The Geology of Stratigraphie Sequenees

Springer-Verlag Berlin Heidelberg GmbH

Andrew D. MiaU

The Geology of Stratigraphie Sequences

With 337 Figures and 11 Tables

Springer

Prof. Dr. Andrew D. MiaU Department of Geology University of Toronto 22 Russell Street Toronto, Ontario MSS 3Bl Canada

Library of Congress Cataloging-in-Publication Data. Miall, Andrew D. The geology of stratigraphie sequences/Andrew D. Miall. p. cm. Includes bibliographical references (p. 397-421) and indexes. 1. Geology, Stratigraphie. I. Title. QE651.M46 1996, 551.7-dc20 96-26786

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ISBN 978-3-642-08215-3 ISBN 978-3-662-03380-7 (eBook) DOI 10.1007/978-3-662-03380-7

© Springer-Verlag Berlin Heide/berg 1997 Originally published by Springer-Verlag Berlin Heidelberg New York in 1997 Softcover reprint of the hardcover 1 st edition 1997

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For Charlene, Christopher,

and Sarah

Preface

Sequence stratigraphy represents a new paradigm in geology. The principal hypothesis is that stratigraphie successions may be subdivided into discrete sequences bounded by widespread unconformities. There are two parts to this hypothesis.

First, it suggests that the driving forces which generate sequences and their bounding unconformities also generate predietable three-dimensional stratigraphies. In re cent years stratigraphie research guided by sequence models has brought about fundamental im­provements in our understanding of stratigraphie processes and the controls of basin architecture. Sequence models have provided a powerful framework for mapping and numerieal modeling, enabling the science of stratigraphy to advance with rapid strides. This research has demonstrated the importance of a wide range of processes for the generation of cyclie sequences, including eustasy, tectonics, and orbital forcing of climate change. The main objective of this book is to document the sequence record and to discuss our current state of knowledge about sequence-generating processes.

To a considerable extent, however, these significant developments have been obscured by a controversy em erging from the second part of the sequence stratigraphy paradigm. It has been proposed that stratigraphie sequences are superior as chronostratigraphic in­dicators to all other forms of stratigraphie data, and that they therefore comprise the ideal basis for a superior standard of geologieal time. The main theoretical basis for the paradigm is the supposition that global stratigraphie successions are controlled primarily by eustatic sea-Ievel changes. However, as this book demonstrates, the basie premise of the paradigm remains unproven. There is no convincing, independent evidence that a suite of globally correlatable cycles exists. Current chronostratigraphic dating techniques do not permit the level of accuracy and precision in sequence correlation daimed for the global cyde charts that have been published by Peter Vail and his former Exxon collea­gues and coworkers. These charts rest on aseries of assertions unsupported by published data. There has been considerable controversy on this point. A second objective of this book is to review these developments in detail, drawing on all available published lit­erature. Examples are given from around the world, and the controversies and advances associated with sequence stratigraphy are fully described.

I may be known by some readers as a sceptic in the area of sequence stratigraphy, on the basis of aseries of critical papers published in this area, plus numerous lectures given around the world. It needs to be emphasized that I find many of the developments of sequence stratigraphy to be exciting and important. There is no doubt that the emergence of sequenee stratigraphy constitutes an important revolution in sedimentary geology, to add to those that have already been brought about by developments in plate tectonics, geophysical basin modeling and the coneept of the process-response sedimentary model.

Part of this book is devoted to a discussion of the uses to whieh sequence stratigraphy can be put in the field of petroleum geology, and how the exploration and production processes may be facilitated by the employment of sequence stratigraphie techniques. It is to be hoped that the balanced approach of this book - scepticism, plus an equal focus on the positive aspects of the subject - represents the best form of scientific synthesis, and lends the book credibility and usefulness.

