Depositional, diagenetic, and subsidence history of the Redwall Limestone, Grand Canyon National Park, Arizona
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Authors Sylvia, Dennis Ashton
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/558026 DEPOSITIONAL, DIAGENETIC, AND
SUBSIDENCE HISTORY OF THE
REDWALL LIMESTONE, GRAND CANYON
NATIONAL PARK, ARIZONA
by
Dennis Ashton Sylvia
A Thesis submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In Partial Fulfillment of the Requirements For the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 8 5 STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of require ments for an advanced degree at the University of Arizona and is deposit ed in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotations from or reproduction of this manuscript in whole or in part may be granted by the head of the major department of the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholar ship. In all other instances, however, permission must be obtained from the author.
SIGNED: /jLuftLfl ^ - Su Ln&j
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
S. M. Kidwell Date Assistant Professor of Geosciences a c k n o w l :wKewia,NTS
The writer gratefully acknowledges the very generous research grant provided by the Grand Canyon Natural History Association. Addi tional support was provided by the Laboratory of Geo tectonics in the
Department of Geosciences at the University of Arizona. Special thanks are given to S. M. Kidwell for her guidance and enthusiastic support throughout the project. Thought-provoking discussions with R. Armin and
L. Lemke are gratefully acknowledged. Appreciation is extended to dissertation committee members J.F. Schreiber, Jr. and W. R. Dickinson for their suggestions and support. Photographs contributed by A. Hess significantly enhanced the quality of this work, her help is gratefully acknowledged. A. Wortman, J. Schenk, and L. Lenke are thanked for their companionship and assistance in the field. Appreciation is extended to personnel of the National Park Service at Grand Canyon National Park, particularly K. Davis of Resources Management and Planning who assisted in obtaining and amending collection permits and also to the people in the Backcountry Reservation Office, who greatly facilitated coordinating extended trips into the Canyon. Appreciation is also extended to the superintendent of Grand Canyon National Park, R. W. Marks, for granting permission to conduct this investigation within the Park. Invaluable assistance was provided by Fred Harvey Mules, Inc., particularly T. At water, who transported the rock samples collected along South Kaibab trail up to the rim and also provided much-appreciated drinking water while in the Canyon. W. Bilodeau, Department of Geosciences is acknow ledged for providing field supplies throughout the study. Personnel of the Department of Geosciences Business Office are thanked for maintaining the financial records for this project. Special thanks go to S. G. Syl via for assistance in editing the manuscript. Deep appreciation is extended to my wife, Sandy, and son, Sean, who provided support through out the course of this study.
iv TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS...... ix LIST OF TABLES ...... xviii A B S T R A C T ...... xix INTRODUCTION ...... 1 P u r pose...... 1 Area of Investigation ...... 2 Methods ...... 5
REGIONAL ASPECTS ...... 7
Regional Stratigraphic Aspects ...... 7 Tectonic Framework ...... 8 Pre-Mississippian Tectonic Cratonic Elements...... 8 Antler Orogeny and Foreland Basin Development...... ' ...... 10 Paleogeography...... 14 Paleoclimatology...... 15
PREVIOUS WORK ON THE REDWALL LIMESTONE...... 18
Historical D e v e l o p m e n t ...... 18 Underlying Strata ...... 19 Overlying S t r a t a ...... 20 Paleontological Studies ...... 20 Whitmore Wash Member...... 21 Thunder Springs Member...... 26 Mooney Falls Member / ...... 30 Horseshoe Mesa M e m b e r ...... 32 Post-Redwall, Chesterian Limestone, "Surprise Formation"...... 34 Depositional Cycles ...... 36
v TABLE OF CONTENTS - CONTINUED
Page
DEPOSITIONAL ENVIRONMENTS ...... 40
Introduction ...... 40 Previous W o r k ...... 43 South Kaibab Trail Section...... 44 Discussion...... 68 Conclusion...... 70
DIAGENESIS...... 73
Introduction ...... 73 Dolomitization...... 74 G e n e r a l ...... 74 Petrographic Observations (This study)...... 75 Dolomitization Model ...... 92 Silicification...... 94 General...... 94 Field Observations...... 95 Petrographic Observations...... 97 Silicification Model ...... 113 Recrystallization ...... 117 Introduction ...... 117 General Recrystallization Characteristics...... 118 Petrographic Observations ...... 119 Mold Formation...... 123
DIAGENETIC HISTORY...... ^ ...... 125
G e n e r a l ...... 125 Criteria Used In Diagenetic Interpretation ...... 126 Whitmore Wash - Thunder Springs Diagenetic Subfacies ...... 136 Whitmore Wash Diagenetic oubfacies ...... 136 Thunder Springs Diagenetic Subfacies ...... 138 Mooney Falls - Horseshoe Mesa Diagenetic Facies ...... 140 Mooney Falls Diagenetic Subfacies ...... 140
vi TABLE OF CONTENTS - CONTINUED
Page
Horseshoe Mesa Diagenetic Subfacies...... 146 Diagenetic Model ...... 148 Conclusion...... 153
EFFECTS OF ANTLER TECTONISM ON REDWALL SHELF SEDIMENTATION ...... 157
Modeling...... 158 F l e x u r e ...... 159 Loading Considerations ...... 163 R e s u l t s ...... 173 Discussion...... 176 Conclusions...... 178
CONCLUSION ...... 180
APPENDIX A: SOUTH KAIBAB TRAIL MEASURED SECTION ...... 183
APPENDIX B: MODIFIED CLASTICITY INDICES...... 201
APPENDIX C: STRATIGRAPHIC SECTION REFERENCES ...... 206
APPENDIX D: GENERAL ANALYTICAL SOLUTIONS FOR BASIN SUBSIDENCE...... 213
APPENDIX E: GEOHISTORY DIAGRAMS ...... 216
REFERENCES...... 230
X
vii THIS THESIS HAS MO PAGE viii LIST OF ILLUSTRATIONS
Figure Page
1. Index Map of the Study Area in the Grand Canyon Region ...... 3 2. Early Mississippian Tectonic Features of eastern ^ Nevada and Northern A r i z o n a ...... 3. Paleogeography and Atmospheric Circulation and Upwelling for Early Mississippian T i m e ...... 16
4. Isopach Map of the Whitmore Wash Member of the Red wall L i m e s t o n e ...... 22
5. Photograph of Well-developed Moldic Porosity in the Whitmore Wash Member Along South Kaibab T r a i l ...... 23
6. Isopach Map of the Thunder Springs Member of the Redwall L i m e s t o n e ...... 27
7. Isopach Map of the Mooney Falls Member of the Redwall Limestone ...... 31
8. Isopach Map of the Horseshoe Mesa Member of the Redwall L i m e s t o n e ...... 33
9. Generalized Comparison of Eustatic Cycles Interpreted in the Redwall Limestone and Coeval S t r a t a ...... 35 / 10. Irwin's Theoretical Epeiric Sea Sedimentation Model Compared with the Distribution of Recent Shallow Marine Sediments...... 41
11. Comparison of Gradients of Major Carbonate Platforms and Banks from the Silurian to the Tertiary...... 42
ix LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
12. Distribution of Redwall Limestone Depositional Environments and Facies in Accordance with a Modified Shaw- Irwin Model of Epeiric Sea Sedimentation ...... 45
13. Depositional Environment, Lithology, Moldic Porosity, and Modified elasticity Index for the Whitmore Wash Member of the Redwall Limestone Along South K aibab Trail ...... 46
14. Photomicrograph of Crinoidal-Bryozoan Grainstone Facies (IIB), SKT-29 ...... 48
15. Depositional Environments, of Redwall Limestone Samples collected along South Kaibab T r a i l ...... 49
16. Depositional Environment, Lithology and Modified elasticity Index for the Thunder Springs Member of the Redwall Limestone Along South Kaibab Trail ...... 50
17. Lithology and Depositional Environment for Part (1) of the M o o n e y Falls M ember of the Redwall Limestone Along South Kaibab Trail ...... 51
18. Lithology and Depositional Environment for Part (2) of the Mooney Falls Member of the Redwall Limestone Along South K a i b a b Trail ...... 52
"V
X LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
19. Lithology and Depositional Environment for Part (3) of the Mooney Falls Member and All of the Horseshoe Mesa Member of the Redwall Limestone Along South Kaibab Trail ...... 53
20. Photomicrograph of Pelletiferous- Algal-Calcisphere Wackestone 54
21. Photomicrograph of Fine-Grained, Well- Sorted, Coated Grain-Pelletiferous- Packstone 55
22. Photomicrograph of Pellet!ferous Grainstone 56
23. Photomicrograph of Oolitic-Pelletiferous Grainstone 57
24. Photomicrograph of Bioclastic Hash- - Pelletiferous Grainstone ...... 58
25. Photomicrographof Medium-Grained, Well- Sorted, Oolitic Grainstone ...... 59
26. Photomicrograph of Moderately Recrystallized (R-3), Medium-Grained, Moderately Well- Sorted Bryozoan-Crinoidal Grainstone ...... 60
27. Photomicrograph of Fine- to Medium- Grained, Well-Sorted, Coated Grain- Crinoidal-Bryozoan Grainstone ...... 61
28. Photomicrograph of Fine- to Medium- Grained, Moderately Well-Sorted, Coated Grain-Crinoidal-Bryozoan Grainstone ...... 62
xi r
LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
29. Photomicrograph of Recrystallized (R-2), Fine- to Medium-Grained, Poorly Sorted, Crinoidal- Bryozoan Grainstone 63
30. Photomicrograph of Overpacked Crinoidal Grainstone 64
31. Photomicrograph of Fine- to Medium- Grained, Poorly Sorted, Bryozoan- Crinoidal Packstone 67
32. Mean elasticity Values for Redwall Limestone Samples Collected along South Kaibab Trail ...... 71
33. Photomicrograph of Slightly Corroded Dolomite Rhcmbohedra in Chert Matrix 77
34. Photomicrograph of Slightly Corroded Dolomite Rhcmbohedra in Chert Matrix 78
35. Photomicrograph of Partially Dedolomitized, Corroded Dolomite Rhombs in Chert Matrix ...... 79
36. Photomicrograph of Mosaic of Hypidiotopic Dolomite Crystals ...... 80
37. Photomicrograph of Idiotopic Dolomite Texture in Vicinity of Mold 82
38. Photomicrograph of Euhedral Dolomite Rhombs Penetrating Sparite-Filled Mold 83
xii LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
39. Photomicrograph Depicting Moldic Porosity in Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies ...... 84
40. Photomicrograph of Sparite-Filied Mold in the Upper Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies ...... 86
41. Photomicrograph of Euhedral Dolomite Rhombs "Floating" in Sparite-Filled Mold ...... 87
42. Histogram of Dolomite Rhomb Size tribution...... 88
43. Cumulative Curve of Dolomite Rhomb Sizes ...... 89
44. Photomicrograph of Iron-Oxide Coated, Euhedral Dolomite Rhombs Penetrating Sparite-Filled Mold ...... 91
45. Photograph of Nodular Cherts in the Whitmor& Wash Member along South Kaibab Trail ...... 96
46. Photograph of Intercalated Chert and Dolomite (and Dolostone) Beds in the Thunder Springs M e m b e r ...... 98
47. Photograph of Chert Lenses and Nodules in the Upper Horseshoe Mesa M e m b e r ...... 99
48. Photomicrograph of Void Progressively Infilled with Microquartz and Mega quartz 100
49. Photomicrograph of Oolite Replaced by Microcrystalline and Megaquartz ...... 101
xiii LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
50. Photomicrograph of Oolite Replaced by Chert in Thunder Springs Member 102
51. Photomicrograph of Brachiopod Infilled First With a Thin Fibrous Quartz Crust, Followed by Microcrystalline Quartz, and Megaquartz . . . . 103
52. Photomicrograph of Silica- Replaced Oolites ...... 104
53. Photomicrograph of Silica- Replaced, Previously Micrite- Coated, Allochems ...... 105
54. Photomicrograph of Growth Lamellae in a Void-Filling Quartz Crystal 106
55. Photomicrograph Illustrating Poikilo- topic Texture in Upper Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies ...... , 108
56. Photomicrograph Illustrating Poikilo- topic Texture in Upper Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies ...... 109
57. Photomicrograph of Silica-Replaced Dasycladacean Algae in Whitmore Wash Member ..."...... 110
58. Photomicrograph of Unsilicified Allochems in Chert Matrix, 111
59. Photomicrograph of Chert Surrounding Neomorphic Calcite Cores of Crinoid Grains ...... 112
xiv LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
60. Photomicrograph of Silicified, Sponge Spicule Wackestone From the Top of the Mooney Falls Member . . 115
61. Photomicrograph of Tetraxon Sponge Spicule From a Partially Silicified, Recrystal1ized (R-3) Coated Grain Grainstone ...... 116
62. Photomicrograph of Leached Allochems Infilled with Sparite . . . 120
63. Photomicrograph of Completely Micritized Oolites . . . . 121
64. Photomicrograph Showing Drusy Sparite Crusts Around Perimeter of Grains, 122 65. Photograph of Solution Seam at the Base of Horseshoe Mesa Member along ----- 127 South Kaibab Trail ...... 66. Lithology, diagenesis, and . inferred diagenetic environments of the Redwall Limestone ...... 129
67. Photomicrograph of Thick Micrite Rims on Allochems in the Mooney Falls Menber, Mooney Falls Diagenetic Subfacies, 130
68. Photomicrograph of Blocky Sparite Cement Derived From a Blocky Sparite Which Surrounds Grains ...... 133
69. Photomicrograph Showing Drusy Crust Around Perimeter of Oolites 134
xv LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
70. Photomicrograph of Well-Developed Syntaxial Cements on Grains Without Micrite Rims ...... 135
71. Photomicrograph of Large Crinoid Ossicle 142
72. Photomicrograph Showing Broken Micrite Rims of Leached Allochems ...... -... 144
73. Photomicrograph of Blocky Sparite Infilled Ostracode 145
74. Paradiagenetic Sequence for Redwall L i m e s t o n e ...... 149
75. Schematic Depicting Out-Building of Freshwater Lens Beneath Red- wall S h e l f ...... 150
76. Reconstructed Depths to Basement of Antler Foreland Basin, Adjacent Shelf Margin and Shelf, and Modeled Depths to Basement ...... 161
77. Schematic Illustrating Concept of Peripheral Bulging ...... 162 \ 78. Evolution of the Antler Foreland Basin, Adjacent Shelf Margin and Shelf, Nevada and North western Arizona ...... ^ ...... 164
79. Palinspastic Restoration Accounting for Sevier Thrusting and Cenezoic E x t e n s i o n ...... 166
xv i LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
80. Stratigraphic Correlation Chart Depicting Chronometric Ages, Biostratigraphic Zonations, Stratigraphic Sections, and Depositional Environments Utilized in This S t u d y ...... 167
81. Flysch Trough and Submarine Rise Subsidence C u r v e s ...... 170
82. Shelf Margin and Western Shelf Subsidence C u r v e s ...... 171
83. Eastern Shelf Subsidence Curves ...... 172
84. Schematic Diagrams Showing Phases and Inferred Tectonic Elements of the Antler Orogeny ...... 175
xvii LIST OF TABLES
Table Page
1. Dolomite Crystal Size Distribution (in Micrometers) of Samples Taken From the Whitmore Wash Member of the Redwall Limestone Along South Kaibab T r a i l ...... 90
2. Major Diagenetic Phases ...... 154
xviii ABSTRACT
Flexural modeling and depositional and diagenetic analyses suggest that the Mississippian Redwall Linestone records a single major transgressive-regressive cycle punctuated by a lengthy stillstand during the Osagean, and that sedimentation was primarily controlled by coeval
Antler tectonics. Five depositional environments, ranging from a low- energy, restricted shelf-lagoon to a high-energy, crinoidal bank environ ment chronicle the Redwall depositional cycle. Two early diagenetic
facies, each with two diagenetic subfacies, were recognized. Diagenetic
facies and subfacies boundaries are largely coincident with member boundaries. Dolomitization and silicification characterize diagenesis in
the lower two members while recrystallization and, to a lesser extent,
silicification characterize diagenesis in the upper two members. Member
recognition is primarily based upon diagenetic character. Two-dimension
al finite difference modeling shows that initial Redwall shelf inundation
is related to Antler thrust loading while subsequent emergence is due to
relaxation of elastic stress or seaward migration of a peripheral bulge.
xix Frontispiece: View along South Kaibab Trail - looking north from cave in Horseshoe Mesa Member of the Redwall Limestone.
x x INTRODUCTION
Purpose
The purpose of this investigation is to use a synthesis of flexural modeling and depositional and diagenetic analyses to reassess previous interpretations of Redwall depositional history. A depositional analysis of sedimentary facies of the Redwall Limestone along the well- exposed South Kaibab trail, Grand Canyon National Park, provides a comparison with previous paleoenvirormental interpretations. Secondly, the sequence of early diagenetic environments affecting Redwall sediments records relative transgressions and regressions of the Redwall Sea.
Thus, the early diagenetic history is particularly important in inter preting the Redwall's depositional history. Finally, „ the Redwall
Limestone is part of an extensive sheet of Lower Mississippian shallow marine carbonates that occurs throughout the Cordilleran miogeocline.
These shelf carbonates are largely contemporaneous with the Antler orogeny. Thus, an investigation of the relationship,between the Redwall and coeval Antler tectonics is germane to understanding shelf sedimenta tion. The Redwall shelf's response to thrust and sediment loading due to coeval Antler tectonics can be assessed using flexural modeling. An
integration of the above approaches will provide a more accurate inter
pretation of the unit's depositional history.
1 \ 2
Area of Investigation
The study was conducted in the stratigraphic section of Redwall
Limestone along South Kaibab trail. Grand Canyon National Park. Because
of limitations imposed upon the number and location of specimens taken
within the Park, dense sampling of this single, well-exposed section was
chosen over sparse sampling of several, less well-exposed sections to
obtain maximum resolution of depositional cycle fluctuations and dia-
genetic patterns.
The stratigraphic sections examined in the Grand Canyon are shown
on the index map (figure 1). Lithologic thicknesses and composition,
biostratigraphic data and paleobathymetric information crucial to the
regional aspect of this study were obtained from supplementary published
and unpublished analyses of the Redwall and coeval, deeper water facies
1 of the adjacent shelf margin and foreland basin (see index map, figure
2). 3
Figure 1. Index map of the study area in the Grand Canyon region. 4
EARLY MISSISSIPPIAN TECTONIC FEATURES
Figure 2. Early Mississippian tectonic features of eastern Nevada and northern Arizona. 5
Methods
The South Kaibab trail stratigraphic section was measured enploying a Jacob's staff (metric) with a two-directional dip clinometer, a metric tape, and a Brunton compass. The sampling interval was by sedimentation unit or at an interval of 2 or 3 meters in the thicker sedimentation packages. Approximately 90 samples were collected in the field from horizons of a distinctive lithologic nature, unusual bioclas- tic fabric or containing a rich assemblage of biogenic material. In other sections, only reconnaissance samples of distinctive beds were taken and lithologies and bedding characteristics noted. These sections serve only in a supplementary capacity.
In the field, beds were grouped into genetically-related inter vals. These intervals were described according to lithology (Folk, 1962,
1974), texture (Dunham, 1962; Embry and Klovan, 1971), bedding character
istics (after McKee and Weir, 1953), size, abundance and taxonomic composition of megafossil, topographic expression, color (weathered and unweathered, refined in the lab) and other special properties (e.g., odor).
Rock descriptions of the collected samples were based primarily
upon petrographic examination and employ Dunham's (1962) carbonate rock
classification scheme. Allochemical constituents, matrix and cement
identification, diagenesis, and paragenetic sequences were studied in
thin section. Conventional petrography was augmented by SEM photography,
etching (immersion in dilute hydrochloric acid), staining, and acetate 6 peels of etched and stained surfaces. Petrographic examination of the thin sections indicated that insoluble residue analyses were not war ranted for this section. REGIONAL ASPECTS
Regional Stratigraphic Aspects
Areally pervasive sheets of Mississippian shallow-marine carbon ates occur throughout the Rocky Mountain Province and extend into the
Cordilleran miogeosyncline. Rose (1976; see also Sando, 1976) subdivided these carbonates into a lower depositional complex ranging in age from
Kinder hook i an to early Meramecian and a thinner, more restricted, upper depositional complex ranging in age from middle Meramecian through
Chesterian. The Redwall Limestone constitutes the lower depositional complex in northern Arizona. Other stratigraphic units recognized within the lower complex include: the Lodgepole and Mission Canyon Limestones, or Madison Group, of Idaho, Montana, North Dakota, Wyoming, and Utah; the
Gardison and Deseret Limestones of Utah; the Leadville Limestone of
Colorado and Utah; and the Monte Cristo Limestone of Nevada and Utah.
The flexural modeling part of this study is based on stratigraph ic sections from the typically clastic-free shelf carbonates of the
Redwall Limestone, the shelf margin cargonates of the Monte Cristo Group, and the flysch-like sequences of the Antler foreland basin and continuous
submarine rise. These units are within Rose's lower depositional complex or are correlatives of it.
7 8
Tectonic Framework
Redwall sedimentation was affected by both Pre-Mississippian
tectonic features and by ongoing tectonism of the Antler orogeny.
Pre-Mississippian, Cratonic Tectonic Elements
During Mississippian time, a linear positive area, the Transcon
tinental Arch, extended southwestward from the Canadian Shield into central Arizona. The Defiance-Zuni Positive (see: McKee, 1951, p. 484,
Plate 1C; Kelley, 1955, Figure 5; Huddle and Dolbrovolny, 1952,
Figure 26; Wilson, 1962, p. 31; McKee and Gutschick, 1969, p. 572-573;
Pierce, Keith, and Wilt, 1970, p. 47), an uplift, tended from west-
central New Mexico to east-central Arizona and formed part of the
southern terminus of the Transcontinental Arch. McKee and Gutschick
(1969, p. 572-573) believe the Defiance Positive to have been active
during the Mississippian. Others, however, (e.g.. Pierce, et al., 1970)
contend that Mississippian strata were more laterally continuous in the
Defiance uplift region but are now more constricted due to erosion
resulting from Post-Mississippian uplift.
Positive elements extended southwest from the Defiance-Zuni
uplift. Several names have been assigned to these elements: the Payson
Ridge (McKee and Gutschick, 1969, p. 573; Racey, 1974, p. 21); Pine and
Christopher Islands (Teichert, 1965, Plate 27); the Granitic Holbrook,
Pine, Christopher Mountain, and Chediski Ridges (Huddle and Dobrovolny,
1952, Figure 17); and the Payson Headland (Stoyanow, 1942, p. 1268-1270, 9
1274). Mazatzal Land, an area presently of Precambrian rocks, was another positive feature in north-central Arizona at this time. This area was recognized by Ransome (1916, p. 166) and later named by Stoyanow
(1936, p. 462) for a probable submarine ridge during the Paleozoic era.
Ransome (1916, p. 166), Barton (1925, p. 237), Stoyanow (1936, p. 462,
507; 1942, p. 1272), Huddle and Dobrovolny (1952, p. 91), and Wilson
(1962, p. 31) believe that Mazatzal Land was a positive elenent during the Mississippian, but McKee (1951, p. 485-487) contends that it is the result of a ppst-Paleozoic event which has resulted in denudation down to
Precambrian strata.
Bissel (1974, p. 83) considered the Wasatch Line (Kay, 1951) and
its southwestern continuance, the Las Vegas Line, to have been active tectonic components throughout Mississippian time, behaving as a tectonic hinge-line during this period. The Antler foreland basin persisted west of the Las Vegas-Wasatch Line throughout the Paleozoic and until mid-
Triassic time. The eastern margin of the Roberts Mountain allochthon formed the western border of the basin. The western edge of the basin generally parallels the Las Vegas-Wasatch Line. The present position of
the Early Mississippian shelf edge closely corresponds to the Mesozoic
Sevier thrust. Sandberg, et al. (1982, p. 691, 717) suggested that
facies changes and differing strata competence of the Mississippian rocks may have been a factor in determining the location of later thrusting. 10
Antler Orogeny and Foreland Basin Development
The Antler orogeny is one of several erogenic events which occurred around the edges of North America at approximately the same time. Other orogenies include the Ellesmerian (Arctic), Acadian (Atlan tic) , and the Proto-Ouachita (Gulf of Mexico). Unlike the others, the
Antler orogeny did not involve plutonism or severe metamorphism.
