Paleocurrents and Depositional Environments of the Dakota Group (Cretaceous), San Miguel County, New Mexico

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Authors Bejnar, Craig Russel

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Link to Item http://hdl.handle.net/10150/244084 PALFACURRENTS AND DEPOSITIONAL ENVIRONMMT5

OF THE DAKOTA GROUP (CRETACEOUS),

SAN MIGUEL COUNTY, NEW MEXICO

by

,Crag Ru.s s el Bejnar

A Thesis Submitted to the Faculty of the

DEPARTMENT OF GEOSCIENCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1975 STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of re- quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made.

Requests . for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg- ment the proposed use of the material is in the interests of scholar- ship. In all other instances, however, permission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

4/-Am..d RIC " F. WILSON Associate Professor of Geosciences ACKNOWLEDGMENTS

I want to thank Dr. Richard F. Wilson, my thesis director, for his visit in the field, suggestions, and critical review of the manu-

script. Thanks are also extended to Dr. Joseph F. Schreiber, Jr., and

Dr. Gerhard O. W. Kremp for their help and critical review of the

manus c rip t.

I gratefully acknowledge the help given by my fellow graduate

students: William Sulkoske for his generous aid in pollen preparation and for numerous helpful suggestions, Art Trevena forour many fruit- ful discussions, Bill Purves for the initial computer programs, and

Steven Wampler for the computer plotter routines. Special thanks goes to Dr. Schumacher who unselfishly gave his time to helpme with the photographic work. My thanks are extended to Jan Drlik, my valuable field assistant, and Louise Drlik for typing the manuscript.

I acknowledge with appreciation the financial assistance for the summer field work provided by Waldemere Bejnar and Associates,Inc.

iii TABLE OF CONTENTS

Page

vi LISTOF ILLUSTRATIONS. .

LISTOF TABLES . ix x ABS'MA CT .

INTRODUCTION. i

Location i

Scope of Investigation . . i

Geomorphology and Structure . . 3 Regional Concepts of the Dakota Group...... 4

STRA.TICRAPHY . 9

Field Problems . . 9 Generalized Section. il Lower Sandstone Unit 11

Middle Shale Unit. . 19 Upper Sandstone Unit 21

SEDIMENTARYSTRUCTURES . 25

Stratification 25 Cross- Stratification . 26 Ripple Marks . 30 Soft Sediment Deformation. 34

PALEONTOLOGY. . 38

Root Casts . . . 38

Trace Fossils. . 40 Pollen and Spores . . 44 Sample Collection. . 46 Maceration Procedure 46 Identification . 48

PALEOCURRENTDIRECTIONS. . 51

Sampling Procedure . 51 Data Reduction 53 iv v

TABLE OF CONTENTS-Continued

Page

Cross- Strata Variability . . . . 55 Paleoslope and Shoreline Strike. . 57

HEAVYMINERAL ANALYSIS . 60

Methods 60

Results. . . 61

Provenance . . 65

Paleoclimate . 67

INTERPRETATION OF DEPOSITIONAL ENVIRONMENTS. . 69

Lower Sandstone Unit . 70 Middle Shale Unit. . . 73 Upper Sandstone Unit . . 74 Paleote ct onic Setting. . 75 Depositional History . . . 77

APPENDIX A: MEASURED SECTIONS . . 80

APPENDIX B: CROSS -STRATIFICATION MEASUREMENTS . . 107

APPENDIX C: STATISTICAL DATA ON CROSS -STRATIFICATION. . 133

REFERENCES. 145 LIST OF ILLUSTRATIONS

Figure Page

1. Index Map and Location of Study Areas . 2

2. General View of the Three Units in the Dakota Group

in North- Central New Mexico. . . 12

3. Basal Cretaceous Strata in North -Central New Mexico ..in pocket

4. Photomicrograph of Sandstones in the Lower Sandstone Unit 13

5. Limonite- Cemented Nodules (right) Grading into Con- tinuous Cementation (left) in Lower Sandstone Unit at Coyote Creek 15

6. Secondary Quartz Veinlets in Lower Sandstone Unit at Montezuma 15

7. Maximum Size of Pebbles in Lower Sandstone Unit of

the Dakota Group . . 16

8. Photomicrograph of Chert Pebble Containing Foramini- fera in Conglomerate from the Lower Sandstone Unit

(plain light). . . . 1$

9. Chert Pebbles Displaying White Tripolitic Weathering in the Lower Sandstone Unit at Box Canyon. Scale is in Inches 1$

10. Intercalated Green Shales and Sandstones at the Con- tact of the Pajarito Shale and the Lower Sand- stone Unit of the Dakota Group at the Trujillo

Section. . 20

11. Photomicrograph of Sandstone in Middle Shale Unit at Romeroville Gap. Dark Areas Are Carbona-

ceous Matter - . 20

12. Middle Shale Unit at Coyote Creek. Note the Channel Sandstone (center right) 22

vi v]..7.

LIST OF ILLUSTRATIONS Continued

Figure Page

13. Textural Changes in a Poorly Sorted, Fine-Grained, Carbonaceous Sandstone Produced by Burrow(left)

in Upper Sandstone Unit at Romeroville . . . . 24

14. Wood Fragment Molds in Bedding Plane in Upper Sand- stone Unit at Sapello. . . . 24

15. Principle Types of Cross -Stratification: Tabular - Planar (left) and Trough (right) . . . . 26

16. Trough Cross -Stratification in the Dakota Group . . . 28

17. Tabular- Planar Cross -Stratification in the Dakota Group. 29

18. Ripple - Marked Set of Cross -Strata in the Lower Sand- stone Unit at Kearny Gap Looking Toward the North- west. Hammer Gives Scale. . 31

19. Symmetrical Wave Ripples in Float from the Upper

Sandstone Unit at Montezuma. . . . 35

20. Soft Sediment Deformation: Load Casts and Overturned

Cross- Stratification ...... 36

21. Sand- Filled Root Casts in Middle Shale Unit at Coyote

Creek...... 39

22. Skolithos Tubes in Upper Sandstone Unit at McAllister Lake between Location 9 and 10 (Figure 1) 39

23. Ophiomorpha Burrows in Upper Sandstone Unit . o . 41

24. A Block Diagram Showing U -in -U Tubes with Spreiten

(From MacKenzie, 1968, p. 11) O 42

25. U -in -U Burrows in the Upper Sandstone Unit. . 43

26. U -Tube in Upper Sandstone Unit at Montezuma. Pencil is 15 cm long. 45

27. Planolites in Bedding Plane in the Upper Part of the

Lower Sandstone Unit at Arroyo Hermanos. . 45

28. Pollen and Spores in the Dakota Group . 49 viii

LIST OF ILLUSTRATIONS - -Continued

Figure Page

29. Paleocurrent Directions in Lower Sandstone Unit of the Dakota Group in North -Central New Mexico. Arrows show Locality Mean Direction and 95 Percent Confidence Level. 54

30. Comparison of Cross -Stratification Directions in Lower and Upper Sandstone Units of the Dakota Group in North- Central New Mexico. . 5$

31. Compass Rose Diagrams of Cross -Stratification in

in Lower Sandstone Unit...... in pocket

32. Variation in Current Direction within the Lower Sandstone Unit at Box Canyon 59

33. Percentage of Opaque and Non -Opaque Fractions of Heavy Minerals in Each Unit at Romeroville Gap 62

34. Average Composition of the Non - Opaque Heavy Minerals from All Intervals Plotted Against Grain Size. 62

35. Photomicrograph of Well Rounded and Euhedral Zircon

(Four Phi Size). . . . 64

36. Hypothetical Models Illustrating Textural and Geo- metrical Characteristics of Common Alluvial En- vironments. A. Piedmont Formed of Alluvial Fans; B. Braided Streams; C. Low Sinuosity Stream; D. Strongly Meandering Stream 71

37. Paleotectonic Map of the Western Interior of the United States during Early Cretaceous Time. . o 76 LIST OF TABLES

Table Page

1. Nomenclature of Basal Cretaceous Strata of the Western

Interior of the United States . . . 5

2. Measurements and Orientations of Ripple Marks at Kearny Gap...... 32

3. Ripple Mark Indices at Kearny Gap Compared with Indices of Particular Environments . . 34

4. Maceration Procedure. . . 47

5. Non-Opaque Heavy Mineral Composition Percentages. . 63

6. Varieties of Zircon and Tourmaline in Each Phi Size

Class . 66

ix ABSTRACT

The Dakota Group surrounding Las Vegas, New Mexico, consists of three units: 1) a basal, predominately trough cross- stratified, con- glomeratic sandstone, 2) middle intercalated, thin- bedded sandstone and carbonaceous shale, and 3) upper, predominately tabular- planar cross - stratified, sandstone containing trace fossils. These units represent, respectively, 1) a fluvial piedmont plain, 2) fluvial coastal plain, and 3) a beach, littoral, and shallow marine complex. The cross- stratification in the lower sandstone unit indicates an easterly paleo- slope. The cross -stratification in the upper sandstone unit has a bi- modal distribution almost at right angles to the paleoslope, suggesting deposition by longshore currents. The standard deviation of the cross- stratification in the lower sandstone unit of 78° is typical of fluvial deposits. The standard deviation in the upper sandstone unit of 97° indicates a marine origin.

x INTRODUCTION

The basal Cretaceous Dakota Group has been wellstudied in many places. This thesis examines the Dakota Group's southernmost occurrence along the Front Range ofthe Rocky Mountains. An under- standing of this area is critical to the eventual understanding of the relationships of the basal Cretaceous strata to the southeastin the Tucumari basin.

Location

The area of this study is located in north-central New Mexico in the vicinity of Las Vegas, New Mexico (Figure 1) .Study was con- centrated on two overlapping areas, one along the north trending

Creston Ridge for about 28 miles from La Cueva to Romeroville, the other extending 32 miles eastward from Romeroville to Trujillo

(Figure 1).

Scope of Investigation

Stratigraphic sections, spaced a few miles apart, were measured and described during the summer of 1974. Laboratory pro- cedures involved study of thin sections, heavy minerals, and palyn- morphs in an attempt to differentiate the stratigraphic units within the Dakota Group. Field classification and terminology were checked against the thin sections. The heavy mineral analysis provided supplementary data for the source material of the sandstone and, to

1 Figure 1.Index Map and Location of Study Areas

Location Name

1 Romeroville Gap 2Kearny Gap 3 Arroyo Hermanos 4Montezuma 5 Bonita Ranch 6Sapello 7North of Sapello gCoyote Creek 9Box Canyon 10Pagosa Canyon 11Canon Del Agua 12Mesa Lauriano 13 Conchas Canyon 14Trujillo 15Unmeasured section east of Las Vegas 16Valmora 2

Q

NEW '·'E XI CO

State Highway

Interstate Highway Locations

fezuma

1Las Vegas

...... ;,.;--~~

~12 La Liendre

N 5 o 5 10 miles H E3 E3 E

Figure 1. Index Map and Location of Study Areas 3

some extent, paleoclimate and paleotectonism. Because no body

fossils, except petrified logs, are preserved in the Dakota Group

in this area of study, emphasis was placed on differentiating types

of trace fossils in the sandstones, and extracting palynmorphs from

the shales and carbonaceous sandstones. These remains shed light upon the general paleoenvironment though not directly on the depo- sitional environment of the sediments at the instant they were laid

down.

Paleocurrents that deposited the Cretaceous sandstones were

determined from cross -strata dip directions. Separate paleocurrent

analyses were done for cross -strata in the lower sandstone unit and

the upper sandstone unit. From this work a general paleoslope and

shoreline strike was determined.

Depositional environments of the rock units in the Dakota

Group were deduced by the use of sedimentary structures, general

lithologies, stratigraphic relationships, and fossils present.

Seldom can a paleoenvironment be assessed from any one of these, and

even a combination of all available data is limited to an extent determined by preservation and exposure.

Geomorphology and Structure

The boundary of two major physiographic provinces, the Rocky

Mountains and the Great Plains, occurs in the area surrounding Las

Vegas, New Mexico. The contact is very abrupt with the ruggedSangre de Cristo Mountains rising to the west and the rolling LasVegas

Plateau spreading out to the east. Structurally, the broad, very asymetric, doubly plunging Las Vegas syncline lies along this contact

with the western flank steeply dipping to overturned, and the eastern

flank always dipping less than 10 degrees to the west.

The steeply dipping Dakota Group forms the first ridge or hog- back along the syncline's western flank. This prominent landmark, known as the Creston Ridge, trends sinuously north to south the whole

extent of the field area, clearly exposing the Dakota Group in numer- water gaps that cut through the ridge.

At right angles to the Creston Ridge the sharply defined

southern edge of the Las Vegas Plateau, called the Canadian Escarp-

ment, is capped by the Dakota Group. Although this provides numerous

east -west exposures, the overlying Graneros Shale is stripped off and

the exact thickness of the Dakota Group cannot be determined.

Regional Concepts of the Dakota Group

In many places in the Western Interior of the United States the basal Cretaceous rock units can be separated into three major

divisions (Table 1). Much confusion and a voluminous literature have been generated for over a century by attempts to correlate and name these rocks. The name Dakota Sandstone was first applied to the

entire basal Cretaceous sandstone sequence by Meek and Hayden (1$61,

P.419). Since then the term Dakota has been used variously by various authors. These problems have been described in other reviews

(Long, 1966; Owen, 1966) and will not be treated comprehensibly here.

A tripart division of the Dakota is found in the Las Vegas areal consisting of a lower conglomeratic sandstone, a middle Table 1. Colorado Nomenclature of Basal Cretaceous Strata of the Western InteriorChama of the United States This Southeast Southeast Tucumcari Young, 1960Plateau Owen, 1969 Basin Bejnar, 1975 Paper Waage,Colorado 1953 McLaughin,Colorado . Waage,ColoradoFront 1955 Range BasinGriggs and MancosShale MancosShale ShaleGraneros ShaleGraneros ShaleGraneros 1954 BentonShale Reed, 1959 Natur- 0 stonesand-upper stonesand-upper DakotaSandstone DakotaSandstone South ' DakotaSandstone 2a tionFormaita -- -o shalemiddleunit (5 oP, shalemiddlemiunit le Gencairn - K1owashale ° :Platttion ShalePajarito -)o W unit o unit H o shalemember . o ` - o ig Forma-tiontainMOu-Cedar Qó unitstonesand-lower P unitstonesand-lower +)m w-dó ""- memberstonesand-Lytle -° -Ñ w ó Cheyennememberstonesand - r 1Sd-stoneLytle ShaleTucumcariSandstone Rica Morrison Morrison Morrison Morrison Morrison Morrison . Morrison Formation Formation Formation Formation' Formation Formation . Formation Mesa ... 6 carbonaceous shale, and an upper sandstone. These three units probably correlate with the Colorado terminology: 1) of Waage (1953); 2) of

McLaughin (1951); and of Waage (1955) as is suggested in Table 1. The

Colorado Front Range terminology (Waage, 1953; Kauffman, Powell, and

Hattin, 1969) for the overall Cretaceous stratigraphy is in general use in north -central New Mexico east of the Sangre de Cristo Mountains.

Formerly the Purgatoire Formation and Dakota Sandstone were recognized units lying below the Graneros Shale and above the Jurassic Morrison

Formation. No further subdivision was made in the Las Vegas area probably because the basal Cretaceous is so thin when compared with the Colorado Cretaceous section.

To the southeast of the study area in the Tucumcari basin a three part division had been made in the Purgatoire Formation. These divisions, the Tucumcari Shale, Mesa Rica Sandstone, and Pajarito Shale, were recognized in this study area only at Trujillo, the easternmost section. How these correlate with the Dakota Group is not yet fully known (Jacka and Brand, 1972, p. 106) . Following the suggestion of

Griggs and Reed (1959) for the Purgatoire Formation in the Tucumcari basin, the designation Purgatoire Formation has been abandoned by most

authors, for example, Bachman and Dane (1962), in north -central and northeastern New Mexico.

Correlation westward across the southern Rocky Mountains from the Raton Basin into the Chama Basin (Owen, 1969) shows a three part

division almost identical to that in the Las Vegas area. The terms proposed by Owen (1969) for these units, the lower sandstone unit, the 7 middle shale unit , and the upper sandstone unit, are adopted for this paper. Post - Dakota Cretaceous marine shales are referred to as Marcos

Shale or as various tongues of it west of the Rockies , .and as Graneros

Shale along the Front Range. All writers have recognized the as a basically transgressive sequence starting in the east and migra- ting westward. Detailed correlations are difficult due to the lack of time marker horizons and to the rock stratigraphic units which are only exposed on the flanks of separated basins and are of different ages.

In the San Juan Basin the basal Cretaceous sandstones show local transgressive- regressive intertonguing with the Marcos Shale.

Many of these tongues have local formation or member status, for ex- ample, the Tres Hermanos Sandstone, Twowells Sandstone Tongue, Cubero

Sandstone Tongue, etc. Young (1960) divided the Dakota Group on the

Colorado Plateau into two formations, the Cedar Mountain Formation, which is non-carbonaceous, and the Naturita Formation, which is carbonaceous. Although the section is many times thinner, the basal

Cretaceous of this thesis area, hundreds of miles distant and probably of different age, shows this same basic relationship of upward increas- ing carbonaceous matter.

The divisions of the Dakota Group in the different basins are not strictly time - stratigraphic or rock -stratigraphic units, but are a consequence of the same or similar sedimentary processes operating in different places at different times during the Cretaceous trans- gression. The vertical sequence is dependent on the areally adjacent environments of deposition(Walther's Law of Facies) within overall sedimentary process (Visher, 1965, p.41), in this case a slow transgression of an epicontinental sea. STRATI GRAPHY

The Dakota Group lies everywhere on dark green shales and

lighter sandstones in the Morrison Formation of Jurassic age. In Colo-

rado this lower contact of the Dakota Group varies from disconformable

to conformable (Waage, 1955; Haun, 1959, p. 2 -4). Where exposed in the

Las Vegas area the Dakota- Morrison contact is apparently a paraconform-

ity with only local channeling.

The Graneros Shale, a black shale containing Upper Cretaceous

marine foraminifera (Eicher, 1965) , lies on top of the Dakota Group

everywhere in this area. The bottom few feet of the Graneros Shale are

commonly very sandy, and mark a rapid but gradational lithologic change.

This brackets the bulk of the Dakota into the Lower Cretaceous,

though the very top of it may be lower Upper Cretaceous. The age of the middle shale unit seems to be Albian, uppermost Lower Cretaceous,

from pollen data discussed under Paleontology.

Field Problems

Sixteen locations for study were selected on the basis of

accessibility, areal spacing, exposure, and owner permission. Cross -

stratification orientations for paleocurrent analysis were taken at all

of these. At 13 of the locations stratigraphic sections were measured using a 100 foot steel tape held perpendicular to the bedding. These

sections are described in Appendix A.

9 10

Generally access was good, though several land owners would not

grant trespass because of previous abuses. The base of the sections is

typically covered by debris from the cliff -forming Dakotaon the slope

forming shales and sandstones of the Morrison Formation. The east -

west series of sections (locations 1 tog in Figure 1)were measured

along the escarpment of the Las Vegas Plateau, where the Dakota Group

forms the cap rock. These sections all have eroded tops making only

the minimum thickness of the Dakota Group measurable.

Faulting along the upturned Creston Ridge also hampered meas-

urement. Small- displacement, high -angle faulting is common, especially

at Romeroville Gap and Kearny Gap. This does not seriously affect the

thickness measurements. Larger scale vertical faulting of over 100

feet at Coyote Creek necessitated making a composite section in which

there were no overlapping strata. The thickness here represents only

minimum thickness. Bedding plane faulting in the nearly verticallyup-

turned beds in the Creston Ridge is difficult to recognize. At Sapello

movement along and within the middle shale unit is evidenced by the

sheared texture of the black shale and slickensides on the surrounding

sandstone. Just north of the measured section at Montezuma the usual uppermost shales of the Morrison Formation are faulted out by a pre-

dominantly bedding plane fault which W. Bejnar (in press) has traced

for over a half mile. This faulting brings white Morrison sandstones in direct contact with very similar white Dakota sandstone.Further to the north this same fault probably accounts for the apparent thinning

of the Dakota Group reported by Baltz and Bachman (1956,p. 103). 11

Generalized Section

In most of the outcrops studied the Dakota Group can be divided into three major units: a lower sandstone unit, a middle shale unit,

and an upper sandstone unit (Figure 2). The middle shale unit is missing in some of the sections in the eastern part of the field area

(Figure 3, in pocket).

All the sandstones in the Dakota Group are light -colored, sil- ica- cemented, quartz arenites by Folk's classification (196$, p. 124).

In thin section the grains are overwhelmingly common quartz with

straight extinction under crossed nicols. Chert makes up one to five percent of the sand grains in each unit. Three forms of silica cement the rock. Quartz overgrowths in optical continuity with adjacent grains are the most common form (Figure 4a) ;Chert (recrystallized opal ?) is next (Figure 4b) ;and opal cementation is very minor. Some clay matrix is present in the conglomerates of the lower sandstone unit and silty sandstones in the middle shale unit; however, some silica cement is almost always present in addition.

Lower Sandstone Unit

The lower sandstone unit ranges in thickness from 63 to llg

feet with a mean of 91 feet (excluding the Trujillo section). This unit comprises about 75 percent of the complete Dakota section. The main rock type is a pale grayish orange to very light gray, conglomer- atic to fine- grained, moderate- to well- sorted, silica- cemented, quartz

arenite (Figure 4). It is the best cliff former in the Dakota Group.

