Isotope Chronostratigraphy. Theory and Methods

338 Pages·1988·5.739 MB·English

by  Douglas F. Williams, Ian Lerche and W. E. Full (Auth.)

Academic Press Geology Series
Mineral Deposits and Global Tectonic Settings—A. H. G. Mitchell and
M. S. Garson—1981
Applied Environmental Geochemistry—1. Thornton (ed.)—1983
Geology and Radwaste—A. G. Milnes—1985
Mantle Metasomatism—M. A. Menzies and C. J. Hawkesworth (eds.)—1987
The Structure of the Planets—]. W. Elder—7957
Fracture Mechanics of Rock—Κ Κ. Atkinson (cd.)—1987
Isotope Chronostratigraphy: Theory and Methods—Douglas F. Williams, Ian
Lerche, and W. E. Full—1988
Isotope Chronostratigraphy:
Theory and Methods
DOUGLAS F. WILLIAMS
Department of Geology
University of South Carolina
Columbia, South Carolina
IAN LERCHE
Department of Geology
University of South Carolina
Columbia, South Carolina
W. E. FULL
Department of Geology
Wichita State University
Wichita, Kansas
ACADEMIC PRESS, INC.
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COPYRIGHT © 1988 BY ACADEMIC PRESS, INC.
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Library of Congress Cataloging-in-Publication Data
Williams, Douglas F.
Isotope chronostratigraphy : theory and methods / Douglas F.
Williams, Ian Lerche, William Full.
p. cm. — (Academic Press geology series)
Includes index.
ISBN 0-12-754560-3 (alk. paper)
1. Stratigraphie correlation. 2. Oxygen—Isotopes. 3. Carbon-
-Isotopes. I. Lerche, I. (Ian) II. Full, William. III. Title.
IV. Series.
QE652.5.W55 1988
551.7'01-dcl9 87-27129
CIP
PRINTED IN THE UNITED STATES OF AMERICA
88 89 90 91 9 8 7 6 5 4 3 21
PREFACE
Isotope Chronostratigraphy has a long and involved history, the exact
beginning of which is difficult to pinpoint. In some ways it is the logical
outgrowth of a chapter on Pleistocene oxygen isotope stratigraphy written
for the book Principles of Pleistocene Stratigraphy Applied to the Gulf of
Mexico, edited by N. Healy-Williams (1984, IHRDC Press). Publication of
that book, and subsequent pilot projects with several enterprising petroleum
companies, enabled a small group of faculty, students, and technicians at the
University of South Carolina to form the Isotope Stratigraphy Group for the
purpose of refining the stratigraphy of Plio-Pleistocene exploration wells from
offshore Gulf of Mexico. Because of the proprietary nature of that work,
however, very little of the exciting results could be published in the open
literature. Thus, the industry as a whole remained relatively unaware of this
innovative technology.
More directly, this book is derived from a short course that the senior author
presented to seven of the major petroleum companies in February and
November 1985. As he does in this book, Williams attempted to show in his
short course the potential of using stable oxygen and carbon isotope records
for making detailed stratigraphie correlations of exploration sections of
Tertiary and, quite possibly, Mesozoic age. The short course was designed
to familiarize petroleum geologists and stratigraphers with this new form of
chemical stratigraphy. Its intent was also to remove some of the mystery about
stable isotopes as they had been used in the past and to establish some
principles for properly interpreting stable isotope records in stratigraphie and
chronostratigraphic frameworks. One of the outgrowths of these short course
presentations, however, was the realization that a more quantitative approach
was necessary if isotope chronostratigraphy was to be carried to its ultimate
potential. Thus Lerche and Full entered the picture.
As mathematicial geologists, Lerche and Full have a grasp of ways to
manipulate geophysical, geological, and geochemical data. We have teamed
together in an effort to document some of the available approaches for
xi
xii Preface
analyzing isotope data as time series information. The combination of the
empirical models with the quantitative approaches described herein makes
isotope chronostratigraphy a more powerful tool both in exploration sections,
where pure chronostratigraphic information may be the desired end product,
and in marine sections where the primary aim is to gain further understanding
of the paleooceanographic history of ocean basins. We do not claim to have
monopolized all the potential approaches either empirically or mathematically.
Developments in the study of isotope distributions in sedimentary rocks, and
in the refinement of mathematical treatments of data, are sufficiently rapid
that even as quickly as the publishers bring this book to print, new editions
will be needed to keep abreast of new advances.
