university of

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Structural geology of North Americ

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Structural Geology

of

North America

HARPER'S GEOSCIENCE SERIES

CAREY CRONEIS, Editor

Structural provinces of North America, shown to the edge of the continental shelf.

Digitized by the Internet Archive

in 2012 with funding from

LYRASIS Members and Sloan Foundation

http://archive.org/details/structuralOOeard

Structural Geology

of North America

SECOND EDITION

A. J. EARDLEY

Professor of~(5eology and Dean

College of Mines and Mineral Industries

University of Utah

HARPER & ROW, PUBLISHERS, NEW YORK AND EVANSTON

STRUCTURAL GEOLOGY OF NORTH AMERICA, Second Edition

Copyright 1951 by Harper & Row, Publishers, Incorporated Copyright © 1962 by A. J. Eardley

Printed in the United States of America

, IT

All rights reserved. No part of the book may be used or reproduced in any manner whatsoever without written permission except in the case of brief quotations embodied in critical articles and reviews. For infor- mation address Harper & Row, Publishers, Incorporated 49 East 33rd Street, New York 16, N. Y.

l-M

Library of Congress catalog card number: 62-17482

3. RESUMl OF STRUCTURAL GEOLOGY OF NORTH AMERICA

Major Tectonic Divisions

12

CONTENTS

EDITOR'S INTRODUCTION PREFACE TO THE FIRST EDITION PREFACE TO THE SECOND EDITION

1. INTRODUCTION

Purpose of Book Method of Presentation Kinds of Illustrations Maps for Collateral Use Authority for Stratigraphic Correlations Exercises

2. STRUCTURAL TERMINOLOGY

Need of Standard Terms for Regional Structures Meaning and Choice of Terms for This Book Terms for Structural Disturbances Classification Used for Crustal Disturbances

XI

xiii xv

1

4. PRECAMBRIAN TECTONIC PROVINCES 22

Distribution of Precambrian Rocks Canadian Shield Arctic Stable Region Precambrian Provinces of the United States

5. CENTRAL STABLE REGION OF THE UNITED STATES 37

General Characteristics Pre-Devonian Basins Transcontinental Arch Eastern Interior Basins and Arches Northwestern Interior Basins and Arches

6. PALEOZOIC CORDILLERAN GEOSYNCLINE 63

Divisions and their Characteristics Basins and Uplifts of the Western United States and Southern British Columbia Eugeosyncline in Southeastern Alaska, Northern British Columbia, and the Yukon Sum- mary of Orogenic History

7. APPALACHIAN MOUNTAINS 91

Major Structural Divisions Relations to Geomorphic Provinces

8. SOUTHERN AND CENTRAL APPALACHIANS 97

Extent and Divisions Major Elements of Stratigraphy Folded and Thrust-Faulted Appalachian Mountains Blue Ridge Province Pied- mont Province Summary of Orogenic History

9. EASTERN TRIASSIC BASINS 128

Distribution of Basins Nature of Triassic Rocks Structure of Basins Origin of Basins Late Triassic Phase (Palisades Orogeny)

10. ATLANTIC COASTAL PLAIN AND ADJACENT OCEAN BASIN 135

Extent and Character of Sediments Stratigraphy Structure Con- stitution of Continental Shelf and Adjacent Atlantic Ocean Crust

11. NEW ENGLAND APPALACHIAN SYSTEMS 154

Divisions of New England Appalachians Hudson Valley-Lake Cham- plain Region Central and Eastern New England Carboniferous Basins

VI

CONTENTS

12. MARITIME APPALACHIANS 189

Definition Geomorphic Provinces Stratigraphy Igneous Rocks Structures Tectonic History

13. NEWFOUNDLAND APPALACHIANS 203

Physical Divisions Stratigraphy Intrusions Major Structural Divi- sions and Their Characteristics Tectonic History Major Tectonic Re- lations of Greater Acadia

14. OUACHITA, MARATHON, AND COAHUILA SYSTEMS 223

Ouachita System Marathon System Coahuila System

15. WICHITA AND ANCESTRAL ROCKIES SYSTEMS

AND THE TEXAS FORELAND 237

Wichita System Texas Foreland Ancestral Rockies System

16. THE LATE PALEOZOIC ZONES OF FAULTING AND CRYPTOVOLCANIC OR METEORITE IMPACT STRUCTURES 253

Foreland Arcuate Fault Zone Lake Superior Fault Zone Cryptovol- canic or Meteorite Impact Structures

17. MESOZOIC SYSTEMS ALONG THE PACIFIC 260

Western Nevada Northwestern Nevada Central and Northern California Oregon Southern California Nevadan Orogeny An- cestral Coast Range System Columbia System

18. ROCKY MOUNTAINS IN MESOZOIC TIME 291

Triassic Geography Early Jurassic Geography Early and Mid-Cre- taceous Orogeny

19. LATE CRETACEOUS AND EARLY TERTIARY ROCKY MOUNTAIN SYSTEMS-THE LARAMIDE OROGENY 295

Definition of Laramide Orogeny Belts of Deformation Relation of Belts of Deformation to Crustal Constitution