Limonite cement along with silica is not common but is locally abundant 12

a. Upper sandstone unit and middle shale unit at Romeroville Gap.

b. Lower sandstone unit at Pagosa Canyon.Note the discontinuous nature of the bedding.

Figure 2. General View of the Three Units in the Dakota Group in North -Central New Mexico. 13

a. Medium -grained sandstone cemented by quartz overgrowths (crossed nicols).

b. Medium- grained sandstone cemented by chert (crossed nicols).

Figure 4. Photomicrographs of Sandstones in the Lower Sandstone Unit. 14

(Figure 5). Along the Creston Ridge locally abundant secondary quartz veinlets lace the sandstone (Figure 6) .

The distinctive features of the lower sandstone unit are the prevalence of conspicuous medium -scale trough cross- stratification, which is described under Sedimentary Structures, and chert - pebble conglomerate lenses. The conglomerate lenses are not basal. They are predominately in the upper half of the lower sandstone unit in the measured sections (Figure 3, in pocket). Conglomerate comprises as much as 30 percent of the lower sandstone unit in some places but averages less than 10 percent. The quantity of conglomerate varies greatly between closely spaced exposures. Most of the conglomerate forms lenses a few feet thick which grade into coarse sandstone, but some discrete conglomerate -filled channels are over 10 feet thick.

Other conglomerate zones are persistent across an outcrop and approach sheet -like form. Within many sandstones in the lower sandstone unit there are layers of chert one or two pebbles thick. These probably represent lag concentrates along a channel floor.No persistent

traceable contact could . be established at the base of the conglomeratic zone, though a change in the stream regime during the lower sandstone deposition is evident.

The conglomerate is dominately white to gray to black chert with very minor reddish quartzite, white quartz, and sandstone frag- ments that vary in size from three inches down to granule size (less than 1/4 inch) . A plot of maximum pebble sizes at various localities

suggests a fining to the east (Figure 7). The light gray to black 15

Figure 5. Limonite- Cemented Nodules (right) Grading into Continuous Cementation (left) in Lower Sandstone Unit at Coyote Creek.

Figure 6. Secondary Quartz Veinlets in Lower Sandstone Unit at Montezuma. 16 :.rt SR?'C-Y.- MAX. SIZEOF: CHERT PEBBLES 3 inches 2 1/2 inches 2 inches

I 1/2 inch

e I inch 1/2 inch

it

fat) N 5 0 5 10 miles

Figure 7. Maximum Size of Pebbles in Lower Sandstone Unit of the Dakota Group. 17 chert is fossiliferous. It contains recognizable bryozoans and fusulinids (Figure 8). Apparently silicified Paleozoic carbonates were the source of these pebbles.Many chert pebbles have dense gray centers surrounded by thick weathered rims of white tripolitic chert

(Figure 9). Some are completely weathered.

The conglomerate beds in the lower sandstone unit are generally more weakly cemented than the surrounding sandstones forming underhangs in the field. The cement is generally a variable admixture of a white clay material and silica.

In the lower portion of the sandstone unit at most sections, thin clay -gall conglomerate and discontinuous, light -green claystone layers can be found. Minor amounts of chert are associated with the play galls. The clay galls are obscure because they weather rapidly.

The size of these clay clasts is as much as seven by two inches in cross section, averaging perhaps an inch in diameter. The clay galls form part of a poorly delineated, repeated, vertical sequence consist- ing of (from top to bottom) :

3) trough cross -stratified sandstone

2) thin, discontinuous, clay-gall conglomerate

1) an erosional surface.

Some of these scour surfaces show as much as six feet relief.

At Arroyo Hermanos trace fossils (Planolites) were found within a single bedding plane. No vertical burrows are in the lower sandstone unit. The only carbonaceous matter is in the uppermost portions of the lower sandstone near the contact with the black shales of the middle 18

Figure 8. Photomicrograph of Chert Pebble Containing Foraminifera in Conglomerate from the Lower Sandstone Unit (plain light).

Figure 9. Chert Pebbles Displaying White Tripolitic Weathering in the Lower Sandstone Unit at Box Canyon. Scale is in Inches. 19 unit. Silicified logs were found at the bases of thick conglomerate layers at four different localities.

The lower sandstone unit at Trujillo is only 36 feet thick- almost half the minimum thickness elsewhere. The entire Cretaceous section is 120 feet, which approximates the average for. the Dakota elsewhere in this area (Figure 3). The Mesa Rica Sandstone at Trujillo does not contain marine fossils as it does to the east and southeast

(Phillips, 1973). The Pajarito Shale at Trujillo may be a tongue of marine shale between two genetically similar rocks (Figure 3). The lateral relationships between the Dakota Group and the Mesa Rica Sand- stone have not been satisfactorily worked out (Jacka and Brand, 1972).

No conglomerate is present at Trujillo. The lower sandstone unit of the Dakota Group and the Pajarito Shale at least locally are intercal- ated at their contact for a thickness of five feet (Figure 10).

Middle Shale Unit

The middle shale unit consists of two intercalated lithologic types: silty, fine- grained sandstone and black carbonaceous shale. It characteristically weathers to a covered slope.The middle shale unit is persistent from north to south, and varies from 9 to 17 feet in thickness (Figure 3a). Along the west to east traverse, the unit is thinner and discontinuous (Figure 3b). Little or no carbonaceous material is present east of Mesa Lauriano.

The shale generally is grayish olive to medium dark gray and weathers to lighter grays. The sandstone typically is light gray to 20

Figure 10. Intercalated Green Shales and Sandstones at the Contact of the Pajarito Shale and the Lower Sandstone Unit of the Dakota Group at the Trujillo Section.

Figure 11. Photomicrograph of Sandstone in the Middle Shale Unit at Romeroville Gap. Dark Areas are Carbonaceous Matter. 21 grayish orange and weathers grayish yellow.Both the sandstone and shale contain dark disseminated carbonaceous matter(Figure 11). The sandstones especially abound with wood fragments replaced by limonite or as empty molds. Pollen and spores are present in unweathered samples from this unit. Rare, poorly preserved leaf impressions are present in float. In 1972 the author found an exterior mold of a con- iferous cone in the sandstone of the middle shale unit at Montezuma.

The middle shale unit at Coyote Creek is unique in three re- spects. All but two feet of horizontal black shales and thin sand- stones have been truncated by a small paleoriver channel. The ero- sional surface and channel sandstone are clearly visible in Figure 12.

Dramatic evidence like this of at least a partially fluvial environ- ment for the middle shale unit is not found elsewhere. Root casts are another unique feature discussed under Paleontology. The third feature is a load cast or load pouch described under Sedimentary Structures.

Upper Sandstone Unit

The base of the upper sandstone unit was picked at the top of the highest black shale of the middle shale unit. The sandstones above this horizon consist of three distinct lithologic types. The most com- mon of these is a light gray, fine- tomedium -grained, well-sorted, silica -cemented, very well indurated quartz arenite that weathers to grayish orange pink or pale red. Its distinctive features are vertical trace fossil burrows and /or well-developed, small -scale tabular planar cross -stratification. 22

Figure 12.Middle Shale Unit at Coyote Creek.Note the Channel Sandstone (center right). 23

The second distinct lithologic type is a mottled very light gray and dark gray sandstone that weathers with dark yellow orange blotches. It is clayey, fine to medium grained, and moderate to poor

sorted with fine irregular dark carbonaceous partings and swirls. The distinctive feature of this sandstone is the complete destruction of bedding by extensive bioturbation. This probably accounts for its poor sorting. Photomicrographs of this type of sandstone show the textural changes that can be produced by a single burrow (Figure 13 )

The third type of sandstone contains no trace fossils. It is characterized by a profusion of carbonized wood fragments, some re- placed by limonite, and wood molds, which leads to a roughly weathered surface (Figure 14). This type of sandstone comprises the entire upper sandstone unit at Coyote Creek.Here the upper sandstone is grayish yellow to mottled light and dark gray, clayey, fine to medium grained, well to moderate sorted, and well indurated. This lithologic type re- sembles the better sorted sandstones in the middle shale unit.

Overall the sandstone in the upper sandstone unit tends to be finer grained than in the lower sandstone unit , but it varies from fine to coarse grained.Hand specimens from the two units often cannot be distinguished from each other. Stylolitic bedding surfaces are common in the upper sandstone unit. The top of the upper unit usually forms the top of the exposure and is eroded to some degree, hence only mini- mum thicknesses can be recorded.However most eroded sections are close in thickness to the few complete sections. The thickness varies between 10 and 45 feet. 24

Figure 13. Textural Changes in a Poorly Sorted, Fine -Grained, Carbonaceous Sandstone Produced by Burrow (left) in Upper Sandstone Unit at Romeroville.

Figure 14. Wood Fragment Molds in Bedding Plane in Upper Sandstone Unit at Sapello. SEDIMENTARY STRUCTURES

Primary sedimentary structures in the study area include strat- ification, cross -stratification, and ripple marks. These structures occur in a wide variety of modern sedimentary environments, yet each different environment has a slightly different set of flow conditions which leaves its mark, making the study of sedimentary structures use- ful in paleoenvironmental reconstructions.Penecontemporaneous sedi- mentary structures include soft sediment deformation and burrows. The trace fossils are discussed in the section Paleontology.

Stratification

The thickness of the strata in the lower sandstone unit is highly variable, and ranges from laminae a few millimeters thick to

20 -foot -thick conglomerate beds. Most commonly, however, beds range from one to four feet in thickness.The bounding surfaces of strata are typically not parallel in the lower sandstone unit, and the indivi- dual strata are seldom traceable across an outcrop (Figure 2b).

The stratification in the middle shale unit is thinner and has a greater length to thickness ratio in cross section than in the lower sandstone unit, though many of the thinner strata still pinch out with- in an exposure (Figures 2b and 12). The middle shale unit consists of two alternating lithologies. The black shales have a maximum thickness of four feet at Romeroville Gap and dwindle to a few inches or not

2.5 26 being present at all to the east. The individual sandstone strata in the middle shale unit vary from two feet to less than an inch in thick- ness when they are present.

The stratification in the upper sandstone unit varies in thick- ness from a maximum of three feet to less than an inch (Figure 2a).

Some of the woody zones within the upper sandstone unit display discon- tinuous wavy bedding delineated by layers of wood fragment molds.

Stylolitic bedding surfaces are not uncommon in this unit. Bioturbated zones several feet thick have destroyed the stratification and cross- stratification in several areas.

Cross-Stratification

Cross-stratification occurs in abundance at every outcrop visited and is by far the most common sedimentary structure. The classification system proposed by McKee and Weir (1953) was used to divide the sets of cross-strata into tabular planar and trough cross- stratification types (Figure 15).

Tabular - Planar Tro ugh

I i ~-----~ 'I

Figure 15. Principle Types of Cross-Stratification: Tabular-Planar (left) and Trough (right). (From Pettijohn, Potter, and Siever, 1973, Figures 4-5, p. 109.) 27

In the field, three dimensional views of the cross - stratification are scarce, making positive identification of the cross -stratification typedifficult at times. In several places essentially no shade differences between the cross -strata within one set exist, rendering them almost impossible to see and causing the set to resemble massive bedding. Trough cross -stratification (Figure 16) predominates in the lower sandstone unit, while tabular- planar cross - stratification (Figure 17) predominates in the upper sandstone unit.

The sandstones in the middle shale unit are generally thin bedded and massive.

Sets of trough cross -stratification range from 0.5 to 10 feet and average about two feet in thickness measured at right angles to bedding. These fall into medium -scale cross -stratification of McKee and Weir (1952, p. 386). The cosets tend to be lenticular. The sets of tabular - planar cross -strata are much thinner averaging less than a half foot in thickness, ranging from small to medium scale.

Cross -strata dip angles average 20° and have a standard devia- tion of 7.5° in the lower sandstone unit; dip angles in the upper sand- stone unit average 21° and have a standard deviation of 6.6°(from

Appendix C). The average dip angles fall near the lower limit of high - angle cross - stratification (20 °) according to McKee and Weir(1953,p.

386). Jacob (1ß73, p. 104) suggests 15° for this lower limit. ,.- . ,. - 28 z a ,_-._.;}.- .,

4^ a 7 v. '4111 di; / lr íÌ . C / . #-41i ''

At ^ rä..//Lifclf...- a. Horizontal exposure of lower sandstone unit at Box Canyon

b. Lower sandstone unit in cross -section at Montezuma

c. Very steeply upturned beds in lower sandstone unit looking down section (cross- stratification appears upside down).

Figure 16. Trough Cross -Stratification in the Dakota Group 29

I w J f a. Upper part of the lower sandstone unit at Coyote Creek

b. Upper sandstone unit at Mesa Lauriano.Note apparent 1$0° reversal in one set. Set thickness averages 1/2 foot.

Figure 17. Tabular- Planar Cross- Stratification in the Dakota Group 30

Ripple Marks

Ripple marks have been used as indicators of paleocurrents and paleoenvironments for many years although uncertainty in their inter- pretation still exists (Harms, 1969; Tanner, 1967; Potter and Pettijohn,

1963). Unfortunately, ripple marks were found in situ only at Kearny

Gap. At several other localities, ripple marks were observed in float associated with the upper sandstone unit.

The ripple marks at Kearny Gap are near the top of the lower sandstone unit (bed 5, location 2 in Appendix A). The ripple marks occur on at least five separate cross -strata surfaceswhich are two to five cm apart. The set itself is much larger than most within the en- tire Dakota Group (Figure 1g). The bedding planes (bdp) are structur- ally tilted 38° eastward, the cross -strata (x -bd) tilt southeastward at

560, and the ripple crests are oriented almost north -south and plunge about 36° (Figure 18). The ripple crests clearly do not lie parallel to the strike of the cross -stratification even after structural rota- tion corrections have been made (Table 2).

The simple structural rotation does not include any possible plunge on the syncline flank at Kearny Gap, but the direction of plunge is such that it would make the ripple marks run more nearly at right angles to the strike of the cross- strata (90° rake). The plunge angle is small anyway, much less than 10 °.

The low parallel ripples are orientated essentially parallel to the original dip of the cross- strata (Table 2). This form of ripple mark is common in modern eolian sands where they are caused by wind 31

Figure 1$. Ripple- Marked Set of Cross -Strata in the Lower Sandstone Unit at Kearny Gap Looking Toward the Northwest.Hammer Gives Scale. 32

Table 2. Measurements and Orientations of Ripple Marks at Kearny Gap

structural dip S81E 380 corrected bedding horizontal on bedding plane plane dip

original dip of cross- S52E 56° S20E 280 stratification dip ripple mark original SOg 360 S16E 27° orientation orientation

original rake of ripple 85° mark in cross - strata 46° rake

- V/WIf IMO .r ripple spacing 5.0 cm, range 1.7 to 7.5 cm length of 2 cm (?) short side length of 2 to 3 cm ( ?) long side ripple height 3 mm, range commonly 2 to 4 mm with a maximum of 8 mm 33 eddies that swing around the sides of the duneand sweep laterally across the dune face(Steidtmann, 1974, p. 183$). "Moreover, if the ripples had been formed in water by waves acting on a sloping face, the spacing and height of the ripples would vary in response todepth

changes down this slope," (Walker and Harms, 1972, p. 2$2). These variations are not found at Kearny Gap.

Three environmentally sensitive indices were calculated for this set of rippled cross -strata from the primary data in Table 2 using the following relations (Tanner, 1967) :

ripple index (RI) = ripple spacing/ripple height,

ripple symmetry index (RSI) = length of long side of ripple length of short side of ripple and

continuity index (CI) = length of crest ripple spacing

The RSI was difficult to determine because of the extreme shallowness

of the troughs, less than three mm, which are flat bottomed.

The high values of RI and CI at Kearny Gap(Table 3) indicate

that the ripple marks are wind derived. The -sandstones here are not

the typical fine -grained, eolian sandstones with RI's from70 to 30,

but rather medium -grained and well -sorted. Harms (1969, p. 38e)

reports RI's of 10 to 15 in such eolian sands. The more questionable

RSI suggests a possible wave orswash origin. This particular set of

ripple marked cross -strata at Kearny Gap has beendescribed as "eroded

(flat- topped to round- crested) oscillatory wave ripples which formed in

the intertidal zone. These wave ripples are excellent indicators of 34

Table3. Ripple -mark Indices at Kearny Gap Compared with Indices of particular Environments (based on Tanner, 1967, p. $9)

index Kearny Gap limits environment

RI 17 15 wave or water current >_17 wind or swash

CI >18 >10 swash, r-'? nd, or wave >15 wind or ::we

RSI 1 to 1.5 (?) wave or swash >3 wind or water current

of shoreline strike..." (Phillips, 1973,p. 40) . The bulk of evi- dence is against this interpretation.

Other ripple marks found in float from the upper sandstone unit have a different form from those at Kearny Gap (Figure 19). They are symmetrical straight ripples of probable wave origin. Typically these ripple marks have a ripple spacing of five cm and a height of about six mm for an RI of about eight.

Soft Sediment Deformation

Figure 20 shows two types of soft sediment deformation: load casts (ball and pillow structures) and overturned cross -- stratification.

One load cast or load pouch is present at Coyote Creek in the middle shale unit. "Load casts are indicative of no particular environment.

The only requirement is deposition of sand on a water-saturated hydro - plastic layer." (Pettijohn, Potter, and Sievert 1973, p. 124)

Instability is set up when higher density sand overlies a less dense 35

Figure 19. Symmetrical WaveRipples inFloat from the UpperSandstone Unit at Montezuma 36

a. Load cast in the middle shale unit at Coyote Creek.

b Overturned cross -stratification in the lower sandstone unit at Trujillo.

Figure 20. Soft Sediment Deformation: Load Casts and Overturned Cros s- Stratification. 37 mud. A vertical readjustment of material forms the load pouch. This readjustment may be sudden, caused by a shock, e.g., an earthquake, with liquifaction of the mud as suggested by the experiments of Kuenen

(195$,p. 17).

The upper portions of many cross-strata in the vicinity of

Las Vegas, New Mexico, become vague due to readjustment of the grains caused by fluid drag of the currents flowing over the deposited sand

(Pettijohn et al., 1973, pp. 370- -373). If cohesion of the sand is low enough and the fluid drag is high enough, the forset beds will distort so that their dip directions are upstream. Clearly overturned cross - strata are rare in this area. One excellent example of this type of soft sediment deformation was found in a room -sized, lower-sandstone, talus block at the Trujillo section (Figure 20b). PALEONTOLOGY

The Dakota Group in the vicinity of Las Vegas, New Mexico con- tains few fossils. The only body fossils are carbonized wood fragments and wood molds in the middle shale and upper sandstone units, silici- fied logs at the bases of conglomeratic channels in the lower sandstone unit, and sand -filled root casts in the middle shale unit at Coyote

Creek. No shell fossils or their molds were found in this area. Trace fossils are widespread and locally abundant in the upper sandstone unit. Five different types were recognized. Palynomorphs were exam- ined from two locations in the carbonaceous middle shale unit.

Root Casts

Two one -foot -thick shale beds at the top of the middle shale unit at Coyote Creek contain hundreds of sand- filled, downward - bifurcating, downward- tapering, cylindrical casts (Figure 21). These casts are probably root casts of small trees or brush which must have densely covered this area. Some of the root casts can be traced with difficulty through a two inch sand bed between the two shales.Much carbonaceous matter is included in the clayey, silty, fine- grained sandstone that makes up the casts.

38 39

Figure 21. Sand- Filled Root Casts in Middle Shale Unit at Coyote Creek.

Figure 22. Skolithos Tubes in Upper Sandstone Unit at McAllister Lake between Locations9and 10 (Figure 1). 40

Trace Fossils

Trace fossils are poor index fossils -- many range from

Cambrian to Recent -- and are of limited use in stratigraphy.However, they are extremely useful in paleo-- ecological investigations (Howard,

1972). Not only are certain types limited to particular facies, but trace fossils, unlike body fossils, can never be transported into an- other environment. The trace fossils with the widest distribution in the field area are vertical burrow casts. The two principal genera of these are Skolithos Haldeman ( Scolithus Hall) and Ophiomorpha Lundgren

(Halymenites Sternberg).

Skolithos tubes (Figure 22) are vertical burrows with a diameter of about two mm and a length averaging 10 to 20 cm.A maxi- mum length of 30 cm was foundat the Conchas Canyon section. Skolithos tubes are straight, never branched, and are typically crowded.They are probably made by worms or phoronids(Hgntzschel, 1962, p. 215).

Skolithos tubes are in the indurated, moderate- to well - sorted, medium- to coarse-grained sandstones of the upper sandstone unit, except for a single questionable occurence in the middle shale unit at Canon Del Agua.

Ophiomorpha is a vertical, unbranched, one to two cm in diameter tube, with wart -like ornamentation on the exterior of the tube, but smooth on the inside. Hence, the burrow casts are smooth.

These tubes vary in length from 15 to 25 cm. They may occur singly as in Figure 23a, or less commonly, closely spaced(Figure 23b). Weimer

and Hoyt (1964) convincingly argue that the maker of Ophiomorpha 41

a. Single Ophiomorpha burrow in cross -stratified sandstone at Montezuma. The pencil parallels bedding.

b. Packed Ophiomorpha burrows on West Side of Canon Del Agua.