The Antler orogenic belt extends from the Mojave Desert north- northeastward across central Nevada to central Idaho. It is bounded on the east by cratonic miogeoclinal rocks and on the west by the upper
Paleozoic rocks of the Golconda allochthon, which was emplaced during the
Sonoma orogeny (Permo-Triassic, Speed, 1977) . The orogenic belt is primarily composed of eugeosynclinal Devonian and older Paleozoic rocks thrust eastward over coeval shelf sediments along the Roberts Mountain thrust. The autochthonous miogeoclinal strata which underlie the over- thrusted allochthon include shelf and shelf-break deposits of Precambrian
•to mid-Late Devonian age (Stewart and Poole, 1974; Poole, 1974). These
Pre-Mississippian sediments accumulated along a passive continental margin which resulted from latest Precambrian rifting (see: Sears and
Price, 1978; Stewart and Suczek, 1979; A m i n and Mayer, 1983; Bond and
Kominz, 1984). Lowell (1960), Matti and McKee (1977), and Rowell, et
al. (1979) believe that the western edge of the Roberts Mountain alloch
thon coincides with the early Paleozoic shelf break. It may also be
coincident with the inferred limit of the Precambrian basement which is 11 contiguous, in the subsurface, with the North American eraton (Armstrong, et al., 1977; Kistler and Peterman, 1978). During the Mississippian, the
Antler orogen shed a thick clastic sequence of flysch eastward into the developing foreland basin.
The most prominent event of the Antler orogeny was emplacement of
the Roberts Mountain allochthon. Emplacement occurred during a relative ly brief period of time near the Devonian-Mississippian boundary (smith and Ketnef, 1968, 1977). Ketner and Smith (1981, 1982) have more recently proposed that the allochthon was emplaced during the Mesozoic, but Speed and Sleep (1982, p. 818-819) and Dickinson, et al. (1983, p. 483) have presented cogent arguments refuting Mesozoic displacement along the thrust. Nilsen and Stewart (1980, p. 301-302) have proffered
several possible alternate tectonic mechanisms for Antler thrusting,
including flake tectonics, continent-arc collision, back-arc thrusting,
and incipient subduction.
The conceptual model favored here is that of a passive margin
colliding with an island-arc system (Moores, 1970; Dickinson, 1977, 1981;
Dickinson, et al., 1983; Speed, 1977, 1979; Speed and Sleep, 1982).
Allochthon emplacement across the autochthon, a minimum distance of 75 to
125 km (Dickinson, et al., 1983, p. 487), may have required from less
than 5 to as much as 12 m.y. (smith and Ketner, 1968; Johnson and
Pendergast, 1981; Harbaugh and Dickinson, 1982; Dickinson, et al.,
1983). The Antler accretionary prism was composed of multiple imbricate 12 thrusts (Speed and Sleep, 1982, p. 819, see also Oldow, 1984, p. 175) and intricate folds (Wrucke in Nilsen and Stewart, 1980, p. 299; Evans and
Theodore, 1978) which were tectonically, emplaced above the miogeoclinal sediments of the underthrusting continent. The relative motion of the two plates may have been at a highly olbique angle (Speed and Sleep,
1982, p. 820). Subduction ceased early in the Mississippian (Speed and
Sleep, 1980). Speed and Sleep (1982, p. 820) suggest that convergence resumed seaward of the Antler arc, the arc became sutured onto the craton, and the oceanic arc initially attached to the continent became detached and foundered (Speed and Sleep, 1982, p. 820).
Preceding emplacement of the allochthon, the miogeoclinal shelf was affected by the impending collision. According to the model, the platform was broadly downwarped, facilitating deposition of the Pilot
Shale and producing the diachronous carbonate banks of the Joana Lime stone (Speed and Sleep, p. 819). Speed and Sleep (1982, p. 825) and
Johnson and Pendergast (1981) have suggested that stratigraphic features preceding subsidence of the Antler foreland basin may be related to pulses of uplift (flexural bulge migration) resulting from passage of the continental margin over the arch of the approaching Antler trench (see also: Dickinson, et al., 1983, p. 502). Events that may track the eastward migration of the flexural bulge include: Late Frasnian and
Famennian turbidites in the Pilot Shale recording passage of the leading edge of the bulge; intra-Famennian lacunae within the Pilot Shale 13 representing erosion during passage of the bulge's crest (see: Sandberg and Poole, 1977; Gutschick and Rodriguez, 1979); accumulation of the
Joana Limestone in the shallow waters trailing the bulge's passage; and deepening of the Joana Sea indicating the continued easterly migration of
the forebulge. Dickinson et al. (1983, p. 502-503) believe that Pilot and Joana deposition may have been related to deformation associated with
the outer arch. This deformation possibly affected the outer arch as early as 5 to 15 m.y. before thrusting began, the period of time probably
required for Pilot and Joana deposition. They also believe that deposi
tion of the Chairman Shale in a deep foreland trough marks final alloch-
thon emplacement, over an estimated period of approximately 5 m.y., a
rate which is consistent with modern plate convergence rates.
The development of the Antler foreland basin is reflected by the
increasingly basinal conditions west of the Grand Canyon occurring during
the Early Mississippian. The foreland basin resulted from the thrust
loading at the continental margin and concomitant downflexure of the
miogeocline. Mississippian elastics derived from the Antler erogenic
highlands were deposited in this downwarped foreland basin east of the
thrust front (Poole, 1974; Wilson and Laule, 1979). In the central
Diamond Mountains of Nevada (near the depoaxis of the Antler basin)
approximately 1050 m of fine-grained clastic strata accumulated in
steadily deepening waters. This retrogradational phase (Harbaugh and
Dickinson, 1981) consisted of submarine-slope and submarine-fan deposits 14 and marked the first of two distinct phases of sedimentation (Harbaugh and Dickinson, 1981). The second, progradational, phase contained about
1200 m of delta-slope and delta-platform sediments. These coarse-grained elastics accumulated in gradually-shoaling waters. The finer-grained detritus of the retrogradational phase of submarine slope and fan deposits is assigned to the Chainman Shale. The Chairman Shale along with part of the underlying Joana Limestone are correlatives of the
Redwall Limestone.
Paleoqeography
The Mississippian cratonic seas of the Cordillera and Midcon
tinent regions were connected around the southern extension of the
Transcontinental Arch and where they formed the Redwall-Escabrosa Sea in
Arizona (Gutschick and Sandberg, 1983). The Redwall Shelf extended
eastward from the Arch into southwestern Colorado (Leadville Limestone;
Armstrong and Mamet, 1976) and northward into Utah where it merged with
the Madison Shelf. The nature of the southwestern boundary of the
Redwall-Escabrosa Shelf is ambiguous due to the paucity of well data in
southwestern Arizona (McKee, 1947, 1951; Miller, 1970), second of data on
the Paleozoic of Mexico, in general (e.g., Lopez-Ramos, 1969), and to the
complexity of the region's post-Mississippian history (Pierce, 1976). I
15
The Kinderhookian paleoequator crossed the midpoint of the
Arizona-Utah border and extended southwestward across northwestern
Arizona (figure 3; also see Sandberg et al., 1982, figure 14). The
Meramecian paleoequator retained the same orientation as the Kinderhook
ian equator but had moved northward, bisecting the Nevada-Utah border.
Paleocliroatology
The Mississippian climate of northern Arizona was probably
dominated by hot and humid tropical maritime air. Vagaries associated
with the seasonal fluctuation of the intertropical convergence zone
(ITCZ), effects of land-water distribution, unknown vertical wind shear
(and its seasonal variation), oceanic circulation patterns and a slightly
different rotational velocity during the Mississippian make speculation
beyond a climatic group conjectural.
The Redwall Sea probably was not frequented by tropical cyclones,
but was possibly in an area of cyclone genesis. Hurricanes are most
cornnon in the western portions of major oceans and are less corrmon in the
eastern portions. Hurricanes forming today off the west coast of Mexico,
in the eastern Pacific, are the result of a combination of weak vertical
wind shear and persistence of low-level convergence associated with the
ITCZ (Chang, 1972, p. 113). These conditions may have existed over the
Redwall Sea, but other prerequisites are also necessary for tropical
storm nucleation. The requisite minimum water temperatures (sea surface
temperature, SST) for the formation of warm-core cyclones (hurricanes/-
typhoons) is 26 to 27 degrees Centigrade (Palmen, 1948). These tempera- 16
Figure 3. Paleogeography and atmospheric circulation and upwelling for Early Mississippian time (Parrish, 1982; with permission). 17 tures were probably met or exceeded in the Redwall Sea. The minimum coriolis parameter for sufficiently strong rotation (from Bjerknes' circulation theorem), however, was not net at such low latitudes. Palmen
(1952) stated that "the great majority of the cyclones of the tropical north Pacific form in latitudes south of 6 degrees north but intensify rapidly only in the zone 6 degrees north to 15 degrees north."
Thus, although tropical storm generation was possible in the
Redwall Sea, the occurrence of typhoons or hurricanes was very unlikely.
In conclusion, most storm activity on the Redwall shelf was probably of a localized, but relatively intense, convective nature, and not likely to be preserved in the stratigraphic record. Therefore, causes of recog nized event deposits other than hurricanes (i.e., tempestite deposits, see Seilacher, 1982, p. 162-174) should be considered for graded beds recognized in the Redwall Limestone. PREVIOUS WORK ON THE REDWALL LIMESTONE
Historical Development
The Redwall Limestone has an extensive history of geologic research. Named by Gilbert in 1875, it originally included both younger and older rocks than are presently included in the formation. Only the
800 foot massive limestone cliff of Gilbert's (1875) original 2500 foot
"Red Wall Group" is included in the current Redwall Limestone formation.
The type section was selected by Darton (1910) in Redwall Canyon, a canyon in the Shinumo drainage basin on the north side of the Grand
Canyon. Darton (1910) redefined the formation by proposing restricting the Redwall to Mississippian-age strata and introducing the name Supai
Formation for the overlying Pennsylvanian-age strata. Noble (1922) formalized Barton's (1910) redefinition and subdivided the Redwall into three members. Studies by Gutschick (1943) and Easton and Gutschick
(1953) led to the recognition of four traceable members in the formation
(I, II, III, IV). McKee (1958) recognized the four members (lower, middle, upper middle, and top) in the subsurface of the Black Mesa Basin of northeastern Arizona, later renaming these A, B, C, and D (McKee,
1960). He subsequently designated type section areas within the Grand
Canyon for these members and named them, in ascending order, the Whitmore
Wash, Thunder Springs, Mooney Falls, and Horseshoe Mesa Members (McKee,
18 19
1963). Lithologies, thicknesses, areal extent, and biostratigraphy of the four members are provided in McKee and Gutschick (1969). Generally, thicknesses increase toward northwestern Arizona and decrease toward the
Zuni Defiance Positive element and toward the Payson Ridge.
Underlying Strata
The Mississippian Redwall Limestone urtconformably overlies the
Devonian Muddy Peak Limestone in extreme northwestern Arizona (Longwell,
1949; McNair, 1952). In much of the western Grand Canyon, however, the
Lower Mississippian Redwall rests unconformably on the Upper Devonian
Temple Butte Limestone (McKee and Gutschick, 1969). This is the case along the South Kaibab trail section studied in this report. In the eastern Grand Canyon, the Middle Cambrian Muav Limestone directly
underlies the Redwall (McKee and Gutschick, 1969). Farther east, in the
Black Mesa Basin, the Upper Devonian to Lower Mississippian Ouray
Limestone (Elston, 1960; Parker and Roberts, 1963; Baars, 1966) imme
diately underlies the Redwall. Kent (1975) included the Ouray Limestone
within the Redwall Limestone, stating that the Ouray represented the
earliest stage of the Lower Mississippian sequence. Along the southern
margin of the Colorado Plateau, the Redwall unconformably overlies the
Devonian Martin Formation (Teichert, 1965; McKee and Gutschick, 1969). 20
Overlying Strata
In most of the central part of the Grand Canyon, the Redwall is unconformably overlain by the Pennsylvanian Supai Formation. A post-
Redwall, Chesterian limestone, "Surprise Formation" (Beus and Billings ley, 1984), is present along the Bright Angel trail in the Grand Canyon
(McKee and Gutschick, 1969). McKee and Gutschick (1969) interpret the
Chesterian limestone as being a remnant of an areally more extensive unit, but Kent reported that no evidence of this post-Redwall limestone exists in the Black Mesa Basin east of the Grand Canyon. The Redwall
Limestone is unconformably overlain by the Pennsylvanian Callville
Limestone in extreme northwestern Arizona (McNair, 1952; Langenheim,
1963; McKee and Gutschick, 1969), the Pennsylvanian Molas Formation in
the Black Mesa Basin area (Parker and Roberts, 1966; Kent, 1975), and the
Pennsylvanian Naco Formation along the southern margin of the Colorado
Plateau (Huddle and Dolbrovolny, 1943; McKee and Gutschick, 1969).
Paleontologic Studies
Numerous paleontologic studies have been completed on the Redwall
Limestone. Foraminiferal biostratigraphic studies, which proved to be
most useful for regional correlation in this investiation, include those
by Zeller (1957), Skipp (1963, 1969), and Mamet and Skipp (1970). Racey
(1974) studied Redwall conodont fauna. Other biostratiraphic studies
have been completed on blastoids (Macurda, 1969), brachiopods (McKee and
utschick, 1969), bryozoa (Duncan, 1969), cephlapods (Furnish, 1969), 21 corals (Easton and Gutschick, 1958; Sando, 1969), crinoids (Brower,
1969), gastropods (Yochelson, 1969), and pelecypods (Yochelson, 1969).
Whitmore Wash Member
McKee (1963, p. C21) identified the type section of the Whitmore
Wash Member along Hurricane fault north of the Colorado River. At this
location, the Member contains 101 feet (33 m) of very fine-grained dolomite. To the north and west, the Whitmore Wash consists of lime
stone; it becomes dolomitic to the southwest in the Grand Canyon Region.
The Whitmore Wash thickens from east to west from 70 to 80 feet (23 to 26 m) thick in the eastern Grand Canyon to more than 200 feet (61 m) at
Iceberg Canyon (see figure 4).
In the Grand Canyon area, the Whitmore Wash is primarily a fine
grained replacenent dolomite. Where it is limestone, the Member contains
well-rounded bioclasts and ooids with a clear sparite cement (McKee and
Gutschick, 1969, p. 26). Molds of ooids, corals, brachiopods and other
animals which had calcareous structures are abundant in seme dolomitized
sections (see figure 5). Species of these fossils are numerous in the
formation's limestone lithologies; this suggests a replacement origin for
the dolomite. Increasingly basinal conditions toward the northwest are
suggested by: (1) the isopach map of the Whitmore Wash Member and (2) the
pervasive dolomitization to the east of the Grand Canyon and less
complete dolomitization to the northwest (McKee and Gutschick, 1969,
p. 562). 22
Figure 4. Isopach map of the Whitmore Wash Member of the Red wall Limestone (modified from McKee and Gutschick, 1969). 23
Figure 5. Photograph of well-developed moldic porosity in the Whitmore Wash Member along South Kaibab Trail. 24
McKee and Gutschick (1969, p. 562) postulated a penecontempora- neous metasomatic replacement on or below the sea floor as the origin of the pervasive fine crystalline dolomite. The laterally traceable nature of the dolomite and the presence of protodolcmite in the western Grand
Canyon (Blackman, in McKee and Gutschick, 1969, p. 106) support this interpretation. A syngenetic or penecontemporaneous origin for the dolomite was also postulated by Kent (1975, p. 78), who based his argument upon its similarity to the dolomites of other workers
(Deffeyes et al., 1965; Tiling et al., 1965; and Shinn et al., 1965).
The magnesium source for the replacement dolomite may have been derived from unstable high magnesium calcite (biogenic) and from magnesium diffusion in nearshore (McKee and Gutschick, 1969, p. 562). McKee and
Gutschick (1969, p. 563) interpreted localized areas of clear, coarse to very coarse crystalline dolomite to be post-emergence, tectonic dolomite. Other researchers (Smith, 1974? Kent, 1975; and Purves, 1978) who have done petrographic studies of the unit have recognized two distinct rhombohedral dolomite crystal sizes - a fine crystalline,
penecontemporaneous dolomite and a coarse crystalline, secondary dolo mite. Kent (1975, p. 114) suggested that the Dorag dolcmitization model
(Badiozamani, 1973, p. 965) was a possible mechanism for forming the
secondary dolomite.
Insoluble residue analyses of the Whitmore Wash yielded less than
2 percent residue (McKee and Gutschick, 1969, p. 27). The absence of 25 siliclastic residue and evidence for bottom currents (cross-bedding) suggests a low, tectonically inactive adjacent land mass during Whitmore
Wash deposition. "
The basal Whitmore Wash Member is diachronous (McKee and Gut- schick, 1969, p. 30). Age determinations based upon brachiopods and foraminifera suggest a Kinderhook age in the western Grand Canyon and an early Osage age further east (i.e.. South Kaibab trail). The member is entirely below the Osage—Meramec boundary which occurs near the top of the Mooney Falls Member (see figure 80).
In summation, petrographic analyses of the Redwall Limestone have been accomplished in the Grand Canyon Region (McKee and Gutschick, 1969),
Black Mesa1 Region (Kent, 1975) and in central Arizona (Smith, 1974).
Whitmore Wash lithologies include: fine-grained limestone and dolomite, algal packstone, pelleted packstone, oolitic packstone, oolitic grain-
stone, and crinoidal grainstone. Lithofacies patterns, depositional diachroneity, penecontemporaneous dolcmitization, and the location of the
zero isopach line of the Whitmore Wash suggest that the shoreline lay to
the east and to the southeast of the Grand Canyon area and that the
Kinderhookian-Osagean transgression across the miogeocline progressed
from the west toward the east. 26
Thunder Springs Member
The Thunder Springs Member type section .is located at the head of the Thunder River in the central Grand Canyon. It is the most distinc tive member of the Redwall. The unit consists of thin bedded carbonates alternating with irregular thin beds and elongate lenses of chert. The member's upper and lower boundaries are recognizable by narrow but prominent benches and by the occurrence of bedded chert within the unit. In the Grand Canyon area, the Thunder Springs thins from 100 feet (33 m) in the west to 70 feet (23 m) in the east (see figure 5).
The lowest chert bed in the Redwall marks the base of the Thunder
Springs Member. The Whitmore Wash-Thunder Springs contact is conformable in most sections. Where not conformable, the irregularity can be attributed to differential settling, compaction or postconsolidational solutioning (McKee and Gutschick, 1969, p. 37).
The predominant carbonate in the western and in the northern part of the area is limestone and dolomites; dolomitized limestones predom inate in the southern areas. The limestone ranges from a fine- to a very coarse-grained texture. Generally, the dolomites are finely-crystalline with a homogeneous texture (McKee and Gutschick, 1969, p. 40). Bedding thicknesses are highly variable, from 1 to 2 inches (2.5 to 5.0 an) to as much as 12 inches (30.5 cm).
Fossil abundance and diversity increase from west to east (McKee
and Gutschick, 1969, p. 42). The fauna in the eastern area is dominated 27
Figure 6." Isopach map of the Thunder Springs Member of the Red wall Limestone (modified from McKee and Gutschick, 1969). 28 by fenestellid bryozoans, in the central area by crinoid ossicles, and in the west, both bryozoans and crinoid ossicles are abundant. Endothyrid foraminifera are absent or scarce in the Thunder Springs throughout the
Grand Canyon area. Texturally, the member is predominantly a pelleted crinoidal packstone with tripolitic chert (Kent, 1975). In the subsur face of the Black Mesa Region, Kent (1975, p. 31) reports that the crinoidal packstone may be consecutively overlain by crinoidal and oolitic grainstone and pelleted packstone. McKee and Gutschick (1969) and Kent (1975, 1978) agree that the Thunder Springs is unconformably overlain by the Mooney Falls Member.
The most conspicuous aspect of this unit is the regionally pervasive presence of chert. Thunder Springs chert is White to light grey, opaque, and porcelaneous. Chert beds are from 1 to 3 inches (2.5 to 7.6 cm) thick but their thickness is highly variable. Chert may occur as either nodules or in the more characteristic bedded form. Abundant, well-preserved molds and fossils are common in the cherts; well-preserved fossils are uncommon in the associated carbonates.
Both the dolomites and the cherts are secondary. McKee and
Gutschick (1969, p. 42) cite petrographic evidence, biofacies variation,
and geographic distribution as evidence for the dolomite * s secondary
origin. Parker and Roberts (1963, 1966), McKee and Gutschick (1969),
smith (1974), and Kent (1975) all suggest a penecontemporaneous replace
ment by silica prior to or during lithification. All authors concur on 29 the parediagenetic sequence - calcite replaced by silica followed by dolomitization. Several silica sources have been suggested: submarine volcanism (McKee and Gutschick, 1969, p. 114; Kent, 1975, p. 73-74), upwelling (McKee and Gutschick, 1969, p. 114; Smith, 1974, p. 59; Kent,
1975, p. 73-74), silica-rich riverine waters (McKee and Gutschick, 1969, p. 114), and sponge spicules (Purves, 1978, p. 166). Sandberg and
Gutschick (1980) and DeCelles and Gutschick (1983) believe that fossil radiolarians and siliceous sponge spicules are the silica source for the coeval Osagean Deseret Limestone and Brazer Dolomite formations of Utah.
The lack of evidence for volcanism associated with the coeval
Antler orogeny and the low-latitude Early Mississippian geographic position of the Red wall Sea argue against volcanism or upwelling, respectively, as the silica source. However, upwelling cannot be entirely ruled out as a silica source. Equatorial open-ocean divergence is a possibility (Parrish, 1982). The presence of sponge spicules is, however, incontrovertible. The spicules may have been the silica source
for the production of bedded and nodular cherts. The process of cherti-
fication remains problematical as does the silica source. Knauth (1979)
has proposed a credible model for chert replacement in limestone which
may have implications for chert replacement in the Redwall. These
problems are currently being addressed (Hess, thesis in preparation). 30
Mooney Falls Member
The Mooney Falls Member forms the conspicuous sheer walls of the
Redwall Limestone. The type section at Mooney Falls in Havasu Canyon consists of 312 feet (95.1 m) of variable—textured, but consistently pure limestone. Total stratal thickness decreases eastward, thinning to zero toward the Zuni-Defiance Positive element (figure 7). The contact between the Thunder Springs and the Mooney Falls appears unconformable
(McKee and Gutschick, 1969, p. 54 and 55), but whether this unconformity represents subaerial or submarine erosion is uncertain (McKee and Gutschick, 1969, p. 55).
The Mooney Falls is thick to very thick bedded in contrast to the underlying and overlying members. Texture varies from fine- to very coarse-grained. Grain types include peloids, crinoid ossicles, fragmen tary bioclastic debris (hash), and oolitic units (upper part of member in the western Grand Canyon). Three textural types are recognized in the
Mooney Falls Member south of the Grand Canyon Region (McKee and Gut schick, 1969, p. 59-67): crinoidal limestone (grainstone or packstone), peloidal-oolitic, endothyrid limestone (packstone or grainstone), and aphanitic limestone. Fine-grained dolomite, algal wackestone, oolitic packstone, oolitic grainstone, foraminiferal grainstone, crinoidal grainstone, and crinoidal packstone are present in the subsurface of the
Black Mesa region (Kent, 1975, p. 33-35). Generally, textures vary from
a fine-grained dolomite to a crinoidal packstone back to a fine-grained 31
Figure 7. Isopach map of the Mooney Falls Member of the Red wall Lime stone (modified from McKee and Gutschick, 1969). 32 dolomite in the sequence described above. The textural pattern has a mirrored symmetry whose axis is the middle of the member.
Several zones of thin-bedded or lensoidal cherts are present near the Mooney Falls-Horseshoe Mesa contact. The chert zones do not repre sent the same horizon everywhere (McKee and Gutschick, 1969, p. 61).
The Mooney Falls records the maximum marine transgression of the shelf (McKee and Gutschick, 1969, p. 62) during Osagean time. McKee and
Gutschick (1969, p. 68) felt that the thick—bedded Mooney Falls Member passed upward into the thin-bedded Horseshoe Mesa Member without a stratigraphic break. In contrast, Kent and Rawson (1980, p. 102) interpreted an unconformity at the base of the Horseshoe Mesa Member along South Kaibab trail.
Horseshoe Mesa Member
The Horseshoe Mesa Member is 38 feet (11.6 m) thick at its type
section along Grandview trail at Horseshoe Mesa. The unit thins to zero
to the east and south and thickens to 125 feet (38.1 m) at Parashant
Canyon to the northwest (figure 8). Post-Redwall erosion accounts for
part of the strata! thickness variation. Bedding thickness typically
varies between two and twenty-four inches. Thin-bedded, lensoidal chert
occurs near the unit's base at several localities.
The unit is composed of very pure, nondolomitic, aphanitic
limestone. Fossils (e.g., pellets, braciopods, pelecypods, corals,
foraminifera, and algal structures) are present but rarely common in this 33
\
Figure 8. Isopach map of the Horseshoe Mesa Member of the Red wall Limestone (modified from McKee and Gutschick, 1969). 34 member. The texture, restricted fauna, and thin bedding suggest a shoaling-upward sequence within the Horseshoe Mesa Member.