20. CANADIAN AND MONTANA ROCKIES 302

Major Systems of Canadian Cordillera Divisions of Canadian and

Montana Rockies Mountain Belt Foothill Belt Age of Thrusting The Rocky Mountain Trench

21. IDAHO BATHOLITH AND THE OSBURN FAULT ZONE 319

Extent Composition Age Conclusions

22. CENTRAL ROCKIES 327

Spatial Relations Orogenic Deposits Southwestern Montana Southeastern Idaho and Western Wyoming Wasatch Area of Utah Central Utah Southwestern Utah Western Utah Southern Nevada

23. CENTRAL MONTANA ROCKIES 351

General Features Central Zone of Uplifts Zones of En Echelon Faults Stages of Orogeny Igneous Centers Structures of the Northern Great Plains

24. WYOMING ROCKIES 361

General Characteristics Teton— Gros Ventre— Wind River Element Beartooth Range Owl Creek and Washakie Mountains Heart Mountain and Related Features Absaroka Range and Yellowstone Park Big Horn Range and Big Horn Basin Black Hills and Powder River Basin Sweetwater Range Wind River Basin Hanna Basin Late Tertiary Downfaulting of Sweetwater Range Laramide Pattern and Cenozoic Stages in the Sweetwater Range Region Rawlins Up- lift Washakie Basin Green River Basin Uinta Mountains Rock Springs Uplift Laramie Range and Basin and Medicine Bow Range Hartville Uplift Regional Uplift in Late Cenozoic

25. COLORADO AND NEW MEXICO ROCKIES 389

Extent of Laramide Deformation Colorado Rockies New Mexico Rockies Central New Mexico Porphyry Belt Guadalupe and Mara- thon Uplifts

26. COLORADO PLATEAU 407

General Geology Asymmetrical Arches and Basins Salt Anticlines Laccolithic Mountains Upheaval Dome Volcanic Fields High Pla- teaus of Utah Age of Uplifts and Volcanism Epeirogenic Move- ments and Isostatic and Seismic Considerations

CONTENTS

27. SOUTHERN ARIZONA ROCKIES 426

Physiographic Characteristics and Divisions Paleozoic and Meso- zoic Basins Use of Terms, Laramide and Nevadan Orogenies Mes- ozoic and Cenozoic Geology of Southeastern Arizona Mesozoic and Cenozoic Geology of Southern Arizona Geology of West-Central Arizona Nevadan Orogeny (?) Igneous Cycles and Mineraliza- tion Tertiary Normal Faulting Conclusions Regarding Tectonic History

28. ROCKIES OF NORTHERN MEXICO 440

Mexican Geosyncline Sonoran Region El Paso— Rio Grande Thrust Belt Plateau Central and Sierra Madre Oriental Parras Synclin- orium Orogenic History Foothill Belt

29. COAST RANGES OF THE PACIFIC AND THE SAN ANDREAS FAULT SYSTEM 452

Major Divisions Central Coast Ranges of California Southern Coast or Transverse Ranges of California Northern Coast Ranges of Cali- fornia San Andreas Fault System Coast Ranges of Oregon and Washington

30. BAJA CALIFORNIA AND SONORA SYSTEMS 480

Baja California Gulf of California Sierra Madre Occidental

31. MIDDLE AND LATE CENOZOIC SYSTEMS

OF THE CENTRAL CORDILLERA 493

General Divisions and Their Characteristics Basin and Range System Late Cenozoic Trenches of the Rocky Mountains Geophysical Evi- dence Exploring Tensional Tectonism in Western North America Seismic Velocity Layers in the Eastern Great Basin

32. PACIFIC SUBMARINE PROVINCES 515

Discovery of Strong Submarine Relief Submarine Provinces Aleu- tian Trench Bering Sea Floor Pacific Floor off Mexico and Central America Fracture Zones Deep Sea Provinces Hawaiian Ridge Mid-Pacific Mountains Circum-Pacific Tectonics

33. IGNEOUS AND TECTONIC PROVINCES

OF THE WESTERN CORDILLERA 532

Objectives Concept of Igneous Provinces

34. IGNEOUS AND TECTONIC PROVINCES

IN SOUTH AMERICA 537

Chile and Argentina Peru, Bolivia, Ecuador, and Columbia Post- Batholithic Belt Parana Basin Basalt Field

35. IGNEOUS AND TECTONIC PROVINCES IN MEXICO 549

Geosyncline Batholithic Belt of the First Cycle Post-Batholithic Volcanism Batholithic Belt of the Second Cycle Metamorphic and Intrusive Belt Relation to Depressed Belts

36. IGNEOUS PROVINCES IN WESTERN UNITED STATES 553

Eugeosynclinal Province Batholithic Province Post-Batholithic Prov- inces of the Batholithic Belt Provinces of the Miogeosyncline and Shelf Relation of Tectonic to Igneous Provinces Distribution of Primary Magmas

37. IGNEOUS AND TECTONIC PROVINCES

OF WESTERN CANADA 583

Geosyncline Orogenies Beltian Geanticline Batholithic Province Post-Batholithic Volcanism Relation of Volcanism to Tectonic Prov- inces