Figure 23. Ophiomorpha Burrows in Upper Sandstone Unit. 42

burrows was a marine decapod crustacean. These authors show that

modern burrows of Callianassa major Say exhibit a nearly identical

form and similar environmental distribution to Ophiomorpha burrows in

the Dakota in Colorado. The modern burrows are abundant in well-

sorted, massive- bedded sands in wave -agitated littoral and shallow

neritic conditions, especially in the zone between mean sea level and

low tide on beaches that face the open ocean (Weimer and Hoyt, 1964, p. 763).

Also in the well -sorted, commonly cross- stratified beds of the

upper sandstone unit are U- tubes, Arenicolites Salter, and U -in -U

tubes, Rizocorallium Zenker and Corophioides Smith.Generic identifi-

cations were not made in the field because of the typically poor ex-

posure of these fossils.

U -in -U tubes are U- shaped with spreiten which are the concave-

upward, connective links joining the vertical portions of the "U"

(Figure 24). U -in -U tubes tend to be larger than the simple U- tubes;

however, commonly the spreite are poorly preserved and the distinction

between these forms is difficult to observe. Figure 25 is a bedding plane view and a cross -sectional view of U -in -U burrows.

Figure 24. A Block Diagram Showing U -in -U Tubes with Spreiten (From MacKenzie, 1968, p. 11). 43

a. View of bedding plane at Mesa Lauriano section thatcontains profuse U -in -U burrows.

b. Cross section of U -in -U burrow, Rizocorallium, at Montezuma. Note the spreiten between the vertical tubes.

Figure 25. U -in -U Burrows in the Upper Sandstone Unit. 44

U -tubes are simple U- shaped, round burrows perpendicular to bedding. The unsculptured, pencil -sized tubes are separated by about three cm and are commonly about eight cm long (Figure 26). Similar burrows are made today by Polychaeta marine worms (Moore, Lalicker, and Fischer, 1952, p. 458).

In contrast to the foregoing trace fossils which more or less co- inhabited the same high -energy, sand environment, two distinct trace fossils from a relatively quieter environment are found in the carbonaceous, silty sandstones of the upper sandstone unit.Thalassi- noides Ehrenberg consists of tubes about one cm in diameter forming largely horizontal, branched, tunnel systems. The forks are Y- shaped without special surface ornamentation. Commonly Thalassinoides is so profuse that it obliterates both bedding and previously formed burrows.

It is largely responsible for the bioturbated zones in the upper sand- stone unit. Hntzschel (1962, p. 218) says these tunnels are produced by decapod crustaceans. Planolites Nicholson burrows are five to ten mm wide and irregular in course and direction(Figure 27). They are in the bioturbated beds of the upper sandstone unit and have a single occurrence in the upper part of the lower sandstone unit. Grant and

Owen (1974, Fig. 11, p. 244) have also found Planolites in the lower sandstone unit in the Chama Basin.

Pollen and Spores

The lack of time marker horizons is a serious problem in the basal Cretaceous sandstones of the Western Interior. Macrofossils 45

Figure 26. U -Tube in Upper Sandstone Unit at Montezuma. Pencil is 15 cm long.

Figure 27. Planolites in Bedding Plane in the Upper Part of the Lower Sandstone Unit at Arroyo Hermanos. 46 are limited to plant fragments and wide- ranging trace fossils.Pollen and spores in the shales of the Dakota Group were extracted and exam- ined as a check on the time- stratigraphy. The initial expectation was that the transgressive nature of the Dakota Group could be shown, but poor preservation and the lateral pinchout of the middle shale unitin the eastern part of the thesis area prevented any such conclusions.

Palynororphs also shed light on the environment, vegetation, and cite dig the deposition of the Dakota Group.

Sample Collection

Shale samples were collected in the black to gray carbonaceous shales in the middle shale unit at seven localities. Only two,

Romer-oville and Coyote Creek, contained extractable palynomorphs.

The thin green mudst ones and clay galls in the lower sandst one unit and uppermost Morrison Formation proved to be barren . as did the Pa ja- rito Shale at Trujillo. Pollen and spores are susceptible to oxida- tion which may explain the low productivity of the surface samples taken. In the road cut along Interstate Highway 25 at Romeroville, samples were taken every six inches in the 10 -foot -thick middle shale unit. Selected samples of these were processed.At Coyote Creek all the shale beds in the middle shale unit were combined into a single composite sample.

Maceration Procedure

The palynomorphs were extracted from the shales using standard maceration procedures (Kummel and Raup, 1965) , as outlined in Table 4. 47

Table 4.Maceration Procedure

1) crush sample until it passes a 6o meshscreen,

2) place 5 grams shale in stirofoamcup,

3) cover with dilute hydrochloric acid to remove carbonates,

4) wash three times with distilled water,

5) slowly add 50 percent hydrofluoric acid, cover residue with approximately 2 cm of acid,

6) let stand about 24 hours, agitate periodically,

7) wash four times with distilled water,

8) transfer to centrifuge tube,

9) add 25 ml Schulze's solution (25 ml nitric acid and potassium

10) place in hot water bath for 15 minutes, agitate often,

11) wash three times with distilled water,

12) add 25 ml potassium hydroxide (5 percent solution),

13) place in hot water bath for 5 minutes, agitate often,

14) wash until supernatant liquid is clear, repeat steps 12 and 13 if necessary.

15) heavy liquid separation if necessary,

16) wash three times in distilled water,

17) wash two times in alcohol (95 percent solution),

18) place in storage vial in 95 percent alcohol. At step 14 in Table 4 all the black humic matter was often not broken down, and the potassium hydroxide treatment was repeated. This still often left some humic matter, but the palynomorphs began to corrode so this treatment was not continued further. Generally the extracted palynomorphs were very dark colored and many were poorly preserved.

Identification

Strew mounts of the samples were made.A drop of residue from the maceration process was placed on a slide in glycerine jelly, covered with a glass cover slip, and sealed with nail polish. The

slides were scanned for pollen and spores, the coordinates of which were recorded for later reference and photographing. Many slides con- tained no recognizable palynomorphs, but all contained leaf cuticle.

The pollen and spores that were found at Romeroville Gap and Coyote

Creek (Figure 2$) showed no significant variations either areally

or stratigraphically.

The pollen and spores in the middle shale unit are all

terrestrial. They represent the palynomorph types from (in order of

abundance) ferns, lycopods, conifers, gymnosperms, and perhaps prima -

tive angiosperms. If the black shales were marine or saline lagoon

deposits, hystrichospheres and dinoflagellates would probably be

present as they are elsewhere in Cretaceous strata(Manum and Cookson,

1964).

Index palynomorphs unfortunately were not found, but the over-

lapping ranges of the pollen and spores in the middle shale unit Figure 2 3. Pollen and Spores in the Dakota Group

a. Cicatricosis orites cf. C. magnus Döring 1965, fern spore of the Sc izaeaceae group

b. Cicatricosisporites cf. C. dorogensis Potonie and Gelletich 1932, fern spore of the Schizaeaceae group

c. Lycopodiacidites sp., lycopod spore

d. Dictyophyllidites sp., fern spore

e. Cyathidites minor Couper 1953, fern spore

f. Gleicheniidites sp.., fern spore

g. sulcate pillen grain, gymnospermous pollen or primitive angiospermous pollen

h. poorly preserved pollen grain (sulcate?), gymnospermous pollen or primitive angiospermous pollen

i. unknown affinities

j. bisaccate coniferous pollen

k. Alisporites 22., coniferous pollen

1. Alisporites 22. ,coniferous pollen

m. fungal spore

n. Schizocystia cf. S. laevigata Cookson and Eisenack1962 49

a. c.

d. e. f.

g. h. l.

m. n.

Figure 28. Pollen and Spores in the Dakota Gr up. 50 indicate an upper Lower Cretaceous age, that is, either Aptian or

Albian. This age is in agreement with most authors for this area.

(McGookey, 1972, p. 194 -195). No tricolpate pollen grains were posi- tively identified. Tricolpate pollen had evolved by Albian time, but at many Albian localities in the literature no tricolpate pollen is

found (Kremp, personal communication).

Marine body fossils in other areas indicate a Cenomanian age for the upper part of the upper sandstone unit (Owen, 1969, p. 91).

The lack of fossils in the lower sandstone unit makes its age more uncertain within the Lower Cretaceous. PALEOCURRENT DIRECTIONS

Directional sedimentary structures form in response to currents that deposit them. Of these, ripple marks and cross -stratification are present in the Dakota Group in this thesis area.Ripple marks were found in place only at Kearny Gap as discussed previously under

Sedimentary Structures. Because these ripple marks may be eolian, they were not used to determine paleocurrent direction. The long axes of four petrified logs were measured. Their orientations lie almost equally spaced around the compass rose in a random distribution from which no paleocurrent inferences can be made.

Cross -stratification was so common at every location that

statistically meaningful measurements could be made. Cross -strata, in both ancient and modern sediments, have the maximum dip direction of the cross -strata surface (foreset bed) lying parallel or subparallel to the direction of the average local current (Potter and Pettijohn,

1963, p. 81). Thus by measuring the maximum dip direction, the approx- imate paleocurrent direction can be determined.

Sampling Procedure

Cross-stratification directions can be compared at several levels: within sets of cross-strata, between sets withinoutcrops, or between outcrops within the studyarea. The most accurate estimates of mean direction are obtained by making thecomparison where the most

51 52

variability is present (Potter and Olson, 1954, p. 63). In most cases this is the variability between outcrops. The general procedure adopted for this study was to select outcrops spaced a few miles apart along the two outcrop areas and to sample vertically, in a strati - graphic sense, all available cross -strata sets, taking one cross -strata dip azimuth reading from each set. A Brunton compass was laid directly on the exposed cross -strata surfaces to measure direction of maximum dip; no apparent dips were used. The cross- stratification directions from the upper sandstone unit and lower sandstone unit of the Dakota

Group were recorded separately. The lateral range of the sampling was extended enough to collect 25 to 30 dip directions from each outcrop.

This many were not always taken because the high induration by silica cement would not allow the cross - strata to be broken out. Often, especially in the upper sandstone unit, where only a few cross- strata were exposed in the entire outcrop area, every accessible cross -strata surface was measured . Structural dip was taken by averaging the dip of several bedding planes at each outcrop.

In addition to the above systematic treatment of the sandstone in the Dakota Group, cross -strata dip directions were measured in the

Mesa Rica Sandstone at Trujillo and in two divisions within the lower sandstone unit at Box Canyon to detect internal changes in current directions within that unit. 53

Data Reduction

In order to regain the original horizontality of the beds and initial dips of the cross -strata, the University of Arizona C.D.C.

6400 computer was used to rotate the beds at each location about the horizontal axis of structural deformation. This data is presented in

Appendix B. A second rotation may be used to correct for the axial plunge. However, graphs by Ramsey (1965) show that the greatest possible angular error from ignoring the plunge in this area would be

less than five degrees. Out of 673 cross -strata dip measurments six were discarded because their corrected dips were less than five

degrees. In most of these cases bedding planes were probably mistaken

for cross -stratification.

In the lower sandstone unit at each location, corrected cross-

strata dip directions were assigned unit magnitude and added vector -

ally (gaup and Miesch, 1957). The direction of the resultant vector

is called mean azimuth in Appendix C and is plotted in Figure 29.

The resultant magnitude, R, divided by the number of unit vectors, n,

is the consistency factor or consistency ratio. This is an indicator

of how well the data is grouped.Another way to express this is in

terms of percent, (R/n)lOO, or azimuth vector weight.One other

measure of central tendency that was calculated was the standard

deviation, a, by the formula:

where xi = each observation and xi-x-2 = calculated mean. i=1 5l~

Grand Mean n=544 ""-J' .:

. . . . - " . ': . :-:.;.'

.', .,. ~ ..

:) 0 5 ")ilas sr::·.....,. :-.:"Y'S-"- . -:E-·3..,..·--:--_-----...;;-. ~----"--::::----4

- ... d R Figure 29. Paleocurrent Directions in Lower Sandstone Unit of the Dakota Group in North-Central New Mexico. Arrows show Locality Mean Direction and 95 Percent Confidence Level. 55

An identical treatment of dip angle was made and recorded as mean dip, dip vector weight, and standard deviation of dip (Appen- dix C).

The range of mean was calculated at the 95 percent confidence level. At this confidence level there is a 95 percent probability that the true mean lies within the specified range about the calcu- lated mean. This specified range is usually expressed as x±d, where d is one half the range of mean. Such confidence intervals were ob- tained from the standard deviation by Stein's Law: 2d= T-c-where T is interpolated from a t-- distribution statistical table (Selby, 1967, p. 906). This formula shows that the higher the standard deviation, the higher the uncertainty value, d, and conversely the greater the number of readings ,the smaller the value of d. In the lower sand-

stone at all locations, except one, the mean cross -strata azimuths are within200 at the 95 percent confidence level (Figure 29).

The same statistics were calculated for the grouped data from

all locations in both the lower sandstone unit and the upper sandstone

unit. Sparse data prevented calculation of separate statistics for

each outcrop in the upper unit. The studies at Box Canyon within the

lower sandstone unit and at Trujillo in the Mesa Rica Sandstone are

also so treated in Appendices B and C.

Cross - Strata Variability

The variability of cross -strata orientations is due to the

natural variability in sedimentary processes, such as meandering and 56 longshore currents, and to changes through time in such factors as direction and gradient of the paleoslope. One measure of this vari- ability, the standard deviation, of several modern streams ranges from

20° to as much as 83° depending upon gradient and sinuosity (Hamblin,

195$, Figure 2$). High- gradient braided streams have the lowest standard deviations; highly sinuous meandering streams have the high- est standard deviations (Allen, 1965, pp. 163-164) in stream deposits.

Regional variances of cross -strata in three marine deposits ranged from 830 to 870 standard deviation, whereas those from fluvial- deltaic deposits ranged from 710 to 770 standard deviation (Pryor, 1960,

Table 4). However, at the outcrop level, marine and fluvial environ- ments usually cannot be separated by the variance in current directions.

The standard deviation of the cross-stratification dip azimuth directions from the lower sandstone unit in the Las Vegas area is 78 °.

This standard deviation indicates that the lower sandstone unit is a fluvial deposit, perhaps of a meandering stream for the .standard devia- tion is at the high end for a fluvial environment.

The upper sandstone unit has a standard deviation for the cross- stratification directions of almost 970. This indicates a marine en- vironment with highly variable current directions . A relatively small

sample size (53 measurements) also contributed to the magnitude of the

standard deviation. 57

Paleoslope and Shoreline Strike

Establishing the paleoslope, the topographic gradient at the time of deposition, relies on two assumptions: 1) that current flow can be inferred from the cross -stratification and 2) that the paleo- slope can be deduced from paleocurrent directions. whereas assumption

1) is almost always correct, assumption 2), while valid for the fluvial environment, is not valid when eolian and shallow marine environments are considered (Selley, 1968, p. 102). In fluvial deposits the major- ity of modern and ancient cross -stratification studies produce uni- modal downslope current patterns (Potter and Pettijohn, 1963, p. 81).

A bimodal current pattern is typical of a shallow marine environment

(Pettijohnet al., 1973, p. 137). Here tidal forces may produce cur- rents perpendicular to the paleoslope as in the case of a variable longshore current or parallel to the paleoslope as in an estuary.

A comparison of the compass roses of the grouped data from all locations in the lower sandstone unit with that of the upper sandstone unit shows distinct differences, a unimodal distribution in the lower sandstone unit and a bimodal distribution in the upper sandstone unit

(Figure 30). The unimodality of the lower sandstone unit suggests a fluvial origin and a regional paleoslope to the east. The plot of mean directions at each locality in the lower sandstone unit also indicates that the flow of the Early Cretaceous river systems in this area was easterly (Figure 29) .

In contrast to the grouped data from all locations, thecompass rose diagrams for the separated localities in the lower sandstone unit 5$

. upper sandstone unit n = 53

b. lower sandstone unit n =5L4 Figure 30. Comparison of Cross -Stratification Directions in the Lower and Upper Sandstone Units of the Dakota Group in North -Central New Mexico.

are mostly polymodal (Figure 31, in pocket). At Box Canyon the mean dip directions of the excellently exposed cross -strata shifted at different stratigraphic levels within the lower sandstone unit.

Thirty -two independent measurements of cross -stratification were taken both above and below the prominent conglomerate zone (bed 4, location

9 in Appendix A). The rose diagrams of these measurements display a pronounced change in current directions from southeast to southwest

(Figure 32). The rose diagram of the whole unit essentially shows the same modes weighted somewhat according to the relative thickness of the cosets from which they come. The polymodality at the outcrop level in the lower sandstone unit is due to cross -stratification that is consistent in direction between intervals. These changes may re- flect sequential point bar deposits of a meandering river system, and probably not a variable paleoslope. 59

below conglomerate' above conglomerate entire lower sandstone n =32 n =69 n =32

Figure 32. Variati on in Current Direction within the Lower Sandstone Unit at Box Canyon.

The compass rose of the grouped data from all locations in the upper sandstone unit is distinctly bipolar with modes N. l5 °W. and

S. 15°E., almost at right angles to the paleoslope (Figure 30). This distribution suggests that the upper sandstone unit formed in a shal- low marine environment. The cross -stratification directions probably represent the results of longshore currents paralleling the shoreline

strike. HEAVY MINERAL ANALYSIS

Initially, the heavy mineral study attempted to find strati - graphically diagnostic heavy mineral assemblages. This failed. The study also was employed as a tool to determine the source of the sand and to shed some light on paleotectonics and paleoclimate.

Methods

Small samples were chipped from each sandstone bed in each unit at Romeroville Gap. These were crushed to 1/4 inch, disaggregated by hand with an iron mortar and pestle, and sieved by whole phi grades of

Wentworth's size classification (Folk, 1968, p. 25) using U.S. Stand- ard Sieves on a Ro -Tap shaker. The 3 phi (less than 250,u, greater than 125;0, 4 phi (less than 125,u, greater than62.5;0, and 5 phi

(less than 62.5,u, greater than 31;a) size fractions from each unit were then separated into heavy and lightfractions by standard heavy liquid techniques (Willard, 1964, p. 6), utilizing tetrabromomethane

(sp. gr. 2.95). A teaspoon (about 10 grams) from each size fraction of sand from each unit was processed.

The heavy minerals recovered were contaminated by flakes of iron from the mortar and pestle. These were removed with a hand mag- net. Very little, if any, magnetite or ilmenite was observed in the magnetic fraction. The non -magnetic heavy mineral grains were mounted on glassslides in Caedax and were identified optically with a petro- graphic microscope.

60 61

Results

Opaque minerals make up over half the total heavy mineral fraction (Figure 33), especially in the coarser sizes. This was deter- mined by a point count of 100 grains on each slide. Limonite is by far the most common opaque mineral in all units of the Dakota Group; smaller amounts of leucoxene and sperical black tourmaline ( ?) are also present. In addition, pyrite, with a texture which suggests replace- ment of organic material, is present in the carbonaceous sandstones of the middle shale unit.

Approximately 300 non -opaque heavy mineral grains per slide were identified and counted in the 5 phi and 4 phi sizes.The 3 phi size is dominated by the opaque fraction as well as there being fewer total grains per slide. In this size every non -opaque grain on each slide was counted. This ranged from 10 to 25 grains, except for the middle shale unit which consists of virtually all opaque material.

The results are tabulated as percentages of the non -opaque fraction in Table 5. Zircon and tourmaline provide the bulk of the non -opaque fraction. The amount of each of these is strongly grain size depend- ent (Figure 34). Zircon represents over 90 percent of the non -opaque fraction in the 5 phi size but drops to less than 50 percent in the coarser sizes. Conversely, tourmaline increases in abundance in the larger phi sizes. This probably is due to the difference in initial size of the two minerals in their original source rocks. Zircon con- sists of two clearly distinct types, well -rounded, frosted grains and clear, euhedral crystals (Figure 35). Tourmaline is essentially all 62

lower ss. unit lower ss. unit middle sh. unit upper ss. unit beds 1 -3 bed5 beds 6 -7 beds 8-9 100 non - non- non- opaques opaques opaques \\\

\\Nopaques opaques opaques p qes

504yl30 50;6 40 30 5¢ 4¢ 30 50 4 39; GRAIN SIZE

Figure33. Percentage of Opaque and Non -Opaque Fractions of Heavy Minerals in Each Unit at Romeroville Gap.

Tourmaline 5¢ 40 30 S IZ E

Figure 34. Average Composition of the Non -Opaque Heavy Minerals from All Intervals Plotted Against Grain Size. 63

Table 5. Non -Opaque Heavy Mineral Composition Percentages

Romeroville lower ss. unit lower ss. unitmid. sh. upper ss. unit Section beds 1 -3 bed 5 beds 6 -7 beds 8-9

Phi Size 5 4 3 4 3 5 4

Zircon 91 40 50 90 61 63 94 38 85 62 13

rounded 56 23 40 49 29 28 54 20 49 40 13 euhedral 15 7 10 12 13 16 18 7 17 11 angular 20 10 29 19 19 22 11 19 11 lavendar 1 1 1

Tourmaline 2 50 40 21 12 2 26 12 31 80

rounded brown. green 1 35 30 2 13 3 2 21 8 21 33 brown X 14 10 X 4 9 + 2 9 47 blue to green 1 1 1 1 1 1 angular blue to green i 3

Garnet 1 3 4 5 16 i 9 X 1 6

brown 1 2 3 4 16 i 5 X 6 clear X 1 1 1 X

Rutile 1 2 10 2 2 5 1 2

Hornblende 1 i 2

Chlorite 1 1 3 1

Light-green iso- tropic unknown 1 5 2 6 7 1 19 i

Other 3 2

Total percent 100 99 100 101 101 101 101 99 100 99 99

Total number 328 298 10312300 25302 297318 334 15 grains counted

X denotes presence of less than one percent. 64

Figure 35. Photomicrograph of Well- rounded and Euhedral Zircon (Four Phi Size) 65 very well -rounded and sub-spherical. Color variations of the tourma- line were recorded, but the somewhat gradational variations and the strong pleochroism hampered these determinations. Table 6 shows that there is no regular variation in the varieties of these two minerals with phi size or stratigraphic unit.

