Effect of pressure and temperature on clay mineral potassium-argon ages G. S. Odin	307
16-	Potassium-argon dating of tectonized glauconies M. Conard, H. Kreuzer & G. S. Odin	321
17-	Argon behaviour in clays and glauconies during preheating experiments G. S. Odin & M. Bonhomme	333
18-	Kinetics of the release of argon and fluids from glauconies J. L. Zimmermann & G. S. Odin	345
19-	Potassium-argon dating of washed, leached, weathered, and reworked gkauconies G. S. Odin & D. C. Rex	363
20-	How to measure glaucony ages G. S. Odin	387
*Section IV: Utilization of high temperature rocks as geochronometers*
21-	The genesis of bentonites A. F. Person	407
22-	The dating of bentonite beds H. Baadsgaard & J. F. Lerbekmo	423
23-	The dating of plutonic events N. H. Gale	441

Section V: The Cambrian to Triassic times
24-	The data from Scotland and the Carboniferous time scale H. A. F. de Souza	455
25-	Numerical dating of Caledonian times (Cambrian to Silurian) N. H. Gale	467
26-	Numerical dating of Hercynian times (Devonian to Permian) G. S. Odin & N. H. Gale	487
27-	A calibration point in the Late Triassic: the tin granites of Bangka, Indonesia H. N. A. Priem & E. H. Bon	501
28-	Late Triassic-Early Jurassic time-cscale calibration in British Columbia, Canbada R. L. Armstrong	509
29-	Triassic radiometric dates from eastern Australia J. A. Webb	515
30-	The Triassic time scale in 1981 G. S. Odin & R. Létolle	523
*Section VI: The Jurassic to Palaeogene times*
31-	Radiometric dating of the Albian-Cenomanian boundary G. S. Odin & J. C. Hunziker	537
32-	The Jurassic and Cretaceous time scale in 1981 W. J Kennedy & G. S. Odin	557
33-	Rubidium-strontium glaucony ages, SE Atlantic Coastal Plain, USA W. B. Harris	593
34-	Dating of the Palaeogene D. Curry & G. S. Odin	607

35-	Introduction: Individual radiometric studies of stratigraphically calibrated samples G. S. Odin	633
	Résumés NDS 001 à NDS 251 auteurs divers	659
36-	Potassium-argon calculation using conventional constants R. Siegenthaler	949
37-	The Phanerozoic time scale in 1981 G. S. Odin, D. Curry, N. H. Gale & W. J. Kennedy	957
	Références	961
	Index	1005