38. SPATIAL RELATIONS OF MAJOR TECTONO-IGNEOUS

ELEMENTS AND ORIGIN OF MAGMAS 588

Relation of Batholithic Belt to Eugeosyncline Previous Orogeny in Eugeosyncline Relation of Post-Batholithic Compressional Orogeny to Geosyncline and Shelf Relation of Post-Batholithic Volcanics to Batholithic Belt Relation of Post-Batholithic Volcanic Fields to Strato- volcanoes Post-Batholithic Volcanics to Trenches Relation of Anti- clinoria to Other Elements Origin of Magmas Techtono-lgneous Provinces and Deep-Seated Earthquakes Crustal Tension and Mag- matism

Vlll

CONTENTS

39. ALASKA AND THE YUKON 605

Geomorphic Provinces of Alaska Paleozoic Geosyncline and Related Orogeny Triassic and Jurassic Geanticline and Adjacent Basins Cretaceous Basins and Geanticlines Mesozoic and Cenozoic Oro- genies Tertiary Volcanic Rocks Aleutian Volcanic Belt Siberian Tectonic Connections Yukon Territory and the District of Mackenzie Cenozoic Trenches and Faults

40. CANADIAN ARCTIC 633

Geography and Geologic Provinces of the Arctic Archipelago Low- lands and Plateaus Fold Belts— The Innuitian Region Arctic Coastal Plain Correlation with Alaska and the Yukon Pleistocene Epeirog- eny and Climatic Changes Orogenic Belts of Greenland Arctic Ocean Basin

41. GULF COASTAL PLAIN

General Characteristics Structural Geology Igneous Rocks Tam- pico Region, Mexico Florida Platform Crustal Structure of Gulf of Mexico

650

42. ANTILLEAN-CARIBBEAN REGION 670

Geographic Provinces Greater Antilles Lesser Antilles Puerto Rico Trench and Gravity Anomalies Caribbean Region and Seismic Profiles Origin of the Caribbean Basins, Trenches, and Rises Pos- tulated Eastward Shift of Caribbean Block

43. SOUTHERN MEXICO AND CENTRAL AMERICA 696

Major Geologic Divisions Crystalline Belt Permian Fold Belt Late Cretaceous and Early Tertiary Fold Belt Southern Gulf Coastal Plain Yucatan Peninsula Volcanic Fields and Faulting Isthmian Volcanic Link Relation to Greater Antilles Mammalian Fossil Record and Land Connections

BIBLIOGRAPHY 709

INDEX 739

COLOR PLATES

The signature of color plates follows page 14.

Plate 1. Precambrian Orogenic Belts

Plate 2. Cambrian Tectonic Map

Plate 3. Ordovician Tectonic Map

Plate 4. Silurian Tectonic Map

Plate 5. Devonian Tectonic Map

Plate 6. Mississippian Tectonic Map

Plate 7. Pennsylvanian Tectonic Map

Plate 8. Permian Tectonic Map

Plate 9. Triassic Tectonic Map

Plate 10. Jurassic Tectonic Map

Plate 11. Early Cretaceous Tectonic Map

Plate 12. Late Cretaceous Tectonic Map

Plate 13. Tectonic Map of the Cretaceous-Tertiary Transition

Plate 14. Early Tertiary Tectonic Map

Plate 15. Late Tertiary and Quaternary Tectonic Map

IX

EDITOR'S INTRODUCTION

A. J. Eardley's Structural Geology of North America has, since its pub- lication in 1951, become something of a landmark in the geological litera- ture of the New World. This is demonstrated by the broad base of its foreign sales and the fact that, at home and abroad, the volume has re- ceived heavy use by stratigraphers, geophysicists and other specialists, as well as by the structural geologists for whom it was written. Moreover, although originally conceived as a textbook for advanced undergraduates, Structural Geology soon became a handy and valued general source book for nonacademic professional and economic geologists.

Dr. Eardley, however, has always considered that his magnum opus was somewhat out of date even before the first edition was put through the publishing mill. Accordingly, immediately after the book was issued, he set about the onerous task of revising it. For a full decade now he has devoted a considerable amount of his time and efforts to the current re- vision. The self-imposed "labor of Hercules" has been particularly frus- trating and time consuming because during the fifties numerous basic concepts of structural geology have undergone radical change. Thus, fondly held theories of less than ten years ago are now either discarded

or seriously challenged. In addition, a vast quantity of new field data hai been accumulating so rapidly that revisions can scarcely keep up with the scientific progress.

Dr. Eardley has taken full cognizance of the rapidK evolving theo- retical concepts, as well as of the flood of new information. As a result this edition of Structural Geology is far from being a reprint in many chapters it is so extensively revised as to be essentiall) a new volume. But in addition, much of the best of the first edition reinainv .iud thus it is likely that this volume will continue to be the standard text and reference work in a subdiscipline of geologv that is of prime significance in the proper understanding of all other phases of the subject

The structural evolution of a continent! Relatively few scientific writers have painted on such a broad canvas as Dr. Eardley. Hi' is something of a rarity even among such artists, for he not only works with a broad brush but also takes pains to fill in the details.