Other non -opaque heavy minerals found in the Dakota Group at

Romeroville Gap include garnet, rutile, chlorite, hornblende, and an unidentified light green isotropic mineral with many dark granular in- clusions.

Mankin (1958, p. 123), in a regional study, took samples from

Romeroville Gap, lumping the entire Dakota Group together. Mankin found 29 percent opaque minerals here, but a 50 percent average for the Dakota in northeast New Mexico. Of the non -opaques he found 51 percent tourmaline, 39 percent zircon, 6 percent rutile, 3 percent hornblende, and 1 percent staurolite. These results are compatible with mine if Mankin relied largely on the coarser grains for identifi- cation and counting. What his actual procedure was in this respect is not stated.

Provenance

The heavy mineral assemblage in the Dakota Group is basically an ultra- stable assemblage of zircon and tourmaline with some rutile, garnet, and a few other metastable minerals. The distinct varieties of zircon, well -rounded and euhedral, suggest at least two sources.

In Todilto Park in northwestern New Mexico, Willard (1964, p. 42) observed "that the colorless and light lavendar zircon grains fluoresce Table 6. Varieties of Zircon and Tourmaline in Each Phi Size Class RoverovilleSection lower ss. unit beds 1 -3 lower ss, unit bed 5 middle sh. unit beds 6 -7 upper ss.beds unit 8 -9 mean ZirconPhi Size 5 4 3 5 4 3 5 4 5 4 3 % euhedral rounded 1661 1857 (20)(go)* 5413 4721 4425 1957 1853 2057 1864 (100) (0) 5519 Total angular 2299 100 25 100 (0) 32..._..99 .3199 ...... 3099 2399 100 29 _...2299 100 _.._18 100 __. (0) 100 _...26 Tourmaline %brownish green (50) 70 (75) (b7) 62 (25) (100) . _. 80 67 68 41 61 %brown blue to (50) (0) 28 2 (25) (o) (33) (0) 19 (75) (0) (o)(0) 15 4 17 29 3 59 0 33 7 Total green * Percentages in brackets are based on fewer than five grains. 100 100 100 100 100 100 100 01099 101 100 100 100 67 and that the colorless and deeply colored, rounded grains do not im- plies that they are from different ultimate sources."The idiomorphic zircon is an indicator of a volcanic source (Callender and Folk,

1958). The hornblende also is probably of volcanic origin (MacKenzie and Poole, 1962, p. 70).

The extreme rounding of the majority of the zircon grains and all the tourmaline grains suggests they are at least second cycle, de- rived from sedimentary rocks. Most of the original detrital quartz grains, i.e., without the secondary quartz overgrowths, are also very well rounded. The diverse types of tourmaline also suggests that the immediate source was sedimentary (Krynine, 1916). The underlying

Morrison Formation contains similar euhedral and rounded zircon grains and well -rounded tourmaline grains along with a larger suite of meta- stable heavy minerals (Nankin, 1958, p. 85). The sediments of the

Morrison Formation and the Dakota Group probably came from the same source area. Some of the Dakota Group may be reworked Jurassic Morri- son Formation.

Paleoclimate

While no climatic interpretation can be advanced with certainty for the Dakota Group, I agree with the bulk of writers that the cli- mate was warm and humid (Jacka and Brand, 1972, p. 106; Willard, 1964,

P. 44; Millis on, 1964; Nankin, 1958, p. 128; etc.). Evidence for this is the nearly complete removal of feldspar and climate -sensitive heavy minerals, and the thick tripolitic weathering rinds on the chert 6$ pebbles. The abundance of silica-cementation may be suggestive of a humid climate (Mankin, 1958, p. 128). The presence of ferns of the

Schizaeaceae -group as indicated by their spores is compatible with

such a climate. INTERPRETATION OF DEPOSITIONAL ENVIRONMENTS

The criteria used to reconstruct the paleoenvironment of the rocks within the Dakota Group include general lithology; type, modal- ity, and statistical variability of cross-stratification; sand b .i.y morphology; fossils; clay mineralogy; and position in a vertical se- quence. Two particularly environmentally sensitive aspects of lith- ology are texture and sorting. Detailed size analysis was not done because many of the sandstones cannot be disaggregated due to the high degree of induration by silica cement, and because the grains are covered by quartz overgrowths which makes them larger than they were when they were deposited. Grain size has a direct relation to the competency of the currents that deposited the sediments which, in turn, depends on interwoven factors of gradient, load, carrying med-

ium (water or air), bed form, and so forth.

Practically all types of cross -stratification have been found in a wide range of environments. Still, some generalizations are widely recognized. Tabular- planar cross -stratification is most common in marine sands and in eolian dunes; trough cross -stratification is typical of fluvial environments. Unimodal distributions of cross - stratification dip directions are typical of fluvial environments, while subequal bipolar distributions occur in tidally influenced marine

69 70 sediments. Exceptions to all of the above statements have been re- ported, but the associations they imply can be used as supporting evidence.

The absence of marine macrofossils and the abundance of ter- restrial plant remains are indicative of terrestrial sediments. Shales that contain terrestrial pollen and spores would probably also contain hystrichospheres and dinoflagellates if the shales were of marine origin. Many vertical trace fossil burrows occur today over a fairly restricted range in the littoral and shallow marine environments. Other trace fossils have a greater environmental range.

Only a limited range of environments can border on any partic-

ular environment . For example, tundra is not c ompatable with a sabkha, but a tidal flat is. The most common areally adjacent environments form common vertical sequences during transgressions or regressions

(blather's Law). Thus from the knowledge of one environment in a common sequence, the stratigraphicallyadjacent strata can be pre- dicted.

Lower Sandstone Unit

The coarse- to medium -grained, moderate -sorted, predominately trough cross -stratified sandstones of the lower sandstone unit, which

contain some well -developed channel and irregular scour surfaces, are

the product of a fluvial environment. The unidirectional modality and

low variance (790 standard deviation) of the trough cross -

stratification also point to this conclusion. The only fossils in 71 this unit are silicified logs in conglomeratic channel fills and a few coaly pods near the top of the unit; no marine fossils arefound.

The overall geometry of the Dakota sand body is ablanket sand- stone, though regionally its details are complex. The alluvial models proposed by Allen (1965, p. 163 -165) suggest that the lowersandstone unit was either formed by a braided stream or a low sinuosity,meander-

ing stream (Figure 36).

Rock Other facies Mainly topstrotum deposits

Coorse fon, chonnel bar, or meander bell deposits

Figure 36.Hypothetical Models Illustrating Textural and Geometrical Characteristics of Common Alluvial Environments. A. Piedmont Formed of Alluvial Fans ;B. Braided Streams; C. Low Sinuosity Stream; D. Strongly Meandering Stream. 72

The lack of topstratum or floodplain fine -grained sediments indicates a low ratio of suspended to bed load, which is typical of braided and coarse- grained, point-bar deposits (McGowen and Garner,

1970, p. 70). The lack of mud could also be due to extensive sorting and reworking of the sediments under very slow rates of deposition.

The discontinuous mudstone layers and clay -gall conglomerates in the lower sandstone unit are more common in braided stream sediments than

in more homogeneous point bars (Smith, 1970, p. 3010). On the other hand, the variance in the cross -stratification dip directions within the lower sandstone unit is relatively high for stream deposits, which supports deposition by a meandering stream system.

Fluvial systems vary within a whole spectrum between braided and highly meandering channel patterns, such that categorizing even modern streams may be difficult. "An ancient fluvial sequence domi- nated by foreset cross -strata and trough -fill cross -strata could be either lower point -bar, chute bar, crossover, or braided -stream deposits." (McGowen and Garner, 1970, p. 91). All references cited on this subject stress the uncertainty in trying to reconstruct the morphologies of paleorivers.

The ripple marks at the top of the lower sandstone unit at

Kearny Gap are probably eolian in origin. Wind, not uncommonly, re- distributes unconsolidated sand lying exposed on the sides of stream channels (Allen, 1965, p. 161). The coarseness of the sandstone in which the ripple marks are found and the relatively low RI for eolian 73 ripple marks support the association of eolian and fluvial environments that deposited the upper part of the lower sandstone unit at Kearny Gap.

Middle Shale Unit

The middle shale unit is fine -grained, carbonaceous sandstones intercalated with black carbonaceous shales. This bespeaks of a rela- tively quiet, but fluctuating, environment much like floodplains of low -gradient rivers today. The shale-sandstone lithofacies is persis- tent along the north -south paleoshoreliTic strike, but is discontinuous at right angles to it. Facies which parallel coastal shorelines are usually relatively near sea level and in proximity to the coast.

The channel sandstone at Coyote Creek (Figure 12) is litholog- ically similar to the fluvial sandstones in the lower sandstone unit.

Most of the sandstones in the middle shale unit are finer grained,

thinner bedded, and more carbonaceous than the lower sandstone unit.

Fossils in the middle shale unit are overwhelmingly terres-

trial plant remains that consist of wood fragments molds, carbonized

films, and palynomorphs of ferns and conifers. The large root casts

at Coyote Creek indicate dry land to fairly shallow water. No diag-

nostically marine plant remains or palynomorphs are present . A

single Skolithos tube (?) was observed in the sandstone of this unit.

In the Chama Basin, "The presence of highly kaolinitic shales

within the Dakota indicates that the environment of deposition of

these shales was largely fluvial and low -salinity paralic and that no

offshore marine shales are present..." (Grant and Owen, 1974,p. 24$). 74

The same probably holds true in the Las Vegas area because of the close correlation of all units and similarity in shale descriptions.

Upper Sandst one Unit

The overall lithology of the upper sandstone unit is coarser grained than the middle shale unit and finer grained than the lower sandstone unit. The depositional environment of the upper sandstone unit was of an intermediate energy between the other units. In the well -sorted sands of the upper sandstone unit are diagnostic trace fossils, such as Ophiomorpha, that place the depositional environment of the main sandstone type in the wave -agitated littoral or shallow neritic zones along a beach face. These sands commonly have small - scale, tabular - planar cross -stratification which shows 1$0° reversals in current direction. Such bipolarity is commonly marine. The modes of the bipolar distribution of current directions are almost at right angles to the paleoslope; hence, they parallel the paleoshoreline.

The very high variance of the cross -stratification directions (97° standard deviation) is also indicative of a marine environment. The ripple marks associated with the upper sandstone unit are symmetrical ripples typical of the wave -agitated littoral environment.

The bioturbation in the poor -sorted, carbonaceous sandstones in the upper sandstone unit appear to be marine sediments below wave base or protected from the sorting of wave action by a bar or barrier island. The thin- bedded sandstones typified by the presence of pro- fuse carbonized wood fragments and wood molds are not clearly marine. 75

These sands may have been deposited in marine environments, although they contain a large terrestrial component.

Paleotectonic Setting

Both this study and regional studies of the petrology and heavy mineral suits of the Dakota Group indicate that the primary

source area was dominated by mature sandstones and cherty carbonate rocks (MacKenzie and Pool, 1962, p. 70; Long, 1966, p. 81; Mankin,

195$, p. 106). The only highlands during Early Cretaceous in the

Western Interior of the United States were the Siever orogenic belt

in western Utah and highlands in southern New Mexico and Arizona

(McGookey, 1972, p. 191)as shown on the paleotectonic map (Figure

37). The regional paleogeographic setting may be complicated by rem-

nants of small uplifts in southern Colorado, where the Dakota Group

rests nonconformablyon Precambrianrocks (Owen, 1969, p. $9).

The Mogollon Highlands in eastern Arizona and the Burro Uplift

in southwestern New Mexico shed great quantities of coarse elastics

during Jurassic and Early Cretaceous time over southern Arizona, south-

ern New Mexico, and northern Mexico (Kottlowski and Foster, 1962,

p. 2094) . However, no conglomerates in the Dakota Group occur across

west-central New Mexico (Landis, Dane, and Cobban, 1973). This area

lies between the southern highlands and my area of study.The conglom-

erates, at least, in north -central New Mexico could not have come from

the Mogollon Highlands or Burro Uplift unless erosion completely

stripped sediment equivalent to the lower sandstone unit inwest -

central New Mexico before the deposition of later Cretaceous sandstone. 76

_ -- - -

,

Colorado

Utah

Ariz. study areaF.-

l

N

N.Mex. x,100 - i9h1

Figure 37. Paleotectonic Map of the Western Interiorof the United States during Early CretaceousTime. (After McGookey, 1972; Long, 1966, p. 80.) 77

Paleocurrent analysis indicates the source material for the Dakota

Group in north--'central New Mexico came from the west and not the

southwest.

The Siever orogenic belt, some 500 miles to the west, is the probable source of the basal Cretaceous elastics in northern New Mexico.

Sediments of Jurassic through Eocambrian age, including a thick Paleo-

zoic carbonate section, were eroded from the Siever orogenic belt dur-

ing Late Jurassic through the Cretaceous Periods (Armstrong, 1968).

The rapid decrease in pebble size in the lower sandstone unit

from west to east does not necessarily require a nearby source.

Rivers will transport three inch or larger pebbles for long distances

until they are no longer competent to do so, at which point the size

will rapidly drop off. Pebble size distributions in southeast Colorado

(Long, 1966, Plate 6, p. 42) show the same relationships as in north-

central New Mexico (Figure 7).

Depositional History

The units within the Dakota Group in the vicinity of Las Vegas,

New Mexico, record a conformable succession of three major environments

(from top to bottom):

3) littoral, beach, lagoon, marine complex;

2) coastal plain;

1) piedmont plain

which have been recognized by various authors in other areas (Kauffman,

et al., 1965, pp. 110 -111; Owen,1969,p. 90; Jacka and Brand, 1972,

p.106). This vertical sequence is fairlyuncomplicated in the 7$

Las Vegas area, clearly documenting the regional transgression of the

Cretaceous seaway that eventually inundated the entire Western Interior of the United States.

The initial deposition of the Dakota Group began on essentially horizontal Jurassic rocks (a paraconformity) by braided and /or coarse - grained, meandering rivers which flowed easterly from their source in the Siever uplift in western Utah. The rivers may have turned south- ward on the eastern edge of the study area (Figure 29), toward the en- croaching embayrnent of the Cretaceous sea to the southeast (Reeside,

1957, p. 513). The rivers worked over the sediments enough to sort out the muds and leave predominately moderate -sorted sands. Sometime after half the sandstone in the lower unit had been deposited, a marked change in stream regime brought an influx of fossiliferous chert gravel. A pulse of rapid tectonic uplift to the west or northwest could account for this change in regime.

As the source area wore down and sea level rose, the Cretac- eous rivers in the area of study became meandering rivers, which deposited fine -grained, carbonaceous sands and muds over extensive flood plains. This was a period of relative quiesence in a swampy coastal plain covered by ferns, conifers, and primitive angiosperms.

Sea level continued to rise and the surf zone reworked the terrestrial sands. The well -sorted sands of the beach face or shallow bar were inhabited by a number of organisms whose only remains are burrows they had made in the shifting sands moved by variable longshore currents. The carbonaceous sands which escaped extensive 79 sorting by waves were churned by other burrowing organisms insearch of food. The imprint of a terrestrial source on some ofthe sand- stones in the upper sandstone unit is visible in the millionsof wood fragments that were probably reshuffled by the transgressing sea.

Finally as the shoreline move westward, the entire areain north -central New Mexico was submerged below wave baseand the sandy marine shales of the Graneros Shale were deposited. APPENDIX A

MEASURED SECTIONS

The description of the rock colors and their number designations were obtained from comparisons with the Rock -color

Chart (Goddard, 1948). 81

Location 1: Romeroville Ga

Measured at the old road cut in the Creston Ridge along the north side of the frontage road east of Romeroville; long 105 °16' W., lat 35 °31' N.

Erosional surface:

Dakota Group: Feet

Upper sandstone unit: may not be complete

9. Sandstone, grayish yellow (5Y$/4), weathers same color, coarse -grained, moderate -sorted; silica cement, well - indurated; planar bedding; U -tubes and Thalassinoides

uncommon; many stylolitic bedding surfaces . . . 2

8. Sandstone, weathers grayish yellow (5Y$ /4), mottled in upper part, fine -grained grading upward to medium- grained, well- to moderate -sorted; silica cement, well- indurated to rubbly where shaly and bioturbated in upper part; Thalassinoides and other trace fossils indistinct, wood fragment molds; irregular patches and swirls of

dark carbonaceous matter in shaly sandstone...... 10

Total of upper sandstone unit (incomplete) 12

Middle shale unit:

7. Shale and sandstone; shale, mostly grayish olive (10Y4/2), locally pale greenish yellow (10Y8/2), weathers grayish olive (10Y4/2), silty, carbonaceous, friable; sandstone, grayish yellow (1018/4), weathers same color, very fine grained, silty, poor- sorted; silica cement, firm; several continuous to discontinuous beds; abundant carbonized wood and wood fragment molds; unit weathers to numerous rounded

ledges . 10

6. Shale, grayish olive (5Y8/4) to grayish black (N2), silty,

carbonaceous, friable. . . .

Total of middle shale unit . 14

Lower sandstone unit:

5. Conglomeratic sandstone, grayish yellow (5Y8/4), weathers same color, medium- to coarse -grained sand, pebblesas much as 2 inches in diameter,very poor sorted; silica cement, well- indurated; conglomerateand coarse -grained 82

Feet sandstone predominate in the base of the unit fining up- ward to medium -grained sandstone containing wood fragment molds; conglomerate lenses as much as 4 feet thick, pebbles are gray to white chert and very minor reddish quartzite; unit weathers to rounded cliff. 20

4. Shale, grayish olive (10Y4/2) both fresh and weathered, locally very sandy, fissile to moderately indurated; white clay material along joints one mm thick; unit weathers to slope or underhang . 4

3. Sandstone, light gray (N7), weathers same color, fine- grained, moderate- to poor-sorted; silica cement, friable to moderately indurated; predominate trough cross - stratification with minor planar bedding; unit weathers

to slope . 16

2. Mudstone, grayish olive (10Y4/2), weathers same color, moderately friable

1. Sandstone, grayish olive (10Y4/2), weathers yellow orange (ioYi6/6), medium- to coarse- grained, moderate-- to well - sorted; silica cement; mudstone pebble conglomerate zones as much as one foot thick present; predominate trough cross-stratification with minor planar bedding; unit

weathers to steep slope. . 38

Total of lower sandstone unit. 79

Total of Dakota Group (incomplete) .105

Morrison Formation (unmeasured); intercalated olive green shales and dark to light sandstones. 83

Location 2: Kearny Gap

Lower sandstone unit measured north side and middle and upper units measured south side of gap in the Creston Ridge along State Highway 283; long 1050152 -' W., lat350332'N.

Covered interval: unmeasured

Dakota Group: Feet

Upper sandstone unit: may not be complete

8. Sandstone, medium dark gray (N4) with carbonaceous wisps of grayish black (N2), weathers mottled very light gray (N8) and medium dark gray (N4) with irregular dark yel- lowish orange (10YR6/6) limonite staining, fine- to medium -grained, moderate -sorted; silica cement, firm; bioturbated, Thalassinoides common; unit weathers to rubbly slope . 5

7. Sandstone, very light gray (Ne), weathers light brownish gray (5YR6/i), medium -grained sand to fine -grained gran- ules, clayey at base, very poor sorted; silica cement, indurated to friable at base; tabular planar cross -

stratification; unit weathers to cliff . . . 3

Total of upper sandstone unit (incomplete) g

Middle shale unit ( ?):

6. Covered. 17

Total of middle shale unit ( ?) 17

Lower sandstone unit:

5. Sandstone, very pale orange (lOYR/2) , weathers same to pale red (5R6/2), medium -to coarse- grained, well - sorted; silica cement, well - indurated; ripple marks; cross -

stratified; unit weathers to cliff . . 24

4. Conglomerate, very pale orange (loYR/2), weathers gray- ish orange (10YR7/4), gray chert and minor quartzite pebbles as much as 2 1/2 inches in diameter, clayey top and bottom, very sandy in middle of unit,very poor

sorted; unit less resistant than unitson either side. . . 16 $4

Feet

3. Sandstone, bluish white (5B9/1), weathers same color, medium- to coarse -grained, moderate- sorted; silica cement, well- indurated; few obscure claygalls present; small -displacement faulting occurs throughout this unit; medium-scale trough cross -stratification common;

unit weathers to cliff . . . . 51

2. Shale, dark greenish gray (SGY4/l), weathers light

greenish gray (5G/l), sandy, fissile...... 2

1. Sandstone, very light gray (Ne), weathers same color, fine- to medium -grained, silty, moderate -sorted;

silica cement, firm; unit weathers to rounded cliff. . 5

Total of lower sandstone unit...... 98

Total of Dakota Group (incomplete) . . . . . 123

Morrison Formation (unmeasured): olive green shales and sandstones. $5

Location 3: Arroyo Hermanos

Measured at the north side of Arroyo Hermano where it cuts through the Creston Ridge approximatelyone mile west of Las Vegas; long 105 °15' w., lat 35 °36' N.