Andrew D. Miall

Acknowledgements

My own interest in sequence stratigraphy began slowly, as my work on regional basin analysis for the Geological Survey of Canada matured in the late 1970s, and I am grateful to this organization for introducing me to the scope and sweep of large-scale regional analysis. My developing knowledge of basin analysis provided me with a practical view of the subject that induced scepticism. In particular, my work in the Canadian Arctic in­cluded attempts to adjudicate debates between various biostratigraphic specialists who could not agree on the dating of certain subsurface sections that I was trying to correlate. My critique of sequence stratigraphy as a chronostratigraphic tool developed from this starting point. A few individuals in GSC discussed the early concepts with me and helped me to realize that something important was going on. Among these Ashton Embry stands out. Later, Jim Dixon's work provided food for thought.

Discussions with the main protagonists of seqnence stratigraphy have met with mixed success. I would, however, like to acknowledge these colleagues for contributing to the development of my ideas: Phil Allen, Bert Bally, Chris Barnes, Sierd Cloetingh, Jim Co­lern an, Bill Galloway, J ake Hancock, Makoto Ito, David J ames, Alan Kendall, Dale Leckie, Peter McCabe, Dag Nummedal, Henry Posamentier, Brian Pratt, Larry Sloss, John Suter, Peter Vail, John Van Wagoner, Roger Walker, Tony Watts. Discussions with my wife, Charlene Miall, a social scientist, regarding the nature of science as a human endeavor, have been most helpful.

This book began life as an in-house report prepared for the exclusive use of the Japan National Petroleum Corporation in 1993. I am grateful to the Corporation for permission to publish their report, and to my employer, the University of Toronto, for providing the time for me both to write the original report and to prepare the material for the revisions incorporated into the final book.

Much of the material in Chapter 13 appeared in a contribution to the PaleoScene series in Geoscience Canada. I am grateful to Darrel Long for stimulating the writing of the paper, and to series editor Godfrey Nowlan and critical reviewers John Armentrout and Terry Poulton for their invaluable comments.

The entire manuscript was critically read by Brian Pratt and Phil Allen. I am most grateful to them for undertaking this onerous task, for their painstaking efforts in completing it, and for their numerous thoughtful and helpful comments. Remaining errors and omissions are, of course, my responsibility.

And once again, I must thank my wife Charlene and my children Christopher and Sarah for their encouragement, love and support.

Contents

I Review of Current Coneepts ................................ .

1

1.1 1.2 1.3 1.4

2

2.1 2.2 2.2.1 2.2.2 2.2.3 2.3

2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.4

3

3.1 3.2 3.3 3.4 3.5

4

4.1 4.2 4.3 4.4 4.5

5

Introduetion ........................................... .

Sequenee Stratigraphy: A New Paradigm? ...................... . From Sloss to Vail ....................................... . Problems and Research Trends: The Current Status ............... . Stratigraphie Terminology .................................. .

Methods for Studying Sequenee Stratigraphy ................... .

Introduetion ........................................... . Ereeting a Sequenee Framework ............................. . The Importanee of Uneonformities ........................... . Facies Cydes ........................................... . Stratigraphie Arehiteeture: The Seismie Method .................. . Methods for Assessing Regional and Global Changes in Sea Level, Other Than Seismie Stratigraphy ............................. . Areas and Volumes of Stratigraphie Units ...................... . Hypsometrie Curves ...................................... . Backstripping ........................................... . Sea-Level Estimation from Paleoshorelines and Other Fixed Points .... . Doeumentation of Meter-Seale Cydes ......................... . Integrated Teetonie-Stratigraphie Analysis ...................... .

The Four Basie Types of Stratigraphie Cyde .................... .

Introduction ........................................... . The Supereontinent Cyde .................................. . Cydes with Episodicities of Tens of Millions of Years ............. . Cydes with Million -Year Episodicities ......................... . Cydes with Episodicities of Less Than One Million Years .......... .

The Basie Sequenee Model ................................. .

Introduction ........................................... . Terminology ........................................... . Depositional Systems and Systems Traets ...................... . Sequenee Boundaries ..................................... . Other Sequenee Coneepts .................................. .