The geological fraternity has been indebted to Dr. Eardley for an ex- cellent compendium on structural geology, and that indebtedness is now- increased through an exceptional initial task that has become even better done in its redoing.

( ' u.i ■> (. I iNl is

Rice University June, 1962

XI

PREFACE

TO THE FIRST EDITION

This book is addressed especially to advanced undergraduates in geol- ogy. I doubt that it could have been written on a more elementary level and still presume to use the common terminology of the numerous source publications and the language of the professional geologists. In fact, some instructors may consider the book too advanced for undergraduates. I have endeavored, however, to take such measures as will make it under- standable to the student who has had basic courses in mineralogy, lithology, and structural geology. It will be well if he has had a course in stratigraphy in which correlation problems have been discussed and in which some attention has been given to the sedimentary environments and sources.

The reader's attention is lost most frequently by the use of unfamiliar formational, fossil, and geographic names. Generally I have not used

formational names in the text but, instead, have referred to the dep< by period, epoch, or stage, and have listed the formational names in charts. This has the advantage of easing the reading of the text and still making the student aware of the many formations in the various parts ot the country. At the same time it sets the stage for meaningful stratigraphic studies in other courses.

I have discussed stratigraphic correlations only where necessary, anil have relied on the latest authoritative correlations in the literati.: graphic names have been treated with care, and I believe all that have been mentioned are on accompanying maps and figures, or on other well- known maps which are referred to as the occasion arises. Where petro- graphic research has been referred to, I have attempted to discuss it in such terms that the student with a knowledge of the common roik names will understand.

Several professors who teach structural geology have expressed to me the need for a text that treats structural geology from a regional point of view, hut I doubt it the present volume is what they want, or that it can be used as a substitute for the standard textbooks on principles. It may be that in those departments where structural geology is taught as a senior course, the hook could be used, and principles could he developed col-

xui

XIV

PREFACE TO THE FIRST EDITION

laterally. I think, however, that principles will suffer this way. I have the book in mind for an advanced course in regional or structural geology.

I hope also that the book will prove attractive to professional geologists, because some of the maps and ideas about the many fascinating problems of continental growth may be new to them. I also trust that they will not hesitate to set me right about any errors I have made.

Parts of the North American continent are so well known that it did not seem worth-while to do more than describe them briefly and sum- marize the conclusions that have been so well presented by others. In certain areas, however, I had to marshal the evidence and present it in some detail in order to sustain an original interpretation. For this reason, all parts of the continent may not seem equally treated. I had to bear in mind the professional geologist as a reader when drawing original con- clusions.

A series of paleogeologic maps and paleotectonic maps is included in the book. These, I hope, will be referred to repeatedly. They differ decidedly from the familiar paleogeographic map, and for structural studies are much more illuminating. As geologic studies progress, the maps will un- doubtedly bear correction, but I have been impressed repeatedly with the adequacy of our knowledge to date in establishing many important rela- tionships.

left

Where possible I have referred to late summary reports, and have left the reader to go to these, if he wishes all the original references. Where good summary reports are lacking, I have referred to the basic investi- gations. Our literature bearing on die structural development of the con- tinent is so extensive that I have been continuously beset by the fear that I have missed an important reference, especially for those regions with which I am least familiar.

The research and writing of this book was done at the University of Michigan, where the geologic library is extensive, the departmental facil- ities are all that were needed, the time to do research work was abundant, and my former associates on the staff were most helpful and congenial. I remain very appreciative of these facilities and opportunities at the Uni- versity of Michigan.

Miss Dolores Marsik has helped over several years as typist, and Dr. Ruth Bastanchury Boeckerman has assisted in editorial work and has done the final typing. Mr. Derwin Bell assisted in the drafting of many of the figures and plates.

A. J. Eardley

January, 1951

PREFACE

TO THE SECOND EDITION

The second edition is an extensively revised version of the first. Seven new chapters have been added, one on the Precambrian orogenic belts and six on the igneous provinces of the western cordillera. Igneous rocks are accorded a more significant place here than in the first edition. South- ern Mexico and Central America are treated in a separate chapter as is also the Canadian Arctic. The colored maps of the summary in Chapter 3 have been extensively revised, and several new ones are included.

Better index maps have been added throughout and an attempt has been made to produce an understandable text independent of outside sources of information. However, such maps as the geologic and tectonic maps of the United States and Canada and the several state maps will be indispensable for instructional purposes and should be available to the student or professional geologist reading the book.

The second edition marks a time of major transition in structural geol- ogy. In the past geologists have seen evidence in nearly every mountain system of crustal compression, but now a number of authorities postulate earth expansion, differential uplift, and crustal tension. The folds and thrust sheets are being interpreted as gravity slide phenomena from re- gions of marked uplift. Vertical movements along with distention and wrenching are considered to be the primary aspects of crustal deforma- tion— not horizontal compression.