Graneros Shale (unmeasured): black shale, basal 17 feet covered

Dakota Group: Feet

Upper sandstone unit:

10. Sandstone, mottled very light gray (N8) and dark gray (N4), weathers same color with dark yellow orange (iom6/6) blotches, fine- to medium -grained, moderate- to poor -sorted, clayey; silica cement, firm but breaks along fine irregular dark gray carbonaceous partings and swirls; bioturbidation evident but separate burrows

indistinct; bedding irregular to thickly laminated . . . 4

9. Sandstone, very light gray (N$), weathers same color, medium -grained, well- to moderate -sorted; silica cement, thin carbonaceous swirls locally present, very well - indurated to firm; Thalassinoides and U -tubes present; medium- to fine -scale bedding, not conspicuously cross -

stratified; unit weathers in prominent relief...... 6

Total of upper sandstone unit...... 10

Middle shale unit ( ?)

8. Covered, float suggests rubbly bioturbated shalt' sand- stone and/or sandy shale 10

Total of middle shale unit ( ?) 10

Lower sandstone unit:

7. Shaly sandstone, bluish white (5B9/1), weathers mottled same color and yellow orange (ioYR6/6), fine- grained, moderate- sorted; silica cement, firm to friable; unit weathers to partially covered slope; bottom of unit is a 3- inch -thick moderate olive brown (5Y4/4) siltstone,

well- indurated, with wavey fine laminae. . 9 86

Feet

6. Conglomerate, light gray (N7), weathers same color with

brown limonite staining (10YR6/6 to 5YR3/4), matrix is coarse- to medium- grained sand, pebbles average approx- imately 3/8 inch in diameter with a maximum of one inch in diameter, very poor sorted; silica cement, well- indurated to friable; pebbles are black to white chert

and uncommonly purple quartzite; unit weathers to slope. . 2

5. Sandstone, verypale orange (1OYR8/2), weathers dark yellowish orange (10YR6/6), medium -grained, well- so-Lted; silica cement; firm; few thin chert- pebble conglomcrate stringers; medium- to small -scale cross- stratifica .gin;

unit weathers t o slope . . 11

4. Sandstone, grayish orange pink (5YR7/2), weathers same color, medium- to coarse -grained, medium - sorted; silica cement, well -indurated; medium -scale trough cross- stratification with lesser planar bedding, unit weathers to cliff 6

3. Conglomerate, light gray (N7), weathers same color with

brown limonite staining (10YR6/6 to 5YR3/4), matrix is coarse- to medium -grained sand, pebbles average approx- imately 3/$ inch in diameter with a maximum of one inch in diameter, very poor sorted; silica cement, mostly well - indurated; pebbles are black to white chert and

rarely purple quartzite; unit weathers to rounded cliff. . 6

2. Sandstone, grayish orange pink (5ïr7/2), weathers same color, medium- to coarse -grained, medium -sorted; silica

cement, well- indurated; a couple discontinuous thin con- glomerate lenses; four widely- spaced, finely - laminated, shaley sandstone layers; local scour shows a minimum of 6 feet of erosion; Planolites in a single bedding plane; medium -scale trough cross -stratification predominates with lesser massive and planar bedding, unit weathers to cliff ...... 34

1. Sandstone; grayish orange pink (5YR7/2), weathers same color, medium -grained, well-sorted; silica cement, firm to friable; thin- bedded, averaging6inches thick; unit

weathers to slope or underhang . . 20

Total of lower sandstone unit. . . $8

Total of Dakota Group. . . 108

Morrison Formation (unmeasured): top 5 feet covered, olive green shale. Location 4: Montezuma

Measured in gap in the Creston Ridge below Bradner Dam; long 105°16' w.,lat 35 °39' N.

Graneros Shale (unmeasured): black shale

Dakota Group: Feet

Upper sandstone unit:

7. Sandstone, very light gray (N$) to brownish gray (5YR4/i) with black carbonaceous wisps, weathers to mottled patches of same color and dark yellowish orange (ioYR6/6) due to limonitic staining, fine- to medium -grained, moderate- sorted; silica cement; Thalassinoides and other trace fossils indistinct because of the high degree of

bioturbation . . . 17

6. Shale, mottled light gray (N7) to black (N2), very sandy, black carbonaceous streaks throughout with occasional carbonized wood fragments as much as 1/2 inch in diameter; Thalassinoides and other bioturbation; gradational con-

tact with sandstone above. . . 22

5. Sandstone, white (N9), weathers same color, medium -grained, well - sorted; silica cement, well - indurated; Skolithus common at top of unit, some carbonized wood; few clay galls and chert granules in basal part; massive with few planar tabular cross-stratification sets a few inches in thick-

ness . . 102

Total of upper sandstone unit. . . 30

Middle shale unit:

4. Shale, medium dark gray (N3), weathers light gray (N7), friable, carbonaceous; discontinuous sandstone as much as 1/2 foot thick contains carbonized wood fragments, wood molds, and a coniferous cone mold. 9

Total of middle shale unit . . 9

Lower sandstone unit :

3. Sandstone, very pale orange (10YR8/2), weatherssame color to grayish orange pink (10R$/2) and pale yellowishorange (ion/6), medium- tocoarse- grained, moderate- sorted; silica cement, firm; medium-scale trough $8

Feet

cross -stratification with minor tabular planar cross -

stratification and planar bedding. . . 2

2. Sandy conglomerate, very light gray (N7), weathers same color and dark yellowish orange (10YR6/6), matrix is medium- to coarse- grained sand mixed with clay in upper part, pebbles average approximately 3/4 inch with a max- imum diameter of 3 inches, very poor sorted; pebbles consist of dark gray to white chert and minor purple

quartzite .

1. Sandstone, very pale orange (lOYR/2), weathers same color to grayish orange pink (10R8/2) to pale yellowish orange (ioYR/6), medium- to coarse- grained, moderate - sorted; silica cement, firm to well- indurated; light green mudstone galls present in zones a few inches thick with clasts as much as several inches long; couple one inch thick beds of fissile sandstone; medium -scale trough cross -stratification predominates with lesser

massive to planar bedding...... 73

Total of lower sandstone unit. . . . . 82

Total of Dakota Group. . . . . 121

Morrison Formation (unmeasured): olive green shale, mostly covered. Location 6: Sapello

Measured at cliffs south of the Sapello River beside State Highway 3 near the village of Sapello; long 105 °1172' W., lat 35 °46' N.

Graneros Shale (unmeasured): black shale

Dakota Group: Feet

Upper sandstone unit:

$. Sandstone, very light gray (N8) to grayish orange pink (5YR7/2) with few wisps of grayish black (N2) carbonized material, weathers mottled light gray (N7) and dark yellow orange (1OYR6/6), medium- grained, moderate -sorted; silica cement, indurated; bioturbated by Thalassinoides; apparent fault con- tact with bed below making thickness uncertain 1$

7. Conglomerate, weathers grayish orange (1OYR7/4) to grayish orange pink (5YR7/2), matrix is fine- to coarse -grained sand, larger clasts were mostly wood fragments (now molds) with some shale and chert pebbles as much as 1/2 inch in diameter; silica cement, well -indurated; some indistinct cross -stratification 9

Total of upper sandstone unit . . . . 27

Middle shale unit:

6. Sandstone, grayish orange (1OYR7/4), weatherssame to dark yellowish orange (1OYR6/6), coarse- to very coarse grained, moderate -sorted; silicacement, in- durated; many secondary quartz veinlets up to a few mm wide; medium -scale trough cross- stratification . 9

5. Shale, weathers completely to mottled pale gray- ish yellow (lOY/2) and dark yellowish orange (10YR6 /6) limonite stain; much disturbed by tec-

tonic slippage within the shale bed. . . . 2

4. Sandstone,grayishorange (1OYR7/4), weathers same to dark yellowish orange (lOrR6/6), coarse- to very coarse grained, moderate -sorted; silica cement, well- indurated; many secondary quartz veinlets; obvious

slickensides . . . 2 90

Feet

3. Shale, identical with shale in unit 5...... 4

Total of middle shale unit ...... 17

Lower sandstone unit:

2. Conglomeratic sandstone, very light gray (N9), weathers pale yellowish orange (10M8/6), medium - to very coarse grained sand, poor -sorted, pebble layers of gray chert with minor reddish quartzite form layers one to two pebbles thick at intervals of a few feet, few cross -stratified discontinuous pebble layers as much as eight inches thick; sil- ica cement, firm to very friable near top of unit;

planar bedding and trough cross- stratification . . 33

1. Sandstone, very light gray (N9), weathers grayish orange pink (lOit/2), mostly coarse- to very coarse grained sand with few chert, quartzite, and quartz pebbles as much as one inch in diameter occurring singly and in discontinuous thin layers; silica cement, well - indurated ;. very prominent medium -scale trough cross-

stratification . . . . 84

Total of lower sandstone unit. . . 117

Total of Dakota Group. 161

Morrison Formation (unmeasured); olive green shales. 91

Location 7: North of Sapello

Measured on the north side of a small intermittent stream where it cuts through the Creston Ridge three miles north of the village of Sapello; long 105 °16, lg., lat 35 °49' N.

Graneros Shale (unmeasured); black shale

Dakota Group: Feet

Upper sandstone unit:

6. Sandstone, very pale orange (lOYR/2), weathers pale yellowish brown (10YR6/2), medium- grained, well- sorted; silica cement, very well indurated; few Skolithus present; stylolites along many bedding planes; small -scale tabular planar cross- -

stratification; unit weathers to prominent ledge . . 10

Total of upper sandstone unit . . . 10

Middle shale unit (?):

5. Covered...... 14

Total of middle shale unit . 14

Lower sandstone unit:

4. Sandstone, pale yellow orange (10YRB/6), weathers yellowish brown (1OYR6/2), medium- to coarse - grained, moderate -sorted; silica cement, well -

indurated. 22

3. Covered. . . . 18

2. Sandstone, very pale orange (1OYR8/2), weathers mottled same color to gray (N7) with reddish brown limonite staining, medium- to coarse - grained, moderate- sorted; silica cement, firm to friable; mostly planar bedded with some trough

cross -stratification . . 27

1. Sands t one, very pale orange(l0YR8/2 ), weathers same color, medium -grained with fine granule lenses as much as one inch thick, moderate -sorted; silica cement, well- indurated; medium -scale trough cross-

stratification; unit weathers to cliff . . . . 46 92

Feet

Total of lower sandstone unit. . . . . 93 2

Total of Dakota Group...... 1172

Covered interval (unmeasured): friable dark sandstones and olive green shales of the Morrison Formation below. 93

Location 8: Coyote Creek

Measured approximately 22 miles north-north-east of the village of Golondrinas. Upper sandstone unit measured at cliff due west of gauging station on Coyote Creek. Middle shale unit measured at the gauging station. Lower sandstone unit measured approximately 4mile north of the gauging station at cliffs on the west side of the canyon. There is over l00 feet of vertical displacement between this lower partial measured section and the upper two partial sections; long l05 °10' W., lat 35 °55' N.

Erosional surface:

Dakota Group: Feet

Upper sandstone unit: may not be complete

7. Sandstone, grayish yellow (5Y7/2) to mottled light and dark gray (N8 and N2), fine- to medium -grained, well- to moderate- sorted, locally shaley; silica

cement, indurated; much carbonaceous matter; some layers contain profuse limonite -coated wood frag- ment molds which produces a very rough weathered surface; discontinuous planar bedding 12 to 3 feet

thick...... 45

Total of upper sandstone unit (incomplete) 45

Middle shale unit:

6. Sandstone and shale; sandstone, light gray (N6 to N$) with few layers light olive gray (5Y6/i), medium- to coarse -grained, poor- to moderate- sorted; silica cement, well - indurated; shale, black (Nl) to medium dark gray (N4), weathers lighter gray up to very light gray (N$); thicknesses of the two lithologies vary from a few inches to several feet (average about 3 feet thick); wood fragments and molds in sandstone; black carbon films in all shales; sand- stone root casts extend down into underlying shales; erosional surface within the unit shows 10 feet

of scour . . 12

Total of middle shale unit 12- 94

Feet

Lower sandstone unit:

5. Sandstone, grayish pink (5R8/2), weathers grayish orange (1OYR.7/4) ,fine -grained, moderate -sorted; silica cement, well -indurated to firm; case hardened on weathered surface; discontinuous wavey laminae common; mostly small scale tabular planar cross -stratification, generally less than one foot thick 16

4. Conglomerate, grayish orange (10YR7/4), weathers dark yellow orange (10YR6/6), matrix medium- to very coarse grained sand, pebbles of gray towhite chert, dusky red (5R3/4) quartzite and dark gray quartz with a maximum diameter of 12 inches, poor -sorted; conglomerate lensesdiscontinuous; prominent trough cross -stratification with sets

less than 2 feet thick . . . 16

3. Sandstone, white (N9), weathers dark yellow orange (10YR6/6, medium- to coarse -grained, moderate - sorted; silica cement, indurated to friable; green clay gall conglomerate near middle of unit; small circular limonite- stained areas common, some places coalescing completely over a large area. . 56

2. Conglomerate, weathers dark yellow orange(10YR6 /6), matrix coarse- grained sand, clasts of irregularly - shaped green mudstone as much as 3 inches in diameter, uncommon granules of chert; silica cement, well- indurated; prominently cross -stratified 2

1. Sandstone, white (N9), weathers grayish orange (10YR7/4), fine- grained, well -sorted; silica cement, indurated to firm; case hardened; much dark surface staining; planar laminated with some small -

scale trough cross -stratification . 12

Total of lower sandstone unit . . . . 102

Total of Dakota Group (incomplete) . . . 1592

Covered slope; Morrison Formation outcrops about 20 feet below the base of the exposed rock. 95

Location 9: Box Canyon

The upper sandstone unit and middle shale unit were measured at the cliffs along the Gallinas River just south of Box Canyon. The lower sandstone unitwas measured in the cliffs along the north side of Box Canyon approximately 0o mile to the east of the Gallinas River; long 105°12-i' W., lat 35°32' N.

Erosional surface:

Dakota Group: Feet

Upper sandstone unit: may not be complete

7. Sandstone, white (N9), weathers very pale orange (lom8/2), fine -grained, well-sorted; silica cem- ent, indurated; few fragments of carbonized wood and wood molds; small -scale tabular planar cross- stratification . 4

Total of upper sandstone unit (incomplete) . . 4

Middle shale unit:

6. Intercalated shale and sandstone; shale, medium

cark gray (N4), weathers very light gray (Ne);

sandstone, same as unit 7. .

Total middle shale unit. . . 6

Lower sandstone unit:

5. Sandstone, white (N9), weathers grayish orange pink (5YR7/2), medium- to very coarse grained, poor-- sorted; silica cement, firm to indurated; case hardened; medium -scale trough cross -stratification

predominant...... 26

4. Conglomerate, very light gray (N$), weathers same with pale yellow orange (ioYR/6) staining, matrix coarse- to very coarse grained sand, pebbles of white to dark gray chert and reddish quartzite have maximum diameter of 2 inches; obvious channel fill, channel approximately 60 feet wide; petrified wood

at base of unit. . . 8 96

Feet

3. Sandstone, white (N9), weathers very pale orange (lon/2), medium- to coarse -grained, few pebble layers, poor -sorted; silica cement, indurated. 9

2. Conglomerate, same as unit 4 ...... 2

1. Sandstone, very pale orange (lOYF/2), weathers same with pale yellow orange (ioYR/6) and dark gray staining, medium- to coarse- grained, medium- - sorted; silica cement, indurated; medium -scale trough cross -stratification and indistinct planar

bedding...... 44

Total of lower sandstone unit (incomplete) . . . $9

Total of Dakota Group (incomplete) 99

Covered slope (unmeasured). 97

Location 10: Pagosa Canon

Measured at cliffs on the north side of Pagosa Canyon near its junction with the Gallinas River; long 105°10' VT., lat 35°30' N.

Erosional surface:

Dakota Group: Feet

Upper sandstone unit: may not be complete

10. Sandstone, white (N9), weathers grayish orange pink (loR/2), medium- to fine -grained, well -sorted; sil- ica cement, indurated to friable; case hardened; Skolithus present; few stylolites along bedding planes; tabular planar cross -stratification, thin bedding averaging 4 to 6 inches; unit weathers to

Cliff' 0 10

9. Sandstone, white (N9), weathers grayish orange pink (loR/2), medium- to fine -grained, well -sorted; sil- ica cement, indurated to friable; case hardened; tabular planar cross -stratification, thin bedding; unit weathers to cliff 7

Total of upper sandstone unit (incomplete 17

Middle shale unit: not present

Lower sandstone unit:

$. Conglomerate, very light gray (Ne), weathers light brown (5YR6/4), matrix medium -t o very coarse grained sand and white clay; pebbles of dark gray to white chert and minor quartzite as much as one inch in diameter; unit weathers to underhang

7. Conglomeratic sandstone, white (N9), weathers light

to dark yellow (ioYR/6 to 10YR6 /6), coarse- to very coarse grained with scattered pebbles as much as one inch in diameter, poor -sorted; silica cement, indurated; prominent trough cross -stratification; unit weathers to cliff 11

6. Conglomerate, very light gray (N8), weathers light

yellow orange (ioYiß/6), sand and clay matrix, pebbles of light to darkgray chert and minor quartzite as much as 2 inches in diameter,irregu- larly shaped mudstone clastsas much as7by 2 inches 9$

Feet

in cross section, petrified log at basal contact; unit is lenticular, 30 feet wide; unit weathers to shallow underhang . 5

5. Conglomeratic sandstone, identical with conglom- eratic sandstone in unit 7 4

4. Conglomerate, very light gray(N8), weathers light yellow orange (ioYR8/6), sandand clay matrix, pebbles of light to dark graychert and minor quartzite as much as 2 inchesin diameter; unit

weathers to rounded cliff. . . . 0 .. . 3

3. Sandstone, white (w9), weathers to grayish orange pink (lOYR/2), medium- to coarse-grained, moder- ate-sorted; silica cement, indurated; unit weathers

to cliff . . . . 8

2. Conglomerate, identical to unit 4. . 5

1. Sandstone, white (N9), weathers grayish orange pink (10YR8/2), medium- to coarse -grained, moderate -sorted; silica cement, indurated; one thin discontinuous green mudstone layer in middle of unit; medium -scale trough cross -

stratification; unit weathers to cliff . . 32

Total of lower sandstone unit (incomplete) . 72i

Total of Dakota Group (incomplete) 8/ 2

Covered slope (unmeasured). 99

Location 11; Canon Del Agua

Measured at cliffs on the east side of Canon Del Agua opposite State Highway 67 where it starts its descent into the canyon; long 105° 01' W., lat 35 °29' N.

Erosional surface:

Dakota Group: Feet

Upper sandstone unit: may not be complete

9. Sandstone, white (N9), weathers light brownish gray (5YR6/i), fine- to coarse -grained, moderate -sorted; silica cement, firm; case hardened; few wood frag- ment molds; wedge planar cross -stratification; thin lenticular bedding; stylolites along bedding planes;

unit weathers to cliff . 10

Total of upper sandstone unit (incomplete) . . 10

Middle shale unit:

$. Shale, weathers very light gray (Ne), sandy; limon- ite occurs around plant remains. 3

7. Sandstone, very light gray (N$) and pale brown (5YR5/2), weathers moderate yellowish brown (1OYR5/4), medium - to coarse- grained, moderate -sorted; silica cement, friable to indurated; case hardened; sharp lenticu- lar colored areas due to limonite in silica cement;

rare obscure Skolithus ( ?), unit weathers to ledge . 3

6. Shale, weathers very light gray (N8), sandy; fine - grained sandstone layer; carbonized wood and wood

fragment molds; unit weathers to slope . . . 7

Total of middle shale unit . . . 13

Lower sandstone unit:

5. Sandstone, pale orange (l0YR/2), weathers same color, medium- to coarse -grained, moderate -sorted; silica cement, firm to friable; planar bedding, some small - and medium -scale trough cross-

stratification; unit weathers to cliff . . 3 100

Feet

4. Conglomerate, very light gray (Ne), weathers same color, matrix coarse- to very coarse grained sand; pebbles of dark gray to white chert and minor quartz- ite as much as one inch in diameter; silica cement,

firm; unit weathers to rounded cliff . . . 2

3. Sandstone, identical with unit 5 53

2. Sandstone, moderate olive brown (5Y4/4), weathers grayish yellow (5Y/4), medium- to coarse-grained, slightly clayey, poor -sorted; silica cement, gener- ally friable with a few well indurated layers; laminated; unit weathers to steep slope. 4

1. Sandstone, dusky yellow (5Y6/4), weathers same, coarse -grained, well-sorted; silica cement, friable

unit weathers to slope . . 14

Total of lower sandstone unit. . . 76

Total of Dakota Group (incomplete) 99

Covered slope (unmeasured). 101

Location 12: Mesa Lauriano

Measured at cliffs on the north side of Mesa Lauriano; long 104057P W., lat 35025' N.