The Global Cyde Chart ................................... .

3

3 3 9

11

15

15 15 15 21 22

30 30 31 33 40 43 48

49

49 51 52 53 56

57

57 57 59 65 67

71

XII

11

6

6.1 6.2 6.2.1 6.2.2 6.3 6.3.1 6.3.2 6.4

7

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9

8

8.1 8.2 8.3 8.4 8.5 8.6 8.7

III

9

9.1 9.2 9.3 9.3.1 9.3.2 9.4

10

10.1 10.2 10.2.1 10.2.2 10.2.3 10.2.4

Contents

The Stratigraphie Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Cycles with Episodicities of Tens to Hundreds of Millions of Years . . . . 79

Climate, Sedimentation, and Biogenesis . . . . . . . . . . . . . . . . . . . . . . . . . 79 The Supercontinent Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 The Tectonic-Stratigraphic Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 The Phanerozoic Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Cycles with Episodicities of Tens of Millions of Years .............. 85 Intercontinental Correlations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Tectonostratigraphic Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Main Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Cycles with Million-Year Episodicities ......................... 99

Extensional and Rifted Clastic Continental Margins . . . . . . . . . . . . . . . . 99 Foreland Basin of the North American Western Interior ............ 101 Other Foreland Basins ..................................... 108 Forearc Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 115 Backarc Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 120 Cyclothems and Mesothems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 125 Carbonate Cycles of Platforms and Craton Margins . . . . . . . . . . . . . . .. 128 Evidence of Cyclicity in the Deep Oceans ....................... 137 Main Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 138

Cycles with Episodicities of Less Than One Million Years . . . . . . . . . .. 139

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 139 Neogene Clastic Cycles of Continental Margins ................... 139 Pre-Neogene Marine Carbonate and Clastic Cycles . . . . . . . . . . . . . . . .. 149 Late Paleozoic Cyclothems .................................. 157 Lacustrine Clastic and Chemical Rhythms . . . . . . . . . . . . . . . . . . . . . .. 161 Clastic Cycles of Foreland Basins ............................. 167 Main Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 180

Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 183

Long-Term Eustasy and Epeirogeny . . . . . . . . . . . . . . . . . . . . . . . . . .. 185

Mantle Processes and Dynamic Topography ..................... 185 Supercontinent Cycles ..................................... 185 Cycles with Episodicities of Tens of Millions of Years .............. 191 Eustasy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 191 Dynamic Topography and Epeirogeny. . . . . . . . . . . . . . . . . . . . . . . . .. 198 Main Conclusions ........................................ 199

Milankovitch Processes .................................... 201

Introduction ............................................ 201 The Nature of Milankovitch Processes . . . . . . . . . . . . . . . . . . . . . . . . .. 202 Components of Orbital Forcing ............................. " 202 Basic Climatology ....................................... " 202 Variations with Time in Orbital Periodicities . . . . . . . . . . . . . . . . . . . .. 205 Isostasy and Geoid Changes ........... . . . . . . . . . . . . . . . . . . . . .. 206

Contents XIII

10.2.5 The Nature of the Cyclostratigraphie Data Base. . . . . . . . . . . . . . . . . .. 206 10.2.6 The Sensitivity of the Earth to Glaciation ....................... 208 10.2.7 Glacioeustasy in the Mesozoic? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 210 10.2.8 Nonglacial Milankovitch Cyclicity . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 211 10.3 The Cenozoie Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 214 10.4 Late Paleozoic Cyclothems ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 216 10.5 The End-Ordovician Glaciation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 222 10.6 Main Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 222

