UNLV Retrospective Theses & Dissertations

1-1-1997

Sequence stratigraphy, sedimentology, and correlation of the undifferentiated Cambrian dolomites of the Grand Canyon and Lake Mead area

Viacheslav Sergeevich Korolev University of Nevada, Las Vegas

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Repository Citation Korolev, Viacheslav Sergeevich, "Sequence stratigraphy, sedimentology, and correlation of the undifferentiated Cambrian dolomites of the Grand Canyon and Lake Mead area" (1997). UNLV Retrospective Theses & Dissertations. 3332. http://dx.doi.org/10.25669/rlc2-a4bm

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SEQUENCE STRATIGRAPHY, SEDIMENTOLOGY, AND

CORRELATION OF THE UNDIFFERENTIATED CAMBRIAN

DOLOMITES OF THE GRAND CANYON AND LAKE MEAD AREA

by

Viacheslav S. Korolev

A thesis submitted in. partial fulfillment of the requirements for the degree of

Master of Science

in

Geoscience

Department of Geoscience University of Nevada, Las Vegas

August, 1997

______

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1387137

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Thesis of Viacheslav S. Korolev for the degree of Master of Science in Geology is approved.

Vdi--- — Chafrpersc^I, Stephezfhx M. Rowland, Ph.D.

Examining Committee Member, Frederick Bachhuber, Ph.D.

Examining Committee Member, David L. Weide, Ph.D.

Graduate Faculty Representative, Robert M. Winokur, Ph.D.

Dean of the Graduate College, Ronald W. Smith, Ph.D.

University of Nevada, Las Vegas July 1997

11

_____

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT

In the Grand Canyon and Lake Mead areas of Nevada, Arizona and Utah, there is a light-colored dolomite succession that conformably overlies the Cambrian Muav Limestone; McKee (1945) referred to these rocks as undifferentiated Cambrian dolomites, and their age and correlation have remained uncertain. Seven stratigraphie sections were studied, including those at Quartermaster Canyon, Mile-269 Canyon, Diamond Bar Ranch, Devil's Cove, Tramp Ridge, Whitney Ridge, and Frenchman Mountain. The thickness of the undifferentiated dolomites increases to the west from 78 meters at Diamond Bar Ranch to 371 meters at Frenchman Mountain. In the Grand Canyon area, the undifferentiated dolomites are unconformably overlain by Devonian rocks, while in craton-meirgin sections the undifferentiated dolomites are conformeibly overlain by the Upper Cambricin Nopah Formation. Within the undifferentiated dolomites eight depos itional facies were established: (1) burrow-mottled facies; (2) flat-pebble grainstone facies ; (3) stromatolite facies; (4) oolitic-grainstone facies ; (5) bioclastic- grainstone facies; (6) ribbon-rock facies ; (7) nodular facies; and (8) laminite facies. The depos itional environment represented by each facies was established.

iii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I identified seven depositional sequences within the undifferentiated dolomite succession. Each sequence is represented by an upward-shallowing succession of facies that is bounded at the top by a zone of maximum exposure and very commonly by an unconformity. The undifferentiated dolomite succession was subdivided into two lithologically distinct units. On the basis of lithostratigraphy and sequence stratigraphy, these two units were correlated between the sections examined in this study, and they are coitpared with several sections in the Basin and Range Province and the Lake Mead area that were described by Gans (1974) and Montaflez and Osleger (1993, 1996). I have correlated the undifferentiated dolomites (together with the upper three members of the Muav Limestone) with the Banded Mountain Member of the Bonanza King Formation and the upper part of the Emigrant Formation in the Basin and Range Province. The undifferentiated dolomites correspond to a biostratigraphically well defined Cambrian interval in the Basin and Range Province that contains the Bolasoidella, Cedaria. and Crepiceohalus trilobite zones. The overlying Nopah Formation contains the Aphelaspis biozone. Therefore, the undifferentiated dolomites sure Middle-Upper Cambrian in age. In the Grand Canyon, only the lower part of the

IV

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. undifferentiated dolomites survived pre-Devonian erosion and is assumed to be entirely Middle Cambrian. Following recommendations of the North American Commission on Stratigraphie Nomenclature (1983) and the International Subcommission on Stratigraphie Classification (1987) , I suggest the formal name "Frenchman Mountain Dolomite" for the rock unit previously referred to as the undifferentiated dolomites.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

ABSTRACT...... iii LIST OF FIGURES...... viii ACKNOWLEDGEMENTS...... xi CHARTER 1 INTRODUCTION...... 1 1.1. Purpose of the Study...... 1 1.2. Brief Review of Previous Reseeurch...... 4 1.3. Study Area and Location of Measured Sections..... 9 1.4. Methods of Study...... 13 1.5. The Problem of Defining the Middle -Upper Cambrian boundary...... 14 1.6. General Geology...... 16 CHAPTER 2 REGIONAL STRATIGRAPHIC RELATIONSHIPS...... 19 2.1. Introduction...... 19 2.2. Regional Stratigraphie and Lithologie Correlation...... 22 2.3. Biostratigraphy...... 42 CHAPTER 3 SEDIMENTOLOGY...... 45 3.1. Introduction...... 45 3.2. Lithofacies...... 45 3.2.1. Burrow-mottled facies...... 47 3.2.2. Flat-pebble grains tone facies...... 58 3.2.3. Stromatolite facies...... 60 3.2.4. Oolitic grains tone facies...... 68 3.2.5. Bioclastic grains tone facies...... 73 3.2.6. Ribbon rock facies...... 74 3.2.7. Nodular facies...... 78 3.2.8. Laminite facies...... 80 CHAPTER 4 SEQUENCE STRATIGRAPHY...... 86 4.1. Introduction...... 86 4.2. Peritidal and Subtidal Cycles Within the Undifferentiated Dolomites...... 92 4.3. Third-Order Depositional Sequences and Sequence Boundauries...... 100 4.4. Brief Comparison with the Work of Montaüez and Osleger (1993, 1996)...... 113 4.5. Conclusion ...... 119 CHAPTER 5 AGE OF THE UNDIFFERENTIATED DOLOMITES...... 121 CHAPTER 6 FRENCHMAN MOUNTAIN DOLOMITE...... 123

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 7 SUMMARY AND CONCLUSION...... 129 REFERENCES...... 13 5 APPENDIX A: MAPS AND LOCATIONS...... 148 APPENDIX B: MEASURED STRATIGRAPHIC SECTIONS...... 155 Frenchman Mountain...... 155 Whitney Ridge...... 150 Tramp Ridge...... 164 Devil ' s Cove...... 17 0 Diamond Baur Ran c h ...... 173 Mile-269 Cemyon...... 175 Quaurtermaster Canyon...... 177

Vll

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

1. Regional relationships of Cambrian undifferentiated dolomites to overlying and underlying s trata...... 5 2. Nomenclature previously used and suggested in this study for Muav Limestone and undifferentiated dolomites...... 7 3. Map of the research area...... 11 4. Biozonation scale for Middle-Upper Cambrian of North America...... 15 5. Correlation of sections in the Grand Canyon with those in the Basin and Range Province...... 20 6. Correlation chart of undifferentiated dolomites...... 23 7. Chert nodules and silicifled stromatolites at the base of Unit I, Quartermaster Canyon...... 28 8. Cross-stratified beds. Unit I, Quartermaster Canyon 31 9. Rose diagram showing bimodal distribution of cross-stratified beds measured at Unit II of Quartermaster Canyon...... 32 10. Cambrian-Devonian stratigraphie unconformity (Devil's Cove section)...... 34 11. Cambrian-Devonicin stratigraphie unconformity (Mile-269 section)...... 34 12. Generalized stratigraphie column of Banded Mountain Member of the Bonanza King Formation showing informal units of Gans (1974)...... 40 13. Schematic correlation chart of the Banded Mountain Mbr., Bonanza King Formation and undifferentiated dolomites...... 41 14. Lithofacies established for the undifferentiated dolomites, their stratigraphie distribution, and interpreted depositional environment...... 46 15. Burrow-mottled facies. Subfacies la. Unit I, Frenchman Mountain...... 50

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16. Burrow-mottled facies. Subfacies lb. Unit I, Diamond Bar Ranch...... 51 17. Burrow-mo 11 led facies. Sub facies Ic, Unit I, Frenchman Mountain...... 53 18. Peloidal wackestone. Unit I, Frenchman Mountain...... 55 19. Flat-pebble grains tone facies. Intraclas tic-grains tone layer. Unit I, Frenchman Mountain...... 59 20. Stromatolite facies (subfacies 3a). Large, partly silicified SH-stromatolite, Unit I, Whitney Ridge..... 62 21. Stromatolite facies (subfacies 3a, 3b) . Low-profile LLH- stromatolites superimposed on high-profile SH- stromatolites. Unit I, Whitney Ridge...... 62 22. Oolitic grains tone facies. Unit-1, Frenchman Mountain. .70 23. Oolitic grains tone facies. Finely-laminated flat pebbles and ooids. Unit I, Frenchman Mountain...... 70 24. Bioclastic grains tone facies. Large echinoderm plates. Unit II, Traitp Ridge...... 75 25. Bioclastic grainstone facies. Euhedral dolomite crystal, anhedral dolomite crystals, and glauconitic peloids, Unit II, Frenchman Mountain...... 75 26. Ribbon-rock facies. Unit I, Frenchman Mountain...... 76 27. Modular facies. Unit I, Frenchman Mountain...... 76 28. Modular facies. "Laddar back" structure. Unit I, FrenchiticUi Mountain...... 79 29. Laminite facies. Mechanical laminite. Unit I, Frenchman Mountain...... 79 30. Laminite facies. Cryptomicrobial laminite. Unit I, Mile-269 Canyon...... 83 31. "Thick" peritidal cycles. Unit I, Frenchman Mountain. ..94 32. "Thick" peritidal cycles. Unit I, Quartermas ter Camyon...... 96 33. "Thin" peritidal cycles. Unit I, Devil's Cove...... 98

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34. Major karst horizon at the base of Sequence 1, Frenchman Mountain...... 103 35. Incised valley fill deposits. Top of Sequence 5, Frenchman Mountain...... 110 36. Comparison with Montanez and Osleger's (1993) work....118

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

I would like to acknowledge my thesis committee members, Drs. Stephen M. Rowland, Frederick Bachhuber, David L. Weide, and Robert M. Winokur for their assistance and professional advice during the course of ray graduate studies and the preparation of my thesis. I want to extend special thanks to ray thesis advisor. Dr. Stephen M. Rowland, who proposed to me a very interesting research topic, inspired me to undertake the adventurous fieldwork in the Grand Canyon, and provided helpful guidance through all the stages of this research. This project especially benefitted from his extensive field experience and outstanding scientific discipline. Drs. Cathy Summa provided independent and critical points of view towards the many problems encountered during this study. Her advice was especially helpful in completion of the sedimentologic and sequence stratigraphie parts of this project. Drs. Isabel Montaflez and David Osleger critically reviewed the Sequence Stratigraphy chapter and provided their stratigraphie log for the Frenchman Mountain section. I appreciate the help of Nathan F. Stout, who drafted the map and some of the stratigraphie columns for this

XI

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. thesis. I also thank Dr. Alison R. Palmer for his advice during a field trip to the Whitney Ridge section. Field and laboratory equipment was kindly provided by the UNLV Department of Geoscience. Some of the equipment and field gear was provided by a grant from the UNLV Graduate Student Association and by Scroungers Scholarship from UNLV Geoscience Department. Finally, I would like to thank all my friends for their support, and most of all ray wife Lera for her love, patience and care which made it possible to complete this study.

XU

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 1

INTRODUCTION

1.1. Purpose of the Study

The Cambrian Tonto Group of the Grand Canyon region

is one of the most famous sedimentary succession in the

world. It is commonly presented in textbooks as an

example of a transgressive sequence, beginning with

nearshore coarse sandstones of the Tapeats Sandstone at

the bottom, overlain by distal finer-grained siliciclastic

rocks of the Bright Angel Shale, and capped by still more

distal carbonates of the Muav Limestone. The essential

features of the Tonto Group were outlined and described

over fifty years ago in a now classic paper by E. D. McKee

(1945) . McKee divided the Muav Limestone into several

members, aind he identified a thick (up to 13 0 m) , light-

colored dolomitic unit conformeibly overlying the Muav

Limestone. He excluded these dolomites from the Muav

Limestone and informally referred to them as "Cambrian

I

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 undifferentiated dolomites." The age of this dolomitic

unit was uncertain due to an absence of fossils. It was

presumed to be mostly Middle Cambrian but "...may include

Upper Cambrian and possibly Ordovician strata" (McKee,

1976, p. 52). Also, the correlation of the

undifferentiated dolomites between the Grand Canyon region

and the Basin and Range Province was problematic.

The age and correlation of these undifferentiated

and unnamed dolomites is important- for several reasons.

First, because these strata crop out in both the Basin and

Range Province and the Colorado Plateau, detailed

correlation of these dolomites between provinces and

within the Basin auid Rsinge Province will be helpful for

addressing structural problems in the Lake Mead region

(e.g. Rowland et al., 1990) . Second, aui understanding of

the age and depositional history of this interval will

contribute to our knowledge of the nature of the Cambrian

carbonate platform in western North America, which is

perhaps the best exposed and most frequently visited

Paleozoic carbonate platform in the world. Third,

■sedimentologic and stratigraphie aspects of these rocks

can contribute data for addressing fundamental problems of

sedimentary geology, such as the process of dolomitization

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 and the origin of cyclic sedimentation in carbonate rocks.

Finally, in spite of the fact that the Grand Canyon is

visited by hundreds of geologists and geology students

each year and is one of the most famous and intensively

studied geologic features on earth, these undifferentiated

dolomites have remained undated, uncorrelated, and unnamed

for over fifty years; the challenge of finally getting

these rocks sorted out is perhaps justification enough for

this study.

The objectives of this study are: (1) to determine

as precisely as possible the age of the "undifferentiated

dolomites ; " (2) to estaüolish the relationship between this

interval and underlying and overlying rocks; (3) to

subdivide this interval, using a variety of approaches ;

and (4) to correlate these deposits over a large area,

including parts of the Colorado Plateau and the Basin and

Range Province, using lithostratigraphy, biostratigraphy,

and sequence stratigraphy. Sequence stratigraphy is an

especially important and useful approach for correlation,

because, in the absence of fossils, traditional

stratigraphie methods do not work well on this dolomitic

interval of rock.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.2. Brief Review of Previous Research

McKee (1969) provided a summary of the history of

geologic investigation in the Grand Canyon. Here I review

research on Cambrian rocks of the Grand Canyon region, and

the area to the west, paying particular attention to the

"undifferentiated dolomites."

The first geologic investigation of the Grand Canyon

region took place in 19th century beginning with Marcou

(1856). Newberry (1861) described the Paleozoic

stratigraphy of the Grand Cauiyon region from exploration

of the Canyon itself and the land to the south. This work

was followed by the Western Reconnaissance Survey that

involved Marvine (1875), Gilbert (1875), Powell (1875),

Dutton (1882), cuid other geologists attracted by natural

features and the geological value of the Grand Canyon.

The term "Tonto Group" was first used by G. K.

Gilbert (1874) to describe the "classic" sandstone-shale-

limestone transgressive succession in the Grand Canyon

(Fig. 1).

Detailed studies of Cambrian strata began with

Walcott (1883). Noble (1914, 1922), working in the

central Grand Canyon, defined the Tonto Group and divided

it into the Tapeats Sandstone, the Bright Angel Shale,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Grand Canyon w / \ ______

Temple Butte Formation

Fig. 1. Schematic diagram showing regional relationships of Cambrian undifferentiated dolomites to overlying and underlying strata (modified from Beus, 1990).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 and Che Muav Limestone (Fig. 1). Noble (1922) described

the dolomitic strata above the Muav Limestone, exposed

between Garnet Canyon and Pipe Creek, referring to them as

"Division A" (Fig. 2). Longwell (1928) tentatively

correlated a sandstone-shale-1imestone succession at

Whitney Ridge in the Lake Mead area with the Tapeats

Sandstone, Bright Angel Shale, suid Muav Limestone of the

Grand Camyon region. Schenk and Wheeler (1942) were the

first to use Basin-and-Range nomenclature for the Cambrian

of the western Grand Canyon; they referred to the rock

interval comprising the undifferentiated dolomitic strata

as "Cambrian and post-Cambriam limestones and dolomites."

McKee (1945) divided the Muav Limestone into seven members

and used the informal name "Cambrian undifferentiated

dolomites" for Noble's (1922) "Division A," the uppermost

dolomitic succession at Bass Camyon. McKee (1945)

described the following three distinct types of dolomite :

1. White to buff, gramular, hard, massive dolomite.

2. White to yellow, aphamitic (porcelain-textured),

thin-bedded dolomite showing fine, irregular laminae on

weathered surfaces.

3. Steel-gray, fine-grained, thick-bedded dolomite

that weathers with olive, silty surfaces amd forms

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Schenk Gilbert Noble and McKee Wood Brathovde This 1 8 7 5 1922 Wheeler 1945 1956 1986 Study 1942 Cambrian (?) IV llndlffarantlatatf SUPRA Grand Frenchman DIVISION and Post- III Wash Mountain Oolomltaa MUAV A Cambrian II Oolofflita Dolomite Limestones 1 s and Dolomiles 1 w z Mead Limestone 1 fS 1 3 3 1PEASLEY I UMESTONE I 1 1 1 1 1

Fig. 2. Nomenclature previously used and suggested in this study for Muav Limestone and undifferentiated dolomites (modified from Brathovde, 1986) .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. resistant cliffs.

These three types are very different from the two

major types of dolomite (rusty-brown dolomite and mottled

dolomite) of the underlying strata of the Muav Limestone.

Wood (1956) used the informal term "Supra Muav" for

this same unit exposed at the Yampai Cliffs located south

of the Grand Canyon.

The most recent research on the undifferentiated

dolomites was a Northern Arizona University M.S. study by

Brathovde (1986), who proposed that this dolomite unit be

named the Grand Wash Dolomite. He measured several

sections in the Grand Canyon area, and he studied the

stratigraphy, paleontology, and sedimentology of this

unit. Brathovde described several facies and interpreted

their depositional environments, but he was not able to

determine the precise age of the undifferentiated

dolomites, nor did he correlate them with other

formations- Elston (1989) commented that according to the

rules of the Code q£. Stratigraphie Nomenclature (1983)

Brathovde's proposed name "Grand Wash Dolomite" cannot be

used because the name "Grand Wash" is already in use for a

different stratigraphie unit, the Grand Wash Basalt, in

the same area.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 Descriptions of Upper Cambrian sections from regions

adjacent to the Grand Canyon have been made by a number of

researchers, including Longwell et al. (1965), Morgan

(1968), Billingsley (1970), Moore (1972), Kepper (1972,

1976), Gans (1974), Matthews (1976), Steed (1979), and

Cooper et al. (1982).

Detailed stratigraphie and sedimentologic studies of

the Middle-to-Upper Cambrian Bonanza King Formation in the

Basin and Range Province were conducted by Palmer and

Hazzard (1956) , Gans (1974) , and Montanez and Osleger

(1993; 1996) . The latter papers, by Montanez and Osleger,

are important to the present study because they show that

the undifferentiated dolomite interval is correlative with

the upper part of the Banded Mountain Member of the

Bonanza King Formation. Montanez and Osleger (1993 ; 1996)

provide a sequence-stratigraphic framework for the Bonanza

King Formation that is extended in this study to the

undifferentiated dolomites.

1.3. Study Area and Location of Measured Sections

The study area is located on the eastern margin of

the Basin and Range Province and the westernmost part of

the Colorado Plateau, including the western Grand Canyon

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10 (Fig. 3). It extends for more than 300 km (240 miles),

from the Last Chance Range in the northwest to

Quartermaster Canyon in the southeast.

The undifferentiated dolomites are well exposed in

the western Grand Canyon where they form steep, prominent

cliffs above the Havasu Member of the Muav Limestone.

Immediately to the west of the Grand Canyon, they also are

represented by lithologically distinct rocks with

recognizable correlative patterns. Farther westward,

however, they gradually develop lithologie features common

to the Basin and Range Province and distinct from those of

the Colorado Plateau.

One of the major complications involved with the

study of these rocks is the extremely difficult access to

some of the sections, especially to those in the Grand

Canyon. Other complications are caused by structural

problems in the Basin and Range Province and variable

erosion that removed a significant part of the

undifferentiated dolomites and some overlying beds.

Sections measured in the Grand Canyon area, where

strike-slip faulting and low-auigle normal faulting have

not occurred, allow us to understand the stratigraphy and

facies changes of the undifferentiated dolomites in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I l

Lost Chance Range

\

Nopa Range

0 25 50 75 KILOMETERS

O 20 40 60 m il e s

Fig. 3. Map of research area. Solid triangles indicate locations of sections measured in this study and from other works. IR = Indian Ridge, DR = Desert Range, FM = Frenchman Mountain, WR = Whitney Ridge, DC = Devil's Cove, TR = Tramp Ridge, DB = Diamond Bar Ranch, 269 = Mile-269 Canyon, QM = Quartermaster Canyon.

.1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 different directions, from east to west and from south to

north.

Seven sections were measured during this study: (L)

Quartermaster Canyon, (2) Mile-269 Canyon, (3) Diamond Bar

Ranch, (4) Devil’s Cove, (5) Tramp Ridge, (6) Whitney

Ridge, and (7) Frenchman Mountain (Fig. 3).

At both Frenchman Mountain and Whitney Ridge, a

complete succession of undifferentiated dolomites is

preserved and is conformably overlain by the Ndpah

Formation. Containing trilobites of the Aphelaspis zone

in the lower part, the age of the Nopah Formation is

biostratigraphically well constrained and determined to be

earliest Late Cambrian. Also Frenchman Mountain is easily

accessible and highly referenced Cambrian section located

on the westernmost edge of the craton. In this work I

focus on the Frenchman Mountain section as a possible

holostratotype for a new formation (see chapter 6) .

In the other five locations, the Nopah Formation was

either not deposited or wascompletely removed by pre-

Middle Devonian erosion. Some of the sections measured in

this study had previously been measured by earlier

workers, including McKee (1945), Hardy (1986), Brathovde

(1986), and Montanez and Osleger (1993).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 The study area also includes some sections in the

Basin and Range Province described by Montanez and Osleger

(1993), including Indian Ridge, the Nopah Range, and the

Last Chance Range (Fig. 3). I collected samples from some

of these localities and studied them in hand-specimen and

thin-section.