Erosional surface:

Dakota Group: Feet

Upper sandstone unit: may not be complete

9. Sandstone, very pale orange (l0YRE/2), weathers pale red (10R6/2), coarse -grained, moderate-sorted; silica cement, well- indurated; few thin lenses of clay galls and wood fragment molds; small -scale tabular planar cross -stratification, thickness averages approximately one foot (range one inch to two feet) ;unit weathers to ledge 1$

S. Mostly covered; float suggests very friable shalt' sandstone, weathers pale greenish yellow (10Y$/2) with reddish brown limonitic spots, fine- grained,

poor- sorted; weather to covered slope. . . . . 12

7. Sandstone, very light gray (NB), weathers same color to grayish red (10R4/2), medium- to coarse-grained, moderate -sorted; silica cement, indurated; few dis- continuous chert -granule stringers, one graule thick; Ophiomorpha and Skolithus common, carbonized wood in other beds; irregular undulating thin planar bedding most common, some small -scale tabular planar cross- stratification; stylolites along bedding; unit weath-

ers to overhang. . 7

Total of upper sandstone unit (incimplete) 37

Lower sandstone unit:

6. Muddy sandstone, greenish white (5GY9/l) , weathers same color, clay to medium-grained sand with few chert- granule stringers with grains as much as ¡inch in diameter, very poot -sorted; friable; unit weathers to

undercut . . 5

5. Conglomeratic sandstone, yellowish gray (5Y8 /l), weathers grayish orange (1OYR7/4), coarse -grained, poor -sorted over all; silica cement; thin cher- granule stringers; few clay gall layers with clasts as much as 6 inches in diameter; prominent medium- scale trough cross -stratification; unit weathers to cliff. 19 102

Feet 4. Conglomerate, yellowish gray (5Y8/l), weathers grayish orange (IOYR7/4), matrix is coarse sand, pebbles average approximately 2 inch in diameter with a maximum diameter of 2 inches, poor -sorted; silica cement, firm; pebbles consist of white to very dark gray chert with rare purple quartztite; silicified log at base of unit; unit weathers to

subdued cliff. . 36

3. Sandstone, grayish orange (1OYR7/4), weathers same color, medium- to coarse -grained, moderate - sorted; silica cement, friable to firm; planar bedding with less medium- to small -scale trough cross -stratification; unit weathers to cliff 12

2. Sandstone, same as unit 3; except not as well

cemented and weathers to steep slope . 9

1. Sandstone, same as unit 3; thin chert - pebble and clay -gall conglomerate layer in middle of unit...... 37

Total of lower sandstone layer . 118

Total of Dakota Group (incomplete) . . 155

Morrison Formation (unmeasured): intercalated green shales and sandstones; weathers to slope. 103

Location 13: Conchas Canyon

Measured approximately 4 miles south of State Highway 65 at cliffs on the west side of the Conchas River; long 104°51' W., lat 35 °3221 N.

Erosional surface:

Dakota Group: Feet

Upper sandstone unit: may not be complete

S. Sandstone, dusky yellow (5Y6/4), weathers through various shades of greenish gray and red to moder- ate red (5R4/6), medium- grained; silica cement, indurated; many ovoid depressions (clay molds?) on some bedding planes; little cross - stratification; unit weathers to rubbly steep

slope. . 4

7. Covered. . 12

6. Sandstone, very light gray (N$), weathers pale red (5R6/2), medium- to coarse -grained, moderate- sorted; silica cement, well -indurated; tabular planar cross -stratification; unit weathers to

cliff. .

5. Sandstone, white (N9), weathers pale red (5R6/2), medium- to very coarse grained, moderate -sorted; silica cement, firm to indurated; few limonite nodules as much as one inch in diameter, locally forming very rough weathered surface; aboundar_t Skolithus as much as 13 inches in length at top of unit; tabular planar cross -stratification and possible trough cross -stratification; unit weathers to cliff. 10

Total of upper sandstone unit (incomplete) . . 30

Middle shale unit: not present

Lower sandstone unit:

4. Sandstone, very light gray (Ne), weathers pale red (5YR6/2, medium- tocoarse -grained, moderate - sorted; silica cement, well -indurated; well- developed medium -scale troughcross -stratification; unit weathers to cliff 13 104

Feet

3. Conglomeratic sandstone, moderate orange pink (5YR8/4), weathers moderate brown (51R4/4), medium -grained sand with granules as much as 2 inch, slightly clayey; silica cement, friable

to indurated; unit weathers to undercut. . . 2

2. Sandstone, identical with unit 4 . . . . l4

1. Conglomeratic sandstone, very light gray (N8), weathers pale red (5R6/2), medium -grained sand with granules as much as ¡inch in diameter,

poor -sorted; silica cement, indurated. . . . 1+

Toi,al of lower sandstone unit (incomplete) . 63

Total of Dakota Group (incomplete 93

Covered (unmeasured). 105

Location 14: Trujillo

Mesa Rica Sandstone measured at top of escarpment in road cut along State Highway 65 just south of the village of Trujillo. Pajarito Shale and Dakota Group measured approximatelyone mile south of Tru- jillo at cliff at top of escarpment; long 104 °41' W., lat 35 031' N.

Erosional surface;

Dakota Group: Feet

Upper sandstone unit; may not be complete

6. Sandstone, white (N9), weathers pale red (5R6/2), medium -grained, moderate -sorted; silica cement, indurated to firm; case hardened; few Skolithus, Ophiomorpha, and U- tubes; tabular planar and probable trough cross -stratification; unit weathers to cliff. 2

5. Sandstone, same as unit 6 but with no trace fossils. 10

Total of upper sandstone (incomplete). 12

Middle shale unit:

4. Clayey sandstone, white (N9), weathers same color, medium -grained sand with white clay matrix, bi- modally well -sorted; some silica cement, well- indurated to friable; thin layers of clay and irregular clay masses common; few discontinuous black shale layers as much as several inches thick; wood replaced by limonite and wood casts; unit weathers with very rough surface texture to under-

hang . 5

Total of middle shale unit . 5

Lower sandstone unit:

3. Sandstone, white (N9), weathers moderate orange pink (5YR/4), medium- to coarse -grained, moderate - sorted; silica cement, very friable to indurated; small limonite nodules locally abundant ina few layers, generally less than4 inch in diameter; small - and medium -scale troughcross -stratification; locally weathers with box -work -likesurface texture; unit weathers to roundedcliff 36 106

Feet

Total of lower sandstone unit. . 36

Total of Dakota Group (incomplete) . . 53

Pa j arit o Shale:

2. Covered, infered shale, grayish red (5R.11/2) and pale greenish yellow (10Y8/2), variegated; fissile to blocky; silty; probably interbeds

with the base of unit 3...... 18

Total of Pajarito Shale. . 18

Mesa Rica Sandstone;

1. Sandstone, very pale orange (10YR8/2), weathers grayish orange pink (5YR7 /2) with common gray black (N2) surface stain, fine- to medium- grained, medium- sorted, minor clay; silica cement, well- indurated; Planolites present in few bedding planes; few vague ripple marks; cross -stratification and planar lamination, unit weathers to cliff 54

Total of Mesa Rica Sandstone . e 54

Total Cretaceous section (incomplete . 125

Morrison Formation (unmeasured): variegated purple and blue -green shales. APPENDIX B

CROSS -STRATIFICATION MEASUREMENTS

This appendix contains three sets of cross -strata on _tati ons

given as direction (azimuth) of maximum dip and the number of degrees

of dip from the horizontal in this direction as REGIONAL ASIMUTH and

REGIONAL DIP. Cross -stratification orientations as measured in the

field are recorded as X -BED ASIMUTH and X -BED DIP. The calculated

orientations of the original cross-strata are recorded as CORRECT.

AXIMUTH and CORRECT. DIP. All measurements are in degrees and tenths

of degrees.

107 108

LOCATION 1 ROMEROVILLE GAP

MAP COORDINATES LONGITUDE= 105° 16' LATITUDE= 35° 31.5'

NUM3ER OF CROSS -BED READINGS = 19

REGIONAL REGIONAL X -BED X- BE0 CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH Dip 94.0 14. 119.0 38.0 130.6 25.9 94.0 14.0 135.0 34.0 154.3 25.0 94.0 14.0 156.0 23.0 191.4 20.4 94.0 14.3 90.0 33.0 87.3 19.1 94.0 14.0 50.0 32.0 28.1 23.8 94.0 14.0 119.0 38.0 130.6 25.9 94.0 14.0 170.0 9.0 237.1 14.6 94.0 14.J 69.0 20.0 30.9 9.3 94.0 14.0 50.0 46.0 37.8 36.9 94.0 14.0 110.0 21.0 136.3 8.4 94.0 14.0 74.0 39.0 64.8 26.2 94.0 14.0 99.0 27.0 104.0 13.1 94.0 i4.û 70.0 25.0 46.1 13.4 94.0 14.0 65.0 39.0 52.6 27.5 94.0 14.3 72.0 45.0 64.3 32.4 94.0 14.7 82.0 34.0 74.6 20.5 94.0 14.0 120.0 28.0 140.4 16.5 94.0 14.0 117.0 39.0 127.3 26.6 94.0 14.0 102.0 32.0 107.6 18.2 109

LOCATION 2 KERNEY GA0

MAP COORDINATES LONGITUDE= 105° 15.5' LATI TUD`= 35° 33,5'

NUM3ER OF CROSS -BED READINGS = 26

REGIONAL REGIONAL X-BED X-BEO CORRECT. CORRECT. AZIt!UTH DIP .AZIMUTH DIP AZIMUTH DIP 99.0 38.0 111.. 0 50 . 138.3 14.6 99.J 38.0 81.0 54.0 53.4 20.5 99.0 38.0 112.0 47.0 148.3 12.5 99.0 38.0 94.0 56.0 85.7 1.8.4 99.0 38.3 92.0 54.0 79.0 16,8 99.0 38.0 65.0 48.0 19.6 25.0 99.0 38.0 120.0 59.0 143.4 26.0 99.0 38.0 95.0 47.0 80.8 9.4 99.0 38.0 111.0 45.0 152.3 10.6 99.0 38.0 96.0 58.0 91.6 20.1 99.0 38.0 108.0 46.0 139.4 10,0 99.0 38.0 99.0 59.0 99.0 21.0 99.0 38.0 154.0 40.0 208.) 33,8 99.0 38.0 143.6 49.0 186.4 31.7 99.0 38.0 148.0 42.0 201.5 31.1 99.0 38. 0, 151.0 34.0 217.5 30.1 99.d 38.0 156.0 40.0 209.0 35.0 99.0 38.0 104.0 44.0 129.6 6.8 99.0 38.0 128.0 56.0 159.5 27.5 99.0 38.0 96.0 50.0 88.0 12.2 99.0 38.0 55.0 61.0 27.0 39.7 99.0 38.0 147.0 38.0 208.3 29.0 99.0 38.3 90.0 60.0 78.7 23.0 99.0 38.0 7 0. 0 44.6 15.1 19.8 99.0 38.0 85.0 43.0 32.3 10.4 99.J 38.0 135.0 42. 0 193.5 23. 2 110

LOCATION 3 ARROYO HERMANOS

MAP COORDINATES LONGITUDE= 105° 15' LATITUDE= 35° 36'

NUM3ER OF CROSS -BED READINGS = 29

REGIONAL REGIONAL X-3ED X-9E3 CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 72.ú 21.3 65.0 27.0 43.4 6.6 72.0 21. 0 55.0 26.0 10.4 8.4 72.0 21.0 70.0 26.0 62.0 5. 1 72.0 21. 0 65.0 27.0 43.4 6.6 72.0 21.0 55.0 26.0 10.4 8.4 72.0 21.0 70.0 26.0 62.0 5.1 72.0 21.0 62.0 28.0 36.7 8.1 72.0 21.0 75.0 16.0 242.6 5.1 72.0 21.0 51.0 33.0 23.7 15.2 72.0 21.3 63.0 11.0 261.6 10.3 72.0 21.0 360.0 15.0 294.2 21.5 72.0 21.0 63.0 26.0 22.6 6.9 72.0 21.0 99.0 21.0 174.6 9.6 72.0 21.0 77.0 44.6 80.9 23.1 72.0 21.0 25.0 22.0 323.1 16.8 72.0 21.0 5q.0 32.0 38.2 12.4 72.6 21.0 50.0 43.0 34.1 24.6 72.0 21. t0 53.0 45 . 0 35.6 26.5 72.0 21.5 65.0 s0.0 50.3 9.5 72.0 21.0 123.0 39.0 151.4 29.8 72.0 21.0 110.0 20.0 184.0 13.1 72.0 21.0 44.3 14.0 289.4 10.8 72.J 21.0 27.0 43.0 3.3 31.2 72.0 21.0 84.0 44.0 93.0 23.8 72.0 21.0 91.0 48.0 102.2 28.8 72.3 21.0 51.0 25.0 358.0 9.1 72.0 21.0 41.0 35.0 11.2 19.8 72.0 21.3 55.0 42.0 41.4 22.6 72.0 21.ù 101.0 46.0 117.9 29.1 111

LOCATION 4 MONTEZUMA

MAP COORDINATES LONGITUDE= 105° 16' LATITUDE= 35° 39'

NUMBER OF CROSS-BED READINGS = 52

REGIONAL REGIONAL X-3E3 X-BED CORRECT. CORRECT. AZIMUTH DIP A'IMUT'H Orp AZIMUTH OIP 30.0 94.0 267.0 90.0 199.6 8.1 80.0 94.0 275.0 75.0 27.7 18.4 80.0 94.0 282.0 84.0 356.1 22.0 80.J 94.0 255.0 57.0 71.4 29.4 80.0 94.0 270.0 76.3 36.0 14.0 80.0 94.0 254.0 84.0 151.3 6.3 8300 94.0 268.0 86.J 350.3 8.0 80.0 94.0 271.0 74.0 38.7 16.2 80.0 94.0 268.ú 77.0 39.2 12. 0 80.0 94.0 211.0 73.0 23.8 24.4 94.0 277.0 76.0 21.9 19.5 ÿ83.0 " 'J . iJ 94..0 264.0 58.3 72.8 28.3 80.0 94.0 265.0 69.0 64.5 17. 7 80.0 94.0 285.0 69.0 27./ 29,7 83.0 95.0 280.0 57.0 55.6 32.2 83.0 95.0 275.0 44.0 70.6 42.3 83.0 95.0 257.1 62.0 96.3 23.7 83.0 95.0 265.0 72.0 74.6 13.1. 95.0 264.0 53.0 81.7 35. 0 83.0p83.0 95.0 230.0 50.0 56.6 33.0 33.0 95.3 275.0 53.0 65.6 33.8 83.0 95.3 270.0 52.0 73.0 33.6 83.0 95.L 290.0 52.0 50.1 41.1 83.0 95.0 272.0 85.0 353.4 9.0 83.0 95.0 250.0 63 ù 111.0 25,3 83,0 95.0 265.0 75.0 72.0 10.2 83.0 95.0 260.0 80.0 113.6 5.8 83.0 95.0 280.0 70.0 36.7 22.3 83.0 95.0 270.0 37.0 157.3 7.3 83.0 95.0 2740 66.0 54,9 21. 8 83.0 95.0 274.0 60.0 61.7 27.1 83.0 95.0 292.0 65.0 31.7 34.3 83.0 95.0 260.0 77.0 103.1 8.5 83.0 95.0 259.0 81.0 127.6 5.6 83.0 95.0 275.0 67.0 51.4 21.4 112

LOCATION 4 MONTEZUMA (CONT. )

REGIONAL REGIONAL X--BED )(BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 83.0 95.0 266.0 78.0 60.2 7.6 83.0 95.0 262.0 80.3 94.2 501 83.0 95.0 270.0 64.0 66.0 22.0 83.0 95.0 265.0 69.0 76.3 1.6.1 83.0 95.0 264.0 58.0 81.1 ßr7.0 83.0 95.3 277.0 76.0 27.1 16.5 83.0 95.0 275.0 75.0 34.1 15.5 83.0 95.0 281.0 73.0 28.7 21.3 83.0 95.0 267.0 90.0 224.3 6.4 83.0 95.0 268.0 77.0 51.7 9.4 83.0 95.0 271.0 74.0 48.1 13.5 83.0 95.0 268.0 86.0 161.9 5.1 83.0 95.0 254.0 84.0 166.2 9.0 13.0 95.0 270.0 76.0 46.0 11.3 13.0 95.0 265.0 57.0 79.4 28.1 83.0 95.0 282.0 Fi4.ú 356.9 18.9 83.0 95.9 285.0 69.0 31.8 26.7 113

LOCATION 5 BONITA RANCH

MAP COORDINATES LONGITUDE= £05° 16.5' LATITUDE= 35° 42'

NUM3ER OF CROSSMBED READINGS = 10

REGIONAL REGIONAL X 8ED X BE0 CORRECT. CORRECT. AZI i.IUTH DIP AZIMUTH DIP AZIMUTH QIP 90.0 130.0 237.0 80.0 177.1 32.5 90.0 100.0 240.0 60.0 146.1 34,4 90.0 130.0 243.0 74.0 164.3 27.0 90.0 130.0 235.0 70.0 159.3 35.2 90.0 100.0 245.0 65.0 144.5 28.1 90.0 100,0 275.0 65.0 73.1 15.7 9ï1.0 100.0 276.0 85.3 140.4 7.8 90.0 100.3 290.0 6 8. 0 34.5 22.6 90.0 100.0 250.0 55.0 123.0 30.9 90.0 100.0 280.0 80.0 .9 9,8 114

LOCATION 6 SAPELLO

MAP COORDINATES LONGITUDE= 105° 14.5' LATITUDE= 35° 46'

NU43ER OF CROSS-BED READINGS = 26

REGIONAL REGIONAL X »BED X -BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 124.0 67.0 100.0 79.0 57.6 25.8 124. 0 67.0 134.0 75.0 175.5 12.4 12 4. 0 67.0 125.0 87.0 126.9 20.0 124.0 67.0 135.0 b6.0 221.8 10.1 124.0 67.0 140.0 68.0 213.2 14.8 124.0 67.0 150.0 80.0 190.7 28.0 124.0 67.0 /07.0 88.0 83.4 26.7 124.0 67.0 94.0 77.0 48.1 30.2 124.0 67.0 118.0 75.0 87.6 9.8 i2 4. n 67.0 113.0 89.0 96.6 24.5 124.0 67.J 105.0 79.0 64.3 21.7 124.0 67.0 118.0 66.0 22.5 5.6 124.0 67.0 114.0 67.0 32.0 9.2 124.0 67.0 115.0 71.0 57.8 9.3 124.0 67.0 93.0 83.0 57.3 33.8 124.0 67.0 121.0 83.0 113.3 16.3 124.0 67.0 105.0 90.0 82.6 29.5 124.0 67.0 104.0 90.0 81.0 30.1 124.0 67.0 101.0 87.0 72.6 29.9 12 4. 0 67.0 107.0 85.0 79.1 24.4 124.0 67.0 111.0 90.0 93.4 26.2 124.0 67.1 102.0 45.0 339.4 2 7. 7 124. 0 67.0 95.0 45.0 344.0 32.3 124e 0 67.0 94.0 80.0 53.4 31.5 124.0 67,0 95.0 86.0 63.8 33.9 124.0 67.0 135.0 81.0 162.7 17,5 115

LOCATION 7 NORTH OF SAPELLO

NAP COORDINATES LONGITUDE= 105° 16' LATITUDE= 35° 49'

NUMBER OF CROSS --BED READINGS = 17

REGIONAL REGIONAL X -BED X--BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 100.0 122.0 268.0 42.0 126.1 18.4 100.0 122.3 265.0 52.0 159.8 13.7 100.0 122.0 3 35.0 74.4 27.0 100.0 122.3 2`7L1.(0] ('ti . 1'0]U 47.0 67.2 13.5 130.0 122.0 285.0 55.0 47.1 5.1 100..0 122.0 291.0 50.0 55.1 11.9 100.0 122.0 260.0 60.0 11.4 17.2 100.0 122.0 260.0 80.0 55.5 28.7 10i.0 122.0 255.0 65.0 21.3 23,0 100.0 122.0 295.0 56.0 23.1 12.7 100.0 122.0 265.0 60.0 14.9 13.0 100.0 122.0 292.0 22.0 92.5 36.7 100.0 122.0 271.0 44.0 123.8 15.6 100.0 122.0 286.0 22.0 96.2 36.2 100.0 122.0 245.0 55.0 174.4 29.2 100.0 122.) 261.0 74.0 48.4 23.5 100.0 122.3 251.0 69.0 25.9 28.1 116

LOCATION 8 COYOTE CREEK

MAP COORDINATES LONGITUDE= 105° 10' LATITUDE= 35° 55'

NUM3 EliOF CROSS -BED READINGS = 26

REGIONAL REGIONAL X -E3ED X -BEJ CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 218.0 10.0 333.0 29.0 346.8 34..3 218.0 10.0 210.0 27.0 205.6 17. 1 218.0 1n.0 54.0 25.3 49.8 34.7 218.,0 10.0 105.0 30.0 91.3 35. 0 218.0 10.0 65.0 15.0 54.6 24.3 218.0 10.0 174.0 16.0 136.4 11.2 218.0 10.0 190.0 14.0 148.2 7.0 218.0 10.0 155.0 25.0 132.8 22.2 218.0 10.0 114.0 23.0 94.3 27.1 218.0 19.0 82.0 32.0 73.2 39.7 218.0 10.0 167.0 14.0 122.4 10.9 218.0 10.) 35.0 25.0 35.8 35.0 218.0 10.0 221.0 34.0 222.1 24.0 21g.0 10.0 301.0 15.0 336.0 16.9 218.0 13.0 111.0 23.0 91.9 27.5 218.0 10.0 265.0 24.0 286.9 18.6 218.0 10.0 203.0 29.0 195.9 19.5 218.0 10.0 155.0 22.0 129.1 19.5 218.0 10.0 96.0 22.0 79.7 28.5 218.3 10.0 i35.0 18.0 105.3 19.4 117

LOCATION 9 BOX CANYON

MAP COORDINATES LONGITUDE= 105° 12.5' LATITUDE= 35°32'

NUMBER OF CROSS-6E0 READINGS = 69

REGIONAL REGIONAL X_gEO X--BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 274.0 7.0 314.0 31.0 323.1 26.0 274.0 7.3 30.0 15.0 48.7 19. 1 274.0 7.0 83.0 16.0 86.2 22.9 274.0 7.0 72.0 11.0 80.4 17. 7 274.0 7.0 205.0 22.0 187.3 20.5 274.0 7.0 310.0 17.0 329.5 12.0 274.0 7.0 350,0 22.0 7.6 21.4 274.0 7.0 306.0 10.0 348.1 5.5 274.0 7.0 275.0 22.0 275.4 15.0 274.0 7.0 75.0 21.0 79.5 27.7 274.0 7.0 216.0 18.0 194.1 15.4 274.0 7.0 190.0 19.0 169.9 19.5 274.0 7.0 136.0 16.0 123.9 21.7 274.0 7.0 150.0 18.0 135.7 22.6 274.0 7,0 11.0 27.0 23.9 28.6 274.0 7.0 280.0 2:J.J 281.8 22.0 274.0 7.0 350.0 14.0 18.4 14.0 274.0 7.0 190.0 22.0 172.7 22. 3 274.0 7.0 245.0 13.0 219.1 7.7 274.0 7.0 199.0 19.0 178.3 18.4 274.0 7.0 15.0 21.0 31.3 23.3 274.0 7.0 40,0 29.0 48.8 33.6 274.0 7.0 90.0 22.0 90.9 29.0 274.0 7.0 198.0 20.0 178.4 19.5 274.0 7.0 190.0 10.0 153.4 11.6 274.0 7.0 88.0 15.0 89,9 22. 0 274.01 7.0 110.0 13.0 104.5 19.8 274.0 7,3 70.0 10.0 79.7 16.6 274.0 7.0 76.0 11.0 82.9 17.8 274.0 7.0 233.0 25.0 220.6 20.2 274.0" 7.0 187.0 20.0 168.2 20.8 274.0 7.0 175.0 25.0 161.1 26.9 274.0 7.0 195.0 22.0 177.5 21.7 274.0 7.0 182.0 18.0 161.7 19.5 274.0 7.0 128.0 19.0 119.4 25.1 118

LOCATION 9 BüX CANYON (CONT.)