The upper contact of the Horseshoe Mesa Member is a well-devel oped karst surface. Relief of up to 40 feet (12.2 m) has been recognized
(McKee and Gutschick, 1969, p. 76-78). Kent (1975, p. 35) reports that the member has been largely removed by pre-Supai erosion.
Post-Redwall, Chesterian Limestone, "Surprise Formation
A hiatus representing the upper part of Meramec and lower part of
Chester time separates the Horseshoe Mesa Member from the Chesterian
"Surprise Formation" (McKee and Gutschick, 1969; Beus and Billingsley,
1984). Chesterian rocks were recognized along the Bright Angel trail in the Grand Canyon by McKee and Gutschick (1969, p. 74). Recently, however, channel-shaped bodies of fossiliferous marine and non-marine strata have been recognized by Beus and Billingsley (1984) from the Bat
Tower area eastward to Marble Canyon. They named the unit the "Surprise
Formation." This limestone lies within the upper depositional complex of
Rose (1976). The upper depositional complex (Rose, 1976) had not been
recognized previously in northern Arizona. The "Surprise Formation”
consists of lens-shaped valley-fills up to 120 m thick and 370 m wide
(Beus and Billingsley, 1984). Deposition of the unit is confined to
ancient stream channels developed atop the Redwall Limestone. Litholo
gies range from basal fluvial deposits to shallow marine or intertidal
deposits (Beus and Billingsley, 1984). Redwall Limestone Escabrosa Limestone Overthrust Grand Canyon | Black Mesa Yavapai Cnty, Belt AZ 13]
submergence
Modoc Ls.
[1 ] McKee & Gutschick (1969) [4 ] Bahlberg (1977) using Norby (1971) [ 2 ] K ent (1975) for age control. [3] Smith (1974) [5] Purves (1978) 16] Sanberg et al. (1982)
Figure 9. Generalized comparison of eustatic cycles interpreted in the Redwall Limestone and coeval strata. (Modified from Purves, 1978) 36
Depositional Cycles
Three transgressive-regressive (TR) cycles have been interpreted
in the Mississippian sequence of the Grand Canyon area (McKee and
Gutschick, 1969, p. 587-590; figure 9). McKee and Gutschick (1969, p. 588) considered the Redwall to be a shallow shelf carbonate which
thinned eastward and southward against the Zuni-Defiance Positive element
and Rayson Ridge, respectively. Each of the four members of the Redwall was linked to a eustatic event (McKee and Gutschick, 1969, p. 588-590). McKee and Gutschick (1969, p. 588-590) suggested that the sealevel fluctuations resulted from differential shelf subsidence rates.
The Redwall Sea transgressed relatively flat—lying Devonian and
Cambrian strata during late Kinderhookian to early Osagean time and
deposited the Whitmore Wash Member. The sea shallowed to zero in
northeastern Arizona and lapped against the Payson Ridge to the south
east. McKee and Gutschick (1969, p. 588) believe that the cherty Thunder
Springs represents the first regional emergence. They cited the thin-
bedded nature of the unit as evidence for regression which they attrib
uted to a lessened subsidence rate. A regional erosional unconformity
atop the Thunder Springs delimits the end of the first TR cycle in the
Redwall (McKee aid Gutschick, 1969, p. 589). The nature of the erosional
surface, whether subaerial or submarine, and the magnitude of the hiatus
are both unresolved. Less than one foraminifera 30he may be missing.
The Mooney Falls Member records the second, geographically more extensive 37
Osagean transgression. Five well-developed subcycles reflect a "fluct uating marine environment" during Mooney falls deposition (McKee and
Gutschick, 1969, p. 589). Bedded (coalesced nodules) chert, similar to that of the Thunder Springs Member, is present in the upper Mooney Falls
Member. Oolitic limestones like those in the upper Whitmore Wash Member are also present near the top of the Mooney Falls Member (McKee and
Gutschick, p. 589). The Meramecian Horseshoe Mesa Member records the final Red wall emergent event. A regional subaerial unconformity is represented by a karst surface developed on top of this member. The locally present Chester!an "Surprise Formation" (Beus and Billingsley,
1984; McKee and Gutschick, 1969, p. 74 and 590) is evidence for a third
TR cycle. It is separated from the second TR cycle by an upper Meramec- lower Chester hiatus.
Smith (1974) and Kent (1975) studied the depositional facies recorded in the Redwall Limestone outside the Grand Canyon area. They utilized the concepts developed by Shaw (1964), Irwin (1965), and Coogan
(1972) for epeiric sea sedimentation. Smith (1974) recognized two and possibly three cycles of deposition in the Redwall Limestone of Yavapai
County, Arizona. The first cycle is represented by the transgressive
Whitmore Wash Member and by the regressive Thunder Springs Member. Smith
(1974, p. 58-62) cites the presence of nodular and bedded chert, silt-
stone stringers, and an erosional unconformity as evidence that the
Thunder Springs represents the first regression. The second major
transgression is recorded by the Mooney Falls Member. Unlike the first 38 cycle which is symmetrical (e.g. Coogan, 1972), Smith (1974) noted that the second cycle is assymetric in facies pattern and lacks Irwin's (1965) deposit ional zones III and I la. The Horseshoe Mesa Member is not preserved in Smith's study area. He believes that it represents a continued shoaling phase following deposition of the upper Mooney Falls
(Smith, 1974, p. 63).
East of the Grand Canyon in the Black Mesa Region, Kent (1975) studied the Redwall Limestone in the subsurface. He discerned two TR cycles, as did McKee and Gutschick (1969) and smith (1974). Kent (1975) termed them the upper and lower depositional cycles. The lower cycle includes the Whitmore Wash and Thunder Springs members. The upper cycle includes the Mooney Falls and Horseshoe Mesa members (undifferentiated).
In contrast to McKee and Gutschick's (1969) and smith's (1974) interpre tation of the Thunder Springs as a regional regression, Kent (1975, p. 43) considered it to be an open marine facies. Additionally, Kent
(1975, p. 119) discerned three subcycles in the upper depositional cycle. Like Smith (1974), Kent (1975) recognized the asymmetry of the second depositional cycle and employed concepts formulated by Coogan
(1972) and Matthews (1974) to explain asymmetric shelf carbonate se quences.
Hansen (1976) recognized three TR events in the correlative Monte
Cristo Limestone of southern Nevada, developed basinward of the Redwall
Limestone. He also recognized fourteen subcycles within the three TR
cycles. Hansen interpreted an overall shallowing upward trend for the 39
Mississippian rocks in southern Nevada. Rose (1976, p. 453) also recognized one transgressive-regressive cycle in the Monte Cristo
Limestone of southern Nevada.
Purves (1976) discerned two major ecstatic cycles in the Escabro- sa Limestone of central and southern Arizona. He also recognized two subcycles in the second cycle. His observations of cyclic sedimentation correspond closely to those of Kent (1975). In contrast to McKee and
Gutschick (1969), Purves (1976, p. 228) concurred with Kent (1975) that the Thunder Springs records deeper water sedimentation. Purves (1976, p. 227 and 228) noted a "eustatic out-of-phase relationship" between deposits of the Redwall and Escabrosa Limestones. He also suggested that the upper TR cycle may have been deposited in deeper water (Purves, 1976, p. 221). DEPOSITIONAL ENVIRONMENTS
Introduction
The clastic-free sediments of the Redwall Limestone were deposit ed on a homoclinal ramp (see Read, 1982, 1984) below a shallow epeiric sea in a humid tropical environment. Shaw (1964) and Irwin (1965) have outlined a model describing the sedimentary facies established in such an environment (figure 10). They postulated that hydraulic energy would be the primary control of deposition on such wide, shallow seas with such low depositional slopes (less than one foot per mile, see figure 11).
Irwin (1965, p. 450) predicted that three energy zones character ized by different water energies would control the type of sediment forming on the sea floor. The resultant sedimentary facies belts would be oriented approximately parallel to the strand line and would laterally grade into one another perpendicular to the strand. The three energy zones of Irwin are: (1) Zone X - a low energy zone lying below effective wave base in the open sea; sediments are characterized by micrite with arenitic and ruditic shelly bioclasts. (2) Zone Y - a high energy environment, where the kinetic energy of waves and currents is dissi pated; sediments are characterized by worn and abraded arenitic bioclasts of copious and diverse fauna. And lastly (3) Zone Z - an extremely
shallow, low energy zone lying landward of Zone Y; sediments are charac-
40 meters I 400 . ' '' ' to to Mlometera loeee WT evapoft ) o flte o p a v e (WITH Kliomeiere 80 -- SO * — r* PERSIAN GULP cal a ic t e r o e h t HL , HLY CALCILUTITE SHELLY , SHALT Iwin) (Irw EIET BELOW SEDIMENT RGY G ER N E W O L AE BASE WAVE HLY CALCILUYITE SHELLY
KLTL CALCAREMTE SKELETAL EIET ABOVE SEDIMENT IH ENERGY HIGH AE BASE WAVE (locally) REEF# - "
i lf NONMARINE 1 H 42 0 so 100 I KILOMETERS MIDDLE SILURIAN . ILLINOIS 3 km ■ H - SHELF BASIN DEVONIAN , ALBERTA BASIN BANKS IN ROCKY MOUNTAIN OUTCROPS AMKS MADISON GROUP . MISSIS6IPPIAN . WILLISTON BASIN 36 KM CRATON *1 ;------1------1 1 LAGOON PERMIAN REEF COMPLEX . NEW MEXICO CRATON LAGOON KIRKUK OLlGOCpNE REEF , IRAQ. CRATON 10km -H- Figure 11. Comparison of gradients of major carbonate platforms and banks from the Silurian to the Tertiary (redrawn from Wilson, 1975). 43 terized by pelmicrites. Irwin (1965, p. 450-451) predicted that due to the low gradient of the shelf, these energy zones would have been up to hundreds of miles wide. Previous Work Snith (1974) and Kent (1975) applied the Shaw—Irwin sedimentation model to the Redwall Limestone. Smith (1974, p. 48) recognized a skeletal grains tone facies and an oolitic grainstone facies within Sedimentation Zone II and subdivided Zone II accordingly. Kent <1975, p. 108) felt that the Shaw—Irwin model adequately explained the Redwall*s lower depositional unit (Whitmore wash and Thunder Springs Members) , but was inadequate to explain the asymmetry of sedimentary facies he recog nized in the upper depositional unit (Mooney Falls and Horseshoe Mesa Members). He proposed Coogan's (1972) revision of Irwin's symmetrical model to account for the observed facies asymmetry. Kent (1975, p. 119) further argued that Matthews' (1974) modification of Coogan's model explained the transgressive "pulses" he recognized in the upper deposi tional unit. This study supports Snith's (1974) conclusion that a modified Shaw-Irwin sedimentation model is applicable to Redwall sediments. Seibold (1970) has pointed out that the paleogeography and paleoclimate must be considered when applying a generalized sedimentation model such as the Shaw-Irwin model outlined above. This is particularly true of the Redwall Limestone where a much wider high energy zone (Zone Y) is 44 recognized. Subdivision of Sedimentation Zones II and III results in a model which more aptly explains the depositional facies recognized within the Redwall Limestone (figure 12). South Kaibab Trail Section The Thunder Springs, Mooney Falls, and Horseshoe Mesa strata along South Kaibab Trail offer a good to excellent opportunity to examine the depositional histories of these members. However, ascertaining the Whitmore Wash's depositional history requires piercing the "diagenetic veil" of pervasive dolanitization which masks this unit's original textures. Consequently original textures were inferred based upon mold size and frequency analyses (see figure 13). This method is obviously subject to error; original allochemical composition is underestimated due to the "erasure" of grains by diagenetic processes. The inferred textures of this unit indicate that Whitmore Wash sediments were deposited in an open-shelf environment. This conclusion is supported by undolomitized crinoidal-bryozoan grainstones (Zone IIB) collected from the Whitmore Wash along South Kaibab trail (figure 14) and by coeval undolomitized oolitic grainstone facies (Zone IIIA) occurring to the south and southeast, toward Paleohighs. Thus, although the nearly complete dolanitization of the Whitmore Wash is a serious impediment to the study of its depositional history, it is not an insurmountable obstacle. 45 LOW ENERGY HIGH ENERGY LbweERGY IC FM LE ti SHELFWARD I LANDWARD GfW t» CRINOID ‘BANK’ OPEN SHELF o o u n c “BANK" RESTRICTED SHELF - LAGOON ■ IB B B CRINOIDAL CRNODAL - BRYOZOAN oounc pelletferous ALGAL - CALCISPHERE C31AMSTONE GRANyPACKSTONE 3RANSTONE gran/packstone WACKESTONE CRINOID AL DEBRIS E RACHKDPOOS BRYOZOANS — a l g a e tALMOST EXCLU81VH.Y) 3RYOZOANS ALGAL LUMPS CALCISPHEFES COATED GRANS CttNODS ' OSTRACOOES FORAMS ------GASTROPODS FORAMS OSTRAC00ES CRMOCS ytraclasts OOLTTES BRYOZOANS FORAMS OOLITES CRMODAL CRANSTONE CRNOOAL-BRYOZOAN PELLETFEROUS PACK/GRANSTONE QRAN/PACKSTOI€ BRYOZOAN-CRNOOAL .OOUTIO-PELLETFEROUS ALGAL-CALCISPHERE WACKESTONE PACK/GRANSTONE grapupackstone COATED GRAIN OSTRACOOE-ALGAL-PELLETFEROUS GWC%)ALHwUMP-OOLmC GRAIN/PACKSTONE p a c k s t o n e CRANSTONE Figure 12. Distribution of Redwall Limestone depositional environments facies in accordance with a modified Shaw-Irwin model of epeiric sea sedimentation. Interpretation based on this investigation. 46 e # E moldlc'porosity elasticity Index DEPOSITIONAL i SAMPLE m ENVIRONMENT ‘ O SKT- •nllllroetera sitJ_I jC a e A33z,C,Cg,8e Coated Grain Grslnetone < 2 6 < 2 4 OPEN SHELF MB A,B,Bz,C,Cg Algal-Bryozoan- V.V4 :<20 Crinoidal rx-:-:b Qralnston® < 19 C ly/;, < 1 8 3 3 ? ----- I < 1 6 c Re s t r ic t e d SHELF < 1 5 G i IIIB I 13 47 Along South Kaibab trail, most of the Red wall sediments are inferred to have been deposited above effective wave base (figure 15). Figures 13 and 16 through 19 depict the lithologies observed along the trail. Five depositional facies have been identified in this section, and are labeled according to my modification of Irwin (figure 12). They are, landward to seaward, the: (1) algal-pelletiferous pack/wackestone facies representing Sedimentation Zone IV (figure 20); (2) pelletiferous rain/packstone facies representing Sedimentation Zone 1 1 IB (figures 21-24); (3) oolitic rainstone facies representing Sedimentation Zone IIIA (figure 25); (4) crinoidal-bryozoan grain/packstone facies representing Sedimentation Zone I IB (figures 26-29); and (5) crinoidal grainstone facies representing Sedimentation Zone IIA (figure 30). These five facies are the products of four depositional environments, ranging from the restricted shelf-lagoon environment to the oolitic "bank" environment to the open-shelf environment to the crinoidal "bank" environment. A restricted shelf-lagoonal depositional environment is indicated by the algal-calc i sphere wackestone and pelletiferous grain/packs tone facies. These are Sedimentation Zones IV and IIIB respectively. Reduced circulation and possibly some variation in salinity and temperature resulted in the less diverse and less abundant fauna recognized in this environment. Zone IV is the most shoreward zone recognized in this study. Algal-calcisphere wackestones record very low energy conditions. In 48 Figure 14. Photomicrograph of crinoid-bryozoan grainstone facies (IIB). Silicified chert sample from the lowest one-third of the Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies. Bryozoans, ostracodes, brachiopods, and dasycladacean algae present. Silica-replaced micrite coatings surround many grains. Note thin crust surrounding void spaces which were later infilled with chalcedony. Thin section SKT-20, PP, x35. 49 mi 2 : < LL > HI z O o s 1 5 § 1 H I to < tu cco t X Figure 15. Depositional environments of Redwall Limestone sanples collected along South Kaibab trail. /S 50 m • elasticity index DEPOSITIONAL e E ENVIRONMENT * SAMPLE SKT- millimeters b 1.0 2.0 36 B.c (R-4) I 3 5 B.CJE (R -4) 34 CrinoMal Qretnetone CRINOID "BANK" m - 3 ) HA 3 7 B,C, (R -4) 3 3 B.C.Cg.Oo (R-3) OPEN SHELF 32 (R -4) IIB 31 B,Bz,C,F,0 (R-4) 3 0 B,Bz,C (R -4) Figure 16. Depositional environment, lithology, and modified elasticity index for the Thunder Springs Member of the Redwall Limestone along South Kaibab trail. See Figure 13 for key. DEPOSmONAL ENVIRONMENT SAMPLE SKT- CrinolcUHfiryozoan Grainatone (R-2) Bryozomn-CHmoW#! Gratmaton* (R-3) Chno&dat-Bryozoan Gratmaiom# 0H2) OPEN SHELF Cf Bayozoan Paokaton# (R-3) MB Bryozoarr-Crinoldal Gralnatona (R-2) CjCo/ Coated Grain Packet### (FM ) B,CJF Coated Grain Packatone (R-4) Coated Grain Gralnetone (R-2) Crlnotdal-Bryozoan Gramatooe (R-2) • (CrinokJal-Bryozoan. Packatone) (R-4) Crlnoldat-Bryozoan Gralnetone (R-2) I Crtnoldal Gralnetone (R-3) B,C m-4) GRINOID eBANKe . MA l Figure 17. Lithology and depositional environment'for Part (1) of the Mooney Falls tfeirber of the Pedwall Limestone along South Kaibab trail. See Figure 13 for key. Figure t h e i t o o n e y F a l l s M e m b e r o f t h e R e d w a l l L i m e s t o n e a l o n g S o u t h K a i b a b trail. See Figure 1 MOONEY FALLS (part 2) # E © © : a S r=r 3=3 18. 3 OoWcQmlnatom# (R-2) 3 6 < l< K 64 : < Packetone) 2 6 < ,fIP (R-3) B,Cf,I.P 0 6 < 5 *- ) -* (* 65 < < < ctoPeHru risom R- ) -3 (R brainstorm Oc^tio-P^etHerous 6 6 < Packetone 6 5 < < 5 5 c (R- c 5 5 < oii Qantn (R-2) Qralnatone Oolitic 49A < 0 5 < 1 5 < C Qralnatone(R-1) Oolitic 2 5 3 < 5 ^ _ Crlnoldat-ForamlnlferaKoatedGrain __ L i t h o l o g y a n d d e p o s i t i o n a l e n v i r o n m e n t f o r P a r t 9 Paekatooe (R-3) 59 58 57 1 s (R-4) Ss 61 54 54 67 Coated Qraln-Pelletlterous Qralnatone (R-3) Qralnatone CoatedQraln-Pelletlterous 67 SAMPLE SKT- (R-5) (R-5) B.C£,I,P (R-4) (Crinoldal-Bryozoan (R-4) B.C£,I,P ,,, (lcatcPceoe (R-4) Packetone (Bloclaatlc B,C,F,I lcetc ath eeietWeioue h t Ha Blocleetlc fl£ A rlaoe R- ) -3 (R Qralnatone oii rlaoe (R-2) Qralnatone Oolitic CXJPfio 13 0 .F,O. (OoHtlc. (R-4) Qralnetene) 2 4 for key. CC,,, Bryozoan-Crlnoldal ,C,Co,F,l,P ) (otcQantn) (R-4) (OoHtlc Qralnatone) OOLITIC •BANK' OOLITIC ‘ BANK' BANK' ‘ OOLITIC OPENShELF DEPOSITIONAL RESTRICTED ENVIRONMENT MIA MB SHELF IIIA I IIIB (2) of 52 53 m DEPOSITIONAL SAMPLE SKT- ENVIRONMENT < 82 Ostracode-Pelletlferous Grelnetone (R-2) I RESTRICTED SHELF / LAGOONAL < 8 1 Pellellferoue Graln/Packstone CR-2) iw (Coated Grain Packstone) (R-4) Algal-Calclapherk-Wack-eetone Oawacode- PeHaWeroua Grelnetone C 7 7 C,COpP (Coated Graln-Crinoidal Peek/ Grelnetone) (Rt4) RESTRICTED SHELF ggzjCgof (Coated Grain-PelletWeroua |||B C 76 Grelnetone) (R-4) C 75 Slltstone Solution Seam C 74 B 3 z,C ,l (Coated Grain-Pe#etlteroos Packstone) (R -4) C 73 (R-5) C 72 CrlnoWal-Oolltk Grelnetone (R-3) OOLITIC 'BANK- C 71 Oolitic Grelnetone (R-2) O etracode-Algal-Pelletlferoue Packstone (R-3) RESTRICTED § 70 (unevenly graded to Sponge Spicule Wackeetone) SHELF ^ 69 CO CrlnoldaH.ump-Oolltlc Grelnetone (R-3) S o OOLITIC 'BANK"" CrlnoldaH-ump-Oolltlc Grelnetone (R-3) IIIA Figure 19. Lithology and depositional environment for Part (3) of the Mooney Falls Member and all of the Horseshoe Mesa Member of the Bedwall Limestone along South Kaibab trail. See Figure 13 for key. 54 Figure 20. Photomicrograph of pelletiferous-algal-calcisphere wackestone. Restricted shelf depositional environment (IV) in the Horse shoe Mesa Member. Note brachiopod infilled with sparry calcite. Thin section SKT-79, PP, x35. 55 Figure 21. Photomicrograph of fine-grained, well-sorted, coated grain- pel let if erous-packs tone, SKT-67. Restricted shelf depositional environ ment (I I IB) in the upper Mooney Falls Member. Note worm tubes in the lower right of photo. Thin section SKT-67, PP, x35. 56 Figure 22. Photomicrograph of pelletiferous grainstone. Restricted shelf depositional environment (IIIB) in the upper Horseshoe Mesa Member. Inner whorls of gastropod are filled with sparry calcite while outer whorls are filled with pellets. Thin section SKT-81, PP, x35. 57 Figure 23. Photomicrograph of oolitic-pelletiferous grain- stone. Restricted shelf depositional environment (IIIB) of the upper Mooney Falls Member. Note blocky sparite cement and micritized grains. Thin section SKT-66, PP, x35. Figure 24. Photomicrograph of bioclastic hash-pelletiferous pack/grainstone. Restricted shelf environment (IIIB) of the Mooney Falls Member. Note micrite rims, micritized grains and leached allochems, blocky sparry calcite cement. Thin section SKT-64, PP, x35. 59 Figure 25. Photomicrograph of medium-grained, well-sorted, oolitic grainstone. Nuclei are primarily forams and crinoids. Original micrite surrounding oolites has neomorphosed to microspar. Blocky sparry calcite forms cement. Oolitic bank depositional environment (IIIA). Thin section SKT-53, PP, x35. 60 Figure 26. Photomicrograph of moderately-recrystallized (R-3), medium-grained, moderately well-sorted, bryozoan- crinoidal grainstone. Bryozoan grains are micrite-coated. Syntaxial overgrowths surround uncoated crinoid grains. Sparry calcite cement. Note blocky sparite infills hollow echinoid spine and ostracode. Thin section SKT-39, PP# x35. 61 Figure 27. Photomicrograph of fine- to medium-grained, well-sorted, coated grain-crinoidal-bryozoan grainstone. Thick micrite rims coat nearly all grains. Note mud-filled zooecia in bryozoan fragments. Open shelf depositional environment (IIB). Thin section SKT-42, PP, x35. 62 Figure 28. Photomicrograph of fine- to medium-grained, moderately well-sorted, coated grain-crinoidal-bryozoan grainstone. Most grains are micrite coated. Syntaxial cement surrounds uncoated crinoid ossicles. Open shelf depositional environ ment (IIB). Thin section SKT-42, PP, x35. 63 Figure 29. Recrystallized (R-2), fine- to medium-grained, poorly sorted, crinoidal-bryozoan grainstone. Grains are worn and abraded and have we11-developed micrite rims. Open shelf depositional environment (IIB). Ihin section SKT-47, PP, x35. 64 Figure 30. Photomicrograph of overpacked crinoidal grain- stone. From the lower part of the Mooney Falls Member, Mooney tails Diagenetic Subfacies. Substantial packing preceded cementa tion, note sutured grain contacts. Micritic areas between crinoid ossicles may be the remains of crushed micrite-coated grains. Thin section SKT-38, PP, x35 . 65 addition to the algae (primarily dasyclads) and calcispheres which dominate this environment, brachiopods, crinoids, foraminifera, oolites, and ostracodes from the more seaward environments also occur. Zone IV was only recognized near the top of the Horseshoe Mesa Member. This zone grades laterally into the algae and calcisphere-rich sediments of the adjacent pelletiferous packstones. The pelletiferous grain/packstone facies (IIIB) is the more shoreward record of the restricted shelf—lagoonal environment. Evidence of burrowing and sediment-ingesting organisms is abundant in this facies. Fecal pellets form the primary grain constituent in this Zone. Ostracode-algal-pelletiferous pack/grainstone, ostracode-pelletiferous grain/packstone, bioclastic hash-pelletiferous pack/grainstone, pel letiferous pack/grainstone, oolitic-pelletiferous grainstone, and crinoidal-lump-oolitic grainstone facies record this environment. Within Zone IIIB, algal, calcisphere, gastropod and ostracode content increases landward. Bryozoans, crinoids, fossil hash, foraminifera, and oolites increase seaward. Brachiopods, thickly-coated grains (proto-oolites), echinoid spines, lumps and sponge spicules are also present in this environment. Sedimentation Zone IIIB grades laterally into Zone IIIA, which is the oolitic "bank" facies. The oolitic "bank" facies constitutes Sedimentation Zone IIIA of the modified Shaw-Irwin depositional model. It is composed almost 66 exclusively of well-roundedt well—sorted oolites. Oolite nuclei in clude: brachiopod shell fragments, bryozoans, crinoids, echinoid spines, foraminifera, gastropods and ostracodes. Other non—skeletal components include in ter clasts, algal lumps, and proto-oolites. The absence of micrite and the well-rounded and well-sorted particles indicate that Zone IIIB was a zone of strong marine currents and wave activity. Grain dissolution and broken micrite rims suggest that this environoent may have been periodically exposed to subaerial weathering. The oolitic "bank" environment (Zone IIIA) grades seaward into the open-shelf environment (Zones IIB and C). The open-shelf environment is represented by Sedimentation Zones IIB (crinoidal-bryozoan grain/packstone facies). The fauna is very diverse in this facies. Many of the allochems are reworked, abraded (figure 31), micrite-coated, mud-filled, and overpacked. However, crinoid ossicles rarely have micrite rims. This may be the result of the larger crinoid ossicles being in hydraulic equilibrium with the micrite- coated grains. Energy in this environment appears to have been less than in tiie adjoining crinoidal "bank" and oolitic "bank" environments. The open-shelf facies represents a somewhat deeper-water, lower-energy environment. It is well developed in the Mooney Falls Member. Brachio- pods, bryozoans, crinoids and algal lumps are common. Intraclasts, oolites, pellets, proto-oolites, fish scales and gastropods are present. Sedimentation Zone IIC grades shelfward into the crinoidal-bryozoan 67 Figure 31. Photomicrograph of fine- to medium-grained, poorly sorted, bryozoan-crinoidal packstone. Many grains are worn and abraded and have very thick micrite rims. Cement is blocky sparry calcite. Open shelf deposi- tional environment (IIB). Thin section SKT-49, PP, x35. 