The writer sees much in favor of the hypothesis of primary vertical movements and has perhaps accorded it greater attention than some will like. However, he has also attempted to present the geology of the several provinces as the authorities have depicted them. Certain sections of the book, therefore, reflect the orthodox concepts of compression, win other parts will seem to emphasize primary vertical movements with sec- ondary folding and thrusting. It will take another ten years to resoK e the irregularities and to warrant the preparation of a more definitive third edition.

A. J. Eardli v

June, 1962

xv

Structural Geology

of

North America

1.

described. Theories of diastrophism thai have been proposed for certain

structural systems are summarized, and current concept! of mmintalii building and continental development .ire presented where approprj

INTRODUCTION

PURPOSE OF BOOK

The purpose of the book is to describe the structural evolution of the North American continent. The chapters concern the formation and con- stitution of the mountain systems, basins, arches, and volcanic archi- pelagos; the beveling of the highlands; and the filling of the basins. In short, they treat of the procession of deformational and sedimentary events. Not only does the book seek to chronicle the crustal unrest of the continent, but it also tries to summarize the supporting evidence.

The igneous provinces and their relation to the tectonic provinces are treated. The advances in geophysics in deciphering deep crustal structure are referred to, and the constitution of the crust in several regions is

METHOD OF PRESENTATION

The structural history of the continent is one both of time and of geo- graphic position. The major scheme of organization of the book could, therefore, follow one or the other. For instance, if organized on a time basis, all the structural events over the whole continent would be re- viewed period by period. If on a geographic basis, the structural history of each major province would be followed from the beginnil .'en-

zoic time to the present. Neither course when rigidly pursued worked out well, but if the chapter headings are scanned, it will he apparent that l phasis in organization has been placed on geographic position.

The necessity of treating a succession of deformational events in a cer- tain province without serious interruption early became plain, and it decided that the great mountain systems whose histories run through several periods of time must be treated as units. The growth of the con- tinent in its several provinces has been described first during the Paleo- zoic, and then, in general, the great structural units of the MesozotC and Cenozoic have been considered. In the resume of the structural evolution of the continent, Chapter 3, the paleogeologic and paleotectonic maps are presented, and there the development, period by period, is reviewed.

KINDS OF ILLUSTRATIONS

Considerable effort has been made to illustrate every important point developed in the text. Maps, cross sections, and block diagrams are used. Photographs have little value because the structural features described are usually immensely larger than photographs reveal. If the reader de- sires to know the nature of the topographv, other books with a wealth of photographs should be referred to, such as Fenneman's Physiography of the United States, Lobeck's Gcomorplwlogy. Hinds's Geomorphology, and Atwood's Physiography of North America.

STRUCTURAL GEOLOGY OF NORTH AMERICA

MAPS FOR COLLATERAL USE

The book is not intended to stand entirely alone. The reader or in- structor should have the following maps for ready reference, preferably mounted and hanging on the wall at short range.

The Geologic Map of the United States, 1932 edition

The Geologic Map of Canada, 1957 edition

The Geologic Map of North America, 1946 edition

The Tectonic Map of the United States, 1944 edition

Landforms of the United States, 1939. Map by Erwin Raisz

The Tectonic Map of Canada, 1950

The Geologic Map of South America, 1950

These maps will be referred to repeatedly. Although the book contains many illustrations, it does not reproduce the features of the above maps, and if they are not consulted when referred to, the continuity will be interrupted, the evidence not clearly understood, and perhaps the con- clusions not appreciated or properly evaluated.

AUTHORITY FOR STRATIGRAPHIC CORRELATIONS

Most field work in structural geology is based on previous paleontologic and stratigraphic work. A report on the structural geology of an area is not considered worth while unless the formations are dated. The principal method of dating is by the fossils present, and therefore, the structural geologist is dependent upon the paleontologist, except in Precambrian terranes. It is conceivable, but not probable, that a sequence of deforma- tional events could be worked out in a local area without reference to fossils or to nearby stratigraphic columns, but to date the events and to relate them to others in widely separated areas is generally impossible without fossils.

A series of articles has appeared in the last few years in the Bulletins of the Geological Society of America that summarize the formational cor- relations throughout North America for each geologic period. They have been prepared by the Committee on Stratigraphy of the National Re- search Council, and are taken in this book as authority in relating the

numerous orogenic episodes throughout the continent. They are as follows :

Chart No.

1. Cambrian formations of North America, Howell et al., Bull. Geol. Soc. Am., vol. 55, pp. 993-1004, 1944.

2. Ordovician formations of North America, W. H. Twenhofel et al., Bull. Geol. Soc. Am., vol. 65, No. 3, 1954.

3. Silurian formations of North America, C. K. Swartz et al., Bull. Geol. Soc. Am., vol. 53, pp. 533-538, 1942.

4. Devonian formations of North America, G. Arthur Cooper et al., Bull. Geol. Soc. Am., vol. 53, pp. 1729-1794, 1942.

5. Mississippian formations of North America, J. Marvin Weller et al., Bull. Geol. Soc. Am., vol. 59, pp. 91-196, 1948.

6. Pennsylvania formations of North America, R. C. Moore et al., Bull. Geol. Soc. Am., vol. 55, pp. 657-706, 1944.

7. Permian formations of North America, A. A. Baker et al., Bull. Geol. Soc. Am., vol. 71, pp. 1763-1801, 1960.

8. Cretaceous formations of the western interior of the United States, Bull. Geol. Soc. Am., vol. 63, pp. 1011-1044, 1952.