REGIONAL REGIONAL X 3E3 X3E0 CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 274.0 7.0 175.0 20.0 157.6 222 274.0 7.0 212.0 2j.0 195.5 2(.6 274.0 7.0 22.0 12.0 46.8 15 .'6 274.0 7.3 35 7. 0 11.0 31.0 123 274,0 7.0 40.9 23.0 51.1 27.7 27 4. 0 7.0 29.0 86.6 35.9 {85.0 274.0 7.0 180.fl 25.0 165.7 26.4 274.0 7.0 27.0 13.0 48.8 17.0 274.0 7.0 262.0 14.0 250.7 7.3 274.0 7.1 256.0 13.0 237.4 6.7 274.0 7.0 189.3 14.0 162.0 15.1 274.0 7.0 230.0 1.1.0 191..1 7.7 274.0 7.0 166.0 18.0 148.4 21.2 274.0 7.0 106.0 8.0 100.5 14.9 274.0 7.0 249.0 19.n 236.2 13. 0 274.0 7.0 14,0 16.0 35.2 18.5 274.0 7.0 23.0 20.0 38.8 23.2 274.0 7.J 277.0 20.0 278.6 13.0 274.0 7.0 15.0 17.0 34.9 19.5 274.0 7.0 199.0 21.0 1.80.4 20.3 274.9 7.0 240.0 13.0 211.8 8.2 274.0 7.0 151.0 14.0 133.2 18.7 274.0 7.0 129.0 12.0 116.5 18.2 27 4. 0 7.0 24100 13.0 213.2 8.1 274.0 7.0 355.0 12.0 26.9 12.9 274.0 7.0 14.0 26.0 27.2 28.0 274.0 7.0 240.0 14.0 214.9 9.1 274.0 7.0 210.0 19.0 189.2 17.1 274.0 7.0 97.0 21.0 96.3 28.0 274.0 7.0 155.0 22.0 142.2 26.1 274.0 7.0 159.0 21.0 144.9 24.7 274.0 7.1 99.0 14.0 97.4 21.0 274.0 7.0 121.0 21.0 114.7 27.4 274.0 7.1) 151. 0 9.0 126.6 14.1 119

LOCATION 9 BOX CANYON ABOVE CONGL.

MAP C00?, DI NATES LONGITUDE= 105° 12.5' LATITUDE= 35°32'

NUMBER OF CROSS-BED READINGS = 32

REGIO4AL REGIONAL X°'3ED X-BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 274.0 7.0 247.0 29.0 GiJ. LJ 274.0 7.0 235.0 30.0 225,7 24.9 274.0 7.0 248.0 27.0 240.1 20.9 274.0 7.9 255.0 20.0 245.7 13.6 274.0 7.0 230.0 25.0 217.1 20.5 274.0 7.0 198.0 21.0 /79.4 20.4 274.0 7.0 225.0 30.0 214.2 25.9 274.9 7.0 270.0 33.0 269.0 26.0 274.0 7.0 198.0 33.0 189.0 36. 8 274.0 7.0 217.7 27.0 203.8 23.9 274.0 7.0 255.0 27.0 249.0 20.5 274.0 7.3 239.0 22.0 214.7 17.6 274.0 7.0 260.0 31.0 256.3 24.3 274.0 7.0 219.0 20.) 200.0 16.9 274.0 7.0 190.0 21.0 171.9 21.4 274.0 7.0 212.0 27.0 198.4 24.4 274.0 7.0 210.0 198.0 27.6 274.0 7.0 218.0 35.0 208.7 31.6 274.0 7.0 232.0 31.0 222.6 26.2 274.0 7.0 201.0 25.0 185.7 23.8 274.0 7.0 203.0 26.0 188.4 24.6 274.0 7.0 211.0 21.0 192.5 18.8 274.0 7.0 224.9 26.0 210.9 22.1 274.0 7.3 223.0 25.0 209.1 21.3 274,0 7.0 218.0 31.0 207.0 27.6 274.0 7.3 23?.0 30.0 222.2 25.2 974.0 7.3 222.0 3 0. 0 210.9 26.2 274.0 7.0 231.0 22.0 215.9 17.5 274.0 7.0 239.0 25.0 227.9 19.7 274.0 7.0 274.0 26.0 274.0 19.0 274.0 7.0 255.0 30.0 249.9 23.5 274.0 7.0 240.0 25.0 229.1 19.6 120

LOCATION 9 BOX CANYON BELOW CONGL.

MAP COORDINATES LONGITUDE= 105° /2.5' LATITUDE= 35° 32'

NUMBER OF CROSS-..BED READINGS = 32

REG I ßW,L Rr GI O1AL X-ßtD X3 7A CORRECT. OCIOP RRECT. AZIMUTH DIP AZIMUTH OIP AZIMUTH 274.0 7.0 76.3 11.0 82.9 17. 8 274.J 7.0 16J.0 19.0 144.3 22,7 274.0 7.0 72.0 24.0 76.6 30.6 274.0 7.0 354.0 25.0 9.2 24.7 274.0 7.3 280.0 29.0 281.8 22.0 274.0 7.9 80.0 23.0 83.0 29.8 274.fi 7.3 40.0 20.0 52.6 24.7 274.0 7.0 140.0 15.0 126.2 20.5 274.0 7.3 134.0 13.0 120.5 18.9 274.0 7.0 56.0 28.0 62.7 33.8 274.0 7.0 60.0 12.0 72.2 18.2 274.0 7. J 207.0 17.0 133.3 15.6 274.0 7.0 92 . 0 19.0 92.5 26.0 274.3 7.0 162.0 27.0 150.6 30.3 274.0 7.0 25.0 14.0 46.1 17.7 274.3 7.0 331J.0 1.8.0 351.8 15.2 274.G 7.0 42.0 13.0 59.3 18.2 274.0 7.0 220.0 18.0 198.4 15.0 274.0 7.9 238.0 15.0 214.6 10.2 274.0 7.3 350.0 10.0 28.9 10.7 274.0 7.0 106.0 15.0 102.3 21.9 274.0 7.0 169.0 13.0 144.9 16. 3 274.0 7.0 355.0 10.0 32.5 11.3 274.0 7.0 54.0 17.0 65.0 22. 8 274.0 7.3 188.0 35.0 178.0 35.1 274.0 7.1.1 176.0 21.0 159.3 23.0 274.0 7.0 105.0 30.0 103.1 36.9 274.0 7.0 132.0 19.6 122.5 24.9 274.0 7.0 212.0 12.0 177.1 10.7 274.0 7.0 223.0 21.0 205.6 17.4 274.0 7.0 132.0 19.0 122.5 24.9 274.0 7.0 145.0 13.J 128.0 18.2 121

LOCATION 10 PAGOSA CANYON

MAP COORDINATES LONGITUDE= 105° 10' LATITUDE= 35° 39'

NUMBER OF CROSS -BED READINGS = 50

REGIONAL REGIONAL XBED X -BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 0.3 O.i) 221.0 24.E 221.0 24.0 0.0 0.0 247.0 19.0 247.0 19.0 0.0 0.0 298.0 26.0 298.0 26,0 0.0 0.0 190.0 29.0 190.0 29.0 0.0 0.0 225.0 26.0 225.0 26.0 0.0 0.0 235.0 21.0 235.0 21.0 0.0 0.0 50.0 15.0 50.0 15.0 0.0 0.0 220.0 23.0 220.0 23.0 0.0 0.0 140.0 2.3.0 140.0 23.0 0.0 0.0 117.0 2ú.0 117.0 20.0 0.0 0.0 228.0 21.0 228.0 21.0 0.0 0.0 160.0 19.0 160.0 19.0 0.0 0.0 209.0 29.0 209.j 29.0 0.0 0.0 158.0 15.0 158.0 15.0 0.0 0.0 192.0 22.0 192.0 22.0 0.0 0.0 /80.0 23.0 180.0 23.0 0.0 0.0 36.0 20.0 16.0 20.0 0.0 0.0 80.0 27.0 80.0 27.0 0.0 0.0 194.0 20,0 194.0 20.0 0.0 0.0 138.0 16.0 138.0 16.0 0.0 0.0 147.0 24.0 147.0 24.0 0.0 0.3 247.0 19.0 247.0 19.0 0.0 0.0 242.0 15.0 242.0 15.0 0.0 0.7 81.0 19.0 81.0 19.0 0.0 0.0 34.0 18.0 34.0 18. 0 0.0 0.0 100.0 27.0 100.0 27.0 0.0 U.0 150.0 26.0 150.0 26. 0 0.0 0.0 13.0 24.0 13.0 24.0 0.0 0.0 69.0 12.0 69.0 12.0 0.0 0.0 /08.0 25.0 108.0 25.0 0.0 0.0 5.0 18.0 5.0 18.0 0.0 0.0 280.0 22.0 280.0 22,0 0.0 0.0 57.0 19.0 57.0 19.0 0.0 0.0 55.0 30.0 55.0 30.0 0.0 0.0 47.0 17.0 47.0 17.0 122

áO3ATI0N 10 PAGOSA CA NYOV (CONT.)

REGIONAL RE3IONAL X-RED X-E3 EJ 30RREC T. CORr?ECT . AZI MUTH DIP AZIMUTH DIP AZIMUTH UI P 0.0 0.0 53.0 25.0 53.0 25.0 0.0 110.0 24.0 110.0 24.0 0.0 U.0+0.3 4.0 24.0 4.0 24.0 0.0 0.0 33.0 2í7.ú 33.0 2ù.0 0.0 0.0 186.0 22.0 186.0 22.0 0.0 0.0 20.0 13.0 20.0 13.0 C.) 0.9 51.0 23.,.3 51.0 23.0 0.0 0.0 15300 21.0 153.0 21.0 0.0 0.0 145.0 34.0 145.A; 34.0 0.0 0.0 8ß..0 18.0 81.0 18.0 0.0 0.0 97.0 16.0 97.5 16.0 0.0 0.0 185.0 2o.0 185.0 26.0 0.0 0.0 101.0 18.0 101.0 18.0 0.0 0.3 184.0 20.0 184.0 20.0 0.0 0.3 26.0 16.0 26.0 16.0 123

LOCATION il CANYON DEL AGUA

MAP COORDINATES LONGITUDE = 105° 1 ' LATITUDE= 35° 29'

NUMBER OF CROSS -BED READINGS = 11

REGIONAL RESIONAL X- BED X -BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 358.0 4.0 270.0 22.0 260.1 22.2 358.0 4.0 125.0 23.0 131. 8 25.6 358.0 4.0 74.0 16.0 88.1 15.5 358.0 4.0 97.0 19.0 108.0 20.0 358.0 4.0 150.0 12.0 156.8 15.6 358.0 4.0 115.0 11.0 130.3 13.3 358.0 4.0 330.0 11.0 316.0 7, 7 351.0 4.0 58.0 16.0 71.6 14.4 358.0 4.0 156.0 12.0 156.!3 15.6 358.0 4.0 335.0 12.0 324.5 8.5 358.0 4.0 337.0 17.0 331.0 13.3 124

LOCA TI ON 12 MESA LAURIANO

MAP COORDINATES LONGITUDE= 104° 57.5' LATITUDE= 35° 25'

NUMBER OF CROSS-BED READINGS = 38

REGIONAL REGIONAL X-9ED X-BED CORRECT. CORRECT. AZIMUTH DIP A7IMUTH DIP AZIMUTH DIP 232.0 8.0 213.0 18.0 199. 3 10.7 232.0 8.0 223.0 18.0 216.1 10.2 232.0 8.0 205.0 14.0 177.5 7.8 232.0 8.0 143.0 19.6 120.8 20.4 232.0 8.0 123.0 6.0 81.9 11,4 232.0 8.0 105.0 21.0 91.8 26.6 232.0 8.0 131.0 10.0 97.i 13.9 232.0 8. 0 81.0 18.0 72.5 25.3 232.0 ß.0 117.0 21.G 101.2 25.4 232.3 8.0 142.0 18.0 345.2 19.6 232.0 8.0 29.0 17.0 36.0 24.6 232.0 8.0 136.0 11.0 102.5 14.2 232.0 8.0 90.0 15.0 77.9 22.8 232.0 8.0 220.0 18.0 211.0 10.3 232.0 8.0 31A.0 11.0 355.6 13.2 232.0 800 202.0 13.0 169.0 7,3 232.0 1.0 20i.0 26.0 189.6 19.6 232.0 8.0 1C0.0 16.0 84.9 22.1 232.0 8.0 185.0 23.0 167.4 18.4 232.0 8.0 55.0 14.0 53.9 22.0 232.0 8.3 160.0 17.0 133.1 16. 3 232.0 8.0 58.0 34.0 57.0 42.0 232.0 8.0 190.0 17.0 164.8 12.2 232.0 8.0 97.0 17.0 83.5 23.3 232.0 8.0 7.0 17.0 20.5 23.3 23Z.0 8.0 132.0 21.0 113.5 23.7 232.0 8.0 25.0 12.0 35.5 19.5 232.0 8.0 86.0 24.0 78.3 30.9 232.0 8.0 75.0 18.0 68.3 25.5 232.0 8.0 334.0 27.0 348.1 29.6 232.0 8.0 342.G 14.0 5.7 18.3 232.0 3.J 170.0 14.0 136.0 12.4 232.0 8.3 25.0 18.0 32.9 25.4 232.0 8.0 34. 0 19.0 39.1 26.7 232.0 8.0 120.0 16.0 99.3 20.4 125

LOCATION 12 MESA LAURIAND (CONT. )

REGIONAL REGIONAL X-"3EJ X- BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH OIP 232.0 8.3 66.3 23.0 62.6 30.8 232. 0 8.0 353.0 19.0 8.8 24.1 232.0 8.0 6.0 15.0 21.2 21.3 126

LOCATION 13 CONCH AS CANYON

MAP COORDINATES LONGITUDE= 104° 51' LATITUDE= 35° 32.5'

NUMBER OF CROSS -BED REA DIN S = 31

REGIONAL REGIONAL X-BED X-BE3 CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DTP AZIMUTH DIP 0.0 0. 0 61.0 29.0 61.0 29. 0 0.0 C1. 0 72.0 3 0. 0 72.0 3C.0 0.0 0.0 105.0 20.0 105.0 20.0 0.0 0.0 90.0 18.0 90.0 18.0 0.0 0.0 110.0 23.0 110.0 23. 0 0.0 0.0 251.0 20.0 251.0 20.0 0.0 O.9 116.0 19.0 116.0 19.0 0.0 0.0 192.0 25.0 192.0 25.0 0.0 0.0 200.0 29.0 200.0 29.0 0.0 0.0 143.0 23.0 143.0 23.0 0.0 0.0 192.0 19.0 192.0 19. 0 0.0 0.0 176.0 19.0 176.0 19.0 0.0 0.0 205.0 22.0 205.0 22.0 0.0 t0 . 0 254.0 2 7. 0 254.J 27. 0 0.0 0.0 145.0 23.0 145.0 23.0 0.0 0:1 215.0 21.0 215.0 21.0 0.0 0.0 281.0 22.0 281.0 22.0 0.0 0.3 217.0 24.0 217.0 24. 0 0.0 0.0 250.0 14.0 250.0 14.0 0.0 0.0 312.0 16.0 312.0 16.0 0.0 0.0 28400 14.0 284.0 14.0 0.0 0.0 177.0 19.0 177. J 19.0 0.0 0.7 295.0 24.0 295.0 24.0 0.0 0.0 179.0 19.0 179.0 19. 0 0.0 0.0 17r).0 17.0 176.0 17.0 0.0 0.0 246.0 11.0 2 46. 0 11.0 0.0 0.0 99.0 12.0 99.0 12.0 0.0 0.0 108.0 19.0 108.0 19.0 0,0 O.) 179.0 19.0 179.0 19.0 0.0 0.0 165.0 13.0 165. 0 13.0 0.0 0.0 123.0 23.0 123.0 23. 0 127

LOCATION 14 TRUJILLO

MAP COORDINATES LONGITUDE= 104° 41' LATITUDE= 35° 31'

NUM3ER OF CROSSBED READINGS = 24

REGIONAL REGIONAL X-8ED XBED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 19.0 6. l 97.0 27.0 99.1 21.1 89.0 6.0 270.0 11.0 269.7 17.0 89.0 6. 0 53.1 13 . G 29.9 8.9 89.0 6.0 100.0 29.0 102.6 23.1 89.0 6.0 343.0 23.0 330.6 25,3 89.0 6.0 261.0 21.0 262.7 27.0 19.0 6.3 31.0 2 2. 0 24.3 18.8 89.0 6.0 352.0 16.0 332.9 17.7 89.0 6.3 7.0 15.0 344.7 15.3 89.0 6. 0 114.0 27.9 /20.3 21.7 39.0 6.3 128.0 26.] 137.4 21.6 89.0 6.0 279.0 10.0 279.3 15.9 89.0 6.7 200.9 22.0 212.4 24..8 89.0 5.0 70.0 16.0 59.5 10.5

89.0 Fi . ) 100.0 18.0 105.3 12.2 89.0 6. 0 115.0 12.0 136.5 7.1 89.0 6.0 180.0 11.0 208.0 12.6 89.0 6.0 125.0 18.0 139.6 13.6 89.0 6.0 128.0 22.0 139.8 17.7 89.0 6.0 154.0 22.1; 168.9 20.2 89.0 6.0 185.0 13.0 239.9 14.9 89.0 6 . 0 205.0 21. 0 217.2 24,2 89.0 6.0 190.0 13.0 212.2 15.3 89.0 5.0 185.0 11.0 211.8 13.1 128

LO;ATION 14 TRUJILLO MESA RICA SS.