1.4. Methods of Study

Fortunately, the stratigraphie sections in the Grand

Canyon area are almost perfectly horizontal and are

without significant structural complications. Lithologie

correlation of the sections was completed on the basis of

stratigraphie positions and distinct lithologies.

Pétrographie study of thin sections using a

polarizing microscope has clarified the depositional and

diagenetic environments and their lateral changes within

units. More than thirty thin sections from the most

lithologically distinct stratigraphie units were prepared

during this study, but systematie descriptions of these

thin sections are not included in this thesis.

Faunal characteristics of the undifferentiated

dolomites in the Grand Canyon area were not studied due to

the almost total absence of preserved fossils in this unit

Reproduced with permission ot the copyright owner. Further reproduction prohibited without permission. 14 (McKee, 1945; Brathovde, 1986; Middleton and Elliot, 1990;

Beus, 19 90). Fossil assemblages in strata of the same

stratigraphie level were documented in the Muddy Mountains

by Resser (1945) and in the Desert Range by Fenton (1980) .

Other fossil occurrences and problems of biostratigraphic

control are discussed in Chapter 2.

1.5. The Problem of Defining the Middle-Upper

Cambrian Boundary

Placement of the Middle-Cambrian / Upper-Cambrian

boundary within the undifferentiated dolomites is

problematic because the Middle-Upper Cambrian boundary is

not well defined in North America (Palmer, 1981; Ludvigsen

and Westrop, 1985).

Palmer and Hazzard (1956) and Palmer (1965) located

the Middle-Upper Cambrian boundary at the base of the

Cedaria zone. As shown in Fig. 4, Ludvigsen and Wes trop

(1985), having proposed the three new Upper Cambrian

stages for North America considered the Bolaspidella and

Cedaria zones to be Upper Cambrisui. However, this work

was criticized by many workers including Witzke (1985),

Longoria (1985), and Robison et al. (1985). Referring to

Ludvigsen and Westrop (1985), Brathovde (1986) placed the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15

PERIOD BIQZONE Saukia

Saratogia 1 m Taenicephalus

0 Dunderbergia or Elvinia q! a: Dunderbergia D Aphelaspis Middle-Upper Cambrian boundary Crepicephafus as proposed by Palmer (1981) (used in this study) Cedaria s Middle-Upper Cambrian boundary (0 as proposed by Palmer and Hazzard (1956), Bolaspidella Palmer (1965) (used in Monteriez and Osleger. 1994)

I Ehmaniella Middle-Upper Cambrian boundary o as proposed by Ludvigsen and Westrop (1985) (used by Brathoved, 1986) o Glossopleura "O 2 5 Alberteila-Mexicella

Plagiura-Poiiella

Fig. 4. Biozonation scale for Middle-Upper Cambrian of North America.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 Middle-Upper Cambrian boundary at the base of the

Bolaspidella zone. Montanez and Osleger (1993), having

referred to the earlier work by Palmer (1965) considered

the Middle-Upper Cambrian boundary to be at the base of

the Cedaria zone. In this study, I refer to Palmer (1981)

and consider the Crepicephalus zone to be the lowermost

Upper Cambrian biozone.

1.6. General Geology

The Colorado Plateau is a relatively stable tectonic

block; the Phanerozoic strata that comprise it have

undergone very little deformation compared to other areas

in the southwestern United States. The Cambrian

succession of the Grand Canyon and Lake Mead areas appears

to be autochthonous with respect to the Cretaceous Sevier

orogeny (Palmer euid Nelson, 1981) , with the exception of

the beds in the upper plate of the Muddy Mountain thrust,

which were not included in this study. During Miocene

extension, the Cambrian rocks, among others, in the Lake

Mead area were displaced by extensive normal and strike-

slip faulting during the development of basin-and-range

topography (Wernicke et al., 1988). Frenchman Mountain,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 for example, apparently moved several tens of kilometers

westward (Rowland et al., 1990).

The Cambrian rocks in the Grand Canyon are

represented by the Tonto Group (Fig. 1), which consists of

a transgressive siliciclastic and carbonate succession

deposited over the gently sloping, eastern cratonic margin

of the Cordilleran miogeosyncline (Wanless, 1973).

Middle-to-Upper Cambrian sediments, generally similar to

those in the Grand Canyon, are exposed from Mexico to the

Canadian Rockies along the Cordilleran eastern

geosynclinal margin (Wanless, 1973). This sandstone-

shale-limestone succession is well exposed along the

Colorado River in the western Grand Csuiyon and its side

canyons, where the Cambrian strata are about 400 meters

thick (McKee, 1945). They pinch out to the east, and are

exposed again in the Juniper Mountains and the Black Hills

in west-central Arizona (Middleton and Elliott, 1990). At

Frenchman Mountain (Fig. 3) , Cambrisin strata are over 900

meters thick (Longwell et al., 1965). To the west of

Frenchmsm Mountain, the thickness of the Cambrian section

dramatically increases; in ranges located about 50

kilometers northwest of Frenchman Mountain the Cambrian

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 strata are more than 2,73 0 meters thick (Longwell et al.,

1965) .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2

REGIONAL STRATIGRAPHIC RELATIONSHIPS

2.1. Introduction

The Grand Canyon area lies on the cratonic margin

just to the east of the Cordilleran miogeocline (Wanless,

1973), and in the southwestern part of the Colorado

Plateau. The stratigraphie divisions of the Middle-Upper

Cambrian section of the Graind Canyon were established and

studied in detail by McKee (1945), whose stratigraphie

nomenclature was adopted by stratigraphers working in this

region.

Traditionally, geologists working in the Basin and

Range Province have used a separate stratigraphie

nomenclature from that used in the Colorado Plateau

Province. However, in spite of some lithologie

variabilities and thickness chcmges, some mappable,

distinct units can be traced from the Colorado Plateau

into the Basin and Range Province. Figure 5 shows the

19

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20

MIOGEOCUNAL CRATONAL SECTIONS SECTION DESERT RANGE (Fenfon,l980) l a k e MEAD AREA WESTERN meters GRAND CANYON Q 1400- M '^FRENCHMAN ^ MOUNTAIN TRAMP RIDGE DEVIL'S COVE

WBanded ^quartermaster Mtn. UNCLASSIFIED ^CANYON % 1000^ O Mbr. DOLOMITES FERN GLEN undo#*, del Herat* Mtr. ColeueyCyMftf. Q 8 0 0 - ..jyav — KOmebCYm.Hk Limestone P*ocbSP4*.Ubr.

Komooft Cora Mbc 600- Bright Angel Shale

a 400-

200 -

^Carrara Fm.

Fig. 5. Correlation proposed by Korolev and Rowland (1993) of sections in the Grand Canyon with those in the Basin and Range Province. See Figure 3 for locations of all sections exept Fern Glen; Fern Glen section is located in the Central Grand Canyon 85 km eastnortheast of Quartermaster Canyon (stratigraphy from Rowland et al., 1994) . C bb = Banded Mountain Member of Bonanza King Fm. and correlative strata. C bp = Papoose Lake Member of Bonanza king Fm. and correlative strata. Names to left of stratigraphie column are trilobite zones, Ced = Cedaria zone, C = Crepicephalus zone, A = Aphelaspis zone, D = Dunderburgia zone. Question marks indicate that the exact position of a zone boundary is not known due to insufficient diagnostic fossils.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21 correlation proposed by Korolev and Rowland (1993) of

Middle and Upper Cambrian strata between these two

provinces primarily on the basis of distinctive

lithologies. The upper part of the Muav Limestone and the

undifferentiated dolomites in the Grand Canyon area were

correlated with the Banded Mountain Member of the Bonanza

King Formation in the Desert Rsinge (northwestern Clark

County, Nevada), Nopah Range (southwest of Spring Mts.),

and the upper part of the Emigrant Formation in the Last

Chance Range.

Precise correlation between regions uses trilobite

assemblage zones. No fossils have yet been reported from

the Grand Canyon undifferentiated dolomites. In the Basin

and Range Province, however, the trilobite zones for the

corresponding interval of rocks are well established, as

shown in Fig. 4 (Palmer and Hazzard, 1956; Palmer, 1965,

1981).

Frenchman Mountain is a very important locality in

this study because of its unique stratigraphie

characteristics and geographic position. On the one hand.

Frenchman Mountain is located on the western edge of the

craton, and its Cambrian section can be correlated with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 other cratonal sections in the Lake Mead area and the

Grand Canyon (Fig. 6). On the other hand, the lithologie

characteristics of the Cambrian section at Frenchman

Mountain are comparable with those in the Basin and Range

Province, so Basin and Range stratigraphie terminology

traditionally has been applied to the Frenchman Mountain

section (Longwell et al., 1965; Gans, 1974; Montanez and

Osleger, 1993). Furthermore, at Frenchman Mountain the

strata correlative with the undifferentiated dolomites are

overlain by other Cambrian strata of known age; in most

other cratonal sections these younger Cambrian strata were

removed by pre-mid-Devonian erosion (Fig. 5).

2.2. Regional Stratigraphy and Lithologie Correlation

The Tonto Group sediments were deposited under

predominantly marine conditions on the tectonically stable

southwestern part of the North American craton (Stewart

and Poole, 1974; Stewart and Suczek, 1977). The

stratigraphie nomenclature for the Cambrian of the Grand

Canyon area has remained constant since McKee (1945)

subdivided the Muav Limestone into seven members.

However, up to the present time, no detailed stratigraphie

study of the undifferentiated dolomites has been

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FRENCHMAN MOUNTAIN

TRAMP RIDGE

WHITNEY RIDGE U 1 —7l'^7/~

S3Z jE B !3B2

^0 1 € 12 TT ]0

EBEEBZ 9 '7—v— i/— 8^ 1 Zr E o 6 o .«Î

ZilW. L» V •J

3 3 2 0 0 3

Hovosu Mbr. Havasu Mbr.

Fig. 6• Correlation chart of und Small numbers refer to f measured section. Roman identfiable subdivisions dolomites.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. - Limestone - Laminite

RIDGE - Glauconite - Cross-bedding

- Dolomite - Fossil Fragments

DEVIL’S COVE - Chert - Storm deposits

• • • • I -Oolite Bioturbation

- Stromatolite I - Dunderberg Shale

QUARTERMASTER CANYON

DIAMOND BAR RANCH

Zl^ZLHZj

ir50m E25ZZEZÎ

Hovosu Mbr.

: o f undifferentiated dolomites. :er to field units unique to each . Roman numerals refer to regionally Lvisions of the undifferentiated

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 conducted. McKee (1945) separated these dolomites from

the Muav Limestone, but he considered them to be a

continuation of the Cambrian succession of the Grand

Canyon. Brathovde (1986) suggested that this unit lay

within the Bolaspidella trilobite zone, and he considered

it to be Upper Cambrian following the controversial

proposal of Ludvigsen and Westrop (1985) (see Fig. 4).

In the western Grand Canyon the undifferentiated

dolomites are typically light-gray, fine-grained, thin-

bedded dolomite strata that are up to 130 m thick and are

conformably overlying the Muav Limestone. The distinctive

"cliff-and-slope" topography, discussed below, is

characteristic of this unit in the Grand Canyon region and

also in the Lake Mead area to the west. The alternating

more resistant and less resistant intervals probably

represent lithologie response to fourth- and fifth-order

sea-level changes. This phenomenon is examined in more

detail below.

In their International Geologic Congress "Colorado

River Guidebook," Beus and Billingsley (1989, p. 127)

described the undifferentiated dolomites as conformable on

the Muav Limestone throughout the Grauid Canyon region. In

the same guidebook Elston (1989, p. 131) refers to this

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 contact as disconformable. Beus (1990, p. 110) again

described the contact between the Muav Limestone and the

undifferentiated dolomites as conformable. My detailed

study of this stratigraphie boundary at several

localities, including the western Grand Canyon, indicates

that there is no angular discordance and no conspicuous

erosional surface separating these two units. In some

places, this contact is represented by a transition zone

and gradational changes of lithofacies were observed.

Also, the lithofacies analysis indicates no distinct sea-

level change at this stratigraphie level. The

undifferentiated dolomites, therefore, conformably overlie

the Middle Cambrian Muav Limestone.

In spite of the fact that to the west of the Grand

Canyon the lithology of the undifferentiated dolomites

changes significantly, the present study shows that some

distinguishable lithologie patterns can be traced from the

Grand Canyon to as far as Frenchman Mountain.

The location of the easternmost feather edge of the

undifferentiated dolomites has not yet been determined: it

presumably lies somewhere in the central Grand Canyon.

Wood (1956) documented the southeastemmost occurrence of

the "Supra-Muav" (undifferentiated dolomites) southeast of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 Cross Mountain, in central Arizona. The thickness of this

unit significantly increases northwestward, along with the

entire Paleozoic section (Figs. 5, 6). The decrease in

thickness in the southern Grand Wash Cliffs and the

Diamond Bar areas is interpreted also to be caused by

significant erosional truncation of the uppermost portion

of the undifferentiated dolomites. My measurements show

that the undifferentiated dolomite succession at Mile-269

Canyon is 107 meters thick and at Quartermaster Canyon

this succession is 117 meters thick (see Appendix B).

In order to solve numerous correlation problems in

the absence of biostratigraphically useful fossils, I

needed to evaluate the reliability of marker beds and the

consistency of lithologie characteristics. Because the

sediments accumulated under constantly changing

depositional environments and continuous sea-level

changes, this evaluation was difficult, but, on the other

hand, favored sequence stratigraphie approach. However,

some of the units mentioned below have consistant

lithologie characteristics over a large area, and using

them for correlation purposes seems to be reasonable. The

following is a general description of some lithologie

characteristics of the undifferentiated dolomites.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 The stratigraphie base of the undifferentiated

dolomites was found to be fairly consistent throughout the

study area, including sections in the Basin and Range

Province. In the Grand Canyon, the contact between the

youngest member (Havasu Member) of the Muav Limestone and

the overlying undifferentiated dolomites is gradational

and does not show an abrupt change in lithology

(Brathovde, 1986). It is defined by a transition zone,

approximately 3 meters thick, in which medium-to-dark

gray, burrow-mottled, thickly bedded, relatively resistant

dolomitic limestone of the Havasu Member below grades into

the overlying light-to-medium gray, less resistant, finely

laminated dolomite of the undifferentiated dolomites. In

the cratonal sections to the west, the contact between the

Havasu Member of the Muav Limestone and the

undifferentiated dolomites is represented by more abrupt

change in lithology than in the Grand Canyon. The basal

unit in the western sections is also characterized by

mechanically and cryptomicrobially laminated dolomite with

abundant buff-colored cherty lenses and well-preserved,

partly silicified stromatolites (Fig. 7).

Brathovde (1986) subdivided the undifferentiated

dolomites into four litho-stratigraphie units

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28

Fig. 7. Massive, moderately-to-dark brown chert nodules and silicified stromatolites at the base of undifferentiated dolomites. Unit I, Quartermaster Canyon.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29 corresponding to four distinct lithologie rock types.

Brathovde's (1986) units I, II, and III are fairly

distinct and mappable throughout the western Grand Canyon

area, but they become less distinguishable to the west

toward Frenchman Mountain, where their lithologie

characteristics change significantly. Because of this

inconsistency, I have partially abandoned the

stratigraphie terminology of McKee (1945) and Brathovde

(1986) and defined new, more general units for the

sections measured during this study (Fig. 4).

As shown in Fig. 6, I have divided the

undifferentiated dolomites into two units. My unit I

correspond to Brathovde's units I, II, and III;

my unit II correspond to various lithologies within

Brathovde's Unit IV.

Unit I is represented by different lithologies,

including light-gray, thin-bedded, commonly mudcracked,

cryptomicrobially laminated and stromatolitic dolomite and

massive, medium-gray to dark-gray, burrow-mottled, fairly

resistant dolomite. This unit has a very distinct

'laminite marker interval (field unit 3 at Frenchman

Mountain, Tramp Ridge, and Devil's Cove) that is 10 to 15

meters thick (Fig. 6) . The thickness of Unit I increases

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 from 80-100 m in the Grand Canyon to 355 m at Frenchman

Mountain.

Unit II is a prominent, non-bedded interval of very

light-gray to medium-gray, homogeneous, bioclastic

grainstone that contains abundant echinoderm fragments,

trilobite spines and glauconitic pellets. This rock

interval is traceable throughout the western part of the

study area and is quite consistent in thickness (about

40 m) . It is partly preserved at Tramp Ridge, and

completely preserved at Whitney Ridge and Frenchman

Mountain (Fig. 6}.

The lithologies listed above also correspond to

McKee's (1945) three lithologie types (see page 5 of this

thesis). McKee, however, did not indicate the

stratigraphie position of these lithologie types within

the undifferentiated dolomites. Unit IV of Brathovde

corresponds to my Unit II (Fig. 6) and presumably is

equivalent to McKee's "Type 1 dolomite."

Brathovde (1986) identified a traceable interval of

stromatolites, "algal" laminae, and oolites at the top of

his Unit I at several localities. Although I did not find

oolites within this stratigraphie interval in the western

Grand Canyon, the stromatolites and cryptomicrobial

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31

\

Fig. 8. Cross-stratified beds, represented on three-dimensional surface. Unit I, Quartermaster Canyon.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32

Bimodal paleocurrents in cross-bedding: N35E S27W nslO S63W N35E N35E S18W N40E N45E S30W MOW

Rose diagram showing bimodal distribution of cross-stratified beds measured at Unit I of Quartermaster Canyon.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. JJ laminices are conspicuous and rendered this a laterally

persistent marker bed throughout the study area.

A very resistant interval of finely laminated,

light-gray dolomite with large-scale cross bedding occurs

within the upper part of Unit I at Quartermaster Canyon

(Fig. 8). The prevailing bimodal currents flowed toward

the northeast and southwest (Fig. 9). Within the same

stratigraphie interval at Mile-269 Canyon, a bimodal

distribution of paleocurrents was documented from a

similar cross-bedded interval associated with intraclastic

strata.

The contact between the undifferentiated dolomites

and overlying Devonian strata is erosional. Because the

basal Devonian is represented by very recessive and

crumbly dolomite (Fig. 10) , this contact is poorly exposed

in sections of the western Grand Canyon measured during

this study. In most cases, this contact shows a sharp

lithologie contrast between light-gray, finely laminated,

non-resistant Cambrian dolomitic mudstone below and dark

to medium-gray to purple, thickly bedded, non-resistant,

pitted, Devonian dolomite above (Fig. 11). In the central

Grand Canyon, these non-resistant Devonian strata have

been referred to the "C member" of the Mountain Springs

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34

t U

Fig. 10. Cambrian-Devonieux stratigraphie unconformity. Large-scale erosional surface at the top of Unit II of the Devil's Cove section, overlain by the Temple Butte Formation.

Fig. 11. Cambrian-Devonian stratigraphie unconformity Eroded surface within Unit I at Mile-269 Canyon section.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 Formation (Rowland et al., 1994). This lowermost Devonian

bench-forming interval is only a few meters thick; it is

overlain by dark-gray, cliff-forming, stromatoporoid-

bearing limestones or dolomites of the Temple Butte

Formation.

In the Basin and Range Province, the strata that are

correlative with the undifferentiated dolomites lie within

the Bonanza King Formation (Fig. 5), so it is necessary to

review the essential features and history of research on

that unit.

The carbonate rocks of the Bonanza King Formation

were deposited under generally shallow conditions in a

passive-margin setting (Fenton, 1980; Montanez and

Osleger, 1993). The age of the upper part of the

lithologically distinct Bonanza King Formation remains

problematic. Hazzard and Mason (1953, cited by Brathovde,

1986) measured this formation at Sheep Mountain and

concluded that its upper part is Cambrian and that it is

disconformably overlain by Devonian rocks.

Palmer and Hazzard (1956) found paleontological

evidence indicating that the Bonanza King Formation is

Middle-to-Late Cambrian in age. They correlated this

formation between the Providence Mountains, the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 Goodsprings District, and the Nopah Range, however the

Middle-Upper Cambrian boundary was not precisely located.

Barnes and Palmer (1961) correlated the Cambrian

Yucca Flat Formation on the Nevada Test Site with the

Bonanza King Formation in the Nopah Range. They found

lithologie similarities between those two rock intervals

and proposed using the Bonanza King Formation name for the

Test Site locality. They identified a persistent, brown-

weathering siliceous carbonate succession about 13 m

thick, located 730 meters below the top of the formation,

that served as a marker bed for dividing the Bonanza King

Formation into two members. They called the lower portion

the Papoose Lake Member, and the upper portion the Banded

Mountain Member (Fig. 5) . This brown-weathering siliceous

interval was included in the Banded Mountain Member and is

believed to be correlative with a regional marker bed

containing the Middle Cambrian trilobite Ehmania in the

Desert Range, the Spring Mountains, and the Nopah Range

(Bames and Palmer, 1961) . The same brown-weathering

interval was also correlated with unit 7A of Hazzard

‘(1937) in the Nopah Range. Despite the fact that the

location of the Middle-Upper Cambrian boundary could not

be located precisely within the Bonanza King Formation,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 B a m e s and Palmer (1961, p. 102-103) suggested that "at

least the upper 3 00 feet, and probably the upper 700 feet,

is of Late Cambrian age."

Secor (1962) concurred with the Middle-Upper

Cambrian age of the Bonanza King Formation based on

outcrops in Red Rock Canyon in the Spring Mountains. He

also considered the dolomites above the Bonanza King

Formation to be Cambro-Ordovician in age.

Longwell and others (1965) considered the age of

this undifferentiated unit to be Cambrian, having accepted

McKee's informal name — Dolomite and Limestone

Undifferentiated — for this rock interval exposed in

several localities in the northern suid western parts of

Clark County, Nevada. Undifferentiated strata were

included in the Goodsprings Dolomite in the southern part

of the Spring Mountains (Longwell et al., 1965, p. 18;

Gans, 1974) . Longwell et al. (1965, p. 19) pointed out

the growing tendency to use the name Bonanza King

Formation for the entire Cambrian section of carbonate

rock below the Dunderberg Shale in southern Nevada.

Gans (1974) determined that the Bonanza King

Formation comprises the lower half of the Goodsprings

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 Dolomite, a unit that Hewett (1931) had established for

the southern Nevada and eastern California region. Gans

(1974) was able to correlate much of the upper part of the

Goodsprings Dolomite with the Upper Cambrian Nopah

Formation. In order to solve correlation problems in the

cibsence of fossils in almost entirely dolomitized rock,

Gans (1974, p. 190) used "key marker beds, stratigraphie

position, chert zones, and any other distinctive

lithologie features." Gans (1974, p. 190-194) subdivided

the Bonanza King Formation into 17 mappable units and

correlated them throughout the southern Basin and Range

Province.