This work would not have been possible without the aid and cooperation
of a great number of our colleagues in industry, at the University of South
Carolina, at Wichita State University, and at other institutions. In particular,
we acknowledge the encouragement and insights we have received from Robert
Ehrlich, Richard Fillon (Texaco), Barry Kohl (Chevron), Christopher Kendall,
and Nancy Healy-Williams. Nick Pisias, Nick Shackleton, Ken Miller, James
P. Kennett, and Maurice Renard are thanked for generously sharing not yet
published data. We also thank the staff of the Isotope Stratigraphy Group
(David Mucciarone, Dwight Trainor, Judy McClendon, Mary Evans, Steve
Hardin, and Jeff Corbin) for their unselfish efforts in generating the data
and thereby producing the exciting results we have obtained to date in our
exploration work. Tom McKenna is thanked for the thankless job of getting
the computer programs, written in Wichita by Full, to run on the USC
mainframe. We thank John Haramut and David Mucciarone for drafting the
figures. David Krantz helped significantly with editing portions of the book.
Donna Black, Sheri Howell, and Joyce Goodwin did outstanding jobs of
typing various parts of the book. We thank our families for the forbearance
and tolerance that only families can give during the many weekends, nights,
and holidays we worked on this book. Last but not least, Williams and Lerche
thank James R. Durig, Dean of the College of Science and Mathematics,
for his ardent support of our research programs.
Chapter 1 Introduction
I. Rationale for a New Chemical Stratigraphy
Dwindling reserves and oil production quotas in traditional producing
areas and generally shallow water depositional systems have combined to
force the petroleum industry to undertake unprecedented efforts to stream-
line its petroleum exploration efforts. Many of these efforts have been
directed toward (1) developing new techniques for more accurately locating
hydrocarbon source rocks and their related oil and gas reservoirs and (2)
exploring deeper water environments in both traditional and frontier explor-
ation areas. Unconventional and innovative approaches are therefore
needed; very often these approaches lead to unexpected breakthroughs in
exploration efforts, particularly in deeper water environments where some
interpretations of standard foraminiferal zonations (Fig. 1) have come in
conflict with interpretations of seismic sequence boundary patterns and
other geophysical interpretations. While many of these foraminiferal zon-
ations have worked exceedingly well in zones 1-3 (Fig. 2) during decades
of exploration in onshore and shallow-water drill sites, the stratigraphie
behavior of many shallow-dwelling benthic species or assemblages becomes
less reliable in the deeper zones 4-6. At the very least, their behavior becomes
less understood in many exploration wells when combined with other data.
A number of benthic foraminiferal zonations used by the petroleum industry,
primarily in sections from shallow-water environments, commonly yield
stratigraphie intervals with average durations in excess of 500,000 yr
(Fig. 1). In addition, some of the benthic datums are strongly controlled
by facies changes and thus tend to be regionally diachronous.
As it becomes necessary to explore the deep-water blocks of the Gulf of
Mexico for major petroleum and gas reservoirs in the late Tertiary and
ι
2 1. Introduction
Ν. American Ericson Β Θ η t h i c
Climate Stages Zonat ion Zonation
WISCONSIN _
SANGAMON
SANGAMON FAUNA
I L L I Ν Ο I Α Ν
GLACIAL
TRIMOSINA A
YARMOUTH "* -
LU ^ ^ INTERGLACIAL
Ζ LATE " ^ TRIMOSINA Β
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CO
LU (LATE
I NEBRASCAN) ANGULOGERINA
α. GLACIAL Β
CRIS TELLERIA
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LE Ν ΤIC U L IΝ A 1
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BULIMINELLA 1
Fig. 1. Conceptual placement of the North American climate stages and a commonly used
foraminiferal zonation for the Plio-Pleistocene of the Gulf of Mexico Basin based on selected
index species. (From Stainforth et al, 1975.)
Fig. 2. Schematic representation of the bathymetry and informal depth classification of a passive continental margin.
4 1. Introduction
Pleistocene sediments of the continental slope, time-stratigraphic schemes
of a high resolution are needed for precise intercorrelation of exploration
wells. Conventional stratigraphie techniques simply cannot provide the
necessary resolution in many cases because (1) the Pleistocene is a relatively
brief period of geologic time and lacks an adequate number of biostrati-
graphic markers; (2) the Gulf of Mexico has received enormous accumula-
tions of terrigenous sediments during the Pleistocene because of glacio-
eustatic sea level fluctuations; and (3) shifting depocenters and regional
unconformities, whether because of salt tectonics or sea level changes, make
it difficult to accurately correlate wells in time and space dimensions.