68 grain/packstone facies (IIB) and landward to the oolitic "bank" facies, Zone III A. Zone IIB is gradational with the more seaward crinoidal grainstone facies. Algal, bryozoan, coral, foraminiferal, and oolite content increase landward toward Zone IIC, while crinoid content in creases seaward toward Zone IIA. Echinoid spines, interclasts, pellets, proto—oolites, and lumps also occur in this facies. The crinoidal "bank" environment, Sedimentation Zone IIA, is the most seaward environment recognized along South Kaibab trail, the fossil content of this facies is almost entirely crinoid "plates and ossicles. The allochems show few signs of abrasion and only rare micrite rims. The micrite content of this environment is nearly nil. Sediments formed in this environment are typically overpacked and frequently exhibit solu- tioning at grain-to-grain contacts. Excellent examples of this environ ment are present in both the Thunder Springs (top) and Mooney Falls (bottom one-third) Members. Discussion The Redwall Seas appear to have progressively deepened throughout deposition of the Whitmore Wash, Thunder Springs and basal one-third of the Mooney Falls (figure 15). A stillstand subsequently ensued. The stillstand was followed by a long, slow regression punctuated by three minor transgressive pulses. The pulses may be due to local variations and not regionally significant. Antithetically, these pulses may be punctuated aggradational cycles (PACs, Goodwin and Anderson, 1980; 69 Anderson et al., 1984) and represent synchronous depositional events resulting from eustatic changes. In fact, Ross et al. (1985) feel that such events may be synchronous and worldwide. Thus they may be correlat- able with the three transgressive pulses recognized by Kent (1975, pp. 119-120) in his upper depositional unit. However, due to the lack of temporal control, it is uncertain if the pulses recognized in the two studies are coeval. Kent (1975, p. 117) suggested that "periodicity" in subsidence caused the recognized pulses. He (1975, p. 119) proposed Matthews' modification of Coogan's model (1967) to explain these trans gressive events. Previously, two major transgressive-regressive (TR) cycles had been interpreted in the Redwall Limestone. The lower TR cycle was believed to be represented by the Whitmore Wash and Thunder Springs Members, while the upper TR was represented by the Mooney Falls and Horseshoe Mesa Members. Along South Kaibab trail, a single major TR cycle with a minor regression or stillstand during early Mooney Falls deposition (see diagenetic discussion) and possibly another during Horseshoe Mesa deposition, adequately explains Redwall deposition. The key point in previous TR interpretations has been recognition of an unconformity between the Thunder Springs and Mooney Falls Members. The nature of this unconformity is nebulous. As McKee and Gutschick 70 (1969, p. 589) pointed out, it may be either subaerial or submarine in origin. Along South Kaibab trail, this contact appears to be primarily the result of diagenetic contrast in adjacent lithofacies. Sedimentation Zones IIA and IIB are immediately adjacent to the contact. If the contact represents the end of the first TR cycle, then evidence of a subsequent regressive event for the first TR and of all the transgressive deposits of the second TR are absent. Crinoidal "bank" and open-shelf environments are the only recorded environments adjacent to this bound ary. Considering the nature of the "unconformity" (stratigraphic and temporal), presence of adjacent facies across the unconformity, and, to a lesser degree, elasticity index calculations (figure 32), this study suggests that a single major TR cycle with a minor regression (or stillstand) during Mooney Falls deposition offers the best explanation for observed Redwall sedimentation. Conclusion The foregoing discussion illustrates the applicability of the Shaw-Irwin sedimentation model to Redwall Limestone deposition. Using the model in conjunction with the results of diagenetic and tectonic studies, this study suggests that a single major TR cycle (with two minor regressions) offers the simplest explanation for the observed features of Redwall deposition. Thus, the Redwall Limestone chronicles the period from initial shelf submergence in the Kinderhookian to the final with drawal of the Redwall Sea in the Meramecian without a significant break in sedimentation, although erosion may have removed part of the final iue3. Mean Figure 32. lected along South Kaibab trail. WHITMORE WASH . THUNDER SPRINGS MOONEY FALLS elasticity elasticity 1.0 millimeters 2.0 values for Redwall Limestone sanples col 3.0 # 1.0 millimeters millimeters 2.0 71 3.0 72 in sedimentation, although erosion may have removed part of the final regressive episode. DIAGENESIS Introduction Members of the Redwall Limestone have been diagenetically modified to various degrees by several different processes. Recrystalli— zation, dolomitization and silicification are all important within the formation. In many instances, the degree of diagenetic overprinting is so severe that it obfuscates or even obliterates primary texture, rendering an interpretation of the original depositional facies tenuous. This is particularly true of the Whitmore Wash Member along the South Kaibab trail, where dolomitization has erased almost every vestige of original rock texture. Several petrographic investigations have addressed diagenesis in the Redwall. These include: McKee and Gutschick (1969) in the Grand Canyon Region, Smith (1974) in Yavapai County, and Kent (1975) in the Black Mesa Region. 73 74 Dolomitization General In the Grand Canyon area, the Whitmore Wash and the Thunder Springs Members are regionally dolomitized. The degree of dolomitization decreases to the north and west and increases to the south and east toward thinner strata. McKee and Gutschick (19697 p. 562) interpret the eastward increase in dolomitization along with the eastward thinning in isopachs as indicating more shoreward facies lying,to the east. McKee and Gutschick (1969, p. 105 and 562) recognize a single even, fine-grained texture in the Whitmore Wash and Thunder Springs dolomites. The authors interpret localized areas of medium- to coarse grained textures to be tectonic dolomites (i.e., associated with fault ing) . They have suggested that the laterally pervasive, fine-crystalline dolomites are the products of penecontemporaneous metasomatic replacement on or below the sea floor. They further suggest that the magnesium for replacement was furnished by the unstable high-magnesium calcite consti tuting invertebrate skeletal fragments and by magnesium diffusion from the more saline near-shore waters. Unlike McKee and Gutschick, Smith (1974, pp. 36-37) and Kent (1975, pp. 75-79) recognize, a two-fold division of dolomite textures: (1) a fine-grained dolomite whose rhombohedra have maximum lengths of 0.1 irm or less, and (2) a coarse-grained dolomite with a mean length of 0.1 mm or greater. Kent (1975, p. 78) suggests a supratidal, penecontempora- 75 neous origin for the fine-grained dolomites. His rationale is based upon the dolomite's similarity to the syngenetic or penecontemporaneous dolomite of other workers (Illing et al., 1965; Deffeyes et al., 1965; ar^l Shinn et al., 1965) and on facies relationships. He offered two hypotheses concerning the origin of the more coarsely crystalline dolomite found in the Thunder Springs Member (Kent, 1975, pp. 112-114): (1) refluxing brines moving parallel to bedding? and (2) mixing of phreatic seawaters and fresh groundwater (Dorag dolcmitization model; Badiozamani, 1973). Smith (1974) also recognized two crystal sizes, a smaller size of less than 0.1 mm, and a larger class averaging 0.2-0.3 nrn. However, he felt that the dolomite was the product of late stage diagenesis and was not penecontemporaneous (Smith, 1974, p. 56). To support his argument, he cites ossicle-shaped voids surrounded by large dolomite rhombs and dolonitized skeletal grainstones and packstones. Petrographic Observations (This Study) Along South Kaibab trail, dolcmitization occurs in the lowest three members of the Redwall. The lowest member, the Whitmore Wash, is nearly completely dolonitized. Dolcmitization is less complete in the overlying carbonate beds of the Thunder Springs Member. The degree of dolomitization decreases from nearly 100 percent in the Whitmore Wash to approximately 80 percent in the overlying carbonates in the Thunder Springs. Several irregularly-spaced dolonitized intervals are present in 76 the Mooney Falls Member, but these are volvmetrically insignificant. The dolomites generally represent early replacement of mudstones and wackestones as evidenced by inferred original textures. However, dolcmitization has occurred in Redwall carbonates having a wide range of inferred original textures, from mudstones to grainstones. This suggests that the primary control on dolcmitization was residence at a diagenetic horizon, while secondary control was original texture. A degree of fabric selectivity is indicated by the occurrence of numerous corroded dolomite rhombohedra within a chert matrix (figures 33 and 34) Thunder Springs and Mooney Falls Members). This observation indicates that there were two phases of dolcmitization, an incomplete "porphyroid" phase and a later pervasive dolcmitization phase. The "porphyroid phase" dolomite rhombs represent an incipient stage of dolcmitization. This early dolcmitization stage appears to have been fabric selective since these "seed" crystals occur only in the groundmass (figure 35). This is consistent with Shukla and Friedman's (1983, p. 708) observation that incipient dolcmitization is strongly fabric- selective. The pervasive dolcmitization stage is the diagenetically more important stage. Nearly complete dolcmitization of the groundmass (matrix + cement) has resulted in a mosaic of interlocking hypidiotopic dolomite crystals (figure 36; see Friedman, 1965). Shukla and Friedman (1983, p. 710 and 711) refer to this kind of dolcmitization fabric as 77 Figure 33. Photomicrograph of slightly corroded dolomite rhombohedra in a chert matrix. Evidence of an early, pre-chertification phase of dolomiti- zation which was later interrupted by silicification. Partially dedolomitized, note red staining. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section TS510-20L (courtesy of A. Hess), stained (ATS), PPm xlOO. 78 Figure 34. Photomicrograph of slightly corroded dolomite rhombohedra in a chert matrix. Same view as Figure 33, but under crossed-nicols. Thin section TS510-20L (courtesy A. Hess), stained (ARS), XN, xlOO. 79 Figure 35. Photomicrograph of partially-dedolomitized, corroded dolomite rhombs in a chert matrix. This is evidence of an early porphyroid phase of dolomitira- tion arrested by later silicification. Whitmore Wash Member Whitmore Wash Subfacies. Thin section WW510-3 (courtesy a ' Hess), stained (ARS), XN, x35. 80 Figure 36. Photomicrograph of mosaic of hypidiotopic dolomite crystals. Note straight crystal boundaries and numerous enfacial junctions. Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies. Thin section SKT-23, PP, xlOO. 81 "type 3" fabric. The "type 3" fabric typically destroys the precursor carbonate's texture. The hypidiotopic fabric is inferred to be the result of restricted growth due to the proximity of other nucleating grains. The dusty areas enclosed within dolomite crystals suggest growth of the dolomite crystal beyond the boundary of the precursor carbonate (Shukla and Friedman, 1983, p. 711). The hypidiotopic texture indicates that the dolomite crystals formed below the "Critical Roughening Tempera ture" (CRT) for dolomite, which further indicates a low-temperature, early diagenetic origin (Gregg and Sibley, 1984, p. 929 ) for these dolomites. The dominant hypidiotopic texture grades into an idiotopic texture where less interference occurred (e.g., in the vicinity of molds; figure 37). Dolomite rhombohedra often penetrate molds (figure 38). Where this occurs, the penetrating rhombs are nearly euhedral and are larger than the surrounding dolomite crystals. Dolomite crystal size typically increases from matrix-rich areas toward the molds. The sediments were at least partially lithified prior to complete leaching. Preservation of molds and euhedral dolomite rhombohedra projecting into open molds supports this conclusion. Leaching (figure 39) probably occurred in conjunction with dolomitization, possibly providing a source (partial) of magnesium (aragonite and high-magnesium calcite from allochems) for dolomitization. In the upper Whitmore Wash, molds are frequently infilled with sparite which has been incompletely 82 vicinity'of Photomicrograph of idiotopic dolomite texture in Whitmore Wash Member, Whitmore T h i n section SKT-25, PP, x250. Wash Diagenetic Subfacies. 83 Figure 38. Photomicrograph of euhedral dolomite rhombs penetrating sparite-filled mold. Sparite in mold partially replaced by silica. Note chert in pore space above and left of mold. Dolomite crystal size is much greater in the vicinity of the mold. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section SKT-35, XN, X35. 84 Figure 39. Photomicrograph depicting moldic porosity in Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies. Note molds of crinoid ossicles. Thin section SKT-25, PP, x 3 5 . 85 replaced by silica (figure 40). Dolomite rhombs sometimes "float” in these mold-filling sparites (figure 41; see Lohmann and Meyers, 1977). Dolomite crystal size distribution is unimodal and not bimodal as observed in the studies of Smith (1974) and Kent (1975). Grain size distribution was determined by point counting thin sections. Approxi mately 200 grains were counted in each dolomitized thin section. The property noted was maximum apparent crystal diameter. Point counting results of 2237 grains yielded an average grain size of 74.9 micrometers (approximately 0.75 mm) with a standard deviation of 33.6 micrometers (figures 42 and 43 and see Table 1). Although a bimodal distribution was not noted, there was a wide range of cyrstal sizes. This is primarily due to increased grain size in the vicinity of molds. Several observations, deviate from the observed unimodal size distribution: very-fine crystalline hypidiotopic dolomite replaces original micrite in one thin section and small veinlets of very finely-crystalline euhedral dolomite rhombs cut across several thin sections. The first deviation occurs in a single bed and may be the product of unique conditions (interstitial fluids + timing) along with a mudstone precursor. In the second deviation, dolomite rhomb veinlets don't appear to be genetically related to the predominant dolomites. Instead, they probably formed during a later stage of dolomitization. iron-oxide coats many of the dolomite crystals (figure 44). Granules of iron-oxide frequently surround the periphery of dolomite rhombs and are often included within the growing crystals. Iron-oxide 86 Figure 40. Photomicrograph of sparite-filied mold in the upper Whitmore Wash Member, Whitmore Wash Diagenetic S u b f a c i e s . Euhedral dolomite rhombs around and possibly within sparite- filled molds. Note poikilotopic texture. Sparite partially replaced by silica. Thin section SKT-27, PP, x35. 87 % % % : ™ S ” iS-in?«°LS,:edr*1 a°1°“ “ Ih°"“ Note hypidiotopic texture of dolomite matrix. Mold is of a partial crinoid stem. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section TS510-10L (courtesy of A. Hess), stained (ARS), pp, x35. Dolomite Rhomb Size Distribution in the Whitmore Wash Member, South Kaibab Trail grain size [pm ] Figure 42. Histogram of dolomite rhomb size distribution. Whitmore Wash Member along South Kaibab trail. Member along South Kaibab trail. Kaibab South along Member iue 3 Cmltv cre f ooie hm szs Wimr Wash Whitmore sizes. rhomb dolomite of curve Cumulative 43. Figure cumulative percent 00 .0 0 5 40.00 00 .0 9 9 0.00 6 30.00 80.00 70.00 5.00 9 20.00 98.00 90.00 10.00 99.50 99.80 99.90 99.95 0.20 0.10 50 .5 0 05 .0 0 2.00 1.00 5.00 ri sz [jm] jjm [ size grain 5 0 5 0 15 5 15 200 175 150 125 100 75 50 25 J ______OT KAI TRAIL B A IB A K SOUTH HTOE AH MEMBER WASH WHITMORE I J ______sti i n tio u trib is D of Curve ulative um C oo t Gan ze iz S Grain ite Dolom o o 1 o O O O 89 Table 1. Dolomite Crystal Size Distribution (in Micrometers) of Samples taken from the Whitmore Wash Member of the Red wall Limestone along South Kaibab Trail. Figures 40 and 41 show Cumulative Data. oooooooooo. OHc-imtrintoi^cooioo OOOOOOOOr4r-4r4r-li-4r-4r-lr- SKT 14 186 7 24 43 26 1 22 14 6 8 6 11 5 6 2 0 3 1 1 0 76 38 SKT 15 173 5 15 26 25 19 21 13 21 11 6 6 2 1 2 0 0 0 0 0 69 28 SKT 16 185 0 16 23 13 20 26 18 12 20 10 6 8 3 10 0 0 0 0 0 79 34 SKT 17 199 0 0 2 4 14 13 20 5 20 37 24 14 14 9 10 8 2 1 2 114 34 SKT 18 199 0 23 31 46 29 15 28 13 6 2 2 0 2 0 1 0 1 0 0 69 24 SKT 22 206 0 8 14 11 29 28 38 25 20 17 3 7 3 1 0 0 0 2 0 83 28 SKT 23 199 8 12 24 29 18 32 17 17 20 4 9 1 3 1 1 3 0 0 0 78 31 SKT 24 165 0 14 36 53 17 19 8 9 7 2 0 0 0 0 0 0 0 0 0 59 19 SKT 25 181 51 41 37 22 17 77 :S- 1 0 0 0 0 0 0 0 0 0 0 0 45 17 SKT 26 185 20 35 45 25 17 24 7 2 7 1 2 0 0 0 0 0 0 0 0 51 22 SKT 27 177 0 8 24 19 13 29 25 15 16 14 5 4 2 0 1 1 0 0 1 79 32 SKT 29 182 0 2 4 10 13 22 37 23 27 17 8 7 4 4 2 2 0 0 0 97 27 oVD 91 Figure 44. Photomicrograph of iron-oxide coated, euhedral dolomite rhombs penetrating sparite-filled mold. From the uppermost Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies. Thin section SKT-29, PP, xlOO. 92 often forms clots within the pore spaces of the dolomites. Not surpris ingly, iron-oxide is ubiquitous in this formation, since the formation underlies the iron-rich Supai redbeds. The mosaic of hypidiotopic crystals, the cloudy nuclei of the dolomite grains, the leached bioclasts (molds), and the lack of associ ated evaporites suggest an early replacement origin for the pervasive dolomites. Dolomitization Model Several different processes have been proposed to explain dolomitization. These models include: (1) seepage refluxion, (2) deep burial dolomitization, (3) evaporative pumping, and (4) meteoric mixing. Three requisite conditions must be met before extensive dolomitization can occur (Morrow, 1982, p. 95): (1) a source of magnesium ions must be present; (2) the magnesium ions must be constantly replenished; and (3) the composition of the solution must be conducive to dolomitization. Longman (1981, p. 133) noted another prerequisite - that the model must be consistent with the paleoclimatology. In order to assess the applicability of any of these models to the dolomites and dolostones of the Redwall, it is necessary to consider the characteristics of the dolomites formed by each process. Character istics to be considered include scale and spatial relationships, major stratigraphic and paleogeographic relationships, internal facies rela tionships, and petrographic relationships (Morrow, 1982, pp. 99-102). 93 Redwall dolomitization occurs over a laterally extensive area. The area of dolomitization appears to have been paleohydrologically controlled, with areas to the south and east (toward paleohighs) more dolomitized. There is no evidence of primary evaporites associated with the dolomites. These observations, plus evidence of a humid tropical climate (regional karstification), and lack of associated facies indica tive of a strongly evaporative environment largely rule out the seepage refluxion and evaporative pumping models. Moreover, the fine- to medium- crystalline hypidiotopic dolomite crystals appear to be the product of shallow burial, thus eliminating deep burial dolomitization as a possible candidate. The remaining mixed-water model is consistent with all the above considerations. The mixed-water (meteoric mixing) model accounts for evaporite- free dolomites. This model was developed by Hanshaw et al. (1971) to explain dolomitization under the influence of fresh groundwater in a Tertiary carbonate aquifer in Florida. Badiozamani (1973) applied this model to the Ordovician of Wisconsin, and suggested the term "Dorag" (Persian for mixed-blood) dolomitization for this process. In this process, the magnesium ions required for dolomitization are derived primarily from seawater and the delivery mechanism is the continual circulation of seawater induced by the flow of fresh groundwater (Land, 1973). The model requires a relatively stable hydrologic setting, which provides sufficient continuous recharge to establish a mixing cell with seawater over a long period of time, in order to drive the dolomitization 94 reaction (Land, 1983, p. 15). A number of authors (e.g., Runnels, 1969; Matthews, 1971) have illustrated that meteoric phreatic water with only a minor amount of magnesium, when combined with marine water, forms a fluid which may be undersaturated with respect to calcite. Badiozamani (1973, p. 968) has calculated that in brackish water, dolcmitization should occur in the zone between 5 to 30 percent seawater which is undersaturated with respect to calcite and supersaturated with respect to dolomite. In conclusion, because of the apparent paleohydrologic control, absence of evidence for primary evaporites, evidence for a humid, tropical environ ment, and evidence for shallow-burial dolomite, the mixed meteoric-marine water (Dorag) model is the preferred model to abbount for Redwall dolcmitization. Silicification General Silicification occurs to varying degrees in all four Redwall Limestone members. Unquestionably, it is best developed in the Thunder Springs Member, which is considered to be middle to late Foraminifera Zone 8, middle Osagean (Mamet and Skipp, 1970; also see: Skipp, in McKee and Gutschick, 1969). Parker and Roberts (1966, pp. 2423-2424) and McKee and Gutschick (1969, p. 39) have correlated Thunder Springs chert to cherty intervals within the Anchor Limestone (southern Nevada), Gardison and Deseret Limestone (Utah), and Keating Formation (southeastern 95 Arizona). It may also correlate with cherts of the Madison Limestone (Wyoming) and Joana Limestone (Nevada). DeCelles and Gutschick (1983) have argued that, although coeval, these compositionally-banded shelf- margin cherts may not be genetically related. Parker and Roberts (1966, p. 2428), McKee and Gutschick (1969, p. 114), Smith (1974, p. 58), and Kent (1975, p. 68) all agree that silicification (chertification) preceded lithification, thus it was either early diagenetic of penecontenporaneous. As stated earlier, the silica source is problematical and no consensus has, as yet, been reached. Field Observations Nodular chert was observed in all Redwall manbers. The nodules are typically concentrated along horizons rich in coarse-grained bio- clastic material. Silicification is best developed in the Thunder Springs Member. Here, coalesced nodules produce the "bedded" appearance characteristic of this member. Lensoidal and nodular chert occur in the other members, but are less well-developed. The Redwall1s nodular, lensoidal, and "bedded" cherts are white to light grey, opaque, and porcelain-like. Horseshoe Mesa cherts appear laminated due to alternating light (off-white) and dark (grey) banding. The first occurrence of chert in the Redwall along South Kaibab trail is approximately 10 m from the base of the Whitmore Wash Member, somewhat below the middle of the unit (see figure 45). Several other irregular and discontinuous chert horizons are present in the upper half of this 96 Figure 45. Photograph of nodular cherts in the Whitmore Wash Member along South Kaibab Trail. L. Lemke pointing to first observed chert occurrence at approximately 10 m from base of unit. Whitmore Wash Diagenetic Subfacies. 97 member. In the Thunder Springs, individual chert "beds" are non-uniform in thickness and are highly irregular, varying laterally from 0 cm to approximately 20 cm in thickness (figure 46). Intercalated carbonate beds are also highly variable in thickness but are typically twice as thick. Bedding becomes markedly thicker toward the top of the unit. The Mooney Falls Member has well-developed chert horizons at about 30 m from the top and at the top. However, chert nodules and lenses are conspic uously absent from most of this member. Finally, chert lenses and nodules are common in the upper half of the Horseshoe Mesa Member (see figure 47). Petrographic Observations Silica replacement ranges from incipient silica replacement of sparite to completely silicified massive cherts. Chert, chalcedony, and megaquartz were observed in thin section (figure 48). Chert is the dominant replacement silica. The groundmass and most allochens, particu larly the smaller ones, are typically replaced by chert and microquartz (figures 49 and 50) while micro- and megaquartz infill fossil molds (figures 51, 52 and 53). Crystal growth faces are present in void filling quartz crystals (figure 54). As noted above, unreplaced, isolated, corroded dolomite rhombs occur within the cherts. In areas of very incomplete silicification, such as in most of the Mooney Falls, sparite cement and sparite-replaced bioclasts were the first to undergo silica replacement. Large areas of the thin sections which are incom pletely replaced by silica are enclosed by a single calcite crystal 98 Figure 46. Photograph of intercalated chert and dolomite (and dolostone) beds in the Thunder Springs Member. Note distinct stratigraphic expression. Photo taken along South Kaibab Trail. 99 Figure 47. Photograph of chert lenses and nodules in the upper Horseshoe Mesa Member. Cherts are typically off-white and have medium grey nuclei. Horseshoe Mesa Diagenetic Subfacies. 100 Figure 48. Photomicrograph of void progressively infilled with microquartz and megaquartz. Chert forms surrounding matrix. Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies. Thin section SKT-20, XN, xlOO. 101 Figure 49. Photomicrograph of oolite replaced by chert and megaquartz (principally the nucleus). Megaquartz surrounds oolite. