The coal deposits and cretaceous stratigraphy of the western part of Black Mesa, Arizona

Item Type text; Dissertation-Reproduction (electronic); maps

Authors Williams, George Arthur, 1918-

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/565389 THE COAL DEPOSITS AND CRETACEOUS STRATIGRAPHY OF THE WESTERN PART OF BLACK MESA, ARIZONA

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George Arthur Williams it

A Thesis .'N V submitted to the faculty of the Department .of Geology in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in the Graduate College, University of Arizona

1951

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CONTENTS Page LIST OF ILLUSTRATIONS...... v i

ABSTRACT...... XV

CHAPTER I 1 INTRODUCTION...... 1 G eneral s ta te m e n t...... 1 Purpose of study ...... 1 L ocation and e x te n t of a r e a ...... 3 Methods of study ...... 4 Acknowledgments...... 13 CHAPTER I I ...... 15 GEOGRAPHY...... 1? Topography...... V...... 1? Climate and vegetation...... 17 G en e ra l...... 17 R eco rd s...... 18 Seasonal and year to year variations ...... 19 Character of rainstorms ...... 19 S o i l ...... 20 Wind...... 20 V e g e ta tio n ...... 20 Drainage and water supply...... 21 Water su p p ly ...... 22 Local in d u s t r i e s ...... 23 CHAPTER I I I ...... 24 HISTORICAL REVIEW 24 Previous investigators.. 24 Nomenclature...... 25 G en e ra l...... The underlying rocks.. 26 Lower C retaceous ro ck s 28 Upper Cretaceous rocks 29 CHAPTER IV 40

219722 i l l

GENERAL STRATIGRAPHY AND STRUCTURE OF BLACK MESA AREA...... 4 0 Lower Jurassic rocks ...... 40 Glen Canyon group ...... 40 Upper J u r a s s ic r o c k s ...... 41 San Rafael group ...... 41 M orrison fo rm a tio n ...... 42 Upper Cretaceous rocks...... 43 Dakota (?) sandstone...... 43 Mane os shale..... i ...... 44 Mesaverde group...... 44 S tr u c tu r e ...... 45 CHAPTER V...... 49

RELATION OF DAK0TA(?) SANDSTONE TO UNDERLYING MORRISON FORMATION...... - 4 9 General statement...... T e x tu r e ...... Composition...... Primary structures...... Y/estwater Canyon sandstone member...... Cow Springs sandstone member...... Dakota (?) sandstone...... Summary of comparison of Dakota (?) sand­ stone and underlying Morrison formation.... Criteria for field identification ...... Westwater Canyon sandstone member...... Cow Springs sandstone member...... Dakota (?) sa n d sto n e ...... Determination of source-rock for Dakota (?) s a n d s to n e ...... Morrison-Dakota contact...... u

CHAPTER VI...... 6 5

CRETACEOUS STRATIGRAPHY...... 6 5 Dakota (?) sandstone.... G e n e ra l...... Dakota-Mancos contact Conglomerate member. . T ex tu re...... Composition...... Primary structures. Sandstone member...... T exture...... Composition...... Primary structures. I n c lu s io n s ...... Iv

Secondary s t r u c t u r e s ...... 82 S ilt stone-clay stone member...... T e x tu re ...... Composition...... Primary structures...... C o al...... Secondary structures...... V...... Sand-shale ratio of Dakota (?) sandstone 8. Flora and fauna/...'...... 91 Depositional history...... 91 Mane os s h a le ...... 94 G e n e r a l ...... Dakota-Maneos contact...... 96 Basal sandstone member...... 97 T e x tu r e ...... 97 Composition...... 99 Primary structures...... 100 Fauna...... 100 ,C lay stone member...... 101 T e x tu r e ...... 101 Composition...... 101 Primary structures ...... '.'/.. 104 Inclusions...... 104 Siltstone member...... 106 T e x tu r e ...... 106 Composition...... 107 Primary structures...... 108 I n c lu s io n s ...... 109 F a u n a ...... „ 110 Alternating si 11stone-sandstone member..." I l l T e x t u r e ...... V 111 Composition...... /...... 113 Primary structure ...... 114 Secondary structures in the Maneos shale. 116 Bentonite in the Maneos sh a le ...... /. 118 Maneos-Mesaverde contact...... 121 Depositional history of the Maneos shale. 122 Mesa verde group...... '. 127 G en e ra l...... 127 Maneos-Mesaverde contact...... 131 Basal sandstone member...... ’...... " /../ 131 G en eral...... T e x tu re ...... 136 C om position...... 141 Primary structure...... 143 Arkosic sandstone member...... 164 T e x tu re ...... 165 C om position...... 168 Primary structures...... 169 I n c lu s io n s ...... 170 Coal-bearing member...... 170 T e x tu re ...... 178 V Composition...... 180 Primary structures.. 181 Inclusions...... 182 Cyclic sedimentation 182 Gnarly bedding...... 184 C o a l...... 185 Upper sandstone member 189 T e x tu re ...... 190 Composition...... 192 Primary structures.. 192 Inclusions...... Deposit Iona1 history.. 19!? CHAPTER VII 200 HISTORICAL SEQUENCE...... 200 Erosion surface below Dakota (?) sandstone.. 200 Dakota (?) sedimentation...... 201 Events during Mane os sedimentation ...... 203 Transgressive near-shore deposition...... 203 Basal sandstone member...... 203 Off shore deposition...... 203 Claystone member...... 203 Sandstone member...... " ...... 205 R eg ressiv e n e a r-s h o re d e p o s itio n ...... 205 Alternating siltstone-sandstone member. 205 Events during Mesaverde sedimentation ...... 206 G en e ra l...... 206 Beach deposition...... 206 Basal sandstone member...... 206 Deltaic deposition ...... 207 ■ Arkosic sandstone member...... 207 Cyclic sedimentation..'...... — . . 208 • Coal-bearing member...... 208 Transgressive near-shore deposition ...... 208 Upper sandstone member...... 208 Summary...... , 209 Relation of Black Mesa to adjoining areas 209 CHAPTER V I I I ______. . . . 212 ECONOMIC FEATURES...... ______...... 212 G e n e ra l...... V...... 212 Petroleum Possibilities ...... 212 Coal deposits ...... 213 DESCRIPTION OF MEASURED SECTIONS...... 218 BIBLIOGRAPHY...... 269 v i

PLA.TES 11 to 45...... 275

ILLUSTRATIONS

P la te s 1. Areal geologic map of Cretaceous rocks, Black Mesa, northern portion ...... in po ck et 2<> Areal geologic map of Cretaceous rocks, Black Mesa, southern portion ...... in pocket 3. Correlation chart for Dakota(?) sandstone, western portion Black Mesa area, Arizona, Kayenta to Cow Springs ...... in po ck et 4. Correlation chart for Dakota (?) sandstone, Western portion Black Mesa area, Arizona, Cow Springs to Blue Canyon...... in p o ck et 5. Correlation chart for Dakota(?) sandstone western portion Black Mesa area, Arizona, Blue Canyon to Coal Mine canyon...... in p o ck et 6* Correlation chart for Maneos shale, Western portion Black Mesa area, Arizona, Cow Springs to Marsh P ass...... in p o ck et 7. Correlation chart for Maneos shale, western portion Black Mesa area, Arizona, Cow Springs to Blue Canyon...... in pocket 8. Correlation chart for Mesaverde group, west­ ern portion Black Mesa area, Arizona, Cow S p rin g s to Marsh P a s s ...... in p o ck et 9. Correlation chart for Mesaverde group, West­ ern portion Black Mesa area, Arizona, Cow Springs to Blue Canyon...... in p o ck et 10. Fence diagram of Upper Cretaceous rocks...... in pocket

PHOTOGRAPHS

1 1 . Fig. 1. Trenching to obtain good exposures... 275 Fig. 2. Continuous recording-density-settling d e v i c e ...... 275 v i i P la te s 12. Fit;. 1. Cretaceous section, Loloiaai Point... 2?6 Fie. lad.land topography resulting from w eath erin g of th e I.'.ancos sh ale in Blue Canyon...... 276 13. Fig. 1. Demoiselles, as seen in Harsh Pass.. 277 Fig. 2. Coal-bearing member of the Mesaver- de g ro u p ...... 277 Fig. 3• Lower escarpment of Black F.osa capped by Dakota (?) sandstone ...... 277 14. Fig. 1. Toreva block five miles east of Rod Lake...... 278 Fig. 2. Contact of upper pediment and nan- cos shale, one mile north of Blue Canyon...... 278 Fig. 3• Rounded gravels which comprise the lower p ed im en t...... 278 15. Fig. 1. Vortical cliff formed by the upper sandstone member of th e m esaverde g ro u p ...... 279 Fig. 2. Channel on BorrIson-Dakota contact be­ tween the Dakota (?) ss. and the Y/estwater Canyon sandstone member... 279 Fig. 3. Channel on LI or r i s on-Du k 01 a contact.. 279 16. Fig. 1. Channels on LIorrison-Dakota contact. 280 Figi 2. Channels on LIorrison-Dakota contact near the mouth of Coal Bine Canyon.. 230 17. Fig. 1. Conglomerate lenses in the Conglomer­ ate member of the Dakota (?) sandstone 281 F ig . 2. C lose-up of above g r a v e ls ...... 281 Fig. 3« Contact of Cow Springs sandstone member and Dakota (?) s a n d s t o n e ...... 201 Fig. 4. Gravels distributed throughout in th e conglom erate member of th e Da­ k o ta (?) sa n d sto n e ...... 281 10. Fig. 1 Vertical and lateral variations in th e D akota(?) sa n d sto n e...... 70 Fig. 2. Lateral variations in the coal de­ p o s i t s ...... 70 Fig. 3. Sequence of facies resulting from deposition in Dakota (?) sandstone... 70 19. Fig. 1. Contact of Cow Springs sandstone member and Dakota (?) sa n d sto n e...... 282 v i i i P la te s F ig . 2. Contact Cow Springs sandstone mem­ ber . Dakota (?) san d sto n e, showing coal resting directly on Cow Springs 282 F ig . 3 . Mud pellets in the Dakota (?) sand­ sto n e ...... 282 20. F ig . 1 Vertical and lateral variations in bedding of the Dakota(?) sandstone.. 84 F ig . 2. Local variations in bedding in Da­ k o ta (?) sa n d sto n e ...... 84 21. Fig. 1. Contact Dakota (?) sandstone and b a s a l sandstone member of th e jjaneos 283 F ig . 2. Sulphurous sublimate resulting from burning coal beds, Coal Mine Canyon 283 F ig . 3. Coal Mine, Coal Mine Canyon...... 283 22. Fig. 1. Plant fragments from bone in Dakota (?) sandstone coal seam...... 284 F ig . 2. Cross-section of rippled bedding from Dakota (?) sandstone ...... 284 23. Fig. 1. Slumped area resulting from burning, coal scams...... 285 F ig . 2. Erosions1 remnant of burned area, w hite la y e r of a s h ...... 285 F ig . 3 . Natural slag ...... 285 24. Fig. 1. Sandstone dike in black shale and . coal of the Dakota (?) sandstone in Longhouse v alley ...... 286 F ig . 2. Medial escarpment resulting from siltstone layers at the base of th e s i l t s t o n e member of th e M aneos.. 236 F ig . 3 . Fossiliferous nature of basal sand­ stone member of the Maneos shale.... 286 2%. Fig. 1. Cephalopod impressions in siltstone member of th e Mane os s h a l e ...... 287 F ig . 2. Ripple marks from underside of sand­ stone layers in alternating silt­ stone -sand stone member of the Maneos 28? F ig . 3. Worm trails on the underside of sand­ stone layers in the alternating siltstone-sandstone member of the Maneos sh ale...... 287 26. Fig. 1. Worm tra il in underside of sandstone layer in the alternating siltstone- sandstone member of the Maneos shale. 288 F ig . 2. Protuberances from the sandstone lay­ ers of the alternating siltstone- sandstone member of th e Maneos...... 288 ix

P la te s Fig. 3. Cross-section of a septeria from the Mane os s h a le ...... 288 27. Fig. 1. Large concretion in the Siltstone member of the Mane os shale ...... 289 Fig. 2. Cone-in-cone from siltstone layers in th e s i l t s t o n e member of th e Man- cons s h a le ...... 289 Fig. 3• Cone-in-cone showing- manner in which th e la y e rs p a r t ...... 289 28. Fig. 1. Concretion layer showing cone-in­ cone in th e o u te r la y e r s ...... 290 Fig. 2. Melikarian structures..../...... 290 29. Fig. 1. Maneos shale, black shale variety,,« 291 Fig. 2. Bentonite ana gypsum capping the led g es in Blue C a n y o n ...... 291 Fig. 3* Vegetation growin along the benton-- i t e b e d s ...... 291 30. Fig. i. Contact of the Maneos shale and the overlying Me saver de group...... 292 Fig. 2. Alternating siltstone-sandstone mem­ ber of the Mane os shale ...... 292 31. Fig. 1. Black shales and coals overlying th e b a s a l member of th e M esav crd e.. . 293 Fig. 2. Surface markings on the basal sand­ stone member of the Mesavcrde group. 293 Fig. 3. Surface markings on laminae of the beach sandstone...... 293 32. Fig. 1. Scollop-like structures which are believed to be beach cusps...... 294 Fig. 2. Cross-section of a specimen of the basal sandstone member of the Mesa- v e rd e ...... 294 Fig. 3• Laminae in the basal sandstone mem­ ber of th e M esavcrde g roup...... 294 33• Fig. 1. Quartz grains from the basal sand­ stone member of the Mesaverde group 295 Fig. 2. Thin section of same sandstone as th a t above...... 295 34. Fig. 1. Thin section of laminated part of th e b a s a l sandstone member of th e M esaverde g ro u p ...... 296 X

P la te s Fig. 2. Gross-lamination of the basal sand­ stone member of the Liesaverde...... 2?6 Fig. 3• Continuation of the same sets ...... 296 3?. Fig. 1. Cross-lamination in the upper fore­ shore of the beach deposits of the b a s a l sandstone member of th e Llesa- verde group...... 297 Fig. 2. Contination of the above laminae.... 297 Fig. 3. Upper foreshore cross-lamination in the basal sandstone member of the Mesaverde group...... 297 Fig. 4. Lower contact of the upper foreshore z deposits...... 297 36. Fig. 1. Upper foreshore cross-lamination in the basal sandstone member of the M esaverde...... 298 Fig. 2. Alternating "torrential" and hori­ z o n ta l c ro s s -la m in a tio n ...... 298 Fig. 3• Alternating "torrential" and horizon­ t a l c r o s s -la m in a tio n ...... 298 Fig. 4. Low-angle compound cross-lamination. 293 37- Fig. 1. Individual grains by oblique light.. 299 Fig. 2. Individual grains by oblique light.. 299 38. Fig. 1. Thin-section of Arkosic sandstone member...... 3 00 Fig. 2. Thinpsection of arkosic sandstone member...... 300 39. Fig. 1. Large-scale low-angle compound cross- lamination in the arkosic sandstone. 301 Fig. 2. Alternating "torrential" and horizon­ tal cross-lamination ...... 301 Fig. 3- Alternating "torrential" and horizon­ tal cross-laminatinn...... 301 40. Fig. 1. Thin, sandy siltstone beds which occur in the arkosic sandstone ...... 302 Fig. 2. Low-angle compound, large-scale cross-lamination ...... 302. Fig. 3. Low-angle compound, cross-lamination 302 Fig. 4. Alternating "torrential" and hori­ zontal cross-lamination with low- angle compound in arkosic sandstone. 302 41. Fig. 1. Iron concretions showing spongy, llmonite which make up concentric c i r c l e s w ith hollow c e n te r s ...... 303 Fig. 2. Iron cemented sandstone concretion w ith hollow c e n te r ...... 303 x i

P la te s 42. Fi£. 1. Small-scale foreset bedding alter­ nating ntorrential" and horizontal in th e c o a l-b e a rin g member of th e M esaverde group...... 304 Fig. 2. Intricate bedding and cross-lamina­ tion as shown by the weathering of the sandstone layers in the coal-bear- .ing member...... 304 I''ig. 3. Weathering along bedding planes indicates the intricate bedding found in the sandstone layers of the coal-bearing member...... 304 Fig. 4. Plunging festoon cross-lamination... 304 43. Fig. 1. Pseudo-cross-lamination as a result1 of ripples on a horizontal surface.. 305 Fig. 2. Large iron concretions in sandstone layer of the arkosic sandstone member 305 Fig. 3. Crumpled bedding in sandstone layer of the coal-bearing member due to some form of s o f t rock d e fo rm a tio n .. 305 Fig. 4. Crumpled bedding believed duo to shrinkage subsequent to deposition.. 305 44. 1'ig. 1. Cow Springs Coal Mine loading chute. 306 Fig. 2. "Brazil nut concretions!?...... :..::. 306 45. Fig. 1. Sandstone concretions in upper sandstone member m esaverde g r o u p .... 307 Fig. 2. Examples of the above sandstone c o n c re tio n s ...... 307

F ig u re s 1. Map of Arizona, index map of area ...... 5 2. Diagrammatic sketch of continuous recording d e n s ity - s e tt lin g d e v ic e ...... 9 3. Settling time for samples containing very fine sand. Continuous recording density­ settling apparatus ...... 11 4. Results of continuous recording-density­ settling apparatus ...... 103 5. Correlation chart of Cretaceous rocks...... ; 30 6 . Grain-size distribution in samples of Cow S p rin g s ...... 74a x i i P in u re s 7. Trends of Pre-Dakota streams as seen in channels in Blue Canyon...... 63 8. G rain siz e d is t r i b u t i o n in sandstone member of D akota(?) sa n d sto n e ...... 73 9. G rain s iz e d is t r ib u t io n in sandstone member of Dakota (?) sa n d sto n e ...... 74 10. Dip bearing of cross-lamination ...... 78 11. Dip bearing of cross-lamination...... 79 12. Dip b ea rin g of c r o s s - la m in a tio n ...... 80 13• Histograms and cumulative curves of typical s a n d s to n e ...... 98 14. Grain size distribution of the alternating. silt stone-sand stone member, I.iancos shale.... 112 15. Rippled bedding in alternating siltstone- sandstone member of the Maneos shale ...... 117 16. nom enclature of b ea ch ...... 132 17. Size-frequency distribution in basal sandstone member...... 138 18. Size-frequency distribution of basal sand-. sto n e member...... 139 19o Typical cross-lamination in the lower fore­ shore deposits of the Mesaverde group of B lack Mesa...... 147 20. Dip b ea rin g of c ro s s -la m in a tio n ...... 148 21. Dip b ea rin g of c ro s s -la m in a tio n ...... 149 22. Dip bearing of cross-lamination ...... 150 23. Diagrams of cross-lamination ...... 152 24. Typical example of beach type cross-lamination 153 25. Type C cross laminations ...... 154 26. C and Cross laminations ...... 155 x i i i F ig u res 27. Typical cross-lamination in the upper fore­ shore of the Mesaverde group...... 156 28. Dip b ea rin g of c ro s s -la m in a tio n ...... 159 29- Typical cross-lamination in baclcshore depo­ s i t s ...... l 6l 30. Vertical tubes that occur in the beach sand­ s to n e ...... 162 31. Dip bearing of arkosic member...... 171 32. Dip bearing of arkosic member...... 172 33. Dip b earin g of a rk o s ic member...... 173 34. Dip bearing of arkosic member...... 174 35* Dip b earin g of a rk o s ic member...... 175 36. Dip b earin g of a rk o s ic member...... 176 37* Typical Cretaceous cyclothem of Black Mesa.. 179 38. Variation in cool seam...... 187 39* Grain-size distribution in samples of upper sandstone member of the Mesaverde group..... 191 40. Dip bearing of upper sandstone member...... 194 41. Diagrammatic sketch of the relative move­ ment of the Cretaceous seas in relation to B lack Mesa...... 204 42. Analysis of upper Cretaceous Black M esa..... 210

TABLES

1 Relation of Upper Jurassic to Cretaceous in Black Mesa...... 27

2 Textural comparison of the Westv/ater sand­ sto n e member and Dakota (?) sa n d sto n e ...... 51 x iv

T ables 3 General characteristics of Westwater Canyon sandstone...... 52

4 Heavy minerals in Y/estwater Canyon sandstone 53 5 Iron content and mineral composition im­ mediately below Cow Springs-Dakota contact.. 60 6 Data obtained from a 50-gravel count...... - 68 7 Sand-shale ration of the Dakota (?) sandstone 90 8 Proximate analysis of Dakota coals of Black lies a ...... 88 9 Heavy minerals in the basal sandstone mem­ ber of Mesaverde group...... 102 10 Carbon content of black shale in Maneos s h a le ...... 105 11 Heavy minerals in the upper sandstone member 115 12 Settling analysis of samples from two ben­ tonite beds...... 120 13 Heavy mineral analysis of samples from the basal sandstone member...... 142 14 Statistical study of cross-lamination in basal sandstone member of Mesaverde group... |.47 15 Statistical.analysis of dips from individual laminae in upper foreshore deposits ...... 151 16 Medians, coefficients of sorting, and skew­ ness in terms of phi units, from Arkosic sandstone member...... 166 17 Textural study of maximum-minimum grains encountered in single laminae of the arkosic sandstone member...... 168 18 Proximate analysis of the coals of the coal- . bearing member...... 188 XV ABSTRACT The Cretaceous deposits of this study are confined to the western portion of Black Llesa, Navajo Reservation, Arizona. They contain three formations, the Dakota (?) sandstone or lower escarpment, the i.lancos shale or mid­ dle slope, and the I.Iesaverde group or upper escarpment. The Dakota (?) sandstone consists of four lithologic types discussed as follows: 1. conglomeratic member; 2. sandstone member; 3• siltstone member and 4. coal. The members grade laterally from a thick sandstone, contain' ing conglomerates, in the north,to thin shaly siltstone in the south. The Dakota (?) sandstone represents a trans­ gressive continental deposit. The Maneos shale is divided into four members based on lith o lo g y : 1. B asal sandstone member th a t i s le n tic u la r and n ea r-co q u in a in p la c e s ; 2 . c la y sto n e member th a t i s predominately black shale with numerous thin bentonite lay­ ers; 3. siltstone member that contains small amounts df black shale and bentonite with sandy siltstone layers which form a medial escarpment. The presence of sand indicates a change from transgression to regression; 4. alternating siltstone-sandstone member that has primary structures which show near-shore current action. The Maneos shale thins to the southwest indicating an old shoreline. The I.Iesaverde group is divided into four members: 1. a basal sandstone member that has primary structures indi- x v l eating a beach deposit. 2. An arkosic sandstone member which is conglomeratic in places and contains an abundance of unaltered feldspar. 3. Coal-bearing member characterized by cyclic sedimentation. The cycle is: 1. Sandstone subgraywacke 2. Slltstone

3 . L ig n ite 4. Coal

5, L ig n ite 6. S llts to n e 7. Sandstone graywacke This member contains the largest amount of coal on Black Mesa. 4 . The upper san d sto n e member r e p re s e n ts a t r a n s ­ gressive near-shore deposit. The various lithologic members are examined in detail with respect to texture, composition, and primary structures with inclusions and other features discussed where encountered. The economic possibilities tire discussed. The petro­ leum possibilities of the Upper Cretaceous deposits are very poor but the coal deposits are extensive. At the present time three factors prohibit large scale coal mining: 1. inaccessibility; 2. lack of an adequate water supply; and 3. lack of markets for sale of products. CHAPTER I

INTRODUCTION

General Statement

The investigation reported in this;paper was undertaken to satisfy the increasing demand for more detailed Information regarding the Cretaceous stratigraphy and coal deposits of Black Mesa, central part of the Navajo Indian Reservation, north central Arizona (Fig. 1). The study was initiated in th e summer of 1949 and continued until the spring of 1951• The lithologic units encountered in the course of the study are well exposed and consist of the Dakota (?) sand­ stone and the overlying Maneos shale and Mesaverde group.

Purpose of Study

The primary purpose of the study Is to determine the areal distribution, structural features, and deposltional history of the Cretaceous rocks of the area. The secondary purpose is to study the coal deposits and report on possible reserves. Understanding of the deposltional history necessl- 2. tates a study of lithologic changes, both horizontal and ver­ tical, and a petrological study of the various units. Paleon­ tological studies were undertaken to determine age relation­ ships for correlation purposes. Recent interest in the Black Mesa region related to petroleum possibilities previously had prompted study of Upper Jurassic rocks (Harshbarger, 1949). Because a continuation of the study of this area seemed desirable, this problem was undertaken.

Cretaceous rocks in the southern portion of this area have been very competently studied by Joseph I. Snow, but the work was never brought to completion. The present re­ port does not cover the area studied by Snow, but continues along a similar line. First, it was planned that the coal potentialities of the area would be thoroughly investigated in relation to geol­ ogy, mining and marketing of the product. However, the latter part of the project had to be abandoned because of the in- accessability of the various operating coal mines, since the Navajo Indians who own and operate the mines object to visi­ tors. Surface plants were visited however, and product sam­ ples taken even though no statistics could be obtained. 3 . Location and Extent of Area

Black Mesa is in the west central portion of the Nava­ jo Indian Reservation, Arizona. The northern part of the Mesa is in the Navajo Indian Reservation and the southern part in the Hopi Indian Reservation. It is approximately between parallels 35° - 30*, and 36° - 4^*, and meridians 109° - 451 and 1110 - 00* (Fig. 1), The area is unsurveyed except for Townships T25N through T31N, R13E through R2$B (referred to the Gila River meridian and base line) which are in the southern part of the Mesa. The western part of Black Mesa, which is the part cov­ ered by this study (Fig. 1, pi. 1 and 2), lies approximately between parallels 35° - 4£>1 and 36° - 4^*, and meridians 110° - 1?1 and 1110 - 15*« It includes approximately 1000 square miles along the western edge of the mesa and extends about 15 miles into the mesa. Along the long axis there is approximately 70 miles of continuous exposure of Cretaceous rocks. The area is reached by U. S. Highway 89 from Flagstaff, Arizona, through Cameron, Arizona, to Route 1, Navajo Indian Reservation. Leaving Highway 89 approximately 10 miles north of Cameron, Route 1 is a graded dirt road leading to Tuba City, twelve miles from the turn-off. In Tuba City, a veri­ table oasis in the desert, the United States Indian Service maintains a large hospital and school. Continuing north on 4 . Route 1 from Tuba City within a few miles Black Mesa can be seen on the northern horizon. The route passes through Ton- alea (Red Lake), Cow Springs, and fin a lly , Kayenta, a ll Ind­ ian Trading posts. From Kayenta, which is the hub of a ll roads leading into the northern part of the Reservation, ; Route 1 continues north into Utah. It is much traveled by tourists seeking the scenic beauty of Monument Valley 20 miles north of Kayenta. The southern part of the area is on Route 2 which ex­ tends in an easterly direction via Moenkopl and other Hopi villages to Ganado, east of Black Mesa. Cretaceous rocks form the escarpment of Black Mesa. They are entirely to the east of Route 1 as one travels north and can easily be followed by the eye for 50 miles. The strikingly white underlying Jurassic sandstones in many places form the lowermost part of the escarpment but the feature is caused by the more resistant overlying DakotaC?) sandstone.

Methods of Study

Field work was started in the summer of 1949 and consisted of a reconnaissance of the entire area to be studied. The accessib ility of the better exposed Cretaceous rocks was in­ vestigated for later use. Because the only topographic map that has been published (USGS, Reconnaissance Map, Marsh Pass sheet 1892) i s old and 5 .

I 1 Thesis area [s^X N B lack Mesa Fig. 1.-Index map of area 6. inaccurate, it became necessary to use aerial mosaics pre­ pared by the Soil Conservation Service and a. planimetric map of the "Navajo Country" (Scale; 1" ■ 6 miles) compiled by the office of Indian Affairs, 1937• Following reconnaissance, detailed sections of Creta­ ceous strata were measured. Because the Maneos shale por­ tion of one section due south of Cow Springs Trading Post was poorly exposed, this part was trenched to obtain good ex­ posures (Pi. 11, fig. 1). By virtue of this very accurately measured section, a standard for comparison became available. In the subsequently measured sections lithologic units could be readily recognized and the progress of the study was speed­ ed up. While measuring lithologic units close search was made for fossils and careful notes were taken of the exact loca­ tion of all that were found. Upon completion of each section job a more careful examination was made for additional fossil localities and further collections were obtained from the lo­ calities previously noted. Finally, a characteristic area was chosen for very de­ tailed study and each lithologic unit was carefully walked in its entirety, with measurements at every notable change or every few hundred yards. Each lithologic unit was examined for features which might a ssist in correlation and/or in de­ termining the depositional history of the unit. Laboratory work was initiated in the f a ll of 1950 and 7 . carried on until the spring of 1951* The measured sections were plotted on a sufficiently large scale so that actual rock specimens could be put in their respective places on the drawings. With the rock specimens in place, a tentative cor­ relation based on megascopic lithology was made and samples were chosen from significant horizons for mechanical analysis. Individual rock units were described in accordance with the form given by Short and McKee (1951) for the description of sedimentary rocks in a measured section. The color of each rock specimen was determined by comparison with the standard color chart (National Research Council, 1948). The texture was determined by visual comparison with measured standards based on the Wentworth classification (Wentworth, 1926, p. 24). The sphericity of the grains was determined by compar­ ison with the Rittenhouse Visual Sphericity Chart (Rittenhouse, 1943, p. 79-81). Shapes of gravels in the conglomerates were measured and calculated according to the Zingg classification chart (after Krumbein, 1941, Fig. 3, P* 66). The roundness of each was determined by comparison with the roundness chart of Krum­ bein (1941, p. 64-72) and described by applying the compar­ ison numbers of his scale. Samples chosen for mechanical analysis from the correla­ tion chart were broken down with wooden blocks, (toe hundred gram samples were weighed and placed in a weak hydrochloric acid solution, washed, and dried. The remaining portions were subjected to a screen analysis using the "Tyler Standard 8. Screen Scale" screen series (Twenhofel, W. H., and Tyler, S. A., 1941) and the Tyler automatic "Ro-tap" screen shaker♦ The data obtained from mechanical analyses were plotted into simple histograms and accumulative frequency curves. Median diameters and quartile diameters were found from the graphs and used in determining the skewness and degree of sorting of selected samples according to the manner prescribed by Payne (1942, p. 1697-1770). These data were then compared with those calculated by the Trask (1932, p. 67-76) method. All calculations were performed using the phi-scale. Heavy mineral analyses were made; first, on several test samples using all fractions and finally, on the two largest fractions, as it was found these gave satisfactory results representing the entire sample. Other factors given in the descriptions of the measured section were determined by following the procedure suggested by Short and McKee (1951). The Maneos shale consists of several hundred feet of very fine clastic sediments and the usual methods of mechanical screen analysis could not be applied in determining textural properties. A density-settling method was used instead. The apparatus employed is a modification (Fig. 2 and PI. 11, fig. 3) of the continuous recording settling device used by Doeglas (1936, p. 19-40). It consists of a glass tube, 3 inches in diameter and 4 feet long, containing water. At the bottom of the tube is a gland which supports a copper con- 9 .

Introduction of specimen Balance arm

Counter weight

Indicator arm G lass tube

Weight scale

Wire

Gland

F i l l — Drain

F ig . 2.-Diagrammatic sketch of continuous recording density­ settling device. (Modifications after Doeglas, 1936) 10. tainer by means of four thumb screws. The top is open for the introduction of the sample. A balance arm is so placed at the top that the right side centers over the tube and is connected to a collecting pan at the bottom of the tube by means of a very fine wire. The other side of the balance arm has a counter-weight to offset the weight of the pan and wire. The indicator arm is connected to the center of the balance arm as on a chemical balance. The apparatus is so balanced that when empty the indi- cator arm is at the extreme right. This places the pan as high as possible and allows the maximum movement of the arm. When a certain amount of sediment settles in accordance with a previously determined standardization, readings can be made on the indicator arm. The apparatus was fir s t standardized using screen-sized samples and the time of settling was noted. Several inaccur­ acies were encountered in introducing the sample. The in itia l velocity imparted to the grains upon introduction is the largest error. Grain size has considerable effect on the settling time and the results of three tests using different sizes of material are shown in Figure 3• The results as determined by tr ia l are as follow s$ fir s t, the removal of a ll sand sizes by mechanical analysis. Second, introduce the sample in a wet state, very rapidly, using a spray to remove adhering particles, and third, timing should not start until the first sediment is seen to pass a 10 inch g. ig F Time in m inutes -etig ie o smls otiig ey ie sand- fine very containing samples for time .-Settling 3 otnos eodn dniystln apparatus density-settling recording Continuous Cental ortc r te ra l retica eo h T s ie sand fine ns ri sz i mm in size grain otis si Contains n smaller and

11.

12. mark below the point of introduction. The inaccuracies encountered tend to lessen the value of the apparatus but i t is su fficien tly accurate to warrant further use. The results of settling tests using the contin­ uous recording apparatus and checked by the Bouyoucos hydrom­ eter , are given in Figure 4. Settling test were also conducted on bentonites of the Mancos shale in an attempt to determine their usefulness for correlation. These te sts, however, were not conducted in the continuous recording device due to the time element involved in the settling of such fine Material. Coal deposits were sampled and proximate analyses made. No ultimate analysis was made due to the lack of necessary equipment. Three samples obtained from the producing mines were analyzed to determine the calorific content of the coal. Sand-shale ratios and clastic ratios were calculated following the method of Krumbein, Dapples, and Sloss (1948, p. 1903-1923) which consists of substituting thicknesses of the respective sediments in the following formula: Sand-shale ratio = Conglomerate 4 Sandstone S h a le ; The sand-coal ratio was determined by similarly substituting in the following formula:

Sand-coal ratio = Conglomerate 4 Sandstone 4 Shale Coal Statistical studies of cross-stratification were made fo r some of the more im portant rock u n its and p lo tte d on 13. rosette charts using the dip correction method as given by Reiche (1938, p. 905). The very detailed stratigraphic section (No. 2) measured south of Cow Springs Trading Post is presented as an example of the rocks encountered in the area (PI. 10). In addition, correlation charts composed of the principal sections measured is included (Pis. 3,4,5,6,7,8, and 9). The maps, correlation charts, and cross-stratification studies were completed and the manuscript written in the Spring of 1951.

Acknowledgments

Grateful acknowledgment is made to the Shell Fellowship Fund, without which this work would not have been possible, and to Dr. Harold S. Colton, director of the Museum of Northern .Arizona, for providing living quarters and permitting the use of the laboratory facilities. The aid and counsel of the members of the Faculty, particularly Professor Edwin D. McKee, under whose guidance this work was undertaken, is sincerely appreciated. The writer appreciates the aid given by several field assistants, especially Mr. Richard Wilson, whose "jeep" made travel in certain parts of the area possible. The continuous assistance of Mr. L. F. Brady is appre­ ciated. His mechanical abilities in the construction of the settling device was of inestimable value. 14. The writer wishes to thank Dr* Erling Dorf and Dr. J. B. Reeside, Jr. for examining the flora and fauna collected in the area. Finally, the writer wishes to thank his wife, Bervette Williams, for the constant encouragment and assistance given, especially in compilation and subsequent typing of the man­ uscript. 1 5 .

CHAPTER II

GEOGRAPHY

Tonography

Black Mesa Is a portion of the Colorado Plateau phys­ iographic province as defined by Fenneman (1931). The broad Colorado Plateau comprises 100,000 square miles of more or less flat-lying or slightly tilted rocks which have been highly dissected. The area is characterized by steep walled canyons, cliff-enclosed mesas and buttes, monocline1 ridges, and terraced plateaus, with stream-cut canyons as deep as the mountains of the region are high. Black Mesa, a first order mesa, is in the central por­ tion of the Navajo section of the Colorado Plateau. A map of the region (Fig. 1) shows Black Mesa to be a somewhat oval­ shaped elevated area which rises in the northeast to an ele­ vation of 8,000 feet at Lolomai Point (PI. 12, fig. 1) and slopes downward toward the south and west. The higher por­ tions of the north and northeast sides are very steep walled and tend to form benches which very few streams dissect. The south and southwest portions of the mesa have been eroded so that in these areas the mesa no longer has the continuity seen in the north. The effect of rock resistance on topography is such that each formation may readily be distinguished. Black Mesa has a lower and an upper escarpment, separated by a long debris-covered slope. The lower escarpment consists of Jurassic formations capped by resistant Dakota (?) sand­ stone. The debris-covered slope is formed from Mancos shale which is easily eroded and develops into a badland topography (PI. 12, fig . 2). The upper escarpment is composed of rocks of the Mesaverde group which, in the northern part of Black Mesa, form sheer vertical cliffs, but in the south form ledg­ es separated by slope-forming shales. The area surrounding Black Mesa is much lower in ele­ vation and generally lacking in relief. Rocks of this wide expanse offer li t t le resistance to the wind, with the re­ sult that large areas of dunes, separated by other areas of bare rocks, occur here. Dunes in many areas have been formed from sand which has been blown from on top of the mesa by the prevailing winds. This gives rise to finger-like ridges radiating from the mesa (Hack, 1941, p. 244). Marching, dunes form in the valleys and are of the barchan type. Hack, (1941 p. 244) described dunes of the longitudinal type which occur in the southernmost part of the area. In many areas the fin ­ ger -lik e dunes protect underlying sediment from erosion by streams, thus, the combination of dune and underlying sedi­ ment gives the appearance of a much more extensive dune than is actually present. In most places where dunes occur, the underlying material is Mancos shale which is impervious to ground water. Because the dunes themselves are permeable an abundant vegetation occurs along the contact of the sand with the underlying shale and this tends to anchor the sand in place. Peculiar topographic forms such as demoiselles, natural bridges, and rock-monuments make the country one of unusual scenic beauty (PI. 13, fig. 1).