For purposes of regional mapping, the two formal

units established by Bames and Palmer (1961) within the

Nevada Test Site area have become widely used: the lower

Papoose Lake Member and the upper Banded Mountain Member.

The Banded Mountain Member of the Bonanza King Formation

thickens westward from 400 m near Las Vegas and in the

eastern Mojave Desert to 1330 m in the Last Chance Range,

representing the transition from craton-margin facies to

shelf-edge facies (Montanez and Osleger, 1993) . Gans

(1974) subdivided the Bsuided Mountain Member into ten

informal units, which he described as "generally uniform

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 in lithology and thickness" (Gans, 1974, p. 190). These

stratigraphie subdivisions are still widely used. Short

descriptions and a generalized stratigraphie column of

Gans's (1974) informal units of the Banded Mountain Member

are presented in Figure 12.

Gans (1974) correlated his generalized section of

the Banded Mountain Member in the central Spring Mountains

with the Cornfield Spring section in the Nopah Range

measured by Hazzard (1937) sind with the cratonal section

at Frenchman Mountain (Fig. 13). In the absence of

fossils for correlation, he used stratigraphie positions

and lithologie characteristics. He suggested that the

Banded Mountain Member is quite consistent and can be

reliably correlated using marker beds throughout the

region.

Detailed decimeter-scale measurement of the Banded

Mountain Member, including lithologie description and

correlation of this rock interval between six localities

in the southern Great Basin, has been carried out by

Montanez and Osleger (1993). They correlated between

sections using sequence stratigraphie methods (Fischer

plots). Along with Gans (1974), they applied the basin-

and-range stratigraphie nomenclature to Frenchman

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40

Nopah Rn.

ebb>10 Lighc-çray, medluB-crystaUIne suezosle. ddge-formlng dolomite. Very conrlscent lu tblckness : 37 co 45 m. ebb4 Distinctive marker bed of medium-gray peloldal dolomlcrlte. Felolds are 0.5 to 1.0 mm In diameter and weather on the rock surface as dark pits. Thickness 9 to 18 o.

e b M Light-gray to plnklsh-gray laminated dolomlcrlte commonly weathering as small blocky ridges. Gradational with underlying unit 7 and overlying unit 9. Thickness 18 to 24 m.

Very resistant, cliff forming, dark-gray mottled dolomite, similar to unit 4. ebb-7 Average thickness 60 m.

Dark-gray dolomite with abundant large chert nodules. Very similar to unit 3. G b M Thickness varies from 42 to 120 m.

G b W Cyclic sequence of dark- and Ught-gray weathering dolomlcrltes occurring in bands 1 to 3.6 m thick. Thickness of unit Is variable from 18 to 90 m.

Gbb4 Very resistant, cUff-formlng, dark-gray mottled dolomite. Average thickness 120 m.

Dark-gray dolomite. Contains abundant large (7-15 cm) blue-black chert nodules Gbba and stringers. Average thlOcness about 54 m.

Dolomitic sequence of Im-thlck alternating dark- and Ught-gray bands. Contains no Gbba chert. Some places bands are absent. This unit can be Indistinguishable from unit 3. The average thickness 30 m for the northern sections and 21 m for the southern sections.

Thln-bedded, fine-grained silty dolomite. Forms non-resistant orange weathering slopes, Gbb-1 contrasting with generally dark-gray Banded Mountain sequence. Average thickness 12 to 15 m.

Pipoose Lalw Wbmber

Fig. 12. Generalized stratigraphie column of Banded Mountain Member of the Bonanza King Formation showing informal units of Gans (1974) (not to scale).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41

Nopah and ReaPng C en n i Spring Frenchman Soring Ranges MounWne Meuntatn

SOm 12m Unit II *m Gbb-9 I2m 7K SOm Cbb-8 M m

23m Cbb-7 SOm Unit I 332 m 105 m SOm

Cbb-5 Mm u. 7H iSm

120m 7G l62m N

Cbb-3

Cbb-2 Cbb-1 ISm

29m

70 SOm

7C I2m

113m

7A II m

Gans's 1974) corelation

Fig. 13. Schematic correlation chart of the Banded Mountain Mbr., Bonanza King Formation euid undifferentiated dolomites (Based on Hazzard, 1937 and Gans, 1974).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 Mountain. During my work, I studied suitability of the

Fischer-plot technique for correlation between the Grand

Canyon and Lake Mead area sections. I came to the

conclusion that this method should not be used at

Frenchman Mountain because depositional cycles at this

locality can not be consistently traced along the section.

Within the undifferentiated dolomites at Frenchman

Mountain, on the basis of analysis of stacking patterns,

Montanez and Osleger (1993) identified four third-order

depositional sequences.

2.3. Blostratlgraphy

On the Colorado Plateau, the stratigraphie interval

corresponding to the undifferentiated dolomites contains

very few fossils. In the Grand Canyon, no identifiable

fossils are reported from and above the Havasu Member of

the Muav Limestone (Resser, 1945). Within correlative

rocks in the Basin and Range Province, fossils are scarce

as well. This absence of fossils can partly be attributed

to a general scarcity of living organisms in restricted

environments of very shallow water and significantly

increased salinity (Palmer, 1971). Diagenetic alteration

in general and significamt dolomitization of the rock in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 particular, may also have contributed to the absence of

fossils.

However, well preserved fossils are known from the

intervals below the undifferentiated dolomites. In Peach

Springs Wash, Resser (1945) reported the late Middle

Cambrian trilobite Solenopleurella porcata from a bed 50

meters below the top of Havasu Member of the Muav

Limestone. Late Middle Cambrian fossils were also found

at the base of the Peach Springs Member in the western

Grand Canyon.

In areas adjacent to the Colorado Plateau,

identificÜDle fossils from the undifferentiated dolomites

have been reported from several localities. Resser (1945)

described Middle Cambrian trilobites from this interval in

the Muddy Mountains. Abundant early Late Cambrian

trilobites sind brachiopods were reported from the top of

the Bonanza King Formation in the Desert Range by Fenton

(1980). South of the Grand Canyon, Stomps (1978)

documented trilobite fragments from the boundary interval

of the Muav Limestone and undifferentiated dolomites. He

also described early Late Cambrian fossils from the

interval above the Muav Limestone from sections at Whitney

Ridge (Virgin Mountains) and the Virgin River Gorge.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 Studying the Whitney Ridge section, Longwell et al. (1965)

reported the following Late Cambrian Crepicephalus zone

trilobites from the upper part of the undifferentiated

dolomites approximately 32 meters below the top:

Apsotista sp., Dytremacephalus sp•, Pterocephaiia sp.,

Grepicephaius sp., Kinastonia sp., and Llanoaspis cf. k,.

undulata Lochman. From the undifferentiated dolomites

north of Whitney Ridge, trilobites were found comparable

to the fossils reported from just below the Dunderberg

Shale in the Great Basin (Longwell et al., 1965). The

Crepicephalus zone was established 30 meters below the

Devonian contact at the same locality. In the Virgin

River Gorge section. Steed (1979) reported trilobites

belonging to Crepicephalus zones in the upper part of the

Bonanza King Formation about 35 meters below the base of

the Nopah Formation. All these fossil occurrences are

scattered and rare and do not define the Middle-Upper

Cambrian boundary in cratonal sections of undifferentiated

dolomites, nor do they permit precise correlation between

remote sections.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 3

SEDIMENTOLOGY

3.1. Introduction

The Middle-Upper Cambrian sedimentary succession of

the Grand Canyon and Lake Mead areas exhibits a wide

variety of sedimentary facies representing depositional

environments that range from low-energy, deep-subtidal

environments to high-energy, storm-influenced tidal flats.

In this chapter, I describe the lithofacies of the

undifferentiated dolomites, and interpret the depositional

environments in which they form. Terminology follows

Dunham (1962).

3.2. Lithofacies

I have defined the following eight major facies for

the undifferentiated dolomites: (1) burrow-mottled facies;

(2) flat-pebble grainstone facies; (3) stromatolite

facies; (4) oolitic-grainstone facies; (5) bioclastic

grainstone facies; (6) ribbon-rock facies; (7) nodular

45

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7) ■DCD O Q. C g Q.

"D CD

C/) 3o' O

"O8

3. CO3" i 3 suprat(d«l zone DEPOSITIONAL ENVIRONMENTS CD high t i d e------Lamlnlte facies loterildal-supratldal, quiet-energy tidal-flat environment

3. Nodular facies Shallow-Intertidal, unstable-energy environment 3" CD Ribbon-rock facies intertidal zone Shallow-Intertidal, near-shore, wave-dominated environment "OCD O Bloclastlc-gralnstone facies g> g> g> © \ shallow-subtldal, high-energy environment Q. — low t i d e ------Oolltlc-gralnstone facies ###### \ high-energy oolitic shoal O 3 Stromatolite facies ^ ^ deep-subtldal to shallow-sublldal, low-energy environment ■o O Flat-pebble grainstone facie; subtidal zone deep-subtldal to shallow-subtldal, high-energy environment I 1 ww } CD Burrow-mottled facies deep-subtldal to shallow-subtldal, low-energy environment Q.

oc ■o CD (/> Fig, 14. Lithofacies established for the undifferentiated dolomites, their stratigraphie distribution, and o ’ 3 interpreted depositional environments.

I; 47 faciès; and (8) laminite facies. Fig. 14 summarizes the

characteristics of these facies and their interpreted

depositional environments.

3.2.1. Burrow-mottled faclea

The volumetrically most abundant facies of the

undifferentiated dolomites is the burrow-mottled facies,

which consists of medium-to-dark çrray, thick-bedded,

burrow-mottled dolomitic mudstone and wackestone, with

rare grainstone interbeds. This facies is common in the

Grand Canyon, as well as in the Lake Mead area. In the

Lake Mead section it comprises approximately 50 percent of

the entire thickness of the undifferentiated dolomites.

Most commonly, the burrow-mottled facies is interbedded

with other facies, however in the Lake Mead area it is

present in continuous (up to 30 m thick) monofacial

intervals (see Appendix B). McKee (1945) used the terms

"marbled" or "mottled" facies for equivalent facies within

the Muav Limestone.

In the burrow-mottled facies, individual burrows in

moderately-burrowed rock are commonly oriented vertically.

Their length can reach up to 7 to 10 cm, and they are

commonly 1.5 to 2 cm in diameter. Horizontal burrows are

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 more common on bedding planes of intensively-burrowed rock

than in moderately burrowed rock. The burrows, which were

originally filled with lime mud, are now occluded by

coarse calcite mosaic, making them distinctively lighter

in color and more prominent than the surrounding matrix.

In addition to the wide burrows, very narrow,

randomly oriented calcified burrows are found in several

intervals. These narrow burrows are 2-3 mm in diameter

and typically 3-5 cm long.

In thin section, fossil fragments in the burrow-

mottled facies are very rare. Some eocrinoid plates and

highly fragmented, unsorted trilobite spines were

observed.

As described by Brathovde (1986), the burrow-mottled

facies has a crystalline mosaic texture commonly

represented by xenotopic (anhedral to subhedral) dolomite

and calcite crystals that are characterized by irregular

and curved intercrystalline boundaries and undulatory

extinction. Less commonly, the mosaic texture consists of

rhombic, euhedral dolomite crystals with well defined,

straight intercrystalline boundaries.

In most exposures, the burrow-mottled facies is

fairly homogeneous and exhibits no primary structures

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49 other than burrows. The intensive burrowing presumably

destroyed any pre-existing depositional features.

Cross-stratification in the burrow-mottled facies is

rare; when present it commonly occurs within interbedded

grainstone beds that are less than 0.5 m thick. No

subaerial exposure features were observed in the burrow-

mottled facies.

The burrow-mottled facies can be subdivided into

four subfacies on the basis of bedding thickness,

intensity of bioturbation, presence of peloids, and

associated lithology. Subfacies la comprises thinly

bedded (individual beds are 5-15 cm thick) , medium gray,

burrow-mottied mudstone (Fig. 15) . This subfacies is

commonly interbedded with thin (up to 5-7 cm) , sand-size,

nodular beds, and thin ribbon rock (mudstone-grainstone)

interbeds that vary in thickness from 2 to 10 cm.

Relatively thin (10-20 cm) beds of intraclastic grainstone

are also abundant. Generally, these interbeds can be

traced laterally across the extent of the outcrop.

According to the ichnofsüoric index of Droser and Bottjer

(1986), which reflects the intensity of bioturbation,

these beds have an intensity of 2 to 3.

Subfacies lb (Fig. 16) consists of poorly preserved.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50

Fig. 15. Burrow-mottled facies. Subfacies la.. Unit I, Frenchman Mountain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51

Fig. 16. Burrow-mottled facies. Subfacies lb.. Unit I, Dieutiond Bar Ranch. Pocket knife is 9 cm long.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 ^slutively thick (up to 3 meters) beds of intensively

bioturbated (ichnofabric index 4 to 5), dark-gray mudstone

interbedded with very rare thin beds of flat-pebble

intraclastic grainstone. The latter contain intraclasts

of large, commonly micritic flat pebbles up to 2 cm long

that are frequently imbricated.

Subfacies Ic consists of thick (up to 5 meters)

intervals of dark-gray to very dark-gray, non-stratified,

intensively bioturbated mudstone (Fig. 17). The

ichnofabric index in these intervals can reach 5 to 6. In

these intervals, sedimentary features are almost totally

destroyed by burrow-mottling activity. Less intensively

burrowed, thin beds of subfacies lb are commonly present

within these intervals.

A very typical alternation of subfacies of the

burrow-mottled facies can be represented by the following

sequence of thin (5-15 cm) beds in stratigraphie order:

ic-lb-lc-la-lb-lc-lb-lc-lb-lc-lb-lc-lb-la. The sequence

of alternating subfacies la, lb, and Ic is interrupted in

some places by very thin layers of non-resistant, crumbly-

weather ing, greenish-red silty limestone. The bases of

depositional cycles are usually represented by more

intensively bioturbated subfacies (Ib-lc). The tops are

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53

f

Fig. 17. Burrow-mottled facies. Subfacies Ic., Unit I, Frenchman Mountain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 marked by less bioturbated subfacies (la-lb).

Subfacies Id is shown in Fig. 18. It is represented

by moderately burrowed (ichnofabric index 2-3) peloidal

packstone to wackestone. Relatively thick (0.5-1.5 m) ,

burrow-mottled dolomitic beds of this peloidal subfacies

are commonly medium-gray and are fairly resistant to

weathering. The dolomitized micritic peloids are commonly

oval in shape with rounded edges; they range in size from

0.2 mm to about 1 mm. The rock is often significantly

altered by diagenesis such that in thin section individual

peloids are not discernible and can be seen only as

ghosts. The peloids commonly have a clotted internal

structure.

Brathovde (1986) also reported the occurrence of

peloids associated with burrow-mottled rock in the upper

part of his Unit II.

Interpretation, af.iiepgsitioiial environiaeiits

The predominance of lime-mud and burrow-mottling,

rarity of cross-stratification, and sübsence of subaerial

exposure features all suggest deposition in a generally

quiet, subtidal environment (cf. Goldhammer et al., 1993)

that was occasionally interrupted by high-energy events.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55

Fig. 18. Thin section of peloidal wackestone. Distinct peloid- shapped gosts (desolved peloids). Polarized light, magnification 1:100. Undifferentiated dolomites. Unit I, Frenchman Mountain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 indicated by the intraclastic-grainstone beds. Subfacies

la, because of its association with thin, sandy, nodular

beds and mudstone-grainstone (ribbon-rock) interbeds, is

interpreted to have formed in relatively shallow subtidal-

peritidal environments above fair-weather wave base.

Thicker, more intensively burrowed beds of subfacies lb

are interpreted to have formed in a deeper environment,

presumably below fair-weather wave base but eibove mean

storm wave base. This is also supported by the flat-

pebble intraclastic grainstone beds associated with this

subfacies. Intraclastic-grainstone layers, containing

large, imbricated, micritic flat pebbles, record the

influence of periodic storm events. Droser and Bottjer

(1986) interpreted similar burrow-mottled, Cambrian

carbonates with ichnofabric indices of 3 to 5 to have

formed on the inner shelf. The rare fossil fragments

(predominantly eocrinoids) are generally interpreted to

record deposition in a slightly restricted, relatively

deep lagoon environment (Palmer, 1971). The absence of

sedimentary structures, absence of fossils, and lack of

.grainstone interbeds in the thick burrow-mottled mudstone

beds of subfacies Ic suggest a relatively quiet, even

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 deeper subtidal environment, probably below mean storm

wave base.

Peloidal texture, as seen in subfacies Id, can form

in a variety of depositional environments. The origin of

micritic peloids in carbonate rocks is still not well

understood (James et al., 1976; Macintyre, 1977, 1984,

1985; Land and Moore, 1980; Lighty, 1985). Micritic

peloids are usually considered to be either fecal pellets

or micritized grains (Beales, 1958; Folk, 1959). Coniglio

and James (1985), however, concluded that some peloids

could be derived from the breakdown of calcareous

microorganisms such as Girvanella and Epiphyton. Chafetz

(1986) suggested that precipitation of marine calcitic

peloids can be bacterially induced. Micritic peloids in

reef cavities may result from internal precipitation of

carbonate mud (Macintyre, 1977, 1984, 1985; Reid,

Macintyre, and James, 1990).

Although the peloidal subfacies Id cannot be

precisely placed in the specific environment due to the

problematic origin of peloids, based on its association

with other subfacies within the burrow-mottled facies, it

is here interpreted to represent shallow peritidal

environment above fair-weather wave base.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 3.2.2. Flat-pebble grainstone facies

Within the undifferentiated dolomites, the flat-

pebble grainstone facies is commonly represented by

relatively thin (5 to 30 cm) intraclastic beds. Thick (up

to 1 m) beds are also present. The flat-pebble grainstone

facies is commonly interbedded with thick (up to 2 m)

burrow-mottled and ribbon-rock intervals.

Micritic flat pebbles have rounded edges, are

generally poorly sorted, and are sometimes imbricated

(Fig. 19) . They generally range from 0.03 cm to 5 cm in

size. Commonly, finely laminated texture is preserved

within the flat pebbles. No grading was observed within

flat-pebble interbeds.

Associated with flat pebble intraclasts are

subrounded to rounded micritic grains that are 0.02 cm to

3 cm in size.

Interpretation of depositional environment

Flat-pebble grainstone beds cam. form under high-

energy conditions even in relatively deep water (Frugel,

1982) . They commonly form aÜDOve storm-weather wave base.

Imbrication of intraclasts shows relatively stable

paleocurrent direction. The micritic composition of the

•iW

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59

Fig. 19. Flat-pebble grainstone facies. Intraclastic- grainstone layer. Large, partly imbricated micritic flat pebbles. Unit I, Frenchman Mountain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 intraclasts and their laminated texture indicate that the

source area was probably a quiet, mud-rich environment,

presumably a tidal flat. Association of the flat-pebble

grainstone beds with burrow-mottled and ribbon-rock facies

indicates their deposition in a relatively energetic,

shallow-subtidal environment.

3.2.3. Stromatolite facies

The stromatolite facies is very abundant within the

study area. Several types of stromatolites are present

and include relatively large domal to low-profile and

laminar forms. Low-profile, LLH-C (close laterally-linked

hemisphere ids) auid LLH-S (space-linked hemisphere ids)

(terminology after Logan et al., 1964) are abundcint and

are preferentially found interbedded with the laminite

facies. Domal, vertically stacked hemispheroids (SH-C of

Logan et al., 1964) are also found at several localities

within the undifferentiated dolomites. In the Colorado

Plateau sections, the stromatolite facies is present at

many intervals including the stratigraphie base of the

formation within Unit I (Brathovde, 1986; present study).

To the west of the Grauid Canyon, stromatolites commonly

take the form of 5 cm to 2-meter thick domes or slightly

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 branching columns. For the most part, laterally linked -

LLH-S/LLH-C stromatolites are found at Tramp Ridge,

Whitney Ridge, and Frenchman Mountain.

Laminae in the stromatolites commonly vary in

thickness from 1-2 mm. They range from continuous-

parallel to discontinuous non-parallel and wavy forms. In

the undifferentiated dolomites, the synoptic relief of the

laterally-linked stromatolites varies from 2-30 cm.

Within the stromatolitic facies, orange to dark

brown silicification patterns are common, resulting in

abundant chert nodules, lenses, and silicified portions of

stromatolites.

Two major subfacies are established for the

stromatolite facies: subfacies 3a, high-profile, close-

laterally linked (LLH-C) stromatolites and stacked (SH-C)

domal stromatolites (Fig. 20) and subfacies 3b, low-

profile close-laterally linked (LLH-C) and spaced-

laterally linked (LLH-S) stromatolites that are

gradational into laminar forms (Fig. 21) . Subfacies 3a is

commonly associated with burrow-mottled and ribbon-rock

facies, and subfacies 3b is commonly associated with the

intraclastic-grainstone and laminite facies.

In the undifferentiated dolomites, high-profile

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62

Fig. 20. Stromatolite facies (subfacies 3a). Large, high- profile, partly silicified domal (SH) stromatolite Undifferentiated dolomites. Unit I, Whitney Ridge.

Fig. 21. Stromatolite facies. High-profile, inclined SH-stromatolite (subfacies 3a) with superimposed low-profile LLH-stromatolites (subfacies 3b). Indicate gradually shallowing depositional environment. Unit I, Whitney Ridge.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 stromatolites are most commonly represented by close-

linked hemispheroids (LLH-C) shown in Fig. 20. The

distance between individual domes ranges from 1-2 cm to

approximately 20 cm. The synoptic relief of the high-

profile laterally-linked stromatolites ranges from 20-40

cm. Generally, the stromatolites of this subfacies are

symmetrical. However, relatively large (up to 1 m in

diameter and 0.5 m high), asymmetric, domal stromatolites

crop out within field unit 10 at Whitney Ridge (Fig. 18).

They lean approximately 30-40° to the south.

SH-stromatolites are represented by individual domes

that are not linked with other stromatolites. The laminae

in the stromatolites are most commonly continuous wavy-

parallel and range from 1-3 mm in thickness. This type of

stromatolite corresponds to type "SH-C" (discrete

structures of vertically stacked hemispheroids) of the

Logan et al.,(1964) classification. The synoptic relief

of this type of stromatolites ranges from 30-50 cm.