11 Tectonic Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 225

11.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 225 11.2 Rifting and Thermal Evolution of Divergent Plate Margins . . . . . . . . . .. 228 11.2.1 Basic Geophysical Models and Their Implications for Sea-Level Change. 228 11.2.2 Some Results from the Analysis of Modern Data Sets. . . . . . . . . . . . . .. 233 11.3 Tectonism on Convergent Plate Margins and in Collision Zones . . . . . .. 238 11.3.1 Magmatic Arcs and Subduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 238 11.3.2 Tectonism Versus Eustasy in Foreland Basins .................... 239 11.3.2.1 The North American Western Interior Basin . . . . . . . . . . . . . . . . . . . .. 243 11.3.2.2 The Appalachian Foreland Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 250 11.3.2.3 Pyrenean and Himalayan Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 251 11.3.3 Rates of Uplift and Subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 252 11.3.4 Discussion.............................................. 254 11.4 Intraplate Stress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 255 11.4.1 The Pattern of Global Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 255 11.4.2 In-Plane Stress as a Contral of Sequence Architecture .............. 256 11.4.3 In-Plane Stress and Regional Histories of Sea-Level Change . . . . . . . . .. 259 11.5 Basement Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 263 11.6 Other Speculative Tectonic Hypotheses . . . . . . . . . . . . . . . . . . . . . . . .. 264 11.7 Sediment Supply and the Importance of Big Rivers ... . . . . . . . . . . . .. 265 11.8 Environmental Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 269 11.9 Main Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 269

IV Chronostratigraphy and Correlation: Why the Global Cyde Chart Should Be Abandoned. . . . . . . . . . . . . . .. 271

12 Time in Sequence Stratigraphy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 273

12.1 Introduction ............................................ 273 12.2 Hierarchies of Time and the Completeness of the Stratigraphie Record .. 273 12.3 Main Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 279

13 Correlation, and the Potential for Error . . . . . . . . . . . . . . . . . . . . . . .. 281

13.1 Introduction ............................................ 281 13.2 The New Paradigm of Geological Time? ........................ 282 13.3 The Dating and Correlation of Stratigraphie Events:

Potential Sources of Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 284 13.3.1 Identification of Sequence Boundaries . . . . . . . . . . . . . . . . . . . . . . . . .. 286 13.3.2 Chronostratigraphic Meaning of Unconformities . . . . . . . . . . . . . . . . .. 286 13.3.3 Determination of the Biostratigraphie Framework . . . . . . . . . . . . . . . .. 288 13.3.3.1 The Problem of Incomplete Biostratigraphic Recovery. . . . . . . . . . . . .. 288 13.3.3.2 Diachraneity of the Biostratigraphic Record ..................... 289

XIV

13.3.4 13.3.5 13.3.6 13.3.7 13.3.8 13.4 13.4.1 13.4.2 13.4.3 13.4.4 13.5

14

14.1 14.2 14.3 14.3.1 14.3.2 14.3.3

14.4

v

15

15.1 15.2 15.2.1 15.2.2 15.3 15.3.1 15.3.2 15.3.3 15.3.4 15.3.5 15.4 15.4.1 15.4.2 15.4.3 15.5

16

16.1 16.2 16.3 16.4

Contents

The Value of Quantitative Biostratigraphic Methods . . . . . . . . . . . . . . .. 291 Assessment of Relative Biostratigraphic Precision. . . . . . . . . . . . . . . . .. 293 Correlation of Biozones with the Global Stage Framework ........... 295 Assignment of Absolute Ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 296 Implications for the Exxon Global Cyde Chart. . . . . . . . . . . . . . . . . . .. 298 Correlating Regional Sequence Frameworks with the Global Cyde Chart. 300 Circular Reasoning from Regional Data . . . . . . . . . . . . . . . . . . . . . . . .. 300 A Rigorous Test of the Global Cyde Chart ...................... 302 A Correlation Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 304 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 306 Main Condusions ....................................... " 306

Sea-Level Curves Compared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 309

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 309 The Exxon Curves: Revisions, Errors, and Uncertainties . . . . . . . . . . . .. 309 Other Sea-Level Curves ................................... " 311 Cretaceous Sea-Level Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 313 Jurassic Sea-Level Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 316 Why Does the Exxon Global Cyde Chart Contain So Many More Events Than Other Sea-Level Curves? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 320 Main Condusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 320