Climate and Vegetation

General

The Navajo country as a whole is deficient in rainfall and the temperature ranges from that of intense heat to se­ vere cold. Rainfall and temperature sta tistic s are very meager, however, some data are reported from Tuba City and Kayenta (Fig. 1). - Differences in elevation control the climate to a con­ siderable extent. Summer days are generally warm to hot but prevailing winds make even the hottest days bearable, while in winter these same prevailing winds make the weather dis­ agreeable. Many of the canyons are so deep that they restrict air circulation, resulting in extreme heat locally during the summer months. 1 8 - Records

The following are records taken at Tuba City and Kayenta as given In "The Climate of Arizona" (1945)$

Normal monthly and annual precipitation for the state (from date of establishment to 1940 Inclusive) Station____ Elevation____ No. years._____ Annual Kayenta 5640 23 8.65 Tuba City 4591______^8______6.73

Average number of days with 0.01 Inch or more of precipitation Station No. years Annual Kayenta 22 52 Tuba City 37 36

Mean maximum, mean minimum, and mean temperature Station No. years Annual Mean Min. 37.7 Kayenta 23 Mean Max. 67.9 Mean 52.8 Mean Max. 70.3 Tuba City 36 Mean Min. 39.8 Mean ___51,1—

Average Annual Snowfall (Inches) Station____ No. years_____Annual Kayenta 22 16.5

Tuba City 3 7 13*4 19. Lack of data from the top of Black Mesa makes a complete climatic picture impossible. Gregory (1916, p. 60) estimates the precipitation at Lolamai Point on top of Black Mesa (PI. 12, fig . 1) to exceed 15 inches per year, using as a basis for his conclusion, the type of vetetation prevalent on the mesa.

Seasonal and Year to Year Variations

Gregory (1916) states that the variation in precipitation from year to year ranges from one half the normal to twice the normal. The importance of this cannot be overemphasized when the agricultural and grazing conditions are so dependent on the annual precipitation. Spring is the dry season with the wet season occurring in the summer. This condition is not favorable for good agriculture because the wet season comes so late that plants cannot develop properly before the first frost.

Character of Rainstorms

The characteristic rainstorms of the area are violent local showers. Gentle rains lasting for any appreciable length of time are very rare. In general, showers rarely last longer than 30 minutes and often a month’s entire precipitation w ill fall within a few minutes time. 20 The lightning which accompanies these cloud bursts is very disturbing to the geologist. Sometimes nearby trees and rocks are split giving a considerable sense of insecurity.

Soil The so il is , in general, very sandy and low in humus material. However, due to the low water table and lack of rainfall, the removal of the humus material by leaching is minor. Perhaps the most important fact in this regard is that the soil lacks only water to make it excellent for agricultur­ al purposes.

Wind

The wind blows almost continuously the entire year. No velocity data are available, but Gregory (1916) estimates the wind to exceed 3 miles per hour as an average. The pre­ vailing direction is from the southwest with some variations to the south.

Vegetation

The vegetation varies considerably depending on the elevation and the amount of precipitation.. Gregory’s report on ground water of the Navajo country (1916) contains the most extensive discussion of the vegetation. 21 The following is a brief summary of the zones present in the areas 1. Zone of cottonwood, cactus and yucca between 3,500 and 5,000 feet above sea level. 2. Zone of sagebrush and greasewood between 5,000 and 6,000 feet. 3. Zone of pinon and juniper between 6,000 and 7,000 feet. 4. Zone of yellow pine between 7,000 and 8,500 feet. Black Mesa is noticeably lacking in trees of the Zone 4, especially yellow pines of commercial value. Some small or stunted yellow pines occur, but lack of precipitation prevents large growth.

Drainage and Water Supply

Runoff of precipitation in the Black Mesa area divides, with the northern part going to the San Juan River and the southern going into the Little Colorado River. The cliffs of Black Mesa are the main divides. The mesa surface slopes to the southwest with its drainage going to the Little Colorado River, via Biko Hodoe Klizg, Blue Canyon Wash, Moenkopi Wash, which are connected to form an extensive drainage system. East of Blue Canyon, Dinnebito Wash drains to the south and west. (Pis. 1 and 2). Black Mesa is bounded on the east by the Chinle Valley :2Z. which drains to the north into the San Juan River. On the west, Marsh Pass forms a drainage divide with Tyende Creek draining into Chinle Wash. South of Marsh Pass, the Begash- ib ito Wash, Shonto Wash, and Klethla Valley drainage unite to form a broad valley which loses its gradient in the vicin­ ity of Cow Springs, where intermittent lakes are formed (Pis. 1 and 2). There are no perennial streams in the area.

Water Supply The water supply for domestic and animal use comes pri­ marily from catchment basins where the sporadic ralnfalllis collected. The streams of the area furnish only a minor part of the water. Very li t t l e sub-surface stream water is u tilized . Springs in the area are very rare, however, a few seeping springs exist where water is collected and preserved in catch­ ment basins. Some subsurface water has been tapped by d rillin g . The Soil Conservation Service has built many small earth dams to collect water for the purpose of desilting the streams, however, too often the dam is built of aeolian sand which permits loss by seepage. The water problems encountered in the area are discussed by Gregory (1916). 23', Local Industries

The principal Industry of the Black Mesa region is stock raising. Sheep far exceed a ll other stock, however, in the last few years the number of cattle has shown a marked increase. Horses are raised for trade and as a means of trans­ portation. The production of blankets constitutes one of the Nava- jos’ principal sources of income. The making of Indian jewel­ ry has never been a large industry in this area but is on the increase at the present time. Several coal mines are now in operation on Black Mesa and they provide labor for a num­ ber of Havajos. In the late 1930‘s and u n til 1941, a Cali­ fornia business group operated a copper mine on the Kaibito Plateau, 50 miles north of Tuba City, however, the low grade of the ore and lack of water caused i t to close down. 24.

CHAPTER III

HISTORICAL REVIEW

Previous Investigators

The early workers who traversed the Black Mesa area made reconnaissance surveys which contributed to the exploration of the area with only casual reference to the geology. By 1906, when Gregory (1917) started his geological study of the Navajo country, approximately 40 per cent of the region had been examined. Prior to his professional paper, sever­ al contributions briefly discussed the geological relation­ ships in Black Mesa (Darton, 1910; Campbell, 1911; and Greg­ ory, 1916). Gregory (1917, p. 9) discusses the exploration and geological work done by the early investigators and gives results of the first careful study of the area. The only study of coal possibilities that has been made on Black Mesa is the work of Campbell and Gregory (1911). The fir s t use of formational names on Black Mesa is by Greg­ ory who applied the Upper Cretaceous nomenclature of north­ western New Mexico and southwestern Colorado. Reagan (1925, 1926, 1932) made several studies of Black Mesa, in which he applied the nomenclature of the Cretaceous of southern Utah 25- and named one new formation. A stratigraphic section of Cretaceous rocks on the north­ east face of Black Mesa was published by Reeside and Baker (1929) and contributed toward the correlation with other areas. The work of Sears, Hunt and Hendricks (1941), and of Pike (1947) in adjoining areas are especially helpful in work­ ing out the relationship of Black Mesa to the corresponding Cretaceous deposits of northwestern New Mexico and southwest­ ern Colorado. Gregory and Moore’s (1931) studies are used to determine the relationship of Black Mesa deposits to those of southern Utah. ’ Many workers have contributed to the literature on the corresponding Cretaceous rocks of adjoining areas in Arizona, New Mexico, Utah and Colorado. These studies have a direct bearing on the present investigation.

Nomenclature /

G en eral

G ilbert (1877) subdivided the Cretaceous in the Henry

Mountains into seven form ations, which he named, in descending order, Masuk sandstone, Masuk shale, Blue Gate sandstone, Blue Gate shale, Tununk sandstone, Tununk shale, and Henry’s Fork group. Succeeding geologists, however, found great dif­ ficulty in recognizing these formations with the result that 26;. Cross (1899) introduced the term "Maneos shale" for the shales above the Dakota (?) sandstone and adopted (after Holmes, 1877) the term "Mesaverde" for the sandstone sequence overlying the shales. This three-fold nomenclature has per­ sisted to the present. It is important to note that as one leaves the type localities of each formation the character of the sedimentary rocks changes, and this has caused the introduction of new formational names that tend to confuse the general picture. The nomenclature of the Upper Cretaceous deposits which occur in the Black Mesa region was given fir s t by Gregory (1917, P* 70). Gregory studied the entire Navajo country which in­ cludes the San Juan Basin and Mount Taylor regions of north­ western New Mexico, and in his work he followed the nomencla­ ture applied fir s t by Dutton (1885) and later by Shaler (1907). Gregory states (1917, p. 70):

"My knowledge of the Dakota, Mancos, and Mesaverde in the area studied by Shaler (1907) and also at Black Mesa is the basis for using these terms to Include all Cretaceous beds in the Navajo country."

The Underlying Rocks

The following brief summary (Table 1) of the underlying Upper Jurassic rocks of Black Mesa (Harshbarger, 1949, p. 22) is given here in order to clarify the relative position of the Cretaceous strata of Black Mesa. TABLE 1 Relation of Upper Jurassic to cretaceous in Black Mesa (Harshbarger, 1949, p. 22)

CRETACEOUS Dakota (?) sandstone

Westwater Canyon sandstone member lorrison Recapture shale Cow member Springs formation sandstone Salt Wash

Northern Northern phase sandstone member Southern Southern phase j j

JURASSIC Entrada San sandstone Rafael. -• Group Carmel formation

Navajo Sandstone Glen Canyon Kayenta Group formation

Wingate sandstone 2 8 , The Morrison formation comprises the Upper Jurassic rocks of Black Mesa. The relationship of the Cretaceous rocks to the various members of the Morrison formation can be clear­ ly seen in Table 1. Only two members are important to this paper: the Westwater Canyon sandstone member of the northern phase and the Cow Springs sandstone member of the southern phase.

Lower Cretaceous Rocks

The presence of conglomerates at the base of the Dakota(?) sandstone has raised the question of their being Lower Cre­ taceous in age. Coffin (1921, p. 90) describes a conglomer­ ate which occurs near the top of the old McElmo formation of southwestern Colorado. He tentatively calls the conglomer­ ate Hpost-McElmo" but does not assign it any more definite age, Stokes (1944, p. 965), la his work in Emory County, Utah, proposes that similar (?) conglomerates be called the Buckhorn conglomerate member and the overlying varicolored shales be called the Cedar Mountain shale member. In the same paper, Stokes (1944, p. 989) proposes to call both mem­ bers the Cedar Mountain group, and tentatively gives them a Lower Cretaceous age. In a recent study by Stokes and Phoenix (1949), the "post McElmo11 beds are given the name of Burro Canyon group which is questionably called Lower Cretaceous. The conglomerates of Black Mesa Jiave been mentioned :2% as being equivalent in age to the Burro Canyon group, how­ ever, they do not seem more than lenticular conglomerates occurring at the base of the Dakota (?) sandstone and are not of a different age than the Dakota (?) sandstone. Heaton (19I?0, p. 166) shows Lower Cretaceous to be pre­ sent in Northern Arizona and ca lls i t Comanche. In the present study, however, no Lower Cretaceous was found in the Black Mesa region and it is felt that the lithologic evidence is insufficient to warrant a separation.

Upper Cretaceous Rocks

A correlation chart of Cretaceous is presented (Fig. 5) to fa c ilita te correlation of the Black Mesa Cretaceous forma­ tions with the adjacent regions and to the standard Great Plains section. The name, Dakota formation, was proposed by Meek and Hayden in 1862 (p. 419) for the basal "yellowish, reddish, and occasionally white sandstone, with, at places, alterna­ tions of various-colored clays and lignite beds". The type section was chosen in the h ills back of the town of Dakota, Nebraska. The name Dakota sandstone has been used over ex­ tensive areas with many of the uses having a doubtful basis. The United States Geological Survey, in an effort to clear up the problem, restricted use of the name Dakota sandstone to areas east of the Front Range, while those west of the Kaiparowits Black Mesa Son JuanlOOmi Std. Great Plains

Pictured Cliffs; s.'s Fox Hills s s

wis sh

Mesaverde* Group':. Pierre sh

Eagle s s Telegraph Creek

Mancos Carlile s h Greenhorn Is

Graneros sh

Dakota (?) ss

Fig. ^.-Correlation chart of Cretaceous rocks UJ o S i- Front Range, occupying approximately the same stratigraphic position, have been tentatively assigned the name Dakota (?) sandstone. Gregory (1917) applied this term to the basal sandstone of the Cretaceous rocks of Black Mesa. The Dakota (?) sandstone of Black Mesa consists of about equal amounts of sandstone and shale with a coal as the upper­ most unit. The sandstones and shales are lenticular and re­ place one another at various horizons. In the northern part of the area there is a basal conglomerate which occurs as lenticular to irregular masses in a grayish-yellow to brown medium-grained sandstone. In the extreme southern part of the area, neither conglomerate nor sandstone is present but shales and coals rest directly on the Cow Springs sandstone. As recognized here the Dakota (?) sandstone consists of the basal formation of the Upper Cretaceous rocks and is composed of conglomerate, sandstone and mudstone, and occurs through- . out the area. No marine fauna has been found in these rocks. Reeside (1951), after studying fossils found by the writer in the overlying Mancos shale states that "any representative of the Graneros shale of the plains has to be in the Dakota or the unit is not represented in the Black Mesa area". The name Mancos shale was fir s t used by Cross (1899) to describe the "dark-gray to lead-colored shales" which over- lie the Dakota (?) sandstone in Mancos Valley near the town of Mancos, Colorado. Gregory (1917) applied this name to the dark gray to black shales which overlie the Dakota(?) sandstone In Black Mesa. Reagan (1925, p. 285), In a reconnaissance examination of Black Mesa, drew on Gilbert’s nomenclature to describe a basal portion of the Mancos shale. He found the following members; Tununk shale, Tununk sandstone, and Mancos shale. The writer believes that the siltstones and coals of the Dakota (?) sandstone are the rocks which Reagan identified as Tununk shales. Because they are believed to be of con­ tinental origin, the writer can see no reason for calling them Tununk shale which in the type section is definitely of a marine origin. Overlying the coal is a lenticular sandstone containing an abundance of Gryphaea newberryj Stanton and Exogyra colum- bellq Meek. This sandstone does not occur in the northern part of the mesa. The writer believes this unit is the sand­ stone which Reagan correlated with Gilbert’s Tununk sandstone The writer does not feel that Reagan is justified in corre­ lating this lenticular unit over such a great distance. Es­ pecially is this true when the original work of Gilbert is examined, for he gives very little information concerning the fauna or lithology of these members. Reeside and Baker (1929, p. 32) measured a section on the northeast face of Black Mesa and found no evidence to support the Tununk sandstone or Tununk shale. They believed Reagan to have misinterpreted slumped material as Tununk sand stone and shale. Upon examining the published section of 3 3 , Reeside and Baker, It is believed by the writer that the sec­ tion was measured in a part of Black Mesa where the lower sandstone is not present* No attempt w ill be made in the Black Mesa section to distinguish between correlative members of the Maneos shale. As identified in this study the Mancos shale includes the fossiliferous sandstones and dark gray to black shales which are above the coals at the top of the Dakota (?) sandstone and below the non-fossiliferous basal Mesaverde sandstones. The writer submitted a collection of Mancos shale fo ssils to John B* Reeside, Jr. for identification and he states:

"The strata up to about 30 feet above the base of the Mancos shale contain fauna equivalent to the typical Greenhorn limestone of Gilbert, i . e . , of Bridge Creek member of the Greenhorn of western Kansas. The fos­ sils of the upper part of the Mancos ally it with the lower member (Fairport) of the Carlile of the Plains."

The Mancos shale of Black Mesa is considered equivalent in lithology to the Tropic shale of the Kaiparowits Plateau as described by Gregory and Moore (1931, p. 98) and the age relationships as determined by Reeside for Gregory and Moore (1931) p. 110} Reeside and Baker, 1929* p. 36) indicate a similar to slightly younger age (Fig. 5)• The Mancos shale of Black Mesa represents only the basal portion of the Mancos shale of southwestern Colorado and the San Juan Basin of northwestern New Mexico (Fig. 5) • The 3 4 , relationship of the Mancos shale of Black Mesa to the forma­ tions of the Book Cliffs area of Utah is not clear, but based on the correlations made by Spieker (1949* P« 59) and Hea­ ton (1950, p. 1660) it is equivalent to the Tununk shale and possibly the lower portion of the Perron sandstone. The Mesaverde group on Black Mesa is essentially no different lithologically from that found in the type sec­ tion. Holmes (1877, p, 245, 248, PI. 35) proposed the name Mesaverde for an "Upper Escarpment Sandstone", a "Middle Coal Group" and "Lower Escarpment Sandstone" which overlies mas­ sive shales (Mancos) in the Valley of Rio San Juan, south­ western Colorado and northwestern New Mexico. Collier (1919, p. 296) renamed the lowest division the "Point Lookout Sand­ stone", the middle division the "Menefee formation", and the upper escarpment "Cliff House sandstone"* Reeside (1924) believes the Mesaverde to be essentially a sandstone equivalent of the Mancos shale and as both formations transgress time he considers the two planes to have been deposited simultan­ eously. The basal portion of the Mesaverde of Black Mesa is be­ lieved (Pike, 1949, p. 12) to be the same regressive sandstone that is represented by the Gallup sandstone (Sears, 1925) in the San Juan Basin and the "Tocito lentil of the Mancos" of Northwestern New Mexico (Reeside, 1924, p. 9). The con­ tact between the Mancos shale and the Mesaverde group is arbitrarily placed where the basal sandstones of Mesaverde 35 group become predominant over the shaly sandstones and silt- stones of the Mancos shale. Several thin tongues of shales occur In the basal Mesaverde of Black Mesa but no marine fauna has been found in them to indicate an intertonguing of the Mesaverde with the Mancos such as is found in the San Juan b a s in . Only a meager fauna has been found in the Mesaverde of Black Mesa but Reeslde and Baker (1929, p. 34) have assigned it an age of Niobrara. The writer tentatively correlates it with the Niobrara of the Great Plains on the basis of a collection of fossils made from one horizon in the Upper Mesaverde goup which contains Inoceramus deformls Meek, Inoceramus unabundus Meek and Ostrea congests Meek. Pike (1947, PI. 12) shows the topmost formation of Black Mesa to be the near-shore point where the Lower Hosta sand­ stone and the Upper Hosta sandstone of the San Juan Basin unite to form a single sandstone member. Under this condition, the massive sandstone represents the maximum transgression of the Lower Hosta sandstone. Or, it may represent the near­ shore deposits at the start of the regression in which the Upper Hosta sandstone was deposited. In Black Mesa, the upper massive sandstone is considered to be transgressive. Because the distance from type sections in Colorado and New Mexico makes correlation between members uncertain,, no attempt has been made to use the various member names of the Mesaverde as recognized elsewhere. 3 6 , Overlying the Mesaverde group of the type section is a shale which Cross (1899, P* 4) named the Lewis shale from exposures near the former army post of Fort Lewis in Colorado. The Lewis shale at the type section is 2290 feet thick (Roe- side, 1924, p. 17) whereas in the San Juan Basin, New Mex­ ico, it is only 76 feet thick. Reagan (1925) reported 20 to 30 feet of this shale in the Black Mesa area, however, Ree- side and Baker (1929, p. 36) do not concur. No evidence of it s presence in the Black Mesa area could be found by the writer. Reagan (1925, p. 291) reported also the presence on Black Mesa of the Pictured C liffs sandstone (Holmes, 1877, p. 249) which conformably overlies the Lewis shale in south­ western Colorado. Reeside and Baker (1929, p. 36) on the other hand, found no evidence of any formations above the Mesaverde in their examination of Black Mesa. Reagan (1925, p. 291; 1935, p. 235) gives the following description of a series of sandstones, shales, and coals in the region:

"After proceeding inland for some distance, say ten miles, coal bearing, fresh-water and brackish-water beds are exposed in canyons and further on southward they become the surface rocks over quit© an area."

He (1925, p» 291) called this group of deposits the Zilhlejlni formation and considered It equivalent to the Fruitland for­ 3 7 . mation of southwestern. Colorado. The area described by Rea­ gan was visited and the rocks present were examined. The writer believes that Reagan failed to take into consideration either the dip of the strata toward the center of the basin or the work of erosion which has dissected the mesa to the southwest, exposing sandstones, shales, and coals of the mid­ dle portion of the Mesaverde group. Thus, Reagan mistook these rocks for a younger formation. The name, Zilhlejini forma­ tion, therefore, should apply to the middle portion of the Mesaverde group. Reeside and Baker (1929, p. 33) believe the fauna described by Reagan (1925, 1926, 1932) to be correctly designated and they assign it to Niobrara age. This is in complete agreement with the age of the coal-bearing member or middle Mesaverde sandstones, shales, and coals of this p a p e r.

Several large mesas rise above the dissected portion of Black Mesa and are capped by the massive uppermost sandstone described in this paper. One such mesa is four miles south of the Cow Springs Trading Post. Reagan (1932, p. 236) applied the names Kirkland shale (Bauer, 1916, p. 244) and Ojo Ala­ mos sandstone (Brown, 1910, p. 267-274) of southwestern Colo­ rado and northwestern New Mexico respectively, to the rocks of these mesas which overlied his Zilhlejini formation. Apparently these correlations, like those below, are not v a lid . The Mesaverde group of Black Mesa very closely resembles 38% the Straight Cliffs sandstone as described by Gregory and Moore (1931, p* 100) in the Kaiparowits Plateau. Reeside and Baker, (1929, p. 37) found the Mesaverde formation on Black Mesa to be of Niobrara age and equivalent in age to the "typical" Mancos shale of the San Juan Basin. They believe, with respect to age relationship, that there is no reason "even in an elastic usage of the term" to cor­ related the Black Mesa Mesaverde with the Mesaverde of other regions. The writer believes the Mesaverde of Black Mesa to be similar in lithology to the Mesaverde of adjoining areas but concurs with Reeside and Baker in respect to age relationships. The Mesaverde group as recognized in this paper consists of a lower massive sandstone with minor mudstone units, a middle sequence of sandstone, shales, and coals, and an up­ per massive sandstone. No member or tongue names seem ju sti­ fied at this time. Tertiary rocks occur in scattered areas around and on Black Mesa but their discussion is beyond the scope of this paper. The only deposits of recent age which the writer encountered are those forming two pediments (PI. 14, fig . 2, fig. 3)• The upper pediment contains gravels ranging in size from pebbles to boulders, up to 4 feet in diameter, com­ posed of quartz, chert, and minor amounts of limestone and sandstone. The thickness of these varies considerably, with 24 feet being the maximum noted. The pediment is best seen 39- on the road from Tuba City to Oraibi where it forms a ledge to the right of the road. East of Red Lake Trading Post the pediment can be seen overlying the Mancos shale, Dakota (?) sandstone and Cow Springs sandstone at a low angle. The lower pediment is not as distinct as the upper ped­ iment and the gravels which it contains are almost entirely of Upper Cretaceous sandstones. Individual gravels are of granule to cobble size. The two pediments indicate two cy­ cles of erosion that have occurred prior to the present cy­ cle. 40.

CHAPTER IV

GENERAL STRATIGRAPHY AND STRUCTURE OF BLACK MESA AREA

Lower Jurassic Rocks

Glen Canyon Group

The oldest rocks exposed in the Black Mesa area are those of the Glen Canyon group of Lower Jurassic age (Table 1). This group consists of, in ascending order, the Wingate sandstone, the Kayenta formation and the Navajo sandstone. The Wingate sandstone is a reddish-brown, fine-grained sand­ stone which is, in part, massive. This formation can be seen to good advantage in the west wall of the Comb Ridge monocline in Marsh Pass where i t reaches an elevation equal to that of the Cretaceous rocks of Black Mesa. For a more detailed description, the reader is referred to Harshbarger (1949, p. 30) and to Callahan (1951)• The Kayenta formation is easily recognized as a distinct slope between massive reddish-brown c lif f s along the Comb Ridge monocline in Marsh Pass. It consists of light-red to reddish-brown, thin-bedded sandstones and siltstones, with ■4.V minor beds of limestone. The areal distribution of this formation is essentially the same as that of the Wingate sandstone, and is best seen in the Kayenta-Marsh Pass area north and west of Black Mesa. The Navajo sandstone is the upper member of the Glen Canyon group and consists of a reddish brown to light brown fine-grained, weakly cemented sandstone. The most character­ istic feature of the Navajo sandstone is the extremely large, truncated wedge-shaped cross-lamination of the high-angle compound type. The Navajo sandstone weathers into vertical and near vertical c lif f s which in many places resemble giant conchoidal fractures. These overhanging c lif f s are locally undercut to form cave-like zones in which early Indians built the great cliff dwellings found in the area. Navajo sandstone forms the surface of the region west of Black Mesa. Excellent exposures are also in the upthrown side of the Comb Ridge monocline in Marsh Pass where they reach an elevation as high, if not higher, than the most elevated point on Black Mesa.

Upper Jurassic Rocks

San Rafael Group

Unconformably overlying the Glen Canyon group is the San Rafael group likewise of Jurassic age (Table 1). Within this area it consists of the Carmel formation and the Entrada sand­ 42. stone. The Carmel formation consists of alternating layers of white sandstones and red friable sandy siltstones. The Entrada sandstone is a reddish-brown, massive sandstone which contains minor amounts of shale. The San Rafael group can best be seen in the vicin ity of Red Lake, Blue Canyon and Coal Mine Canyon.

Morrison Formation

The Morrison formation is represented in Black Mesa (Table 1) by a northern phase and a southern phase (Harsh- barger, 1949) which are contemporaneous but of different lithology. The northern phase consists of the Salt Wash sand­ stone member, Recapture shale member, and Westwater Canyon sandstone member. The southern phase consists of the single Cow Springs sandstone member. The Salt Wash sandstone member consists of sandstones interbedded with minor amounts of shale and rests conform­ ably on the Entrada sandstone. The Salt Wash sandstone mem­ ber outcrops in the Kayenta-Marsh Pass area where i t inter­ tongues with the Cow Springs sandstone. A few miles farther south in Marsh Pass it disappears. The Recapture shale member in the Black Mesa area con­ sists of thin-bedded reddish brown shales which contain thin layers of a yellowish-gray sandstone. The Recapture shale can best be seen in the Marsh Pass area, but a few miles 4 3 . south i t is not present. The Westwater Canyon sandstone member consists of a fin e­ grained, yellowish-gray, thin-bedded sandstone interbedded with reddish-brown to light-gray shales. The member is characterized by the great irregularity of the bedding. It very closely resembles the overlying Dakota (?) sandstone and like the Dakota it contains ferruginous material. The ■' Westwater Canyon sandstone can be seen in Marsh Pass but a few miles south of here i t disappears. The southern phase of the Morrison formation consists of a single member, for which Harshbarger has proposed the name 11 Cow Springs sandstone”. It can best be seen at the type section south of the Cow Springs Trading Post. It con­ sists of a "greenish-gray to yellowish-gray, fine-grained, cross-bedded, firmly cemented quartzose sandstone" (Harsh­ barger, 1949, p. 55).

Upper Cretaceous Rocks

Dakota (?) Sandstone

The Dakota (?) sandstone unconformably overlies the West- water Canyon sandstone member in the north and the Cow Springs sandstone member in the south (Table I 5 Pis. 3, 4, and 5). The Dakota (?) sandstone consists of a yellowish-gray to dusky- yellow, thin-bedded, fine-grained, firmly-cemented, sandstone interbedded with yellowish-gray to black, fissile siltstones and minor claystones. Goal occurs in the slltstones. Be­ tween Cow Springs Trading Post and Marsh Pass the Dakota dips beneath the alluvium, but in a ll other parts of the area it outcrops (Pis. 1 and 2).

Maneos Shale

The Mancos shale forms a long slope between the Dakota (?) sandstone or lower escarpment and the c lif f s of the Mesaverde group above. It consists of light gray to black, f is s ile , weak shales which contain a basal sandstone and a few thin sandstones in the upper portion (Pis. 6 and 7)» Mancos shale surrounds the mesa as a long, highly dissected slope below the cliff-forming basal sandstones of the Mesaverde group and forms the surface of the mesa around Coal Mine Canyon.

Mesaverde Group

The Mesaverde group contains three parts which can readily be determined by their physiographic expression (Pis. 8 and 9)« The basal Mesaverde consists of cliff-form­ ing, yellowish-gray to white, fine-grained to conglomeratic sandstone which alternates with sandy siltstone. The mid­ dle portion of the Mesaverde consists of ledge-forming, yel- 45- lowish gray to brown, fine-grained sandstones alternating with yellowish-gray to black, slope-forming siltstones and claystones containing many coal seams (PI. 13, fig. 2). The upper part of the Mesaverde consists of a yellowish- gray, fine-grained, massive, sandstone which in the northern part of the mesa forms a vertical cliff three hundred feet high (PI. 15, fig . 1) whereas in the southern part, step- like remnants remain.as a capping to the highest buttes and mesas. Rocks of the Mesaverde group form the surface of Black Mesa and have the largest areal distribution of any group in the area (Pis. 1 and 2).

Structure

Black Mesa is a shallow structural basin, synclinal in nature, and containing a number of minor folds (Pi. 1). The Black Mesa basin is bounded on the north and west by the Comb Ridge monocline, and on the east by the De Chelly upwarp. On the south the Little Colorado River, a physiographic fea­ ture, forms the boundary. The southern part of the mesa is the center of a broad downwarp which Gregory (1917, p . 112) proposed to call the Tusayan downwarp. The southern border of the basin coincides with the center of the Tusayan downwarp and contains a num­ ber of minor folds. The north rim of Black Mesa ends in the southern exten- 46', sion of the sharply upturned Comb Ridge Monocline. The monocline can be seen best in Marsh Pass (Pi. 13, fig . 3) where Upper Jurassic rocks form the west wall and Upper Cre­ taceous rocks form the east wall of the pass. North of Marsh Pass, the monocline swings to the east and then north­ east, terminating at Elk Ridge In southeastern Utah. South of Marsh Pass, the Comb Ridge Monocline continues to the southwest (Pis. 1 and 2). Six miles east of Red Lake this monocline joins another monoclinal structure which trends southeast-northwest. Several minor structures are found in the southern por­ tion of Black Mesa, k small monocline in the Blue Canyon area has a north-south strike and continues north to the vi­ cinity of Red Lake where it joins the Comb Ridge Monocline. West of Red Lake there is clear evidence of the contin­ uation of a monoclinal structure:,. It is not uncommon for monoclines of the Colorado Plateau to divide. The East Kai- bab monocline divides several times and at one place the angle between the two monoclines approaches 90 degrees (Babenroth and Strahler, 1945, p. 112; McKee, 1951). The evidence in Black Mesa indicates that the Comb Ridge monocline, the monocline in Blue Canyon, and the Monoclinal structure west of Red Lake are parts of a split monocline. The dip of the strata east of Red Lake (Pis. 1 and 2) shows that the Blue Canyon monocline is a continuation of the Comb Ridge monocline. k careful search was made for any structures which might 47. be pre-Cretaceous in age but the only structure found in the underlying Jurassic rocks was a gentle, shallow monocline somewhat obscured, which can best be seen in Coal Mine Can­ yon. In it dips are less than 4 degrees so the exact attitude of the beds was not determined. At Howell Mesa (Pi. 2) a shallow synclinal trough occurs with its long axis coinciding with the long axis of Black Mesa. The dip of the limbs do not exceed 5 degrees. Harsh- barger (1949, p. 10) reports the structure of the finger- like mesas of the southern border of Black Mesa to consist of "gentle-dipping, shallow synclinos". Northeast of Cow Springs, several flexures occur in the Comb Ridge monocline. They are anticlines plunging 4J> degrees southeast at the edge of Black Mesa. Within a half mile to the southeast the plunge has decreased to 5 degrees. In several places where flexures occur, the Jurassic formations, capped by the Dakota (?) sandstone are excellently exposed as c lif f s . Great slump blocks up to a half a mile in length and 300 feet in width, occur in the area (PI. 14, fig. 1). These blocks are in essentially the same position as the parent rock, giving a very deceptive rock sequence. Relche (1937> p. 538) described and named these slumps "Toreva Block". He defined Toreva blocks to consist "essentially of a single large mass of unjostled material which, during descent, has undergone a backward rotation toward the parent cliff about a horizontal axis which roughly parallels it". He explained the slide as being duo to "low-dipping strata in which one or more relatively coherent beds rest upon others which are either incoherent or capable of becoming so when wetted".

The coherent beds ore Mesaverdd basal sandstones and the in­ coherent bed is Maneos shale. Successive slides often occur gibing step-like appearances. Two such slides have occured in historic time creating local quakes (Reiche, 1937» P« 5 4 7 ).

k definite joint system which can be directly related to the monoclines is present in the rocks of Black Mesa. In the northwestern part of the mesa, the joints are systems with a single set at right angles to the monocline, and another set parallel to the monocline. The joint systems have, almost without exception, two joint sets, one at right angles to the axis of the monocline and another parallel to the axis of the m o n o c lin e . 49.

CHAPTER V

RELATION OF DAKOTA(?) SANDSTONE TO UNDERLYING MORRISON FORMATION

General Statement

Comparison of the Dakota (?) sandstone with the underlying Morrison formation is made (1) to determine and indicate the criteria which can be used to recognize the formations in the field , and (2) to determine whether or not the Morrison formation was the source-rock for the Dakota(?) sandstone. The Dakota (?) sandstone on Black Mesa is underlain by the Morrison formation, represented in the north by the Westwater Canyon sandstone member and in the south by the Cow Springs sandstone member. These two members, together with the Dakota (?) sandstone are compared with respect to texture, composition, and primary structures. A statistical study of its cross­ lamination shows the Dakota (?) sandstone to have been derived from the south or southwest, so the Westwater Canyon sand­ stone member which is confined on Black Mesa to the northern part, could not have supplied the sediment. The Cow Springs member, on the other hand, was considered a possible source. 50 Texture

A. textural comparison of the Dakota (?) sandstone and the underlying formation can be seen in Table 2. The Westwater Canyon sandstone member of the Morrison is coarser-grained (Table 2) and more poorly sorted than is the Dakota(?) sandstone, whereas, the Cow Springs sandstone member of the Morrison is finer-grained (Figs. 6,8, and 9) and better sorted than is the Dakota(?) sandstone. This indicates that the Dakota (?) sandstone could not have been derived primarily from the Cow Springs sandstone. The presence of gravel and poorly sorted, coarse grains of sand point to a source-rock other than the Cow Springs sandstone, though possibly minor parts of the Dakota (?) sandstone are reworked sediment derived from it .

Composition

A comparison of compositional features of the Westwater

Canyon sandstone and Cow Springs sandstone members of the

Morrison formation with those of the Dakota (?) sandstone is shown in Tables 3 and 4. Few diagnostic differences exist in the general charac­ teristics (Table 3) of the formations. The sand-shale ratio differs greatly, however, because the Dakota (?) sandstone contains much more shale than does the underlying formation. 51.

TABLE 2 Textural comparison of the Westwater sandstone member and Cow Springs sandstone member of the Morrison formation, and Dakota (?) sandstone.

Westwater Cow Dakota (?) Canyon Springs sandstone member member

Color Yellowish- White to Yellowish- gray It. gray gray Average Grain-size 0.35 mm. 0.80 to 0.19 0.95 Sphericity 0.75 to 0.93 0.85 to 0.93 Roundness: Angular 12# 5$ 5$ Sub-angular 42$ 25$ 26$ Sub-rounded 36$ 55$ 55$ Rounded 10$ 15$ 15$ Coefficient of sorting 1.26 Trask's sortings Well sorted Well sorted Well sort­ ed Payne's sortings Fair sorted 70$-good 28$-good 30$-fair 6o$-fair Coefficient of Skewness 0.94 0.95 to 0.96 1.00 Surface 10$ pitted 50$ pitted Pitted Largest Size 0. 5- 1.0 mm. 0. 5- 1.0 mm. Up to 14.1 mm. 5 2 ,

TABLE 3 General characteristics of Westwater Canyon sandstone, Cow Springs sandstone, and Dakota (?) sandstone.

Westwater Cow Springs Dakota(?) Canyon member sandstone member Percent quartz 97 96 92 to 95 Percent feldspar 3 4 to 5 4 to 7 Sand-shale ratio 6.20 to 6.40 to 0.48 to 9.7 5.75 36.0 Sand-coal ratio No coal No coal 2.8 to 32.3 Cement Calcite Predominate Minor Predominate Limonite Common Predominate Common Silica Bonding material Clay Common Rare 53 »• TABLE 4 Heavy minerals in WesWater Canyon sandstone, Cow Springs sand stone and Dakota (?) sandstone.

Westwater Canyon ss Jwc-2-1 3ow Springs ss. member Jcs-10-1 Jcs-2-1 Jcs-4-1 Jcs-5-1 J cs-8-1 Jcs-9-1 Jcs-13-1 Jcs-13-1 Jcs-18-1 Jcs-19-1 J c s~20~1 Dakota (?) sandstone K—11—2 K-10-1 K-10-2

K—6—2

K-4-1 20 33 K -2 -1 K—2—6 K-2-11 29 24 K-16-1

K-19-6 5 4 . Considerable difference exists in the heavy mineral separates from the two formations (Table 4). The Cow Springs sandstone is high in garnet, limonite and hematite, whereas, the Dakota (?) sandstone is very low in these. The presence of leucoxene, titanite, and zircon in the Dakota (?) sandstone and. not in the Morrison formation indicates, at least in part, a source other than the Cow Springs sandstone member for the Dakota.