Low-profile LLH-stromatolites of subfacies 3b are

commonly represented by thin (less than 1 mm), continuous,

wavy-parallel laminae (Figs. 7, 21). These stromatolites

have synoptic relief of less than 5 cm. The hemispheroids

in most cases are close-linked. Very small (1-3 cm from

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64 crest to crest), close-linked domes can be superimposed on

the high-profile space-linked domes (Fig. 21). Rare gold-

brown chert lenses and nodules are common within the low-

profile LLH-stromatolites (Fig. 7). In some stratigraphie

intervals, such chert lenses are very abundant. In some

places, the original laminae can still be observed in the

chert. The low-profile LLH-stromatolite strata are

commonly interbedded with planar, continuous-parallel

laminite beds.

Sedimentary structures

No evidence of subaerial exposure has been found in

the stromatolite facies. However, low-profile LLH and

lateral stromatolites (subfacies 3b) are commonly directly

underlain and overlain by mud-cracked, finely laminated

dolomite. In all western sections, stromatolites are also

associated with thinly-bedded ribbon rock, intraclastic

grainstone, and oolitic grainstone beds.

Interpretation of depositional environment

A deep subtidal to intertidal depositional

environment for the subfacies 3a of stromatolite facies is

supported by the general lack of subaerial exposure

features and close association of this facies with the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 burrow-mottied and oolitic grainstone facies, as well as

with mudcracked, finely-laminated beds. The general lack

of marine fauna can be attributed to restricted

conditions.

Hoffman (1974) studied deep-water and shallow-water

stromatolites from the Lower Proterozoic Pethei Group and,

on the basis of the relation to other facies, concluded

that closely-spaced, columnar-branching (SH-C)

stromatolites with commonly non-distinct laminae grow

below wave base and form platform-submerged facies. Logan

et al. (1964) suggested that columnar (SH) stromatolites

grow under conditions of moderate wave energy and quiet,

protected (lagoonal) environments with increased salinity.

Most high-profile LLH-stromatolites of subfacies 3a

within the undifferentiated dolomites are symmetrical,

suggesting a very low, more or less uniform sediment

supply (cf. Gebelein, 1976). Large, asymmetric, inclined

stromatolites, such as those in Unit I of Whitney Ridge

(Fig. 18) , are interpreted to form under conditions of

preferentially unidirectional currents, selectively

providing lime mud to one side of the stromatolite

(Hoffman,1974).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 In the undifferentiated dolomites, the high-profile

LLH-stromatolites of subfacies 3a have no exposure

features observed and are generally associated with the

burrow-mottled facies. High-profile LLH-stromatolites are

interpreted to form in relatively deep, quiet, subtidal

environment below fair-weather wave base (cf. Logan et

al., 1964).

The low-profile stromatolites of subfacies 3b were

deposited in a shallow subtidal, moderate-energy

environment. The finely laminated texture of

cryptomicrobial laminae was first explained by Logan et

al. (1964), who suggested a periodic nature to the growth

of stromatolites. Numerous workers, including Logan et

al. (1964), Wray (1977), and Pratt (1982), suggested

certain conditions that provide a stable substrate and

consistent growth of microbial mats. These conditions are

(1) slow and constant sediment supply; (2) protection from

sediment-reworking organisms; (3) early cementation of the

substrate; and (4) sufficient time under favorable

conditions to allow precipitation. Furthermore, it was

suggested that such conditions occur most commonly in low-

latitude carbonate platforms under shallow subtidal to

intertidal, relatively warm marine conditions. Several

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 workers, including Ait ken (1967) , B u m e and Moore (1987) ,

and otiiers concluded that the most likely deposition of

stromatolites can be explained by the mechanism of

trapping and binding of fine detritus sediment by blue-

green algae (cyanobacteria). Grotzinger and Reed (1983)

suggested that within cryptomicrobial mats, thin aragonite

crusts and microdigitate stromatolites can be directly

precipitated on tidal-flats or in shallow ponds.

Low-profile, laterally-linked (LLH) stromatolites of

subfacies 3b can tolerate slight wave action and grow

preferentially in protected intertidal flats in the

littoral and sometimes sub-littoral zone (Logan et al.,

1964) . In such conditions the water is not deep enough to

allow the stromatolites to grow into columnar or branching

forms. In modem environments the stromatolites are

formed by continuous flat-lying algal mats, commonly

behind barrier islands. Hoffman (1974), on the basis of

interbedded intraclastic and oolitic grainstones and

oncolites, suggested that laminar (low-profile, laterally-

linked hemispheroids to flat) stromatolites form under

■active wave-reworking conditions of the surf zone.

Low-profile LLH-stromatolites of the

undifferentiated dolomites are generally associated with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 intraclastic-grainstone and oolitic-grainstone beds and

are interpreted to form in moderate energy, shallow-water,

intertidal, platform environments.

3.2.4. Oolitic Grainstone facies

In the Grand Canyon, oolitic grainstone beds are

found within Unit I of the undifferentiated dolomites and

are associated with laminite beds and low-profile LLH-

stromatolites of subfacies 3b. Brathovde (1986) also

reported ooids in thin (up to 6 cm thick) single beds

within stromatolitic intervals. In the Lake Mead area

sections, oolite beds are fairly rare, and are found

mostly in the upper part of Unit I, which is not present

in the Grand Canyon sections (Fig. 6). At Frenchman

Mountain, oolitic grainstone beds are present in some

burrow-mottied intervals of Unit I. Montanez and Osleger

(1993) illustrated a thick interval of "ooid-skeletal

shoal facies" in the upper part of the Bonanza King

Formation at Frenchman Mountain and in other Basin and

Range sections. In my Frenchman Mountain section, this

facies is much thinner and less conspicuous than in

Montanez and Osleger's section, approximately 500 m to the

south of mine. Unit I in most of the western sections

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 contains oolitic grainstone facies within an approximately

20-m-thick interval. At Devil's Cove, the oolitic

grainstone facies forms a prominent, 8-m-thick, laterally

continuous interval (field unit 11, Fig. 4). Well

preserved oolitic beds commonly overlie and underlie

stromatolite layers. In many cases, ooids are present

within individual stromatolite layers.

Oolitic beds are composed of oolitic-intraclastic

grainstone or packstone. The beds are poorly sorted, with

ooids ranging from 0.5-2 mm and intraclasts ranging from

subrounded 2 mm grains to elongated grains up to 1 cm in

length (Fig. 22). Cross-stratification is common. No

grading was observed within the oolitic-grainstone beds.

Small (0.5-2 mm) micrite intraclasts with dissolved

edges and poorly visible internal laminae are commonly

associated with ooids (Fig. 23). Rare, large (up to 2 cm

in length) flat micritic pebbles are also present in these

beds. Intraclasts are typically composed of lime mudstone

and some are internally parallel-laminated. Some of the

intraclasts have very thin oolitic coatings.

Within oolitic grainstone beds, the ooids comprise

up to 80V of the rock volume; the remaining 20% consists

of intraclasts and intergranular porosity.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70

10 mrr

L -'V ■ ?-v

' / ■'(

Fig. 22. Thin section of oolitic grainstone (oolitic-grainstone facies). Large {up to 1.5 mm) concentric ooids, polarized light, magnification 1:150, Unit I, Frenchman Mountain.

30 mm

Fig. 23. Thin section of elongate, subrounded, finely-laminated lime-mudstone intraclasts (flat pebbles) with oolitic- intraclastic grainstone (oolitic-grainstone facies), Unit I, Frenchman Mountain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 I observed no radial ooids in my limited samples.

Ooid nuclei are usually small (up to 0.5 mm),

rounded or elongate micritic grains. Concentric laminae

are highlighted by various alternating dark and light

layers. Micritic envelopes are present on the majority of

grains. Based on the internally laminated texture of the

intraclasts, they are probably derived from a mud-rich,

shallow-water tidal flats.

Pala.Qcuri:ent data

Cross-stratified grainstone beds are very common

within the mechanical laminite subfacies and are found in

many stratigraphie intervals of the undifferentiated

dolomites. In many cases, the paleoflow direction could

not be determined because of the lack of well exposed,

three-dimensional rock faces. However, some well exposed

cross-stratified beds were found within Unit I in the

Grand Canyon (Fig. 8) and within Unit I in most western

sections. Paleocurrent data, based on measurements of

(tabular) cross-stratified beds in Unit I at Quartermaster

Canyon, show bimodal paleocurrents with preferential NE-SW

directions (Fig. 9). A two-meter thick, thinnly-bedded

grainstone interval (oolitic-grainstone facies) with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72 several sets of thin cross-stratified beds is present

within Unit I (field unit 9) at Whitney Ridge, and also

indicates bimodal, predominantly NE-SW paleocurents.

Moreover, in many cases field data, such as numerous

cross-stratified beds, imbricated intraclasts in

intraclastic beds, and the orientation of inclined

stromatolites generally coincide with north and north-west

paleocurrent directions.

Interpretation of depositional environment

Tangential ooids are interpreted to form in

turbulent, high-energy water, where open-marine conditions

favor the growth of tangentially oriented calcite crystals

(Heller et al., 1980). Such conditions exist on broad

oolitic shoals that are open to the sea. Radial-axial

ooids are not very common in marine environments. The

ideal conditions for formation of radial ooids is a

hypersaline, low-energy environment. Such conditions

exist, for example, in the Red Sea, where in lagoons and

ponds, small (not exceeding 0.6 mm in diameter) radial

ooids form in the stagnant, hypersaline water (Friedman et

al., 1973). In the undifferentiated dolomites, the

oolitic grainstone beds form in an open marine, shallow-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 water, relatively high-energy conditions of an oolitic

shoal.

3.2.5. Bioclastic Grainstone facies

Within the undifferentiated dolomites, the

bioclastic grainstone facies is found most commonly in

Unit II, and rarely in the upper part of Unit I, as

several relatively thin intervals. This facies crops out

as generally cliff-forming, light-gray, poorly-stratified

dolo-limestone. Bioclasts in the bioclastic-grainstone

facies are most commonly less than 1 mm in diameter and

are moderately sorted, non-graded, isometric, moderately

preserved eocrinoid fragments and rarely elongate

trilobite fragments. The eocrinoid fragments are

primarily semi-pentagonal low-magnesium calcite plates

(cf. Tucker and Wright, 1992) , frequently dissolved along

the edges. Under polarized light these grains show a

uniform extinction (Fig. 24). The trilobite fragments are

easily identifiable in thin section as well. The rock

types in the bioclastic-grainstone facies range from

bioclastic grainstone to wackestone. The pore space

between grains is occluded by fine micro-spar mosaic. No

shelter porosity was observed.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74 Glauconitic peloids are also common within the

bioclastic-gxainstone facies at several localities,

including Frenchman Mountain, Tramp Ridge, and Devil's

Cove (Fig. 25). The peloids are commonly small (0.5 to 1

mm) , rounded, deep-green grains that occur in the rock

together with the eocrinoid plates.

Interpretation of depositional environment

The poor faunal diversity in the bioclastic-

grainstone facies may indicate a restricted, probed:ly

lagoonal environment (cf. Palmer, 1971) . However,

crinoids are considered to survive in very narrow salinity

ranges that are centered about normal salinities (Sprinkle

and Kier, 1987). Abundant glauconite peloids indicate

deposition on the upper subzone of the shelf (Luchinina,

V., 1990, personal communication.) The general lack of

desiccation features and siltstone interbeds, light-gray

color, and the presence of highly fragmented bioclastic

material suggest deposition in shallow-subtidal, moderate-

to-high energy conditions of the upper shelf.

3.2.6. Ribbon-rock facies

In the undifferentiated dolomites, the ribbon-rock

facies is represented by alternating medium-to-dark gray.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75

30 mm

Fig. 24. Thin section of bioclastic grainstone (bioclastic- grainstone facies). Large echinoderm fragments. Polarized light, magnification 1:200. Undifferentiated dolomites, Unit II, Tramp Ridge.

0L=±=J 10 mm

Fig. 25. Thin section of bioclastic grainstone (bioclastic- grainstone facies). Large euhedral dolomite crystal, anhedral dolomite crystals, and glauconitic peloids. Polarized light, magnification 1:100. Unit II, Frenchman Mountain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 76

— • * - «V ^ ^ _^Z5C^ZZ^^ — t æ

t^..'

Fig. 26. Ribbon-rocJc faciès. Unit 1, Frenchman Mountain.

Fig. 27. Nodular faciès. Unit I, Frenchman Mountain,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 laterally continuous, wavy-parallel and planar-parallel,

thin (from 1-3 cm) , rippled, grainstone beds and even

thinner (0.2 cm to 3 cm) beds of light-gray to rusty-

brownish, silty dolomitic mudstone (Fig. 26) . in some

places, the limestone beds contain mm-scale fine laminae.

Asymmetric ripples within the limestone beds are about 1

cm high, with wavelength of 5-6 cm. Thin vertical burrows

are locally present within the ribbon-rock facies. The

burrows are commonly occluded with sand-size sediment.

Desiccation structures (mudcracks) are not very common

but, where found, are preferentially located along the

ripple crests. The ribbon-rock facies is commonly

associated with nodular intervals and thin burrow-mottled

beds, preferentially of subfacies la and lb.

Interpretation of depositional environment

Ribbon-rock was described by Demicco (1983) as

thinly interbedded coarse-grained limestone and fine­

grained dolostone beds. On the basis of sedimentary

structures and associated facies, the ribbon rock facies

was deposited in shallow-water, relatively quiet

conditions (cf. Demicco, 1983). Preserved asymmetric

ripples indicate presence of paleocurrents. Alternating

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 grainstone-mudstone texture indicates periodically

changing energy of the environment. Abundant ripples and

rare mudcracks, located preferentially on ripple-crests

showing occasional subaerial exposure, suggest deposition

in the shallow-subtidal to intertidal zone, above fair-

weather wave-base.

3.2.7. Nodular facies

The nodular facies is represented by recessive,

laterally continuous, thin (1 to 8 cm) , rippled, graded,

carbonate beds (Fig. 27). The bases of beds are coarse­

grained and the rippled tops of the beds are composed of

silty carbonate. These even, wavy-parallel beds are

flaggy weathering and are separated by very thin (less

then 2 mm), non-resistant, silty carbonate layers. The

bottom of each bed reflects the signature of the

underlying rippled surface. Ripples with symmetric crests

are commonly very well preserved. The ripple-height is

fairly consistent (about 1-2 cm), and the wavelength is 6-

7 cm on average. In some places, a secondary crest trend,

nearly perpendicular to the primary trend, is superimposed

on the major ripple crests, producing "ladder-back"

ripples (Fig. 28) on the bedding surface. Some crests

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79

Fig. 28. Nodular facies. "Ladder back" structures Unit 1, Frenchman Mountain.

Fig. 29. Laminite facies. Planar-parallel, continuous mechanical laminae. Unit I, Frenchman Mountain.

•4*

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 show desiccation features including cracks on the middle-

upper portion of the crests. Some beds are moderately-

burrowed .

Interpretation of depositional environment

Based on the abundant desiccation features and close

association with ribbon-rock layers, the nodular facies

was deposited under shallow-water, peritidal conditions.

The superimposed ripples show a current direction

different from the primary wave-motion direction indicated

by major-ripple crests. These well preserved symmetric

ripples are interpreted to form in a relatively high-

energy, wave-dominated, nearshore setting.

3.2.8. Laminite facies

In the Grand Canyon amd all western sections, the

laminite facies occurs for the most part in the lower

portion of the undifferentiated dolomites as several,

lithologically distinct, recessive intervals, ranging from

5-20 meters in thickness. The laminite facies is composed

of mostly planar-parallel and wavy-parallel, light-gray to

very light-gray, finely laminated (from 0.5-2 mm),

dolomitic mudstone-wackestone and interbedded intraclastic

packstone. Intraclasts in the intraclastic-packstone beds

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 are represented by small (1-3 mm in diameter) subrounded

grains and ooids, as well as fragments of broken laminae.

The laminites form beds that usually range from 0.5-1 m in

thickness, but reach up to 2.5-3 m.

Similar mm-scale fine-laminated rock was referred to

as cryptalgalaminite by Aitken (1967) who described

several characteristics for this rock-type. These include

planar, fine-laminated texture, origin by means of

sediment-trapping and binding by blue-green algae,

association with stromatolites, and common erosion and

desiccation features. The name "blue-green algae" was

subsequently replaced by the name "cyano-bacteria". This

prompted Bume and Moore (1987) to propose that the term

"cryptalgal" be replaced by the term "microbialite."

Bume and Moore (1987) described the following four

processes in microbialite formation: sediment-binding,

inorganic calcification, biologically influenced

calcification, and skeletal calcification. Direct

precipitation of thin aragonitic cmsts within

cryptomicrobial mats was described by Grotzinger and Reed

(1983) .

Goldhammer et al. (1993) proposed the term

"mechanical laminite" for a fine-laminated carbonate rock

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 that owes its origin to tractive deposition of sand-size

sediment and subsequent settling of mud. This results in

a different texture of the laminite, wherein sedimentary

structures typically are well preserved.

The laminite facies is subdivided into two

subfacies: subfacies 8a, mechanical laminite and subfacies

8b, cryptomicrobial laminite (cf. Goldhammer, et

al.,1993).

The mechanical laminite facies is composed of

continuous, planar-parallel, and in some places, rippled

mm-scale laminae (Fig. 29). Laminae are 1-2 mm thick and

are generally parallel, however wavy forms are common.

They are generally continuous but have occasional

disruptions, desiccation features, and evidence of

traction deposition such as low-angle truncation. Thin,

commonly 2-8 cm, intraclastic beds are very common within

the mechanical subfacies. Wavy forms, mud-cracks, and

micro-erosion surfaces are not common but occasionally

occur in this subfacies. The mechanical laminite

subfacies is occasionally associated with low-profile LLH-

stromatolites (subfacies 3b).

Cryptomicrobial laminite is normally represented by

wavy-parallel to wavy non-parallel, in some places

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83

Fig. 30. Laminite facies. Wavy parallel, disrupted, cryptomicrobial laminae. Unit I, Mile-269 Canyon.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 discontinuous, laminae (Fig. 30). Unlike the mechanical

laminite, originated due tractive sedimentation, the

cryptomicrobial laminite originates due to sediment

trapping and binding by microorganisms. No evidence of

tractive sedimentation was observed in cryptomicrobial

laminite. Desiccation features, including abundant

mudcracks, micro-erosion surfaces, and less commonly

teepee structures, are present in this subfacies. The

cryptomicrobial laminite subfacies.is commonly closely

associated with low-profile LLH-stromatolites (subfacies

3b) . Buff and yellowish-brown chert nodules and lenses

are common. In some places fine laminae can be observed

within the nodules. Very thin (2-10 mm thick) interbeds

of non-resistant, fine-grained, pinkish-green, silty

limestone occur in laminite beds, usually in association

with erosion surfaces and solution breccias.

Interpretation of depositional environments

The mm-scale laminae reflects repetitive and

possibly constant depositional environments (cf. Wanless,

1973). On the basis of abundant desiccation features and

association with low-profile LLH-stromatolites, the wavy,

fine-laminated sediments of the cryptomicrobial laminite

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 subfacies are interpreted to have originated in a narrow

range of conditions on periodically exposed tidal flats,

from the upper intertidal to supertidal zone (Shinn,

1983). Abundant intraclastic beds support periodic high-

energy events.

The wavy nature of the cryptomicrobial laminite is

explained by trapping and binding of sediment by

cyanobacteria (Aitken, 1967) or biologically induced

direct precipitation of carbonate from water-column by

micro-organisms including cyanobacteria (Grotzinger and

Reed, 1983).

Compared to the cryptomicrobialite, the mechanical

laminite is interpreted to form due to traction deposition

by tidal currents and storms (Goldhammer, et al., 1993).

It displays fewer desiccation features, including micro-

erosional surfaces and mud-cracks. The thin, silty-

limestone beds in this subfacies are also less common.

The mechanical-laminite subfacies probably represents a

slightly deeper environment than the cryptomicrobial

laminite subfacies.

- i ______

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 4

SEQUENCE STRATIGRAPHY

4.1. Introduction

In. this chapter, I summarize some basic aspects of

sequence stratigraphy are summarized and then describe and

interpret parasequences and depositional sequences within

the undifferentiated dolomites. Sequence stratigraphy is

the study of rock relationships in a framework of usually

repetitive, genetically related strata bounded by surfaces

of erosion or non-deposition, or their correlative

conformable surfaces (Van Wagoner et al. (1988). Sequence

stratigraphy was originally developed for siliciclastic

successions (Vail et al., 1977), but the concepts are

applicable to carbonate depositional systems as well

(Sarg, 1988). The carbonate production rate is

significantly related to accommodation space, which is the

space for potential sediment accumulation that is

86

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 available between the sea floor and sea surface (Jervey,

1988; Posaraentier, et al., 1988). Accommodation is a key

factor influencing the nature and amount of carbonate

production (Sarg, 1988). Change of accommodation is

generally controlled by relative sea-level change that

includes eustacy, tectonics (local subsidence), and

sediment supply. In general, in shallow-water

environments, the greater the available accommodation

space, the more carbonate that can be deposited during a

given time.

The major difference in the application of sequence

stratigraphy to siliciclastic compared to carbonate

systems concerns the mechanism of sediment supply and

production rate. In contrast to siliciclastic sediments,

carbonates, in most cases, do not depend on a distant

source of sediment but are connected to the local

conditions of the carbonate platform directly on which

they are generated. The carbonate production system is

very sensitive to even minor changes in environmental

conditions, and especially to changes in relative sea-

level. Shallow-water carbonate sediments are believed to

be better recorders of sea-level fluctuations than are

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 siliciclastic sediments, whose rates of deposition are

generally less sensitive to water depth (Sarg, 1988).

In this study I paid particular attention to meter-

scale carbonate cycles, which are well-developed in the

undifferentiated dolomites. These cycles are shallowing-

upward peritidal or subtidal rock-successions bounded at

the top by a flooding surface (Fig. 31). Such cycles are

present in both the Grand Canyon and Lake Mead area.

Two types of models have been suggested to explain

the origin of cyclic carbonate sediments in general.