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section TS511-24C (courtesy A. Hess), XN, xlOO. 102 Figure 50. Photomicrograph of chert replacing oolite in Thunder Springs Member, TS51-24C. Large megaquartz crystals surround oolite. Thunder Springs Diagenetic Subfacies. Thin section TS511-24C (courtesy A. Hess), XN, xlOO. 103 Figure 51. Photomicrograph of brachiopod infilled first with a thin fibrous quartz crust, followed by microquartz, and megaquartz (primarily). Chert surrounds brachiopod. Brachiopod shell still largely carbonate. Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies. Thin section SKT-20, XN, x35. 104 Figure 52. Photomicrograph of silica-replaced oolites. Nucleus of oolite is replaced by megaquartz while remainder is chert. Megaquartz surrounds the oolite. Chert replaces matrix and allochems above and below megaquartz-filled void. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section TS511-24C (courtesy A. Hess), XN, x35. 105 Figure 53. Photomicrograph of silica-replaced, previously micrite-coated allochems. Micrite was replaced by chert while nucleus was replaced by megaquartz. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section TS 511-24C, XN, x35. 106 Figure 54. Photomicrograph of growth lamellae in a void- filling quartz crystal. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section SKT-33, PP, x500. 107 resulting in a poikilotopic texture (figures 55 and 56). Varying degrees of destruction accompany silicification. In general, however, replacement preserves much of the original grain's fine details (e.g., exterior test ornamentation of foraminifera). Partially silicified, crust-forming equant-grained sparites and pore-filling sparite cements have retained their original grain morphology through silica replacement. Twinning lamellae are also frequently retained in the partially silica-replaced sparites. This feature is particularly common in the Mooney Falls and Horseshoe Mesa Members. McKee and Gutschick (1969, p. 42, 559, 560) noted that where intercalated dolomites and cherts occur, fossils are much more common within the chert layers and nodules than in the adjacent dolomites. They inferred that silicification occurred in the originally more porous- permeable intervals which contained more bioclastic debris. The authors were aware that poor fossil preservation could be an artifact of destruc tive dolomitization, or actually reflect original textural variations within the rock. Silicification in the Thunder Springs and Whitmore Wash Members predates pervasive dolomitization and leaching in these units. Delicate ly-preserved fossils in the chert "beds" of the Thunder Springs support this conclusion (see figure 57). Areas replaced by chert enclose neomorphic calcite cores of skeletal grains while the precursor matrix is completely silicified (figures 58 and 59). This suggests that neomor phism may have occurred penecontemporaneously with or slightly before 108 Figure 55. Photomicrograph illustrating poikilotopic texture in upper Whitmore Wash Member, Whitmore Wash Diagenetic Subfacies. Compare with Figure 56 taken under plane-polarized light. Thin section SKT-29, XN, x35. 109 Figure 56. Photomicrograph illustrating poikilotopic texture in upper Whitmore Wash Member, Whitmore Wash Diagenetic S u b f a c i e s . Same view as Figure 55, SKT-29, PP, x35. 110 Figure 57. Photomicrograph of silica-replaced dasycladacean algae in Whitmore Wash Member, SKT-20. Illustrates early replacement of delicate fossil material. Matrix incompletely replaced by chert, note areas of unreplaced carbonate. Whitmore Wash Diagenetic Subfacies. Thin section SKT-20, XN, x 3 5 . Ill Figure 58. Photomicrograph of unsilicified allochems in chert matrix. Void-filling bladed quartz crystals surround many allochems while chert replaces matrix. Note megaquartz infilling borings in allochems. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section TS511-22 (courtesy A. Hess), stained (ARS), XN, x35. 112 Figure 59. Photomicrograph of chert surrounding neomorphic calcite cores of crinoid grains. Ghosts of smaller, finer-grained allochems, possibly micri- tized bryozoan fragments, are entirely replaced by chert. Note that larger chert grains surround perimeter of skeletal grains. Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section SKT-33, XN, x35. 113 silicification. It certainly suggests that the well-developed cherts provided an effective barrier to dolomitizing fluids. Silicification occurred very early in the diagenetic history of the sediment, subsequent to incipient dolomitization, but before significant compaction or pervasive dolomitization. The pristine appearance of delicate fossils corroborates this conclusion. Silicification Model Several different models have been proposed to explain silicifi cation in sediments especially when intimately associated with coeval dolomites (McBride, 1979). Thus it is logical to consider a silicifica tion process which is consistent with the model proposed for the associa ted dolomites. The chert replacement model proposed by Knauth (1979) complements the groundwater dolomitization models of Hanshaw et al. (1971), Land (1973), and Badiozamani (1973), which are favored to explain Redwall dolomitization. As in the dolanitization model, there are three prerequisites: (1) a source of silica (opal-A) must be available; (2) the silica must be constantly replenished; and (3) the composition of the mixed waters must be conducive to chertification (e.g., is the system open or closed with respect to COg?) (Knauth, 1979, p. 276). In the proposed model (Knauth, 1979), sediments in the marine- mixed meteoric-marine have interstitial waters which approach supersatur ation with respect to silica (opal-A). Thus the biogenic silica in the sediment is unlikely to dissolve and more likely to invert to quartz. 114 This explains the preservation of delicate sponge spicules (figures 60 and 61) in the Redwall cherts and suggests that an in-si tu source of silica is unlikely. The amount of silica in the Redwall sediments, in fact, argues for an external silica source. This observation is consist ent with Knauth's (1979) model. In the Knauth model, silica is derived from the entire sediment pile through which the meteoric waters migrate and concentrated in the marine-mixed meteoric-marine diagenetic zone. Thus biogenic silica does not need to comprise the bulk of the sediment in which it is deposited. Redwall silica may have been derived from the underlying Early Paleozoic miogeoclinal sediments through which the recharge waters flowed. According to Knauth (1979, p. 276), chertification occurring during mixing-zone dolomitization would result in some cherts that enclose dolomite rhombs. Subsequent dolomitization would dolomitize the surrounding carbonates while preserving the incipient phase of dolonifi xation within the cherts. This is consistent with observations made in some of the Mooney Falls and Thunder Springs cherts. This model also explains why the dolomite rhombs were not silicified while the surround ing calcite was; the fluids in the marine-mixed meteoric-marine environ ment were supersaturated with respect to dolomite. Other workers (e.g., Dietrich et al., 1963) have described this same relationship. Knauth (1979, p. 277) suggests that the form of chert replacement (nodular, lensoidal, or irregular masses) is controlled by the porosity- permeability distribution in the precursor carbonates, the hydrologic 115 Figure 60. Photomicrograph of silicified, sponge spicule wackestone from the top of the Mooney Falls Member. Portion of an unevenly-graded sample. Restricted shelf depositional environment (IIIB). Thin section SKT-70, XN, x 3 5 . 116 Figure 61. Photomicrograph of tetraxon sponge spicule from a partially-silicified, recrystallized (R-3) coated grain grainstone. Open shelf depositional environment (IIB). Thin section SKT-28, XN, xlOO. 117 flow, and various other factors affecting nucleation. These factors were obviously important in the Redwall Limestone in as much as the cherts were concentrated along bedding planes. McKee and Gutschick (1969, p. 42, 559, 560) also suggested that the depositional fabric directly influenced subsequent chertification, and that hydrologic flow (see discussion: Diagenetic Model) was controlled largely by eustatics and paleoclimate. In sumnary, the marine-mixed meteoric-marine chertification model of Knauth (1979) is the preferred model for Redwall chertification. Knauth's chertification model explains both outcrop and petrographic observations of Redwall Limestone cherts and is consistent with the favored dolomitization model. Recrystallization Introduction Previous workers consider Redwall recrystallization to be a secondary event of unknown timing. McKee and Gutschick (1969, p. 104) considered coarse- to very coarse-crystalline calcite and fibrous and bladed void fillings to be diagnostic textures of the recrystallized calcites. McKee and Gutschick (1969) noted that recrystallization was locally important in the lower three members of the Redwall. They felt that the Horseshoe Mesa Member was unrecrystallized. Smith (1974) reported that approximately 60 percent of the Redwall in the Jerome area was recrystallized to seme extent. Smith noted that recrystallization 118 appeared to be independent of facies, but that the lower Thunder Springs and the upper Mooney Falls were the most extensively recrystallized members. Kent (1975, p. 79) recognized a range of degrees of recrys tallization in the Redwall of the Black Mesa Basin. He also recognized an association between stylolites and recrystallized limestones, suggest ing that both may have been the result of post-lithification loading. General Recrystallization Characteristics In this study, the character of diagenesis appeared different in the lower two members than in the upper two members. The Whitmore Wash and the Thunder Springs are almost completely dolomitized or chertified; little limestone remains. In contrast, the upper two members are almost completely composed of recrystallized limestone altered by incipient silicification. Various degrees of recrystallization were recognized in both the Mooney Falls and the Horseshoe Mesa Members, for the purposes of this study, the degree of recrystallization has been subdivided into four categories: (I) unrecrystal1ized or only slightly recrystallized, original texture can be accurately determined; (II) moderately recrys tallized, original texture can be deduced with reasonable confidence; (III) extremely recrystal1ized, original texture largely destroyed by recrystallization but a tenuous conclusion concerning original texture can be drawn; and (IV) completely recrystallized, all vestiges of original texture totally destroyed,. no conclusions possible. These categories encompass Folk's (1956) gamma through zeta recrystallization \ 119 phases. Most thin sections fall within Category II or Category III recrystallization. Petrographic Observations Along South Kaibab trail, recrystallization appears to be independent of lithofacies. It occurs in limestones whose original textures range from wackestones to grainstones. However, in general, the degree of recrystallization does appear to be dependent upon the original texture - least in the grainstones and greatest in the wackestones (see figures 16 through 19). Coalescive and porphyroid recrystallization (Folk, 1965), which are kinds of aggrading neomorphism, are by far the most common forms of recrystallization in this section. In addition, degrading recrystalliza tion was recognized in several thin sections. Inversion was not ob served, but undoubtedly occurred when less mineralogically-stable skeletal material inverted to a more stable form. Numerous large bioclasts have been replaced by fine- to medium- crystalline, equant-grained and bladed sparite (figure 62). Smaller bioclasts have generally been altered to fine-crystalline, equant-grained sparite. Neomorphism converted the original micrite, coating most grains and completely constituting others, to microsparite (figure 63)* Fine- to medium-crystalline equant-grained sparite crusts many of the micrite- coated grains (figure 64). Grain size increases to medium-crystalline at the centers of the pore spaces. Occasionally, enfacial junctions form where crystals radiating from different allochems interfere. Incipient 120 Figure 62. Photomicrograph of leached allochems infilled with sparite. Fine-grained matrix neomorphosed to microsparite. Horseshoe Mesa Member, Horseshoe Mesa Diagenetic Subfacies. Thin section SKT—80, PP, x35. 121 Figure 63. Photomicrograph of completely micritized oolites. Fine- to medium-grained sparry calcite surrounds oolites and infills pores. Mooney Falls Member, Mooney Falls Diagenetic Subfacies. Thin section SKT-49, PP, xlOO. 122 Figure 64. Photomicrograph showing drusy sparite crusts around perimeter of grains, SKT-49. A single, large sparry calcite crystal fills remain der of intergranular area. Note micritized allochems. Mooney Falls Member, Mooney Falls Diagenetic Subfacies. Thin section SKT-49, PP, xlOO. 123 silicification has affected many of the sparites. Typically, silicifica- tion is so incomplete that the grains retain the petrologic characteris tics of the precursor sparite (twinning, birefringence, relief, etc.). Mold Formation Fossil molds are common in the Whitmore Wash and Thunder Springs Members and infilled molds also occur in the dolomitized beds of the Mooney Falls Member. The molds are external molds of marine inverte brates. Numerous excellently-preserved samples have been collected from the cherty layers of the Thunder Springs Member. However, in the intercalated dolomites of the Thunder Springs Member and in the dolomite of the Whitmore Wash Member, only the general shape of the original bioclast is evident. Molds in the Mooney Falls were infilled with sparite which subsequently has been partially replaced with silica. The shape of the original particle is usually well preserved. Comparison charts (Flugel, 1982, pp. 247-257) were used to estimate percent porosity observed in thin section. Where the original depositional texture has been partially erased by dolcmitization, moldic porosity estimates have been used to infer an original depositional texture. The relationship between moldic porosity and original texture is shown in figure 13. As expected, percent moldic porosity is directly related to the inferred original texture; grainstones have a greater moldic porosity than do mudstones. Molds in the Whitmore Wash are generally of bioclastic hash. However, molds of brachiopods, crinoids, gastropods, and horn corals have 124 been reported. In many instances, fossil molds are poorly preserved. Although dissolution significantly beyond the original bioclast's boundaries is unlikely, extensive dolomitization obfuscates the original grain's identity. Molds are better preserved in the Thunder Springs and Mooney Falls Members, where they are often infilled with partially silicified sparite. DIAGENETIC HISTORY General The diagenetic character of the lower two Redwall Limestone members is markedly different from that of the upper two members. Whereas dolomitization and silicification are the dominant forms of diagenesis in the Whitmore Wash and Thunder Springs Members, recrystalli zation and, to a lesser extent, silicification characterize diagenesis in the Mooney Falls and Horseshoe Mesa Members. Additionally, moldic porosity is well-developed in the dolomites of the Whitmore Wash and Thunder Springs Members. Since they appear to be genetically distinct, the interpreted diagenetic histories of the lower and upper two members will be discussed separately. Only penecontemporaneous or synsediment- ary, early diagenetic processes offering insight into the interpretation of the depositional history of the unit will be considered. Late stage diagenesis (e.g., karstification, tectonic dolomites, stylolites, etc.) will not be discussed here, as such a discussion would shed little insight into the Redwall Limestone's depositional history. Two diagenetic "subfacies" are recognized within each of the diagenetic facies in the Redwall Limestone, and the boundaries of these diagenetic facies and subfacies are, with the exception of the Horseshoe Mesa subfacies, coincident with member boundaries. The boundary between 125 126 the Horseshoe Mesa Member and the Mooney Falls Member is largely related to post-Redwall karstification (figure 65). Facies and subfacies are distinguished by the presence or absence of dolomitization, differential preservation of carbonate grains, and degree and apparent timing of silicification with respect to dolomitization. The different diagenetic characteristics of the facies resulted from passage through differing sequences of diagenetic environments. The dramatic difference in diagenetic character between the upper and lower two units is a key factor in interpreting the formation's depositional history. Additionally, this investigation into the diagenetic history addresses the questions: (1) why two "diagenetic facies", each with two "diagenetic subfacies", developed in the Redwall Limestone; (2) what control the original depositional texture exerted over subsequent diagenesis; and (3) how the diagenetic facies relate to the interpreted shelf emergence and submergence cycles. Criteria Used in Diagenetic Interpretation The criteria used here in interpreting carbonate diagenetic textures and environments applies the observations of both Bathurst (1975) and Longman (1980). Heckel (1983) applied conclusions of these earlier works, and others, to Pennsylvanian cyclothems and his work serves as a departure point for this section. These forementioned publications contain detailed discussions of the different diagenetic 127 Following final regression of the Redwall Sea in thn ::=%i:o:r% ::: %::: r : ^ c^ out humid tropical climate during the Hississippian. 128 environments. The Redwall Limestone was affected by four diagenetic environ ments, differentiated on the basis of fluid chemistry and on the distri bution of that fluid in pores. The environments include the marine phreatic (saturated and unsaturated), marine-mixed meteoric-marine, meteoric-mixed meteoric-marine, and the meteoric phreatic (figure 66). The marine phreatic environment is that zone in which all the pore space is saturated with waters of normal marine salinity. Longman (1980, pp. 464-468) subdivided this zone into an active zone and a stagnant zone. The active zone is where seawater readily moves into the sediment resulting in marine cementation. In contrast, the stagnant zone is where sediments are saturated with seawater, but the marine waters move through the sediments too slowly to result in cementation. The dominant cement types from the active marine phreatic are aragonite and high-magnesium calcite. Crystal form ranges from micrite to isopachous rims and boytryoidal accumulations. In this environment, an isopachous crust of micritic or steep-sided rhombic crystals commonly forms (Alexandersson, 1972). Thick rims of fibrous or bladed crusts in the upper Mooney Falls subfacies and in the Horseshoe Mesa subfacies imply a long residence in this environment (fiure 67). Early formation of these crusts can prevent further compaction. Land and Goreau (1970) and MacIntyre (1977) have attributed the formation of pseudopellets (peloids - clusters of micritic, high-magnesium calcite) to this environ- MARINE METEORIC D1AGENEDC ENVIRON MEffT DIAGEhOIC ENVIRONMENT UJ Me, B. Ic Ch. S- O Ec, Sc, gs Dc o X r Me. B Jc > s- < Ec, Sc, Dc. L DmI Crf C Ch, Qz, S-< i II 0)3) I > Dmi, L Ch. S— a I B - boring Dc - druey calcHe cement L-leaching Ch - chorWcmtkm Dm* - dissolution, mold Infilled Me - micrlte envelope Crf - radial flbroui cslclfe Ec - equant grained eparite cement Qz - mega and micro quartz D - dolomltlzation Ic - leopschouc crust S - slliclfication (-) denotes partial (- -) denotes very partial Sc - eyntaxiei-cement Figure 66. Lithology, diagenesis, and inferred diagenetic environments of the Redwall Limestone 130 Figure 67. Photomicrograph of thick micrite rims on allochems in the Mooney Falls Member, Mooney Falls Diagenetic Subfacies. Grains include crinoids, intraclasts, foraminifera, and oolites. Cement is equant-grained blocky sparite. A poorly-developed drusy sparite coating encrusts allochems Thin section SKT-49, PP, x35. 131 ment. Microboring algae and fungi in early cements. are also common from the saturated active marine phreatic environment, but these also occur in stagnant marine phreatic environments. Since the waters are inferred to have been warm, sinificant dissolution (leaching) of unstable grains is unlikely. The stagnant zone dominates the marine phreatic environment. Micritization and minor intragranular cementation are the most important diagenetic processes occurring in this zone. The mixing zone is the zone of transition between the marine phreatic and the meteoric phreatic environments. It is characterized by brackish waters formed by the mixing of waters from both environments. Longman (1980) noted that cements formed in this environment range from micritic and bladed calcite (meteoric side) to isopachous high-magnesium calcite (marine side)• The mixing zone typically oscillates in position due to relative sea level fluctuations and, on a smaller scale, seasonal rainfall variation. In this discussion, the mixing zone has been subdi vided into a marine-mixed meteoric-marine environment and a meteoric- mixed meteoric-marine environment. The marine-mixed meteoric-marine environment is on the marine side of the brackish mixed-water zone. The pore fluids of this zone are supersaturated with respect to quartz and undersaturated with respect to calcite. The products of this zone include nodular and "bedded" chert (Knauth, 1979). The meteoric-mixed meteoric-marine environment is less saline than the marine-mixed meteor ic-marine zone. Waters of this zone are oversaturated with respect to 132 dolomite and undersaturated with respect to calcite. An important effect of this zone is the dolomitization of the sediments (see: Badiozamani, 1973). The meteoric phreatic is the final early diagenetic zone recog nized in the Redwall Limestone. The meteoric phreatic environment lies between the meteoric vadose zone and the meteoric-mixed meteoric-marine zone. Pore waters are filled with fresh waters containing variable amounts of CaCOj. Longman (1980, pp. 473-477) subdivided this zone based on the saturation state of the water with respect to CaCOg. In this work, all diagenetic products of this zone are grouped under the general term meteoric phreatic; no further subdivision was attempted. In the undersaturated waters of this zone, aragonite and even calcite may be dissolved. The final product is moldic or possibly vuggy porosity. The meteoric phreatic zone is typically located below the water table, and is subdivided into a lower saturated zone and an upper undersaturated zone. Porewaters in the saturated zone are over saturated with respect to calcite. Low-magnesium cenent formed in this zone infill both primary pores and secondary molds and include blocky sparite mosaics that derive from the rim cements (figure 68), drusy rims on the periphery of allo- chems (figure 69), and syntaxial overgrowths on echinoderms (figure 70). The slow movenent of the pore waters results in little cementation in this zone. However, the slow movement does result in equilibrium between the sediments and the pore waters, which promotes the neomorphism of aragonite to calcite. The replacement process may be so gentle that the 133 Figure 68. Photomicrograph of blocky sparite cement derived from a blocky sparite which surrounds grains. The clear, blocky sparite is indicative of the saturated meteoric diagenetic environment. Note leached and blocky sparite-filled allochem (center). Well developed micrite rims surround grains (see fish scale, right). Mooney Falls Member, Mooney Falls Diagenetic Subfacies. Thin section SKT-49, PP, x35. Figure 69. Photomicrograph showing drusy crust around perimeter of oolites, SKT-50. A single equant-grained sparite crystal fills remaining void space. Mooney Falls Member, Mooney Falls Diagenetic Subfacime Thin section SKT-50, PP, xlOO. 135 Figure 70. Photomicrograph of well developed syntaxial cements on grains without micrite rims. Iron-oxide highlights cement morphology. Mooney Falls Member, Mooney Falls Diagenetic Subfacies. Thin section SKT-42, PP, x35. 