Primary Structures

Westwater Canyon Sandstone Member

Irregular bedding characterizes the Westwater Canyon sandstone member of the Morrison. Siltstone occurs as le n ti­ cular masses and in places, intertongues with sandstone. The bedding is essentially horizontal but individual beds thicken and thin along the strike. In Marsh Pass, siltstone occurs in many places as very thin layers alternating with light gray sandstone. In other places, the siltstone fills channels in the sandstone. Cross-lamination is principally of the plunging and asymmetrical festoon type. The wedge "torrential" type oc­ curs in some places immediately under the Dakota (?) sandstone. In certain thick units a low angle compound type is present. These various types of cross-lamination are believed to be 55 indicative of a fluviatile environment of deposition. No dip directions of individual laminae were taken. Flat-lying beds are not uncommon in this formation.

Cow Springs Sandstone Member

The Cow Springs sandstone is characterized by long, high- angle compound types of cross-lamination. Other types occur but none is so pronounced. Asymmetrical festoon types occur in localized areas. Some wedge‘ftorrentia1" types are present. Harshbarger (1949, p. 98) determined the direction of source of the sediment to be northerly. The writer measured only a few dips on the cross-lamination but they tend to con­ firm Harshbarger1s findings. Certain distinctive beds in the top of the Cow Springs are discussed under Morrison-Dakota contact.

Dakota (?) Sandstone

The primary structures in the Dakota (?) sandstone are cross-lamination and irregularly lenticular bedding. The cross-lamination is predominantly of the festoon type with some of the low angle compound type. Statistical studies of the direction of the cross-lamination show the direction of the source-rock to have been to the south and southwest. Perhaps part of the material in the Dakota (?) sandstone was 5 6 . derived from the Cow Springs member but evidence points to some other source. Considerable similarity exists between the Westwater Canyon sandstone considered to be a fluvial deposit, and the Dakota (?) sandstone which appears to be a flood plain deposit. Both units are characterized by irregular bedding and festoon type cross-lamination, but the direction of the source-rock is south-southwest for the Dakota (?) sandstone and north for the Westwater Canyon and Cow Springs sandstone members of the Morrison. For a more detailed account of the primary struc­ tures of the Dakota(?) sandstone see Chapter VI, Dakota(?) Sandstone.

Summary of Comparison of DakotaC?) Sandstone and Underlying Morrison Formation

Criteria for Field Identification

Westwater Canyon Sandstone Member. - 1. Yellowish-gray color. 2. Medium-grained. 3. Cross-lamination shows source to have been northerly. 4. Sub-angular grains. 5. Irregularly lenticular bedding. Cow Springs Sandstone Member. - 1. White to light gray color. 2. Fine-grained. 57 3. Cross-lamination shows source to have been north­ erly. 4. Cross-lamination predominantly high-angle compound type. 5. Sub-rounded grains. 6. Massive bedding. DakotaC?) Sandstone. - 1. Yellowish gray color. 2. Fine-grained. 3. Conglomerate at base. 4. Cross-lamination shows source to have been south­ erly. 5* Sub-rounded grains. 6. Irregularly lenticular bedding.

Determination of Source-rock for Dakota (?) Sandstone

1. The Westwater Canyon sandstone member could not have supplied the sediment in the Dakota (?) sandstone because the sediment apparently came from south and southwest whereas the Westwater Canyon sandstone member is to the north. 2. A textural comparison shows the Dakota (?) sandstone to contain coarser-grained, more poorly sorted material than does the Cow Springs sandstone member of the Morrison could supply. 3. The heavy mineral separates show the Dakota (?) sand- 5 8 . stone to contain minerals which the Cow Springs sandstone could not supply. 4. Evidence indicates that the Cow Springs sandstone member could not have supplied many types of sediment in the Dakota (?) sandstone and probably supplied very li t t le , i f any.

Morrison-Dakota Contact

The contact of the Dakota(?) sandstone with the under- lying Morrison formation is marked by an erosional unconform­ ity (PI. 3). The contact is easily visible in the southern part of Black Mesa where the Dakota (?) sandstone rests on the Cow Springs sandstone member of the Morrison formation, but farther north where it overlies the Westwater Canyon sandstone member, the contact is more difficult to distinguish. From a distance, the two sandstones appear similar, but upon close inspection a distinct difference in lithology can be discerned. In some parts of the region a basal conglomerate (PI. 3) occurs in the Dakota (?) sandstone, thus facilitating separation. In other parts, especially to the south, both conglomerate and sandstone are absent at the base and a dark gray shaly mudstone rests directly upon the Cow Springs sandstone (PI. 4 and 5). . The erosional unconformity below the Dakota(?) sandstone apparently represents a considerable passage of time. It 5 9 . marks a hiatus extending from Late Jurassic to what is prob­ ably Late Cretaceous time. Although the Dakota (?) sandstone in this area contains no fossils, its position in the strati­ graphic sequence, conformably below the fossiliferou s Man- cos shale of middle Upper Cretaceous age indicates that it also is probably of Upper Cretaceous age. The Dakota sandstone of the Great Plains consists of a lower and an upper sandstone separated by mudstones. The lower sandstone and the mudstone have: been proven, by faunal evidence (Stose, 1912) to be of Lower Cretaceous age. The upper sandstone (Stose, 1912) is considered to be of Upper Cretaceous age which is the basis for using the name Dakota (?) sandstone for deposits of this type west of the Front Range and for assigning them to Late Cretaceous time. The flora in these sandstones at various localities substantiates the use of this age designation. The Dakota (?) sandstone of one area, however, does not represent the exact time of deposition that it does in other areas for the formation transgresses time planes. It may have started to form during Early Cre­ taceous time and continued forming across the region into Late Cretaceous time. A comparison of the Dakota (?) sandstone of Black Mesa with units of the Standard Great Plains section (Figure 5) was made by Reeside (1951) based on fauna from the Maneos shale immediately above the topmost beds of Dakota (?) sandstone. TABLE 5 Iron content and mineral composition immediately below Cow Springs-Dakota Contact

Iron Content Cement Heavy Iron Minerals Clay Magne­ Bio- Sample No* Percentage Limonitic Calcareous tite Siderite tite Content# VI 2.33 PP P 1.73 V 2 2.05 PP P 1.56 V 3 1.16 PP PP 1.61 l1 2/1 1.74 P P PP 1.73 2/2 0.86 PP P P 2.51 2/3 0.23 PP P 2.13 3/1 1.57 P P P 1.86 3/2 1.21 P P P 2.19 3/3 0.50 P P P P 3.00 P:Present 6 1 . He found the oldest Maneos fauna to be of Greenhorn time, which suggests that the Dakota of Black Mesa is approximately equivalent to Graneros and Dakota time of the Great Plains. Thus, even in its most limited form, the hiatus represents the entire period of Lower Cretaceous non-deposition. The surface on which Dakota(?) sandstone deposition began was examined in d etail. South of Cow Springs Trading Post, the upper portion of the Cow Springs member of the Morrison formation appears to have undergone considerable alteration. The white to greenish-gray color of the sandstone in most places, here is much greener, the rock is firmer and tends to weather into a ledge. The existence of a soil developed prior to or contempor­ aneous with the formation of the Dakota (?) sandstone was there­ fore suspected. The iron content of the sands of three localities was determined at six inches, 18 inches, gnd 5 feet, below the contact. The results show a progressive decrease in iron content below the contact, however, no mineralogical differ­ ence in the iron minerals could be found. Table 5 is a sum­ mary of the results. All of the iron-containing heavy minerals were examined for evidence of possible alteration, but none was found. The heavy mineral separate made up less than one- half of one per cent of the total. Thus, the thesis that pro­ gressive change in iron content in these rocks is due to an / old soil lacks supporting evidence. The clay content of each 62. of the above samples was determined by a volume- per cent settling method as given by McKee (1951)• The results do not show any progressive increase in fine material. Results of this study do not indicate a mineral alteration or progressive textural change which might be attributed to the preservation of old soil. A secondary origin for the iron-content variation des­ cribed above seems probable. A leaching of iron from the over- lying Dakota (?) sandstone, which contains large iron concre­ tions, and subsequent deposition of the iron in the underlying Cow Springs by ground waters, satisfactorily accounts for the progressive downward decrease in iron content. Many of the:; sandstone deposits of the region have a very hard, iron-ce­ mented layer within a few inches to 6 feet of the top. This suggests a secondary concentration of iron material along bedding planes. Channelling along the Morrison-Dakota(?) sandstone unconformity is perhaps the most apparent feature supporting the belief that there is an extensive erosional interval be­ tween these formations. The channels can best be seen in Coal Mine Canyon (PI. 16, fig . 1 and fig . 2), Blue Canyon (PI. 15, fig . 3), and Marsh Pass (PI. 15, fig . 2). In Blue Canyon three channels were plotted and strikes determined and were found to be in a general east-west direction (Fig. 7). In Coal Mine Canyon other channels were examined and the trends likewise were found to be east-west. 6 3 .

Channels Present drainage

Fig. 7 .-Trends of Pre-Dakota streams as seen in channels in Blue Canyon 64. At Marsh Pass is an excellent example of channelling cut into the Westwater Canyon sandstone member of the Morrison. The total depth of the channel is 20 feet and the width 120 feet (PI. 15, fig. 2). 65o

CHAPTER VI

CRETACEOUS STRATIGRAPHY

DakotaC?) Sandstone

General

The oldest formation of Cretaceous age found in the Black Mesa area is that which Gregory (1917, p. 69) believed to be the Dakota sandstone. The Dakota (?) sandstone of Black Mesa is separated from the underlying Upper Jurassic rocks by an erosional unconformity. The basal Cretaceous sandstone of Black Mesa should be called the Dakota (?) formation for it contains numerous layers of siltstone, claystone, and coal, in addition to sandstone (Pis. 3» 4, and ?)• Sandstone beds form the lower part of the group with lenticular conglomeratic masses at the base. Near the top the Dakota (?) sandstone contains more siltstone and i t is covered by a coal bed. The basal conglomerates of the Dakota (?) sandstone are present in the northern part of the area, but not south of the Cow Springs Trading Post (PI. 3). The sandstone unit in the Dakota is thickest at the north end of Black Mesa 6 6 . but splits into two parts, separated by shaly mudstone near Cow Springs Trading Post (PI. 3)» The lower sandstone unit is absent farther south in Blue Canyon (PI. 19, fig. 1) and the upper sandstone is very thin there. Siltstones and clay- stones are minor features in the north but they are the pre­ dominant rocks in the southern part of Black Mesa (PI. 19, fig* 2). Coals persist throughout the area. The Dakota (?) sandstone forms the crest of the lower es­ carpment of Black Mesa (PI. 13, fig. 3), protecting the soft­ er underlying Jurassic rocks. At intervals along the mesa the Dakota (?) sandstone is concealed beneath an alluvium cov­ ering as east of Red Lake Trading Post and south of Marsh Pass, but at all other places in the area it is conspicuous. The Dakota (?) sandstone is thickest in the northern part of Black Mesa, and is progressively thinner toward the south­ west (PI. 3)* In Marsh Pass it is 132 feet thick but in the southwest at Coal Mine Canyon i t is 50 feet. In a north to south line from south of Cow Springs Trading Post to Blue Can yon (PI. 4) it thins from 104 to 34 feet which is the mini­ mum thickness found in the area. In an east-west line from Blue Canyon to Coal Mine Canyon, i t thickens from 34 to 50 feet (PI. 5)« Thus, in general, it is thin in the southern part of Black Mesa and thick in the northern portions.

fr 67 Dakota-Mancos Contact

The contact of the Dakota (?) sandstone with the overlying Mancos shale is easily distinguished. It is marked by the first evidence of marine deposits according to the writer *s views. Some geologists, (Reagan, 192!), 1926, 1932) (Gregory, 1917) however, have limited the name Dakota (?) sandstone to only sandstones and eliminated all shale and coal beds.

Conglomerate Member

Texture. -The basal conglomerate of the Dakota (?) sand­ stone is best seen in the Marsh Pass region. South of Cow Springs Trading Post, the conglomerate is not present (PI. 4 and 5)<» At Coal Mine Canyon 24 miles to the south is a sand­ stone conglomerate but gravels other than sandstone are rare. The basal conglomerate in the Dakota(?) sandstone is very lenticular and in places appears as a superimposed series of lenses, 10-20 inches thick and up to 30 feet in length (PI. 17, fig s . 1 and 2). Locally pebbles occur scattered through­ out the basal sandstone (PI. 17, fig . 4). A gravel count based on fifty specimens show (Table 6) the pebbles to be sub­ rounded (0.6) with a sphericity of 0.81. The matrix is com­ posed of a medium-grained yellowish gray sandstone which is a subgraywacke in places. Few unaltered feldspars are pre­ sent but the aggregation of included clay minerals indicates 6 8 TABLE 6 Data obtained from a 50-gravel count

Sample Number 1-1 5-1 2-1 19-1

Size 9.2 12.7 14.6 10.1 Maximum size 2xl&xl& 2x1x24- 2x1x14 2x2x14- Sphericity 0.81 0.73 0.76 0.52 Roundness 0.6 0.5 0.6 0.42 Shape Class I 17. 0% 19.0% 18. 0% 0.21 Class II 64.0% 69.0 73.0% 0.36 Class III 13. 0% 23. 0% 5.o% 0.27 Class IV 6. 0% 5.0% 4.0% 0.16 Composition Quartz 8. 7 3 4 Chert 16 12 32 6 Jasper 7 5 7 2 Limestone 2 4 —- Sandstone 4 2 1 22 Quartzite 6 14 2 9 Altered volcanics 7 6 5 7 Matrix . 4 10 mesh (Congl.) 86.3 67.5 72.1 Very coarse 4.1 5.6 3.1 Coarse 1.4 5.4 4.0 Medium 2.4 13.4 12.2 Fine 3.4 5.2 5.2 Very fine 1.5 1.6 1.9 S ilt and Clay 0.7 1.3 1.2 Cement 1.0 0.8 4.4 69. that they once were there. Conglomerate 5 miles north of Cow Springs Trading Post consists of cemented pebbles lying on the Cow Springs-Dakota contact. The bed in most places has a thickness of only one pebble and only locally extends more than a foot later­ a lly . The grouping of pebbles suggests remnants of old drainage channels where residual material was collected (PI. 17, fig . 3). A sequence of continental deposits such as would be expected in advance of a transgressive sea are flood plain types in which conglomerates of the type described would represent sediments of the stream channels (Pi. 18, fig. 3). Somposition.-Conglomerate of the Dakota (?) sandstone^ contains gravels which are composed of quartz, quartzite, chert, jasper, flint, altered volcanics, and locally, lime­ stone and sandstone (Table 6). In Coal Mine Canyon, the gravels are composed almost exclusively of a subrounded, light gray sandstone. The matrix is a aedlum-to fine-grained sand. Cement in the conglomerate is calcite and limonite with some silica. Locally, clay minerals forms a bonding material and no cement is present (Table 6). In places, lenticular masses of the conglomerate are completely covered with an iron crust. This results in a very yellow color and a brown­ ish-red top to the deposit. Primary Structures.-Primary structures in the basal conglomerate are not abundant. Their lenticular nature is 70

feet

Sondstone

3ZH? 30 feet

.^ui-d 1.-- V *ticnl an i 1., *nl v r i •: . Lens In . e .' :o u ? sandstone - jouth of Gov j r*i r * d i " o s t •

1 -l-’O o v.T^i < x x ~ c , f 1 ? in r s

Flood plain L a g o o n a Marine Facies Facies Facies

muds

n 71. the most conspicuous feature (PI, 17, fig, 1), No orienta­ tion of individual gravels with respect to one another is noted but they lie with long axes parallel to the bedding planes. Where the conglomerate is scattered throughout the basal sandstone there is in places an aggregation of gravels along cross-lamination planes. The beds have a thickness of only a single gravel. The basal conglomerate is generally in lenticular mas­ ses which overlap one another, but in places, they appear as superimposed layers up to 20 inches in thickness, separa^ ted by 4 to 10 inches of medium- to fine-grained sand. Cross-lamination is not characteristic of the conglomerate.

Sandstone Member

Texture.-The sandstone in the Dakota (?) sandstone is mostly fine-grained, yellowish gray and cross-laminated. In places, the beds are thick and massive, but most individual layers are irregularly lenticular. Some beds are soft and weather readily, but others are firmly cemented and stand as ledges. The sandstone in many places contains mud pellets or shaly, fine-grained sandstone pebbles (PI. 19, fig. 3). Most mud pellets tend to concentrate along bedding planes which causes a honeycomb type of weathering. The average median diameter obtained from the analysis of 42 samples of Dakota (?) sandstone is 0.19 mm. This med- 72 - ian diameter corresponds to the "fine-grain11 portion as giv­ en in the Wentworth classification . Average grain size can best be visualized by referring to the histograms (Fig. 8 and 9)« The degree of roundness is as follows: angular, 5 per cent; sub-angular, 2? per cent; sub-rounded, 55 per cent; and rounded, 15 per cent. Thus a majority of grains are partly rounded. Many also are spherical. Average sphericity ranges from 0.85 to 0. 93} showing that the grains have near­ ly equal axes. Most individual grains are clear or have a pitted surface between conchoidal fractures. The appear­ ance of the grains is similar to that of grains of the Cow Springs sandstone. The average sorting coefficient of 42 samples is 1.26 which is well sorted according to Trask's method and "fair sorted11 according to Payne's method. The average percentage of well sorted samples is 28, while 60 per cent are "fair sorted". The coefficient of skewness is 0.17 which shows that, in general, samples tend to skew in the direction of the coarser material. Composition.-The sandstone member of the Dakota (?) sandw stone is composed of 92 to 95 per cent crystalline quartz grains with 4 to 7 per cent feldspar, a ll of which are so greatly altered that the variety is indeterminable. A sin­ gle fragment of andesine was identified. Many grains are covered with alteration products. Limonitic material occurs as a stain, coating the quartz grains. Clay is another a l- 73

o o O Irx C\J O O Ux CM \D O O O Irx OJ O Vr> OJ H o O O Vx cxj vO • • • • • O Irx CM i~i o H O O O O e • e e • H O O O O

Fig, 8,-Grain size distribution in sandstone member of Dakota (?) sandstone. 74

• • • • • • O O O IrxCM O HO CM O O lr\Xr\ CMvO H O O O O

sandstone. VO cm CM H CM O K -8-5 • • • • O lP\ OlP\ O O iTs c\] o o o o K -9-3 TTTT~ n n 000*1 Fig. 9.-Grain-size distribution in sandstone member Dakota (?) g. Gr n-ie st buton i ape o Cw Springs Cow of samples in n tio u ib tr is d -size in ra -G . 6 . ig F J J c s—1— 1

0 .2 5 0 i m sandstone. n h \ r X O O (\jO lf\ \D O O O • • • » • • o o o nun. o o o o m c i - r Vr\ o oj

74a 75. teration product that adheres to the quartz grains. The clay content Increases upward in the section. Heavy mineral separates from the sandstone member aver­ ages approximately one-half of one per cent of each sample. The order of Importance of the heavy minerals (Table 4) is as follows: zircon, by far the most common In a majority of samples; leucoxene and tourmaline, equal to zircon in some. The three minerals generally occur as sub-rounded grains show­ ing considerable pitting on the surface of grains, however, zircon also appears as elongate prisms with only sligh tly rounded edges. Garnet is present in most samples in minor amounts. Sandstones of the Dakota are "first-cycle" orthoquartzites. Pettijohn (1949, p. 242) points out that such orthoquartzites are the result of intense chemical weathering with only quartz, tourmaline, and zircon being able to survive. Goldstein (1950, p. 89) believes the Dakota (?) sandstone to be a first- cycle orthoquartzite representing a very long period of ac­ cumulation. His reasoning is that today the amount of zir­ con and tourmaline in the streams draining the Front Range is very small and that only with the passage of time could the present day streams accumulate percentages comparable to that found in the Dakota (?) sandstone. Both rounded zircon and subhedral and euhedral zircon grains are present in the Dakota (?) sandstone. These repre­ sent two stages or generations in the supply of this mineral 76. according to Goldstein (1949, p» 89)• The evidence shorn by samples (Table 4) from Black Mesa tends to support the con­ clusions drawn by Goldstein on the basis of Colorado samples though the sources of the sediments must have been greatly separated. There is a definite decrease in the heavy mineral con­ tent of the Dakota (?) sandstone toward the southwest (Table 4)e This may be due to a decrease in sandstone and an in­ crease in sandy mudstone in the Dakota in that direction. The absence of less stable heavy minerals in the Dakota (?) sandstone is no evidence that they were not present originally. Secondary alteration through ground waters may have caused their alteration and removal. Primary structures.-Primary structures in the Dakota (?) sandstone consist of cross-lamination and of irregular lenti­ cular bedding. The cross-lamination is principally the nor­ mal festoon and low-angle compound types. Statistical studies of direction and amount of dip were made for these in order to determine the direction of the source of sediments. The methods used were those recently described by Weir (1951)• . A stereographic projection was used to rotate the effect of the monoclinal dips back to a horizontal plane, thereby ro­ tating the cross-bedding to its originaljposition. The method of illustration is that followed by Weir (1951), Polar coordinate paper is used and divided into 10 degree segments. Equally spaced concentric circles are drawn 77* about the center of the net and represent the number of read­ ings, The number that falls within any one 10 degree seg­ ment is plotted by blacking out the segment to the correspond­ ing concentric circle (Fig. 10). To determine the average direction of the laminations, the latitudes (Cosines) and the departures (Sines) are determined for each reading. The Sines are positive in quadrants one and four, and negative in qua­ drants two and three. The Sine and Cosines are then added algebraically and the results substituted in the formulas

Tangent of Average Direction Angle * Sum of Sines Sum of Cosines

The signs of the "Sum of Sines" and the "Sum of Cosines" de­ termines the quadrant of the average direction. The reliability of any one reading in relation to the average is determined through a consistency factor (Reiche, 1938, p. 905)• By this method the number of readings neces­ sary to accurately determine the average direction can be found by substituting in the following formulas

Consistency factor * V^Sum of Sines)2 4 (Sum of Cosines)2 No. of readings

The results of the calculations made on readings taken in the Dakota (?) sandstone can be seen in Figures 10, 11, and 12. Horth 78.

Figure 10.-Dip bearing of cross-laminations is Dakota (?) sandstone, south end of Marsh Pass 30 readings Each interval-one division Corrected for 20°, N 74 E Regional dip Average degree of dip- 18 _ Resultant dip direction - N 16 E Consistency factor - 0.49 North 79.

Fig. 11.-Dip bearing of cross-laminations in Dakota (?) sand- stone-1 mile south of Cow Springs Trading Post. 30 readings Each interval-one division Corrected for 15°, S 10 E Regional dip Average degree of dip-24 Resultant dip direction - N 1° W Consistency factor - 0.70 N o r th 80.

Fig. 12.-Dip bearings of cross-laminations in Dakota (?) sand­ stone-north end of Marsh Pass. 30 readings Each interval - one division Corrected for 26° S 62 E regional dip Average degree of dip - 16° Resultant dip direction N 21 W Consistency factor - 0.49 81, The average dip direction is to the north and east (N 21 W, N 1 W, N 16 E, N 37 E, N 29 E, and N 12 E), thus showing an origin of the sediments to the south anti west. Sandstones of the Dakota (?) sandstone are characterized by the irregularity in the individual layers. To determine the nature of the bedding in the Dakota (?) sandstone a study was made on a 250 foot section along the strike. The results are shown in Plate 20, fig. 1. Rarely is a layer found which persists for 250 feet. Individual beds pinch out, giving way to a similar sandstone but separated from it by a thin shale layer.

A 40 foot section of a thin-bedded portion of the sand­ stone was carefully measured and the results are shown in Plate 20, fig. 2. This section well illustrates the lenticu­ lar nature of the sandstone. The lenticular sandstones are often replaced laterally by sandy siltstones which, within a few feet, again become sandstone. One section south of Cow Springs Trading Post was carefully examined and measured (PI. 8 and p i. 9). This sec­ tion indicates the sandstone relationships which are typically present. The shales were deposited, followed by a period when very li t t le cla stic sediment entered. The hiatus is repre­ sented by the thin black shale layer. Subsequently lenticular sandstones were deposited. Inclusions.-The sandstone member contains a very prom­ inent iron concretion layer in the basal sandstone or immedi­ 8 2 . ately overlying it. The iron is in the form of limonite, hematite and, locally, pyrite. Several thin layers of py- rite appear to be limonite pseudomorphs after pyrite, but actually are an outer covering of limonite on pyrite. High iron content is a regional characteristic of the Dakota (?) sandstone as illustrated by many wells that draw water from this formation. In some places the water is so high in iron that it is not potable. Interesting inclusions in the sandstone member are the abundant clay pellets (PI. 19, fig. 3)• These are concentra­ ted along bedding planes or on cross-lamination surfaces. A definite concentration of the pellets may give rise to a honeycomb structure upon weathering. The p ellets are composed of very fine sand, silt and clay and some contain evidences of previous bedding. They vary in length up to a maximum of one foot and up to 3 inches in width. South of Cow Springs Trading Post readings were taken on the orientation of clay pellets. The readings on the clay pellets show a general trend of N 30 E which agrees with the slope directions of cross-lamination. Clay pellets in the Dakota (?) sandstone are believed to have been derived from the erosion of shale lenses which are found in the sandstone. Secondary Structures.-Two very interesting small-scale structures occur in Dakota (?) sandstone. One is a rippled- marked surface which is at the top of the sandstone member. The ripple index was determined to range from 3 to 9 with an 8 3 . average of 7. Immediately above the sandstone is a siltston e containing an abundance of carbonaceous material. The car­ bonaceous material concentrates on the bedding planes which are rippled causing them to be conspicuous in cross-section (PI. 22, fig. 2).

Siltstone-Claystone Member

Texture.-The mudstones which are found in the Dakota (?) sandstone are sandy near the base but contain more clay near the top. The color is another distinctive feature which shows progressive upward change. The shale is yellowish-gray at the bottom and becomes progressively darker toward the top, where i t is black. The average texture as determined from the analysis of 20 samples is as follows: fine sand, trace; very fine sand, 3 per cent; coarse s ilt , 21 per cent; fine silt, 46 per cent; and clay, 30 per cent. Composition. -The composition of the shales was determined from an individual grain study, as thin sections were not ob­ tainable. The shales contain much carbon which progressively increases upward. The carbon increase is gs follows: lower third, 3.6 per cent; middle third, 7.86 per cent; and upper third, 12.3 per cent. The upper portion of the shales is essentially a lignite. The cement is calcareous and limonitic material. The clays seem to be very important as a bonding agent. Where 84

—SO

C qwo S F » r In a

P:V>.-'-.

F ig u re Local variations in bedding in Dakota(?) sandstone oi fh Cow Sorinrr ^ra1 • ine; » (Sec ^1 on ? ,

P I. 20 . 8 5 . the clay is the bonding material the calcareous content is negligible. The limonitic material is present in all cases. Primary Structures.-The primary structure present in the shale is negligible. In general, they are fissile to lam­ inated with plant fragments on the bedding planes. In a ll parts of the area, these shales are yellowish gray at the base and become progressively darker upward becoming lign ite near the top. in many places, overlying the lignite, there is an underclay which is flint-like in character, and is a dark gray, very hard siltstone containing excellent plant fragments (PI. 21, fig . 1). Immediately overlying the underclay is a sub-bituminous coal which is, in part, lignite. The coal contains bone (im­ purities) layers up to 12 inches in thickness. The coal is being mined at Coal Mine Canyon (Pi. 21, fig . 3) and trucked to Tuba City for use by the Indian Service. It is within one of the siltstone bone layers that ex­ cellent leaf impressions are obtained (PI. 22, fig. 1). The bone layer can be traced laterally for several miles in Long- house Valley. The coal is very irregular and tends to split into many thin layers separated by bone. The lower contact of the coal is very irregular but the upper contact is generally smooth. A section south of Cow Springs Trading Post was closely ex­ amined and the result is shown in PI. 18, fig. 2. The section well Illustrates the entry of bone layers with subsequent 8 6 . splitting of the coal into two layers.

Coal

The only coal of economic value in the Dakota(?) sand­ stone is the uppermost unit of the formation. The Coal Mine Canyon mine is the only active mine operating in the Dakota coal (PI. 21, fig. 3)• The coal varies in thickness from less than a foot up to 7 feet and is of sub-bituminous rank. Coals are commonly analyzed in two distinct ways. The fir s t is to determine the uncombined elements giving the pro­ portion that each is to the whole and is called the "ultimate analysis". The second method subdivides the coal into units which are based on coke-oven practice, so that laboratory re­ sults will accord with the manufacturer’s results. The units are as follows: (1) Moisture, to determine which, the coal is heated for a specified time to a temperature sligh tly a- bove the boiling point of water. The weight loss is then as­ sumed to be the moisture loss"by the coal. (2) Volatile com­ bustible matter, to determine which, the sample is heated to a red heat for a specified time in a covered crucible to pre­ vent burning of the carbon, with only the volatiles being driv en o ff. (3) Ash, to determine which, the entire sample is completely burned, eliminating all but the incombustible ma­ terial. The difference between the sum of the above weight- percentages and 100 per cent is the (4) fixed carbon content 87. of the coal. In commercial practice, the color of the ash is very im­ portant because of an influence on the character of the clink­ ers. The red color is due to the presence of iron and iron lowers the fusing pb.int of clay, shale and any other siliceous material present which results in the formation of clinkers, A red ash is less desirable than a white ash* The B .t.u ., or British thermal unit, content of a coal is the standard way of expressing the heating value of the coal. It is expressed as B.t.u. per pound of coal. One B. t.u . w ill raise the temperature of one pound of pure water one degree Fahrenheit. The B.t.u. content of coal is very important but due to the special equipment required, i t nor­ mally is necessary to have determinations done by a profession­ al firm. The tests described above were run on 12 samples of Da­ kota coal from various parts of Black Mesa and are shown in Table 8. The ash content is higher than that of most coals from western United States which, in turn, is much higher than that in coals of eastern United States. The fixed carbon content is lower than that of Utah or Colorado coals but the moisture content is approximately the same. The volatile matter is lower in the Black Mesa Coals. In general, the Dakota (?) sandstone coals of Black Mesa are of a poorer grade than the average western coal now being mined, however, the formation of clinkers in them is much less. The ash of the 88 TABLE 8

Proximate analysis of Dakota coals of Black Mesa

Mois- Volatile Fixed Ash B .t.u . Ash Location of Samples ture Matter Carbon color Goal Mine Canyon Sample No. 1 9.9 31.4 44.5 14.2 W Sample No. 2 10.3 33.8 42.3 13.6 io,55o w Blue Canyon 12.6 35.4 38.6 13.4 RW 3 miles north of Blue Canyon 8.5 39.6 39.1 12.8 R South of Cow Springs Trading Post Sample Lower Coal 9.3 33.7 42.5 14.5 R Sample #1 Upper Coal 10.1 31.1 44.4 14.4 W Sample #2 Upper Coal 8.7 29.5 47.3 14.5 R South End Marsh Pass 10.4 34.3 42.5 12.8 R Longhouse Valley 9.8 37.2 39.4 13.6 R North End Marsh Pass 9.8 38.6 40.1 11.5 RW Dump at Coal Mine Canyon 9.5 32.5 44.6 13.4 W Storage Stack at Tuba City 9.8 33.4 43.1 13.7 w

R-red color ash RW-reddish white W-white 89. Coal Mine Canyon coal tends to powder. Natural ash is found where coal has burned out (PI. 23, fig . 2). On the north rim of Coal Mine Canyon, coal beds are now burning (PI. 23, fig . 1). The overlying material has slumped, opening large cracks to the surface which act as natural chim­ neys. Thin whisps of smoke rise from the cracks and, where the smoke emerges, there is a considerable sublimate of sul­ phur deposited (PI. 21, fig . 2). The burning area was ex­ amined in the summer of 1949 and again in the summer of 1950, and at both times was found to be burning with an equal in­ tensity. The combustion is very slow but intense heat is generated. Shales above the coal have been melted, creating a natural slag (PI. 23, fig. 3) and in this slag L. F. Brady (1939, p. 20) found remnants of Gastropods. Experimental work at the United States Geophysical laboratory showed that a temperature of 1200 degrees Centigrade would melt the shale, but it was not enough to melt the silica of which the fo ssils were composed (Brady, 1939, p. 20). Secondary Structures.-A minor structure of significance is small sandstone dikes in the coal member at the south end of Longhouse Valley (PI. 24, fig. 1). The dikes in few places exceed 3 feet in depth, but extend along the strike for at least five feet. Sand-Shale Ratio of Dakota (?) Sandstone.-The Sand- shale ratios and Sand-coal ratios for the Dakota (?) sandstone are given in Table ?• There is a progressive decrease in the 90.

TABLE 7

Sand-shale Ratio of the Dakota (?) Sandstone

Section number Sand-Shale ratio Sand-Coal Ratio NORTHEAST •- SOUTHWEST SECTION (PI. i ) K -ll 3.2 13.3 K-10 9.7 14.8 K-5 9.7 24.0 K-7 1.9 15.7 k-6 2.6 32.3 K-13 2.7 19.0 K-2 3.2 13.3 K-20 5.8 4.6

NORTH - SOUTH SECTION (Pi. 4 ) K-2 3.2 13.3 K-18 1.7 15.7 K-17 1.1 15.7 K-16 1.9 13.3 K-15 5.0 5.3 K-9 0.48 2.8

EAST - 'WEST SECTION (PI. 5) K-21 2.3 3.4 K-19 4.6 2.7 K-20 5.8 4.6 91. Sand-shale ratio toward the south which, in continental deposits, suggests a nearness to the old shore line. The Sand-coal ratio is also decreasing toward the south which indicates an increase in the amount of coal in proportion to the other sediments. The decrease in the coarser elastics indicates the low relief of the land furnishing the sedi­ ment. The seas were near their maximum advance as is shown by the predominance of shale and coal.

Flora and Fauna

No fo s s il fauna has been found in the Dakota (?) sand­ stone of Black Mesa. F ossil plants in the Dakota (?) sandstone are abundant. In Longhouse Valley a 3 inch bone in the coal seam has yielded many leaf and fern impressions. The collections of this flora have been submitted to Dr. Erling Dorf, Prince­ ton University, for identification.

Depostidnal History

At the close of Late Jurassic time was a long period of erosion. The erosion persisted throughout a ll of Early Cretaceous time and extended into Late Cretaceous time. At any one time, a definite sequence of environments is to be expected (Pi. 18, fig. 3) on a coast of low relief. It 92. should include (1) a coarse-grained sand or gravel represent­ ing the most inland portion of the area of deposition. Sea­ ward the material should consist of (2) fine-grained elas­ tics, essentially sand sizes, followed by (3) elastics of silt and clay size. Behind the beach zone, a lagoonal or swamp environment would exist and i t should contain (4) silt and clay elastics intermixed with plant fragments. The swamps develop into basins for the accumulation of (5) coal. Seaward the last continental environment which would be ex­ pected is a beach environment . In an advancing sea, the above environments would be represented by the following vertical sequence of rocks: 5« Coal 4. Siltstone and claystone with lignite 3. Siltstone and claystone 2. Sandstone 1. Conglomerate The sequence of rocks listed above occurs in the Dakota (?) sandstone of Black Mesa. Basal conglomerate represents the most inland coarse-clastic facies of a flood plain. In places, the lenticular nature of the conglomerate suggests old stream channels developed on a flood plain. Surrounding and overlying the conglomerate is a fin e­ grained sandstone. The lenticular nature of the sandstones suggests a flood plain deposit; It probably originated in the ponds and pools that stop the speed of the streams 9 3 . carrying the gravels and sands. The pools and ponds rep­ resent a temporary base-level of deposition. The disappear­ ance of coarse detrital sediments in the southern part of the Black Mesa area suggests a low relief in the adjoining area to the south, the direction from which the sediment came. Overlying and intertongoing with the sandstone are s ilt - stone and claystone. The claystone is flat-bedded, sandy and contains a progressive increase in percentage of plant fragments until a lign ite is reached at the top. Overlying and intertongoing with the siltston es and claystones is a coal deposit. The coal represents the last continental deposit prior to marine invasion. Theoretically, a beach deposit should overlie the coal, however, no structures typical of a beach (Thompson, 1937s p. 732) are present; instead a near-shore sandstone com­ posed almost entirely of Gryphaea newberrvi Stanton and Exogyra columbella Meek rests with apparent conformity on the coal. The fossil material is not fragmental which sup­ ports the concept of origin as a near-shore sand. Two distinct facies are represented in the Dakota (?) sandstone. One developed in a flood plain environment and caused the differentiation in detrital material. The other facies devolved in a lagoonal environment where fine-grained d etrital and carbonaceous material are mixed. The fin a l product of the lagoonal environment is coal. 94 Three rock types make up the flood plain. These are (1) conglomerate (2) sandstone, and (3) siltstone-claystone. The last unit overlaps into the second facies. The second facies is a lagoonal or swamp type which includes a (4) siltstone-claystone unit and a (5) coal unit. The top of the coal represents the last continental deposit of the Da­ kota (?) sandstone before the transgression of the sea that deposited the Maneos shale.