Autocyclic models (Ginsburg, 1971; Wilkinson, 1982; Cloyd

et al., 1990; Kozar et al., 1990) suggest that internal

feedback processes drive accommodation and the resulting

cyclicity. Allocyclic models consider the cyclicity to be

caused by external forces, including mechanisms of

episodic subsidence (Hardie et al., 1986; Cisne, 1986) and

high-frequency oscillations of eustatic sea level (Vail et

al., 1977; Haq et al., 1987). Most allocyclic models

utilize high-frequency eustatic sea-level changes as the

mechanism for generating meter-scale, shallowing-upward

cycles (cf. Grotzinger, 1986; Koerscher and Read, 198 9;

Osleger and Read, 1991; Read et al., 1991).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 The mechanisms driving eustatic sea-level

fluctuations are, themselves, not completely understood.

Some workers have suggested that Pliocene-Pleistocene

eustatic sea-level changes were related to episodic

continental glaciation caused by Milankovitch rhythms,

which are astronomical in nature (Hays et al., 1976;

Berger, 1977). Arguing against a Milankovitch mechanism

for meter-scale cycles in general, Drummond and Wilkinson

(1993) tabulated about 3000 Proterpzoic and Paleozoic

peritidal carbonate cycles auid concluded that they have an

exponential thickness distribution and are aperiodic. On

the other hand, it has been shown that the duration and

periodicity of cycles represented in late Paleozoic and

younger rocks roughly correspond to Milsmkovitch orbital

cycles (Schwarzacher and Haas, 1986; Osleger and Read,

1991; Goldhammer et al., 1993). Grotzinger (1986)

suggested that allocyclic mechanisms were driving such

cyclicity as long ago as the early Proterozoic.

In this study, variable thickness (0.5 to 6 m),

high-frequency cycles exposed in the undifferentiated

dolomites are called "parasequences." This follows the

usage of Van Wagoner et al. (1988), who defined

parasequences as relatively conformeüsle successions of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 genetically related beds usually capped by marine flooding

surfaces. A "flooding surface" is a surface across which

there is an abrupt increase in water depth.

Systematically changing parasequences and parasequence

sets stack together to form "stacking patterns" that are

usually bounded by major flooding surfaces. A succession

of genetically related stacking patterns define a systems

tract. Systems tracts, in turn, are subdivisions of a

sequence. Sequences are defined on the basis of stacking

patterns, their relative positions, types of bounding

surfaces, and facies associations (Van Wagoner et al.,

1988). Depositional sequences are usually bounded by

major unconformities.

According to Goldhammer et al. (1993), in shallow

carbonate settings an idealized sequence consists of the

following three-part succession: (a) a lowstand systems

tract (LST) of very shallow intertidal-supratidal cycles

in the lower part; (b) overlain by upward thickening

subtidal cycles that form a transgressive systems tract

(TST); and (c) capped by a highstand systems tract (HST)

marked by thinning-upward subtidal-peritidal cycles.

Lowstand systems tracts form during a rapid sea-level fall

and thus represent the shallowest part of a sequence.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 Transgressive systems tracts form during general sea-level

rise and represent the deepest part of a sequence.

Highstand systems tracts form during the late part of a

sea-level rise and the early part of a sea-level fall (Van

Wagoner et al., 1988). This model is a useful guide in

the interpretation of the undifferentiated dolomites.

Based on Van Wagoner et al. (1977), a sequence

boundary can be identified in the field on the basis of

evidence of major subaerial exposure and platform-scale

erosion. Within the undifferentiated dolomites, sequence

boundaries manifest themselves in two ways. Some sequence

boundaries are distinctive erosion surfaces with

paleokarst features and/or incised valley fill. Other

sequence boundaries are more subtle, consisting of

relatively thick intervals of finely laminated dolostone

bearing abundant erosion features, such as mudcracks,

teepee structures, erosion surfaces, solution breccias

associated with very thin, greenish silty-limestone

layers.

If we accept the view that meter-scale cyclicity is

driven by eustatic sea-level change, the study of these

cycles provides data that permit us to decipher the

history of sea-level changes. Moreover, the definition of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 sequence boundaries facilitates correlation within the

undifferentiated dolomites.

4.2. Peritidal and Subtidal Cycles within the undifferentiated dolomites

In the Grand Canyon and the Lake Mead area,

depositional parasequences were studied at Frenchman

Mountain, Quartermaster Canyon, and Mile-269 Canyon. In

the Grand Canyon, the dolomitization process has destroyed

many sedimentary features. Diagenetic problems

notwithstanding, parasequences with well defined bases and

caps are much less common in nature than one would expect.

In order to recognize parasequences, a very careful study

of sedimentary textures and petrologic characteristics is

needed. Study of a cyclic succession of rock also

requires very good exposure of each cycle. The

undifferentiated dolomites in the Grand Canyon usually

crop out in very steep walls. While this results in

excellent exposures, it also creates accessibility

problems. For these reasons, only a few localities are

suitable for detailed study of parasequences. Two major

cycle-types occur within the undifferentiated dolomites :

peritidal parasequences emd subtidal parasequences.

Peritidal parasequerices

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93

Peritidal cycles have been described by various

workers, including Osleger and Read (1991), Goldhammer et

al. (1993), and Montanez and Osleger (1993). I observed

two kinds of peritidal cycles, which I will refer to as

"thick" and “thin" cycles.

At Frenchman Mountain, "thick" peritidal

parasequences form distinctive dark-and-light bands in

outcrops of the undifferentiated dolomites (Fig. 31). The

base of each cycle (dark bauid) is typically one to two

meters thick and consists of medium to dark gray,

intensively burrowed mudstone (burrow-mottled facies),

sometimes interbedded with thin alternating grainstone-

mudstone beds (ribbon-rock facies). In rare instances,

high-profile LLH stromatolites (stromatolite facies) are

present in the basal portions of cycles. Thin

intraclastic grainstone beds (flat-pebble grainstone

facies) are often found in the upper part of the burrow-

mottled portion. The upper portion (light band) of a

"thick" peritidal cycle is usually less than one meter

thick, consisting of either thin, rarely mudcracked,

mudstone-grainstone interbeds (ribbon-rock facies), or

finely laminated, intensively mudcracked, sometimes cross-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94

I

Fig. 31. General view of undifferentiated dolomites at Frenchman Mountain. Well defined "thick" peritidal cycles.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 bedded, light-gray dolostone (mechanical laminite

subfacies of the laminite facies). Micro-erosional

surfaces, karst features, and low-relief stromatolites are

common. Some "thick" cycles have a relatively thin (0.5 m

or less) burrow-mottled mudstone bed at the base (burrow-

mottled facies) overlain by a layer of nodular dolomite

(nodular facies) of about the same thickness or less at

the top.

In the Grand Canyon, "thick", peritidal parasequences

form prominent cliff-and-slope topography through the

sections and are usually easy to recognize. The bases of

"thick" cycles there (Fig. 32) are commonly represented by

medium to light-gray, burrow-mottled or nodular, non-

resistant, dolomitic mudstone-wackestone (burrow-mottied

facies). This basal part ranges from 0.2 to 3.0 m in

thickness and typically erodes to form a recess beneath

the more resistant upper part of the cycle. Overlying

this recessive, bioturbated lower portion of the cycle is

a 1-2-meter-thick, light-gray, more resistant, commonly

cryptomicrobially laminated (cryptomicrobial subfacies of

•the laminite facies), dolo-micritic cap with numerous

micro-erosional surfaces and common desiccation features.

Irregular erosional top surfaces and the desiccation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96

6

Fig. 32. General view of undifferentiated dolomites at Quartermaster Canyon. Well defined "thick" peritidal cycles.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 cracks, clearly document subaerial exposure.

At Frenchman Mountain, the "thin" peritidal cycles

are recorded within thick laminite intervals linked with

sequence boundary zones. These 0.3-0.5 m thick cycles are

composed of thin grainstone-mudstone interbeds (ribbon

rock facies) at the base and are capped by thin beds of

cryptomicrobial laminite (laminite facies) . In some

intervals, the bases of the "thin" cycles consist of low-

profile (subfacies 3b) stromatolite beds.

In the Grand Canyon, the "thin" peritidal cycles are

well developed in field unit 4 at Mile-269 Canyon and

field unit 8 at Quartermaster Canyon (Fig. 33) . The base

of each cycle consists of a very thin (1-10 cm) interval

of non-resistant, burrow-mottled or nodular, light to

medium-gray dolomitic mudstone (burrow-mottled facies).

This non-resistant base is typically overlain by a thicker

(up to 0.8-1.0 meters), light gray, resistant dolomite

with well developed cryptomicrobial laminae, mudcracks,

and truncation surfaces at the top (laminite facies).

These cycles form a distinctive topographic profile of

cliffs and benches, with a small recess at the base of

each cliff. Boundaries between cycles are very irregular

because of the centimeter-scale erosional surface at the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98

P

Fig. 33. General view of iindifferentiated dolomites at Devil's Cove. "Thin" peritidal cycles are represented by one meter scale cliff-and-slope topography.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 top of each cycle and the non-resistant characteristic of

the limestone at the base of the overlying cycle. Some

cycles are represented at the bases by 10-20 cm thick

intervals of thinly interbedded mudstone and grainstone

(ribbon-rock facies) capped by thin (less than 15 cm)

nodular intervals (nodular facies) with abundant mudcracks

at the top of individual ripples.

Both the "thick" and "thin" peritidal cycles are

asymmetric. Gradation from burrow-mottled facies to

ribbon rock and laminated facies indicates gradational

upward shallowing, followed by an abrupt flooding surface

that marks the base of the succeeding cycle. No

deepening-upward stacking patterns within such cycles were

observed in this study.

Subtidal Parasequences

Subtidal parasequences occur in several localities,

including Whitney Ridge and Frenchman Mountain. They are

composed of dark to medium-gray, highly bioturbated,

massively-bedded or thick-bedded, dolomitic mudstone-

wackestone at the base (subfacies Ic of burrow-mottied

facies), gradationally overlain by either less

bioturbated, thinner-bedded, medium-gray dolomitic

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 mudstone (subfacies la or lb of burrow-mottled facies) , or

by a LLH-stromatolite layer (stromatolite facies) , or by a

mudstone-grainstone interval (ribbon-rock facies). The

upper lithology is then replaced by intensively burrow-

mottled mudstone (subfacies c) of the overlying cycle.

There is no or very rare evidence of erosion or

subaerial exposure within the subtidal cycles. Commonly

the subtidal cycles are interpreted to represent

gradationally alternating deeper aind shallower subtidal

lithofacies (see chapter 3). In this case, the subtidal

cycles are interpreted to be symmetrical. Such

alternating subtidal units are usually symmetrical, with

equally thick deeper and shallower portions. In some

cases, however, the subtidal units appear to be very

homogeneous, and no cycles csm. be distinguished.

4.3. Third-Order Depoeltional Sequences and

Sequence Boundaries

For the purpose of identifying third-order

depositional sequences, I made a detailed study of the

Frenchman Mountain section. The reader is referred to

Plate I (in pocket), which is a detailed stratigraphie

column of the Frenchman Mountain section. On the basis of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 stacking patterns of higher-frequency cycles, I have

identified seven depositional sequences within Unit I of

the undifferentiated dolomites at Frenchman Mountain.

Third-order sequence boundaries are generally

established on the basis of change in thickness of fifth-

order cycles and overall shallowing of depositional facies

that indicate long-term changes in third-order

accomodation (cf. Goldhammer et al., 1993). Below, I

briefly describe the seven third-order depositional

sequences and sequence boundaries determined within the

undifferentiated dolomites in the Frenchman Mountain

section. Sequence boundaries within the study area are

represented by either a single erosional surface or by a

relatively thick (up to 15 meters) zone of thinly bedded,

cryptomicrobially laminated tidal-flat deposits with

abundant evidence of exposure such as karst horizons,

incised valley fills, and solution breccias, associated

with minor evidence of exposure such as mudcracks, minor

erosional truncation, and disrupted laminae.

Sequence 1 starts 42 meters below the base of the

undifferentiated dolomites (5.5 m above the base of the

section) within the Havasu Member of the Muav Limestone

(Plate I). The sequence boundary is marked by a major

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 erosion, surface represented by a large-scale (about two

meter-thick) karst horizon (Fig. 34) that separates very

light gray, finely laminated, stromatolitic mudstone below

(laminite facies) from medium gray, thinly interbedded

grainstone and mudstone (ribbon-rock facies) beds above.

This surface is associated with a spectacular (1-m scale)

solution breccia auid 0.5 meter-thick greenish clay-rich

limestone bed.

The lower portion of Sequence 1 consists of

relatively thin, mostly peritidal cycles of burrow-mottled

mudstone (burrow-mottled facies), LLH-stromatolites

(subfacies 3b of stromatolite facies), and thin

grainstone-mudstone interbeds (ribbon-rock facies). Some

mudcracked laminite is also present within this thin

(about 5 m thick) interval. The middle portion (next

20 m) of Sequence 1 is composed of generally thick,

thickening upward, subtidal and peritidal cycles with

burrow-mottled bases (burrow-mottled facies). Because

this interval is represented by deepening upward,

peritidal to subtidal facies, and upward thickening

■cycles, it is interpreted to represent the transgressive

systems tract (TST).

The next 11 m consists of relatively thick, deep-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103

#'# ^ j . ^ " a "* - -

Fig. 34. Major erosion surface. Top of Seq. 5, Frenchman Mountain

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 water, subtidal couplets of dark-gray, burrow-mottied

dolostone (burrow-mottled facies) at the base capped by

thin alternating grainstone-mudstone interbeds (ribbon-

rock facies). Since this interval is marked by deep-water

facies with no evidence of deepening, i.e. no evidence of

declining accommodation, it is interpreted to represent

the early highstand systems tract (EHST). The late

highstand systems tract (LHST) is represented by a 4 m-

thick interval of very thin cycles .of shallow-water,

tidal-flat deposits consisting of mudcracked, finely

laminated dolo-mudstone (subfacies 8b of the laminite

facies) and thin, yellowish-gray, silty, limestone beds

(same subfacies). This interval is capped by a minor

erosion surface marked by solution breccia. Because this

interval is represented by very shallow-water facies

showing subaerial exposure and input of siliciclastic

sediments, it is interpreted as a third-order sequence

boundary zone. The entire thickness of Sequence 1 is

about 40 meters.

Sequence 2 begins with an interval about 30 m thick,

whose lower part is composed of stromatolite-based, thin

peritidal cycles that are commonly capped by finely-

laminated dolo-mudstone (laminite facies). Desiccation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 features in the finely-laminated caps and erosive contacts

between individual cycles are common. In the upper part

of this interval there are relatively thick peritidal

couplets with burrow-mottled bases (burrow-mottied facies)

and thinly-interbedded, grainstone-mudstone (ribbon-rock)

caps. An upward change from thin, cryptomicrobial-

laminite beds to stromatolite-based cycles indicates a

transition from a tidal-flat to a shallow-subtidal

depositional environments. Overlying this interval is a 7

m-thick succession of relatively thin (0.5 m-thick) cycles

consisting of burrow-mottled rock (burrow-mottled facies)

at the base, capped by thin, alternating, medium-gray

intraclastic grainstone and grainstone-mudstone interbeds.

Cycles in this portion of the section thicken up-section

and represent successively deepening depositional facies,

suggesting an overall increase in accommodation space that

indicates a transgressive systems tract (cf. Goldhammer et

al., 1993) . This interval grades upward into a thick

(about 10 m-thick) succession represented in the lower

part by thin (0.3-0.5 m thick) peritidal cycles, composed

of thin grainstone-mudstone interbeds (ribbon rock facies)

and cryptomicrobial laminite beds (laminite facies). In

the upper part, this succession consists of very thin

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 (0.2-0.3 m thick) cycles composed at the bases by

stromatolite beds (stromatolite facies) and capped by

finely laminated beds (laminite facies), with abundant

mudcracks and micro-erosional surfaces and thin (about i

cm) greenish-red silty-limestone layers. Because this

part of the sequence shows an overall shallowing

succession of upward-thinning cycles and is represented by

very shallow, peritidal and supratidal carbonate deposits

interbedded with some siliciclastic material, it is

interpreted to represent the highstand systems tract that

probably contains the third-order sequence boundary. The

entire thickness of Sequence 2 is about 50 meters.

The lower portion of Sequence 3 is a 14-m-thick

interval of upward-thickening, thick peritidal cycles

consisting of couplets with burrow-mottled bases (burrow-

mottled facies) and finely-laminated caps (laminite

facies). In the upper part of this interval, the laminite

facies is not present, and the cycles are capped by thin

beds of alternating grainstone-mudstone interbeds (ribbon-

rock facies). Thickening cycles, suggesting a gain in

accommodation and deepening depositional environments, are

interpreted to represent the transgressive systems tract.

The next 14-m-thick interval is composed of thinner.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 subtidal-peritidal cycles with burrow-mottled mudstone at

the base of each cycle, and thin intervals of very chin

grainstone-mudstone interbeds at the top. This interval

is characterized in the upper part by thin beds of nodular

dolostone and a minor erosion surface, marked by solution

breccia. Burrow-mottled mudstone beds within this

interval are rare. Thinning upward cycles, along with the

interpretation of gradually shallowing upward depositional

environments, suggest that this interval represents the

early highstand systems tract. Directly overlying this

portion is a 9 m-thick succession of thin, light-gray,

finely laminated, mudcracked, and cross-bedded dolomite

beds {subfacies 8a and 8b of the laminite facies). The

overall thinning upward of the cycles, the presence of two

major karst horizons, solution breccia, and abundant minor

erosion surfaces support the interpretation of this

interval as a third-order sequence boundary zone. The

entire thickness of Sequence 3 is about 35 m.

The lowest nine meters of Sequence 4 consists of

thick peritidal parasequences with bases of burrow-mottied

dolostone(burrow-mottled facies) and caps of laminite

(mechanical laminite subfacies). This interval is

interpreted as a transgressive systems tract. The next

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 108 54 m is composed of progressively upward-chinning

periCidal cycles with burrow-mottled dolostone bases

(burrow-mottled facies) and flaggy-weathering, nodular

dolostone (nodular facies) or cryptomicrobial laminite

(laminite facies) caps. Some mudcracks, micro-erosion

surfaces, and intraclastic-grainstone beds are present.

Intraclastic-grainstone beds are abundamt in the upper

part of this interval. Solution breccias are also common,

especially in the upper part. On the basis of stacking

patterns auad depositional facies, this interval is

interpreted to represent an early highstand systems tract.

This is overlain by a 4-m-thick zone of finely laminated

mudstone interbedded with thin cross-bedded grainstone

beds and thin (about 1 cm-thick) beds of greenish silty

dolostone. It is marked at the top by a minor erosion

surface. This zone is interpreted as a late highstand

systems tract, which also coincides with the third-order

sequence boundary zone. Sequence 4 is about 60 meters

thick.

Sequence 5 begins with a thin (7 m-thick) interval

of alternating thin beds of finely laminated mudstone,

nodular dolostone, and stromatolite beds. The

stromatolites are low-profile LLH-stromatolites in the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 109 lower part (subfacies 3b of the stromatolite facies) and

high-profile stromatolites (subfacies 3a) in the upper

part. This basal interval of Sequence 5 is also

characterized by rare, thin, oolitic beds and rare,

brownish chert nodules in the lower part, and several

minor erosion surfaces. On the basis of the upward-

thickening cycles and transition of low-profile forms of

stromatolites to high-profile forms, this interval is

interpreted to represent the transgressive systems tract.

Directly overlying the basal interval is a 36-m-thick

succession that begins with thick peritidal, stromatolite-

based cycles (high-profile LLH-stromatolites capped by

finely laminated dolo-mudstone) with rare thin (0.5 m-

thick) burrow-mottled and nodular beds. The middle

portion of this succession is represented by relatively

thick nodular intervals, thin alternating beds of

intraclastic grainstone, oolitic grainstone, and very thin

grainstone-mudstone interbeds. Thin, burrow-mottled beds

are also common in this portion. The uppermost nine

meters is mainly composed of finely laminated, mudcracked

dolo-mudstone with rare, thin, coarse-grained, burrow-

mottled grainstone beds. Within the dolo-mudstone

intervals there are some cross-stratified, fine-grained.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 110

Fig. 35. Incised valley fill deposits. Third-order sequence boundary located at top of Sequence 5 Unit I, Frenchman Mountain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ill grainstone beds. The top of this interval is represented

by a major erosion surface with three meters of relief

(Fig. 35). This major erosional surface is interpreted to

be a third-order sequence boundary. On the basis of the

upward thinning cycles and shallowing depositional facies,

this interval is interpreted to represent the highstand

systems tract. The entire thickness of Sequence 5 is

about 45 meters.

Sequence 6 begins with a 2-m-thick interval of

shallow cryptomicrobial laminite that is capped by a minor

erosion surface. Overlying this interval is 4 m of deep

subtidal facies composed of intensively burrowed,

internally non-stratified dolostone (burrow-mottled

facies). The upward deepening deposits suggest a

transgressive systems tract. The overlying 27-m-thick

interval consists of thinning-upward peritidal cycles.

The bases of these cycles are either stromatolites (high-

profile LLH-stromatolites) or burrow-mottled-dolostone,

while the caps are mudcracked, finely laminated dolostone

or nodular, flaggy-weathering dolostone. Oolitic-

intraclastic grainstone beds are present in this interval

and are associated with the laminite facies. Minor

erosion surfaces are rare. On the basis of upward-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 thinning cycles and the overall shallowing upward

depositional environments, I interpret this interval to

represent an early highstand systems tract. This interval

grades into a 5 m-thick zone composed of finely-laminated,

cryptomicrobial, dolo-mudstone interbedded with mechanical

laminite. Abundant ripped-up laminae and minor erosion

surfaces characterize this zone, which is interpreted to

represent a late highstand systems tract and a third-order

sequence-boundary zone. The entire thickness of Sequence

6 is 35 m.

Sequence 7 begins with a 15-m-thick interval of thin

(0.2-0.3 m), alternating ribbon-rock and nodular-dolostone

cycles. These grade into thicker (up to 1 m thick) cycles

with burrow-mottled bases and nodular tops. The upper

part of this basal 15-m-thick interval is composed of

relatively thick (up to 2 m), dark-gray, intensively

burrow-mottled dolostone. The upward-thickening cycles

represent successively deepening depositional

environments, auid I interpret this interval to represent a

transgressive systems tract. Overlying this basal

interval is a thick (55 m thick) succession consisting

mostly of poorly-bedded, medium-gray, moderately-burrowed

dolostone with occasional flat-pebble grainstone (flat-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 pebble grainstone facies) and intraclastic-grainstone

beds. The upper 10 meters of this 55-m interval is

composed of 1 m-thick, interbedded, burrow-mottled and

nodular strata and, at the very top, by light-gray,

skeletal, dolomitic wackestone with rare, large (up to 1.5

mm in diameter), glauconitic peloids. On the basis of

upward shallowing deposits, this interval is interpreted

to represent the early highstand systems tract. Due to

very poor exposure of the overlying strata, the overlying

third-order sequence boundary cannot be precisely located

here. The entire thickness of Sequence 7 is about 80

meters.