9. Cretaceous formations of the Greater Antilles, Central America and Mexico, R. W. Imlay, Bull. Geol. Soc. Am., vol. 55, pp. 1005-1046, 1944.

10. Marine Cenozoic formations of western North America, C. E. Weaver et al, Bull. Geol. Soc. Am., vol. 55, pp. 569-598, 1944.

11. Cenozoic formations of the Atlantic and Gulf Coastal Plain and Caribbean Region, C. Wythe Cooke et al., Bull. Geol. Soc. Am., vol. 54, pp. 1713- 1724, 1943.

Additional correlations charts

Thickness and general character of the Cretaceous deposits in the western interior of the United States, Preliminary Map No. 10, J. B. Reeside, Jr., U.S. Geol. Survey, Oil and Gas Investigations, 1944.

Nomenclature and correlation of the North American Continental Tertiary, H. E. Wood, 2nd, et al., Bull. Geol. Soc. Am., vol. 52, pp. 1-48, 1941.

Paleotectonic maps of the Jurassic system, U.S. Geol. Survey, Miscellaneous Geological Investigations, Map 1-175, 1956.

Paleotectonic maps of the Triassic system, U.S. Geol. Survey, Miscellaneous Geological Investigations, Map 1-300, 1959.

EXERCISES

Four types of assignments and exercises are feasible. The first is the reading and reporting of original articles in the literature. It is hoped that

INTRODUCTION

all articles of outstanding importance are referred to in the text. All publi- cations referred to are listed in the bibliographic index. For emphasis on local areas of interest, die instructor can assign additional publica- tions.

The second type of exercise is the detailing of stratigraphic successions in the different basins and mountain systems. This in itself would consti- tute an extensive course in stratigraphy, but perhaps for local interest, certain stratigraphic details can be fitted into the structural picture.

The third type of exercise is the assembling from the book of all the structural events that occurred nation-wide for each of the periods. Since the book is organized chiefly on a geographic or provincial basis, it will

be an excellent review to cut across provinces on a time basis and sum- marize the events over the entire continent for each period. 'Ih< paleogeologic and paleotec tonic maps and the- bri< i discussion that companies them in Chapter 3 already do this, hut no part of the text is devoted in detail to it.

The fourth type of exercise is the tracing of the geologic history of a county or a state. The commonest types of reports are those that de- scribe the geology of an area with political boundaries, and it will ser\e the student as a good lesson to write a history of such a region. He will have to draw his information from several structural provinces and will find his organization, if complete, both long and complex.

2.

STRUCTURAL TERMINOLOGY

NEED OF STANDARD TERMS FOR REGIONAL STRUCTURES

The posthumous work of Schuchert (1943) is an example of the ir- regular use of names for the large structural features of the United States. He speaks of the Cincinnati anticline and the Cincinnati geanticline, evi- dently interchangeably, and the Nashville dome in the same sense as the Cincinnati anticline. McFarlan (1943), in his book on the geology of Kentucky, defines the Cincinnati arch as a major structure which includes the Jessamine dome and the Nashville dome, but in several places he refers to the arch as a dome. In Colorado the Ancestral Rockies are com- monly called highlands and geanticlines, in New Mexico they are land-

masses, in Texas they are uplifts and arches. The buried Nemaha "Mountains" in Oklahoma and Kansas have been called a ridge. There are a number of other terms for which no standard structural meaning has evolved. The professional geologist may not experience any difficulty or inconvenience in this loose and local application of names for the large structural features of the earth's crust, but for the student it is confusing. I have felt impelled to define and classify for his sake, because the book is addressed to him. In so doing, however, I feel at many turns there will be objections, largely on the grounds of provincial usage.

In view of the undesirability of multiplying technical words, it seems necessary to assign specific meanings to common words in their several fields of usage. For instance, the word system when used in stratigraphy denotes the rocks formed during a period of geologic time; when used geographically it generally signifies a group of ranges with unifying char- acteristics; and when used structurally it indicates a group of related joints, faults, dikes, or the like. It is probably better to give a word such as system several meanings rather than use a new word, or a less common and, perchance, a less appropriate one. The commonest usage of a term should weigh heavily in formulating a definition for it.