Maneos Shale

General

The Mancos shale was named by Cross (1899, p. 4), who examined it s exposures, near the town of Mancos, Colorado, In the type area, the Mancos shale overlies the Dakota (?) sandstone and is overlain by the Eocene San Manuel forma­ tion, The name was applied by Cross and Spencer (1899) to shales which lie between the Dakota (?) sandstone and rocks of the Mesaverde group, a ll of which are well exposed along the north face of Mesaverde, near Mancos, Colorado. Use of the name has since been extended into New Mexico, Utah, and Airzona. In northwestern New Mexico the name Mancos shale was applied by Shaler (1907, p* 378) to the shale immediately overlying the Dakota (?) sandstone and underlying the cliff- 95. forming sandstone which he considered to belong to the Mesa- verde group, Gregory (1916) followed the procedure of Sha- ler in naming the Maneos shale of Black Mesa. The Mancos shale of Black Mesa consists of siltstone and claystone, with locally distributed sandstone. Benton­ ite layers are abundant. The shaly mudstone which is the dominant rock is dark gray to black. The sandstone is gray­ ish-yellow and forms lenses, k single concretionary lime­ stone occurs near the bottom of the section. Limey silt concretions and septaria layers are at many horizons and at the base of the Mancos is a sandstone which is highly fossiliferous (PI. 24, fig. 2). In most places, as along the east side of Klethla Valley, this sandstone varies with­ in short distances from a few inches to 20 feet in thick­ ness. It is yellowish gray, weakly cemented, more or less flat-bedded and, because of its distinctive lithology and fossiliferous nature, can easily be distinguished from beds of the underlying Dakota (?) sandstone. The upper third of the Mancos shale contains many thin sandstone layers which, as illustrated in Blue Canyon, typically form ledges. The fauna in the Mancos shale is quite varied and diag­ nostic. On the basis of a collection by the writer, Reeslde (1951) places the lower portion (up to 30 feet) of the Man­ cos shale in this area as equivalent to the Greenhorn limestone of Gilbert and he considers the upper Mancos of this area equivalent to the lower member (Fairport) of the 96, Carlile of the Great Plains. Thus, the Maneos of Black Mesa is equivalent to the lowermost part of the Mancos shale of the San Juan region. The lower sandstone is designated the "basal sandstone memberu. O verlying the b a sa l sandstone member, the lower two-thirds of the Mancos shale consists of claystone and siltstone with the claystone predominating. This portion is termed the “claystone member". The upper third consists of s ilt s t o n e w ith minor cla y sto n e and sandstone and i s termed the " s ilts to n e member". The uppermost s ilt s t o n e w ith very thin sandstone layers is called the alternating siltstone- sandstone member. At the north end of Marsh Pass the Mancos is 628 feet thick. Five miles north of Cow Springs Trading Post it is 550 feet (PI. 1 and 6) and one mile south of Cow Springs Trading Post it is 562 feet thick (Pis. 2 and 6). In Blue Canyon (Pis. 2 and 7) south of the other sections, it has a thickness of 600 feet. Member thicknesses are given on Plates 6 and 7» Thus the Mancos shale thins toward the west and south, with its thinnest portions in the extreme west.

Dakota-Mancos Contact

The Dakota-Mancos contact is placed arbitrarily below strata containing the lowest marine fauna. This is, in most places, immediately above the uppermost Dakota coal 9 7 . seam. South of Cow Springs Trading Post a 25 foot fo s s ll- iferous sandstone rests directly on the coal (PI. 24, fig. 2). At the north end of Longhouse Valley (PI. 1) no sand­ stone is present but at the south end a 22 foot fossilifer- ous sandstone rests on the coal. At Tsegi Trading Post in Marsh Pass a very thin, sandy, oyster-bed occurs immed­ iately above the coal. At Blue Canyon no sandstone is pre­ sent, however, at Coal Mine Canyon a near-coquina lie s immed­ iately over the coal. The abundance of fossil evidence in the basal portions of the Maneos shale makes the lower con­ tact easily determined.

Basal Sandstone Member

Texture.-The basal member of the Mancos shale consists of a yellowish-gray, medium- to fine-grained, thick-bedded sandstone which, in part, is near coquina in nature. The median diameter of the sand as determined from 16 samples is 0.16 mm. (Fig. 13). This places the sandstone in the "fine sand" category of the Wentworth classification. The degree of roundness of grains is as follows: angular, 10 per cent; sub-angular, 30 per cent; sub-round, 40 £er cent; round, 20 per cent. Most of the grains consist of clear vitreous quartz with 50 per cent having pitted surfaces. Specimens from the basal sandstone member are "well sort­ ed" according to the classification of Trask (1932, p. 72) 9 8 .

CM H CM O i T x • • • • • • O(M O p Xf\ O O O vO lr\ CM H O O O O

stones. sandstone Lower of shale. member Mancos

000 Fig. 13.-Histograms and cumulative curves of typical sand­ 99. as their coefficients of sorting (So) vary between 1.1 and 1.2. This sorting is much better than the average of 1.45 given by Stetson (1937> p. 57) as the coefficient of sorting for a near-shore sand. McKee (1945, p. 41) gives a range from 1.2 to 1.94 for the Tapeats sandstone which he considers to be a near-shore sand. The range of sorting shows the ba­ sal sandstone member of the Maneos shale to be better sorted than the near-shore Tapeats sandstone. The sphericity of grains in the basal sandstone varies between 0.79 and 0.95 with the great percentage having near- equal dimensions. The coefficient of skewness varies from -0.05 to 0.05 which shows the sands to be about equal in amount of coarse and fine material. The sandstone member of the Maneos shale consists of 15 to 30 per cent shells (PI. 24, fig . 2). These are not frag­ mental but complete sh ells. Gryphaea newberrvi Stanton has a small upper, value which in many beds is in or near it s liv ­ ing position, an indication of the lack of any appreciable wave action during deposition. Composition.-Composition of the basal sandstone member of the Mancos shale ranges from 70 per cent quartz and 30 per cent shell fragments to 85 per cent quartz and 15 per cent shell fragments with an average nearer the former. Feldspar is noticeably absent in the sandstone. It contains consider­ able silt and clay as is to be expected for this sandstone grades laterally into siltstone and claystone. 219722 100. Three heavy mineral separates were determined, (Table 9) for the basal sandstone. They show a striking similarity to the separates from the Dakota(?) sandstone (Table 4). Zir­ con is by far the most important heavy mineral, with tour­ maline second. The zircon has rounded edges and locally is completely spherical. The tourmaline varies in color and is also rounded. Leucoxene which shows evidence of alteration, is common. Limonite and hematite are present as mineral grains and as a stain on grains of other minerals. Rutile is also present in variable amounts. The cement is calcareous and lim onitic, and a minor amount of clay bonding is present. Primary Structures.-Primary structures in the basal sand­ stone member are noticeably absent. Neither cross-lamination nor bedding can be recognized. The sandstone contains an abundance of fossil material but no structures related to alignment or layering of the fossils are apparent. Fauna.-The basal sandstone member of the Maneos shale is a near-coquina, in places (PI. 24, fig. 2). On the bas­ is of a collection by the writer, Reeside (1951) reported : the following faunas present in the basal sandstone member.

Exogyra columbella Meek Ostrea prudentia White Gryohaea newberryi Stanton Exogyra olisioonensis Sharpe var. forresteri Reeside Alectnyoria, sp. Exogyra perpelxus Whitfield Nenitae, sp. 101. The above fauna is equivalent to that of the "Greenhorn lime­ stone of Gilbert, i . e . , of the Bridge Creek member of the Greenhorn of western Kansas (Reeside, 1951)•

Claystone Member

Texture.-The average median diameter of the d etrital particles in fine samples from the claystone member is 0.003 mm. which falls within the coarse clay size of Krumbein and Sloss (1951) p» 71) clay classification. Complete textural analyses were made using the continuous-recording density­ settling device and the results obtained from three samples are shown in Figure 4. Composition.-The claystone member of the Maneos shale is composed of tiny quartz grains with various unidentified minerals. The calcareous content of the claystone is less than 10 per cent. This member is predominantly a black shale Beds of light gray and yellowish gray shale occur but rarely exceed 10 feet in thickness. Because these mottled yellowish gray and black mudstones weather to a .light o liv e, the Maneos has been referred to as "olive drab" by many writers. Most of the shaly mudstone in this member of the Mancos on Black Mesa are of the mottled variety with black dominant. This black color is due to the carbon content of the claystone (Table 10)» The mottled effect is believed due to partial oxidation of carbon before burial. 102. TABLE 9 Heavy minerals in the basal sandstone member of Mesaverde group......

0 ...... - — .... - ...... - 1 ...... - — ? 0)

o ©TOiiH S I O> o O b o U2...... Barite Garnet Illmenlte Epidote. Clinozoisite Hornblende Limonite and Hematite Tourmaline a Titanite Zircon ^ Kvanite ^ K-2 2 - 9 9 9 7 2 3 31 37 * K-13 11 11 14 5 2 4 37 27 K-7 1 7 7 12 9 * 2 30 39 103. n 11 ! i TTTTT K-5 — 9— K-2 — 9 — K-9 _8__ _8__

_7 __ — 7 — _ O--

- ! > - — 4__ — 4 — — 3 _ — 3 — — 2_ l T“2 — I 1 _ r L i _ 1 0 __rr 1 o i t 64 afs 1024 32 128 ya^ A.-Grain-size distribution in claystone jhember of Mancos shale.

Fig. 4.-Results of continuous recording-density-settling ap­ paratus. 104. Primary Structures.-The claystone member of the Mancos shale is a variegated claystone with alternating light and dark laminae. The laminae are essentially horizontal, but con­ tain many minor variations, such as thickening and thinning of individual laminae. The light laminae contain a higher percentage of silt than do the dark laminae. Rubey (1931, P» 52) notes that alternating light and dark laminae may be due to variation in any or all of three factors: (1) coarseness of particles, (2) amount of organic matter, and (3) amount of calcium carbonate and s i l t . The presence of coarse and fine particles is undoubtedly the cause of many of the laminae in the Mancos shaly mudstones. A variation in carbon content may also be a cause of laminae but the presence of calcium carbon­ ate probably is not important in the Black Mesa deposits. Several samples of the claystone member were examined in an effort to relate fissility to structural causes. Dif­ ferences in alignment of individual grains are noted but nothing sufficiently pronounced to explain the degree of fis­ sility in the claystone. Inclusions.-The claystone member of the Mancos shale in­ cludes about 30 feet above its base a concretionary limestone with an abundance of fossils. The concretions are ovoid in shape and form a very pronounced series of knob-like eleva­ tions. They have concentric layers composed of silty lime­ stone with structureless centers. Such concretionary lime­ stone according to Pettljohn (1949, p. 299) represents an 105. TABLE 10 Carbon content of black shale in Maneos shale

Per cent Per cent Sarnnle No. Carbon Sarnnle No. Carbon K-2-10 1.72 K-9-15 2.61 K-2-13 1.08 K-9-17 2.75 K—2—16 2.32 K-9-22 3.56 K-2-17 1.76 K-2-23 1.28 K-2-19 1.94 K-9-25 3.02

K-2-21 i a i K—9—26 1&22. Average I.69 Average 3.07 K-5-7 1.71 K-19-6 1.62 K-5-7 1.56 K-19-7 1.73 K-5-10 1.42 K-19-8 1.80 K-5-13 1.59 K-19-9 2.22 K-5-15 2.03 K-19-10 3.09 K-5-15 1,72 K-19-11 i* ia Average I.67 Average 1.93 K—13-14 1.56 K-13-14 2.38 Total Average 2.17 K-13-16 3.56 K—13**l8 2.57 K-13-21 1.89 K-13-26 3*05 ' Average 2.05 Sample numbers refer to: Cretaceous, Section No., Unit Ho. (See Measured Section) 106. accumulation of calcium carbonate, probably in low places where currents w ill not disturb i t , and subsequent consolidation and compaction. The cephalopod Baculites is by far the most com­ mon fossil in this limestone, furthermore, the layer is an im­ portant key bed for i t occurs throughout Black Mesa and the fossils help identify it. Fauna.-The lower portion of the claystone member of the Maneos shale contains:

Serpula intrica White Anorrhais prolabiata (White)? Inoceramus fra g ilis Hall Cyrtochilus gracile (Shumard) and Meek Lucina .invents Stanton Exiteloceras pariense (White) Cardium oauoerculum Meek Exlteloceras corrueatum Stanton Lunatia n. sp. and Lunatia Neocardiocera s septemseriatum n. sp. a ff. L, coneInna (Cragin) Hall and Meek Metoicoceras whitei Hyatt Turritella whitei Stanton, Cerithlum, n. sp. Drenanochilus ruidum (White)

All of the above fo s sils occur in or below the limestone con­ cretion bed, 30 feet above the base of the Mancos shale. These fo ssils also are equivalent to the Bridge Creek member fauna of the Greenhorn limestone of western Kansas (Reeside, 1951)o

Siltstone Member

Texture.-The average median diameter of d etrital parti­ cles in five samples from the claystone member is .003 mm. 107. which falls within the coarse clay size of the Kriunbein and Sloss (1951) p. 71) clay classification . The average median diameter in five samples from the siltston e member is 0.015 mm. which is a medium s i l t . The above median diameters are indicative of the difference between the claystone member and the siltstone member of the Maneos shales. Because the Maneos shale is a variegated mudstone with alternating light and dark laminae, a composite mechanical analysis is not reliable unless an equal number of laminae is used. The light laminae contain more s ilt than the dark. Another method to show the textural change from the clay mem­ ber to the s ilt member is to determine the average amount of the coarsest material in the samples of each member. All mechanical analyses of Maneos shale showed small amounts of very fine sand. The percentage generally was less than one per cent. Wet screening with specially cleaned screens was effective separating the sand samples. Ten sam­ ples from the claystone member averaged 0.12 per cent very fine sand. A similar number of samples from the siltston e member averaged 0.96 per cent very fine sand. Thus, the increase in amount of the coarsest material in the siltstone member is shown both by a complete textural analysis (Fig. 4) and by wet screening for the coarser material. Composition.-The siltston e member of the Mancos shale forms the upper portion of this formation on Black Mesa. The siltstone is composed principally of minute quartz grains and 108. clay materials and includes up to 0*96 per cent very fine sand. The presence of the sand is Indicative of the overlapping of shore sands onto the off-shore mud of this member. The presence of the sands is an initial effect of. the change from a transgressive condition to one of regression. Evidence of this change is also found in a color difference-dark gray and black being replaced by yellowish-gray. Some minor deposits of black shale occur in the siltstone member but these rarely are over five feet in thickness. On the other hand, very thin sandy siltstone that shows evidence of having been re­ worked is a feature of the regressive environment. The ceph- alopod Collignoniceras (“Prionotroois”) woollgari (Mantell) is abundantly preserved as external molds on the undersides of reworked layers (PI. 25> fig . 1). The sandy siltston e layers vary in thickness up to 6 feet and locally stand as ledges or slope cappings which collectively form a ridge mid­ way up the slope of the Maneos shale (PI. 24, fig, 3). Primary structures.-The siltstone member of the Maneos shale contains numerous thin, discontinuous layers of a sandy siltstone which have structures indicative of reworking. An abundance of worm trails suggest reworking. External molds of the cephalopod Collignoniceras ("Prionotropls") woollgari (Mantell) on undersides of layers appear to have been broken and fragmented during transportation (Pi. 25, fig . 1). These fo ssils also show evidence of having:: been accumulated by currents in the muds and subsequently buried and preserved by 109. silt. In the clays tone and siltstone of the siltstone member no primary structures have been observed. Inclusions.-The siltstone member of the Mancos shale con­ tains an abundance of concretions which occur singly and in layers (PI. 28, fig. 1). Many form septaria (PI. 26, fig. 3) and in places they are grouped together in layers. The ori­ gin of these concretions involves rolling by currents which enlarged them. This is demonstrated by the abundance of shark’s teeth and other fossils which are concentrated in them. Subsequent compaction of the limestone concretions has caused the larger ones-those above one foot in diameter (PI. 27> fig. 1) to develop cone-in-cone structures on the outer layers (PI. 27, fig. 2). These develop on the tops and bot­ toms, but only feebly on the sides. Gone-in-cone also occurs in flat beds. The origin of cone-In-cone is considered by most geologists to be the result of pressures exerted on the concretion by overlying sediment. Differences in opinion lie as to how and in what combination these pressures were exerted. Richardson (1923, p. 88) advocates an origin of cone-in­ cone structure due to crystallisation pressures in the forma­ tion of calcite, coupled with the load of overlying sediment. Such a theory does not satisfactorily explain the movement of one cone with respect to another. Furthermore, the devel­ opment of the cone has been shown by Tarr (1932, p. 716) to be subsequent to the development of the calcite fib ers. The theory of origin advanced by Tarr (1932, p. 716) is 110 one of pressure and solution# Most geologists favor this theory. According to it, pressures exerted by the overlying load cause shearing to occur and solution lubricates the movement along the shear zones. The presence of minute a- mounts of clay in the shear zones is accounted for as residual material left after solution of the calcite. The cone-in-cone structure in the Maneos shale is be­ lieved to have been formed by the pressure and solution method. Flat-bedded cone-in-cone structure which also occurs in this formation has the bases of cones protruding beyond the surface of the cone layer (PI. 27> fig. 3). This is explained as the result of subsequent removal of load, thus allowing the ernes to resume their original positions (Twenhofel, 1950, p. 6 ll) . Septaria (PI. 26, f i g . 3) occur in abundance in the silt- stone member of the Maneos. The origin of septaria is considered (Richardson, 1919, p . 327) to be (1) formation of a body of aluminous gel, (2) case-hardening of the exterior, dehydration of the interior, and formation of a shrinkage crack pattern, and (3) partial or complete filling of the cracks, thereby producing the vein network of the nodule. Weathering removes all of the material except the box work structure of the vein pattern in some places and the structure is then called a meli- karia (PI. 28, f i g . 2). An excellent illustration is given by PettiJohn (1949, p . 142). Fauna.-Fossils from the siltstone member of the Maneos a re : 1 1 1 . Inoceramus fr a e llls (Hall and Meek) Collignonlceras (Prionotropis") woollgarl (Mantell) They are equivalent to the fauna of the Lower Carlile of the Great Plains. (Reeside, 1951)•

Alternating siltstone-sandston# member

;; Texture.-The uppermost member is a siltstone which con­ tains thin sandstone layers. The thin-bedded sandstone lay­ ers are believed to have formed under near-shore conditions. The sandstone layers become progressively thicker upward. Where sandstone predominates over siltston e, the Mancos-Mesaverde contact has been arbitrarily placed. An analysis of 10 sam­ ples from the siltstone portion shows a median diameter of .033 mm. which is a ncoarse silt" in the Wentworth classifica­ tion. This siltstone contains up to 3 per cent very fine sand. An analysis of 10 samples from the sandstone layers show the median grain diameter to be 0.09 mm. which constitutes very fine sand (Fig. 14). The degree of roundness is as follows: angular, 20 per cent; sub-angular, 50 per cent; sub-rounded, 35 per cent; and rounded, 15 per cent. Most of the grains are clear vitreous quartz. The coefficient of sorting (So) of the sandstone layers is 1.12 which is “well sorted" according to Trask's classi­ fication. In Payne's classification It is “good-sorting". An So of 1.12 is very low when compared to results of Stetson 112

OO o XrN OJ OO irx c\J VO O O O Xtn CU CXrx OJ r-i O O O lr\ C\J vO • • • • • O ITS CM H O rH O O O O • 9 • • • H O O O O

Fig.-14.-Grain size distribution of the alternating siltstone- sandstone member, Maneos shale. 113 o (1937, p. 57) and of McKee (1945, p. 41) who found 1,45 to be typical of near-shore sand. In the Mancos shale the exception­ ally good sorting for a sand believed to have formed near shore may be due to a source which furnished no coarse frag­ ments or may be due to the regressive character of the deposit. The sphericity of the grains varies between 0,59 and 0.89 with the majority being 0.81. The degree of roundness is lower for the fine sediments (Russell and Taylor, 1937, p. 225) than for the coarser sand. The coefficient of skewness ranges between 0.1 and - 0.3 with the average at -0.14 showing that the peak of the frequency curve is on the coarse side of the median. Composition.-The siltston e portion of the alternating siltstone-sandstone member is composed of 85-90 per cent quartz and 10 to 15 per cent clay minerals. The sandstone layers in the siltstone-sandstone member are composed of 96 to 95 per cent quartz and 4 to 5 per cent feldspar. No ce­ ment, except a minor amount of silica, is present, but clay forms a bonding material. Silt and clay content is high, which is to be expected, since the sandstone layers grade lat­ erally into siltstone. Heavy minerals in the sandstone layers do not differ greatly from those of the basal sandstone member. The zir­ con content is high and includes angular prisms. Tourmaline, both clear and pink varieties, and ru tile are present in minor amounts. Muscovite is much more noticeable than in 114. other Maneos shale samples. 4 tabulation of data on the heavy minerals is shown in Table 11, Primary structure.-The siltstone-sandstone member of the Mancos shale is cross-laminated with a low-angle, compound type which is destroyed in many local areas by reworking. Where worm tra ils are abundant, the bedding is lik ely to have been destroyed. The discontinuous nature of low angle cross-lamination made statistical studies impractical. The upper contact of the sandstone layers in the silt- stone-sandstone member is generally smooth and devoid of many surface markings. In contrast, the lower contact in many places has ripple marks, plant fragment impressions, and worm tra ils impressed into i t . The ripple marks are asymme­ trica l and have indexes that vary between 7 and 11. 4n aver­ age direction of the crests is S 30 E (PI. 25, fig. 2). Evidence of reworking is the abundance of worm-trails preserved on the undersides of sandstone beds (PI. 25, fig. 3). Some of these worm-trails measure 2 to 3 inches in diam­ eter. Where the worm-trails are broken ;fr#e of the:.rock they show a characteristic pitted undersurface (PI. 26, fig. 1). In places, as south of Cow Springs Trading Post, the worm trails are so abundant as to give the appearance of a tangled mat of 1 to 2 inch rope. Some of the trails exceed 16 inches in length. In some of the thinner layers of sandstone and siltstone they appear to have destroyed all bedding struc­ tures. 115.

TABLE 11 Heavy minerals in the upper sandstone member . . ___

O 3 s O 0 9CS -P Actinolite and Tremolite Anatite Illmenlte Leucoxene Barite Limonite Limonite and Hematite Eoidote and Clinozoisite Kyanite Rutile Titanite Zircon 1 Tourmaline ......

K-2 * 3 13 4 18 3 2 3 22 28 K-5 1 9 7 27 6 1 2 18 29 K-13 2 17 2 16 9 2 4 23 25 K-19 2 6 9 9 4 7 3 24 36 K -ll * 12 3 17 1 7 6 23 31

♦Present 1 1 6 . The siltstone that separates the sandstone layers of the slltstone-sandstone member contains some very interesting fea­ tures. One is the rippled-bedding which is so abundant (Fig. 15)• Another is bedding that has been destroyed presumably through development of worm tra ils that are represented as casts in overlying sandstone (PI. 25, fig. 3; PI. 26, fig. 1). A third is a group of round concretionary-like tubes with the appearance of a cluster of grapes which extends down into mud­ stone from overlying sandstones (PI. 26, fig. 2). The sand has filled a group of holes in the shales to form these struc­ tures. The holes probably were formed originally by some form of burrowing lif e . The individuals vary from 1 inch to 1/16 of an inch in diameter with many intermediate sizes , in any single specimen.

Secondary Structures in the Maneos Shale

Much of the f is s ilit y in mudstones is of a secondary origin according to Rubey (1931, p. 40). He relates this feature to the amount of folding which has deformed the rock. His findings indicate that the stronger the folding the greater the f is s ilit y . Evidence from Black Mesa tends to support this conclusion. Minor slickensides are also charac­ teristic of the more steeply tilted rocks. F is s ility of the bituminous Genessee shale is attribu- 1 1 7 . inches 18

1 5

12

9

6

3

------15 inches r*.\vvj Sandstone iw—I1...mm.—....»4 — I Shales oal fragments Fig. 15.-Rippled bedding in alternating slltstone-sandstone member of the Maneos shale. 1 1 8 . ted. by Hard (1931) to compaction. He believes the original layers to have been of considerable thickness but this thick­ ness to have been reduced through subsequent compaction which also made the shale fissile. Ho evidence has been found in Black Mesa to support or reject this theory, but compaction under any conditions should reduce the original thickness, unless lateral flow occurs.

Bentonite in the Maneos Shale

At many horizons in the Maneos shale bentonite layers occur (Pi. 29, fig. 1). These bentonites are rarely over 6 inches in thickness but can be traced as much as 3 miles lat­ erally (PI. 24, fig. 3). In local studies, therefore, the bentonites are excellent as time markers. In Blue Canyon where the Mancos shale is exposed with bad-land topography (PI. 12, fig. 2) twelve bentonite beds were traced laterally by walking, but only two, both of which exceeded 6 inches, could be traced more than one-half mile. One of the two was traced along strike for approximately 3 miles (PI. 24, fig. 3). South and east of Cow Springs Trading Post a single ben­ tonite occurs 18 feet below the top of the Mancos shale. Be­ cause of it s position and ease in locating, i t was chosen as a test case. At Columnar Section 2 (PI. 2) only the single 4 inch bentonite bed occurs, whereas 5 miles to the northwest at Columnar Section .13 (PI. 1), five bentonites occur, all of 1 1 9 . which are less than two inches in thickness. Three miles south of Columnar Section 2, at Columnar Section 18 (PI. 2) no benton­ ites were found. A one-foot bentonite bed occurs in Blue Canyon at 246 feet above the base and 114 feet higher is a 6- inch benton­ ite bed. Samples taken every 50 yards for 200 yards were used for settlin g tests to determine the value of such anal­ ysis in using bentonites for correlation purposes. The re­ sults as shown in Table 12, indicate that no appreciable difference occurs between the two bentonites. The conclusion is reached that the bentonites of Black Mesa are important locally as time markers but can not be distinguished from one another. * In Blue Canyon at Columnar Section 5> a bentonite occurs in the top of the Dakota coal seam, which, as traced along the strike, rises in the section. About a half mile along the strike this bentonite has risen into the basal fossilfer- ous Mancos shales. This is an example of a bentonite bed that can be demonstrated to be parallel to a time plane. It gives strong support to the local use of bentonites as key beds and as time markers. In Blue Canyon bentonites are very resistant to weather­ ing because they swell and do not erode except in extremely heavy and prolonged rains. As a result, the area has devel­ oped into a series of benches, each with a swollen bentonite bed as a capping. Leached gypsum from overlying rocks is con- 1 2 0 . TABLE 12 Settling analysis of samples from two bentonite beds

Per cent Per cen t Per cent Sancle No. Coarse silt Fine s i l t . ___ Clay K /l 18.0 16.0 66.0 K/2 23.0 17.0 60.0 K/3 27.0 21.0 52.0 K/4 25.0 14.0 61.0 K/5 19.0 13.0 68.0 K/6 21.0 19.0 60.0 K/7 16.0 17.0 67.O K/8 24.0 21.0 55.0 Average 61.5 k /H 16.0 19.0 65.0 K/12 14.0 21.0 65.0 K/13 18.0 14.0 68.0 K/14 17.0 19.0 64.0 K/15 10.0 20.0 70.0 K/16 19.0 17.0 64.0 K/17 17.0 19.0 64.0 K /l8 14.0 14.0 Z2*0 Average 66.5 1 2 1 centrated above the impervious bentonite beds. Were the heat of the sun has dried the bentonite and the gypsum, a sur­ face which appears quite firm results, but this surface w ill support no weight. When walked upon i t allows a person to sink to his knees in a white gypsum-bentonitic dust (PI. 29, fig . 2). The impervious bentonites are further useful in correla­ tion because ground water cannot penetrate them, hence, vege­ tation that grows in the shales tends to concentrate immed­ iately above the bentonites. This gives a definite alignment to the shrubs and is of considerable help in tracing a ben­ tonite layer (PI. 29, fig. 3).

Maneos-Mesaverde Contact

The Maneos shale grades upward into sand of the Mesaverde (PI. 30, fig. 1 and 2) so an arbitrary contact is selected where sandstone becomes predominate over siltsto n e. This con­ tact is especially interesting because immediately overlying an alternation of siltstone-sandstone, considered a near-shore deposit, is a sandstone believed to have formed as a beach. The formation boundary therefore is at the base of the beach sandstone. The layers of near-shore origin are very thin at the bot­ tom but progressively thicken upward in the formation. Be­ tween these sandstones is a sandy siltstone which shows evi- 1 2 2 . deuce of considerable reworking. Rippled laminae are abundant In the siltstone and In many places the overlying sandstones have rippled under-surfaces (PI. 25> fig. 2).

Deposltional History of the Maneos Shale

The uppermost member of the Dakota (?) sandstone is a coal which represents the last continental’deposit prior to the advance of the Maneos sea. The basin of accumulation must have been sinking to allow the sea to transgress. The fir s t marine deposits to be laid down in the advancing sea were the sands of the lower sandstone member. These are yellowish gray and fine-grained and they contain an abundance of.well-preserved fossils. No evidence of reworking is not­ ed and the fossil evidence indicates that deposition was im­ mediate. The basal sandstone of the Mancos appears to have been deposited in a near-shore environment below the level of in­ tense currents. Lack of bedding cannot easily be explained, but probably is due to continuous deposition without currents of sufficient strength to sort and stratify the sand. .4 con­ stant deposition of sand and marine organism also would explain the lack of recognizable layers. The grains are dominantly of fine-grained sand with a median diameter of 0.16 mm, which is small compared to the 1 2 3 . findings of others (Stetson 1937» p. 57) (McKee, 194$, p. 41) -who have examined near-shore sands. Schalk (1938, p. 41), in his study of a beach on Cape Cod, notes that fine material is carried out by the waves and that it becomes progressively finer off-shore. He also points out that the median diameter of the sand on a beach is a measurement of the amount of fine material that has been carried away by the waves. This empha­ sizes the Importance of currents prevalent at the time of dep­ osition for if the currents are very weak, the percentage of fine material on the beach will remain high. In addition, if only fine material is being supplied and currents are weak then the near-shore sand as well as the beach sand w ill show a very small median diameter. Russell and Russell (1939, p. 171), in his study of the Mississippi delta, notes that the beaches are all “fine sand with very little coarser sed­ iment". He also states that the expected deposits out in the Gulf would be fine sand and s i l t . The basal sandstone member of the Mancos shale is be­ lieved to have been formed as a near-shore sand which was re­ ceiving only fine-grained sediment, deposited in a sea of weak currents. The claystone member of the Mancos shale is believed to have been formed as a nearshore sand which was receiving only fine-grained sediment, deposited in a sea of weak currents. The claystone member of the Mancos shale is a dark gray to black claystone with some siltstone, deposited in a trans- 124. gresslve sea. The water apparently was deep enough to he below the depth of effective wave currents. A lack of dis­ turbed bedding and of current structures supports such a theory. No appreciable changes in texture or structure indi­ cating that progressively finer sediments were being deposited upward in the section are recognized, however, lime content shows a slight increase upward. The absence of a lime facies in the Mancos section suggests that no great quantities of lime were being supplied to the sea or that too much mud was being introduced to permit accumulation of lime deposits. The claystone member is composed predominantly of black shale but has many minor variations. The carbon content, based on an average of 10 samples, is 2.17 per cent. Trask (1939, p. 429) found that 0.3 per cent carbon would impart a black color to sediments. The samples examined for the presence of pyrite showed only a trace. Black shales may originate in either of two ways: first, where the carbon is retained in a sediment and has no time to oxidize because of rapid burial by subsequent sediment (Kubey, 1931); second, where black muds form in a toxic environment. Under the first condition, black shales can form in any environ­ ment provided there is an adequate supply of carbon material and the rate of accumulation is sufficiently fast to bury the carbon, thereby excluding oxygen and k illin g the oxidizing bacteria. Excellent examples of the second environment are the barred basins of Norway (Strom, 1936). In such toxic en- 125. vironments, stagnant water develops due to a barrier which prevents disturbing current action. Subsequent development of hydrogen sulphide excludes a ll oxygen and so carbon is pre­ served .. The Mancos shale contains an abundance of black shale in the lower portions, whereas, the upper part is a light olive shale. The extensive areal distribution of the Mancos shale is such as to cast doubt on the presence of a barred basin of stagnant water. Also, the lack of pyrite and the presence of an abundance of bottom dwelling fossils indicates an environ­ ment which is not toxic. The claystone member of the Mancos shale shows no evidences of current action and the alternating laminae of light and dark sediment believed to represent an­ nual or seasonal changes such as described by Rubey (1931, p. 21). The mottled appearance of the Mancos shale with many black and yellowish gray splotches having no orientation can best be explained by rapid burial below wave base where car­ bonaceous material was deposited and partial oxidation occurred prior to burial. The presence of current deposits having such an irregular pattern as shown by the mottled claystone seems inconceivable. Thus, the black shales of Black Mesa are believed to have had their origin in a stable shelf environment where the sediment was entering su fficien tly fasttto bury and preserve the carbon, at least in part. The presence of bentonite beds in the Mancos shale is 126, indicative of volcanic action which furnished the ash. At­ tempts to find structures that would indicate whether the ben­ tonites were water-borne or air-borne to the point of deposi­ tion were unsuccessful. Blue Canyon, the lateral passage of a well-defined bentonite bed from a coal layer into overlying claystone suggests an air-borne origin. The limited nature of the bentonites, however, does not lend support to such an interpretation. The absence of primary structures makes the problem complex and at the present time i t is unsolved. The basin of deposition in which the Mancos shale formed continued to sink until the claystone member had been accumu­ lated. Following th is, conditions changed. The siItstone member in the upper portion of the formation shows that very fine sand and silt were being introduced. The influx of this detrital material indicates an overlapping of near-shore sands on the offshore muds. The seas must have been regressing as they were being fille d with sediment. The sediment entering the basin of accumulation was more rapid than the sinking of the basin. Thus, the filling of the basin results in regres­ sion. Grabau (1924, p. 732, 734) was the first to point out that regression results when sedimentation exceeds the rate of sinking. He noted that there need be no interruption in sedimentation at a distance from shore. Sears, Hunt, and Hendricks (1941, p. 101-119) in a study of regressive deposits in the Upper Cretaceous of New Mexico showed that Mcontinued sinking, even if slight, provides room 127. beneath the profile of equilibrium for deposition of near­ shore sediments upon earlier off-shore ones, without erosion between". Similar conditions are believed to have occurred In the Mancos shale of Black Mesa. Therefore, the siltston e member of the Mancos shale was deposited as a result of sed­ imentation exceeding the rate of sinking and that it was de­ posited in water of sufficient depth beyond the range of ef­ fective currents. The alternating siltstone-sandstone member of the Mancos shale is the regressive counterpart of the basal sandstone member. It is believed to be a near-shore sand, deposited al­ ternately with sandy muds in an environment where current ac­ tion was much more pronounced than in the earlier deposits as evidenced by ripple marks and minor cross-lamination. Sand­ stone beds progressively thicken upward and are overlain by a massive sandstone considered of beach origin.

Mesaverde Group

General

The Mesaverde group was named by Holmes (1877, p. 35) for Cretaceous strata having a three-fold division which are exposed at Mesa Verde in Montizuma County, southwestern Colo­ rado. The three divisions as described by Holmes are the "lower escarpment sandstone", the "middle coal group", and 128. and the “upper escarpment sandstone". The names Point Look­ out sandstone, Menefee formation, and Cliff House sandstone, respectively, were given by Collier (1919, p. 296) to the units of the threefold group. Because the individual formations are not traceable to many localities, the name Mesaverde has been used for the group throughout the west. A threefold group of rocks which forms the upper part of Black Mesa were referred by Gregory (1917, p. 75) to the Mesa­ verde group. It consists of a lower escarpment sandstone, a ledge-slope coal sequence in the middle and an upper escarp­ ment sandstone. These units are clearly exposed on the north and northeast faces of Black Mesa. The lower escarpment sandstone has a basal member which is believed to have been formed as a beach and w ill be termed the “basal sandstone member". Above this sandstone is an ar- kosic deposit of deltaic type which is the most prominent key-bed on Black Mesa. It is a sandstone, locally an arkose, that is a conspicuous feature for 70 miles along the western side of the mesa. It w ill be termed "arkosic member11. Above the arkosic member is a series of strata consisting of thin-bedded sandstone, mudstone, lignite and coal which w ill be termed “coal-bearing member". Cyclic sedimentation is the most pronounced feature of this member. Overlying the coal-bearing member is a massive sandstone. It forms the crest of the mesa in the north and northeast sec­ tions, forming a sheer cliff up to 300 feet in height. It 129. w ill be termed Mupper sandstone memberH* The Mesaverde group Is composed mainly of continental deposits with only minor amounts of marine deposits Included, At the north end of Black Mesa thin marine deposits occur within 200 feet of the base of the Mesaverde group. Marine fo s sils from one horizon, 180 feet above the base, have been tenta­ tively identified by the writer as equivalent to the Niobrara fauna of the Great Plains, In a section 4 miles south of Kayenta on the northeast side of Black Mesa Reeside and Baker (1927, p. 34) found a fauna of Niobrara age 110-185 feet above the formation base. Because the Mesaverde group of Black Mesa is equivalent in age to the Niobrara of the Great Plains, it is the same age as the lower part of the Mancos shale of the San Juan Basin. Except for the upper sandstone member, beds of the Mesaverde are believed to be regressive deposits. Thus, the Mesaverde group of the San Juan area is of younger age than the Mesaverde of Black Mesa (Fig. 5). The topography of Black Mesa is greatly influenced by the resistance of the coarse-grained, arkosic member and by the weak coal-bearing member that is capped by a resistant, cliff-forming sandstone. In the southern portion of the mesa the upper members of the Mesaverde have been eroded away leav­ ing the arkosic member as the crest of the mesa. The crest is formed by the dip slope of this member and only in a few places in this area are remnants of the upper two members preserved. Locally, sandstone beds of the coal-bearing member 1 3 0 . form ledges separated by slopes of mudstone. S till higher in the section is the upper sandstone member with several thin coal seams that cause it to break into ledges, though farther north it forms a sheer cliff (Pi. 15, fig. 1). The thickness of the Mesaverde group on Black Mesa is greatest south of Cow Springs Trading Post and least in the northeast corner (PI. 8 and 9)« South of Cow Springs i t is 1162 feet thick and in Marsh Pass 837 fe e t. The arkosic mem­ ber (Pis. 8 and 9) is 3&5 feet thick south of the Cow Springs Trading Post (Section 2) and 470 feet at Longhouse Valley (Section 5) but only 265 feet at the north end of Marsh Pass (Section 11). South of Cow Springs Trading Post to Blue Can­ yon the lower part of the arkosic member thickens, but erosion has removed the upper part so exact measurements could not be made. The coal-bearing member is 678 feet thick at Section 2, south of Cow Springs, and 50 feet at Section 5 in Longhouse Valley. It thickens agalns to 272 feet at Section 11 at north end of Marsh Pass. The upper sandstone member which forms the crest ■;of the mesa is thickesttin the north. Because it forms the surface of the mesa, however, an undeterminable amount has everywhere been removed by erosion and it s original thickness can not be measured. The remnants of this member at Section 2, South of Cow Springs Trading Post have a thickness of 122 feet, where­ as at the north end of Marsh Bass they form a 300-foot, ver­ tic a l c lif f (PI. 15, fig . 1). 131. Maneos-Mesaverde Contact

The Mancos-Mesaverde contact has been discussed previous­ ly. The boundary is gradationalcand the contact has arbi­ trarily been placed where the sandstone becomes predominant over mudstone.