The overlying succession of Unit II does not show

well-developed cyclicity and is not suitable for sequence

stratigraphie study.

4.4. Brief Comparieon with the Work of Montaflez and

Oeleger (1993, 1996)

Montanez and Osleger (1993, 1996) studied the

sequence stratigraphy of the Banded Mountain Member and

upper portion of the Papoose Lake Member of the Bonanza

King Formation. The Banded Mountain Member is, in part,

correlative with the undifferentiated dolomites (Fig. 5).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 Their work is especially relevant to my study because they

also included Frenchman Mountain. Their measured section

at Frenchman Mountain is directly east of the Mormon

Temple, approximately 1 km to the south of my Frenchman

Mountain section (D. Osleger, personal communication,

1993) .

The Bonanza King Formation is primarily carbonate

rock, with some intervals of mixed siliciclastic-carbonate

lithofacies. Montanez and Osleger estaiblished three

facies associations in the Bonanza King: peritidal,

shallow subtidal, and deeper subtidal. Their peritidal

association includes intraclast breccia, silty

dololaminite, cryptalgal laminite, microbial boundstone,

and peloidal wackestone-packstone. Their shallow subtidal

association is composed of lenticular-bedded silty

dolomite, lime wackestone, and massive bioturbated

wackestone-packstone. Their deeper subtidal association

includes mixed calcareous siltstone, silty limestone, and

fissile green-brown shale.

All of these lithologies except calcareous siltstone

and shale (both of which belong to the deeper subtidal

association) are present in the undifferentiated dolomites

in cratonal sections, including Frenchman Mountain. The

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 115 Grand Canyon sections generally contain no or very little

silt, being composed primarily of limestone and dolomite,

with minor amounts of silty limestone.

Based on their facies associations, Montanez and

Osleger (1993) established two parasequence types in the

Bonanza King: peritidal and subtidal parasequences. In

the present study I also identified both peritidal and

subtidal cycles, and I further subdivided the peritidal

cycles into "thin" and "thick" cycles. My "thick"

peritidal cycles are the peritidal parasequences of

Montanez and Osleger (1993, 1996), while my "thin" cycles

occur mainly in the Grand Canyon sections and are rare or

absent in the Bonanza King sections, including Frenchman

Mountain (see section 4.2 in this chapter).

Montanez and Osleger (1993, 1996) recorded

systematic changes in parasequence type and thickness and

generated Fischer plots (Fischer, 1964; Goldhammer et al.,

1993, and others) for several sections, including

Frenchman Mountain. During the present study, the Fischer

plot technique was found to be very useful in defining

third-order boundaries and correlating sections within the

Grand Canyon. However, much of the Frenchman Mountain

section consists of non-cyclic intervals of homogeneous-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 116 dolostone, for which I could not generate Fischer plots.

This poor expression of cyclicity at Frenchman Mountain

prevented the use of Fischer plots for correlation between

Frenchman Mountain and the other sections in this study.

Figure 36 is a comparison of the sequences at

Frenchman Mountain identified in this study with those

identified by Montanez and Osleger (1993).

The present study has confirmed Montanez and

Osleger's (1993) observation that most sequence boundaries

within the undifferentiated dolomites are represented by

transitional zones rather than individual horizons.

Exceptions are the distinct karst-marked base of Sequence

1 and the boundary between sequences 5 and 6, the latter

of which is represented by incised valley fill.

Montanez and Osleger (1993) used the Fischer plot

technique to examine long-term variations in parasequence

stacking patterns. They identified four depositional

sequences within the Banded Mountain Member, and

correlated them between sections. In the present study, I

identified seven depositional sequences within the same

stratigraphie interval. The difference in results can be

explained by the fact that Montanez and Osleger's (1993)

measured section at Frenchman Mountain is in a different

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 117 location than my measured section, and some sequence

boundaries are not well exposed in their section (i.e. my

sequence boundaries number 3 and number 6 (Fig. 36) ) .

Also, Montanez and Osleger's (1993) Fischer plot data did

not cover the uppermost (approximately 110 m) interval of

the Bonanza King Formation, where a very probable sequence

boundary zone is located 40-50 m below the base of the

Dunderburg Shale (see this chapter, section 4.1).

Montanez and Osleger (1996) described a major karst

horizon at the very top of their "mixed unit" (the basal

unit of the Bauided Mountain Member) . In the present

study, this karst horizon marks the base of Sequence 1

(see Plate I) .

As shown in Figure 36, all of Montanez and Osleger's

(1993) sequence boundaries (or boundary zones) correspond

to sequence boundaries (or boundary zones) identified in

this study. Their section begins at the base of the

Banded Mountain Member, whereas I started my section 12

meters above the base of the Banded Mountain Member.

Two of my sequence boundaries, between Sequences 2

and 3 and between Sequences 5 and 6 do not have

corresponding boundaries in the Montanez and Osleger

(1993, Fig. 12) column. The boundary between my Sequences

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 118

Frenchman Mountain Frenchman Mtn. after Montanez (present study) and Osleger (1993)

400-

_ 300

major Jcarst

Seq. 4

_ 100

Base of und dolomites A A A A A A A A major )carst

Papoose Lake Member of the 50 m Bonanza King Fm.

[0 m sequence boundary or boundary zone

Fig. 36 Comparison between sequences at Frenchman Mountain section established in this study and in Montafiez and Osleger's (1993) work.

•i-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 119 2 and 3 was identified on the basis of very shallow

carbonate deposits interbedded with siliciclastic material

overlying a shallowing succession of upward-thinning

cycles (see section 4.4 of this chapter. Fig. 36, Plate

I). The boundary between my Sequences 5 and 6 is one of

the most distinctive sequence boundaries in my Frenchman

Mountain section, being marked by a conspicuous erosion

surface (Fig. 35, Plate I). These two boundaries are

apparently not well exposed in the Montainez and Osleger's

(1993) section.

4.5. Conclusion

Studying the successions of high-frequency (fourth-

to-fifth order) depositional cycles and the stacking

patterns of depositional facies made it possible to

identify third-order depositional sequences within the

undifferentiated dolomites.

Each depositional sequence is characterized by a

certain pattern of systems tracts that, in turn, depend on

the overall paleogeography. The lower portion of the

section is represented by depositional sequences with

approximately equal thicknesses of highstand systems

tracts and transgressive systems tracts. Prevailing

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120 periCidal cycles are generally thin (not exceeding 2 m),

stromatolite or burrow-mottled-dolostone based, laminite-

capped, and bearing abundant desiccation features.

Subtidal cycles are not common in the lower portion of the

section. Such patterns are characteristic for shallow-

shelf carbonates that can easily keep pace with third-

order sea-level fluctuations (Goldhammer et al., 1993).

The upper portion of the section is represented by

sequences with very thin transgressive systems tracts and

very well developed, thick, highstand systems tracts. The

transgressive systems tracts that consist of deep subtidal

facies indicate abrupt transgression of the sea. The

highstand systems tracts are marked by relatively thin,

shallowing upward, peritidal cycles, which commonly have

burrow-mottled-dolostone bases and ribbon-rock or nodular-

rock caps. Such patterns of cycles are interpreted to

represent overall, larger scale transgression which is

typical for a gradually deepening passive margin.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 5

AGE OF THE UNDIFFERENTIATED DOLOMITES

Due to an absence of fossils (see Chapter 2), the

age of the undifferentiated dolomites has remained

uncertain since this interval was first identified by

McKee (1945) . Their age has generally been assumed to be

Cambrian to possibly Ordovician. Several attempts have

been made to date this rock interval (Schenk and Wheeler,

1942; McKee, 1945; Wood, 1956; Brathovde, 1986). However,

these attempts have not led to a precise age

determination. Presently the undifferentiated dolomites

are presumed to be Upper Cambrian (see Chapter 2).

Through the use of lithologie and sequence-

stratigraphie methods, in this study I have been able to

correlate between undifferentiated dolomites in the

western Grand Canyon and those at Frenchman Mountain (see

Chapters 2 and 4). The strata at Frenchman Mountain are,

in turn, correlated with the upper portion of the Banded

121

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 122 Mountain Member of the Bonanza King Formation (Fig. 5).

The Bonanza King Formation has fossil control (Palmer,

1965) and is determined to be Middle and Upper Cambrian in

age (Middle-Upper Cambrian biozones of North America are

represented in Fig. 4. However, the Middle-Upper Cambrian

boundary is not precisely located in the Banded Mountain

Member of the Bonanza King Formation.

The undifferentiated dolomites at Frenchman Mountain

are conformsdsly overlain by the well-dated Nopah

Formation. This formation lies within the Aphelaspis

trilobite zone, which is Dresbachian (earliest Late

Cambrian) in age. The Nopah Formation, together with

varying thickness of underlying strata, was removed by

pre-Devonian erosion from all sections east of Whitney

Ridge (McKee, 1945; Longwell et al., 1965; Korolev and

Rowland, 1993) . Thus, in the western Grand Cainyon the

stratigraphie position of the undifferentiated dolomites

is significantly below the base of the Nopah Formation and

is therefore almost certainly Middle Cambrian.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER e

FRENCHMAN MOUNTAIN DOLOMITE

In this chapter I propose a solution to at least two

problems, discussed below, by the introduction of a new

name and formal formational status for the stratigraphie

unit previously referred to as undifferentiated dolomites.

I propose the name Frenchmsui Mountain Dolomite for this

interval.

The first problem deals with the absence of a formal

name for this unit. As mentioned in Chapter 1, the

undifferentiated dolomites were informally named by McKee

(1945). The term "Supra Muav," informally used by Wood

(1956) for this unit at the Yampai Cliffs, is not named

after a geographic locality as required by the North

American Stratigraphie Code (1983), and cannot be accepted

as a formal name. Brathovde (1986) proposed the name

"Grand Wash Dolomites" for the undifferentiated dolomites

in the Grand Canyon and Grand Wash Cliffs area. There are

123

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 124 two problems with this name. The first, as pointed out by

Elston (1989) , is that there is already a formation (the

Grand Wash Basalt) named for Grand Wash. Additionally,

and more problematical, Brathovde's type section in the

Grand Wash Cliffs does not contain a complete section of

the strata that need to be included in this unit, namely

the interval between the Muav Limestone below and the

Nopah Formation above.

The second problem is related to a tradition among

geologists of applying Basin-and-Rauige (i.e. miogeoclinal)

stratigraphie terminology to sections located on the

western edge of the craton and therefore have more in

common with sections on the Colorado Plateau. In some

cases both Grand Canyon and Basin-and-Ramge stratigraphie

terminologies are mixed within a single lower Paleozoic

sequence. For example, at Frenchman Mountain, the

westernmost cratonal section. Grand Canyon terminology is

commonly used for the intervals correlative with the

Tapeats Sandstone and the Bright Angel Shale (Matti et

al., 1993), while the name "Bonanza King Formation" is

used for the overlying sequence of rocks that is

correlative with the Muav Limestone and the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 125 undifferentiated dolomites (Gans, 1974; Matti et al.,

1993; Montanez and Osleger, 1993).

The name "undifferentiated dolomites," as well as

several other synonymous informal names, has been applied

within the Grand Canyon and Grand Wash Cliffs (McKee,

1945; Wood, 1956; Brathovde, 1986) (Fig. 2). Here I

propose a common formation name not only for these areas

but also for all cratonal localities west of the Grand

Canyon, where lithologie characteristics are comparable

with those in the Grand Canyon and where a significantly

thicker interval of Cambrian sedimentary rocks survived

pre-Devonian erosion. The usefulness of finally

establishing a formational name for this unit is clear.

To establish a new lithostratigraphic name the

general procedures of the North American Stratigraphie

Code (1983, p. 851-854) requires the following: (1) an

intent to designate a new unit; (2) designation of

category and rank of unit; (3) selection of name; (4)

specification of stratotype; (5) description of unit ; (6)

definition of boundaries; (7) historical background; (8)

dimensions, shape, and other regional aspects; (9)

geologic age; and (10) correlations. The geologic and

geographic description of type locality or stratotype

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 126 should accompany the description of a new

lithostratigraphic name. In previous chapters I have

discussed the age, boundaries, and historical background

of the informal stratigraphie unit referred to as

undifferentiated dolomites.

Located on the westernmost edge of the craton.

Frenchman Mountain contains a thick succession of strata

that are correlative with the undifferentiated dolomites

of the Grand Canyon (McKee, 1945) and the upper part of

the Banded Mountain Member of the Bonanza King Formation

in the Basin and Range Province. The undifferentiated

dolomites in the Grand Canyon and the correlative

succession at Frenchman Mountain are shown to be

lithologically comparsüDle (see Appendix B) .

The proposed type locality at Frenchman Mountain is

geographically accessible, located adjacent to Las Vegas

(Rowland, 1987). Moreover, the Middle-Upper Cambrian

succession crops out in relatively gentle slopes that

provide much easier access to the section than in the

Grand Canyon. Most importantly, in contrast to sections

in the Grand Canyon and the Grand Wash Cliffs, the

undifferentiated dolomites at Frenchman Mountain are

conformably overlain by fossil-bearing and thus well-dated

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 127 strata of the Nopah Formation, thereby providing a well

defined top to this stratigraphie interval. This, and

several other factors presented above, support Frenchman

Mountain as the best candidate holostratotype of a new

formation (Hedberg, 1976).

In his description of the trauisgressive Cambrian

sequence of the Grand Canyon, McKee (1945) described the

Tonto Group as consisting of the Tapeats Sandstone, the

Bright Angel Shale, and the Muav Limestone. The

undifferentiated dolomites were described separately from

the Tonto Group. However, McKee (1945) suggested that this

interval is a continuation of Middle-Upper Cambrian

sequence.

The present study shows that the undifferentiated

dolomites should be considered a part of the Tonto Group

based on the lithologie characteristics and stratigraphie

position.

Frenchman Mountain Dolomite is proposed here as a

new name for this lithostratigraphic unit, occurring from

the Central Grand Canyon on the east to the western edge

of the Colorado Plateau on the west (Fig. 2). It is

further proposed that this name be used in all cratonal

sections in northwestern Arizona and southern Nevada for

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 128 the sequence of Middle-Upper Cambrian carbonate rocks

conformably underlain by the Muav Limestone and

conformably overlain by the Nopah Formation.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 7

SUMMARY AND CONCLUSION

During this study, several problems dealing with the

age, correlation, and sequence stratigraphy of McKee's

(1945) undifferentiated dolomites were successfully

solved.

The undifferentiated dolomites have been puzzling

geologists with their undetermined age, questionable

correlation, and extremely difficult access, especially in

the Grand Canyon. This dolomitic succession contains no

fossils and has fairly variaüsle lithologie characteristics

throughout the study area. In the present study I suggest

using Colorado Plateau stratigraphie terminology for all

cratonal sections within the Lake Mead region.

The differentiation and correlation of the

undifferentiated dolomites became possible due to several

different methods used in this study and the information

obtained by previous workers. Brathovde's (1986) careful

129

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 130 description of this stratigraphie interval was an

important contribution to this work. He divided the

undifferentiated dolomites in the Grand Canyon area into

four traceable units. In this study I have accepted

Brathovde's three lower units for correlation purposes in

the Grand Canyon. However, I propose that the

undifferentiated dolomites in the study area be subdivided

into two lithostratigraphic units (Fig. 6). Unit II and

the upper portion of Unit I are not preserved in the Grand

Canyon due to pre-Devonian erosion. However, both units

seem to be fairly consistent in the western cratonal

sections and can be used for stratigraphie

reconstructions.

In this study two methods (lithologie correlation

and sequence stratigraphy) were used for correlation of

the undifferentiated dolomites. Lithologie correlation

combines analysis of lithologie patterns, sedimentologic

data, thicknesses of the units, and stratigraphie

position. The sequence-stratigraphic method primarily

involves analysis of peritidal and subtidal cycles

(parasequences) and determining and corelation of third-

order depositional sequences.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 131 On the basis of data collected in this study,

together with the work of Hazzard (1937) , Palmer and

Hazzard (1956), Gans (1974), and Montanez and Osleger

(1993) , I conclude that the upper part of the Muav

Limestone and the undifferentiated dolomites in the Grand

Canyon are correlative with the Banded Mountain Member of

the Bonanza King Formation and the upper part of the

Emigrant Formation (Fig. 5).

In this study I paid special attention to the

relationship between the undifferentiated dolomites and

underlying and overlying rocks. Different workers had

written conflicting statements about whether or not the

undifferentiated dolomites conformably overlie the Muav

Limestone (Beus and Billingsley, 1989; Elston, 1989; Beus,

1990) . Field observations in the Grand Canyon and Lake

Mead areas showed the absence of a conspicuous erosion

surface at the indicated stratigraphie level. The contact

between the Muav Limestone amd the undifferentiated

dolomites is gradational throughout the study area. In

the Grand Canyon the undifferentiated dolomites are un

conformably overlain by the Devonian "C Member" of the

Mountain Spring Formation (Rowland et al., 1994) . In the

western sections of the study area (Whitney Ridge,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 132 Frenchman Mountain) they are conformably overlain by

lowermost Upper Cambrian rocks of the Nopah Formation.

The age of the undifferentiated dolomites has

remained uncertain since McKee (1945) first identified

this interval. This study now permits a determination of

the age of this rock interval. The correlative strata in

the Basin and Range Province (Bauided Mountain Member of

the Bonauiza King Formation) are Middle and Late Cambrian

in age and lie within Bolaspidella. Cedaria. and

Crepicephalus trilobite biozones (Fig. 4). The overlying

Nopah Formation is marked at the base by the Aphelaspis

trilobite zone and, according to this, is Upper Cambrian.

Unfortunately, the Middle-Upper Cambrian boundary is not

precisely located within the Banded Mountain Member.

Because a significant part of the undifferentiated

dolomites east of Frenchman Mountain is removed by pre-

Devonian erosion, it is probable that this interval in the

Grand Canyon is entirely Middle Cambriaui.

The sedimentologic and pétrographie data accumulated

during this study allow me to define ten lithologically

distinct depositional facies within the undifferentiated

dolomites: (1) burrow-mottied facies, 2) flat-pebble

grainstone facies, (3) stromatolite facies, (4) oolitic-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 133 grainstone faciès, (5) bioclastic-grainstone facies, (6)

ribbon-rock facies, (7) nodular facies, and (8) laminite

facies (Fig. 14).

The sequence stratigraphy of the rock interval

correlative with the undifferentiated dolomites in the

Grand Canyon and Lake Mead areas was discussed in Chapter

4. Within the undifferentiated dolomites seven

depositional sequences have been recognized (see Plate I) .

Each sequence is represented by a shallowing-upward

succession of rocks and is bounded at the top by a zone of

maximum exposure that is normally associated with an

unconformity. Sequence stratigraphie concepts applied in

this study were very valuable in solving numerous

correlation problems.

The name "undifferentiated dolomites" was informally

introduced by McKee (1945) . Since that time no previous

workers were able to determine the age of this interval,

and no one formally proposed a formation name for this

rock unit on the Colorado Plateau. Having successfully

correlated this interval with trilobite-bearing strata,

according to recommendations of the North American

Commission on Stratigraphie Nomenclature (1983) and the

International Subcommission on Stratigraphie

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 134 Classification. (1987) , I propose the name "Frenchman

Mountain Dolomite" for this rock interval (Fig. i).

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V I J

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX A MAPS AND LOCATIONS

N

Stratigraphie section: Frenchman Mountain Source: Las Vegas NE, Nev., (1967), U. S. Geol. Surv. topographic map Scale: 1 : 24,000 Contour interval: 20 feet Location: T 20 S, R 62 E, sec.24

148

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 149

N

- iBsr

stratigraphie section: Whitney Ridge Source: Virgin Peak, Nev.-Ariz., Provisional Edition (1983), U. S. Geol. Surv. topographie map Scale: 1 : 24,000 Contour interval: 10 meters Location: T 36 N, R 71 E, sec. 28

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150

r ;( 1 @11'=: ; -% - ^

N

f

stratigraphie section; Tramp Ridge Source: Gold Butte, Nev., Provisional Edition (1984), U. S. Geol. Surv. topographie map Scale: 1 : 24,000 Contour interval: 10 meters Location: T 19 S, R 70 E, sec. 7

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151

- m ër-. ( r '

stratigraphie section: Devil's Cove Source: Iceberg Canyon, Nev.-Ariz., Provisional Edition (1983), U. S. Geol. Surv. topographie map Scale: 1 : 24,000 Contour interval: 10 meters Location: lat. 36 10', long. 114 06' (unsurveyed)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 152

N

V-

Stratigraphic section; Diamond Bar Range Source: Grapevine Canyon, Ariz., (1968), U. S. Geol, Surv., topographie map Scale: 1 : 24,000 Contour interval: 40 feet Location: T 30 N, R 16 W, sec. 34

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 153

-i

N

Stratigraphie section: Mile-269 Canyon Source: Bat Cave, Ariz.-Mohave Co., (1971), ü. S. Geol. Surv. topographie map Scale: 1 : 24,000 Contour interval: 40 feet Location: lat. 36 4', long. 113 52' (unsurveyed)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154

stratigraphie section: Quartermaster Canyon Source: Quartermaster Canyon, Arizona - Mohave Co., (1968), U. S. Geol. Surv. topographie map Scale: 1 : 24,000 Contour interval: 40 feet Location: lat. 35 57', long. 113 45' (unsurveyed)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX B

MEASURED STRATIGRAPHIC SECTIONS

FRENCHMAN MOUNTAIN

Thickness in meters Nopah Formation

Medium gray to orange, thin-bedded, slope forming non-resistcuat dolomitic siltstone.

Total thickness : 20.0

Cambrian undifferentiated dolomites

Field units

1 2 . Medium to light gray, coarse grained, non-cyclic, resistant bioclastic grainstone. Contains abundant echinoderm and trilobite fragments as bioclasts. Abundant unsorted deep-green glauconitic pellets become very eibundant toward the top.