Approaches to a Modern Sequence-Stratigraphic Framework. . . . . . . .. 323

Elaboration of the Basic Sequence Model . . . . . . . . . . . . . . . . . . . . . .. 325

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 325 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 325 The Hierarchy of Units and Bounding Surfaces . . . . . . . . . . . . . . . . . .. 325 Systems Tracts and Sequence Boundaries. . . . . . . . . . . . . . . . . . . . . . .. 331 The Sequence Stratigraphy of Clastic Depositional Systems ......... " 337 Fluvial Deposits and Their Relationship to Sea-Level Change. . . . . . . .. 337 The Concept of the Bayline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 341 Deltas, Beach-Barrier Systems, and Estuaries . . . . . . . . . . . . . . . . . . . .. 343 Shelf Systems: Sand Shoals and Condensed Seetions . . . . . . . . . . . . . . .. 350 Slope and Rise Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 355 The Sequence Stratigraphy of Carbonate Depositional Systems . . . . . . .. 357 Platform Carbonates: Catch-Up Versus Keep-Up . . . . . . . . . . . . . . . . .. 357 Carbonate Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 360 Pelagic Carbonate Environments. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 361 Main Condusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 361

Numerical and Graphical Modeling of Sequences ................ , 365

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 365 Model Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 366 Selected Examples of Model Results. . . . . . . . . . . . . . . . . . . . . . . . . . .. 369 Main Condusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 372

Contents

VI

17

17.1 17.2 17.2.1 17.2.2 17.2.3 17.2.4 17.2.5 17.3 17.3.1 17.3.2 17.3.3

17.4

18

18.1 18.1.1 18.1.2 18.1.3 18.2 18.2.1 18.2.2 18.2.3 18.3 18.3.1 18.3.2 18.3.3 18.4 18.4.1 18.4.2 18.5 18.6 18.6.1 18.6.2 18.7

xv

Discussion and Conclusions ............................... " 373

Implications for Petroleum Geology ......................... " 375

Introduction ........................................... " 375 Integrated Tectonie-Stratigraphic Analysis ..................... " 375 The Basis of the Methodology .............................. " 375 The Development of an Allostratigraphie Framework ............. " 375 Choiee of Sequence-Stratigraphic Models ...................... " 376 The Search for Mechanisms ................................. 377 Reservoir Characterization ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 377 Controversies in Practieal Sequence Analysis . . . . . . . . . . . . . . . . . . . .. 378 The Case of the Tocito Sandstone, New Mexieo ................. " 378 The Case of Gippsland Basin, Australia ....................... " 378 Conclusions: A Modified Approach to Sequence Analysis for Practieing Petroleum Geologists and Geophysicists . . . . . . . . . . . . .. 382 Main Condusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 384

Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . .. 385

Sequences in the Stratigraphie Record ........................ " 385 Long-Term Stratigraphie Cycles .............................. 385 Cydes with Million-Year Episodicities ........................ " 385 Cydes with Episodicities of Less Than One Million Years .......... " 386 Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 386 Long-Term Eustasy and Epeirogeny .......................... " 386 Milankovitch Processes ................................... " 387 Tectonic Mechanisms .................................... " 387 Chronostratigraphy and Correlation ........................... 389 Concepts of Time ....................................... " 389 Correlation Problems, and the Basis of the Global Cyde Chart ...... " 389 Comparison of Sea-Level Curves ............................ " 390 Modern Sequence Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 390 Elaboration of the Basic Sequence Model. . . . . . . . . . . . . . . . . . . . . . .. 390 Numerieal and Graphieal Modeling of Stratigraphie Sequenees . . . . . . .. 391 Implieations for Petroleum Geology .......................... " 392 The Global-Eustasy Paradigm: Working Backwards from the Answer? .. 392 The Exxon Faetor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 392 Condusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 395 Recommendations ........................................ 395

References ........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 397

Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 423

Subjeet Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 429