While the petroleum industry is being forced to explore deeper water
environments, part of the academic marine geological community is involved
with stratigraphie and paleoceanographic studies of deep-water marine
sediments. The Deep Sea Drilling Project (DSDP) has made available
numerous marine Tertiary sequences from the continental rise and abyssal
depths of the world's oceans. Representative sections for much of the
Tertiary have enabled deep-water biostratigraphers, paleomagnetists, and
geochemists working with siliceous and calcareous sediments to derive new
techniques, such as isotope stratigraphy, paleomagnetic stratigraphy, teph-
rochronology, and quantitative biostratigraphy. The use of these new tech-
niques to study DSDP sections has led to a fairly detailed picture of the
océanographie and biological history of the oceans during the Tertiary.
However, the academic community has made only limited investigations
with these techniques in continental margin sections from shelf and slope
depths, and this is largely because of the lack of deep drilling capabilities.
Core materials from the Gulf of Mexico margin that do exist, such as the
Shell Eureka boreholes, are regarded quite wrongly by many in the academic
community as not suitable for detailed study. Certainly paleomagnetic work
is not possible, but we have found many of the Eureka cores to contain
excellent material for geochemical and micropaleontological studies.
One of the primary incentives for this book and our research, therefore,
is the idea that the petroleum geology and paleoceanography communities
have a great deal to benefit from each other. In particular, it is our belief
that the oxygen and carbon isotopic records for the Tertiary, as identified
by the DSDP and in exploration boreholes, have the potential to become
indispensable tools for the petroleum geologist and biostratigrapher in their
efforts to identify and define new oil and gas reservoirs in deep-water and
frontier environments. Also, stratigraphie sections from exploration wells
provide unparalleled opportunities to study thick continental margin sec-
tions that otherwise would be unavailable to the academic community.
Toward this goal, the Isotope Stratigraphy Group at the University of
South Carolina has been working to meet some of the petroleum industry's
II. The Model of Isotope Chronostratigraphy 5
needs for precise stratigraphie correlations of exploration wells from deep-
water blocks of the Gulf of Mexico by developing a new form of chemo-
stratigraphy: isotope chronostratigraphy. Most of our work, which began
in 1981, has been directed toward obtaining a high-resolution stratigraphy
for the Pliocene-Pleistocene sections (Healy-Williams, 1984). Our basic
approach is to integrate biostratigraphic and lithostratigraphic information
(preferably quantitative data if available) with oxygen isotope stratigraphy.
From this approach we establish the empirical models for a time-strati-
graphic framework with a resolution that is far superior to conventional
biostratigraphic techniques alone (i.e., "tops" of benthic and planktonic
foraminifera and calcareous nannofossils).
As this text will show, isotope chronostratigraphy offers substantial
improvements in the stratigraphie resolution of exploration wells when
integrated with quantitative biostratigraphy and interpreted using some of
the quantitative methods of data analysis discussed in later chapters. It
should be stressed that these approaches are not restricted to the Gulf of
Mexico or to the stratigraphie interpretation of isotope data. The approaches
developed in this book should work equally well in all marine sedimentary
basins of Tertiary age. It is also our opinion that the use of stable carbon
and oxygen isotope data in stratigraphie sections offers unrealized potential
in identifying chemically defined stratigraphie horizons and mapping
diagenetic gradients in ancient sedimentary basins.
Therefore, our primary purposes in this book are to synthesize the oxygen
and carbon isotopic records for the Tertiary and introduce the concept of
isotope chronostratigraphy. We show how this new technology can be used
in exploration wells in particular and in stratigraphie studies of sedimentary
rocks in general. In addition, we describe some of the quantitative tech-
niques, some standard and some not, for analyzing isotope data as time
series information to improve correlations of complete and incomplete
stratigraphie sections.
II. The Model of Isotope Chronostratigraphy
As shown schematically in Figs. 3 and 4, the oxygen and carbon isotopic
records for Tertiary marine carbonates have distinct signals as functions of
time. The fact that many of the particular features of the records are global
events, driven by large-scale changes in the interconnected ocean-atmo-
sphere-cryosphere system, offers the possibility of deriving a comprehensive
age dating framework to:
1. Make detailed correlations and provide precise time lines between
boreholes using isotope chronostratigraphy;