Total thickness : 39.0

II. Medium to dark gray, non-cyclic, relatively resistant, highly bioturbated, homogeneous dolomite. Fossilliferous mudstone. Abundant storm beds with large (up to 5 cm) flat pebbles as intraclasts. Intraclasts are imbricated in some layers. Rare oolitic grainstone beds (not found in all localities). Rare, small (about 0.2 ram), deep-green glauconitic pellets at top 10 meters. 3 meters from top is non-resistant interval, highly eroded and covered with float.

155

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 156 Total thickness : 70.o

10. Relatively resistant interval, forming several prominent cliffs. Consists of repetitive intertidal cycles (2 meters in average) with dark to medium gray, highly bioturbated dolomite at base and fine laminated dolomitic mudstone at top.

Total thickness : 31.8

9. b. Very resistant, dark gray, highly bioturbated dolomite. Forms prominent cliff. Becomes medium to light gray, less bioturbated dolomite at top. 7.5

a. Light gray, fine laminated dolomite. Forms four separate shallow (intertidal-supratidal) cycles. 6.0

Total thickness : 13.5

8 . Four intertidal depositional cycles. Consist of medium to dark gray, moderately to light burrowed (ichnofabric index 2-3) dolomite at base of each cycle and light to very light gray, fine laminated dolomitic mudstone at top.

Total thickness : 9.6

7. Medium to dark gray, highly to moderately bioturbated dolomite. Becomes medium to light gray, thin bedded dolomite toward top. Lower part is non-cyclic. Upper 5 meters are represented by four symmetrical depositional cycles. Abundant storm beds through whole unit with flat pebbles as intraclasts. Flat pebbles are imbricated in some layers. Total thickness : 22.2

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157 6. Generally non-resistant interval. Light gray, fine laminated dolomitic beds, separated by thin (1 to 5 cm thick), less resistant limestone layers. Well developed shallow intertidal cycles. Abundant intraclasts and common erosional surfaces at top of cycles. Very prominent, 1.6 meters thick, resistant layer of fine laminated oolitic dolomite at bottom part and cherty laminite at top at about 5 meters from base. Abundant domal stromatolites within upper 15 meters. 1.4 meters from base are covered.

Total thickness : 17.0

5. Unconformably overlying unit 4 is commonly dark gray, moderately bioturbated dolomite with very common flat pebble storm beds. In some layers flat pebbles are imbricated and indicate approximately northward paleocurrent. Rare erosional surfaces within intraclastic layers. Subtidal depositional cycles are poorly defined. 16 m thick non-cyclic interval at about 25 meters from base. Upper 2 meters consist of light gray, fine laminated oolitic dolomite with abundant intraclasts and chert lenses.

Total thickness : 60.5

4. b. Unconformably overlain by unit 5 is very light gray, resistant, fine laminated dolomite. Forms several one meter scale cliffs. Conspicuous, big (15 x 1.5 cm) red chert lenses within upper one meter. Major erosional surface at top.

8.0

a. About 3 meters thick, dark gray, intensively bioturbated dolomitic bed. Abrupt contact with very light dolomite below. Grades into medium to light gray dolomite. Upper 11 meters are represented by thick (up to 3 meters)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 158 intertidal cycles with, well developed basal bioturbated and upper laminated parts.

14 .0

Total thickness : 22.0

3 . Thin (20-3 0 cm) beds of generally non-resistant, fine laminated dolomite. Abundant erosional features. Cycles are not developed.

Total thickness : 10.0

2 . Dark to medium gray, very resistant, cliff forming, highly-to non-bioturbated dolomite. Gradational contact with laminite facies below. Well developed symmetrical subtidal cycles. Intensively burrowed, dark gray dolomite at base and less burrowed to non, lighter dolomite, commonly with abundant intraclasts, at top. Flat pebbles are common in intraclasts.

Total thickness : 44-5

1 . About four meters thick transitional zone between dark gray, resistant dolomite of Havasu member of Muav Limestone and light gray, non-resistant undifferentiated dolomites. Overlain by 2 meters thick, resistant bed of light gray, structureless, massive dolomite. Overlain by very light gray, non-resistant, fine laminated dolomite with abundant chert lenses and nodules. Abundant domal stromatolites are commonly silicified and occur within upper 15 meters.

Total thickness : 31.0

TOTAL THICKNESS OF THE UNDIFFERENTIATED DOLOMITES : 371.0

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 159 Havasu-Member of the Muav Limestone.

Medium to dark gray, relatively resistant, intensively burrowed dolomite.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 160 WHITNEY RIDGE

Nopah-Eortnation

Medium gray, finely bedded dolomitic grainstone. Varnished quartz sandstone. Abundant storm beds with ripped up intraclasts and cross stratified layers.

Cambrian undifferentiated dolomites

16. Very light gray to pinkish, massive limestone. Grainstone, almost totally consisting of echinoderm plates. Some layers are highly burrowed. Forms three conspicuous cliffs, corresponding to the three subunits :

c ...... 8 m . b ...... 13 m. a ...... 22 m.

Total thickness : 43 .0

15. b. Medium gray, highly bioturbated dolomite. Non- resistant, slope forming interval. Upper three meters are covered. 11.7

a. Interbedded medium gray, highly bioturbated dolomite, and light gray, laminated dolomite. Well developed peritidal cyclicity. Relatively resistant, cliff forming interval. 9.8

Total thickness : 21.5

14 Medium gray, poorly bedded, non-resistant, slope forming dolomitic grainstone. Storm bed with southward imbricated intraclasts about one meter from the base.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 161 Total thickness : 14.6 13 . Interbedded medium gray, burrow-mottied, non- resistant dolomite and medium gray, finely laminated dolomite. Well developed peritidal cyclicity. Slope forming unit. Thin (0.6 m) interval with greenish (clay-rich ?) layers at top.

Total thickness : 18.8

12 . Light gray, generally non-resistant, slope forming, finely laminated dolomite. Well developed cyclicity. Major erosional surface at the top.

Total thickness : 7.0 - 8.0

1 1 . Dark gray, relatively resistant, cliff forming, mostly bioturbated dolomite. Becomes lighter to the top. Total thickness : 7.3

10 . Very light gray, non-resistant, recess forming dolomite. Finely laminated mudstone with asymmetrical, "tilted over" domal stromatolites. Thin (up to 10 cm) beds of cross-bedded, coarse dolomitic grainstone with abundant intraclasts. Major erosional surface at the top.

Total thickness : 5.5 - 6.5

Medium gray, very resistant, highly bioturbated dolomite. Forms prominent cliff. At the base - 1.6 m intraclastic storm layer overlain by 2 m thick finely laminated bed with bimodal (?) N-W, S-E cross-stratification. Total thickness : 14.0

8 Medium-to-light gray dolomite. Forms 0.6 - 1.0 m peritidal cycles with medium gray, bioturbated dolomite at base and light gray, finely laminated

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 162 dolomite at top. Total thickness : 9.0

Alternating light gray, bioturbated dolomite and very light gray, finely laminated dolomite. Small (up to 20 cm) domal stromatolites from base to about 13 m from base. Light gray, burrowed, intraclastic layer 0.6 m thick overlaying stromatolitic interval. There is an erosion surface with mudcracks at about 3 m below top. Relatively thick (from 3 to 10 m from base) interval contains abundant chert nodules and lenses. Well developed shallow peritidal cycles.

Total thickness : 24.0

6 . Medium gray, relatively non-resistant, bioturbated limestone with burrows filled with fine-grained dolomite. Spheroidal chert nodules at upper part of unit. Prominent, 2.2 m thick cliff forming interval consisting of thin interbedded limestone cuad dolomite beds at about 2 meters from top. Well developed subtidal cycles.

Total thickness : 42 .5

5. Very dark gray, homogeneous, highly bioturbated, very resistant limestone. Forms one single cliff. Small (up to 10 cm) lenses of dark to medium brown chert at very top.

Total thickness : 15.5

4. c. Very dark gray, resistant, highly bioturbated, homogeneous limestone. Forms one cliff. 4.7

b. Very dark gray, not bedded, highly bioturbated limestone. Forms one prominent cliff. 8 .6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 163 Prominent cliff. Gradational change from light gray dolomitic laminite to dark gray, thinly bedded in some places, resistant limestone. Becomes less resistant at top. Abundant bioturbation with horizontal traces. 7.8

Total thickness : 21.1

Very light gray, finely laminated, resistant, cliff forming dolomite. Well developed cycles. Cross stratified, 3 m thick bed of less resistant, slope forming, non-cyclic laminite at base.

Total thickness : 9.4

2 . Alternating thick (up to 1 m) beds of light to medium gray, highly bioturbated dolomite and thin beds of very light gray, finely laminated dolomite. Well developed peritidal cycles. Lowest 5 m covered.

Total thickness : 13.Q

1. Alternating thin beds of light gray burrowed dolomite and very light gray, finely laminated, resistant, cliff forming dolomite. Evidence of subaerial exposure in laminated beds. Well developed peritidal cycles. Total thickness : 7.3

TOTAL THICKNESS OF THE UNDIFFERENTIATED DOLOMITES : 275.0

Havasu Member of the Muav Limestone

Medium to dark gray, coarse grained, thinly bedded dolomite. Medium gray, highly bioturbated dolomite. Thin (up to 5 cm) sandstone layers. Abundant chert nodules. Some cross- stratified beds. Sandstone layers disappear toward the top.

.1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 164 TRAMP RIDGE

Devonian

Dark gray to medium gray, massive cliff forming,thick bedded dolomite grainstone. Fine grained, with common glauconitic patches. Abundant stromatoporoids about 12 m from base. Unconformably overlies Unclassified Dolomite.

Cambrian undifferentiated dolomites

17. Medium gray, well bedded calcitic dolomite. Grainstone to wackestone with aÜDundant 0.2-1 mm glauconitic peloids. Rare reddish oxidized patches. Relatively resistant and dense unit.

Total thickness : 18.0

16. Light to very light gray, pitted, sucrosic dolomite. Poorly bedded in some places. No observable sedimentary textures. Relatively dense and resistant rock but less resistant than unit 13. Total thickness : 10.5

15. Alternation of light gray, highly borrowed, fricüDle dolomite and dark gray, moderately burrowed dolomite. Distinctive cherty spots. Relatively non-resistant, bench-forming unit with no observable cyclicity.

Total thickness : 28.0

14. Alternating layers of light-to-medium gray, highly borrowed, resistant, well bedded, dolomite with non-bedded, homogeneous, light gray, resistant, sucrosic, massive dolomite, and light gray, non- resistant, friable, mottled dolomite. Well

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 165 developed cyclicity. Cycles are 1.1 to 1.6 m thick. Total thickness : 7.0

13 . Alternating layers of medium gray, poorly bedded, relatively resistant, highly burrowed dolomite with dark, non-bedded, less resistant, mottled dolomite. Cherty patches within bedded layers. The thickness of the repetitive cycles varies from l.1 m to 2.0 m.

Total thickness : 16.5

1 2 . The unit is characterized by interbedded light-to- dark gray, highly burrowed, locally bedded dolomite and abundant flat-pebble layers. Some flat pebble layers are grain supported with average pebble size of about 1 cm. Others are matrix supported with well spaced pebbles that range in size from 1 cm to 5 cm.

s. Medium-to-dark gray, resistant, homogeneous, highly borrowed, coarse-grained dolomite. 10 .0

r. Medium gray, poorly bedded dolomite with abundant flat pebbles as intraclasts. Pebbles are disoriented, up to 5 cm in diameter. Large spaces between pebbles. 1.2

p. Dark gray, coarse-grained, highly bioturbated, very resistant dolomite. No observable bedding.

2.5

o. Medium gray dolomite with abundant, evenly spaced, relatively large flat pebbles. Pebbles are 1 cm to 5 cm in diameter. 1.5

n. Light-to-medium gray, finely bedded dolomite with abundant small (up to 1 cm in diameter)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 166 flat pebbles. 2.5 m. Interbedded thin, layers of medium gray, highly bioturbated, homogeneous dolomite and thinly bedded flat pebble conglomerate. Flat pebbles in conglomeratic layers are relatively large (up to 5 cm in diameter). 2.5

1. Alternating, thin (less than 15 cm) conglomeratic layers containing small (up to 1 cm in diameter) and large (up to 5 cm in diameter) flat pebbles. Medium gray dolomite as matrix. 1.2

k. Thinly bedded, medium gray, coarse-grained dolomitic layers. Abundant large (up to 5 cm in diameter) evenly spaced flat pebbles.

3.0

j. Dark gray, thinly bedded, sucrosic, coarse­ grained dolomite with rare elongate intraclasts up to 1 cm in length. 3.0

i. Very light gray, pitted dolomite. Abundant cryptomicrobial laminations with some distinct distorted storm layers. Average size of ripped up clasts about 0.5 cm. 3.5

h. Highly borrowed, dark gray, chert-rich, fairly resistant dolomite. 1.0

g. Medium gray, massive, fairly dense and resistant dolomite with pitted weathering surface. Well preserved fine cryptomicrobial laminations. 1.5

f. Non-resistant, medium gray dolomite. Evenly

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 167 spaced, large (up to 5 cm in diameter) flat pebbles. 3.0 e. Dark gray, non-bedded, sucrosic, coarse­ grained, resistant, highly bioturbated dolomite. 3.0

d. Very light gray, non-resistant poorly bedded dolomite with pitted weathering surface. 0.5

c. Medium gray, non-resistant dolomite with thin layers of flat pebbles. Pebbles are up to 1 cm in diameter and densely packed. 3.0

b. Very light gray to white, friable, non- resistant chalk-like dolomite; laterally persistent bed. 0.5

a. Medium gray, massive, resistant dolomite with abundant, small (up to 1 cm) flat pebbles.

0.5

Total Thickness : 43.5

11 . Very light gray, highly bioturbated, sucrosic, fine-grained dolomite. Alternation of more and less resistant layers. Some layers contain domal stromatolites and laminites. Bioturbated beds are characterized by coarser grained dolomitic sand filling the burrows. Brownish, bioturbated intervals contain chert nodules. Several storm beds with disoriented various in size flat pebbles.

Total Thickness : 17. 0

10 . Dark gray, very resistant, highly bioturbated, fine grained sucrosic dolomite. Large burrows are

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 168 filled with coarser dolomite. Some 0-shape burrows. This unit is ridge-forming.

Total Thickness : 6.0

Cliff-forming, resistant finely laminated dolomite. Medium gray at the base to light gray at the top. Abundant cryptomicrobial laminations and water escape structures. Total Thickness : 10.0

8 . Cycles 20-40 cm thick consisting of dark gray, highly burrowed dolomite or flat pebble breccia at the base of each cycle. Finely laminated, significantly lighter in color dolomite forms cap of each cycle. Total Thickness : 12.5

Medium gray, partly bioturbated, non-resistant, dolomite. Storm beds, characterized by sibundant flat pebbles. Pebbles are up to 6-7 cm in diameter. Rare domal stromatolites.

Total Thickness : 13.5

6 . Light gray, non-resistant, cryptomicrobial dolomite with conspicuous orange chert nodules. Abundcuit domal stromatolites. Most of stromatolites are completely silicified. Several layers are slightly bioturbated.

Total Thickness : 23.Q

5 . Very light gray, non-resistant, highly bioturbated dolomite with pitted weathering surface. Fine cryptomicrobial laminations in some layers.

Total Thickness : 14.5 4 . Dark gray, highly bioturbated, fairly resistant dolomite. Gradually becomes light gray and less

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169 resistant toward the top. Rare cryptomicrobially laminated layers. Laminations increase upward. The interval is slightly more resistant than field unit 3. Total Thickness : 43 .0

Light gray, thinly bedded, non-resistant dolomite. Common cryptomicrobial laminations. Some beds are homogenized by bioturbation.

Total Thickness : 7.0

2 . Dark gray, highly bioturbated, very resistant, cliff forming dolomite. Forms several non- distinct, cliff-like patterns within the unit.

Total Thickness : 33.0

1 . Very light gray, thinly bedded, fairly resistant dolomite. Cryptomicrobial laminations are common. Thin chert lenses and nodules. Bioturbation is present in some beds.

Total Thickness : 59.0

TOTAL THICKNESS OF THE UNDIFFERENTIATED DOLOMITES : 288.5

Havasu Member of the Muav Limestone

Dark gray to buff colored, lumpy-bedded, highly bioturbated dolomite.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 170 DEVIL'S COVE

Devonian

Dark gray, non-resistant, thick bedded, highly bioturbated dolomite, with sucrosic texture. Abundant stromatoporoids in float. Unconformably overlies undifferentiated dolomites. The scale of the unconformity is 1-1.5 m.

Cambrian undifferentiated dolomites

12 . Medium gray, very resistant, highly bioturbated dolomite. Unit becomes less resistant toward the top. Well developed subtidal cycles.

Total Thickness : 36.0

11. Dark gray, resistant, highly bioturbated, sucrosic dolomite. Very thick-bedded oolitic packstone. Peritidal cycles are well developed.

Total Thickness : 8.0

10. Dark gray, resistant, well bedded, highly bioturbated sucrosic dolomite. Storm beds at the base of the unit. Large (up to 5 cm) flat pebbles as intraclasts. Total Thickness : 11.2

9 . Medium gray, very resistant, mostly bioturbated dolomite. Rare cryptomicrobial laminations at the base. Becomes dark gray and less resistant toward the top. Well developed peritidal cycles.

Total Thickness : 33.4

8 . Dark gray, highly bioturbated, very resistant.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 171 cliff forming dolomite. Cycles are not developed. Total Thickness : 5.9

7. Very light gray, non-resistant dolomite. Cryptomicrobial laminations. Cycles are not developed. Total thickness : 4.5

6 . Interbedded dark gray, non-resistant, mostly bioturbated dolomite with non-resistant, light gray, thinly laminated dolomite. Storm bed, containing flat pebbles ranging 2-5 cm in diameter at the base of the unit. Well developed peritidal cycles.

Total thickness : 21.0

5. Medium gray, highly bioturbated, resistant dolomite with scarce chert nodules in the lower part (up to 12.2 m from the base). Light gray, finely laminated dolomite with very distinct chert nodules in the upper part of the unit (up to 26.1 m from the base). The abundance of chert nodules and silicified stromatolites increases toward the top. Peritidal cycles are well developed.

Total Thickness : 26.1

4 . Dark gray, very resistant, cliff forming, highly bioturbated, thick-bedded, dolomite. Becomes light gray, much less resistsmt, finely laminated dolomite toward the top. Peritidal cycles are well developed.

Total Thickness : 50.7

3 . Light gray, very resistant, mostly bioturbated dolomitic packstone. Interbedded with very light gray, less resistant, finely laminated dolomite. Forms 0.5 - 2.1 m thick shallow peritidal cycles.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172 Total Thickness : 1 2 .Q

2. Dark-to-medium gray, bioturbated, very resistant, thick-bedded, cliff forming dolomite with sucrosic weathering surface. Well developed subtidal cycles. Total Thickness : 30.9

1 . Medium gray, moderately bioturbated dolomite, interbedded with light gray, cryptomicrobially laminated dolomite. Abundant brownish and white chert nodules, blocks, aind lenses. Partly silicified stromatolites are common. Cyclicity is not developed. Total Thickness : 34.4

TOTAL THICKNESS OF THE UNDIFFERENTIATED DOLOMITES : 266.0

Havasu Member of the Muav Limestone

Light-to-medium gray, highly bioturbated dolomite with scarce thin cherty layers. Commonly pink in weathered places.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 173 DIAMOND BAR RANCH

Devonian

Unconformably overlying the undifferentiated dolomites is medium-to-light gray, highly bioturbated dolomite. Becomes dark gray upward, with conspicuous stromatoporoids at 3 meters from the base.

Cambrian undifferentiated dolomites

5. Alternating intervals of medium gray, homogenized by bioturbation, massive, resistant, cliff forming dolomite with sucrosic weathering surface, and light gray finely laminated, non-resistant, slope forming dolomite. Unit is not well exposed. Unconformably overlain by Devonian. Well developed peritidal cycles. Total Thickness : 18.9

4 Thin beds of very light gray, relatively non- resistant, slope forming dolomite. Laminate. Some inconspicuous chert nodules and lenses.

Total Thickness : 7.7

3 . Medium-to-dark, very resistant, highly bioturbated, cliff forming dolomicrite. Abrupt color chcuige from very light gray laminite of Unit 2. Remarkable, 35 cm thick oolitic grainstone layer at the base of unit. Two distinct flat pebble layers: at 13 meters from the base and at 18 meters from the base.

Total Thickness : 34.Q 2 . Light-to-medium gray, non-resistant, slope forming dolomite. Abundant thin laminations. Very abundant chert nodules eind lenses. Small (up to 20 cm)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 174 domal stromatolites. Stromatolites are commonly asymmetrical and partly silicified.

Total Thickness : 6.8 1. Very light gray to white, non-resistant, slope forming dolomicrite. Laminite. Sparce white chert lenses (up to 2 cm thick) at 3.5 meters from base and above. Chert lenses become quite abundant at about 9 meters from base. Conspicuous dewatering structures.

Total Thickness : 9.5

TOTAL THICKNESS OF THE UNDIFFERENTIATED DOLOMITES : 76.8

Havasu Member of the Muav Limestone

Medium-to-light gray, relatively resistant, fine­ grained dolomicrite. Occurs in poorly defined ledges 1 to 2 meters thick. On weathered surface of light gray dolomite abundant patches and spots of medium gray dolomite (1 cm or smaller) occur.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 175 MILE 269 CANYON

Dgvonlan

Unconformably overlying the undifferentiated dolomites is medium gray, sucrosic, highly bioturbated, non-resistant dolomite. Abundant stromatoporoids in float. Overlain by dark gray, resistant, cliff forming, sucrosic dolomite of Temple Butte Formation above. Abundant stromatoporoids occur about 8 m above the unconformity.

Cambrian undifferentiate.d dolomites

4 . Very light gray, cryptomicrobially laminated, non- resistant, slope forming dolomite in the lower part (9.1 m). Medium-to-light gray, non-resistant, bioturbated dolomite with scarce chert nodules, medium gray sucrosic dolomite in the upper part (8.2 m) . Storm beds with ripped up flat pebbles as intraclasts are common. Well developed peritidal cycles. Total Thickness : 17.3

3 . Light gray, mostly cryptomicrobially laminated, resistant, cliff forming dolomite. Sharp contact with field unit 2 below. Rare chert nodules and lenses at the base of the field unit. Medium-to- light gray bioturbated dolomite with rare finely laminated beds and storm depositional features (ripped up flat pebbles). Low angle cross bedding and ripple marks. Peritidal cycles are well developed. Total Thickness : 49.7

2 . Interbedded thin (up to 10 cm) layers of medium gray, non-resistant, limy, crumbled dolomite, and more resistant, dark gray, highly bioturbated dolomite. Peritidal cycles are very well

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 176 developed. Slope forming interval. Prominent, 3 m thick layer of light gray, cryptomicrobially laminated dolomite (9 m from the base of the field unit). Total Thickness : 16.9

1 . Gradational contact with underlying unit. Light gray, thinly bedded, , moderately bioturbated, non-resistant, slope forming dolomite. Poorly developed cryptomicrobial laminations at the base. Rare minor chert nodules in the lower part of the unit. Much more resistant than underlying rock. The contact is based on lowest occurrence of laminite. Cycles are not developed.