B a sa l Sandstone Member

General.-Below the arkosic member of the Mesaverde are deposits believed to have been formed as a beach. Outerop3s of this deposit are well exposed in some areas, as south of Cow Springs Trading Post, however, the deposit is not con­ tinuous. Because the postulated origin of these beds is indicated largely by structural features, an understanding of the terms relating to a beach is desirable. Figure 16 is a cross-sec­ tion of a beach with its component parts labeled. A beach is defined by G. K. Gilbert (1890, p. 39) as "The zone occupied by the shore d rift in transit". Johnson (1938, p. 162) uses the term beach to mean only the material in transit but he does not limit it to a definite zone. Thomp­ son (I937, p. 725) restricts the term to the area of the shore or between the limits of the migrating water line. The defin­ ition used by the Beach Erosion Board of the War Department (I938, p. 4) is: "The zone extending from the low water mark Offshore Shore or beach Coast

Foreshore Backshore

Lower-*- Upper Crest of berm A Slope of Berms x Cliff B foreshore X Coast Scarp \ line

High Water Lirre * Low Water Line Plunge point

•Nomenclature of beach (Anonymous, 1938, p. 4$ Thompson , 1937) 333. to the base of the cliff which usually marks the landward lim­ it of effective wave action". In the present study the defi­ nition of a beach as given by Thompson (1937) p. 725) w ill be followed. His definition not only recognizes the transient nature of the material on a beach but also places limits on the component parts of a beach. The use of the term "Lower foreshore deposits" (Thompson, 1937) p. 725) is not recognized by the War Deparment Beach Ero­ sion Board (1938) p. 4 ). The term, however, is believed essen­ t ia l in a study of primary structures. The "lower foreshore" is designated by Thompson to be between the upper lim it of the zone of permanent saturation and the low-water lin e. The im­ portance of this zone is that within it the plunge point (Pig. 16) occurs. The result is an intermixing of littoral currents and wave action due to the turbulence created by the plunge point. The carrying power of the wave is greatest at the plunge point, hence, i t w ill have a profound effect on the structures which occur in the lower foreshore. Near-shore deposits according to Krumbeln (1950, p. 198) are restricted to a zone which starts at the low water mark and extend seaward until the depth becomes 30 feet. Reason for limiting them to that depth is not clear. If deposition between 0 and 30 feet differed from that beyond, then he would be ju stified , however, the term near-shore should be flexib le enough to include any depth out from low-water level as long as the depositional environment is the same. 134, In a regressive and transgressive sea, the sequence of deposits that would be expected is as follows:

Regressive Expected Deposits Transgressive Sea Sea 6 Continental deposits (Deltaic) 1 5 Backshore deposits (includes 2 lagoons and dunes) 4 Upper foreshore deposits 3 3 Lower foreshore deposits 4 2 Nearshore sand 5 1 Offshore mud o

It should be borne in mind that in this situation, as in cyclic sedimentation, all units of a sequence may not be pre­ sent at any one place* Nevertheless, the importance of the sequence should not be minimized. The thickness of a beach deposit is, by necessity, limited below by the depth of the floor of deposition and above by the height of the waves. The floor of deposition in a transgressive sea would be the upper part of the previously deposited beach, however, in a c r itic a l study of the deposits found on Black Mesa no evidence could be found of structures which indicate a beach is preserved during transgression. To preserve a beach in a transgressive sea, the rate of sinking of the basin and the rate of sedimentation must be equal for a sufficient length of time to build up a thick de­ posit; then, to continue preservation the rate of sinking must only very slightly exceed the rate of sedimentation. Thus, 135. a thick beach deposit is laid down but only a very thin layer survives the cutting action of the advancing seas. The thick­ ness must exceed the depth of the turbulence created at the plunge point or the previously deposited material is eroded. It is doubtful if such a condition could exist, in view of the daily, seasonal and special fluctuations which occur. Thompson (1937, p. 733) points out that the “fluctuations in the height of sea water, induced by spring and neap tides, variations in transporting power of the waves and currents, in texture and quantity of sediment in the slope on which sediment is moved, and variations in coincidence of activity among all these factors - all combine to change the profile of equilibrlumM. After considering the above factors contin­ uously in operation on a beach, it is doubtful if such a del­ icate balance between rate of subsidence of the basin and rate of sedimentation could be maintained for any length of time. If the above reasoning is correct then beaches, preserved as a deposit with lateral extent, must be preserved in a re­ gressive sea. Barrell (1906, p. 444) states that beaches on emerged shores would be wa shed away. Barrell is correct in his reasoning, if regression is due to relative changes in the land or the sea, but if regression is due to progressive fillin g of the basin with sediment then the backshore and over- lying deposits would build out as a protective covering. In the deposits, overlying the basal sandstone member there is a thick, arkosic sandstone that has great lateral 136. extente To obtain a uniform deposit over a large area in a regressive sea, the rate of sedimentation must far exceed the rate of sinking of the basin. Such a series of deposits, i.e ., beach followed by deltaic, are deposited on an unstable shelf (Krumbein, e t. a l., 1949, p. 1859). The beach would then be preserved by the rapid advance of the overlying deltaic de­ posits. The sandstone of beach type on Black Mesa is composed of several distinctive beds and these are discussed in order of their occurrence in the section. The sequence is believed to be that deposited in a regressive sea. The scarcity of beach deposits in the geologic record is discussed by Thompson (1937, p. 744). He believes the beach normally is above the depth of marine planation and so is com­ pletely destroyed before preservation can occur. Under cer­ tain conditions, however, beaches are preserved as shown by examples in which the special, characteristic structures are preserved. Texture.-The basal sandstone units which have been inter­ preted as beach sandstones have an average median diameter of 0.13 mm. as determined from the analysis of 20 samples. Using Wentworth’s classification, this median diameter falls in the fine-grained sand category, although locally the sand is med­ ium-grained and in other places very fine-grained. The samples which were analyzed show a slight increase in grain size upward in the section. This may be attributed to a progression 337V In grain size that reaches its climax in the near-conglomer­ atic, arkosic sandstone member overlying the basal sandstone member. Figures 17 and 18 are histograms and cumulative curves of 8 specimens on which a mechanical analysis was run. These show considerable variation in the median diameters of indi­ vidual samples. Such local variations are expectable in any beach deposit because of differences in the size material being moved at any one time. If sampling could be done along the strike of the beach, on the same laminae and at the same dis­ tance from the line that demarks the permanent zone of satur­ ation then the median diameter should be essentially the same over a great lateral distance. Sampling in this manner on a buried beach is impossible, however, with the result that lo­ cal variations in texture are pronounced. In a modern beach deposit, sorting in two directions is being carried on simultaneously. The first is the effect of the uprushing wave which carries material up and along the beach, and the second is the backwash current which carries part of the material back down the beach. The result (Krum- bein, 1950, p. 210) is a concentration of the fine material at the crest of the beach and the coarse material at the plunge point. Much of the fine material would be winnowed out and car­ ried seaward (Schalk, 1938, p. 41). Thus, sorting is effec­ tively being carried on in two directions from the point where 1 3 8 .

Fig. 17.-Size-frequency distribution in basal sandstone member. 1 139. p 1 p 3 4 i 2 3 -4 5 t Tr l i 1 1 1 1 1 1 1 K-5-2 — 90 — K-10-2 . Upper^ -Back shore Fore- 1 — 80 — Shore I | — 70 — ; — 60 — — 50 — FI

— 40 — - — 30 — J — 20 — r — 10 — \j\ i 0 o Jm OLX O O tr\ CVJ O O O Xrx CM O O 1T\ CM xO O O lT\ CM vO mm Olrx CM H O Olrx CM H O • • • • • • • « * • H O O O O H O O O O

K-9-1 K-2-4 Lower Back- Fore­ shore shore

Fig. 18.-Size-frequency distribution of basal sandstone member. w . the wave breaks with finer material being deposited both land­ ward and seaward from the plunge point. The net result of the variations which are involved can be seen in the diversity of the individual samples (Fig. 17, and fig. 18). Specimens of the basal sandstone member examined by me­ chanical analysis all fall within Trask's (1932, p. 72) "well sorted" class and the majority fall within Payne's (1942, p. 1697) "good sorted" class. The average coefficient of sort­ ing of the twenty samples is 1.24 which agrees with the figure, 1.25, as given by Stetson and Upson (1937, p. 57) for modern beach sands. The range of the skewness of the samples on which mechan­ ical analysis was run is -0.05 to 0.017 which indicates that the peak of a frequency curve is on the negative or coarse side of the median. The degree of roundness in grains of the basal sandstone member was determined by visual comparison to the standard given by Krumbein (1941, p. 64). They were found to be angu­ lar, 47 per cent; sub-angular, 32 per cent; sub-rounded, 15 per cent; rounded, 6 per cent(Pi. 33, figs. 1 and 2). The principal constituent in th is sandstone is quartz which shows definite conchoidal fracture and some pitting between fractures. The cement is calcareous, with considerable limonite; Prac­ tically all grains show limonitic staining*;. The size of particles has considerable control over the resulting slope of the foreshore beds, and shape, size and xan. density control the resulting sorting (Krumbein, 1950, p. 209)• The rounding of grains is effected by size, with larger grains being more rounded "than the quartz" (Martens, 1939, p« 210)V Composition.-The composition of a beach is controlled to some extent by the reworking to which the particles are sub­ jected, for the hard minerals survive and the soft ones are being destroyed. The basal sandstone of the Mesaverde on Black Mesa consists of 85 to 95 per cent quartz and 5 to 14 p er cent feldspar, with considerable mica concentrated on the bed­ ding planes (Pi. 33, figs. 1 and 2). Minor amounts of zircon and tourmaline are present. The feldspars seem to persist through­ out. Unaltered varieties are preserved probably because an abundance of felds-ar was being supplied from a nearby source and upon deposition was rapidly buried. Reed (1930, p. 223) describes unaltered feldspars in the California beaches and attributes their presence to a near-by source and a climate unfavorable to chemical weathering. If rapid burial occurs, moreover, the effect of chemical weathering is greatly re­ duced and feldspar is preserved relatively unaltered. Heavy mineral separates of the samples chosen for mechan­ ical analysis are shown in Table 13. The heavy mineral sep­ arate rarely exceeds one-quarter of one per cent of a total sample. Some heavy minerals which were present in the separ­ ates were too small for composition determination. The presence of orthoclase feldspar, biotite and muscovite indicate the source rock to be one of two possibilities. The W!% TABLE 13 Heavy mineral analysis of samples from the basal sandstone member

od m •H ffl 43 H o o i 1 Q CO Sample Number B iotite Muscovite Tourmaline Zircon Magnetite Hi CO

B-2-1 21 47 18 4 10 Lower Foreshore B-2-2 46 oft 11 , 2 5 Upper Foreshore B-2-3 28 38 9 9 16 Upper Bore shore B-2-4 27 47 3 7 16 Backshore (?) B-5-1 32 16 — mm Lower Foreshore(? B-5-2 34 56 5 — Upper Foreshore B-5-3 19 27 17 10 17 Upper Foreshore B-10-1 38 22 9 12 Upper Foreshore B—10—2 26 45 14 7 8 Backshore B—10—3 17 49 10 13 11 Backshore B -ll-1 34 42 11 9 Lower Foreshore (?; B—11—2 30 47 15 4 3 Upper Foreshore B-9-1 18 50 9 16 7 Lower Foreshore B-9-2 26 ?2 7 2 13 Lower Foreshore B-9-3 25 61 8 4 Lower Foreshore B-9-4 27 38 10 20 3 Upper Foreshore B-15-1 31 39 16 7 7 Upper Foreshore (?; B—15—2 17 46 1 19 12 Upper Foreshore B-16-1 19 45 13 3 17 Upper Foreshore B—16—2 21 49 4 12 14 Upper Foreshore m * The fir s t is a granitic rock and the second is a sedimentary- rock. The samll quantity of heavy minerals present indicates a sedimentary source but the presence of unaltered feldspar gives more support to a granitic source. A sta tistic a l study of heavy mineral separates from the various parts.of the basal sandstone member does not show any minerslogical differ­ ence. The presence of the heavy minerals is noted by Martens (1939, p. 210) to be concentrated at the plunge point which is within the limits of the lower foreshore.' The Black Mesa deposits on the other hand do not show any excess heavy min­ eral concentration that might indicate a plunge point. Primary Structure.-Primary structures which serve to distinguish a beach deposit are the most important factors in its recognition. A comparison of these structures as seen in modern beaches with similar structures in ancient deposits is enlightening. The most important type of structure is the laminations which are so characteristic of modern beaches (PI. 32, fig. 2). The individual laminae are due either to the sorting effect of the waves giving textural differences, or to the dark minerals which are concentrated by the waves (PI. 34, fig. 1). Individual laminae in the upper foreshore are at a low angle and can be traced laterally up to 35 feet. Individual laminae in the basal sandstone member vary in thickness with the majority (30#) between 0.1 and 1.0 inch and with an average of 0.3 inch (PI. 32, fig . 3). The thick­ ness of a single laminae according to Thompson (1937, p. 726) 1 4 4 . varies from one grain up to a foot or more, whereas, the thickest dark band noted was 1.2 inches. Laminae in the basal sandstone Member of Black Mesa have the following characteristics:

i Average of 314 readings ——O.lj? inches Average of light bands------O.36 inches Average of dark bands—------0.04 inches Maximum ligh t band------3 feet Maximum dark band------0.17 inches

The thicknesses listed above are less than those measured by Thompson (1937, p. 726), however, compaction may account for the differences. The laminae per inch vary from 5 to 20 (Pi. 32, fig. 2) in the Black Mesa deposits and vertically, are not constant for more than 3 inches. Individual sets of laminae in cross-lamination patterns are not consistent in the number of laminae per inch. An attempt was made to relate the thickness of individual laminae to the angle of a set, but no relationship could be found. Laminae believed to represent the lower foreshore and those of the upper foreshore show no essential differences in thicknesses. Cross-lamination is the supposed lower foreshore deposits of the Mesaverde sandstone is clearly represented. The dips of the laminae are much steeper than other foreshore deposits, and are up to 31 degrees. Preservation of the individual lam- 145- Inae has been generally obliterated. The cementation is very weak, making the preservation such that statistical studies were not practical. Several beds were examined and their structures compared to those in near-shore sands of today. No great differences could be found. The structures do not greatly differ from those of backshore deposits. The trunca­ ted surfaces between individual sets tend to be very irregu­ lar and are not consistent in slope direction. Thompson (1937> p. 738) points out two features which he believes typical of the lower foreshore. The first is a low ridge and trough parallel to the shore formed at the plunge point, the trough, in many places, being fille d with sediment and leveled out. The second feature is the declivity of the slope which decreases toward the sea. The presence of intri­ cate cross-lamination with high-angle slopes should charac­ terize the foreshore deposits. Micaceous material should be much higher here than in other parts of the beach. Figure 19 is believed to be an example of the lower foreshore type of deposition. The sandstone in the Mesaverde, thought to have been formed in the upper foreshore of the beach, has average directions of the cross-lamination as shown in Table 14 and Figures 20, 21, and 22. TABLE 14 Statistical study of cross-lamination in basal sandstone member of Mesaverde group Location No. Average Average Consistency Section (Pl.l) Readings Direction Din Factor Section 2 30 N 29 E 4° 0.54 Section 15 30 N 47 E 3° 0.27 Section 10 30 N 79 E 4° 0.32 Total Average 90 H 47 E 4° 0.37

An average of the 90 readings (Table 14) shows an aver­ age direction of N 47 E and an average consistency factor of 0.37* The spread of individual readings in the statistical study of cross-lamination indicates the low value in using beach lamination as a means of determining direction. Per­ haps the reason is the large number of variable going on at any one time. Thompson (1937, p. 735)# in his study of the beaches of California, notes a cusp-like pattern in weekly changes in profile of foreshore beach. The distance between cusps is up to 140 feet. The laminae were found to conform in dip with the floor of the cusp-like embayments and to thin landward. The direction of dips encountered in such structures vary almost 360 degrees. Nevertheless, if enough readings are taken the average direction can be determined with considerable accuracy. The relationship of grain-size to dip of the laminae was examined but findings are not conclusive. The fineness of the material in the deposits that are considered beach prohibits Fig. 19.-Typical cross-lamination in the lower, foreshore deposits of the Mesaverde group of Black Mesa".

£ <1 1 4 8 . N o r t h

Fig. 20.-Dip bearing of cross-laminations in basal sandstone member of the Mesaverde group. 30 readings corrected for 10° S 10 E regional dip Average degree of dip - 4° Resultant dip direction N 29 E Consistency factor - 0.54 149 N o r t h

Fig. 21.-Dip bearing of cross-laminations in basal sandstone member of the Mesaverde group. 30 readings Each interval-one division Corrected for 12° N 80 E Regional dip Average degree of dip - 3° Resultant dip direction N 4? E Consistency factor - 0.27 N o r t h

Fig. 22.-Dip bearing of cross-lamination in basal sandstone member of the Mesaverde group. 30 readings Each interval - one division Corrected for 20° S 62 E Average degree of dip 4° Resultant dip direction N 79 E Consistency factor 0.32 extensive examination. In all places, the dip angles are low (less than 5 degrees) where the texture is that of fine- or very fine-grained sand. No coarse sand beaches occur in this area. McKee (1951) noted that grain size and type of material, for example, sh ells, composing the beach control the angle of the individual lamination. An analysis of dips in the upper foreshore is as follows:

TABLE 15 Statistical analysis of dips from individual laminae in upper foreshore deposits-basal sandstone member, Mesaverde group Mesaverde Deposits Modern beach-Thompson Degrees No. of readings Per cent No. readings Per cent 0*3 50 55 48 4-7 31 34 34 1000 8-11 8 9 11 12-15 0 0 4 16 or over 1 l 3

The findings as reported in this paper agree with the findings of Thompson for cross-bedding of the upper foreshore. Thompson (1937, p. 732) describes four types of cross- lamination from the upper foreshore (Fig. 23). In the Black Mesa basal sandstone member, all four of these types have been identified. Figures 24, 25, 26, and 27 are examples of the typical varieties encountered in the upper foreshore deposits. (PI. 34, figs. 2 and 3j PI. 35, figs. 1, 2, 3 and 4; PI. 36, fig . 1). 152.

Type D

Fig. 23.-Diagrams of cross-lamination (Thompson, 1937, P. 732). Fig. 24.-Typical example of beach type cross-lamination of basal sandstone member of the Mesaverde group (14 laminae per inch) (Thompson’s types A, B, and D).

H £3 Fig* 25»- Type C cross-laminations (after Thompson. Note: iron concretion and tube borings, gnarly structures below lower foreshore C). Basal sandstone member. •*£T Fig. 26.-C and D Cross-lamination ifter Thompson. Lower foreshore deposit of the basal sandstone member. Fig, 27*-Typical cross-lamination in the upper foreshore of the Mesaverde group of Black Mesa, 156. In the four types of cross-lamination typical of beach­ es (Thompson, 1937> P« 723) only one feature appears to be constant and that is the seaward dip of the surface of depo­ sition or truncated surface. In cross-lamination considered of beach origin in the Mesaverde, the constancy of these dips was examined. Results are as follows: on 24 truncated surfaces the average direction of dip was N 33 E with a range in the readings from N 16 E to N 39 E and a consistency factor of 0.72. The results seem to warrant the use of the truncated surfaces, rather than the individual laminations, in deter­ mining direction of the currents. Perhaps the reason these truncated surfaces are more con­ sistent than dips on laminations, is that they result either from storm erosion which effects the entire beach, or from times of non-deposition before a new influx of sediment, during which time the beach reaches the "profile of equilibrium". The effect of spring and neap tides is essentially a variation which results in a new profile of equilibrium thereby producing a truncated surface. Thompson (1937, p. 733) gives a very good account of the effect of the various factors which create the truncated surface. The relation of each lamination set to adjacent sets in the beach-type sandstone of the Mesaverde was determined. Types C and D (Fig. 23) are most common and Types A and B apparently are restricted to the upper portion of the sand­ stone. This may be due to nearness to the backshore deposits 158. - which would result in landward dips forming in these types (Fig. 23). In many places the laminae are built on rippled surfaces formed on underlying shaly siltstones. In some of the thin sandstones single laminae extend parallel to the supposed beach direction for distances up to 35 feet and per­ pendicular to this direction from bottom to top of the sand­ stone a distance of 12 to 20 feet. Structures which should be expected in the backshore of a beach are varied and are the result of a mingling of envir­ onments. They are the result of the action of subaerial agents on sands deposited by marine agents. On many modern beaches, prevailing winds have built up extensive aeolian deposits which may be the protective coat for earlier beach deposits. The intermixing of the environments, therefore, is the most diagnostic characteristic that occurs in the backshore. The deposition of deltaic material over the deposits of the back- shore also helps in the preservation. The backshore deposits of Black Mesa do not show any appreciable difference in texture from those of the foreshore. The composition is also very similar. Primary structures, however, are radically different. The cross-lamination which is present consists almost entirely of channel-fill (festoon) types and of the wedge "torrential" type. Minor amounts of high-angle, compound cross-lamination occur in the upper por­ tions. Statistical studies on the cross-lamination show the direction to conform with the other parts of the beach (Fig. 28). 1 5 9 . North

Fig. 28.-Dip bearing of cross-lamination in backshore part of the basal sandstone member of the Mesaverde group. 30 readings corrected for 15° N 74 E regional dip Average degree of dip - 23° Resultant dip direction N 32 E Consistency factor - 0.21. It is N 32 E with a dip of 23 degrees and a consistency fac­ tor of 0.21. The most characteristic structure present in the back- shore of the basal sandstone member is the festoon type cross- lamination. It consists of many channels.which are subsequent­ ly filled with sand (Fig. 29)• The presence of dune deposits serving as protective agents overlying the foreshore deposits, was not recognized. In several places, as at Section 5 (PI# 31, fig. 1) a near-black shale, probably of lagoonal origin, overlies the upper foreshore deposits. Such a shale at Sec­ tion 5 splits into four thin shales in a distance of 200 feet. The presence of the lagoonal deposits suggests that a beach may be preserved by encroachment of lagoonal deposits over i t . Several small structures occur in the basal sandstone deposits that lend support to their interpretation as beach sands. Small vertical tubes which transect the laminae (Fig. 30) are a common feature. The tubes are round with diameters between i inch and 3/8 inch and enclose a structureless mass. The laminae generally are bent down ward around the tubes show­ ing that the tubes result from downward-moving objects such as represented by modern sand crabs. In all cases, the tops of tubes are cut off by overlying laminae. Variations in tubes of this type are curved varieties and those with no disturb­ ing of the surrounding laminae. • All probably represent minor variations of a common type. In some parts of the basal sandstone are thin cup-shaped Fig. 29#-Typical cross-lamination in backshore deposits of Mesaverde group of Black Mesa.

H0\ .H Fig. 30.-Vertical tubes that occur in the beach sandstone. iron cemented masses which resemble sh ells, but have no d is­ tinguishable marking (Pi. 31, fig, 2). Perhaps they represent shell fragments that were deposited on a single lamination. These bodies do not transect laminations but are deposited between them. Fucoids are on the upper surfaces of some of the laminations, in the basal sandstone of the Mesaverde (PI* 31, fig. 3)* These may represent the traces of plant material deposited just above the high water mark such as seen on many modern beaches. The presence of swash marks in ancient deposits is diff­ icu lt to determine. Because the sandstones are very well cemented they do not split easily along bedding planes with the result that surface markings are not well preserved. Small networks of ridges have been observed but none that could be traced over 2 feet. The ridges are up to inch in height and appear to represent the lower sides of lamina­ tions that fille d swash marks* Ridges from r ill marks locally form series of parallel, somewhat fan-shaped bands which show the maximum advance of the waves. These r i l l marks are most pronounced in areas where the dip of the upper foreshore beds exceed 5 degrees. Below that angle the effect of the backwash is greatly re­ duced. Where the profile of equilibrium has been reached such erosional features are rare. At Section 10 in Marsh Pass, a series of scallops (PI. 32, fig, 1) occur which resemble cross-sections of beach cusp-like structure is one foot and the length varies up to 12 feet. Arkosic sandstone member

Overlying the deposits considered of beach origin is a series of sandstones which contain features that relate them to a delta where the supply of material is far greater than the rate of sinking of the basin. The deposits form a blank­ et over the entire area. In general, they are fine-grained at the base and contain many thin beds, mudstone layers and thin coal seams. Many bedding surfaces are covered with rip­ ple marks (PI. 25, fig. 2). These deposits probably represent deltaic deposits formed immediately behind the beach. The texture of the arkosic sandstone is progressively coarser upward until it results in arkosic sandstone. %is sandstone is the most distin ctive one on Black Mesa and serves as a key bed throughout the area. Locally, i t is an arkose. A characteristic feature of the unit is granule conglomerate in which unaltered feldspar content and white color make it conspicuous. Above the near**conglomeratic sandstone, the tex­ ture becomes progressively finer until the coal-bearing mem­ ber is encountered. The thickness of the arkosic sandstone (Pis. 8 and 9) varies from 365 feet in the south of Black Mesa to 250 feet in the north, but the key bed in this sandstone remains re- markably constant, between 7 5 and 100 feet. No fauna or flora are known to occur in the sandstones. A thin shaly siltstone near the base of the overlying coal-bearing member contains a meager fauna which, as identified by the writer, consists of Inoceramus deformis Meek, Inoceramus unabundus Meek and Ostrea congests Meek. All of these are of Niobrara age. The contact of the arkosic member deposits with the ba­ sal sandstone member is not easy to determine. It has arbi­ trarily been placed where cross-lamination becomes consistent­ ly different from that of the basal sandstone member and dis? plays the following types: festoon, low and high angle compound, and wedge "torrential'*. The basal sandstone member is so thin that for purposes of mapping it is included with the arkosic sandstone member (Pis. 8 and 9). The upper contact of the arkosic sandstone member has been placed where the continental shales and coals first be­ come predominant. Texture.-The texture of the arkosic sandstone member shows an infinite amount of variation, both laterally and vertically. Between two cross-lamination sets, the texture locally varies from conglomerate of granule size to medium-grained sand. The results of mechanical analysis therefore, have little val­ ue as indicators of grain size. Thirty samples were run to determine whether there is any noticeable lateral change through­ out the area studied and to show the amount of change vertical­ ly in the median diameter. Results are given in Table 16. TABLE 16 Medians, coefficients of sorting, and skewness in terms of phi units, from Arkosic sandstone member. Sanrole No. Mdid oW Skq/ D- 1-1 0.81 0.74 o.o5 D— 1—2* 0.92 0.44 —0.11 D- 2-1 0.96 0.52 0.30 D- 2-2 0.95 0.75 0.14 D~ 2-3* 1.16 0.57 0.27 D- 2-4 1.15 0.59 - 0.05 D- 2-5 0.71 0.25 —0.02 D- 3-1* 1.73 0.80 0.18 D- 3—2* 2.50 0*82 0.17 D- 4-1 0.52 0.52 0.07 D- 4-2* 1.22 0.60 0.36 D-4 -3 0.70 0.67 0.50 K- 5-1 0.95 0.55 0.05 K- 5-2* 0.97 0.60 0.00 K- 5-3 0.36 0.50 0.02 K— 6—1* 1.29 0.72 - 0.08 K- 8-1* 1.46 0.52 0.05 K— 9—1 0.51 o.5o 0.05 K- 9-2 1.74 0.57 0.07 K-10-1 0.20 0.44 0.13 K-10-2* 1.28 0.95 -0.16 K-10-3 0.97 0.56 0.02 K-ll-1* 1.49 0.65 0.15 K—11—2 0.76 o.5o 0.07 K-12-1* 1.33 0.40 - 0.13 K—13—1* 0.96 0.32 - 0.09 K-14-1* 0.47 0.51 0.35 K-15-1* 1.51 0.72 - 0.07 K—16—1* 2.11 0.50 0.26 K-17-1* 0.88 0.57 -0.15 ♦Samples from key bed 14%. The average median diameter of 1? samples is 1.35 mm. with the range from 0.47 to 2.50 mm., an indication of the great variation (PI. 37, figs. 1 and 2). The roundness of grains in the arkosic sandstone member was determined with the following results; angular, 30 per cent; sub-angular, 42 per cent; sub-rounded, 18 per cent; and rounded, 10 per cent. These data show that most of the feld ­ spar is sub-rounded to rounded and has been lit t le altered. The average coefficient of sphericity of these grains ranges between 0.64 to 0.88 which shows the irregularity among them. The surface of the key bed in this member generally weathers white as a result of clay minerals developing through alter­ ation of feldspar. Such alteration is not pronounced on fresh surfaces. Individual grains of quartz generally are pitted and some pebbles appear etched. The average coefficient of sorting in the arkosic sand­ stone falls in the "well sorted” category of Trask's classi­ fication, but in Payne's classification it is between the ”poor-and-fair-sorted” groups. A few samples fall in Trask's "normal sorting" category, but all of these are granule con­ glomerates, rather than sandstones. The largest gravel encountered in the member was at Sec­ tion 13 (PI. 8 and 9) and measured 3/4 of an inch in diameter. The particles, therefore, are of pebble size. Texture tests were run on single cross-lamination layers to determine the range in size. The results shown in Table 17 emphasize the d iffic u lties encountered in applying mechanical analyses to this deposit. Composition:-The arkosic member consists mainly of sand­ stone with approximately 10 per cent siltstone. The principal constituent is quartz which makes up from 65 to 95 per cent of the total grains in various samples. Feldspar forms from 5 to 35 per cent. The alteration of the feldspar is very slight except where the grains are exposed on weathered surfa­ ces. In some parts of the formation no weathering is apparent.

TABLE 17 Textural study of maximum-minimum grains encountered in single laminae of the arkosic sandstone member.

Horizontal Maximum Minimum Distance size size... 1 4 inches* 12 mm. 0.5 mm. 2 2 inches* 16 mm. 1.5 mm. 3 8 inches* 10 mm. 0.25 mm. 4 5 inches 15 mm. 0.5 mm. 5 5 inches 9 mm. 1.5 mm. 6 4 inches 4 mm. 0.5 mm. 7 7 inches 7 mm. 1.0 mm. 8 8 inches 11 mm. 2.5 mm.

♦adjoining layers

Thin-sections show that the feldspar is largely perthite and orthoclase but includes a few grains of andesine (PI. 3 8 , f i g s .

1 and 2)<, Heavy m ineral separates contain negligible amounts 1# 9, of several minerals, Calcareous cement is present In the arkosic sandstone member In minor amounts. Most of the deposits contain clay as a bonding material. Much of the sandstone, however, does not show any cement or bonding material, so is very friab le. Primary structures.-The principal primary structures in the arkosic sandstone member are various types of cross-lam­ ination. The most numerous of these is the low-angle compound type, but the festoon types are locally abundant. A statistical study of the cross-lamination shows the av­ erage direction of dip to be N 32 E. This direetionils an average of 180 readings taken in several parts of the area. Variation in direction for individual beds is a characteris­ tic feature (Fig. 31, 32, 33, 34, 35, and 36). In general, the source-rock of the sediments appears to have been to the west and southwest. The types of cross-bedding vary from place to place with low-angle compound the most pronounced. Examples of these types are shown in PI. 36, figs. 2, 3, 4; Pi. 39, figs. 2 and 3; and PI. 40, figs. 1, 2, 3, and 4. Many thin, flat-bedded layers truncate sets of cross-lam­ ination in the arkosic sandstone member, showing the existence of minor periods of erosion or breaks in sedimentation. In many places erosion surfaces that cut across bedding planes indicate periods when erosion was pronounced for immediately above these erosion surfaces lithology is radically different m * (PI. 39, fig . 1). In most places, sediment above an erosion surface is coarser than that below. The shifting nature of a braiding stream on a delta front would produce differences in texture above erosion surfaces. The presence in the arkosic member of thin layers of carbonaceous shaly mudstone and of plant fragments along bed­ ding planes indicates an abundant plant life in the area be­ ing eroded. Graded bedding occurs in many of the cross-laminated beds. The range in grain size, (Table 17) from one lamination to the next is considerable, and series of laminations show much var­ iation, The graded bedding probably is due to periodic in­ creases of stream flow with continuous deposition. Inclusions.-The abundance of spherical iron concretions is a diagnostic feature of the coarse-grained arkose (PI. 41, figs. 1 and 2). These concretions consist of iron-cemented sandstones with hollow centers, most of which contain limonite in the form of a loose, dry powder. In some locations, the concretions are so abundant that the rock appears to be a con­ cretionary bed. These iron oxide concretions suggest a trop­ ical climate, which is in keeping with evidence furnished by the enclosing arkose (PettiJohn,1949, p. 260).

Coal-bearing Member

The coal-bearing member consists of an alteration of North

F i g . 3 1 .- Dip bearing of arkosic member o f t h e Mesaverde group. 30 readings corrected for - micorracted regional dip. Average degree of d ip . - 23 Resultant dip direction S 86 E * Consistency factor .33 Fig.32.-Dip bearing of arkosic sandstone member of the Mesa verde group. 30 readings corrected for 10° S 10 E regional dip Average degree of dip 21° Resultant dip direction S 33 E Consistency factor 0.33* N o r t h

Fig. 33.©Dip bearing of arkosio sandstone member of the Mesa- verde group. n o 30 readings corrected for 1# S 15 E Regional dip Average degree of dip 20° Resultant dip direction S 83 E Consistency factor 0,55 Horth 174.