136 original aragonitic fabric may be preserved. Whitmore Wash-Thunder Springs Diagenetic Facies A single diagenetic facies is recognized in the Whitmore Wash and Thunder Springs Members. The Whitmore Wash-Thunder Springs facies is further subdivided into two "subfacies" at the Whitmore Wash-Thunder Springs contact. The apparent differences between the two members is largely the result of diagenetic history, accounting for differences in the extent of dolcmitization and silicification of each member. Whitmore Wash Diagenetic Subfacies The Whitmore Wash subfacies is characterized by: (1) nearly complete dolcmitization, (2) leaching of nearly all. carbonate grains without subsequent infilling of molds, and (3) a conspicuous absence of "bedded cherts." Petrographic evidence indicates that dolcmitization was an early diagenetic, replacement process. Paleogeographic and stratigraphic evidence for (1) a humid tropical paleoenvironment (and an attendant lack of associated evaporites), (2) a subtle unconformity representing a regression or stillstand atop the Thunder Springs Member, and (3) a silica-forming diagenetic environment in the overlying Thunder Springs Maiiber (possibly representing a more saline meteoric-marine water mix; Knauth, 1979), suggest that dolcmitization occurred within the meteoric- marine mixing-zone environment (Hanshaw, Back, and Deike, 1971; Badioza- mani, 1973; and Land, 1973). Badiozamani's calculations show that mixing \ 137 meteoric grourxiwaters with up to 30 percent seawater causes saturation with respect to dolomite and undersaturation with respect to calcite. The calcite unsaturated waters probably simultaneously dissolved the unstable carbonate grains and dolomitized the sediments. Undersaturated waters capable of leaching both calcite and aragonite particles exist within the freshwater phreatic zone (Longman, 1980, p. 474). Prolonged exposure to this diagenetic environment likely was responsible for the extensively-developed moldic porosity characteristic of this member. The abundance of molds suggests that the Whitmore Wash sediments passed from a marine phreatic environment to a calcite unsaturated (mixed-water/mete- oric phreatic) environment without sufficient time in the marine environ ment for any of the unstable grains to undergo inversion. However, an isopachous fringe lining several cavities may indicate at least some residence time in the active marine phreatic zone. The Whitmore Wash diagenetic "subfacies" is interpreted to have been most affected by the mixed meteoric-marine diagenetic environment, specifically by waters compositionally on the freshwater phreatic side of this zone. Subsequent exposure to the freshwater phreatic zone (unsatur ated meteoric phreatic) is indicated by the extensive development of moldic porosity. Initial residence in the marine environment is of subordinate importance, since few products attributable to marine phreatic processes (e.g., micritization, absence of leaching, isopachous cements, etc.) renain. The observed diagenetic fabrics are most readily explained by relatively short residence in the marine phreatic environ 138 ment, followed by extensive exposure to meteoric-mixed meteoricMnarine waters, and then to unsaturated meteoric phreatic waters. Thunder Springs Diagenetic Subfacies The Thunder Springs diagenetic subfacies is characterized by: (1) "bedded cherts," (2) dolomitization of carbonate beds, and (3) incomplete leaching of carbonate grains. Silicification was a very early diagenetic process; delicate features in even the most unstable grains were preserved. Petrographic evidence convincingly shows that silicif ication preceded associated pervasive dolomitization. As in the underlying Whitmore Wash dolomites. Thunder Springs dolomites are also early diagenetic. Thunder Springs dolomite predominantly formed subsequent to the associated "bedded" cherts. Some dolomite rhombs, however, are surrounded by chert, suggest ing an earlier phase of dolomitization. Cherts in the Thunder Springs Member are most readily explained by the chertification model proposed by Knauth (1979). This model is very compatible with the Dorag dolomitization model (Badiozamani, 1973) used to explain dolomitization in the underlying Whitmore Wash. Like the Dorag dolomitization model, it is the result of mixed meteoric-marine waters. However, in contrast to the dolomitization model, it occurs on the marine side of the mixing zone. A greater number of fossils is preserved in the chert beds than in the intercalated dolomite beds. This may suggest that silicification occurred preferentially along more porous/permeable horizons. Chert 139 often surrounds inccmpletely-leached grains. These partially-preserved grains are composed of neomorphic sparite. The above observations suggest that: (1) partial inversion preceded chertification or was penecontemporaneous with it, and (2) silicification preceded dolomitiza- tion and may have been partially controlled by original depositional texture. The Thunder Springs diagenetic "subfacies" is interpreted to have been affected by four early diagenetic environments. These are (in chronological order) the: marine phreatic, mixed meteoric-marine (marine- side) , mixed meteoric-marine (meteoric-side), and meteoric phreatic. As in the Whitmore Wash diagenetic "subfacies," the most profound diagenesis occurred during residence in the mixed meteoric-marine environment. Silicification occurred in the more marine, mixed meteoric-marine waters, while dolomitization occurred where the pore fluids were more diluted by freshwater. The observed spectrum of diagenetic products may be consid ered to have operated sequentially: (1) initial stabilization (inversion, neomorphism) of some bioclasts, (2) incipient dolomitization, (3) silicification of the more porous/permeable beds, (4) dolomitization of the sediment, and (5) leaching of most bioclasts (mold formation). 140 Mooney Falls - Horseshoe Mesa Diagenetic Facies The Mooney Falls and Horseshoe Mesa Members are both character ized by recrystallization and partial silica replacement. In contrast to the Horseshoe Mesa Member, the Mooney Falls contains several dolomitized intervals. Chert development in the Horseshoe Mesa is moderately well developed, surpassed only by the "bedded cherts" of the Thunder Springs Member. The presence of "bedded" chert is the basis for diagenetically subdividing the facies. Mooney Falls Diagenetic Subfacies The diagenetic fabric is readily observed in the packstones and grainstones of this diagenetic facies. The Mooney Falls Member is characterized by: (1) recrystallization (aggrading and degrading neomor phism, and inversion), (2) very incipient silicification (tripolitic cherts), and (3) an absence of "bedded" cherts. Medium- and coarse-crystalline equant-grained sparite, syntaxial cements, and micritic coatings cement the dominantly grain-supported textures of this subfacies. The majority of bioclasts in this facies are surrounded by micrite rims. Micritization due to microboring algae and fungi (Bathurst, 1966) most typically occurs in the marine phreatic zone. Here intragranular cement of aragonite and high-Mg calcite occurs within the small pores and microborings in skeletal grains (Heckel, 1984, p. 737). Rims are so well developed in this facies that most grains are consequently classified as coated grains. The thick isopachous micritic rims around most allochems and general lack of compaction features 141 suggest early cementation in the marine-phreatic environment. Saturated meteoric waters produced the later stage of pervasive equant-grained sparite which infills the pore space and the leached grains. Evidence of compaction varies throughout this diagenetic subfa cies. The basal one-fifth (lowest 15 meters, to SKT 44) exhibits substantial overpacking of grains (figures 30 and 71). Slight overpack ing was noted in the overlying 10 meters (to SKT 49) and virtually no overpacking was noted in the remainder of this subfacies. Criteria used to determine the degree of overpacking include: the degree of dissolution or grain breakage that has taken place at the grain boundaries in the packstones and grainstones, and the number and types of grain contacts (i.e., concavo-convex, tangential, point, or longitudinal). Extensive overpacking of grains, accompanied by blocky and syntaxial cements in the lowest 15 m suggests that a high degree of compaction preceded cementa tion by calcite-saturated, Mg-poor waters. Slight overpacking in the overlying 10 m indicates an earlier cementation, possibly marine phre atic, prior to cementation by calci te-saturated, Mg-poor waters. The absence of overpacking and more intense leaching in the overlying 50 m implies more rapid initial cementation prior to compaction (probably in the marine phreatic environment) and leaching in the meteoric-phreatic environment. Heckel (1983, pp. 754-755) suggests that packing fabric may be useful, along with other criteria, in inferring whether calcarenites are transgressive or regressive in nature. Application of Heckel1 s criteria to observations (e.g., cenent, texture, dissolution, etc.) made 142 Figure 71. Photomicrograph of large crinoid ossicle. Uncoated portion of grain (left) has developed a syntaxial overgrowth. Sutured grain contacts are apparent. Euhedral dolomite rhomb within ossicle ( 5:00 position below center of grain). Upper Thunder Springs Member, Thunder Springs Diagenetic Subfacies. Thin section SKT-34, PP, x35. 143 on the calcarenites of this subfacies indicate that the lowest 15 m (approx.) are transgressive, the overlying 10 m (approx.) are transition al (stillstand), and the remaining 50 m (approx.) are regressive. Most grains, even those originally composed of aragonite, have undergone neomorphism to medium crystalline sparite or microsparite (if originally micrite) with very little relict structure preservation. Seme grains were leached out of their micrite envelopes which were subsequent ly infilled with sparite (figure 72 depicts the collapsed micrite rim of a leached oolite). However, the development of micrite rims seems to have protected most of the unstable allcohems from the effects of a later stage of leaching in unsaturated meteoric waters. Extensive leaching suggests that the sediments were exposed to undersaturated meteoric phreatic waters. Additionally, very thick micrite coatings and the neomorphism of many grains indicates that these sediments resided in the saturated marine phreatic environment for some time prior to exposure to unsaturated meteoric waters. Incipient silica replacement is ubiquitous throughout both members. Silica partially replaces some of the cementing sparite crystals as well as the sparite of the recrystallized allochems. The micrite-coating allochems and the original micrite matrix were less affected by the silicification process (figure 73). Selective partial silicification of the sparite suggests that the marine-mixed meteoric- marine waters conducive to silicification did not remain at one horizon 144 Figure 72. Photomicrograph showing broken micrite rims of leached allochems (center). Blocky sparry calcite infills large void. uPP®r FallS Member, Mooney Falls Diagenetic Subf acres. m SKT-68, PP, x35• 145 Figure 73. Photomicrograph of blocky sparite infilling ostracode. Fine-grained matrix has been replaced by chert while sparite in ostracode has been only partially replaced. Note foram to the left. Horseshoe Mesa Member, Horseshoe Mesa Diagenetic Subfacies. Thin section SKT-79 , X N , x35. 146 to allow the silicification process to reach a mature stage. Silicifica- tion succeeded both recrystallization and cementation. .Even in those beds where silicification is nearly complete, recrystallization and cementation appear to have preceded silicification. Several dolcmitized intervals are present in this "subfacies." This indicates that a meteoric-mixed meteoric-marine diagenetic horizon was occasionally established during the diagenetic history of this subfacies. However, the rarity of the dolcmitized intervals suggests that dolcmitization was neither very important in this "subfacies" nor in the Mooney Falls-Horseshoe Mesa facies. In summary, the Mooney Falls subfacies was exposed to a minimum of three diagenetic environments. These are, in chronological order: the saturated marine phreatic, marine-mixed meteoric-marine, and meteoric phreatic. The meteoric-mixed meteoric-marine environment was locally important, and where it is evidenced (dolomite beds), chronologically precedes the marine-mixed meteoric-marine environment. Three subdi visions of this subfacies are recognized based upon degree of com pact ion: a well compacted basal interval, a slightly compacted transi tional interval, and a relatively uncompacted upper interval. Horseshoe Mesa Diagenetic Subfacies The criterion for subdividing the Mooney Falls-Horseshoe Mesa diagenetic facies into two subfacies is the existence of prominent "bedded" cherts in the Horseshoe Mesa subfacies. These occur approxi mately seven meters from the top of the member, well above the Mooney 147 Falls-Horseshoe Mesa contact. The associated limestones are diagenetic- ally indistinguishable from those in the upper part of the Mooney Falls Member. Thus, the above observations and deductions for the regressive calcarenties of the Mooney Falls are applicable to the Horseshoe Mesa subfacies. Silicification is dissimilar to that in the Thunder Springs. Chert "beds" are thinner and less silicified. Additionally, the cherts appear laminated due to alternating dark (grey) and light (off-white) bands. The relative timing of chertification in the Mooney Falls- Horseshoe Mesa diagenetic facies is also different, with silicification following recrystallization. This inferred paragenetic sequence is supported by the observation that silica partially replaces blocky sparite in both subfacies. Consequently, silicification did not occur at as early a diagenetic phase as it did in the Thunder Springs. Knauth's (1979) mixed-water chertification model can also be used to explain Horseshoe Mesa cherts. The well-developed chert horizon indicates long-term maintenance of a silica-saturated horizon (marine- mixed meteoric-marine) as it does in the Thunder Springs. In summary, cementation, inversion, and aggrading and degrading neomorphism preceded silicification. Cementation occurred in two phases: the first was a very early diagenetic process which resulted in early marine phreatic cementation, the second was also early diagenetic, but occurred later in the saturated meteoric environment and resulted in equant-grained pore-filling sparite. The last early diagenetic process 148 was silicification. Incipient silicification has occurred in most beds. Complete silicification is less common than in the Thunder Springs Member, and where it occurs fossil preservation is poorer than in the Thunder Springs. The Horseshoe Mesa diagenetic subfacies is interpreted to have resided in the following three diagenetic environments (in chronological order): marine phreatic, marine-mixed meteoric-marine, and meteoric phreatic. Since much of the Horseshoe Mesa Member was eroded during the hiatus between deposition of the Horseshoe Mesa Member and the overlying Watahomigi Formation of the Supai Group, additional diagenetic environments may be recognized elsewhere. Diagenetic Model The trend in diagenetic textures in the facies and subfacies discussed above is most readily explained by a single progression of diagenetic environments moving through the sediments during a single major transgressive-regressive cycle. This simple pattern is complicated by the introduction of mixed meteoric-marine waters followed by meteoric waters into the sediments during a stillstand or minor regression in the Osage. Figure 74 shows the inferred paradiagenetic sequence for Redwall Limestone Members. During stillstand (or minor regression), a large freshwater lens built out, forming an aquifer beneath the shelf and displacing marine phreatic waters (figure 75). A meteoric-mixed meteoric-marine diagenetic horizon was maintained within the Whitmore Wash sediments. This resulted in dolomitization of the Whitmore Wash sediments, and silicification and iue 4 Pradiagenetic Sqec fr h Rdal Limestone. Redwall the for Sequence c i t e n e g a i d a Par 74. Figure o environments DIAGENETiCSUBFACES THUNDER SPRNGS WHITMOREWASH MOONEYFALLS EAIEIPRAC HHHHI RMR R' EOoR f I TERTIARY. I ' f SEOOtoARY T m 'm R PRIMARY I H H H H RELATIVEIMPORTANCE HORSESHOEMESA ' MARTE-MXED NETEORKy-MARINE MARINE-MIXED METEORIC-MARINE MARINE PHREATIC MARINE PHREATIC METEORIC-MIXED METEORIC-MARINE METEORIC PHREATIC MARINE-MIXED METEORIC-MARNE METEORIC-MIXED METEORIC-MARINE MARINE PHREATIC METEORIC-MIXED METEORIC-MARINE METEORIC PHREATIC MARINE-MIXED METEORIC-MARINE METEORIC PHREATIC METEORIC PHREATX) MARNE MARNE PHREATIC METEORIC-MIXED METEORIC-MARINE TRANSGRESSION STLLSTAND REGRESSION EMERGENCEI I I ,D ImW D,Dp ■Hi miDrnl m m a a m m m Ec, 6^ Dc; L Dni Ch, S-, Qz D,Dp • Ec, Sc, Dc •Sc, Ec, cd r is-,C r~ Z I CZ D I Ch S- ■ I MeA Ic o m . b . ic 149 Landward S h e lfw a rd Figure 75. Schematic depicting out-building of freshwater lens beneath the Redwall shelf. During stillstand, a freshwater lens built-out several tens of kilometers beneath the shelf. Marine waters were displaced and marine-mixed meteoric-marine and meteoric-mixed meteoric-marine diaenetic environ ments were established within Whitmore wash and Thunder Springs Member sediments. These mixed-water 150 diagenetic environments are responsible for the diagenetic features attributed to the Whitmore Wash- Thunder Springs Diagenetic Facies. 151 dolcmitization of the Thunder Springs sediments. As the diagenetic horizons migrated outward and surfaceward in response to continued out building of the freshwater lens, the sediments were progressively exposed to compositionally more meteoric waters. A subsequent regression in Meramec time, during Mooney Falls deposition, caused a reversal of movement of diagenetic environments and compression of the mixed-water diagenetic horizon. Compression of the horizon and a relatively rapid upward migration of the mixed-water zone prevented extensive dolcmitization and silicification in the Mooney Falls sediments. The marine-mixed meteoric-marine diagenetic facies was not able to become sufficiently re-established to produce a "bedded" chert horizon until Horseshoe Mesa time. In most of the Mooney Falls subfacies and in intervals within the Horseshoe Mesa subfacies, exposure to the marine phreatic diagenetic environment resulted in early cementation of the sediments and neomorphism of almost all the bioclasts. Subsequent exposure to the meteoric phreatic diagenetic environment resulted in blocky sparite cement infilling most of the remaining pore space. It should be noted that the stratigraphic position of the diagenetic horizons oscillated. Realization of this fact and the knowledge that much of the Horseshoe Mesa Member has been erosionally removed should clarify the seeming discrepancy of having an episode of silicification (due to mixed waters) post-dating large-scale exposure to the meteoric phreatic environment. The final early diagenetic stage of incipient silicification may be due to the mixed waters zone at the strandline 152 migrating seaward during the final regression. This last phase of silicification was of insufficient duration to silicify more than the most readily silicifiable grains (e.g., sparite cement and sparite- replaced bioclasts). Silicification is so incomplete that most of the optical properties of the calcite (sparite) are retained (e.g., twinning, high birefringence, etc.). Chert nodules and "beds” in the Redwall typically are concentrat ed characteristically in horizons parallel to bedding. This reflects the geometry of the diagenetic horizon, a nearly horizontal zone of mixing which can be maintained over extensive areas. Back and Hanshaw (1970) report that the mixing zone on the Yucatan Peninsula (Mexico) occurs at a depth of 70 meters over many thousands of square miles. Such horizons may result in a horizon of silicification proportional to the thickness of the marine-mixed meteoric-marine diagenetic zone. This explains the cherty horizons in the Thunder Springs and other coeval "bedded" shelf cherts. A difficulty with this model is that a large freshwater lens would have to have built-out many kilometers under the shelf. Longman (1980, p. 463) points out that only under unusual circumstances could meteoric waters be forced under more dense seawater. A long-term stillstand, humid tropical climate, and favorable aquifer may have produced a hydrostatic head capable of displacing the marine phreatic waters. Evidence for submarine freshwater discharge as far as 120 kilometers from the Florida-Hatteras coast has been reported by Manheim 153 (1967). He also reports evidence for vigorous freshwater outpouring more than 200 kilometers from shore. Additionally, Stringfield (1965) calculated that the hydrostatic head of a Florida aquifer was capable of discharging fresh waters from a submarine outcrop to a depth of 500 meters, 100 kilometers from shore. Thus it is plausible that the requisite unusual circumstances of Longman were met during Redwall deposition. Table 2 outlines the five major stages of the proposed diagenetic model. This diagenetic model accounts for the timing and occurrence of all major diagenetic fabrics developed in both diagenetic facies and is consistent with the inferred humid paleoclimatology, paleohydrology, and areal distribution of the diagenetic facies. As with any model, there are observations which don't neatly fit the model, such as the dolomite beds in the Mooney Falls diagenetic sub facies. I have attributed such deviant features to the vagaries of diagenesis. Conclusions Subdivision of the Redwall Limestone into members is largely based on diagenetic character, which reflects: (a) diagenetic environ ments becoming ensconced within certain horizons in the sediment; (b) maintenance of a quasi-static hydrologic equilibrium for a sufficient amount of time for the diagenetic environments to imprint themselves upon the sediments; and (c) the sediment's passage through a different sequence of diagenetic environments to produce the observed diagenetic facies or subfacies. TABLE 2 Major Diagenetic Phases Phase 1: Marine Transgression The Whitmore Wash, Thunder Springs and Lower Mooney Falls were deposited during initial shelf inundation (Kinderhook - Early Osage). Marine phreatic waters invaded the sediments from the west and displaced meteoric phreatic waters eastward and southward toward paleohighs. Phase 2: Stillstand A lengthy stillstand (or minor regression) ensued near the time of maximum transgression, during which the Mooney Falls was partly deposited (Osage). During this time, a large freshwater lens and attendant mixing zones built-out beneath the shelf. The diagenetic horizons were maintained for a sufficient duration to cause dolomitiza- tion of the Whitmore Wash Member and silicification of the Thunder Springs Member. Phase 3: Regression Regression eposed the Whitmore Wash and Thunder Springs sediments to compositionally more meteoric waters (Osage-Meramec). This resulted in the development of extensive moldic porosity in the Whitmore Wash and Thunder Springs members and dolcmitization of the unsilicified Thunder 154 155 TABLE 2 - CONTINUED Springs sediments. Most Mooney Falls sediments remained in the marine phreatic environment long enough to permit early cementation of the sediments, thus preventing the overpacking observed in that part of the Mooney Falls which accumulated during transgression and stillstand. During regression, the mixing zone shrank and "rapidly" moved upward through the sediment pile, preventing silicification or extensive dolomitization of upper Mooney Falls and newly-deposited Horseshoe Mesa sediments. Phase 4: Stillstand A period of stillstand or slowed regression (Meramecian) per mitted development and maintenance of a marine-mixed meteoric-marine diagenetic horizon in Horseshoe Mesa sediments, and is responsible for the formation of well-developed "bedded" cherts within the member. Phase 5: Final Withdrawal Redwall seas finally withdrew from the shelf during Mid-Merame- cian time. Erosion and karstification removed a large part of the Horseshoe Mesa Member 156 TABLE 2 - CONTINUED NOTE: A final. Chesterian, marine incursion onto the Redwall shelf deposited the estuarine sediments of the ’’Surprise” Formation (McKee and Gutschick, 1969; Beus and Billingsley, 1984). The sediments are largely removed in the area of study. They are preserved in more basinward areas of the shelf. EFFECTS OF ANTLER TECTONISM ON REDWALL SHELF SEDIMENTATION The Early Mississippian Antler orogeny profoundly affected sedimentation patterns along the western margin of the North American continent. During the orogeny, the deep oceanic facies of the Roberts Mountain allochthon were unplaced over coeval miogeoclinal sediments of the Cordillera. The emplaced thrust load and the load due to the detritus shed from the subaerial regions of the allochthon resulted in downflexure of the miogeocline. Miogeoclinal downflexure, in turn, probably resulted in transgression and attendant carbonate shelf sedimen tation during the Early Mississippian. Thus, the extensive sheet of Lower Mississippian shallow marine carbonates that occurs throughout the Rocky Mountain Province and westward into the Cordilleran miogeosyn- cline, and which comprises the lower depositional cycle of Rose (1976), may be primarily a consequence of the Antler orogeny and not a result of eustatic fluctuations. This study investigates the relationship between the Antler orogeny and deposition of the Redwall Limestone, a member of Rose's lower depositional cycle of shallow marine carbonates. The quantitative model of lithospheric flexure presented here is offered to explain the broad- scale features of Early Mississippian shelf sedimentation in northern Arizona. Speed and Sleep (1982) have demonstrated the applicability of the flexural model to the Antler foreland basin. Other workers have 157 158 applied flexural models to foreland basin successions. Beaumont (1981) and Jordan (1981) have used flexural models to account for features of the stratigraphic record of the Jurassic-Cretaceous of Alberta and the Cretaceous of the western United States, respectively. More recently, Quinlan and Beaumont (1984) have shown that the Appalachian Basin is the flexural consequence of allochthonous overthrusting. Modeling Factors which influence the nature of the stratigraphic record include: thrust loading, sediment loading, eustasy, compaction, and erosion. The effects of thrust and sediment loading and of compaction are evaluated in this analysis. Other less well-constrained factors which profoundly influence the resultant stratigraphy are the lithospher ic rheological properties. Whether the lithosphere behaves elastically or viscoelastically is problematical. Over long periods of time, continental lithospheric flexure may be better approximated by a visco elastic model. However, good agreement exists between elastic models and the topographic profiles of cratonic basins, trenches, and oceanic islands (e.g., Haxby et al., 1976; Watts, 1978; and Turcotte, 1979). The elastic model is used here. Basement subsidence was determined by two-dimensional finite difference modeling modified from Jordan (1981). Similar analyses have been made for other sedimentary basins (Watts and Ryan, 1976; Beaumont, 1978, 1979, 1981). Antler tectonic effects were analyzed up to 400 159 kilometers cratonward of the allochthon toe (see figure 2). Finite difference modeling was accomplished by dividing the 400 kilometer transect into 25 kilometer-wide elements. The isostatic response to each element was computed across the entire profile and the results sunmed to yield the total isostatic response to all load elements for each of four time slices. Flexure The analytical equations governing subsidence were derived by Hetenyi (1946) (see Appendix D). They describe the flexure of a linear- ly-elastic beam or thin plate due to two-dimensional rectangular loads. The model assesses the effects of thrust and sediment loading based upon the assumption that the lithosphere behaves like a two-dimensional beam of unlimited strength. Isostatic adjustment is achieved by distributing the effects of loading over longer distances with an increase in flexural rigidity. As the thin plate's flexural rigidity is increased, the depression caused by a surface load becomes smaller but laterally more extensive. Antithetically, as the beam becomes weaker, and the flexural rigidity (D) goes to zero, the crust assumes the properties of an Airy- type (point load compensated) crust; vertical deflection due to loading is maximized at the point of load application, while lateral distribution of the load is minimized. In flexural loading, the depth to the basement without sediment cover depends on sediment thickness in adjacent elements as well as the sediment thickness of the local element. Thus, the model 160 allows distribution of the load over a laterally more extensive area than would be possible using a local loading (Airy) model of isostasy. The result is a more realistic model. In our modeling (Sylvia and Armin, 1984), flexural rigidity was varied over a wide range of values. Several combinations of D-values were modeled. The best fits between observed and modeled stratigraphy were obtained when the D-values were varied laterally across the profile, with relatively higher D-values cratonward (10 exp 22.5 to 10 exp 24 [Nt- m]). Modeled profiles were constructed for four time slices from Kinderhook to Chester time. Figure 76 shows basin profiles using a De value of 10 exp 22.5. The constructs represent the best-fitting flexural rigidity values obtained from numerous computer runs. An important consequence of lithospheric flexure key to this investigation is peripheral upwarping. From figure 77 it can be seen that the forebulge width is directly related to the flexural rigidity (D) while the forebulge height is inversely related to flexural rigidity. Thus, the flexural rigidity value will profoundly influence the height and width of the forebulge. If the rigidity changes over time, the forebulge will "migrate” in response, to the change. For example, a decrease in rigidity would result in seaward migration of the bulge. 