Total Thickness : 22.5

TOTAL THICKNESS OF THE UNDIFFERENTIATED DOLOMITES : 106.4

Havasu- Member of. the. Jluav. Limestone

Medium gray, non-resistant, sucrosic, bioturbated dolomite. Beds are not distinctive and laterally continuous. Little rock shelters are the result of weathering. Purple shally component is characteristic for this interval.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 177 QUARTERMASTER CANYON

Devonian

Medium greenish gray-to-purple, non-resistant, well bedded, slope forming dolomite. Beds are about 10 cm thick. Dark - to - medium gray pitted dolomite. Overlain by dark gray, massive, very resistant, cliff forming dolomite of the Temple Butte Formation. Unconformably underlain by the undifferentiated dolomites.

Cambrian undifferentiated dolomites

8 . Cyclic sequence of interbedded, non-resistant, light gray limy dolomite amd resistant, medium-to- light gray, highly bioturbated dolomite. Peritidal cycles are well developed. This interval is significantly covered. Total Thickness : 30.9

7 . Very prominent interval. Medium gray, thick bedded, resistant, cliff forming, highly bioturbated dolomite. Total Thickness : 6.8

6 . Cyclic sequence of interbedded light gray, thinly bedded, non-resistant, limy dolomite and medium- to-light gray moderately bioturbated, very resistant, cliff forming dolomite.

Total Thickness : 32.3

5. Cliff-and-slope forming unit. Medium-to-dark gray, highly bioturbated dolomite. Well developed subtidal cycles. Abundcuit, presumably bimodal cross-stratification in the upper part of the unit.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 178 Total thickness : 15.6

Medium-to-light gray, very resistant, cliff forming, cryptomicrobially laminated dolomite. Interbedded thin layers of non-resistant limy dolomite and fairly resistant, moderately bioturbated, massive dolomite.

Total Thickness : 10.5

3 Very light gray, non-resistant, slope forming, cryptomicrobially laminated dolomite. Abundant chert nodules at the very base of the unit. Cycles are poorly developed. Total Thickness : 9.5

Very resistant, prominent, cliff forming unit. Medium-to-dark gray, highly bioturbated dolomite. Can be subdivided into three one meter thick beds. No observable sedimentary structures.

Total Thickness : 3 .0

1 . Light gray, cryptomicrobially laminated, non- resistant, slope forming dolomite. Poorly developed beds about 20 cm thick. At 5-6 meters from the base there is an interval with conspicuous white chert nodules amd lenses. Some chert nodules are present up to the top of the unit. Total Thickness : 8.5

TOTAL THICKNESS OF THE UNDIFFERENTIATED DOLOMITES : 117.1

Havasu Member of the Muav.Limestone

Light-to-medium gray, very resistant dolomite. Forms steep, prominent cliffs. Locally bioturbated. Orange-gray dolomitic interval at the base of the unit. Very light gray, cryptomicrobially laminated dolomite at the top.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U M irrtrtn tiattd Camorian ooiomius. Fr«nciman nounUwi. Clark Cowity. Nevada

mttars

400.2 Uaoo

h-390

- Coarse I ight gray ooiom ite interfieoded w itn sfccleta I gramstOML Ttiin (S cm) eecs of finely lam inateo dolomitic mudstone Aoundant ccninoderm fragments.

< a>

-380 u

iz

Skeletal grainstone. Abundant ccninodenn plates, some trilooite fragments very aounoant qeep-green glauconitic oeioios. h370

•remarkable green ism glauconitic layer 365.0 witm abimdant black pinte crystals

I I I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -360 359.6

* generally covered interval finely laminated mudstone

SEQUENCE BOUNDARY ZONE ? /WSAA

353.2 - lignt gray, dolomitic wackestone witn some Skeletal fragments and rare, partly disoived glauconite peioids

-350 - alternating tnm nodular and mottled ocds 349.5 - merow-mottled. nonncddco dolomite

• alternating tnm nodular ocos and tnm burrow-mottled oeds 346.7 - moderately beaded, birrow-mottled, coarse grained dolomite

- burrow-mottled, sircosic dolomite

341.2 - alternating layers of burrow-mottled dolomite witn tnm nodular beds -340

- homogeneous burrowed dolomite

■ ooorly-ocddcd. mtcnsively burrowed dolomite

330.1 >Vl -330

(_l z - poorly-oedoeo. intensively oioturoated dolomite witn rare intraclastic grainstone layers m

-same as above

32Z5

1-320

’ poorly-ocdoea. meoium-gray dolomite witn rare intraclasts ana oistinguisnaoie calcified ourrows a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ' wcrly-DcoOM. mcdium-gray dolomite I ^ 1 witn rare intraclasts and distingwisnaole calcified owTows

- resistant, intensively ogrrowed dolomite -3 1 0 • •

I I - moderately bedded, mediwm-gray. burrow-mottled dolomite Rare mtraciastic wacaestone witn large (uo to 3 cm) mtraciasis

3043 ■ poorly bedded, very dark gray, intensively bioturbatcd ddlomite Rare intraclasts

301.6

■ poorly bedded, medium gray, ourroweo -3 0 0 f e w dolomite witn rare intraclasts

297.7

- dark gray, nomogeneus. burrowed dolomite

- dark gray, nomogeneus. burrowed dolomite

2930 - tnm mudstone-grainstone interoeds rock layer

- dark gray, intensively burrowed, thinly beaded dolomite, some gramstone layers —290 289.0-

in

- moderately oedded. medium gray, burrow-mottled dolomite witn rare tnm layers of nodular dolomite

283 2 - tnm mudstone-grainstone interoeds and nodular dolomite

- tnm beds of sucrosic and mtraciastic dolomite - flat pebble conglomerate witn large intraclasts -280 - iignt gray sucrosic dolomite with tnm interoeds 123*278.2 of mechanical lam mite and gramstone layers SEQUENCE SOUND ANY ZONE A/VWV - tnm crypiomicrobial laminite with mudcracks, aouidant nppco-up laminations and minor trosional surfaces - dark gray, burrow-mottled dolomite 2743 - tnm. mudcracked. mecnanical lam mite 273 2 - light gray, non-resistant, burrow-mottled dolomite 27Z6 - medium gray, burrow-mottled dolomite Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -mtflium gray. ourrow-raouiM dolomite 271.4 ■ inin intarMdâ of purrow-mottleo and nodular dolomite -2 7 0 - Booriy bedded, dant gray, ourrow-mottled dolomite Bedding increases toward too miner erosion surface ' thin, light gray mecnanical laminite

‘ interoedded very tnm oeos of ourrow-mottled dolomite and noduiar dolomite X

257.5*

’ very lignt gray cryptomicrooial laminite. mudcracks. ripped-up clasts, and microcrosionai surfaces 2545 - poorly eaposcd. thick mecnanical laminite witn thin ocds of mtraciastic gramstone and occasional mudcracks

251 3 - interoedded Durrow-mottied and nooon rock beds

-250 internally non-stratif lea. burrow-mottled, oeioioai dolomite if) 109* 247.2 - minor erosional surface - thin, white, cryptomicrooial laminite SEQUENCE BOUNDARY - major erosional surface, 245 3 oolitic-skeletal gramstone. mud-cemented AAAAA conglomerate -burrow-mottled, mtraciastic tnm beds witn occasional mudcracks — tnm (10 cm) mtraciastic gramstone bed with moderately imbricated mtraciasts - tnm. cross-bedded, mudcracked mecnanical laminite

-2 4 0 239.6 - thick, light gray mecnanical laminite

- tnm. dark gray, burrow-mottled beds - non-bedoed burrow-mottled dolomite - tnm. cryptomicrooial laminite layers ■o^tnm oeos of medium gray, apnanitic dolomite

- tnm beds of medium gray, burrow-mottled dolomite 2344 - tnm mudstone-grainstone interoeds and mtraciastic gramstone beds - tnmly bedded, medium gray, rippled dolomite with some mtraciastic gramstone oeos Large 231 I flat peoples in mtraciasts - dark gray, burrow-mottled, mtraciastic dolomite -230 - tnm mudstone-grainstone mteroeos witn tnm mtraciastic gramstone beds - tnm interoedded layers of oolitic gramstone. mtraciastic gramstone. and burrow-mottled dolomite

- medium gray burrow-mottleo layer 225.6 g c3C3caa - tnm mtcrbcdddd layers of flat peoble conglomerate, r n a t M oolitic gramstone. and burrow-mottled dolomite Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I « S .6 tnm intcrticodea layers of flat peooie conglomerate, C 3 C 3 C 3 * f o n o t oolitic gramstone. ano ourrow-mottico ooiomitc meomm gray, oirrow-mottlto dolomite oolitic mtraciastic gramstone 222.7* mtraciastic. rmoly laminated dolomite and tnm mottled Mds tnm mudstonc-gramstone mteroeos medium gray, nodular dolomite 220 7 —220 tnm nodular layers and tnm mudstone-grainstone mterocds 2I«6— tnm mudstone-grainstone mteroeos Î5S3ES - finely laminated mudstone and oolitic gramstone - nodular dolomite oed 216.0* - mottled bed witn some mtraciasts and ooids at too - LlH-stromatolites and orownisn cneri nodules - LiM-stromatoiites witn tnm (i cm) oolitic beds Some tnm mottled beds small stacked stromatolites interoedded witn 211 5 tnm cryptomicrooial laminite ano LLM-stromatoiites - dark gray, burrow-mottled ooiomite - minor erosion surface —210 U.H- and stacked stromatolites - minor erosion surface - low-prof I le linked stromatolites y minor erosion surface 206.0 - tnm nooular oeos 20 cm tnick oolitic gramstone layer 2046 minor erosion surface tn - LLM-stromato I ites - minor erosion surface - LLH-stromatoutes 202.1 > mmor erosion surface - tnm cross-bedded cryptomicrooial laminite - medium gray burrow-mottled dolomite bed SEQUENCE BOUNDARY ZONE AAAAA tn -200 - tnm. mudcracked. cryptomicrooial ano mecnanical X laminite interoedded witn tnm, greenisn silty oeds 198.2 - interoedded dark gray mottled dolomite and tnm nodular beds minor erosion surfaces

tnm 16 cm) noouiar oeo - tnm (5 cm) mtraciastic layer - medium gray, tnick mecnanical laminite

- tnm. dark gray burrow-mottled beds

> lignt gray, ripplod. tninly bedded dolomite • tnm mudstone-grainstone mteroeos 190 S — 190 ' tnm interoedded layers of burrow-mottled dolomite, 79*188.8 flat pcooie breccia, and oolitic gramstone

'«7.3-

185.3 - mteroedded medium gray burrow-mottleo dolomite and tnm nodular layers

I8Z4

-dark gray tnmly oeoaeo dolomite — 180 - solution breccia 179.4* - medium gray. tnm. nppied burrow-mottled beds

____ - nodular dolomite and tnm mudstone-arainsion# Of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission J ^ ______

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • poorly okposeo interval of medium gray, ourrow- ffloitied. mtraciastic dolomite, twiggy eodies

' very tnm ocds of lignt gray fine lammite nodular dolomite tnm finely laminated beds and tnm mudstone-grainstone - tnm mudstene-gramstdne mteraeds "nri - modMB gray nomegenueus dolomite - 170 -nodular dolomite - medium gray tnicn lam mi te. ourrow- 1 mottleo dolomite, tnm mudstone-grainstone # o mterbeds. and mtraciastic gramstone oeos 167.1- -nodular dolomite - buTow-fflottied doiom ite - dark gray, nomogenuous dolomite oed 165.0- % - tnm (10-15 cm) layers of ourrow-mottled dolomite, noduiar dolomite, and tnm 163.1- mudstone-grainstone interoeds I6Z2"w o o — mmor erosion surface - tnm mudstone-grainstone interoeds.. tnick beds cryptomicrooial lammite. and mtraciastic gramstone - 160 159.7: - dark gray nodular dolomite - very dark gray burrow-mottled dolomite 65*157.6- -nodular dolomite 157.2- - tnm beds of ourrow-mottled mudstone, tnm mudstone-grainstone interoeds. and nodular dolomite - dark gray nomogenuous dolomite 64*i54l9- “ • mmor erosion surface - tnm planar mecnanical lammite witn wmte cnert nodules - interoedccd tnm. mudcracked. mecnanical lammite 0 > and mtraciastic gramstone. Teepee structures

57*151.1 ■ minor erosional surfaces witn 5 cm deep scours - planar-parallel, cross-oedoea mecnanical lammite. - ISO some mudcracks and teepee structures tnmly bedded burrow-mottled dolomite 146.2- ■ dark gray, non-oeoded. intensively oioturoated dolomite

- wavy, mudcracked cryptomicrooial laminite minor erosion surface

! 4ZS- -minor erosion surface planar-parallel mecnanical lammite 141 4 E 3 = E 3 - lignt gray mtraciastic oackstone bed 141.1 - dark gray, poorly bedded, burrow-mottled dolomite cn - 140 ' mmor erosion surface ■ lignt gray, finely laminated mtraciastic mudstone

' dark gray, non-oedoeo. intensively oioturoailea dolomite Lignter towards too

51*135.5 ■ mudcracked. cross-oedoed lammite

major erosion surface SEQUENCE BOUNDARY AAAAA

130.9 ■ minor erosion surface r 130 129.6 minor erosion surface Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ,*»«#»#» »• w^*we* *6# #

- 130 129.6. - mmor trosion sutace - «udcrsckctf. Uim. wavy laminated. cross-Ocddeo. cryptemicraeiai lammite Some mtraciaus. Abieidamt micrearesien surfacM - miner erosion surface 30 cm deep scoirs " solution oreccia - DtfTowfflottied dolomite ‘ minor erosion surface - tnmly oeaaea noouiar ooiomite - tnmly oedoeo mottled dolomite Twiggy oodies ' mmor erosion surface rco silty-dolomite layer - mediten gray, tnmly Dcdoeo. mtraciastic dolomite mtraciasts are uo-to i 5 cm m size — 120 ' dark gray, nomogenuous dolomite witn dark brown cnert nodules ' mediian gray, rippled, mtraciastic gramstone 116.7 T-n tnm mudstone-grainstone interoeds. ourrow-mottled mudstone beds, nodular dolomite beds, and oolitic -I- gramstone beds I 14.6 ( - 1 114.3 ’ dark gray, burrow-mottled, mtraciastic gramstone Twiggy bodies at tne top ‘ cross-bedded, burrow mottled dolomite IIZ6 ’ tnm mudstone-grainstone interbeds

dark gray, non-oedded. intensively oioturoated dolomite witn occasional tnm (i cm tnick) mteroeos of ribbon rock. 6ecomes more nomogeneous towards r% 110 too i tn

105.9 ’ 5 cm tnick. green, siity lammite bed ' fine, mudcracked cryptomicrooial lammite ’ dark gray, burrow-mottled mudstone

I0Z6 very light gray, mudcracked cryptomicrooial lammite ■ dark gray, burrow-mottled mudstone bed witn some twiggy bodies at top 100.5" ICO ■ very lignt gray, mudcracked cryptomicrooial lammite burrow-mottled oed 34*967* very tnm (d cm) red siltstone beds

tnm. wavy-parallel, mudcracked. cryptomicrooial lammite Low-profile LLH-stromatoiites Tnm AAAAA • • • mtraciastic gramstone mteroeos Abundant micro- erosional surfaces SEQUENCE BOUNDARY ZONE • • • • tn X 92.7

interoedded tnm mudstone-grainstone interoeds. medium gray lammite. and burrow-mottled dolomite beds Some twiggy oodies at base — 90

66.6 - - dark gray, tnm mudstone-grainstone • • • interoeds and mtraciastic gramstone oeos

#62-

* medium bedded, burrow-mottled dolomite witn rare, tnm mudstone-grainstone interoeds 63.7 ffl - darkfnudstoA* gray interoedoeo thin layers of burrowed Reproduced with permission efthe copyright owner Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83.7- - dark gray intcraadacd tnm layers of ourowed mudstone, mtraciastic gramstone. and tnm mudstone-grainstone interoeds 81.5- sm 3 ■ 30 cm tnick mtraciastic gramstone layer witn large flat peoeies m mtraciasts — 80 - tnm muostene-gramstone interoeds ■ dark gray ourrow-mottled dolomite

- tnm mudstone-grainstone interoeds

- Ourrow-mottled dolomite and tnm. ripoled gramstone oeds

18*75.7- ■ mednan gray, tnmly oedded. oiarow-mottied dolomite ■ Ourrow-mottled. mtraciastic mudstone-packstone oed minor erosion surface - very light gray, mudcracked mecnanical lammite

- lignt gray. wavy-Paraliel. tnm. mudcracked -70 cryptomicrooial lammite. low-profile domal and laterally linked stromatolites, and abundant black and dark yellow cnert nodules CM u 67.1- tn 8 65.8- minor erosion surfaces In solution breccia 65.2- - low-prof lie (UP to 5 cm) U.H-stromatolites - interoedded stromatolite layers and cryptomicrooial lammite beds — mmor erosion surface

reddisn green siltstone beds - 60 mmor erosion surface mtraciastic. burow-motlled mudstone, 10*58 9 twiggy bodies minor erosion surface cross-bedded oolitic gramstone bed witn abundant micro-erosion surfaces solution breccia dark-gray, large (uo to IS cm) cnert lenses

- up to 30 cm nign domai stromatolites witn large cnert 4. nodules and lenses —^ tn m ( 5 ^ cm) layers of finely laminated red siltstone —— mmor erosion surface - medium gray, ourrow-mottled dolomite witn small * domal stromatolites and rare scarse cnert nodules ^ solution breccia —- minor erosion surface -50 —- solution breccia - lignt gray, planar-parallel mecnanical lammite No mudcracks - very lignt gray, wavy-lam mated cryptomicrooial lammite Rare rippcd-up layers and common (/) mudcracks SEQUENCE BOUNDARY ZONE AAAAA X —— tnm bed of yeliowisn-gray siliciciastic sand - lignt gray, mudcracked mecnanical lammite witn ammoant micro-erosion surfaces —— tnm bed of yeilowisn-gray siliciclastic sand - mudcracked cryptomicrobial lammite 42.9* H -BASE Of undifferentiated DOLOMITES - dark gray burrow-mettled dolomite tnm mudstone-gramstone mterbeds - 40 -,tnm mudstone-grainstone mteroeos witn wnite and lignt brown cnert nodules (n - ourrow-mottled mudstone and tnm mudstone-gramstone X mterbeds

interoedded tnm waw neds of meaium oraw Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ouTow-fflottlcd dolomite, tnm mudstone-gramstone interoeds. and rare, very tnm cnerty ocds witn small white cnert nodules

I — I 33CE tnm cnerty oed wiin wnite cnert nodules mteroedded mediian gray ourrow-mottled - 3 0 dolomite and tnm mudstone-gramstone mtraciasts

28.2" > minor erosion surface JSJI - medium gray oiarow-mottled dolomite and tnm mudstone-gramstone interoeds

0fT lignt gray planar-earailel mecnanical lammite — minor erosion surfxe - medium gray tnm mudstone-gramstone interoeds 22.4- - - tnm mteroeds of Ourrow-mottled and nooon rock - thin mudstone-grainstone mterocds tn - 20 - Ourrow-mottled dolomite oeds and tnm mudstone-gramstone mterbeds - tnm burrow-mottled beds and tnm mudstone-gramstone interoeds u - tnm mudstone-gramstone mterocds z 8 ■ tnm interoedded intervals of more burrowed dolomite beds witn tnm mudstone-gramstone mterbeds and less burrowed 15.2* dolomite beds ' burrow-mottled dolomite and tnm mudstone-gramstone interoeds wnite small cnert nodules ' tnm mudstone-gramstone mterbeds tnm mudstone-gramstone interbcds XKMXK solution breccia tnm mudstone-gramstone mteroeos and white cnert nodules — 10 minor erosion surface bUTOw-mottled dolomite tnm mudstone-grainstone mteroeos ’ very recessive, deep-green si Ity limestone - tnm mudstone-grainstone mterbeds - small domal stromatolites ^ solution breccia xxxxx 5.5- — major erosion - large ska le karst horizon AAAAA SEQUENCE BOUNDARY - wavy-oarallci. muocracKco mecnanical lammite mterbedded with ripoon rock - thin mudcracked mechanical lammite - large domal stromatolites

—o 0.0 — ihrgmooiite interval - light yellowish-gray mecnanical lammite

LEGEND:

- burrow-iMtlling - «oicanic am

* I !iw laaauciMi - CB*rt TMUlM

]“ - tnm, mtwDcdOM muastana-grainaime - Chart lansn (ribOMi-focki

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SEQUENCE BOUNDARY ■ wa«y-0ar«litl. mudcracKta mecnanical lamimte intenedoeo with rttoon rock

- Uim mudcracked mechanical lammite - large domal stromatolites [nHiBRIs -- ■ ihromMlite mtarval - light yeiidkrifh-grar mecnanical lammite

LEGEND:

-volcanic asm - Mrra«*mMtims I mini

- r;ne iassmatisn ■ cP»f t rîsaiss

• inin. muretdoM -cnert lenses muattMW-grMmie (riMon-rocki - modular taxtm -mudcracKs

' iniraciattic gramstone - teepee structures 1^ ^ I

- oolitic grainstomt - incised valley fill

- minor erosion sief ace • •• - oiociastic grainstano

- glauconitic gramstone - major erosion swiace Ia /w w v I (karst neriaoni

- LLM-stromatoiitos - cross-eedding

- SH-stromatoiites - meters from base of 3S3.2 section

- siltstone - pamtcd marts an rock I I

- nomogeneous dolomite ' transgressive systems tract n i n

■ solution xeccia - nignsiand systems tract MXXKX I HST I

- tnrofflooiite - lowstano systems tract I tS T I

- qiz. sandstone - early nignstand systems tract EHST I

- SMding snows relative color intensity - late nignstand systems tract I lhst

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.