MEANING AND CHOICE OF TERMS FOR THIS BOOK

Arch and Dome

From 1891 to 1903 Foerste spoke of the Cincinnati uplift as an anti- cline, then in 1904 as a geanticline, and Schuchert continued the use of these two terms apparently interchangeably. The first mention of the terms arch and dome for the structure has not been located in the litera- ture, but since 1900 they have been used very commonly and usually synonymously. They are the terms used both provincially and nationally most frequently today. McFarlan ( 1943 ) has distinguished the two in the sense that the Cincinnati arch is an elongate structure and includes two dome-shaped uplifts on it, the Jessamine dome and the Nashville dome, separated by a sag or saddle. Tennesseans will probably not accept the subordination of their Nashville dome to a division of the Cincinnati arch, but the principle of the distinction of arch and dome is appealing. Since

STRUCTURAL TERMINOLOGY

the Cincinnati and Nashville structures are the earliest of the broad, gentle uplifts studied in the United States, they probably should be taken as types, and definitions should be fashioned after their character- istics. At the completion of the present study of the uplifts and depres- sions of the central stable region of the United States, nothing undesirable is recognized in taking the Cincinnati and Nashville structures as types for the United States, if a little latitude in characteristics is tolerated. The terms in this report will be used as follows:

An arch is a gentle, broad uplift with an evident width of 25 to 200 miles and a length conspicuously greater than the width. The structural relief may amount to 10,000 feet or more between a bed at the top of the arch and one of similar age at the bottom of the adjacent basin, but the dip of the beds will generally not exceed 100 feet per mile. The struc- tural relief may have been acquired in part by subsidence of the adjacent basins at a greater rate than the arch area, so that the arch may actually only at times have been an emergent landmass.

A dome is a gentle, round or elliptical uplift of arch proportions. It usually occurs along an arch and expands the arch locally. This regional structural meaning of dome must be distinguished from the usage in con- nection with igneous rock masses (Rice, 1940) and from the much smaller oil- and gas-producing structures such as salt domes or plugs.

Swell

Schuchert ( 1923 ) used the term swell to mean all large, domed areas within the nuclear part of the continent. Rucher ( 1933 ) defined a swell as "an essentially equidimensional uplift without connotation of size or origin." In discussing the structures of the United States the terms arch and dome are sufficient for all broad gentle uplifts, to which the term swell would generally apply, and therefore it has not been necessary to use swell in the following pages, and no attempt to define it further will be made here.

Uplift and Upwarp

Uplift and upwarp are used for a wide variety of structural elevations, and, therefore, should be reserved as noncommittal terms in regard to

size, shape, internal structure, and origin. If it is desired to distinguish the two, uplift might be conceived as implying both small and lai round and elongate elevations, with sharp and gentle variations; whan upwarp would imply simply broad and gentle archings. Nfo precedent

can be cited for this distinction, but a perusal of the literature leaves me with the impression that this is the most general usage, l'rovmc iallv, how- ever, uplift may mean a rather definite type of structure. I will use the terms only in case I am in doubt about the nature of a structural el tion, or desire to use them as synonyms of structures being discussed in order to eliminate repetition.

Basin

Rucher (1933) uses the term basin in a structural sense to mean any essentially equidimensional depression without connoting size or origin, and then gives the Michigan basin as an example. Swell is his antithetical structure of basin. Since the drill in several places has extensively ex- plored the subsurface distribution of the stratified rocks of the continent. a number of downwarps have become firmly entrenched as basins in the literature. Some embrace more than a large state, and some are of county size. Some are fairly elongate, and most all have axial directions. Some are troughlike or furrowlike. It has not proved disturbing in compiling the present review to have basin used in this loose sense, and I believe the variations in meaning will be evident to the student, so there is little urge to attach limitations to the term. The word basin is applied a thousand times each day by petroleum geologists in many variations of meaning, and it would appear unwise to attempt standardization.

Coal basins have not proved to be the same as oil basins or water basins in several places, and also the extent of the commercial materials has not coincided with the greatest thickness of the strata and. therefore, the greatest depression. It seems to me that the major geological features should govern the choice of a geographic name, rather than the distribu- tion of an economic deposit of little relative volume.

The site of maximum subsidence during an epoch, period, or era may not coincide with that of a later one, and some confusion has resulted in the meaning of the term basin in certain areas. This is particularly true

6

STRUCTURAL GEOLOGY OF NORTH AMERICA

on tectonic maps which attempt to show all structures evolved through three eras. I have found it desirable to think of certain basins in a re- stricted time as well as restricted geographic aspect, and to prepare ac- cordingly the tectonic maps that accompany this book.

Geosyncline According to Kay ( 1951 ) :

The term geosyncline should be restricted to a surface of regional extent sub- siding through a long time while contained sedimentary and volcanic rocks are accumulating; great thickness of these rocks is almost invariably the evidence of subsidence, but not a necessary requisite. Geosynclines are prevalently linear, but non-linear depressions can have properties that are essentially geosynclinal.

Classifications of geosynclines are discussed by Kay, who takes the position that all basins having a thick sequence of sediments are one kind or another of geosyncline. However, only two geosynclinal terms will be used in this text, namely, miogeosyncline and eugeosyncline, which are the large linear basins along the margins of North America.

Miogeosyncline

A miogeosyncline is part of the great linear border geosyncline. It lies between the shelf regions of the stable interior of the continent and the outer part of the geosyncline. Its sediments are dominantly sandstone, shale, chert, limestone, and dolomite, almost free of volcanic rock.

Eugeosyncline

An eugeosyncline is the outer part of the border geosyncline and is characterized by an abundance of volcanic rock. In addition there is much graywacke, arkose, dark shale, and chert. The strata are generally altered by low-grade metamorphism.