Fig. 34.-Dip bearing of arkosic sandstone member of the Mesa­ ver de. group. 0 30 bearings corrected for ^ N 74 E Regional dip Average degree of dip 25 Resultant sip direction N 38 E Consistency factor 0.57 N o r t h

Fig, 35.- Bip bearing of arkosic sandstone member of the Mesaverde group. 30 readings uncorrected regional dip. Average degree of dip 25 Resultant dip direction S 88 E Consistency factor O.37 N o r t h

Fig. 36.-Dip bearing of arkosic sandstone member of the Mesaverde group. 30 readings uncorrected regional dip Average degree of dip 17 Resultant dip direction N 73 E * Consistency factor 0.62 17*. rock types formed under conditions of cyclic sedimentation* The member contains sandstone, subgraywacke^, siltston e, clay- stone, carbonaceous varieties of sandstone, lign ite and coal* The most important coal beds of Black Mesa are in th is member. Coal seams up to 14 feet have been encountered but no such thickness persists over great lateral distances. Rocks of the coal-bearing member form the alternating ledges and slopes on the upper sides of Black Mesa (PI. 13, fig . 2). They also form the surface over much of the mesa. They include sandstone, most of which is medium- to fine-grained and intricately cross-laminated. Much of this is a sub- graywacke. Contacts between the beds of varying lithology are gradational. The thickness of the coal-bearing member varies from 250 feet at the north end of Marsh Pass to 50 feet at the south and increases to 675 feet south of Cow Springs Trading Post* The change in thickness toward the south appears to indicate nearness to ashore where fluctuations in the strand line have a pronounced effect. The coal-bearing member is the lithologic unit that Rea­ gan (1925) named the Z ilhejini formation and to which he as­ signed an age equivalent to that of the Fruitland formation of northwestern New Mexico. Reeside (1924, p. 6) states that the Fruitland formation is equivalent in age to late"Pierre and early Fox Hills of the Great Plains section. Reeside and Baker (1929, p. 36) consider the Zilhejini formation equivalent in age to the Niobrara of the Great Plains and the writer agrees 1 7 9 . with this interpretation. The lower contact of the coal-bearing member has arbitrar­ ily been placed where continental mudstone and coal become predominant and where cyclic sedimentation starts. The pre­ cise location of this contact, based on lithology, varies some­ what from place to place. The upper contact of the coal-bearing member is clearly marked by the top of the cyclic sediments and the coal beds and by the base of a massive, cliff-forming sandstone. The cliff is 300 feet high and can easily be recognized. In ad­ dition, its lithology is very different from that of the under­ lying mudstone and coal. Texture.-In the coal-bearing member medium- to very fine­ grained sandstone and subgraywacke grade upward into shaly s ilt - stone, which in turn grades into normal claystone, then into carbonaceous claystone, lig n ite and coal. Above the coal beds this sequence of rock types, grading one into another, is re­ peated in reverse order (Fig. 37). Most of the sandstone does not extend laterally for more than 3 miles and, in places, sandstone facies grade into siltstone facies and these in turn are supplanted by coal. The great lateral and vertical range in lithologic types makes a textural study for correlation purposes of li t t le value. The texture determined from 10 samples taken from the sandstone units has an average median diameter of 0.22 which is classed as fine-grained. The range is from 0.07 to 1.1 mm. Roundness of grains varies so much, 1 7 9 .

iiittiia Sandstone- subgraywaeke

Siltstone

•Lignite Coal

• Lignite

Siltstone

Sandstone-subgraywacke # 0 #

Fig. 37*-Typical Cretaceous cyclothem of Black Mesa f mu. both vertically and laterally, between the various units that no characteristic average can be determined. One unit, ar­ bitrarily chosen, gives the following results based on 3 samples:

Sample No. Hdjd ODd Skad T-2-2 0.17 0.64 0.005 T-2-4 0.23 0.67 0.01 T-2-6 0,19 0,65 0.005 AverageO.20

The average roundness of the sandstone layers is as follows; angular, 21 per cent; sub-angular, 55 per cent; sub­ rounded, 16 per cent; and rounded, 8 per cent. The grains are generally of clear vitreous quartz with small amounts of sur­ face etching. The coefficient of sortlngls 1,73 which falls within the well-sorted class of Trask’s classification but the sorting is fair to poor by Payne’s classification* Most of the rocks in this member are siltstones, but they grade from a sandy siltstone to a clayey siltstone with no single variety predominant. Textural analyses, even in a single layer and for short distances, are notably inconsistent* Composition,-Composition of the sandstone layers varies greatly, but quartz is the dominant mineral. An average speci­ men consists of approximately 88 per cent quartz, and the balance feldspar. Heavy minerals are negligible. In me rock sample of 100 grams only three heavy mineral grains - two of magnetite and one of zircon, were found. Two other samples contained muscovite and biotite, but heavy minerals were not p len tifu l. Pyroxene and hornblende have been noted and 11- monite occurs in all samples as coatings on the grains. Cement consists of calcium carbonate and limonitic mater­ ial. Clay is, in part, a bonding material. The sandstone layers are not entirely sandstone but locally a subgraywacke. Primary structures.-A ll of the sandstone-subfcraywacke beds in the coal-bearing member are cross-laminated. The cross­ lamination involves deposition and bevelling. It includes the alternating "Torrential" and horizontal types with wedge "torrential" the most prominent. These types are present in thin, lenticular masses which resemble channels that have been filled. The laminae may represent foreset beds of small del­ tas which advanced over previous channels (PI. 42, fig. 1), Many of the sandstone-subgraywacke beds weather along bedding planes and these clearly illustrate the irregular nature of the deposits (PI. 42, figs. 2 and 3). Shallow fes­ toon-types of cross-lamination (PI. 42, fig. 4) together with the irregular nature of the sediments, indicate a subaerial environment of deposition. Thus, these beds appear to have formed as deltas behind the lagoons. Sandstone-subgraywacke beds of the coal-bearing member are thin-bedded in the upper part, but s t i l l higher grade into shaly sandstone and then into shaly siltstone (Fig. 37). Many minor irregularities on the bedding planes are reflected in overlying sediments. The siItstone becomes progressively dark­ er upward in the section indicating an increase in carbonaceous material. Finally lignite occurs, overlain by coal. This se­ quence apparently represents a minor transgression of the sea because sediments indicate that the lagoonal environment en­ croached upon subaerial deposits. The reverse sequence above the coal beds is believed to represent a new influx of sediment from the flood plain thus bringing about a minor regression of the sea. In many parts of the coal-bearing member ripple-bedding is responsible for a pseudo-cross-lamination (Pi. 43, fig. 1). McKee (1938, p. 77) shows the characteristicss of this type of lamination in his studies of the Colorado delta and along the Colorado River and suggests a classification (McKee, 1939, p. 72). Ripple cross-lamination in the coal-bearing member on Black Mesa appears to be the Mlevel-surface ripple” type, i.e ., the ripples were deposited on an earlier horizontal sur­ face. Inclusions.-Various types of inclusions occur in many beds of the member but none proved useful in tracing particular horizons. The most common inclusion is a large (1-4}feet), oval-shaped mass of hematite (PI. 43, fig. 2) in concentric bands. Such concretions, due to their hardness, form the crests of small knobs in many places and weather with the spal­ ling off of concentric layers. Fragments form conspicuous tra ils down the slopes of knobs. Cyclic sedimentation.-The importance of a cyclical repe­ tition of events in geologic history is well established. A great variety of cycles has been recognized by various writers. The term "cycle" was first applied to sedimentation of the Pennsylvanian period and given importance through the work of Weller, Wanles?, R. C. Moore and others. Weller (1930, p. 99) defined a "cycle" as a "recurrence, repetition, or a return to the star ing point". No time implication is ihcluded but, if time is to be considered, he suggests:the term "rhythm" be used instead. The cycles of the Pennsylvanian period, a typical se­ quence in ascending order is: (1) sandstone and sandy shale, (2) underclay, (3) coal, and (4) marine limestones and shales. Weller believes the deposition to represent that of a contin­ ental environment f ir s t, followed by subsidence and marine deposition. The origin of the Pennsylvanian period, a typ­ ica l sequence in ascending order is: (1) sandstone and sandy shale, (2) underclay, (3) coal, and (4) marine limestones and shales. Weller believes the deposition to represent that of a continental environment first, followed by subsidence and marine deposition. The origin of the Pennsylvanian cycles is discussed by Weller and Wanless (1932, p. 1103) who attribute them to "eustatic changes in sea level". McKee (1938, p. 129) in his study of the Toroweap forma­ tion of Permian age recognized cyclic sedimentation. The lith­ ologic units involved differ from those in the Pennsylvanian cycles. They are: (1) red beds and gypsum, (2) chemically 184., precipitated limestones, (3) marine limestones with mollusks or brachiopods, (2) chemically precipitated limestones, and (1) red beds and gypsum. The origin of the above sequence in relation to movements of the sea is essentially the same as that of the Pennsylvanian cycles. However, McKee believes the cause to have been "earth movements in the region of depot* sition", A typical cycle as found in the Mesaverde of Black Mesa consists of: (1) sandstone and subgraywacke believed to have been deposited landward of the lagoons, (2) siltstone and claystone probably formed behind and in the lagoons, (3) coal, (2) siltstones and claystones, and (1) sandstone and subgray- wackes (Fig. 37)• The development of this sequence in rela­ tion to movement of the sea is essentially the same as in the Pennsylvanian and Permian cycles described. Here the cycle begins with u p lift which is followed by erosion and subsequent deposition of continental sediments. Though no marine deposits are represented, each cycle of the Cretaceous "returns to the starting point" in the manner of the Pennsylvanian cycles (Weller, 1930, p. 99)• Doubtless each cycle reflects a move­ ment of the sea at some place farther east. Gnarly bedding.-In the uppermost parts of the coal-bear­ ing member several very gnarly sandstone-subgraywacke depo­ sits appear to be the result of local subaqueous slumping (PI, 43, figs. 344). Criteria for the recognition of soft- rock deformation have been examined by Rettger (1935* p. 272). 185. The absence of definite top and bottom confining planes in the gnarly beds of the Black Mesa deposits suggest that they are not the result of submarine slumping* A type of pseudo-bedding described by McKee (1939, p* 80) occurs in mud deposits of the Colorado River delta. McKee states, "It consists of irregular shells that develop around lumps or masses of the same material and in vertical section has the appearance of highly folded beds". He attributes this structure to shrinkage as water is removed. The local nature of the Black Mesa crumpled zones, the absence of confining planes and an undisturbed mass more or less in the center of the folded mass could possibly be attributed to an origin similar to that described by McKee. The size of the Black Mesa folded structures, however, ranges up to 5 times as much as that of the structures described by McKee. In addition, the folded structures of Black Mesa are of sandstone, whereas, the pseudo-bedding described by McKee is in mud. The locally crumpled-structures in the Mesaverde sandstone can not with certainty be attributed to either of the above p o ssib ilitie s. D efinitely, they had their origin through some form of soft rock deformation while in a saturated con­ dition. They may have been formed in pools which were subse­ quently drained, with slumping in a central undisturbed portion, with subsequent deposition conforming to the crumpled beds. Coal.-The coal seams which are found in the coal-bearing member vary in thickness from a few inches up to 14 feet. A 186, statistical study shows 38 coal seams to total 115 feet for an average of 3 feet per seam. If the coal seams under 9 inches are omitted then 24 seams total 105 feet for an aver­ age of 4.4 per seam. By using 3 feet as the minimum mining width, then 10 coal seams with a total of 68 feet remain for an average of 6.8 feet per seam. The above figures seem to indicate that the coal deposits of Black Mesa are extensive and should warrant mining opera­ tions. The principal trouble encountered is the failure of any one seam to maintain its thickness over an appreciable dis tance. Measured sections including a typical coal seam are shown in Figure 38. Much of the coal on Black Mesa is both underlain and over lain by lign ite which might offer some mining problems. It would cause dilution of the coal during its extraction. The composition of Black Mesa coal varies in different seams, with the better grades being closer to the top of the section. The results of 12 proximate analyses are shown in Table 18. The variation in the grade of these coals is in­ dicated by the analyses. The B .t.u. content was determined on two samples and is given in Table 18. Coals on Black Mesa are sub-bituminous In rank and con­ tain consierable ash, but as previously discussed have a desirable white ash. Very few samples show a red ash. Two mines are at present actively mining and shipping coal from the Mesaverde zone. One is the Cow Springs Coal [•{/■v.v.'i Sandstone Siltstone Lignite Coal

Fig. 38. -Variation in coal seam, 1 mile south of Cow Springs Trading Post. 1 8 8 . TABLE 18 Proximate analysis of the coals of the coal-bearing member.

Voli- Fix­ Sample Mgis- t ile ed Ash B .t.u. Col­ Number Location* ture Mater­ Car­ or ia l _ bon Ash 6-1—1 38 f6B*fc below 10.4 36.3 43.7 9.6 W C-2-1 200 f t . above 20.6 32.4 40.8 6.2 W 0-2-2 212 ft. above 15.7 41.9 28.1 14.3 w 0-2-3 270 ft. above 23.5 32.6 33.2 10.6 WR 0-2-4 312 ft. above 18.1 27.4 35.3 19.2 WR 0-2-5 517 ft. above 7.1 37.0 45.5 10.4 W 0-10-1 74 ft. above 16.6 32.6 37.4 13.4 R 0-10-2 116 ft. above 8.4 32.1 45.0 14.5 WR 0-11-1 28 f t . above 17.7 35.3 37.0 10.0 WR 0-11-2 270 ft. above 20,0 28.7 38.4 12.9 W 0—5*1 168 f t . above 4.0 41.8 42.6 11.6 W Kayenta Coal Mine 11.0 37.7 47.1 4.2 11,640 w Cow Springs Goal Mine 17.4 37.0 41.6 4.0 10,450 w *Given in feet from key bed W-lhite ash R-Red ash WR-White-red ash 189. Mine which is located 7 miles north of Cow Springs Trading Post. This mine faces east at a site approximately 3 miles east of the western rim (PI* 44, fig . 1). Approximately 10 tons of coal per day are shipped from here by truck, 120 miles to Flagstaff, Arizona, where the owners have contracts with business firms. A second operating mine is the Kayenta Coal Mine. It is reached from Route 1, five miles south of Marsh Pass, by a road leading 7 miles east of the western rim of Black Mesa. The coal seam is the uppermost one in the coal-bearing mem­ ber. It is 6§- feet thick at the mine entrance. The outcrop is exposed in a stream cut along the valley floor. Kayenta Coal Mine ships approximately the same amount of coal as does the Cow Springs Mine and shipments are made 160 miles to Flagstaff, Arizona by truck.

Upper Sandstone Member

The uppermost deposit on Black Mesa is a massive, fin e­ grained, yellowish gray sandstone. This member is remarkably lacking in bedding planes. It forms the surface rock over the northern part of Black Mesa, but occurs only as remnant buttes and mesas, rising several hundred feet above the surrounding rocks in the southern part. The true thickness of the sandstone is unknown for it forms the present erosion surface of Black Mesa. The maximum thickness is at the north end of Marsh Pass 1 9 0 . itfieBe the rock forms a vertical cliff 300 feet in height. To the south of Cow Springs Trading Post it is 122 feet thick. On the southern end of Black Mesa it has been removed by ero­ sion. The age of this member has not been definitely established :r; because of the scarcity of fo s s ils , nevertheless, Reeside and Baker (1929, p. 36) assign to it an age equivalent to that of the Niobrara of the Great Plains section. 4 single specimen collected in Marsh Pass by the writer has been tentatively 1- dentifited as Inoceramus stanton Sokolow which is of Niobrara age. Texture.-The average median diameter of the upper sandstone member as determined from 7 samples is 0.21 mm. (Fig. 39). This median diameter makes it a fine-grained sandstone. The degree of roundness of it s grains is as follows: angular, 23 per cent; subangular, 33 per cent; subrounded, 37 per cent; round­ ed, 7 per cent. Most of the grains are of clear vitreous quartz; many have surfaces that are etched. The coefficient of spher­ ic ity of the sand ranges between O.69 and O.87 which indicates that the grains are generally oval. The coefficient of sorting in the upper sandstone mem­ ber is 1.18 which, by Trask’s method, is •well sorted”. By Payne’s classification it is "fair sorted". The range shown by the coefficient of skewness is -0.01? to * 0.05 with an aver­ age of 0.005 which shows that there are more of the fine sizes than of the coarse sizes. The largest grains encountered were Q 1 2 3 4 5 100 1111 M-2-1 ~ 9 0 _ M-12-1 8 0 _ 70—

6o—

O O OXTxCXJ O OXrxCMxO O O O ITS cm mm. OXTXCM H o O O Ltn (V xD * * # * * O Irx CM H O M O O O O • • • • . H O O O O

M-14-1

Fig. 39.-Grain-size distribution in samples of Upper sandstone member of the Mesaverde group. 1 9 2 . between 1 and 2 mm. or of very coarse safid. Composition.-The massive sandstone member is composed largely of quartz and feldspar. Typical samples average 88 per cent quartz and the balance feldspar. The feldspar is principally perthite and orthoclase which are indicative of a granitic source. The feldspar shows considerable alteration, with kaolin as the predominant alteration product. Often in leaching the rock in hydrochloric acid prior to mechanical analysis, the feldspar breaks down into clay products. Heavy mineral separates from the upper sandstone member show the following average percentages: biotite, 8 per cent; muscovite, 14 per cent; magnetite, 16 per cent; tourmaline, 21 per cent; zircon, 27 per cant; titianite, 6 per cent; and ru­ tile, 8 per cent. In general, all grains of these separates are rounded. The tourmaline and zircon grains are the least rounded but there are no angular grains. The cement of the upper sandstone member consists of cal­ cium carbonate, limonitic material and a little silica. In places, the included clay acts as a bonding agent. Primary structures.-Primary structures in the upper sand­ stone member consist principally of the compound types of cross-lamination. Minor amounts of the alternating "torren­ tial" and horizontal also are present. The festoon types were noted in two lo c a litie s, but they are not extensively developed. Statistical studies of the cross-lamination in this unit show dip directions of north to northeast, indicating directions 193«» of the source material to the south and southwest (Fig. 40)• 4 variety of flat-bedding occurs in the upper sandstone member south of Cow Springs Trading Post and at Cow Springs Coal Mine road in which the beds are firmly cemented with an iron material but show very little internal structure. In a few places, these thin beds contain small scale alternating «torrential" and horizontal types of cross-lamination. Inclusions.-The lower portion of the massive sandstone contains concretionary forms that differ from concretions in any other bed studied. These concretions were nicknamed "Brazil nuts" in the field because of their resemblance to this type of nut (PI. 44, fig s. 1; Pi. 44, fig . 2). They rarely exceed two inches in diameter and many of them are hol­ low in their centers except for a spongy limonitic material. These concretions appear to be reliable indicators of the par­ ticular horizon that they represent. Accompanying the "Brazil Nut" concretions, are others of variable length (up to 9 feet), circular to oval in cross- section, and composed of very firm sandstone. These have lens-like bodies which taper to a point at each end (PI. 45, fig. 2). Such cigar-shaped bodies lie with long axes hori­ zontal and they occur in parallel groups in one particular horizon. In places they are connected with one another. They appear to represent an old rippled surface in which the ripple troughs were covered with sand of a different texture. This sand also became rippled in such a manner that crests of the 1 9 4 . North

Fig. 40.-Dip bearing of upper sandstone member of the Mesaverde group. 30 readings corrected-uncorrected regional dip. Average degree of dip 2? Resultant dip direction N 42 E Consistency factor 0.45 1 9 5 . new ripples were directly above the troughs of the earlier ripples, thus giving rise to a group of parallel sandstone bodies, oval in cross section, which laterally assume the shape of earlier ripple troughs.

Depositional History

The lower contact of the basal sandstone member of the Mesaverde has been arbitrarily placed where sandstone becomes dominant over siltston e. The basal sandstone member is char­ acterized by long, low-angle, cross-lamination planes of beach type. The sequence of deposits believed to be represented in the basal sandstone of the Mesaverde are those to be expected with a regressive sea. They are as follows: (youngest on top): 5 Deltaic deposits 4 Backshore deposits 3 Upper foreshore deposits 2 Lower foreshore deposits 1 Nearshore sandstone The lower foreshore of a modern beach is characterized by the intricacy of its structures. Short, discontinuous, nearly horizontal foreset laminae, interstratified with mica­ ceous and heavy mineral laminae, are common in the lower fore­ shore. The foreset laminae have angles up to 30 degrees. These 1 9 6 . foreset structures are much smaller than those of the upper foreshore (Thompson, 1937» p. 738). The plunge point should produce a shallow trough which runs parallel to the shore, but in a moving sea this trough might be fille d with a fore- set type of cross-lamination. In the basal sandstone member of Black Mesa believed to be a beach, the structureless mass below the long, low-angle cross-lamination is believed to be lower foreshore deposits. The beds are characterized by their intricate bedding. Mi­ caceous material is concentrated in these beds but a concentra­ tion of heavy minerals is not apparent. No horizontal laminae are found but short foreset laminae have an angle up to 31 degrees. Lower foreshore deposits by themselves might be relative­ ly difficult to recognize in rock outcrop, but in a well-defined sequence their position under definite upper foreshore beds and their structureless character, apparently caused by ter­ mination of the trough at the plunge point, indicate their origin. Laminations terminating in a structureless mass oc­ cur in strata south of Cow Springs Trading Post. These are believed to be of the lower foreshore. The upper foreshore of a modern beach has very distinctive cross-lamination which in few places exceed 5 degrees in dip. Individual laminations can be traced for as much as 100 feet along the strike and up to 25 feet perpendicular to the strike. The presence of the long cross-lamination planes, of light and 1 9 7 . dark laminations with minor surface structures such as r ill marks, swash marks, and fucoids are considered strong evidence of the upper foreshore of a beach deposit. Cretaceous deposits of Black Mesa, interpretated as beach deposits, show the characteristics of modern beaches described above. Thus, considerable evidence is available to ju stify their interpretation as beach deposits. Backshore deposits of modern beaches show an intermixing of a wide range of structures so cause considerable difficulty in interpretation. Here marine deposits are interbedded with those of dunes, deltas, and lagoons. The mixture of these types therefore is characteristic of backshore deposits. Backshore deposits are believed to be present in the Mesa- verde sandstone of Black Mesa. They contain structures typi­ cal of marine, lagoon and delta deposits. No dune deposits are recognized. The marine beds are irregular and thin and can be traced into foreshore structures. The lagoonal deposits contain minor amounts of carbonaceous coal. Rapid deposition of overlying deltaic deposits quite likely was responsible for the preservation of the beach deposits, because of the protec­ tive covering provided. The principal and most diagnostic primary structures of the back shore are filled-channels that form festoons. The festoons are filled by sand layers that conform to the shape of the original channel. They progressively thicken and flat­ ten. 1 9 3 . The arkosic sandstone member, in general, is fine- to medium-grained near the base but becomes progressively coarser upward to the arkosic sandstone bed. Above this the reverse is true, and a progressive upward decrease in the grain size occurs. Primary structures in the arkosic sandstone are most­ ly festoon and low-angle compound types of cross-lamination. Iron concretions occur in the arkose. According to Petti- john (1949, p. 260) such features indicate a warm humid cli­ mate. The Black Mesa basin of accumulation probably was relative­ ly stable during deposition of beach and deltaic deposits. Hence, the rate of sedimentation of the deltaic deposit far exceeded the rate of subsidence and a thin but extensive sheet resulted. The rate of change in texture of the arkosic sandstone member is indicative of the condition of the land mass furnish­ ing the sediment. Uplift of the land-mass apparently was re­ corded by a progressive increase in grain-size and a maximum uplift was indicated by the arkose deposition. Subsequent ero­ sion of the uplifted landmass is reflected in a progressive decrease in grain size. When the landmass neared base level a period of minor fluctuations in the Black Mesa basin of accumulation resulting in cyclic sedimentation. The cyclothem as recorded in Black Mesa was entirely within a continental environment. The rela­ tive movement of the sea is the same as Weller and Wanless 199. (1932, p. 1103) found in the Pennsylvanian cyclothems but the lithologic sequence is reversed, Subgraywacke was deposited on the subaerial portion of Black Mesa delta on the landward side. A minor transgression next resulted in deposition of fresh water or fluvial silts. The time of maximum advance of the sea is represented by the coal beds which were formed as lagoonal deposits back of the shore. Regression then set in and resulted in a reverse of the sedimentary processes described above. During the period of cyclic sedimentation, the Black Mesa basin of accumulation was unstable. At fir s t sinking caused a slow, interrupted transgression, but with more sediment brought- in, a major transgression resulted and very thick, massive, near-shore sandstone was deposited. This sandstone forms the crest-rock of Black Mesa. Both high and low angle, compound cross-lamination is characteristic of this unit. The presence of a shallow water marine fauna and the continuity of the clean quartzose sandstone is characteristic of a transgressive de­ posit in which deposition took place on a stable shelf. 2 0 0 .

CHAPTER VII

HISTORICAL SEQUENCE

Erosion Surface Below DakotaC?) Sandstone

Underlying the Upper Cretaceous deposits of Black Mesa are Jurassic strata of continental origin. A great period of erosion is represented between them. Gregory (1917, p. 61) notes the eroslonal contact but does not discuss the rel­ ative time lapse. Harshbarger (1949, p. 68) believes the ero- sional interval to be “relatively long*. The absence of the topmost member of the Morrison forma­ tion as developed in Colorado and Hew Mexico suggests that the erosion interval started in Upper Jurassic time. Another possibility is that this member had been present there but was removed by subsequent erosion. The evidence from adjoining areas does not support the contention of former extension as far as Black Mesa of later deposits. The erosion interval therefore, probably started immediately after the deposits of Morrison time were formed. Absence of fossils in deposits directly above and below the eroslonal surface makes the lapse of time represented dif­ ficult to determine. Nevertheless, because all of Early Cre- 2 0 1 . taceous time is involved, the hiatus must be of considerable magnitude. The contact between the Morrison formation and the Dakota (?) sandstone is characterized by channeling. The channels range up to 140 feet in length and 20 feet in depth. Many small ones are fille d with gravels.

Dakota C?') Sedimentation

The Dakota (?) sandstone consists of continental deposits probably laid down in front of an advancing sea. The sequence of deposition and depositional environments represented by it is as follows: Lithology Environment 4 Coal Lagoonal 3 Siltstone Outer floodplain 2 Sandstone Floodplain 1 Conglomerate Landward side of floodplain A comparison of the texture and composition of the Mor­ rison formation with that of the Dakota (?) sandstone indicates that the Dakota (?) sandstone could not have been derived pri­ marily from the underlying Morrison. Apparently it came from a source to the south. The basin of accumulation was sinking, the seas transgressing so the above sequence of continental deposits was formed. Landward from the edge of the Cretaceous sea are deposits of the beach, the lagoon and the flood plain. No record of 2 0 2 . the beach environment can be recognized In the Dakota sequence but coal and underclay Indicate the lagoons and various de- trlta l sediments show the floodplain development» Deposits of the ancient flood plain Include a great num­ ber of variations. A general upward gradation from the coarser to the finer sediments apparently represents the change from landward to seaward parts of the plain, brought about as the sea advanced. The conglomerate at the base of the Dakota (?) sandstone represents the landward deposition of streams on the reaching the floodplain and swinging laterally. The sandstone represents the bulk of deposition which occurred on the flood plain nearer the sea. The finest material was de­ posited in the lagoons. These lagoons appear to have slowly developed into goal swamps as is evidenced by the gradual in­ crease in the carbon content of the siltstone. Finally, they changed in to swamps and c o a l was form ed. The c o a l r e p r e s e n ts the last continental deposit prior to an advance of the sea. These deposits seem to indicate conditions of a relatively stable shelf. The texture of the Dakota (?) sediments became progressive­ ly finer as the landmass was worn down and gravels ceased to form. This condition is evidenced by the lack of conglomerate and the decrease in thickness of sandstone toward the south­ west. The old landmass must have been near base level by the time the sea had reached the area of southernmost Black Mesa for the sandstone is almost completely absent and lagoonal 2 0 3 . deposits rest directly on the Morrison formation. To more clearly visualize the movements of the sea as represented by strata on Black Mesa, a diagrammatic chart is presented (Fig. 41).

Events During Mancos Sedimentation

Transgressive Near-Shore Deposition

Basal sandstone member.-Mancos shale.-The fir s t deposit laid down by the advancing Mancos sea was a near-shore sand­ stone. This quartzose sandstone has few bedding structures but contains an abundance of fossils which are believed to be near-shore varieties. This member is not a continuous blanket type of sandstone but is irregularly lenticular. In many places it includes siltstone and claystone containing a similar fauna.

Offshore Deposition

Clavstone member.-Mancos shale.-Overlying the near-shore sandstone are strata formed as offshore mud which contain no evidence of current structures and are essentially thick depo­ sits of fissile black shale. These mudstones are primarily of clay texture with some silt but they contain many thin layers of bentonite which serve locally as key-beds. This porti#n Transgression Regression Bolonced zone Fig. 41.-Diagramingtic sketch sketch 41.-Diagramingtic Fig. eain o lc Mesa. Black to relation LogoonaI Lacustrine FI u via I o SpringsCow of h rltv mvmn o te rtcos es in seas Cretaceous the movement of relative the

Coal- bearing memberbearing Coal- ittn member Siltstone Clays member lone ------BLACK MESA Jurassic Upper 48 mi — 48

Koyenta

Unstable Stable Shelf Shelf 205, of the Maneos shale has been called the elaystone member and it is believed to represent off-shore, mud deposition which occurred when the seas were transgressing (Fig, 41), The clay shows li t t le evidence of change in the basin of accumulation and deposition appears to have taken place on a stable shelf. Sandstone member. -& change of the sea from one that was transgressing to one that was regressing is evidence#by an increase in the sand content of the mudstone. In the southern part of the area, this change is illustrated by several thin, sandy siltstone layers which contain an abundance of cephalo- pod impressions. The sand is believed to represent the influx of near-shore sediment into the off-shore mud during the de­ velopment of a regressive sea (Fig. 41). The change from trans­ gression to regression represents the change from a deposit : laid down on a stable shelf to one laid down on a mildly un­ stable shelf.

Regressive Near-shore Deposition

Alternating siltstone-sandstone member.-Mancos shale.- The upper marine deposit of the Mancos regressive sea is a siltstone, containing some sandstone layers. The sandstone is characterized by very thin layers, separated by the thicker layers of sandy siltstone which show evidence of current ac­ tion. Rippled bedding is abundant. The upper contact of this member is where a predominance of sandstone begins in the 2 0 6 vertical sequence of beds.

Events During Mesaverde Sedimentation

General

The Mesaverde group is composed of lithologic units that are believed to have been deposited on a large delta. The intermixture of continental and marine deposits clearly indicates such an environment, and minor structures within the individual units resemble those of modern deltas. A, great variation in these structures on Black Mesa indicates a diver­ sity of conditions represented by the Mancos shale. The Cretaceous seas, at the end of Mancos shale deposition, were regressing to the northeast as determined by cross-lamina­ tion dips and by the sequence of deposits. The source of the sediment was to the southwest.

Beach Deposition Basal sandstone member.-Mesaverde group.-The nearshore s ilt and sand beds ef the Mancos are overlain by a sandstone bed which has features characteristic of beach deposits.

These deposits have considerable lateral extent and are consid­ ered to have originated during the time of a regressive sea.

They are part of a rock sequence which is as follow s: 207. Regressive Sea 5 Deltaic deposits 4 Backshore deposits 3 Upper foreshore deposits 2 Lower foreshore deposits 1 Near-shore deposits One of the most important factors responsible for pre­ servation of this beach sandstone is the rapidly-deposited, regressive arkosic sandstone that overlies i t . Apparently the beach deposits were buried as fast as they are formed, and therefore protected from subaerial erosion. Where erosion exceeded deposition, as at the mouth of a flowing stream, the beach deposit was not formed. Thus, i t is irregular and, in places, absent along the strike.

Deltaic Deposition

Arkosic sandstone member.-Mesaverde group.-The arkosic sandstone is evidence of a granitic source rock and of recent uplift in nearby land masses. Effect of the uplift is also reflected in the upward, progressively coarser character of the deposits. As the newly raised land mass was worn down the resulting sediments became progressively fine-grained. 208. Cyclic Sedimentation

Coal-bearing member.-Mesaverde group.- The member charac­ terized by cyclic sedimentation in this paper has been termed the coal-bearing member. Its basin of accumulation appears to have reached a state of balance in where each addition of sediment approximately equals the space made available through basin sinking and a fluctuation between transgression and re­ gression results. The cause of cyclic sedimentation is dias- trophism, according to Weller and Wanless (1932, p. 1003). Later Wanless (McKee, 1938, p. 131) revised his ideas and considered cyclic sedimentation eustatic changes in sea level. McKee (1938, p. 131) believes the origin due to "earth move­ ments in the region of deposition". The large number of coal deposits in the coal-bearing member indicates a warm, humid climate. Deposits involved in cyclic sedimentation are continental resulting from depo­ sition on the subaerial portion of a delta at a temporary base level. The temporary base level is controlled by periodic changes in sea lev el. Transgression is caused by periodic sinking of the basin of accumulation followed by erosion which fills the basin of accumulation and causes regression.

Transgressive Near-shore Deposition

Upper sandstone member.-Mesaverde group.-following the ~ 209. regression which deposited the arkosic sandstone, cyclic sed­ imentation took place. It slowly filled the basin causing changes from a more or less stationary basin to one which was slowly sinking, thus bringing about a transgression of the seas. The upper sandstone forming the crest of Black Mesa is a clean, blanket, quartzose sandstone which is typical of a stable shelf (Krumbein, e t. a l ., 1949, p. 1859)• The fo s s il evidence in this unit together with its primary structures, indicate a near-shore transgressive sandstone.

SUMl! ARY

L - Lithologic types (lithotopes) (Krumbein, et. a l., 1949, p. 1859) environments of deposition, tectonic environments (tectotopes), and relative movements of the seas are shown in Figure 42.

Relation of Black Mesa to Adjoining Areas

The relation of Upper Cretaceous rocks of Black Mesa to those of the San Juan Basin of New Mexico, the Kaiparo- wits region of southern Utah, and the Deer Creek and Pinedale, regions of Arizona is shown in a fence diagram, prepared by Pike (1947, PI. 12). The Cretaceous rocks of Black Mesa appear to be the remnant of once-continuous strata, nearest the old southwestern shore lin e, (Plate 10). 210.

Li tho ty pe Environ me n t Tectotype Vtovements of sea Sandstone Marine Neritic Stable Shelf Transgression # Sandstone —- Fluvial, D O Siltstone o* Logoono 1 Cyclic * Coo 1 Unstable o H i a Sedimentation > o Siltstone Lit fora 1 s (transition) # Sandstone Shelf H ; 11 Delta Swamp Sandstone Lacustrine m * (Arkose) ## fluvial ...... Beach sandstone Transition Nearshore sands Regression Mildly Marine Unstable Siltstone Shelf

shale Ma r i ne

o 0 -JT-T- c Neritic 1 Marine — — Clay stone Stable

Transgression in n n n l

Fig. 42.-Analysis of Upper-Cretaceous Black Mesa, in terms of lithotopes tectotopes, and environmental groups. 2 1 1 . The reduction in thickness of the Mancos shale from Marsh Pass to Cow Springs Coal Mine road (Pis. 1, 2, 6) is 78 feet in a distance of 40 miles. Using this reduction as a constant, the Upper Cretaceous seas extended 250 miles to 300 miles beyond Black Mesa. This distance places the old shore line approximately 50 miles north of the present Gulf of California. Thus, the old shore lin e, by swinging a 300 mile arc, might have extended within a few miles of the pre­ sent International Boundary and 75 miles into the State of California. This calculation is in very close agreement with the results given by Reeside (1944) in his paleogeographic maps of Upper Cretaceous time. 212 «

CHAPTER VIII

ECONOMIC FEATURES

General

The economic aspects of Black Mesa can be subdivided into two groups: fir s t, petroleum p o ssib ilities; second, coal de­ posits. Other economic considerations are related to the area - but none has a direct relation to the Cretaceous rocks.

Petroleum P o ssib ilities

Petroleum p o ssib ilities of Upper Cretaceous rocks in the western part of Black Mesa are exceedingly poor. Black Mesa rises as a first-order mesa above the general level of the Colorado Plateau, with Upper Cretaceous rocks exposed on a ll sides. Dips generally are toward the center of the mesa. In the western part of Black Mesa, the Comb-Ridge monocline is the most pronounced structural feature and is responsible for the tilting of the Cretaceous rocks toward the center of the basin. Erosion dissects the central portion of Black Mesa with all drainage toward the southwest. The fact that Cretaceous 2 1 3 . rocks stand, above the surrounding plain and that the majority have been exposed by erosion precludes the presence of any quantity of petroleum. No oil seeps are known to exist In the central portion of Black Mesa. The petroleum p o ssib ilities of Black Mesa are restricted to pre-Cretaceous rbcks. Because the great thickness of early Mesozoic rocks which underlied Black Mesa are of continental origin the petroleum p o ssib ilities are restricted to the still lower Paleozoic strata. Minor structures extending into the underlying rocks occur in the southern part of the Black Mesa area. These structures possibly warrant exploration. The presence of a very low water table would emphasize the exploration of syn­ clinal rather than anticlinal structures. For a more compre­ hensive discussion of pre-Cretaceous structures the reader is referred to Harshbarger (1948, p. 130).