MAP COORDINATES LONGITUDE= 104° 41' LATITUDE= 35° 31'

NU93ER OF CROSS-3ED REA DIN GS = 6

REGIONAL REGIONAL X--BED X-BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 89.0 6.0 195.0 12.0 217.5 14.8 59.0 170.0 14.0 193.9 14.3 c6.0 89.0 U . iJ 322.0 11.0 304.1 15.4 89.0 6.0 109.0 20.0 116.8 14.5 19.0 6.0 107.0 22.0 113.2 16.4 R9.0 6.0 43.0 12.0 14.5 8.9 129

LOC. 15 UNMEASURED SECTION E OF LVS

MAP COORDINATES LONGITUDE= 134° 59' LATITUDE= 35° 35'

NUM3ER OF CROSS-BED READINGS = 21

REGIONAL REGIONAL X -BED X-dBED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 90.0 4.0 45.0 19.0 35.4 16.4 90.9 4.3 102.0 18.0 105.3 14.1 90.0 4.0 76.0 17.0 71.9 13.2 90.0 4.0 161.0 24.1.0 180.1 19.6 90.0 4.0 104.0 20.0 107.3 16. 1 90.0 4.0 353.0 18.0 341.3 18.9 90.0 4.0 330.0 13.0 317.2 15.4 10.0 4. 0 104.0 15.0 108.9 11.2 90.0 4.0 48.0 22.0 40.4 19. 2 90.0 4.0 318.0 22.0 311.5 24.8 90.0 4.0 55.0 17.0 45.8 13.9 90.0 4.0 144.0 13.x? 160.6 11.1 90.0 4.0 315.0 22.0 308.8 25.0 90.0 4.0 93.0 11.0 94.7 7.0 90.0 4.0 334.0 12.0 319.6 14.2 90.0 4.0 153.0 20.0 163.7 18.5 90.0 4.0 146.0 20.0 156.2 18.1 90.0 4.0 76.0 20.0 72.7 16.1 90.0 4.0 162.0 23.0 171.4 22.1 90.0 4. 3 193.0 17.0 204.9 18.3 90.0 4.0 116.0 10.3 131.2 6.6 130

LOCATION 16 VALMORA

MAP COORDINATES LONGITUDE= 104° 55' LATITUDE= 35° 48,5'

NUMBER OF CROSS -BED READINGS = 32

REGIONAL REGIONAL X -BED X -BED CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP 355.0 4.0 120.0 22.0 127.3 24.5 355.0 4.0 315.0 11.0 297.2 8.3 355.0 4.0 105.0 20.0 114.6 21.7 355.0 4.0 185.0 27.0 183.8 30.9 355.0 4.0 112.0 12.0 126.2 14.3 355.0 4.0 152.0 17.0 156.2 20.7 355.0 4.0 211.0 21.0 205.7 24.3 355.0 4.0 100.0 23.0 108.6 24,3 355.0 4.0 266.0 22.0 256.2 22.3 355.0 4.0 65.0 13.0 82.6 12.2 355.0 4.3 113.0 13.0 126.1 15. 3 355.0 4.0 184.0 21.0 182.6 25.0 355.0 4.0 40.0 22.0 48.0 19.4 355.0 4.0 247.0 26.0 239.6 27.5 355.0 4.0 4.0 25. 0 5.6 21.1 355.0 4.0 191.0 13.0 187.3 16.9 355.0 4.0 71.0 12.0 90.1 11.7 355.0 4.3 69.0 23.0 78.4 22,2 355.0 4.3 102.0 21.0 111.3 22.5 355.0 4.0 141.0 12.0 149.2 15.5 355.0 4.0 114.0 10.0 130.2 12.4 355.0 4.0 102.0 11.0 119.2 12.7 355.0 4.0 79.0 20.0 90.0 20.0 355.0 4.0 135.0 20.0 141.1 23.2 355.0 4.0 71.0 13.0 88.6 12.6 355.0 4.0 55.0 16.0 68.6 14.4 355.0 4.0 354.0 14.0 353.6 10.0 355.0 4.0 90.0 20.0 100.6 20.7 355.0 4.0 156.0 24.0 158.5 27. 8 355.0 4.0 204.0 14.0 197.8 17.6 355.0 4.0 167.0 18.0 168.4 22.0 355,0 4.0 233.0 13.0 220.6 15. 5 131

ALL LOCATIONS UPPER DAKOTA SS

NUMBER OF CROSS-BED READINGS = 53

REGIONAL REGIONAL X -RED X -MED CORRECT. CORRECT. AZIMUTH DIP A7IMUTH DIP AZIMUTH f1 I p LOCATION 3 ARROYO HERMANOS

?2.0 21.0 95.0 22.0 16E.0 72.0 21.0 95.0 25.0 148,9 72.0 21.0 101.0 22.0 17C3 LOCATION 4 MONTE ZUMA 83.0 95.0 284.0 77.0 24.9 23.8 83.0 95.0 280.G 55.0 57.5 33.q LOCATION 5 BONITA RANCH 70.0 120.0 275.0 42.0 30.3 26.3 LOCATION 7 NORTH OF SAPELLO 100.0 1 22.0 310.0 55.0 25.1 25.1 100.0 12.2.0 305.0 60.0 11.3 21.5 LOCATION 9 BOX CANYON 274.0 7.0 117.0 27.0 112.7 33.5 274.0 7.0 75.0 19.0 79.9 25.7 LOCATION 11 CANON DEL AGUA 358.0 4,9 345.0 28.0 343.0 24.1 358.0 4.0 55.0 17.0 67.4 15.2 358.0 4.0 350.0 25.0 34F1.6 21.0 358.0 4.0 354.0 2r.0 353.3 21.0 358.0 4.0 26.0 21.0 31.9 17,6 358.0 4.0 335.0 26.0 731.3 22.4 358.0 4. 0 356.0 26.0 355.7 2?.0 358.0 4.0 320.0 29.0 315.0 26.0 358.0 4.0 330.0 2.3.0 324.8 19.6 132

ALL LOCATIONS UPPER DAKOTA SS (CONT. )

REGIONAL REGIONAL X -BED X -BEO CORRECT. CORRECT. AZIMUTH DIP AZIMUTH DIP AZIMUTH DIP

LOCATION 12 MESA LAURIANO 0.0 0.0 315.0 23.0 315.0 23.0 0.0 0.0 156.0 29.0 156.0 29.0 0.0 0.0 275.0 13.0 275.0 13.0 0.0 0.0 83.0 25.0 83.0 25.0 0.0 0.0 219.0 9.0 219.0 9.0 0.0 0.0 59.0 23.0 59.0 23.0 0.0 0.0 175.0 14.0 175.0 14.0 0.0 0.0 113.0 15.0 113.0 15.0 0.0 0.0 225.0 12.0 225.0 12.0 0.0 0.0 85.0 18.0 85.3 18.0 0.0 0.0 207.0 10.0 207.0 10.0 LOCATION 13 CONCHAS CANYON 232.0 8.0 190.0 14.1 156.9 9.6 232.0 8.0 173.0 21.0 151.8 18.2 232.0 8.0 196.0 17.0 172.5 11.5 232.0 8.0 200.0 13.0 166.1 7.5 232.0 8.0 175.0 21.0 153.9 17.9 232.0 8.0 170.0 26.0 153.5 23.3 232.J 8.0 204.0 25.0 192.8 18.3 232.0 8.0 165.0 26.0 148.3 24.0 232.0 8.0 148.0 23.0 129.3 23.5 232.0 8.0 148.0 26.0 131.6 26.3 232.0 8.0 172.0 26.0 155.6 23.0 232.0 8.0 162.0 25.0 144.5 23.4 232.0 8.0 175.0 20.0 152.6 17.0 LOCATION 14 TRUJILLO 89.0 6. 0 286.0 23.0 282.7 28.8 89.0 6.0 39.0 22.0 25.4 18.7 89.0 6.0 355.0 21.0 340.1 22.2 89.0 6.0 26.0 26.0 1.3. 9 23.8 89.0 5.9 163.0 28.0 174.4 26.9 89.0 6.0 188.0 22.0 201.8 23.7 89.0 6.0 315.0 19.0 304.9 23.6 89.0 6. 0 280.0 22.0 277.8 27.9 89.0 6. 3 299.0 1.9.0 292.2 24.4 89.0 6.0 336.0 29.0 32 6. 9 31.8 APPENDIX C

STATISTICAL DATA ON CROSS -STRATIFICATION

133 134

CORRECTED CROSS -3E0 STATISTICAL DATA

ALL LOCATIONS UPPER DAKOTA SS

NUM9FR OF CROSS -BED READINGS = 53

MEAN AZIMUTH= 113.4AZ. VECTOR WEIGHT= 13. S.D. OF AZ. = 96.6

MEAN DIP= 20.6 DIP VECTOR WEIGHT= 99. S.D. OF DIP= 6.6

THE CONSISTENCY FACTOR = .127

RANGE OF MEAN = 2.6.900 1/2 RANGE OF MEAN = 13.400

CORRECTED CROSS -9E0 STATISTICAL DATA

ALL LOCATIONS BASAL DAKOTA SANDSTONE

NUMBER OF CROSS-BED READINGS =544

MEAN AZIMUTH= 108.5 AZ. VECTOR WEIGHT= 34. S.D. OF AZ.= 78.3

MEAN DIP= 20.1 DIP VECTOR WEIGHT= 99. S.D. OF DIP=7.5

THE CONSISTENCY FACTOR = .344

RANGE OF MEAN = 6.611 1/2 RANGE OF MEAN= 3.306 135

CORRECTED CROSS-BED STATISTICAL DATA

LOCATION I ROMEROVILLE GAP

MAP COORDINATES LONGITUDE= 105° 16' LATITUDE= 35° 31.5'

NUMBER OF CROSS -BED READINGS = 19

tlE J.AZIMUTH= 96.6 AZ. VECTOR WEIGHT= 63. S.D. OF AZ.= 57.0

MEAN DIP= 21.2 DIP VECTOR WEIGHT= 99. S.D. OF DIP= 7.6

THE CONSISTENCY FACTOR = .627

RANGE OF MEAN = 27.388 1/2 RANGE OF MEAN = 13.694

CORECT_D CROSS -BED STATISTICAL DATA

LOCATION 2 KERNEY GAP

MAP COORDINATES LONGITUDE= 105° 15.5' LATITUDE= 35° 33.5'

NUMBER OF CROSS --c3ED READINGS = 26

MEAN AZIMUTH= 124.3 AZ. VECTOR rWEIGHT= 49. S.D. OF AZ.= 64.6

VEAN DIP= 21.5 DIP VECTOR WEIGHT= 99. S.D. OF DIP= 9.1

THE CONSISTENCY FACTOR = .433

RANGE OF MEAN = 26.061 1/2 RANGE OF MEAN = 13.030 136

COR2ECTEO CROSS -BEDSTATISTICAL OATA

LOCATION 3 ARROYO HERMANOS

MAP COORDINATES LONGITUDE= 105° 15' LATITUDE= 35° 36'

NUMBER OF CROSS-BED READINGS = 29

MEAN AZIMUTH= 36.4 AZ. VECTOR WEIHT= 43. S.O. OF AZ.= 72.2

MEAN DIP= 15.4 DIP VECTOR WEIGHT= 99. S.C. OF DIP= 8.7

THE CONSISTENCY FACTOR = .483

RANGE OF MEAN = 27.409 1/2 RANGE OF MEAN = 13.705

CORRECTED CROSS -BE0 STATISTICAL DATA

LOCATION 4 MONTEZUMA

MAP COORDINATES LONGITUDE= 105° 16' LATITUDE= 35° 39'

NUMBER OF CROSS -EKED READINGS = 52

M----AN AZIMUTH= 61.7 AZ. VECTOR WEIGHT= 71. S.D. OF AZ. = 50.6

MEAN DIP= 19.2 DIP VECTOR WEIGHT= 93. S.D. OF DIP= 10.2 THE CONSISTENCY FACTOR = .714

RANGE OF MEAN = 14.181 1/2 RANGE OF MEAN = 7.090 137

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 5 BONI TA RANCH

MAP COORDINATES LONGITUDE= 105° 16.5' LATITUDE= 35° 42'

NUMBER OF CROSS -BED READINGS = 10

MEAN AZIMUTH= 126.8 AZ. VECTOR WEIGHTS 61. S.D. OF AZ.= 60.5

MEAN DIP= 24.4 DIP VECTOR WEIGHT= 99. S.D. OF DIP= 10.1

THE CONSISTENCY FACTOR = .6i4

RANGE OF MEAN = 42.634 1/2 RANGE OF MEAN = 21.317

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 6 SAPELLO

MAP COORDINATES LONGITUDE= 105° 14.5' LATITUDE= 35° 46'

NUMBER OF CROSS-BED READINGS = 26

MEAN AZIMUTH= 79.8 AZ. VECTOR WEIGHT= 58. S.D. OF AZ.= 62.9

MEAN DIP= 22.4 DIP VECTOR 104EIGHT= 99. S.D. OF DIP= 8.8

THE CONSISTENCY FACTOR = .577

RANGE OF MEAN = 25.344 1/2 RANGE OF MEAN = 12.672 13$

CORRECTED CROSS-BED STATISTICAL DATA

LOCATION 7 NORTH OF SAPELLO

MAP COORDINATES LONGITUDE= 105° 16' LATITUDE= 35° 49'

NUMBER OF CROSS-BED READINGS = 17

MEAN AZIMUTH= 66.8 AZ. VECTOR WEIGHT = 69. S.D. OF AZ.= 50.6

MEAN DIP= 20.8 DIP VECTOR WEIGHT= 99. S.O. OF DIP= 9.1

THE CONSISTENCY FACTOR = .687

RANGE MEAN = 25.904 1/2 RANGE OF MEAN = 12.952

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 8 COYOTE CREEK

MAP COORDINATES LONGITUDE= 105° 10' LATITUDE= 35° 55'

NUMBER OF CROSS -BED READINGS = 20

MEAN AZIMUTH= 101.3 AZ. VECTOR WEIGHT= 44. S.O. OF AZ.= 76.1

MEAN DIP= 23.6 DIP VECTOR 'rIEIGHT= 99. S.D. OF DIP= 9.1

THE CO;SISTENCY FACTOR= .442

RANGE OF MEAN = 35.480 1/2 RANGE OF MEAN = 17.740 139

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 9 BOX CANYON ABOVE CONGL.

MAP COORDINATES LONGITUDE= 105° 12.5' LATITUDE= 35° 32'

NUM3ER OF CROSS -BED READINGS = 32

MEAN AZIMUTH= 217.4 AZ. VECTOR WEIGHT= 91. S.D. OF AZ.= 25.4

MEAN DIP= 23.0 DIP VECTOR WEIGHT =100. S.D. OF DIP= 4.5

THE CONSISTENCY FACTOR _ .909

RANGE OF MEAN = 9.144 1/2 RANGE OF MEAN = 4.572

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 9 BOX CANYON BELOW CONGL.

HAP COORDINATES LONGITUDE= 105° 12.5' LATITUDE= 35° 32'

NUN 3ER OF CROSS -BED REA OINGS = 32

MEAN AZIMUTH= 107.4 AZ. VECTOR WEIGHT= 52. S.D. OF AZ.= 66.1

MEAN DIPS 21.4 DIP VECTOR WEIGHTS 99. S.D. OF DIP= 7.1

THE CONSISTENCY FACTOR = .522

RANGE OF MEAN = 23.804 1/2 RANGE OF MEAN = 11.902 140

CORRECTED CROSS-BED STATISTICAL DATA

LOCATION 9 BOX CANYON MAP COORDINATES LONGITUDE= 105° 12.5' LATITUDE= 35° 32'

NUMBER OF CROSS -BED READINGS = 69

MEAN AZIMUTH= 125.9 AZ. VECTOR WEIGHT= 35. S.D. OF AZ. = 77.8

MEAN DIP= 19.2 DIP VECTOR WEIGHT= 99. S.D. OF DIP= 6.6

THE CONSISTENCY FACTOR = .348

RANGE OF MEAN = 18.643 1/2 RANGE OF t1EAN = 9.321

CORRECTED CROSS-BED STATISTICAL DATA

LOCATION 10 PAGOSA CANYON

MAP COORDINATES LONGITUDE= 105° 10' LATITUDE= 35° 30'

NUMBER OF CROSS -BED READINGS = 50

MEAN AZIMUTH= 125.6 AZ. VECTOR WEIGHT= 29. S.D. OF AZ. = 80.5

MEAN DIP= 21.5 DIP VECTOR WEIGHT =100. S.O. OF OIP= 4.6

THE CONSISTENCY FACTOR = .290

RANGE OF MEAN = 23.009 1/2 RANGE OF MEAN = 11.505 111 CORRECTED CROSS-BED STATISTICAL DATA

LOCATION 11 CANYON DEL AGUA

MAP COORDINATES LONGITUDE= 105° 1' LATITUDE= 35° 29'

NUMBER OF CROSS -BED READINGS =11

MEAN AZIMUTH= 109.6 AZ. VECTOR WEIGHT= 24. S.D. OF AZ.= 96.9

MEAN DIP= 15.6 DIP VECTOR WEIGHT =100. S.D. OF DIP= 5.4

THE CONSISTENCY FACTOR = .237

RANGE OF MEAN = 64.274 1/2 RANGE OF MEAN = 32.137

CORRECTED COSS -13E0 STATISTICAL DATA

LOCATION 12 MESA LAURIANO

MAP COORDINATES LONGITUDE= 134° 5 7.5' LATITUDE= 35° 25'

NUM1 ER OF CROSS-BED READINGS = 38

MEAN AZIMUTH= 82.7 AZ. VECTOR WEI ;NT= 51. S.D. OF AZ.= 64.7

MEAN DIP= 20.3 DIP VECTOR WEIGHT= 99. S.D. OF DIP= 7.4

THE CONSISTENCY FACTOR = .514

RANGE OF MEAN =21.240 172 RANGE OF MEAN = 10.620 142

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 13 CONCHAS CANYON

MAP COORDINATES LONGITUDE= 104° 51' LATITUDE= 35° 32.5'

NUMBER OF CROSS -BED READINGS = 31

MEAN AZIMUTH= 178.6 AZ. VECTOR 4EIGHT= 45. S.D. OF AZ.= 68.8

MEAN DIP= 20.4 DIP VECTOR HEIGHT =IUD. S.D. OF DIP= 4.9

THE CONSISTENCY FACTOR = .454

RANGE OF MEAN = 25.188 1/2 RANGE OF MEAN = 12.594

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 14 TRUJILLO

MAP COORDINATES LONG I TU!)E= 134° 41' LATITUDE= 35°31'

UUM3ER OF CROSS -BED READINGS = 24

MEAN AZIMUTH= 168.5 AZ. VECTOR WEIGHT= 22. S.D. OF AZ.= 92.6

MEAN DIP= 17.5 DIP VECTOR WEIGHT =1.00. S.O. OF DIP= 5.4

THE CONSISTENCY FACTOR = ..223

RANGE OF MEAN = 39.009 1/2 RANGE OF MEAN = 19.504 143

CORRECTED CROSS-nEO STATISTICAL DATA

LOCATION 14 TRUJILLO MESA RICA SS. MAP COORDINATES LONGI TUDE= 104° 41' LATITUDE= 35° 31'

NU"13ER OF CROSS -BED READINGS = 6

MEAN AZIMUTH= 160.5 AZ. VECTOR WEIGHT= 19. S.D. OF AZ. =10 0.5

'1=AN DIP= 14.1 DIP VECTOR WEIGHT=130. S.D. OF DIP= 2.6

THE CCNSISTENCY FACTOR = .191

RANGE OF MEAN =100.357 1/2 RANGE OF MEAN = 50.179

CORRECTED CROSS -RED STATISTICAL DATA

LOC. 15 UNMEASURED SECTION E OF LVS MAP COORDINATES LONGITUDE= 1)4° 59' LATITUDE= 35° 35'

NUM3ER OF CROSS -3E0 Ri_A OINGS= 21

MEAN AZIMUTH= 96.8 AZ. VECTOR WEIGHT= 29. S.D. OF AZ.= 84.6

MEAN DTP= 16.2 DIP VECTOR 'WEIGHT =10 0. S.D. OF DIP= 4.9 THE CONSISTENCY FACTOR = ,.289

RANGE OF MEAN = 38.409 1/2 RANGE OF MEAN= 19.205 114.

CORRECTED CROSS -BED STATISTICAL DATA

LOCATION 16 VALMORA

MAP CODROINATES LONGITUDE= 104° 55' LATITUDE= 35° 48.5'

NUMBER OF GROSS -BED READINGS = 32

MEAN AZIMUTH= 132.5 AZ. VECTOR WEIGHT= 52. S.O. OF AZ.= 67.8

M5AN DIP= 19.0 DIP VECTOR WEI3HT =100. S.D. OF DIP= 5.7

THE CONSISTENCY FACTOR = .517

RANGE OF MEAN = 24.418 1/2 RANGE OF MEAN = 12.209 REFERENCESVl:..7

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SECTION I 2 3 4 6 8

EXPLANATION K i

(10 upper sandstone ' 201 unit

middle shale unit covered interval

lower sandstone \ 4C sandstone

unit 60 conglomerate o 70

80

90 '3o mudstone 100 or shale IIc O 2 4 6 8 10 12 14 16kilome 120 - -- O 2 4 6 8 10 miles

ffossilsls

WEST EAST #stfossilized wood SECTION I 9 10 11 12 13 14

10 9 BW upper numbers in sections 20 sandstone 7 upper are keyed into the middle shale unit 6 sandstone 10 unit unit in descriptions middle shale Appendix A. o lower IO sandstone Z 20 lower unit LL 30 sandstone o 40 unit Pajarito 50 Shale

60 Mesa 70 Rica 80 Sandstone 90 30 P. 100 HorizontalScale i 0 2 4 6 8 IO 12 14 16 kilometers I10 i 0 2 4 6 10 miles 120

Figure 3. Basal Cretaceous Stratain North-Central New Mexico Bejnor,M.S.thesis, Geojogy,1975 Figure 31.

Compass .Rose Diagrams of Cross­ Stratification in

Lower Sandstone Unit

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