161 Figure 76. Reconstructed depths to basement of Antler foreland basin, adjacent shelf margin and shelf, and modeled depths to basement. APPLIED LOAD (Allochthon) DEFLECTION ■ 0 BASIN PERIPHERAL BULGE MSL DEFLECTION DEFLECTION »0 162 Figure 77. Schematic illustrating the concept of peripheral bulging. Cartoon contrasts basin and peripheral bulge development in a rigid ( D) lithosphere (above) and a weak ( D) lithosphere (below). Amplitude of bulge and deflection of basin highly exaggerated. 163 Loading Considerations A critical part of the analysis concerns the reconstruction of the accretionary prism (Roberts Mountain allochthon). Its shape, size and bulk density during emplacement are largely responsible for the shape and size of the Antler foreland basin. Prism modeling parameters are the same or similar to those used by Speed and Sleep (1982). Figure 78 illustrates the modeled shapes and sizes of the accretionary prism over time. An initial wedge-like geometry is assumed. Simple sheet load profiles were also modeled. The allochthon is modeled as 13 kilometers thick at a distance of 100 kilometers west of the allochthon's toe for the 360 Ma., 355 Ma., and 345 Ma. time slices. It is modeled as 20 kilometers thick at 100 kilometers west of the toe for the 335 Ma. pro file. Accretionary prism density was estimated to be 2.5 g/an^ for calculation purposes. Quantitative estimates of the effects of Roberts Mountain allochthon emplacement and subsequent foreland basin sedimentation also require a knowledge of the spatial and temporal distribution of the applied load, stratal thicknesses, lithologies, chronostratigraphic information and paleobathymetric information were obtained from published and unpublished literature on thirteen stratigraphic sections (Appendix C) distributed from the leading edge of the Roberts Mountain thrust belt in Nevada to a point on the shelf 400 kilometers distant. The stratigraphic sections used in this study are irregularly 164 foreland baain • helf margin Roberts / Mountain 360 Afa. Allochthon Roberta Mountain allochthon modelled as 13 km thick at 100 km west of toe of allochthon for top three profiles ~ 366 Ma. 100 km exaggeration shallow marine ~ 346 Ma. * ■ ■ ■ erosion - » Roberta Mountain allochthon modelled as 20 km thick at 100 km west of toe of allochthon for bottom profile Shapes el Heberts Mountain allochthon rneemed from Speed end Sleep (1SS2). For eimeiictty the position of the toe of the allochthon Is limed lor all profiles. Figure 78. Evolution of the Antler Foreland basin, adjacent shelf margin and shelf, Nevada and north western Arizona. 165 distributed, with respect to both distance from the allochthon and distance along depositional strike. In order to reconstruct the Miss- issippian stratigraphy for isostatic evaluation, the stratigraphic sections were projected onto a transect approximately orthogonal to the structural and depositional strike of the region. This approach per mitted relatively close spacing of stratigraphic control points using localities widely spaced along depositional strike. The assumption is that stratigraphic thicknesses do not vary markedly along depositional strike. The stratigraphic thickness of each 25 kilometer element between control points was estimated based upon an average sedimentation rate between the control points. Palinspastic restoration of the Mississippian stratigraphy across the region was necessary in order to properly evaluate the spatial distribution of the load. The palinspastically-restored stratigraphic sections are shown in figure 79. The reconstruction accounts for the net effects of Mesozoic thrusting and of Cenozoic basin-and-range extension. Palinspastic reconstructions are based on the work of Anderson (1971), Stewart and Poole (1974), Stewart (1980), Guth (1981), Wernicke et al. (1982), and Harms and Coney (1984). Temporal control was acquired by keying biostratigraphic informa tion to the absolute ages obtained from the Correlation of Stratigraphic Units of North America (Childs, 1983). Several different faunal groups, depending on the stratigraphic section's facies, were used for correla tion purposes. The chronostratigraphic correlation chart (figure 80) 166 PALINSPASTIC RESTORATION P»lr*p«stic rwioreiion •ceouifeo lor thn*ting CSlewarl 1980 :St«wwt and Pode. 1974) end Cenozoic e*w»ion (Amdmrmon, 1871; Coney and Hem*, h press ;Gmfi 1881: Slew*!, 1880; Wernicke, el •!, 1982) Figure 79. Palinspastic restoration accounting for Sevier thrusting and Cenozoic extension. STRATIGRAPHIC CORRELATION CHART stratigraphic sections, and deposi- Figure 80. Stratigraphic correlation chart depicting chronometric ages, biostratigraphic zon tional environments utilized in this study. 168 depicts the absolute ages of the stratigraphic units used in this analysis. Faunal zonation schemes used in this study are also depicted. Biostratigraphic information was often insufficient to confidently assign a chronometric age to a particular formation or part of a formation in the flysch trough. When the absolute age bounds for a specific stratal package were indefinite, an average sedimentation rate was assumed between the two adjacent horizons whose absolute age was reasonably well constrained. To calculate the subsidence history of a stratigraphic section, it is necessary to restore it to its original, unccmpacted thickness. Stratigraphic decompaction is based upon the assumption that the thick nesses and intergranular porosities of sedimentary layers decrease as a result of mechanical compaction during burial (Van Hinte, 1978; Perrier and Quiblier, 1974; Steckler and Watts, 1978). It is assumed that porosity reduction, hence stratal thickness, can be related to burial depth and that the rate of reduction is a function of lithology. This relationship is certainly a simplified assumption because the vagaries of diagenesis (e.g., early or late cementation ) can markedly alter the rate of porosity reduction. Bond and Kominz (1984, p. 156) have suggested that the best approach to delithification is to evaluate the maximum and minimum effects of compaction and cementation, thereby establishing a range of acceptable decompacted values. The porosity curve for sandstone is theoretical while the curves for shale and carbonate are regressions through data points. Basin fill densities used in the flexure calcula 169 tions varied from 1.9 [g/cm3] to 2.2 [g/on3] depending on lithology. Deccmpacted sediment thicknesses were computed by backstripping, itera tive removal of overlying stratigraphic units and calculation of the resultant porosity increase, hence stratal thickness increase (density decrease), for each tine-step. A detailed discussion of the method is presented by Steckler and Watts (1978), A m i n (1984) and Bond and Kominz (1984). Geohistory diagrams for all thirteen stratigraphic sections are shown in Appendix E. Additionally, reconstructed basement depths are genetically grouped into flysch trough, submarine rise, shelf margin and shelf to facilitate comparison of subsidence rates (figures 81, 82 and 83). Eustatic fluctuations are not considered in this analysis as they are difficult, if not impossible, to estimate for the Mississippian. There is scanty evidence for extensive glaciation during the Early Mississippian. Consequently, large-scale, rapid glacio-eustatic fluctua tions are highly problematical. However, the possibility of an increase in ridge volume is suggested by the number of orogenies during the Mississippian and Early Pennsylvanian periods (see previous discussion of the Antler orogeny). This may have resulted in a slowly rising sea level (Harland et al., 1982). The thesis of this investigation is that the primary control on Redwall shelf deposition was Antler tectonic effects. This is tested by comparing results of a tectonic model to the observed stratigraphy. Paleowater depth estimates for each section and time-step are based upon M a 360 350 340 330 360 350 340 330 km 1. i 2. 3. Ftysch Trough Submarine Rise 170 Figure 81. Flysch trough and submarine rise subsidence curves. 3G0 350 340 330 360 350 340 330 Shelf Margin 171 Figure 82. Shelf margin and western shelf subsidence curves Ma M a 360 350 340 JJO 360 350 340 330 I i __I__ j _1______l_ — I— _I km km \\ 0.05 - 0.05- 0.10- 0.10- 0.15- 015- 0.20- 0.20- 025- 0.25- X 030 - 0.30- . TR & SK Shelf Shelf 172 Figure 83. Eastern shelf subsidence curves. 173 biofacies and/or lithofacies considerations. The error bars on the geohistory diagrams illustrate the degree of uncertainty in water depth assignments for the different stratigraphic units. The uncertainty, although quite large for some sections at times, is not consequential considering the load imposed by the accretionary prism and sediment loads. In a shallow sea, such as the Redwall Sea, water weight has much less of an effect on lithospheric flexure than does the weight of the strata. This study ignores the effects of erosion as they are considered subordinate to the aforementioned effects. Results Using the above methods and making the above stated assumptions, basement depth profiles were reconstructed for four time slices corres ponding to about 360 Ma., 355 Ma., 345 Ma., and 335 Ma. Absolute ages are based upon the COSUNA chronometric chart. These dates were chosen since they span the time from the initial Kinderhookian, Redwall shelf inundation to the final Chesterian emergence. The dashed lines in figure 76 are the calculated isostatic responses of a laterally-strong basement to thrust, sediment, and water loading. The results are from analytical solutions, thus they are non-unique. However, they are plausible estimates because many of the parameters are reasonably well con strained. The lines represent best fits selected from numerous computer runs in which the flexural rigidity was incrementally varied. Figure 76 compares the reconstructed and modeled basement 174 depths. Mississippian sea level is taken as the datum. The modeled isostatic responses are similar to the reconstructed basement depths except near the allochthon toe. The lack of agreement extends from the submarine rise, approximately 100 kilometers east of the allochthon toe, to the thrust front. All four time slices show a marked deviation between the observed and predicted depths in this segment. The magnitude of the deviation increases with time, becoming an error of 1.5 kilometers at the 335 Ma. time step. Otherwise, the shape and size of the foreland basin is in good agreement with the observed stratigraphy. The shelf is predicted to have been flexed downward with the arrival of the accretionary prism at the miogeoclinal margin in the earliest Kinderhookian (see figure 84). Flexure is predicted to have resulted in shallow marine conditions over the area occupied by the Redwall Sea. Inundation of the shelf persisted until the middle Merame- cian (335 Ma.) when flexural upwarping (forebulging) and subsequent subaerial erosion of the shelf is predicted to have occurred. This is compatible with the sedimentological evidence of subaerial exposure of the shelf during this time. Thus, initial marine inundation of the shelf, existence of shallow marine conditions during the Osagean and Early Meramecian, and subsequent shelf emergence during the Middle-Late Meramecian are predicted to have occurred because of the lithosphere's flexural response to an emplaced load. The geohistory diagrams (figure 81, 82, and 83) were grouped to depict subsidence curves for the flysch trough, submarine rise, shelf Ba«%*nCDW«%We@WOWMGPHMCSAND WFERRED TECTOWC ELB^ENTS OF THE ANTLER OROGB4Y - SOUTHERN NEVADA AND NORTHWESTERN ARIZONA mepmatic arc' KMOetMOOKIAM A. Arrival of eccratlenary am### end magmatic arc. KINDERHOOKHN C. Dominantly molaaee deposition In axial part #1 foreland basin. tfitermittant abelf axposura # e to inward flexere landward of the foreland basin Slew US##) lias#) Figure 84. Schematic diagrams shewing phases and inferred tectonic elerrents of the Antler orogeny - southern Nevada and northwestern Arizona. 176 margin, and shelf sections. A comparison of the different sections reveals a similar subsidence "signature" or history. (Naturally, there is a large difference in the absolute sediment thickness accumulated). This is true for all sections except those of the submarine rise (Ely, South Egan Range, and Pahranagat). The general pattern appears to be convex-up during the early phase of sedimentation, followed by a period of linear sediment accumulation, and ending with a final concave-up segment. This pattern would result in an increasingly rapid initial subsidence followed by a period of slowed, but steady subsidence and ending with a final period of sharply slowed subsidence. The similarity of the geohistory profiles of the flysch trough, shelf margin and shelf suggests a similar causal mechanism for the subsidence of all three groups - allochthon emplacement and sediment loading. Subsidence ceases later in the more basinward sections. Deposition of the Thunder Springs Member of the Redwall Limestone and of the Anchor Limestone Member of the Monte Cristo Limestone occurs at about the inflection point between the period of initial rapid accumulation and the time of steady subsidence (approx. 357 Ma.). This inflection point is also quite apparent in the submarine rise sections, particularly the Ely section where the Joana Limestone was deposited. Discussion The elastic flexural model can account for most of the strati graphic features of the Antler foreland basin and adjacent shelf margin and shelf. The major apparent problem with this model is the misfit 177 between the modeled basement deflection and the reconstructed basement profile at the toe of the allochthon. Varying the flexural rigidity, the least well constrained variable, both spatially and temporally, didn't alleviate this problem. Misfit may be due to one or more of the follow ing: (1) the profile being a composite of many sections which are widely spaced along depositional strike; (2) the use of incorrect thicknesses of foreland basin strata (structural repetitions); (3) the thick stratigraphic sequences near the Roberts Mountain allochthon reflecting a "relaxation" effect of the basement; and (4) the shortcomings of the simple two-dimensional model. The model accounts for the major stratigraphic features of the Redwall. Initial marine inundation of the shelf, existence of shallow marine conditions during the Osagean and Early Meramecian, and subsequent shelf emergence during the Middle-Late Meramecian are all predicted to have occurred solely based upon the lithosphere's flexural response to an emplaced load. No eustatic explanation is necessary to resolve any fundamental aspect of Redwall sedimentation. This is particularly noteworthy with regard to the emergent event which resulted in the karst topography atop the Horseshoe Mesa Member of the Redwall. Previously, this subaerial exposure had been attributed largely to eustatic change. However, this analysis (Sylvia and A m i n , 1984) suggests that the regressive episode may be better explained by tectonic mechanisms of 178 thrust lading and synorogenic sedimentation in the foreland basin. Conclusions The foregoing quantitative analysis shows that lithospheric loading due to thrust and sediment loads is adequate to explain the salient features of Redwall Limestone deposition. Deposition appears to be related to Antler thrust loading and to the evolution of the Antler foreland basin. The timing of events, the proximity of the thrust and sediment loading to the Redwall shelf, a paucity of evidence of glacia tion (to produce a glacio-eustatic sea level rise), a similarity in the subsidence histories, and the ability to explain the observed stratigra phic features solely using the flexural model argue for an underlying tectonic control of Redwall shelf sedimentation. The accuracy of the reconstructions is limited by inaccuracies in load estimates and in estimates of lithospheric rheological properties. However, the width and shape of the modeled basin demonstrate the general applicability of the model. As suggested earlier, a viscoelastic model may have yielded better results. Nonetheless, the less sophisticated elastic model used here is adequate to demonstrate the probable relation ship between Antler tectonics and coeval but distant shelf sedimentation. Primary control of the timing and distribution of Redwall Limestone lithofacies was probably tectonic in nature. Deposition appears to be related to Antler foreland basin. Kinderhookian marine inundation of the shelf is predicted to have occurred due to foreland thrust loading and sedimentation in foreland and shelf areas. A subse 179 quent emergent episode recorded by the Redwall Limestone (a regional karst surface developed on the Horseshoe Mesa Member) may have been related to relaxation of elastic stress and seaward migration of a forebulge. Additionally, chertification of the Thunder Springs Member may have been influenced or controlled by lithospheric flexure - a decrease in subsidence rates resulting in a stillstand. Finally, the predicted repsonse of the Redwall shelf suggests that the formation records a single overall transgressive-regressive (TR) event possibly with a short period of regression at the close of Thunder Springs deposition due to a decrease in subsidence rates. A single TR event is in agreement with other Early Mississippian carbonates in the western United States (lower depositional cycle; Rose, 1976) but contradicts the two TR interpretation of McKee and Gutschick (1969) and Kent (1975). CONCLUSION A synthesis of depositional and diagenetic analyses and flexural modeling provides a more complete picture of Redwall Limestone deposition than obtained previsouly. The models proposed for deposition, diagene sis, and flexure are complementary, simple, and make geologic sense. Five depositional environments were recognized along South Kaibab trail. They range from restricted shelf-lagoonal (IV) to crinoidal "bank" (IIA) environments. The lithofacies range from algal-calcisphere wackestones (IV) to pelletiferous grain/packstones (IIIB) to oolitic grainstones (IIIA) to crinoidal-bryozoan grain/packstones (IIB) to crinoidal grainstones (IIA). Two early diagenetic facies each with two subfacies were recog nized in the Redwall along South Kaibab trail. With exception of the Horseshoe Mesa Member, facies and subfacies boundaries are coincident with member boundaries. The Horseshoe Mesa-Mooney Falls contact appears to be the product of a later (Pennsylvanian) stage of diagenesis during which a regional karst surface developed. Consequently, recognition of member boundaries is largely based upon the diagenetic history of the member. The diagenetic model proposed here employs a combination of Badiozamani's (1973) Dorag dolomitization model and Knauth's (1979) 180 181 chertification model. The mixed-water environments favorable for dolomitization and silicification may be the result of outbuilding of a large freshwater lens beneath the shelf during a lengthy stillstand near the time of maximum transgression. Redwall sediments were deposited on a homoclinal ramp, beneath a shallow epeiric sea, and in a humid tropical environment. Flexural modeling indicates that the Redwall1 s depositional history can be explained in terms of the shelf's response to coeval Antler tectonics. Initial shelf inundation occurred due to thrust loading and sedimentation in foreland and shelf areas. Subsequent emergence appears related to either seaward migration of a peripheral bulge or relaxation of elastic stress in the lithosphere. The Redwall Limestone is the record of a single major transgres sive-regressive cycle. A lengthy stillstand near the time of maximum transgression (Osage) punctuates the cycle. The Whitmore Wash, Thunder Springs, and basal one-third of the Mooney Falls were deposited during transgression and stillstand; the upper two-thirds of the Mooney Falls and all of the Horseshoe Mesa record the final regression of the Redwall Sea from the shelf. Three transgressive-regressive pulses in the major regressive cycle suggest a secondary, eustatic control on Redwall deposition. The three pulses may have regional significance. In conclusion, a new depositional model, a new diagenetic model, and an alternative mechanism for primary depositional control have been 182 proposed for the Redwall Limestone. Additionally, the paleoclimate has been inferred to be humid tropical and not arid and evaporitic as previously suggested. Finally, it has been suggested that Redwall member recognition is largely based upon diagenetic history. appendix a 183 184 REDWALL LIMESTONE South Kaibab Trail -r 10 m. 1 O m . — Layered chert a> cn - - Nodular chert o z z Oolitic grains tone V) o szs Crinoidal grains tone VI Of cr TJC c - r M S i o o JC I 1— 5 a# *o c South Kaibab Trail, Grand Canyon National Park, Arizona South Kaibab trail is the steepest, most direct route to the Canyon floor. The trail is heavily trafficked by mule packtrains which deliver mail and supplies to Phantom Ranch along the Colorado River. Consequently, the trail is well maintained. Three high-angle faults cross the trail. However, only two cut the measured section. The first fault occurs near the base of the measured section, while the second and third cut the section near the top of the Mooney Falls Member. The upthrown blocks are to the north along the faults. Cherty horizons in the Mooney Falls facilitate lateral correlation of the strata. Redwall Limestone: Whitmore Wash Member Lithologic Thickness [m] Unit No. Unit Cumulative Field Description 1 1 11.6 11.6 Dolomite, light brownish grey (SYR 6/1), weathers greyish orange pink, (SYR 7/2), fine-medium crys talline; thin bedded; resistant; well-developed moldic porosity, molds of bioclastic hash; sharp basal contact. 185 186 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description 2 12.3 23.9 Dolomite, greyish orange pink, (SYR 7/2), weathers pale yellow ish brown (10YR 6/2), fine-medium crystalline; thin bedded; resistant; well developed moldic porosity, molds of bioclastic hash; sharp basal contact; chert, light grey (N7), weathers same; nodular, nodules form chert-rich horizons, cherty intervals at 1.4, 1.7, 4.3, and 9.1 meters from base. Sampled intervals: SKT- (m.) 20 (1.4), 21 (2.0), 22 (4.0), 23 (6.0), 24 (8.0), 25 (10.0), 26 (12.0). 