Landmass

Landmass has no specific structural meaning unless used locally as in the Ancestral Rockies of New Mexico, for instance, where an ancient range is referred to as the Pedernal Landmass. The term usually con-

notes a land area whose elevation, climate, and life are the special object of study through the intermediary of the sediments derived from it, or whose changing shore fines form the basis of some paleogeographic study. The term does not usually imply size, relief, or origin, and no specific attributes will be affixed to it in this book.

Highland

In Colorado, two principal uplifts dominated the structural evolution of the area in late Paleozoic time, and they have been referred to by most writers as highlands. They are about 50 miles wide and 200 miles long and structurally were rather abrupt, asymmetrical anticlines which may have been faulted in part along their steep flanks. Except in appli- cation to the Colorado uplifts, the term is used very broadly in the United States, and no one to my knowledge has attempted to define it; nor is it necessary here to do so. It does not seem consistent, however, to say a certain highland was a Zotu-lying area, but the statement may appro- priately be made of a landmass.

Ridge

The buried Nemaha uplift of Oklahoma, Kansas, and Nebraska is gen- erally spoken of as the Nemaha Mountains, but the term Nemaha ridge has also been used, with the implication that ridge has a certain structural significance. The use is almost unique to this area, as far as I know. A ridge, topographically, is generally less than 5 miles long, and its use structurally for the Nemaha Mountains, 200 miles long, is somewhat mis- leading. It is not necessary to use the term in the present review.

The term is used in oceanography to depict very large linear relief features on the ocean floor, such as the Mid-Atlantic Ridge (also Rise) or the Beata Ridge in the Caribbean Sea.

Geanticline

The term geanticline was proposed by Dana in 1873 ( Schuchert, 1923 ) for "the upward bendings in the oscillations of the earth's crust the geanticlinal waves or anticlinoria." According to Schuchert, Dana's typi- cal example was the Cincinnati arch, though later on, Dana also included

STRUCTURAL TERMINOLOGY

far greater, even continental arching. Schuchert generally recognized geanticlines and geosynclines as "complementary structures," but called the land that divided the Cordilleran geosyncline during Mesozoic time into an eastern geosyncline and a western, the greatest of North American geanticlines.

Although Schuchert attempted to clarify Dana's most confused defini- tion, he introduced contradictory thoughts, and therefore did not clarify the meaning of the term. Others have confused the meaning still more. According to Willis ( 1934 ) , "a geanticline is a very large elevation of the earth's surface. The rocks of the geanticline may not be folded may not even be stratified and the anticlinal significance is lost." Lahee ( 1941 ) states that a "geanticline is a very extensive uplift, generally anticlinal in nature (also called a regional anticline)." He gives as examples the "Ar- buckle Mountain Uplift and the Central Mineral Region of Texas," which are two greatly different kinds of tectonic elements. According to Nevin ( 1942 ) a geanticline is a "great upwarp . . . whose dimensions are meas- ured in hundreds of miles. . . . The Ozark Mountains and the Arbuckle Uplift are true geanticlines." These, again, are dissimilar structures. Bill- ings (1942) defines a geanticline as "the counterpart of a geosyncline, (it) is an area from which the sediments are derived. The geanticline that lay southeast of the Appalachian geosyncline is known as Appalachia." In the Dictionary of Geologic Terms (Rice, 1940) a geanticline is "a large, broad, and usually very gentle anticline, commonly many miles in width."

Most of these definitions are widely divergent, and the examples are structures of contrasting size, composition, history, and relation to the central stable interior of the continent. Some of the definitions are synony- mous with terms already defined, such as arch, dome, and landmass.

The confusion in American literature is paralleled by the European. Brouwer (1925) of Holland says that a geanticline is a major uplift of island arc size, complementary to the geosyncline. Collet ( 1927 ) , follow- ing Argand (1916), defines a geanticline as an anticlinal ridge that ap- pears on the bottom of a geosyncline and expresses itself as a land barrier between the seas of the geosyncline. It is at first a long, narrow anticline of considerable size and later evolves into a great nappe. Whether the de-

velopment of a nappe is necessary to demonstrate a true geanticline in not stated or implied. Most Alpine geologists, it is my impression, follow tin- usage of Collet.

King (1937) exemplifies the Alpine usage in his treatise of die evolu- tion of the Marathon system. A structure in west-central Nevada tint rose out of the Paleozoic Cordilleran geosyncline is i ailed a geantu line In Nolan (1928). I have decided to follow the specific usage of Collet, King, and Nolan and will denote a geanticline as a large, elongate, anticlinal fold that develops in the sediments of a geosyncline. It is not a 'geanticline if an uplift in the foreland or shelf area. Two or more geanticlines ma) develop at the same time or following each other in a great geos\ ncline. After the early anticlinal uplift, the great fold usually becomes a complex anticlinorium, several imbricate thrust sheets, or a nappe. It may be largely submarine, and suffer little erosion.

Range

The synonymous use of the terms highland, landmass, mountains, up- lift, arch, and geanticline, all to describe uplifts of the Ancestral Rockies and Wichita systems with fairly similar size and shape, poses a difficult problem,