Coal Deposits

The coal deposits of Black Mesa are extensive and of a fair quality. They are mainly subbituminous with some bitum­ inous present. The fixed carbon content (Table 8 and 18). indicates the coal to be equal in quality to that mined and shipped at Gallup, New Mexico. . The ash content of Black Mesa coal is very high. Accord­ ing to men who use this coal in-large-furnaces, however, it 214. is preferred over New Mexico coals because clinkers do not form. The coal leaves white to cream white powdery ash upon burning. The calorific power of the coal averages 10,500 B.t.u. which, in comparison to other western coals is low. Cretaceous coal beds of Black Mesa are at two horizons. The lower is at the top of the Dakota (?) sandstone, and the upper is in the coal-bearing member of the Mesaverde group. The Dakota (?) sandstone coal seam varies from Inches to 7 feet in thickness. South of Cow Springs Trading Post it is in two seams, the lower up to 6 feet in thickness, and the upper only 5 inches thick (Pi. 18, fig. 2). This bed is quite variable in thickness and may become reduced from 4^ feet to 6 inches in less than a hundred yards. Thus, the Dakota (?) sandstone coal distribution is very erratic and not conducive to large scale mining. One mine in the Dakota coal is operating at present. It is at Coal Mine Canyon approximately 16 miles east of Tuba City on Route 2. The mine is operated by Hopi Indians and the coal is shipped by truck into Tuba City for use in Government installations. The production of this mine varies with con­ sumption. No statistics could be obtained. The coal seam is 6jt feet thick at the mine entrance but contains several thin bone layers. The Mesaverde coal horizon is in the upper part of the formation. The cyclic sedimentation which is so pronounced referred to in this paper as the coal-bearing member, in this member is responsible for a great many thin coal seams (PI. 8). 2 1 5 . The greater percentage of the coal present in Black Mesa oc­ curs in this member. Only 10 of the seams exceed 3 feet in thickness. The thickest single coal seam is 14 feet. This thickness is not consistent but.becomes less in both directions along the outcrop. Two coal mines are at the present time operating at the Mesaverde horizon in the western part of the mesa. The Cow Springs Coal Mine is located 7 miles north of Cow Springs Trading Post and 3 miles back from the edge of the mesa (PI. 1) (PI. 44, fig. 1). The mine is being developed along on two coal seams which are 30 to 90 feet below the massive sandstone that caps the mesa. Approximately 10 tons of coal per day are shipped by truck into Flagstaff, Arizona, 120 miles to the southwest. A proximate analysis of the coal is as follows: Moisture content------17.4 per cent V olitile material------37.0 per cent Fixed Carbon------41.6 per cent Ash content------4.0 per cent B.t.u. content------10,450. When this coal arrives in Flagstaff it consists of pieces approximately the size of walnuts. The rough roads are undoubt­ ed ly the cause of secondary breakage. Excessive fine fragments produced in this manner make the coal dangerous for shipment. Before r a il shipments could be made, this coal probably would require washing to remove coal-dust. 216. The second coal mine in operation in the Mesaverde sand­ stone at present is the Kayenta or Maloney Goal mine* The road to this mine leaves the main road (Route 1) approximately 5 miles south of Marsh Pass. The mine is located about 7 miles in from the mesa rim. The mine is on the bank of a stream which dissects the floor of one of the interior valleys (Pi. 1)• It is poorly located however, because gravity cannot be used in handling the coal. The seam measures 6 feet at the entrance to the only adit. Stratigraphically it is approx­ imately 30 feet below the upper sandstone member in the Cre­ taceous sequence. The coal at the Kayenta mine is bituminous. It breaks into large chunks and even after trucking to Flagstaff (150 miles) the chunks measure up to 10 inches in diameter. A proximate analysis of this coal is as follows:

Moisture content 11.0 per cent Volatile material 37.7 per cent Fixed carbon 47.1 per cent Ash Content 4.2 per cent B.t.u. content 11,640

This analysis places the coal in the bituminous rank. Several factors present problems which must be overcome be­ fore Black Mesa can produce much coal. The first is the in- accessability of the Mesa. The nearest railroad is the Santa 2 1 7 . Fe which is 90 to 150 miles to the south. To transport the coal for such a distance makes the cost prohibitive. The continual bouncing that the coal receives on such along haul produces a great amount of coal-dust. A, second factor related to economic production of the Black Mesa coal is the water requirement. Mining and washing of coal products necessitate great quantities of water which at the present time are not available near Black Mesa. A last factor, but one which probably with time could be reme­ died, is an adequate market for selling the coal. Only a few local industries in and about Flagstaff are now using the coal. The Black Mesa coals are not good coking coals. Complete combustion of the coals leaves only a very white ash. Further­ more, the sulphur content of the coals is very high as evidenced by thin layers of sulphur immediately above the coal seams. The limited portion of Black Mesa covered by this report does not permit one to make a logical estimate of the total tonnage of coal present. Campbell and Gregory (1911, p. 23j3l) estimate the tonnage from beds with a thickness of 3 feet or more to exceed 8 b illio n . The writer has been unable to make any estimates. 218. DESCRIPTION OF MEASURED SECTIONS

SECTION 1, KAYENTA COAL MINE ROAD. 5 MILES SOUTH MARSH PASS (Dip 17° to 2 , S 26 E) PRESENT EROSION SURFACE: Top of Black Mesa CRETACEOUS MESAVERDE GROUP Feet 10.Sandstone: grayish orange, very fine to coarse­ grained, thin-bedded, cross-lamination, medium, compound; iron concretions, abundant, irregular, reddish brov/n; cliff; smooth, reddish-brown, slabby...... 7.0 9. Sandstone: grayish yellow, fine-grained; lime; thin-bedded; cross-lamination, compound, med­ ium; clay p ellets on bedding planes, common, ovoid, It. gray; cliff, smooth, yellowish gray, flaggy; plant remains, imprints, poor, abun­ dant...... 19.0 8 .Sandstone: It. olive gray to black, very fin e­ grained; very thin-bedded; flat, in places gnarled; ledge, rough, dk. gray, slabby; plant fragments, imprints, poor, abundant, becomes carbonaceous near top...... 42.0 7 .Sandstone: dk. yellowish orange to pale brown, fine-grained; laminated; flat-minor channels, cliff, smooth, yellowish brov/n, shaly; plant fragments, molds, fa ir, common; becomes car­ bonaceous near top...... 106.0 6. Concealed...... 27.0 5 .Sandstone: yellowish gray; fine-grained; lime; thick-bedded; cross laminated, medium compound; cliff, smooth, yellowish gray, massive; fucoids. T%.0 Total Mesaverde group 234.0 MANGOS SHALE 4 .Concealed: Slope...... 744.0 DAKOTA (?) SANDSTONE 3. Concealed: Dakota-Mane os contact concealed...... 3.0 2 .Sandstone: yellowish gray, fine grained; thick- bedded; cross-laminated, medium, compound, clay pellets, common, ovoid, yellowish orange; ledge, rough, grayish orange, massive; plant fragments, poor, rare; conglomeratic at base...... 48.0 Total Incomplete Dakota $1.0 2 1 9 .

UNCONFORMITY Feet Erosional surface, 1 to 5 feet relief, gray-green sand granule to pebble-conglomerate. JURASSIC MORRISON FORMATION Westv/ater Canyon sandstone member: 1.Sandstone: yellowish-gray; fine grained, calcar­ eous cement; thin bedded; fla t bedded; c lif f rough, yellowish gray, slabby.

SECTION 2, ONE MILE SOUTH OF THE COW SPRINGS TRADING POST (Dip 15°, S 10 E) CRETACEOUS MESAVERDE GROUP 71. Sandstone: yellowish gray, very fine grained, thick bedded; cross laminated, medium compound, mud pellets, abundant, irregular, light yellow­ ish gray; c lif f , smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 3 2 .0 70.Siltstone: yellowish gray, silt,th in ly laminated flat; slope, smooth, dark gray, fissile, plant fragments, imprints, poor, abundant; contains much coal...... ; ...... 46.0 69.Sandstone:white, fine grained; lime;thin bedded, cross laminated, medium, compound, ledge, smooth, light gray, slabby; plant fragments, molds, poor, common; massive at base...... 42.0 68.Siltstone: pale olive gray, s ilt , laminated; slope; smooth, dark gray, shaly; plant frag­ ments, imprints, poor, common; contains concre­ tion s...... 2 7 . 0, 67. Sandstone: dusky yellow, fine grained, lime, lam­ inated, cross lamination, small, compound; ledge, smooth yellowish brown, platy; plant fragments, molds, poor, common...... 22.0 66.Sandstone; grayish yellow, very fine grained, a l­ ternating with siltstones and coal; thinly laminated, fla t bedded; slope, smooth, dark gray, fissile; plant fragments, imprints, poor, com­ mon...... 33.0 65.Sandstone; grayish yellow, fine grained, very thin bedded; cross laminated, medium, compound; ledge, smooth, yellowish gray, flaggy; plant fragments, mold, poor, common...... 25.0 2 2 0 .

Feet 64.Siltstone: yellowish gray; silt; thinly laminated, flat-bedded; ledge; smooth, brown, fissile; plant fragments, coal, poor, abundant...... 34.0 63*Sandstone: very pale orange, fine grained, lime, thick bedded; cross laminated; iron concretions, common to abundant, ovoid, red brown; cliff; ledge, smooth, yellowish brown, massive| plant fragments, imprints, poor, abundant; thins in 200 yards to a 24" concretion zone, sandstone g iv e s way to s h a le ...... 17.0 62.Sandstone: yellowish gray; very fine grained, lime, very thin bedded; cross lamination; small com­ pound; iron layer at top; weathers into plates; cliff; smooth, It. gray, slabby; plant frag­ ments, imprints, poor, common...... 20.0 6l.Claystone: It. gray; clay; lime; thinly laminated; f l a t bedded; ir o n c o n c re tio n s , common, o v al red brown; slope, smooth, dk, gray, fissile; plant fragments, imprints, pour, abundant...... 11.0 6o.Siltstone and lignite: pale brown; silt; thinly laminated; flat bedded; slope; smooth, brown to black, fissile; plant fragments, imprints, p o o r, abundant; c o n ta in s c o a l...... 40.0 59.Sandstone: pale yellowish orange, very fine grained thin bedded; cross lamination; small, compound; upper layers ferrugenous; weathers into layers like leaves in a book; cliff, smooth, yellowish gray, slabby; plant fragments, imprints, poor, common...... 26.0 58.Siltstone: grayish yellow, silt; thinly laminated, . flat bedded; slope, smooth, dk,' gray to black, fissile; plant fragments, imprints, good, abun­ d a n t ...... 3 1 .0 57.Sandstone: yellowish gray; ned. grained; thin- bedded; cross lamination, low angle, channel­ ling; cliff, smooth, yellowish gray, slabby; plant fragments, molds, poor, abundant; upper contact becomes carbonaceous shale...... 16.0 56.Claystone: yellowish gray; clay; thinly laminated; flat bedded; iron concretions, common, ovoid, yellowish red; slope, smooth, dk. gray; fissile; plant fragments, imprint, poor, abundant; some coal present...... 21.0 55*Sandstone: It. olive gray; very fine grained: lime; thin to thick bedding; cross lamination; medium compound; midway of this sand is a very hard sandstone layer which weathers into thin plates; cliff, smooth, It. gray; slabby to massive; plant fragments; imprints, poor, rare.. 16.0 54.Siltstone: pale yellowish orange; silt; thinly laminated; flat bedded; alternating sands and 2 2 1 .

Feet shales in lower portion;, slope, smdath, dk. gray, fissile; plant fragments, imprints, poor, abundant; some coal with iron concretions.....• . 18.0 53.Sandstone: pale yellowish orange to It. browns very fine grained: lime; thick bedded to thin bedded; cross-laminated, small, torrential; cliff, smooth, yellowish gray, massive to slabby; plant fragments, imprints, poor, ra re ...... 34.0 52.Siltstone: yellowish gray to dark yellowish orange; silt; thinly laminated; flat-lenticular sands; slope, smooth, grayish brown, fissile; plant fragments, imprints, fair, abundant;contains some c o a l ...... 9.0 51.Sandstone: grayish yellow: fine grained; lime; thin bedding; cross-lamination, medium, com­ pound; channeling.ripples; cliff, rounded, yellowish gray; plant fragments, imprints, poor, abundant...... 30.0 50.Claystone: yellowish gray; clay; thinly laminated; f l a t bedded: c o a l le n s , common, e lo n g a te d , b la c k ; slope, smooth, dk. gray, fissile; plant remains, imprints, poor, abundant...... 73.0 49.Sandstone: yellowish gray; very fine grained; thin bedded; cross-laminated, weathers into s h e e ts ; le d g e, ro u g h , brow nish r e d , f la g g y ...... 16.0 48.Claystone: medium gray; clay;thinly laminated, flat bedded; slope, smooth, dk. gray, fissile; plant fragments, imprints, poor, abundant...... 7.0 47.Sandstone: yellowish gray; very fine grained; very thin bedding; cross-laminated, weathers into thin sheets 1/8" thickness; ledge, rough, brownish red, flaggy...... 58.0 46,Siltstone:lt. olive gray; silt; laminated; flat- bedded; slope, smooth, dk. gray, shaley; plant fragments, imprints, good, abundant; lenticular sandstone layers occur...... 25.0 45.Sandstone: grayish yellow; fine grained; very thin bedded; cross-laminated, small, compound; slope, smooth, yellowish gray, flaggy; plant fragments, imprints, poor, abundant...... ' ...... 13.0 44.Sandstone: it. olive gray; very fine grained; thinly laminated; lenticular; slope, smooth, It. gray, fissile; plant fragments, imprints, - poor, abundant: contains iron zone; claystone contains lignite...... 28.0 43.Sandstone: yellowish gray, fine grained: thin bedded; cross-laminated, med. compouna; iron pellets, ovoid, rare, yellow red; slope, rough, brown, slabby; plant fragments, imprints, poor common;...... 136.0 2 2 2 .

F e e t 42.Sandstone:very It. gray to pale yellowish orange? coarse sand;thick bedded: cross-laminated; med. compound; contains granule texture along; cross bedding planes; iron concretions; abundant, oval, yellowish red; cliff, rounded, white, massive... 54.0 41.Siltstone: med. gray; silt: laminated; lenticular bedding; slope, smooth, dark brown, shaly...... 12.0 40.Sandstone: pale yellowish orange; fine grained; lime; thin;’cross-laminated, medium compound, channels; ledge; smooth, yellowish gray, slabby; fu c o id s ...... 128.0 39.Sandstone; yellowish gray, med. sand; lime; thin bedded; irregular patches of iron which show concentric circles; iron concretions, oval yellowish red: ledge, smooth, yellowish gray, slabby; fucoids...... 16.0 38.Sandstone:pale yellowish orange; sand; thin-bed- ed; slight channeling; cliff, smooth yellowish gray, slabby...... 12.0 37.Claystone: med. gray; clay; thinly laminated; flat; slope, smooth, gray, fissile; plant frag­ ments, imprints, poor, abundant; near coal in . areas; lower 3 feet, lignite ...... 12.0 3b.sandstone; grayish orange; fine grained; lime; thin beaded; cross-laminated; medium compound; ripples on bedding planes; iron concretions; rare, oval, reddish yellow; ledge, smooth, yellowish gray, slabby; plant fragments, molds, p o o r, r a r e ...... 18.0 35.Claystone: med. It. gray; clay; lime; thin bed­ ded; cross-laminated; medium compound; ripples on bedding planes; iron concretions; rare, oval, reddish yellow; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, rare ...... 13.0 34.Sandstone: yellowish gray; very fine grained; lime; very thick bedded; cross-laminated. med­ ium, compound; ripple marks; iron concretions, common, o v a l, y e llo w ish re d ; c l i f f ; smooth, yellowish gray, massive; plant fragments, fucoids im p rin ts , good, ab u n d an t...... 58.0 33.Claystone; med. yellowish brown; clay; thinly laminated; slope, smooth, yellowish brown, fis­ s i l e ; ...... 4 .0 32.Sandstone: grayish orange? very thin grained; thick bedded; cross-laminated, medium, compound, ripples, channels; cliff, smooth, yellowish gray, massive; plant fragments on bedding planes, imprints and molds, poor, abundant...... 20.0 31.Sandstone: dark yellowish orange; very fine grained, thinly-laminated; cross-laminated, large, beach, pits, backwash; ledge, smooth, grayish yellow, f i s s i l e ...... 3-0 2 2 3 .

30.Sandstone: Dark yellowish orangej very fine Feet grained; thin; cross-laminated; ledge; smooth grayish yellow; flaggy....-...... 10.0 Total Mesaverde Group 1272.0 MAKCOS SHALE 29.Claystone: It. olive gray to dark yellowish orange; clay; thin bedded; gnarly to flat bedded; slope, smooth, It. gray, flaggy; lenslike sands up to 4 " ...... 20.

28.Claystone: yellowish gray; clay; bentonite ...... 4 * 0 27.Siltstone: mod. yellowish brown; silt; thinly laminated; flat-bedded; concretions with cone- in - cone, y ello w , ovoid, common; slo p e ; smooth, dk. gray, fissile; fishplates, poor, common.... 33.0 26.Siltstone: dusky yellow, silt; thinly laminated;' flat-bedded; concretions with cone-in-cone, y ello w , ovoid common; slo p e , sm ooth, dk. g ray , f i s s i l e ; f i s h p l a t e s , p o o r, common...... 22.0 25.Claystone: pale olive; clay; thinly laminated; flat; concretions with cone-in-cone; yellow, ovoid, common; slope, smooth, dk. gray, fissile; fishplates, poor, common...... 5 .0 24.3iltstone: yellowish gray; silt; thinly laminated; flat bedded: concretions with cone-in-cone; y ello w , ov o id , common; slo p e ; smooth, dk. g ray ; f i s s i l e ; f i s h p l a t e s : p o o r, common...... 5 .0 23.Siltstone: grayish yellow to It. olive gray; silt; lime; thinly laminated; flat bedded; concretions w ith co n e-in co n e, y ello w , ovoid, common; s lo p e , smooth, dk. gray, fissile; fish plates, poor, common...... 21.0 22.Concealed...... 114.0 21.Claystone: yellowish gray; clay: lime: very thin bedded to thinly laminated: flat bedded: slope, smooth, yellowish brown, slabby to fissile; Pelecypods, fucoids, worm tra ils ...... 81.0 20.Siltstone: yellowish gray; silt; very thin bedded to thinly laminated; flat; slope, smooth, yellow­ ish brown, slabby to fissile; Pelecypods, fucoids, worm t r a i l s ...... 24.6 19oClaystone: yellowish gray to med. clay; lime; thin­ ly laminated; flat-bedded; slope; smooth; yel­ lowish brown; fissile; pelecypidds, fish scales. 29.0 iS.Claystone and bentonite: grayish yellow: clay; lime; thinly laminated: flat bedded;slope, smooth, yellowish brown, fissile; pelecypids, fish scale s 2.0 17.Claystone: med. gray; clay; lime; thinly laminated, flat bedded; slope, smooth, black, fissile ...... 2 .0 2 2 4 F eet 16.Claystone: yellowish gray; mottled to black; clay lime cement; thinly laminated; flat bedded; slope, smooth, m o ttled y ello w and b la c k , f i s s i l e ...... 2.0 l^.Claystone: grayish yellow; clay; lime cement; thin­ ly laminated; flat-bedded; slope, smooth, dk. gray, fissile; pelecy, mrcro, fish scales...... 5 .0 14,Claystone: dusky yellow; clay; lime cement; thinly laminated; flat-bedded; slope, smooth, yellow brown, f i s s i l e ; p e le c y p id s; f i s h s c a l e s ...... 6.0 l3.Claystone: grayish yellow; clay; thinly laminated; flat-bedded; slope, smooth, yellow brown, fissile, pelecypods, fish scales ...... 7 .0 12.Siltstone: grayish yellow; silt; clay; thinly lam­ inated; flat-bedded; slope, smooth, yellow brown, f i s s i l e , p e le c y p id s , f i s h s c a le s ...... 36.0 1 1 .C o n c ea led :...... 60.0 lO.Claystone, sandy:yellov/ish gray; fine sand to clay and silt; lime cement; thinly laminated; flat; slope, smooth, dk. gray to black, fissile; fish s c a le s ...... 59.0 9.Sandstone: moderate yellow; fine grained; lime cement; very thick bedded; cliff, rough, yellow­ ish gray, massive; gryphaea, original, good, ab u n d an t...... Total Hancos shale m DAKOTA. (?) SANDSTONE 8 .C o a l...... 1.0 7.Sandstone, carbonaceous, (underclay): medium gray; fine grained; laminated; flat bedded; slope, smooth, coal, shaly; plant fragments; coal, poor a b u n d a n t...... 4 .0 6.Coal to carbonaceous shale: brownish black to dark yellowish brown; silt; laminated; flat bedded; slope, smooth, black, shaly; plant fragments, c o a l, p o o r, ab u n d an t...... 25.0 5.Sandstone:moderate yellowish brown; fine grained; lime cement;thin bedded; cross-laminated, com­ pound; abundant, ovoid, grayish yellow; cliff, smooth, grayish yellow, slabby; plant fragments, imprints, poor, rare ...... 42.0 4.Sandstone:light brownish gray; very fine sand; lime cement; very thin bedded; flat bedded; slope, smooth, very It, gray, slabby ...... 13.0 3.Siltstone: med. It. gray; silt; bedding-very thin bedded; flat bedded; slope, rough, yellowish w h ite , f l a g g y . . . . '...... 7 .0 2.Sandstone: mod. reddish brov/n; fine grained; con­ glomeratic at base; thin bedded; cross-laminated; compound; cliff; rough, grayish orange, slabby plant fragments, imprints, poor, rare ...... 13.0 Total Dakota (?) sandstone 10 5. 0" 2 2 5

Feet UNCONFORMITY: : •. , ' ■ . :• ' v: Erosional surface, 2 feet relief, filled with greenish gray material with occasional pebbles. JURASSIC MORRISON FORMATION Cow Springs Sandstone Member 1.Sandstone: It. gray; fine-grained; clacareous ce­ ment; thin-bedded; cross-laminated, high angle compound; c lif f , rough, white, slabby......

SECTION 3, SOUTH OF COW SPRINGS TRADING POST, ONE-HALF MILE SOUTHWEST OF SECTION 2 (Dip 150, S 16° E) CRETACEOUS MESAVERDE GROUP 16.Concealed uppenportion...... 15.Sandstone: yellowish gray: med. sand;thick-bed­ ded; cross-laminated, med. compound; iron con­ cretions, common, ovoid, yellowish gray; c lif f , smooth, white massive; plant fragments, molds, poor, common...... 17.0 14.Sandstone:white: coarse sand; lime; thick-bed­ ded; cross-laminated; med. compound; iron con­ cretions, common, ovoid, yellowish gray; c lif f , smooth, white, massive; plant fargments, molds, poor, common...... 48.0 13.Sandstone:grayish yellow; fine grained; thin- bedded-cross-laminated, medium-compound; c lif f , smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 35.0 12. Sandstone: grayish yellow; fine grained; thin- bedded; cross-laminated, medium-compound; c lif f smooth, yellowish gray, slabby; plant fragments molds, poor common...... 28.0 11. Siltstone:dusky yellow; s ilt ; laminated; fla t- bedded; slope, smooth, yellowish brown, shaley, plant fragments, imprints, poor, abundant...... 19.0 10.Sandstone;yellowish gray, very fine sand; thick- bedded; cross-laminated; medium-compound; c lif f , smooth, yellowish gray, massive; plant fragment s molds, poor, common...... 136.0 Total Incomplete Mesaverde 283T0 MANGOS SHALE 9.Bentonite : . 3 226

F eet 8.Siltstone:Mod. yellowish brown; silt;thinly lam­ inated; flat; wlope; smooth, dk. gray; fissil; pelecypods, fish scales...... 120.0 7.Bentonite...... 3 6 .Siltstone:dusky yellow; s ilt ; thinly laminated; flat; slope;smooth, dk. gray, fissil; pelecy­ pods, fish sc a les...... 10.0 5.Siltstone:mod. yellowish brown; silt; thinly laminated;large cone-in-cone concretions; com­ mon, ovoid, yellowish brown; slope; smooth, grayish yellow, fissile; pelecypods, fish scales 6.0 4 .Sandstone: dusky yellow; very fine grained; laminated; reworked channels; slope; smooth, yellowish grey, slabby...... 5.0 3.Siltstone:mod. yellowish brown; silt; thinly laminated; flat-bedded; slope, smooth, dk. gray, fis s ile ; pelecypods, fish scales; minor benton­ i t e ...... 31.0 2 .Bentonite...... 3 1 .Concealed...... Total of Incomplete Maneos 17276

SECTION 4, EAST SIDE OF KLETHL6. VALLEY (Dip 23°-60, S 58 E) CRETACEOUS MESAVERDE GROUP 18.Sandstone:grayish yellow, fine sand; lime; thick-bedded; cross-laminated, large, compound; iron concretions, common, ovoid, yellowish red, ledge; smooth, yellowish gray, slabby...... 31.0 17.Sandstone moderate brown;very fine grained; lime, thin-bedding; cross-laminated, medium, com­ pound; ripple marks; ledge, smooth, brown, slabby...... 10.0 16.Sandstone: grayish orange; fine grained; lime; thick bedded; cross-laminated, medium-compound, iron balls, common, ovoid, reddish yellow: cliff, smooth, grayish yellow, massive; plant fragments; imprints, poor, common; iron layer at 7 feet and at 12 feet, at 15 feet becomes thin-bedded...... 80.0 15. Concealed...... 80.0 14.Sandstone; yellowish gray; med. sand; cement, lime; thick-bedded; cross-laminated; medium compound; iron b alls, common, ovoid, yellowish red; c lif f , smooth, white, massive...... 60.0 13.Concealed...... 130.0 2 2 ?

12.Sandstone: dusky yellow; very fine grained; lime, thin-bedded; cross-laminated, medium, compound, cliff; smooth, yellowish gray, flaggy, plant fragments, molds, poor, common...... 15.0 Total Llesaverde Group 426.0

LIA.IIC0S SHALE 11.Concealed...... 584.0 10.Concealed...... 2 1 .0 9.Bentonite...... 8 .Sandstones and siltsto n es...... 16^0 Total Maneos Shale 621.0

DAKOTA (?) SANDSTONE 7 .Concealed, Upper Dakota and Dakota-Mancos shale contact...... 6 .Sandstone: dusky yellos; very fine grained; lime, very thin bedded: flat-minor small scale, cross­ lamination; small scale channeling, slope, smooth yellowish gray, flaggy...... 15.0 5 .Iron surface: yellowish gray, very fine grained, lime; iron zone...... 6 4 .Concealed...... 6.0 3 .Sandstone: yellowish gray; fine grained; lime, thick-bedded; cross-laminated; mud pellets, common, ovoid, yellowish gray; c lif f , rough, grayish orange, massive...... 36.0 Total Dakota (?) sandstone...... 57To

JURASSIC MORRISON FORMATION Y/estwater Canyon Sandstone Member 2 .Sandstone: Greyish yellow; fine grained; lime; thin-bedded; cross-laminated; asymmetrical festoon; ledge; smooth, reddish-brown, slabby.. 36.0 Total Thickness, Westwater Canyon 367o Cow Springs Sandstone Member 1 .Sandstone: white; fine grained; lime; thin to thick-bedded; cross-laminated, high angle, compound, slope, smooth, white to It. gray, slabby to massive...... 2 2 8 .

SECTION 5, EAST SIDE OF LOHGHOUSE VALLEY (Dip 200-10°, II 74° E) PRESENT EROSION SURFACE: Top of Black Mesa CRETACEOUS LIES A VERDE GROUP F eet 29.Sandstone: yellowish gray; fine-grained;very thin- bedded; cross-laminated, small, compound; grades in to s h a le s ; iro n c o n c re tio n s , common, ovoid, yellowish red; ledge, rough, yellowish gray, flaggy; plant fragments, imprints, poor, corn- corn...... 121.0 28,Siltstone: It. olive gray; silt; thinly lam­ inated; flat; slope, smooth, white to die. g ray , f i s s i l ; ...... 17.0 27.Sandstone: grayish orange; fine-grained; thin; cross-bedded; medium, compound, weathers into plates; ledge, smooth, brown, slabby; plant frag m en ts; im p rin ts , p o o r, common...... 18.0 26.Sandstone: mod. yellowish brown; very fine­ grained; thick-bedded; cross-laminated; divides into several sand layers with shale partings; slope, smooth, yellowish gray, massive; plant frag m en ts, m olds, p o o r, common...... 70.0 25.Sandstone: very It. gray; fine-grained; thick- bedded; cross-laminated, large, compound; channels; cliff, smooth, yellowish gray, mas­ s iv e ; worm t r a i l s and p la n t fra g m e n ts...... 5l'*0 24.Siltstone: It. gray, silt; thinly laminated; flat-bedded; slope, smooth, dk. gray, fissile, p la n t frag m en ts, im p rin ts , p o o r, ab u n d an t...... 11.0 23.Sandstone: very It. gray; fine to very coarse grained; thick-bedded; cross-laminated, medium compound; iro n c o n re tio n s , common, ovoid, y e l­ low ish re d ; c l i f f , smooth, w h ite , m assiv e...... 94.0 22.Sandstone: yellowish gray; coarse to very coarse grained; thick bedded; cross-laminated; iron concretions, ovoid, yellowish red, cliff, smooth It. yellow, massive...... 10.0 21.Sandstone: yellowish gray; sand, medium grained; thin-bedded; cross-lam inated; medium, compound, festoon type; iron concretions, common, ovoid, yellowish red; cliff, smooth, grayish yellow, slab b y ; p la n t fra g m e n ts...... 30.0 2 0 .C o al...... 22.0 19.Sandstone:v/hite, fine grained; thin-bedded; cross-laminated; cliff, smooth, yellowish gray, slabby; becomes thin-bedded at top, grad­ ing in to c o a l...... 29.0 2 2 9 . Feet iS.Siltstone: yellowish gray; s ilt; laminated; flat-bedded; cliff, smooth, dk. gray, shaly, plant fragments, imprints, poor, abundant...... 44.0 17.Sandstonei dusky yellow; fine-grained; thin- bedded; cross-laminated, medium low angle and compound; ripples, c lif f , smooth, yellowish gray, slabby...... 108.0 Total Incomplete Mesaverde group 625.0

MANGOS SHALE 16.Mudstone:yellowish gray; s ilt and clay;very thin bedded; reworked; channeling, current markings; ledge, smooth, yellowish gray, flaggy Prionotronis. mold,good, common...... 437.0 15.Mudstones: pale yellowish orange; s ilt and clay; very thin-bedded; reworked; channeling, cur­ rent markings; ledge, smooth, yellowish gray, flaggy; Prionotropis. mold, good, common; bentonite...... 115.(M O 14.Bentonite...... 13. Siltstone: med. dark gray; s ilt ; thinly lamina­ ted; flat; bedded; slope; smooth, black, fis­ sile; Pelecypods, fish scales, orginal hand parts, poor, common...... 35*0 12. Bentonite...... 3 11. Siltstones:yellowish gray; s ilt ; thinly laminated flat-bedded; slope, smooth, dk. gray, fissile, plant fragments, imprints, poor, abundant...... 10.6 lO.Claystone: very It. gray; clay; lime; abundant Metoicoceras, sp., Pelecypods; nodular limy claystone...... 1.0 9.Siltstone: It. gray; clay with s ilt ; thinly laminated; flat-bedded; slope, smooth, dk. gray, fissile; plant fragments, imprints, poor, abun­ dant...... 5.0 8. Bentonite...... 3 7.Siltstone: yellowish gray; s ilt ; thinly lamina­ ted; flat-bedded; slope, smooth, dk. gray, fissile; plant fragments, imprints, poor, abun­ dant...... 26.0 Total Mancos shale 630.O

DAKOTA (?) SANDSTONE 6. Coal...... 5.0 2 3 0 .

F e e t 9 5»Siltstone: grayish brown; lig n ite, carbonaceous siltstone; thinly laminated; flat-bedded; slightly pseudo cross-laminated; ripple marks; slope, smooth, black, fissle; plant fragments, coal, poor, abundant...... 5*0 4 .Sandstone: yellowish gray; very fine-grained; coal and mica concentrate on the bedding planes, very thin-bedding; cross-laminated, small scale channeling, reworking; ledge, smooth, grayish yellow; flaggy...... f ...... 9.0 3 .Sandstone: grayish yellow, very fine-grained; lime; thin-bedded; cross-laminated; small scale; iron layer on bedding planes; iron con­ cretions and mud pellets; common, ovoid, gray­ ish orange; ledge; smooth, grayish yellow, slabby; plant fragments, imprints, poor, corn- common...... 39.0 2 .Conglomerate:grayish yellow; fine-grained; lime; thick-bedded; cross-laminated, medium; sand inclusions; common, ovoid, yellowish gray, cliff, rough, yellowish gray, massive; plant fragments; external mold, poor, common...... 2 .0 Total Dakota (?) sandstone toTo

UNCONFORMITY Erosional, 2 to 3 feet relief, filled with reddish brown sandstone and pebbles. JURASSIC MORRISON FORMATION Westwater Canyon Sandstone Member 1 .Sandstone:yellov/ish gray; medium-grained; lime; thin-bedded; cross-laminated; cliff, smooth, reddish brown, slabby......

SECTION 6, EAST SIDE KIETHLA VALLEY (Dip 60-2°, S 21° E) CRETACEOUS MESAVERDE GROUP 10.Sandstone: yellowish gray, fine-grained; thick- bedded; cross-laminated, medium compound;slope, smooth, white, massive...... 58.0 9.Concealed...... 1 1 9 .0 2 3 1 .

Feet 8 .Sandstone: yellowish gray; fine-grained; thick- bedded; cross-laminated; medium compound; slope, smooth, white, massive...... 21.0 7 .Sandstone: grayish orange; fine-grained; lime; thin-bedded; cross-bedded; cliff, smooth, yel­ lowish gray, slabby...... 38.0 Total incomplete Mesaverde Group 236.0 MANGOS SHALE 6 .Concealed...... 306.0 5 .Concealed...... 565.0 At 565 feet concretionary mudstone-oyster bed occurs. Total Mancos Shale 871.0 DAKOTA (?) SANDSTONE 4 .Coal...... 4.0 3. Concealed...... 30.0 2 .Sandstone: yellowish gray; med.-grained; thin- bedded; cross-laminated, compound, medium; iron nodules, common, ovoid, yellowish gray; ledge, rounded, yellowish gray, slabby...... 80.0 Total Dakota (?) Sandstone 114.0 UNCONFORMITY Erosional, up to 2 feet relief, yellowish gray incolor. JURASSIC MORRISON FORMATION V/estwater Canyon Sandstone Member 1 .Sandstone: grayish olive; fine-grained; lime; thick-bedded; cross-laminated; compound, med­ ium scale; ledge, smooth, light olive gray, slabby.

SECTION 7, SOUTH END LONGHOUSE VALLEY (Dip 16°, S 61° E)

CRETACEOUS MANCOS SHALE 2 3 2 .

5 .Sandstone: yellowish gray; very fine-grained, Feet very thin bedded; flat-bedded, showing many reworked zones; channels; ledge, smooth, yellowish brown, flaggy; plant fragments, molds, poor, common...... $4.0 Total Incomplete Maneos Shale $4.0 DAK0TA(?) SANDSTONE 4 .Coal...... 6.0 3. Concealed...... 34.0 2 .Sandstone: yellowish gray; fine-grained; thick-bed­ ded; cross-laminated, medium compound: channels, iron layer at top; cliff, smooth, yellowish gray, massive...... 6$,0 Total Dakota (?) Sandstone 10$.0 UNCONFORMITY Erosional, 3 to $ feet relief,granule and pebble conglomeratic sandstone...... JURASSIC MORRISON FORMATION Westwater Canyon sandstone Member 1.Sandstones: yellowish gray; medium sand grained; lime; thin-bedded; cross-lamina ted; cliff, smooth, reddish-brown, slabby......

SECTION 8, EASTSIDE KLETHLA VALLEY (Dip 60-2°, S 18 E) CRETACEOUS MESAVERDE GROUP 16.Sandstone: dark yellowish orange; coarse and very coarse grained; thick-bedded; cross-lam­ inated; medium-compound; channels; iron con­ cretions; abundant, ovoid, yellowish red, cliff; smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 4$.0 1$.Claystone:I t . brownish gray; clay and s ilt; lime; thinly laminated; flat-bedded; slope, smooth, dark gray, fissil; plant fragments, imprints, poor, abundant...... 13.0 14.Sandstone: grayish yellow; fine-grained; lime, thin-bedded; cross-bedding, medium compound and in places, torrential; cliff, smooth, yellowish gray, slabby; plant fragments, mold, p o o r, common...... 9*0 13.Siltstone: med. It. gray; silt; lime; thinly 2 3 3

Feet flat-bedded; lens of coal; slope, smooth, dk. gray; fissile; plant fragments, imprints, poor, abundant...... 17.0 12.Sandstone: grayish yellow; fine-grained; lime; thin-bedded; cross-laminated; very hard iron layer on top; iron concretions, common, ovoid, yellowish red; cliff, smooth, rounded, yellow­ ish gray, slabby; plant fragments; molds, poor, common...... 20.0 11.Sandstone: very It. gray; very coarse-grained; lime;thick-bedded; cross-laminated, medium- compound; iron concretions, common, ovoid, yellowish red; cliff, smooth, white, massive, Plant fragments, molds, poor, rare...... 51.0 10.Sandstone: grayish yellow; fine and medium­ grained; lime; lime; thin-bedded; cross-lam­ ination, small, compound; channels, iron con­ cretions, yellow red; slope, smooth, white, slabby...... 55*0 9 .Sandstone: grayish yellow; medium sand grained; thin-bedded; cross-lamination, medium compound; cliff; smooth, yellowish gray, slabby...... 7.0 8.Lignite: contains shale layers as bone...... 2.0 7 .Sandstone: grayish orange; med. to very coarse­ grained; hard iron layer...... 7.0 6.Sandstone:grayish yellow; fine-grained; lime; very thin-bedded; cross-laminated; low angle and medium compound; ledge, smooth, yellowish gray, flaggy, plant fragments, molds, poor, common...... 80.0 Total Incomplete Llesaverde Group 306.0 MallC OS SHALE 5. Concealed...... 581.0 Total Maneos Shale polTo DAKOTA (?) SANDSTONE 4 .Coal: poorly exposed...... 1.0 3. Concealed...... 84.0 2 .Conglomerate: 0 to 2 feet basal conglomerate; grayish yellow; medium-grained; lime; thin; cross-laminated; medium compound; with gravels on bedding planes; c lif f , rough, yellowish- gray; slabby...... 2.0 TOTAL Dakota (?) sandstone 87.0 UNCONFORMITY Erosional, no apparent relief; occasional granule to pebble conglomerate. 2 3 4 . Feet JURASSIC MORE IS OH FORMATION Westwater Canyon Sandstone Member 1 .Sandstone: yellowish-gray; fine-grained; thick-bedded; cross-laminated, high-angle, compound; c lif f , smooth, yellowish brown, massive.