3 8.9 32.8 Dolomite greyish pink (SYR 8/2), weathers moderate greyish pink (SYR 7/2), fine- to medium-crystal line; thin bedded, horizontal bedding; moldic porosity, molds of fossil hash; chert, light grey 187 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description (N7), weathers same, layered and nodular, discontinuous and irreg ular layers become more nodular toward top of unit; cherty intervals at: .75, 1.4, 2.0, and 2.4 (m.) from base; fossils in chert: brachiopods, corals (Rugosan), crinoids, and sponge spicules. Sampled intervals: SKT- (m.) 27 (1.7), 28 (2.0), 29 (8.6) Thunder Springs Member 4 25.3 58.1 Dolomite/tDolostone (gradational) up-section with intercalated chert; dolomite (dolostone) fine- to medium- grained; greyish orange brown (SYR 6/4), light brown (SYR 6/4); weathered; thin bedded; beds vary in thickness (to approx. 40 cm.); chert pinkish grey (SYR 8/1), black patina on weathered surface; thin 188 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description bedded, variable thickness (approx. 0 to 25 cm.), chert beds thickest at approximately 8 and 14 m. from base; chert beds typically thinner than associated dolomite (dolostone); more abundant and better fossil preservation in cherts; crinoidal grainstone; 21.4 m. from base; 15-22 cm. (variable thickness), irregular upper and lower contacts; fossils in chert: brachiopods, crinoids, and sponge spicules. Sampled intervals: SKT- (m.) 30 (2.0) , 31 (2.5) , 32 (8.3) , 33 (9.8), 37 (14.4), 34 (21.5), 35 (22.1), 36 (25.3) 189 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description Mooney Falls Member 5 4.8 62.9 Crinoidal grainstone, very light grey (N8), pinkish grey (SYR 8/1) weathered, black patina on some weathered surfaces; friable; cross- bedded; basal and upper contacts sharp and irregular; fossils: brach- iopods, bryozoans, crinoids, and foraminifera. Sampled intervals: SKT- (m.) 38 (1.7), 39 (3.8) 6 4.6 67.5 Fossil hash grainstone, dominated by crinoidal material, light grey (N7), greyish orange pink (SYR 7/2) weathered; thin bedded; recrystallized; base sharp and irregular; vugs infilled with sparry calcite. Sampled interval: SKT- (m.) 40 (2.3) 190 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description 7 1.7 69.2 Grainstone, poorly sorted, including coated grains and crinoids; very light grey (N8), pinkish grey (SYR 8/1) weathered, black patina on some weathered surfaces; friable; cross-bedded; decreasing grain size from bottom to top of unit; basal and upper contacts sharp and irregular; fossils: brachiopods, bryozoans, crinoids, corals (Rugosans), and foraminifera. Sampled intervals: SKT- (m.) 41 (base), 42 (1.65) 8 2.2 71.4 Grainstone, including coated grains and crinoids, and fossil hash; very light grey (N8), weathers pinkish grey (SYR 8/1); very recrystallized; thin bedded; basal contact sharp and irregular, gradational with over- lying unit; fossils: brachiopods. 191 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description crinoids, foraminifera. Sampled interval: SKT- (m.) 43 (1.0) 17.2 88.6 Fenestrate bryozoan-crinoidal pack/ grainstone; grading upward to a grainstone, poorly sorted coated grains; very light grey (N8) with occasional light grey (N6) zones, weathers greyish orange pink (SYR 7/2); thin bedded; basal contact sharp, gradational with overlying oolitic grainstone; light and dark zonation is due to areas of greater (lighter) and lesser (darker) re crystallization; fossil preserva tion better in darker zones; fossils include brachiopods, bryozoans, corals, crinoids and foraminifera. Sampled intervals: SKT- (m.) 44 (1.0), 45 (4.0), 46 (4.1), 47 (8.0), 192 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description 48 (12.0), 49 (17.0) 10 2.1 90.7 Oolitic grainstone, moderately well sorted, very light grey (N8). weathers light grey (N7); gradational contact with over- and underlying units; friable; fossils include brachiopods, bryozoans, corals, crinoids, and foraminifera. Sampled interval: SKT- (m.) 49 (1.0) [w/i oolitic grainstone], 50 (2.0) [top of unit]. 11 11 1.3 92.0 Bioclastic packstone, very light grey (N8), weathers greyish brown (SYR 7/4) underlying contact grada tional with oolitic grainstone, upper contact sharp and irregular; deeply weathered surface; abundant crinoid, rugosan, and fossil hash. Sampled interval: SKT- (m.) 51 (.7) 193 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description 12 .6 92.6 Bioclastic wackestone (?), greyish brown (SYR 7/4), weathers pale reddish orange (10YR 6/4); both upper and lower contacts sharp and irregular; very recrystal lized. Sampled interval: SKT- (m.) 52 (.3) 13 3.7 96.3 Grainstone, including coated grains and oolites, light grey (N7), weathers greyish orange pink (SYR 7/2); both upper and lower contacts sharp and irregu lar; deeply weathered; gradational to a bioclastic grainstone toward top of unit; fossils: bryozoans, crinoids, foraminifera, and litho- clasts. Sampled intervals: SKT- (m.) S3 (0.23), 54 (3.5) 194 Lithologic Thickness [m] Unit No. Unit Cumulative . Field Description 14 .5 96.8 Dolestone, light brownish grey (SYR 6/1)r weathers light brownish grey (SYR 6/1); medium crystalline; both upper and lower contacts sharp and irregular; moldic porosity, molds of arenitic/ruditic-sized brachiopods and fossil hash; very dark grey zone 5 to 8 an. below upper contact. Sampled interval: SKT- (m.) 55 (.3) 15 2.4 97.3 Coated grain packstone, very light grey (N8), weathers greying orange pink (SYR 7/2); basal and upper contacts sharp and irregular; ellip soidal sparite-filled vugs between this and overlying unit; fossil mold cavities sparite; fossils: brachiopods, cryozoans, crinoids, lithoclasts, oolites. Sampled interval: SKT- (m.) 56 (.15) 195 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description 16 2.4 99.7 Bioclastic wackestone (?), pale brown (SYR 5/2) , weathers pale brown (5YR6/2); partially dolomitized; basal contact sharp, upper contact sharp; variable bedding thickness, thin to thick bedded; very recrys tallized; sparite-filled vugs (50-60 an., long axis; 10 to 15 cm., short axis); moldic porosity; fossils: fossil hash, sponge spicules and crinoid debris dominate. Sampled interval: SKT- (m.) 57 (2.1) 17 3.6 103.3 Pelletiferous packstone, pinkish grey (SYR 8/1), weathers greyish orange (SYR 7/2); grades to a grain- stone toward top of unit; basal and upper contacts sharp; thin bedded; fossils include algae, brachiopods, bryozoans, whole rugosan corals. crinoids, foraminifera, lithoclasts 196 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description and pellets. Sampled intervals: SKT- (m.) 58 (.55), 59 (1.4), 60 (3.3) 18 28.7 132.0 Grainstone, poorly sorted includ ing pellets, coated grains, and oolites, very light grey (N8) to pinkish grey (SYR 8/1), weathers brownish orange (SYR 8/1), black patina on sane weathered surfaces? basal and upper contacts sharp, zone of intense solutioning forms upper contact; thin to thick bedding; most bioclasts are broken; top of unit and of Mooney Falls taken at chert horizon; fossils: brachiopods, bryozoans, crinoids, foraminifera, lithoclasts, oolites, pellets, and worm tubes. Sampled intervals: SKT- (m.) 62 (.5), 63 (4.0), 64 (8.0), 65 (12.0), 66 197 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description (16.0) , 67 (20.0), 68 (24.0), 69 (28.0) , 70 (28.7) Horseshoe Mesa Member 19 6.4 138.4 Oolitic grainstone, pinkish grey (SYR 8/1), weathers brownish orange (10R 6/4); lower and upper contacts sharp, basal contact at top of last Mooney Falls chert; upper contact at solution seam filled with greyish red (10R 4/2) calclu- tite; thick bedded; large unbroken brachiopod valves .65 m. from base; fossils: brachiopods, crinoids, foraminifera, lithoclasts, oolites, and pellets. Sampled intervals: SKT- (m.) 71 (.65), 72 (1.8), 73 (3.6), 74 (6.1) 198 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description 20 .4 138.8 Siltstone, very light grey (N8), stained greyish red (10R 4/2) fills solution seam; contacts sharp, forms prominent notch; very thinly bedded, irregularly bedded; weathers shaly; laterally grades into sparite nodules. Sampled interval: SKT- (m.) 75 (.2) 21 9.7 148.5 Grainstone, including coated grains and pellets, light brownish grey (SYR 6/1), weathers brownish orange (10R 6/4); grades into a packstone at top of unit; upper and lower contacts sharp; thin to thick bedded; solution seam 5.0 m. from base, approximately 15 cm. thick, lime clasts (1.0-2.5 on) included in solution breccia: brachiopods, crinoids, foraminifera, litho- clasts, and pellets. 199 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description Sampled intervals: SKT- (m.) 76 (.9), 77 (4.0), 78 (9.0) 22 7.0 155.5 Pellitiferous packstone, including coated grains, with intercalated chert layers; unit locally grades into a bioclastic wackestone and to a pellitiferous grainstone; limestones are medium grey to pinking grey (N5), (SYR 8/1), weathers brownish orange (10R 6/4) to pale red (5R 6/2); cherts are pinkish grey (SYR 8/1) with medium grey (N5) centers - best developed in lowest chert horizon; contacts sharp; thin bedded; chert forms irregularly bedded layers and nodules; last chert nodule at 7.0 m.; some beds very recrystallized; fossils include alage, brachiopods, crinoids. foraminifera, gastropods, ostracodes, 200 Lithologic Thickness [m] Unit No. Unit Cumulative Field Description oolites, and pellets. Sampled intervals: SKT- (m.) 79 (basal chert), 80 (.3), 81 (3.0), 82 (6.0) TOTAL REDWALL LIMESTONE: 155.5 m. APPENDIX B 201 MODIFIED CLASTICITY INDICES The maximum diameter of the ten largest allochems observed in thin section was measured to obtain a modified elasticity index for the sampled interval. It should be noted that the elasticity index (Carozzi; 1950, 1958) measures the maximum particle size and not the degree of winnowing, which is more characteristic of the water energy. The following chart lists the mean particle diameter of the 10 largest allochems, their standard deviation, and the maximum diameter of the largest particle. The maximum particle diameters for Whitmore Wash sediments are based on mold measurements. Thus any conclusions based upon Whitmore Wash mold measurements must be considered bearing in mind the attendant problems associated with such measurements. SKT- MEAN [rrm.] S.D. [mm.] MAX. [mm.] Whitmore Wash Member 13 .30 .09 .44 14 .35 .24 .94 15 .48 .11 .70 16 .95 .40 1.66 17 . ,94 .64 2.25 18 1.71 .50 2.31 19 1.22 .64 2.90 22 1.00 .35 1.25 202 203 SKT- MEAN [ittn. ] S.D. [mm.] MAX. [ran.] 23 1.92 .56 2.98 25 2.20 .94 4.46 27 2.05 .75 3.60 28 1.76 1.52 4.35 29 1.76 1.01 3.9 Thunder Springs Member 30 .85 .61 1.92 31 .90 .55 1.78 33 1.50 .60 2.55 37 .60 .86 3.15 34 3.20 .45 3.90 35 2.50 1.20 4.20 36 1.60 1.00 3.75 38 2.00 .40 2.55 Mooney Falls Member 39 2.20 .50 3.00 40 1.79 .72 2.40 41 2.25 .67 3.60 42 2.01 .30 2.40 43 2.27 .92 4.35 204 SKT- MEAN [mm.] S.D. [mm.] MAX. [mm.] 44 1.91 .70 3.25 45 2.56 1.47 6.00 46 1.06 .33 1.50 47 1.45 .72 2.19 48 .79 .25 1.20 49 2.03 .50 3.00 49A 2.26 .68 3.78 50 . 2.61 1.98 6.52 51 1.26 .24 1.65 52 1.97 .71 3.30 53 1.84 .35 2.40 54 2.26 .66 3.09 55 .88 .62 2.55 56 2.10 .72 3.00 59 3.10 2.06 7.95 62 1.78 .44 2.64 63 2.35 .76 3.63 64 2.21 .53 3.60 66 1.89 .50 2.70 68 2.16 1.22 4.80 69 1.51 .31 2.10 70 .96 .30 2.31 205 SKT- MEAN [mm. ] S.D. [mm.] MAX. [mm.] Horseshoe Mesa Member 71 1.77 .97 4.23 2.85 76 1.38 .70 79 1.06 .42 1.65 1.08 80 .73 .20 81 1.66 1.31 4.65 3.06 82 1.18 73 APPENDIX C 206 STRATIGRAPHIC SECTION REFERENCES Elko-Carlin Brew, D. A. (1971) Mississippian stratigraphy of the Diamond Peak area, Eureka County, Nevada; with a section on the biostratigraphy and age of the Carboniferous formations by MacKenzie Gordon, Jr.: U.S. Geol. Survey Prof. Pap. 661, 84 p. Dott, R. H., Jr. (1955) Pennsylvanian stratigraphy of Elko and northern Diamond Ranges, northeastern Nevada: Amer. Assoc. Petrol. Geol. Bull., vol. 39, no. 11, pp. 211-2305. Fagan, J. J. (1962) Carboniferous cherts, turbidites, and volcanic rocks in northern Independence Range, Nevada: Geol. Soc. Amer. Bull., vol. 73, no. 5, pp. 595-612. Ketner, K. B., and Smith, J. F., Jr. (1963) Geology of the Railroad mining district, Elko County, Nevada: U.S. Geol. Survey Bull. 1162-B. Roberts, R. J., Hotz, P. E., Gilluly, J., and Ferguson, H. G. (1958) Paleozoic rocks of north-central Nevada: Amer. Assoc. Petrol. Geol. Bull., vol. 42, no. 12, pp. 2813-2857. Smith, J. R., Jr., and Ketner,.K. B. (1975) Stratigraphy of Paleozoic rocks in the Carlin-Pinon Range area: U.S. Geol. Survey Prof. Pap. 867-A. Diamond Peak Area Brew, D. A. (1961) Lithologic character of the Diamond Peak Formation (Mississippian) at the type locality. Eureka and White Pine Counties, Nevada: U.S. Geol. Survey Prof. Pap. 424-C, Art. 191, pp. C113-C115. ______. (1971) Mississippian stratigraphy of the Diamond Peak area. Eureka County, Nevada; with a section on the biostratigraphy and age of the Carboniferous formations by MacKenzie Gordon, Jr.: U.S. Geol. Survey Prof. Pap. 661, 84 p. Nolan, T. B., Merriam, C. W., and Williams, J. S. (1956) The stratigra phic section in the vicinity of Eureka, Nevada: U.S. Geol. Survey Prof. Pap. 276. 207 208 Stewart, J. H. (1962) Variable facies of the Chainman Shale and Diamond Peak Formations in western White Pine County, Nevada, In Geological survey research 1962: U.S. Geol. Survey Prof. Pap. 450-C, pp. C57-C60. Ely Chilingar, G. V., and Bissell, H. J. (1957) Mississippian Joana Limestone of Cordilleran miogeosyncline and use of Ca/Mg ratio in correlation: Amer. Assoc. Petrol. Geol. Bull., vol. 41, no. 10, pp. 2257-2274. Langenheim, R. L., Jr. (1960a) Early and Middle Mississippian stratigraphy of the Ely area. In Guidebook to the geology of east-central Nevada: Interratn. Assoc. Petrol. Geol. and Eastern Nevada Geol. Soc., 11th Annual Field Conf., pp. 72-80. ______. (1961) The Pilot Shale, the West Range Limestone, and the Devonian-Mississippian boundary in eastern Nevada: Illinois Acad. Sci. Trans. 1960, vol. 53, nos. 3-4, pp. 122- 131. Langenheim, R. L., Jr., Barr, F. T., Shank, S. E., Stensaas, L. J., and Wilson, E. C. (I960) Preliminary report on the geology of the Ely No. 3 quadrangle. White Pine County, Nevada, In Guide book to the geology of east-central Nevada: Intermtn. Assoc. Petrol. Geol. and Eastern Nevada Geol. Soc., 11th Annual Field Conf., pp. 30-41. Spencer, A. C. (1917) The geology and ore deposits of Ely, Nevada: U.S. Geol. Survey Prof. Pap. 96, 189 p. Stensaas, L. J., and Langenheim, R. L., Jr. (1960) Rugose corals from the lower Mississippian Joana Limestone of Nevada: Jour. Paleont., vol. 34, no. 1, pp. 179-188. South Egan Range Gutschick, R. C., and Rodriguez, J. (1979) Biostratigraphy of the Pilot Shale (Devonian-Mississippian) and contemporaneous strata in Utah, Nevada, and Montana: Brigham Young Univ. Geology Studies, vol. 26, pt. 1, pp. 37-63. 209 Kellogg, H. E. (1960) Geology of the southern Egan Range, Nevada, In Guidebook to the geology of east-central Nevada: Intermtn. Assoc. Petrol. Geol. and Eastern Nevada Geol. Soc., 11th Annual Field Conf., pp. 189-197. ______. (1963) Paleozoic stratigraphy of the southern Egan Range, Nevada: Geol. Soc. Amer. Bull., vol. 74, no. 6, pp. 685-708. Langenheim, R. L., Jr. (1960a) Early and Middle Mississippian stra tigraphy of the Ely area. In Guidebook to the geology of east- central Nevada: Intermtn. Assoc. Petrol. Geol. and Eastern Nevada Geol. Soc., 11th Annual Field Conf., pp. 72-80. ______. (1961) The Pilot Shale, the West Range Limestone, and the Devonian-Mississippian boundary in eastern Nevada: Illinois Acad. Sci. Trans., vol. 53, nos. 3-4, pp. 122-131. Langenheim, R. L., Jr., Barr, F. T., Shank, S. E., Stensaas, L. J., and Wilson, E. C. (I960) Preliminary report on the geology of the Ely No. 3 quadrangle. White Pine County, Nevada, In Guide book to the geology of east-central Nevada: Intermtn. Assoc. Petrol. Geol. and Eastern Nevada Geol. Soc., 11th Annual Field Conf., pp. 30-41. Reso, A. (1963) Composite columnar section of exposed Paleozoic and Cenozoic rocks in the Pahranagat Range, Lincoln County, Nevada: Geol. Soc. Amer. Bull., vol. 74, no. 7, pp.901-918. Arrow Canyon Range Langenheim, R. L., Jr. (1961) The Pilot Shale, the West Range Lime stone, and the Devonian-Mississippian boundary in eastern Nevada: Illinois Acad. Sci. Trans. 1960, vol. 53, nos. 3-4, pp. 122-131. Langenheim, R. L., Jr., Carss, W. B., Kennerly, J. B., McCutcheon, V. A., and Waines, R. H. (1962) Paleozoic section in Arrow Canyon Range, Clark County, Nevada: Amer. Assoc. Petrol. Geol. Bull., vol. 46, no. 5, pp. 592-609. Langenheim, R. L., Jr., and Collinson, C. W. (1963) Upper Devonian Crystal Pass Limestone of southern Nevada [abstr.]: Geol. Soc. Amer. Spec. Paper 73, p. 45. Longwell, C. R. (1928) Geology of the Muddy Mountains, Nevada: U.S. Geol. Survey Bull. 798. 210 Pierce, R. W., and Langenheim, R. L., Jr. (1972) Mississippian (Tournasian-Visean) conodont zones in the Great Basin, southwestern U.S.A.: Newsletters on Stratigraphy, vol. 2, pp. 31-44. Webster, G. D. (1969) Chester through Derry conodonts and stratigraphy of northern Clark Counties, Nevada: Univ. of Calif. Pub. in Geol. Sci., vol. 79, 121 p. Webster, G. D., and Langenheim. R. L., Jr. (1979) Stop descriptions- seventh day: Clark County, Nevada, In Carboniferous stratigraphy in the Grand Canyon country, northern Arizona and southern Nevada: Guidebook for the 9th International Congress of Carboniferous Stratigraphy Field Trip No. 13, pp. 73-80. Frenchman Mountain Brenkle, P. L. (1973) Smaller Mississippian and Lower Pennsylvanian calcareous foraminifera from Nevada: Cushman Found. Foram. Res. Spec. Publ. No. 11, 82 p. Langenheim, R. L., Jr., Carss, W. B., Kennerly, J. B., McCutcheon, V. A., and Waines, R. H. (1962) Paleozoic section in Arrow Canyon Range, Clark County, Nevada: Amer. Assoc. Petrol. Geol. Bull., vol. 46, no. 5, pp. 592-609. Webster, G. D., and Langenheim. R. L., Jr. (1979) Stop descriptions- sixth day: Clark County, Nevada, In Carboniferous stratigraphy in the Grand Canyon country, northern Arizona and southern Nevada: Guidebook for the 9th International Congress of Carboniferous Stratigraphy Field Trip No. 13, pp. 73-80. Longwell, C. R. (1960) Possible explanation for diverse structural patterns in southern Nevada: Amer. Jour. Sci., vol. 258-A, pp. 192-203. Mamet, B. L., and Skipp, B. (1970) Lower Carboniferous calcareous foraminifera: Preliminary zonation and stratigraphic implications for the Mississippian of North America: Compte Rendu fe Congres. In tern. Strat. Geol. Carbonif., Sheffield, 1967, vol. Ill, pp. 1129- 1146. Pierce, R. W., and Langenheim, R. L., Jr. (1972) Mississippian (Tournasian-Visean) conodont zones in the Great Basin, southwestern U.S.A.: Newsletters on Stratigraphy, vol. 2, pp. 31-44. 211 Webster, G. D. (1969) Chester through Derry conodonts and stratigraphy of northern Clark Counties, Nevada: Dniv. of Calif. Pub. in Geol. Sci., vol. 79, 121 p. Iceberg Canyon - South Kaibab Trail Mamet, B. L., and Skipp, B. (1970) Lower Carboniferous calcareous foraminifera: Preliminary zonation and stratigraphic implications for the Mississippian of North America: Compte Rendu fe Congres. In tern. Strat. Geol. Carbonif., Sheffield, 1967, vol. Ill, pp. 1129- 1146. McKee, E. D. (1958) The Redwall Limestone, In Guidebook of the Black Mesa Basin, northeastern Arizona: New Mexico Geol. Soc. 9th Field Conf., pp. 74-77. (1960) Lithologic subdivisions of the Redwall Limestone in northern Airzona - their paleogeographic and economic signifi cance: U.S. Geol. Survey Prof. Pap. 400-B, pp. B243-B245. ______. (1963) Nomenclature for lithologic subdivisions of the Redwall Limestone, Arizona, In Geological survey research, 1963: U.S. Geol. Survey Prof. Pap. 475-C, pp. C21-C22. McKee, E. D., and Gutschick, R. C. (1969) History of the Redwall Limestone of northern Arizona: Geol. Soc. Amer. Mem. 114, 726 p. McNair, A. H. (1951) Paleozoic stratigraphy of part of northwestern Arizona: Amer. Assoc. Petrol. Geol. Bull., vol. 35, no. 3, pp. 503-541. ______. (1952) Summary of the pre-Coconino stratigraphy of southwestern Utah, northwestern Arizona and southeastern Nevada: Utah Geol. Soc. Guidebk. to the Geology of Utah, No. 7, pp. 45-51. Purves, W. J. (1978) Paleoenvironmental evaluation of Mississippian age carbonate rocks in central and southeastern Arizona: Ph.D. Diss., University of Arizona, Tucson, Arizona, 672 p. Racey, J. S. (1974) Conodont biostratigraphy of the Redwall Limestone of east-central Arizona: M.S. Thesis, Arizona State University, Tempe, Arizona, 119 p. 212 Zeller, E. J. (1957) Mississippian endothyrid foraminifera from the Cordilleran geosyncline: Jour. Paleont., vol. 31, pp. 679-704. APPENDIX D 213 GENERAL ANALYTICAL SOLUTIONS FOR BASIN SUBSIDENCE Basement subsidence was obtained by two-dimensional finite difference modeling modified from Jordan (1981). The equations used were derived from Hetenyi (1946), who analyzed deflections of beams under loads of different configurations. The results used here, and in Sylvia and A m i n (1984), are from analytical solutions and are thus non-unique. However, because the parameters are reasonably constrained, they are plausible estimates. The general analytical solutions are given by: for a sheet load; and (exp - x (co-6 x *■ -i - Ain — ■-*--1)) ], for a wedge-shaped load. where a = ( -|p- ) 214 ( 215 a = Characteristic length determined by flexural rigidity and material filling basin X) = Flexural rigidity of the lithosphere = Vertical deflection = Specific gravity term for the applied load P = Difference between specific gravity of asthenosphere and 2 material infilling basin 9 = Gravity constant h = Height of load x = Distance of subsiding point from applied load Xj = Distance along width of prism load The predicted topography represents the summed total of the isostatic response to all load elements for each time slice. The contribution of the load elements may be either positive or negative at a given point, due to the lithosphere's harmonic response to applied forces. APPENDIX E 216 Ma 330 Diamond Peak Formation Chainman Shale Elko - Carlin Section Webb Fm. 3.0- Geohistory Diagram hJ 3 Chainman Shale - Joana Times tone Geohistory Diagram 330 Hamilton Canyon Formation Chainman Shale Peers Spring Formation Upper a o c 8 Middle E Lower ^ Pilot Shale \ Geohistory Diagram 219 Spotty Wash Quartzite Hamilton Canyon Formation Chainman Shale __ __ Peers Spring Formation __ 1,0 - Joana Limestone South Egan Range Section 1.5- Geohistory Diagram Mo Scotty Wash Quartzite Hamilton Canyon Formation Chainman Shale __ Peers Spring Formation Joana Limestone Pahranagat Section Upper Pilot Shale Geo history Diagram 30 i Battleship Wash Formation __ Yellowpine o. Limestone o . o Bullion S Limestone z u . ----- — < u Anchor Ls. % - — — 2 Dawn Ls. Crystal Pass Limestone Geohistory Diagram 222 Ma 360 350 340 330 Indian Springs Formation Yellowpine & 3 Bullion ^ 0.25 — Limestones (undifferentiated) Anchor Ls.. 0.50- Dawn Ls. Frenchman Mountain Section 0.75- Geohistory Diagram 223 >v v\ 340 3 3 0 Horseshoe Mesa Member 0.1- Mooney Falls Member 0.2 - Thunder Springs Redwall Limestone Member Whitmore Wash 0.3 - Member Geohistory Diagram So Horseshoe Mesa Member Mooney Falls Member Thunder Springs Member Whitmore Wash Member Geohistory Diagram 340 3 3 0 Horseshoe Mesa Member Mooney Falls Member Redwall Limestone Thunder Springs Member __ Whitmore Wash Member Geohistory Diagram 226 XH' 340 3 3 0 __L_ Horseshoe Mesa Member Mooney Falls Member Thunder Springs Redwali Limestone Member Whitmore Wash Member Whitmore Wash Section Geohistory Diagram 227 Ma 360 350 340 330 Horseshoe Mesa Member Mooney Falls Member Thunder Springs Member Whitmore Wash Member Geohistory Diagram 228 340 330 Horseshoe Mesa Member Mooney Falls Member Thunder Springs Member Whitmore Wash Redwall Limestone Member 0 . 3 - South Kaibab Trail Section \ Geohistory Diagram 229 I LIST OF REFERENCES Alexandersson, T. (1972) Carbonate sedimentation in coralline algal nodules in Skagerrack, North Sea: Jour. Sed. Petrol., vol. 42, pp. 441-460. Anderson, E. J., Goodwin, P. W . , and Sobieski. (1984) Episodic accumu lation and the origin of formation boundaries in the Helderberg Group of New York State: Geology, vol. 12, no. 2, pp. 120-123. Anderson, R. E. (1971) Thin-skinned distension in Tertiary rocks of southeastern Nevada: Geol. Soc. Amer. Bull., vol. 82, pp. 43-58. Armin, R. A., and Mayer, L. (1983a) Quantitative basin analysis: Pascal computer program for Laboratory of Geotectonics: Geo science Department, University of Arizona, Tucson, Arizona, 12 p. ______. (1983b) Subsidence analysis of the Cordilleran miogeo- cline: Implications for timing of late Proterozoic rifting and amount of extension: Geology, vol. 11, pp. 702-705. Armstrong, R. L., Taubeneck, W. H., and Hales, P. 0. (1977) Rb-Sr and K-Ar geochronometry of Mesozoic granitic rocks and their Sr isotopic composition, Oregon, Washington, and Idaho: Geol. Soc. Amer. Bull., vol. 88, pp. 397-441. Baars, D. L. (1966) Pre-Pennsylvanian stratigraphy and paleotectonics of the San Juan Mountains, southwestern Colorado: Geol. Soc. Amer. Bull., vol. 79, pp. 333-349. Back, W., and Hanshaw, B.B. (1970) Comparison of chemical hydrogeology of the carbonate peninsulas of Florida and Yucatan: Amer. Jour. Sci., vol. 264, pp. 1-36. Badiozamani, K. (1973) The Dorag dolomitization model - application to the Middle Ordovician of Wisconsin: Jour. Sed. Petrol., vol. 43, pp. 965-984. 230 231 Bambach, R. K., Scotese, C. R., and Ziegler, A. M. (1980) Before Pangea: The geographies of the Paleozoic world: Amer. Sci., vol. 68, no. 1, pp. 26-38. Bathurst, R. G. C. (1966) Boring algae, micritic envelopes and lithification of molluscan biosparites: Geol. Jour., vol. 5, pp. 15-32. ______. 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