SECTION 9, NORTH OF ROAD IN BLUE CANYON (Dip 2°, S 37° E) CRETACEOUS MESAVERDE GROUP 32. Sandstone:grayish yellow; med-grained; lime; thin-bedded; cross-laminated, medium, compound, iron concretions, common, ovoid, reddish yel­ low; slope, rounded, white, slabby...... 10. 0 31.Siltstone: yellowish gray; s ilt ; thinly laminated flat-bedded; slope, smooth, gray, fissile, plant fragments, imprints, poor, rare...... 18. 0 30.Sandstone:very pale orange; very fine to very coarse grained: lime; thick-bedded; cross- laminated, small, compound; cliff, rough, white, massive...... 11. 0 29.Sandstone: grayish yellow; fine-grained; lime; very thin-bedded; cross-laminated; cliff, smooth, yellowish brown, flaggy; plant fragments imprints, poor, rare...... 34. 0 28. Sandstone: pale olive; very fine-grained; thin­ ly laminated; lenticular; slope, smooth, dk. green, fissile; plant remains, imprints, poor, abundant...... 37. 0 27.Sandstone:grayish orange; fine and medium­ grained; hard iron layer; thick-bedded-cross- laminated, medium compound; c lif f , rounded, yellowish brown, massive; plant fragments, molds, poor, common...... 36.0 26.Coal-Lignite-Claystone: brownish gray; thinly laminated; flat, variegated; slope, smooth, black, fissile; wood fragments, coalified, poor, common...... 10. 0 25.Sandstone: yellowish gray; fine-grained; thin- bedding; minor cross-lamination, small scale; ledge, smooth, gray, flaggy; plant frag, molds, poor, abundant...... 0 3. 235o Feet 2 4 .C oal: c o n ta in s sandy bone la y e r s ...... 1 2 .0 23.Sandstone: white to dk. yellowish orange; fine­ grained; lime; thick-bedding; cross-lamination, medium compound; lenticular; cliff, smooth, yellowish brov/n, massive; plant fragments, m olds, good, common...... 36.0 22.Sandstone: yellowish gray and pale yellowish brown; fine-grained; very thin bedding; cross- laminated, lenticular; channels; slope; smooth, dark gray, slabby; wood fragments, coalifled, good, num erous...... 55.0 21.Sandstone: white; medium-grained; thin-bedded; cross-laminated; low angle; channels, festoons in upper portions; cliff, smooth, grayish yel­ low, fla g g y ...... 63.0 Total Incomplete liesaverde Group 325.0 MANGOS SHALE 20.Siltstone: Oliver gray; silt; cone-in-cone at at 14’, concretions at 14', 30'; thinly lam­ inated; flat-bedded; cone-incone concretions, common, ovoid, y e llo w ish orange; slo p e , smooth, dark gray, fissile; pelecypods, fish scales; original hard parts, poor, common...... 54.0 19. Bentonite...... 3 iS.Siltstone: yellowish gray; silt; lime; cone-in­ cone at 1', 16'; concretionary at 11'...... 60.0 17.Siltstone: grayish yellow; fine-grained; lime; very thin-bedded; gnarly, reworked zone; channels; ledge, smooth, yellowish gray, flag­ gy; Prionotropis, sp. Pelecypods, casts, good, abundant; sandstone at 8' and 131, 44', 59'j 95'j 107'; 120', bentonite at 4 5 '...... 141.0 16.Sandstone with cephalopoda; grayish yellow; fine-grained; lime; very thin-bedded; gnarly- reworked zone; channels; ledge; smooth, yel­ lowish gray; falggy; Pridnotropis. sp ., Pelecy­ pods, casts, good, abundant...... 2 .0 15.Siltstone: moderateyellowish brown; silt; lime, laminated; flat-bedded; slope, smooth, dark gray, shaly; Prionotropis, sp., Pelecypods; m olds, good, common...... 32.0 14.Siltstone: med. gray; s ilt ; lime; sandstone occurs as layers at 8, 25> 42 feet. Bentonite at 50’, 52', 54', 55', 58', 60', 63', 64', 65', 71', 76', 78', 80', 81', 83' ...... 83.O 13.Siltstone: med. gray; s ilt ; lime; thinly lamina­ ted; flat-bedded; slope, smooth, It. gray, fissile; Pelecypods, original hard parts, poor, common; contains Bentonite at 1 4 ', 47'. Contains concretions at 4 2 '; ss. layer at 55', 78', 122' .1 2 4 .0 2 3 6 .

la.Siltstone: med. gray; silt; lime; thinly lam­ F e e t inated; slope, smooth, dk. gray, fissile; con­ tains Bentonite at 3', 28', 36*, 42*, 62*; Gryphae at 4 4 '...... 68.0 Total Maneos Shale 564.0 DAKOTAX?) SANDSTONE 11.C oal; c o n ta in s 311 of B e n to n ite ...... 3 .0 1 0 .B e n to n ite :...... 2 .0 9 . C o a l:...... 4 .0 S.Siltstone: It. gray and dark gray; silt; thin­ ly laminated-flat-bedding; slope; smooth, gray, fissile; plant fragments, imprints, poor, abun­ d a n t...... 3 .0 7.Carbonaceous siltstone: black, silt; thinly laminated; flat-bedded; slope, smooth, black, fissile; plant fragments, imprints, poor, abun­ d a n t...... 2.0 6.Siltstone: greenish gray; silt; thin-bedded; flat bedded; slope; smooth, dark gray, slabby; plant fragments, imprints, poor, abundant...... 3 .0 5.Sandstone: yellowish gray; fine-grained; lime; thin-bedded; lenticular; plant fragments along bedding planes; shale fragments, rare, ovoid, yellowish gray; cliff, rough, grayish yellow, slabby; plant fragments, imprints, poor, com­ mon ...... 5 .0 4.Siltstones with coal: graditional from med. It. gray to black silt; silt; thinly laminated; flat; slope, smooth, black, fissile; grada­ tional contact with underlying ss. becomes coal then black siltstone, gradational upper c o n ta c t...... 6.0 3.Sandstone: grayish yellow; fine to medium-grained lime; thin-bedded; lenticular; plant fragments along bedding planes; shale fragments, rare, ovoid, yellowish gray; cliff, rough, grayish yellow, slabby; plant fragments, imprints, p o o r, common...... 6.0 2.Sandstone: banded black and white; fine-grained, lime;very thin; channeling; c liff, rough, gray, fla g g y ...... 6.0 Total Dakota (?) Sandstones 40.0 UNCONFORMITY Erosional, 3 to 16 feet relief, shales and sand stones, minor coals as filling. JURASSIC MORRISOH FORMATION 2 3 7 .

Cow S p rin g s Sandstone Member F e e t 1.Sandstone: It. gray; fin-grained; thick-bedded; cross-laminated; large scale, truncated wedge, c l i f f , smooth, w h ite , m assiv e......

SECTION 10, 3 MILES SOUTH OF TSEGI TRADING POST (Dip 26°-66> S 62 E) CRETACEOUS MESAVERDE GROUP 29.Sandstone: very pale orange; med.-grained;very thick bedded-cross-laminated; cliff, smooth, yellowish orange, massive; Pelecypods, molds, good, r a r e ...... 52.0 28.Siltstone: brownish gray; silt; thinly laminated, flat, to lenticular; slope, smooth, dark gray, fissile; plant fragments, coal, poor, abundant. 30.0 27.Sandstone: white; fine-grained; thick-bedded; cross-laminated; cliff, smooth, eyllowish gray, massive; plant fragments...... 19.0 26.Burnt Shale: pale red, silt; very thin bedded; slope; rough, brown, flaggy; plant remains, im p rin ts , good, common...... 30.0 25.Siltstone: pale red; silt; very thin bedded; slope, rough, flaggy, brown; plant remains, im p rin ts , good, common...... 24.0 24.Burnt Shale: grayish orange; very thin; slope, rough, brown, flaggy; plant remains, imprints, good, common...... 58.0 23.Sandstone: very It. gray; very fine-grained; alternations of sands §nd shales with coals up to 6 feet; very thin-bedded; cross-laminated; compound; slope, smooth, yellowish gray, flaggy, p la n t frag m en ts, im p rin ts , p o o r, ab u n d an t...... 201.0 22.Siltstone: It. brownish gray; silt; thinly lam­ inated; flat to lenticular; slope, smooth, gray, fissile; plant fragments, imprints, poor, ab u n d an t...... 9 = 0 21.Sandstone: yellowish gray and brownish gray, very fine-grained; very thin-bedded; lenticular; ripple marks show psedo-bedding; slope, smooth, gray, flaggy; plant fragments, coalified, poor, ab u n d an t...... 3 5 .0 20.Siltstone: dusky brown; silt; laminated; flat- bedded; slope, irregular, gray, shaly; plant fragments, coalified, good abundant...... 18.0 2 3 8 .

F eet 19.Sandstone: grayish orange; medium-grained; very thick-bedded; cross-laminated; cliff, smooth j brown, massive; plant fragments, molds, poor, c ...... 91.0 18.Conglomerate: pale to dk. yellowish orange; thin-bedded; minor graded bedding; ledge, smooth, y ello w , sla b b y ...... 3.0 17.Siltstone: dusky yellow; silt; thinly laminated, flat-bedded; slope, smooth, brown, fissile, plant fragments, imprints, poor, abundant...... 35.0 16.Sandstone: grayish yellow; fine-grained; very thin-bedded; cross-laminated, small, compound, channels showing reworking; ledge; smooth, yellowish gray; flaggy; plant fragments, im­ p r i n t s , p o o r, ab u n d an t...... 60.0 l^.Siltstone:brov/nish gray; silt; thinly laminated; cross-laminated, small-compound; sandstone, inclusions, rare, irregular, grayish yellow; slope, smooth, black fissile; plant fragments, imprints, poor, abundant; contains coal and silt. 19.0 14.Sandstone: greenish gray; very fine-grained; lime; thin-bedded-; cross-laminated, small, com­ pound; cliff; rounded, yellowish gray; slabby.. 14.0 T otal Lie saver de Group 698.0 MANGOS SHALE 13. C o n c ea led :...... 672.0 l2.Siltstone: It. olive gray; silt; thinly lamina­ ted; flat-bedded; slope; smooth, dark gray, fissile; Pelecypods, fish scales, original hard p a r t s , p o o r, common...... 12.0 ll.Siltstone: med. dk. gray; silt; thin-bedded; ledge, smooth, gray, slabby; Gryphia, original hard p a r ts , good, ab u n d an t...... 7 .0 10.Sandstone: yellowish gray; fine-grained; lime; thin-bedded; gnarly, with channels showing re­ w orking; le d g e , rough, g ray , sla b b y ...... 4 .0 Total Maneos Shale 695.0 DAKOTA (?) SANDSTONE 9.Coal: this coal contains thin ss. leaf zone...... 8.0 8.Siltstone:very It. gray; silt; laminated; chan­ neling; abundant ripple marks; slope, smooth, It. gray, shaly; plant fragments, imprints, p o o r, common...... 5 .0 7.Siltstone: mod. It. gray; silt; thin-bedded; cross-laminated, med. scale, compound; cliff, smooth, It. gray, flaggy ...... 6 .9 2 3 9 .

Feet 6 .Sandstone: pale yellowish brown; very fine­ grained; coated with lime; thin-bedded; cross-laminated, med., scale, compound; surfaces contain heavy iron layer; cliff, rough, yellowish brown, flaggy...... 6.0 5.Sandstone: pale greenish yellow; med.-grained; thick-bedded; cross-laminated; med. scale, compound; mud pellets, abundant, ovoid, gray­ ish yellow; cliff, rough, grayish yellow; massive;...... 95.0 4.Sandstone: white; fine-grained; thin-bedded; cross-laminated; large scale, compound; thin pellets, rare, ovoid, various; cliff, smooth, white, flaggy...... 6.0 Total Dakota (?) Sandstone 126.0 UNCONFORMITY Erosional, 3 feet relief, granule to pebble con­ glomerate. JURASSIC MORRISON FORMATION Y/estwater Canyon sandstone Member 3 .Sandstone and shale: yellowish gray to reddish- brown; medium-grained; lime; sub-angular; thin- bedded; cross-laminated; festoon, asymmetri­ cal and plunging; ledge, smooth, reddish, brown, slabby...... 252.0 Recapture Shale and Saltwash Sandstone Members 2.Sandstone and shales:interbedded but in general the shales overlay the sands; reddish brown.... 300.0 Cow Springs Sandstone Members 1.Sandstone: white; fine-grained; thin-bedded; cross-laminated; medium scale; slope, smooth, white, slabby...... 64.0

SECTION 11, NORTH END OF MARSH PASS (Dip 9°-20, S 5 E) CRETACEOUS MESAVERDE 240

Feet 36 .Sandstone; grayish yellow; fine-grained; lime; very thick-bedded; cross-laminated; large, compound and to rre n tia l; c liff; smooth, yel­ lowish gray, massive; Inoceramus, sp., cast and molds, good, common...... 3 0 1 .0 35.Coal...... 7oO 34.Sandstone: yellowish gray; fine-grained; lime; thin-bedded; cross-laminated, small, compound, ledge, smooth, yellowish gray, slabby; plant fragments, coalified, poor, common...... 21.0 33«Siltstone: grayish brown; silt; at 9% 2‘ of lignite; thinly laminated; flat-bedded; slope, smooth, brown, fissile; part fragments, coal­ ified , poor, abundant...... 17.0 32 .Sandstone:pale yellowish brown; very fine-grained, laminated; channeled, reworked; iron concretions, common, ovoid, yellowish red; ledge, smooth, It. gray, platy; plant fragments, coalified, poor, common...... 9 .0 31.Siltstone: brownish gray; silt; thinly lamina­ ted; flat to lenticular; slope, smooth, brown, fissile; plant fragments, coalified, poor, abundant...... 19.0 30.Claystone: brownish black, clay; thinly lamina­ ted; flat-bedded; slope, smooth, black, fissile, plant fragments, coalified, good, abundant; becomes coal inplaces ...... 15«0 29.Sandstone: yellowish gray; fine-grained; thick- bedded-cross-laminated, small scale, compound, ledge, smooth, yellowish gray, massive; plant fragments, molds,poor, rare ...... 10.0 28.Sandstone to silt: pale yellowish brown to gray­ ish yellow; very thin-bedded; cross-laminated, small; ledge, smooth, yellowish brown, flaggy, plant fragments,coalified, poor, common...... 14.0 27.Coal...... 14.0 260Siltstone; It. brownish gray; silt; thinly lam­ inated; flat- to lenticular; slope, smooth, brown, fissile; plant fragments, coalified, poor, common...... 10.0 2$\Sandstone: grayish yellow to white; fine-grained, thin-bedded; cross-lamination, medium compound; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, rare ...... 21.0 24.Coal: tran sitio n zone from coal to s ilts to n e .... 5.0 23.Sandstone: white; very fine-grained; very thin- bedded; lens; ledge, smooth, brown, flaggy; plant fragments,imprints, poor, abundant...... 15.0 241

Feet 22. L ignite: ...... 3 .0 21.Sandstone: yellowish gray to brownish gray; very fine-grained; thin-bedded; cross-lamina­ tion, small, compound; ledge, smooth, brown, slabby; plant fragments, coalified, poor, com­ mon...... 8.0 20.Sandstone: pale yellowish orange; fine-grained; very thin-bedding; flat-bedded; ledge, smooth, yellowish brown, flaggy; plant fragments, coalified, poor, abundant...... 22.0 19. Coal...... 2 .0 iS.Siltstone: It. brownish gray; silt; very thin- bedded; lenticular; ledge, rough, yellowish gray; flaggy; plant remains, imprints, good, abundant...... 3 .0 17.Sandstone: very It. gray; fine-grained; thin- bedded; cross-bedding, small-compound; ledge, smooth, yellowish brown, slabby; plant fragments, imprints, poor, common...... -5 o0 16.Sandstone: pale yellowish orange; very fine­ grained; top 3 * coal; very thin-bedded; len­ ticular; ledge, rough, yellowish gray, flaggy; plant fragments, imprints, good,common ...... 15.0 15.Sandstone: yellowish gray; fine-grained; thick- bedded; flat-bedded; mud pellets, common, ovoid, gray; ledge, smooth, yellowish gray,massive... 4.0 14.Sandstone to silt: pale yellowish brown to yellowish gray; sand to silt; thin-bedded; cross-laminated: small, compound; ledge, smooth, gray, slabby; plant fragments, molds, poor, c o m m o n !...... 26.0 13.Sandstone: grayish yellow to pale yellowish brown; fine sand with silt pellets; very thin- bedded; lenticular; ledge, rough, yellowish gray, flaggy; plant fragments, itoprints, good, common...... 12.0 12.Sandstone: yellowish gray; very fine-grained; lime; thick-bedded; cross-laminated; medium, compound; ripples, ledge, smooth, yellowish gray, massive...... 11.0 11.Sandstone: grayish yellow; fine-grained; at 5 3 1 ss. becomes white near conglomerate; lime; thick-bedded; cross-laminated, medium, compound, iron concretions; common, ovoid, yellowish orange; ledge, smooth, yellowish gray, mas­ sive; plant fragments, molds, poor, common...... I 69.O 10.Sandstone: white, coarse-grained; thick-bedded; thick; cross-laminated; medium to large com­ pound; iron concretions, common, ovoid, yel­ lowish red; cliff, rounded, white, massive; plant fragments, molds, poor, common...... 24.0 242

Feet 9.Siltstone: brownish gray; silt; coal at 4* lignite at 141; thinly laminated; flat-bed­ ded; slope, smooth, brown, f is s ile ; plant fragments, molds, poor, common...... 16.0 8.Sandstone: pale greenish yellow; fine-grained; thin-laminated; cross-laminated, low angle to medium scale compound; ledge, smooth, gray, slabby; plant fragments, molds, poor, rare...... 45.0 Total llesaverde Group 843.0 MANGOS SHALE 7. Concealed...... 700.0 6. Concretionary lime...... 2.0 5.Sandstone: grayish yellow; fine-grained; fossils, lime; very thin-bedded; cross-laminated, small, scale, compound; ledge, rough, yellow, flaggy, Gryphae, original hardparts, good,abundant... 6.0 TotalManeos Shale 70o.O DAKOTA (?) SANDSTONE 4.Sandstone: grayish yellow; very fine-grained; with thin coals; very thin-bedded; cross-lam­ ina ted, small scale, compound; surface shows much reworking; channeling; ledge, rough, yellow, flaggy; plant fragments, imprints, poor, abundant...... 6.0 3 .Siltstone: yellowish gray; silt; contains coal, thinly laminated; flat-bedding; slope; smooth, yellowish brown, fissile; plant fragments, imprints, poor, abundant...... 30.0 2 .Sandstone: grayish yellow; fine-grained; lime; very thin to t ick-bedded; cross-laminated, large scale; cliff; smooth, yellowish brown, flaggy to massive; plant remains, imprints, poor, common...... 66.0 Total Dakota(?) Santstone 102.0 UNCONFORMITY: Erosional, 3- 2 0 1 relief, filled with granule and pebble conglomerate as lenticular masses in yellowish gray sandstone. JURASSIC MORRISON FORMATION Westwater Canyon Sandstone Member l.Pale olive to mod. bron; very fine-grained; lime, very thin bedding; cross-laminated, med. scale; compound; slope, rough,olive, slabby...... 243

Feet SECTION 12. COW SPRINGS COAL I.1IIIE ROAD (Dip 40-2°, S 45 E)

CRETACEOUS HESAVERDE GROUP 31. Sandstone: I t. brown;, med. sand; contains some coal; very thick-bedded; cross-laminated, medium-compound; c liff , smooth, reddish brown, massive; plant fragments, molds, poor. rare... 3 2 .0 30 .Shale and coal: coal seam at 6 ’; very thin- bedded; flat-bedded; slope, smooth, dk. gray, flaggy; plant fragments, imprints, poor, abundant...... 14.0 29*3andstone:grayish yellow; fine-grained; hard iron layers occur at 5 0 ', 85 *,. I l l ' , 121?, very thick-bedded; cross-laminated; large, compound; c lif f , smooth, yellowish gray; mas­ sive; plant fragments, molds, poor, abundant.. 129.0 28.Siltstone: yellowish gray; silt; contains sev­ eral minor coal seams; laminated; flat to lenticular; slope, smooth, dark gray, shaley; plant fragments, imprints, poor, abundant...... 16.0 27.Sandstone: yellowish gray; fine-grained; hard iron layers occur at 2 2 ', 25‘> 47', 6 5 ' . This sand is same sand that is immediately above the Kayenta Coal Mine; lime; thick-bedded; corss-laminated; medium, compound; iron con­ cretions, abundant, irregular, yellow brown; cliff, smooth, yellowish gray to white, mas­ sive; plant fragments, molds, poor, rare...... 69.0 26.Siltstone: grayish brown, siltstone; at 11' a 1 ' iron layer poorly exposed. At 25* a 2 ' . coal, contains some coal seams...... 54.0 2^,Sandstone: yellowish gray to med. yellowish brown; fine-grained to very fine-grained; thick-bedded; cross-laminated; medium compound; ledge, smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 6.0 24.Coal: weathered; at 3' a 2 ' coal seam, poorly exposed but same sequence as previous shales has coal seams...... 17.0 23.Sandstone: pale yellowish brown, very fine­ grained; lime; thick-bedded; cross-laminated, medium.compound; ledge, smooth, yellowish gray, massive; plants fragments, molds, poor, common...... 7.0 22.Sandstone: yellowish gray to pale yellowish 244.

Feet brown; fine-grained; lower 10* sandstone ledge former; at 24• a 4* coal; lime; thick- bedded; corss-laminated, medium compound; ledge, smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 42.0 21.Siltstone: pale brown; clay; grades upward into coal and finally lignite; finely lamina­ ted; flat-bedded; slope, smooth, brown, fis­ s il e ...... 11.0 20. Sandstone: yellowish gray; fine-grained; ;lime; very thin-bedded; cross-laminated, small,com­ pound; slope, smooth, yellowish gray, slabby; plant fragments, imprints, poor, abundant...... 13.0 19.Claystone: pale brown; clay; grades upward into coal and lignite; finely laminated; flat- bedded; slope, smooth, brown, f i s s i l e ...... 19.0 18.Sandstone: It. brown to dark yellowish orange; very fine sand, ripple marks...... 4.0 17.Siltstone: brownish gray; silt; at 48', con­ cretions zone; at 551 a 4' coal (Lignite) ; laminated; iron concretions, common, oval to elongate, red; slope, smooth, dk. gray, shaly; plant fragments, imprints, poor, common...... 72.0 16.Sandstone: yellowish gray; very fine-grained; lime; very thin-bedded; pseudo-cross lamina­ tion; ripple marks; ledge, irregular, yellow­ ish gray, flaggy; plant fragments, molds, poor, ra re ...... 10.0 15.Siltstone: dusky yellow to brownish gray, silt; thinly laminated; flat-bedded; iron conretions; common,elongate, red; slope, smooth, dark gray, fissile; plant fragments, imprints, poor, common...... 33.0 14.Sandstone: dk. gray to orange pine; very fine grained; lime; very thin-bedded; cross-lamina­ ted; small, compound; iron zones, common, oval to elongated, red; ledge, smooth, yellowish gray, flaggy; plant fragments, molds, poor, rare; th is ss. capped by iron lay er...... 4.0 13.Siltstone: It. olive gray; silt; thinly lamina­ ted; flat-bedded; slope, smooth, It, gray to black, fissile; plant fragments, imprints, poor, abundant; contains a few thin coal areas...... 37.0 12.Sandstone: pale yellowish orange; med.-grained; lime; thin-bedded; crossplaminated, small, compound; ledge, smooth, yellowish gray, slab­ by; plant fragments, molds, poor, common; this has a very hard iron layer in 6" top...... 48J0 245

Feet 11.Sandstone: grayish yellow; med-grained; thick- bedded; cross-laminated up to large scale com­ pound; iron-concretions, common, oval, yellow­ ish red; ledge; smooth, yellowish gray, mas­ sive; plant fragments, molds, poor, rare;;.... 77-0 10.Sandstone: grayish orange; very fine-grained; lime; laminated; lenticular; ledge, smooth, yelowish gray, shaly; plant fragments, im­ prints, poor, common...... 4.0 9.Siltstone; yellowish gray; silt; thinly lamina­ ted; lenticular; slope, smooth, yellowish gray, fis s lie ; plant fragments, r a r e ...... 9.0 8.Sandstone: grayish yellow; fine-grained; lam­ inated; cross-laminated; small; much reworking, iron concretions in zones, common, ovoid, yellowish red; ledge, smooth, gray, platy; plant fragments imprints, poor, common...... 44.0 7.Sandstone: pale yellowish orange to grayish yellow; med. to very coarse-grained; lime; thin-bedded; cross-laminated; medium scale compound; iron concretions, common, ovoid, yellowish gray; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common.. 51.0 6.Siltstone: dusky yellow; silt; lime; thinly laminated; lenticular; iron concretions, com­ mon, ovoid, yellowish red; slope, smooth, yellowish gray, fissile; plant fragments, imprints, poor, r a r e ...... 9.0 5.Sandstone: grayish yellow; fine and med.-grain; lime; thin-bedded; cross-laminated; medium compound; mud p e lle ts, common, ovoid, grayish yellow; slope, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 23.0 4.Siltstone: pale yellowish brown silt to It, brownish gray; silt; thinly bedded; reworked; iron concretions, common, ovoid, yellowish red; slope, smooth, yellowish gray to brown, fissile; plant fragments, imprints, poor, common...... 13.0 3.Sandstone: pale yellowish orange; fine-grained; lime; thin-bedded; cross-laminated; medium compound; slope, smooth, yellow brown, slabby; plant fragments, mold, poor, common...... 73.0 2.Claystone: pale brown and lignite; thinly-bed­ ded; flat-bedded; slope, smooth, black, fis­ sile; plant fragments, imprints, poor, abund- dant; contains coal...... • • •...... 5.0 1.Sandstone: grayish yellow; very fine-grained; lime; very thin-bedded; cross-laminated, med­ ium compound; mud p ellets, abundant, ovoid, It. gray; slope, smooth,gr. yellow, flaggy.... 49.0 Total Incomplete Mesaverde 994.0 2 4 6

Feet SECTION 13, 1 MILE SOUTH OF COW SPRINGS COAL MINE ROAD (Dip 46o-30°, S 14 E) CRETACEOUS MESAVERDE GROUP 50.Sandstone: very pale orange to grayish yellow; fine-grained; lime; thick-bedded; cross-lam­ inated, compound, medium; c lif f , smooth, yel­ lowish gray, massive; plant fragments, molds, poor, common...... 33.0 49.Siltstone: grayish yellow; silt; laminated; flat-bedded; slope, smooth, dark gary, platy, plant fragments, molds, poor, common...... 5.0 48.Sandstone: grayish yellow; fine-grained; lime; thick-bedded; cross-laminated; medium scale compound; ledge, smooth, grayish yellow, mas­ sive; plant fragments, mold, poor, common...... 16.0 47.Siltstone: It. olive gray; silt; 1* ss. at 161 finely laminated; flat-bedded; iron layer, ore, f la t, yellowish red; slope, smooth, dark gray, fissile; plant fragments, imprints, poor, abund­ an t...... 25.0 46.Sandstone: pale greenish yellow; sand, fine­ grained; lime; thick; cross-laminated, compound, medium; iron concretions, common, ovoid, yel­ lowish red; ledge, smooth, yellowish gray, massive; plant fragments, mold, poor, common.... 23.0 45.Siltstone: very It. gray; silt; lime; laminated; slope, smooth, dark gray, p la ty ...... 23.0 44.Sandstone: grayish yellow; med.-grained; lime; thick-bedded; crossdlaminated, medium compound; ledge, rough, yellowish gray, massive; plant fragments, molds, poor, common...... 127.0 43.Siltstone: pale brown; silt; laminated; cross- laminated, small compound; slope, smooth, brown­ ish red; p la ty ...... 13.0 42.Sandstone:grayish yellow; very fine-grained; thin-bedded; cross-laminated, compound, medi­ um; ledge, smooth, yellowish gray; slabby; plant fragments, molds, poor, common...... 13.0 41.Sandstone: grayish yellow; very fine-grained; lime; thin-bedded; cross-laminated, compound, medium; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 25.0 Total Incomplete Mesaverde 313.0 2 4 7 .

Feet MANGOS SHALE. 40.Siltstone: dusky yellow; silt; thinly laminated; concretions and septaria (clay and limed) common, oval, yellowish gray; slope, -smooth, dk. gray, fissile; Pelecypods, fish teeth, cephalopods; original hard parts and casts; good, common...... 45.0 39.Glaystone and Bentonite...... 1.0 38.Siltstone: mod. yellowish brown; silt; laminated; reworked; ridge, smooth, yellowish gray, shaly.. 15.0 37.Siltstone: It. olive gray; silt; Bentonite at 2 8 ’, 41* and 61'; cone-in-cone at 35*; lamina­ ted; reworked; ridge, smooth, yellowish gray, sh aly ...... 76 .O 36.3iltstone: olive gray; silt; laminated; reworked; ridge, smooth, yellowish gray, shaly...... 6.0 35 .Silts tone:yellowish gray; silt; contains a bentonite at top; laminated: reowrked; ridge, smooth, yellowish gray, shaly...... 13. 34.Glaystone and Bentonite...... 33.Siltstone: med. gray; silt; laminated; reworked; ridge, smooth, yellowish gray, shaly...... 11. 32.Glaystone and Bentonite...... 4. 31.Siltstone: dusky yellow; silt; laminated; re­ worked; ridge, smooth, yellowish gray, sh a ly .... 19.

30. Silt stone and Bentonite...... oro 0 0 to o 29.Glaystone: It. olive gray, clay; some fossils; laminated; reworked; ridge, smooth, yellowish gray; shaly...... 29.0 28.Glaystone and Bentonite...... 3 27.Siltstone: yellowish grey to It. olive gray; silt; laminated; reowrked; ridge, smooth, yellowish gray, shaly...... 39.0 26.Siltstone: yellowish gray to olive gray; silt; Bentonites occur in these shales too numerous to count; lime...... 31.0 25.Siltstone: grayish yellow; silt; thin compact sandy siltsto n e; reworked lens; thinly laminated; flat-banded; slope, smooth, dark gray, fissile; shell fragments, original hard parts, poor...... 2 .0 24.Siltstone: yellowish gray, silt; thinly laminated flat-banded; slope, smooth, dark gray, f is s ile ; shell fragments, original hard parts, poor, com­ mon...... 2 .0 23. Clay stone and bentonite...... 1.0 22.Siltstone: yellowish gray; silt; fossils, lime; thinly laminated; flat-banded; slopem, smooth, dark gray, fissile; shell fragments, original hard parts, poor, common...... 9.0 2 4 8 .

Feet 21.Siltstone: It. olive gray; silt; lime; thinly laminated; flat-banded; slope, smooth, dark gray, fissile; shell fragments, original hard parts; poor, common...... 6.0 20.Claystone:yellowish gray, clay, lime; thinly laminated; flat-banded; slope, smooth, dark gray; fissile; shell fragments, original hard parts; poor, common...... 23.0 19*Bentonite with claystone...... 1.0 iS.Siltstone: olive gray, silt; thinly laminated; flat-banded; slope, smooth, dark gray, fissile; shell fragments, original hard parts, poor, common...... 5.0 17. Bentonite...... 3 Ib.Siltstone: yellowish gray; silt; lime; thinly laminated; flat-bedded; slope, smooth, gray, fissile; pelecypods, fish scales, original hard, parts; poor, ra re ...... 11.0 15.Concretionary lime...... 1.0 14.Claystone: yellowish gray; clay; thinly laminated; flat-bedded; slope, smooth, olive gray, fissile; fish scales, pelecypods, original, poor, rare; Gryphaea newberryi...... 7.0 13. Bentonite...... 13.9 12.Claystone; yellowish gray; clay; thinly laminated; flat-bedded; slope, smooth, olive gray, fissile; fish scales, pelecypods, original, poor, rare... 2 .0 11.Coal...... 1.0 10.Sandstone: It. olive gray, very fine-grained; thinly laminated; channeling, slight; ledge, smooth, olive gray, f i s s i l e ...... 4.0 Total Llancos shale 376.0 DAKOTA (?) S ArlDSTOlIE 9.Coal...... 1.0 8.Sandstone: pale orangish yellov/;fine-grained; lime; thin-bedded; cross-laminated, small- scale, compound; ledge, smooth, yellowish white; flaggy; plant fragments, prints, poor, common... 3.0 7.Carbonaceous Shale anf Coal: shows complete gradation from sandstone to coal. Coal contains bone, coal gives way to black siltstone.; thinly laminated; flat-bedded; slope, smooth, black, fissile; plant fragments, occur at coal seams... 7.0 6.Sandstone: grayish yellow; fine-grained; brown­ ish black silt (shale) thin-bedded to thinly- laminated; cross-bedded to small scale; ledge; smooth, yellowish gray, flaggy to fissile; plant fragments, imprints, poor, common...... 3.0 5.Black Shales and Coal at 2*...... 7.0 2 4 9 .

Feet 4.Siltstone: It. gray; silt, becomes darker at top; laminated; flat-bedded; slope, smooth, gray, platy; plant fragments, imprints, poor, common...... l 6o0 3 .Sandstone: yellowish gray; fine-grained; lamina- • ted; cross-laminated, small scale, compound; ripple marks; slope, smooth, yellowish whitek; p laty ...... 22.0 2.Sandstone: grayish yellow, fine-grained; lime; white, very fine-grained; lime; thin; cross-lam­ inated; med, scale, compound; cliff; rough, yellowish white; slabby; plant fragments, im­ prints, poor, common...... 60.0 TotalDakota (?) sandstone 119.0 UNCONFORMITY Erosional, no apparent relief. JURASSIC MORRISON FORMATION Cow Springs sandstone 1.Sandstone: It. gray; fine-grained; lime; thick- bedded; cross-laminated; c liff; smooth, greenish gray; massive...... 3^0 .0

SECTION 14, ONE iJILE SOUTH COW SPRINGS COAL MINE ROAD (Dip 300-6°, S 12 E) CRETACEOUS LIES A VERDE GROUP 40.Sandstone: grayish yellow; very fine-grained; limne; thick-bedded; cross-laminated, compound, med­ ium; iron nuggest, common, various shapes, yel­ lowish brown; ledge, smooth, grayish yellow, slabby; plant fragments and pelecypods, molds and casts, poor, common...... 35.0 39.Siltstone: It. olive gray; silt; lime;thin-bed­ ded; cross-laminated; medium compound, channeled; festoon type; ledge, smooth, yellowish gray, slab­ by; plant fragments, molds, poor, common...... 26.0 38.Lignite and Coal; contains very thin bone...... 10 ^ 37.Concealed...... 42.0 250

Feet 3 6 .Sandstone: yellowish gray; fine-grained; lime; thin-bedded; cross-laminated; medium compound; channeled; festoon type; ledge, smooth, yel­ lowish gray; slabby; plant fragments, molds, poor, common...... 7*0 35. Concealed...... 23.0 34.Sandstone: yellowish gray; very fine-grained; there is a complete gradation from coal to sandstone; lime; thin-bedded; cross-laminated; medium compound; channeled; festoon type; ledge; smooth, yellowish gray, slabby; plant fragments; molds, poor, common...... 14.0 33.Coal...... -...... 10.0 32.Siltstone: It. olive gray; silt; lime; thin-bedd­ ed; cross-laminated; medium compound; chan­ neled, festoon type; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 12.0 3 1 .Sandstone: yellowish gray; very fine-grained; some thin layers of shale; lime; thin-bedded; cross-laminated; medium compound; channeled; festoon type; ledge, smooth, yellowish gray, slabby; plant fragments,molds, poor, common... 65.0 30 .Mudstone: I t. olive gray; s i l t and clay; con­ tains some coal; lime; lig n ite ...... 14.0 29.Coal; weathered...... 4.0 28.Siltstone: It. greenish gray; silt; lime; thin- bedded; cross-laminated; medium compound; channeled, festoon type; ledge, smooth, yel­ lowish gray, slabby; plant fragments, molds, poor, common...... 29.0 2?.Sandstone: pale greenish yellow; very fine- gerained; lime; thin-bedded; cross-laminated; medium compound; channeled, festoon type; ledge; smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 27.0 26,Siltstone: It. olivey gray, silt; lime; coal top 31; thin-bedded; cross-laminated; medium compound channeled, festoon type; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 23.0 25.Sandstone:yellOY/ish gray; very fine-grained; lime; thin-bedded; cross-laminated; medium compound; festoon type; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 34.0 24.Claystone; It. olive gray; thin-bedded; cross­ lamination; medium compound channeled, festoon, ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 6.0 2 5 1

Feet 23.Lignite: grayish brown; contains coal; thin- bedded; cross-laminated; medium compound; chan­ nelled; festoon type; ledge, smooth, yellowish gray; slabby; plant fragments, molds, poor, common...... 12.0 22.Siltstone;It. gray; silt; much concealed; thin-bedded; cross-laminated; medium compound; channeled; festoon type; ledge, smooth, yel­ lowish gray, slabby; plant fragments, molds, poor, common...... 48.0 21.C o a l...... 4.0 20.Siltstone: dusky yellow; silt; thinj-bedded; cross-laminated; medium compound; channeled; festoon-type; ledge, smooth, yellowish gray; slabby;plant fragments, molds, poor, common... 30.0 19.Sandstone: grayish yellow; fine-grained; thinQ bedded; cross-lam inated; medium compound, channeled, festoon typ; ledge, smooth, yellow­ ish gray; slabby; plant fragments, molds, poor, common...... 4.0 18.Siltstone; grayish yellow; silt; lime; concre­ tions; thin-bedded; cross-laminated; medium compound; channeled, festoon type; ledge, smooth, yellowish gray; slabby; plant fragments, molds, poor, common...... 24.0 17.Coal...... 4.0 l6.Siltstone: yellowish gray to moderate yellowish brown; silt; thin-bedded; cross-laminated; medium compound; channeled, festoon type; ledge; smooth, yellowish gray; slabby; plant fragments, molds, poor, common...... 12.0 15.Coal...... 3.0 14.Siltstone: It. gray; silt; lime; thin-bedded; cross-laminated; medium compound; channeled; festoon type; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common... 55*0 13.Sandstone: mod. yellow brown; fine-grained; capped by an iron layer; thin-bedded; cross- laminated; medium compound; channeled, festoon type; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 5«0 l2.Siltstone: dk. yellow brown; silt; thin-bedded; cross-laminated; medium compound; channeled, festoon type; ledge, smooth, yellowish gray; slabby; plant fragments, molds, poor, common... 35*0 11.Sandstone: yellowish gray; very fine-grained; thin-bedded; cross-laminated; medium compound; channeled, festoon type; ledge, smooth, yellow­ ish gray, slabby; plant fragments, molds, poor, common...... 4.0 252

Feet lO.Siltstone: olive:- gray, silt; lime; thin-bed­ ded; cross-laminated; medium compound; chan­ neled, festoon type; ledge, smooth, yellowish gray; slabby; plant fragments, molds, poor, common...... 41o0 9.Grayish yellow; fine-grained; lime; thin-bedded- cross-laminated; medium compound; channeled; festoon type; ledge; smooth, yellowish gray, slabby; plant fragments, molds, poor, common... 3*0 S.Siltstone: It. olive gray; silt;thinly lam­ inated; flat-bedded; slope; smooth, yellowish brown; fissile; plant fragments, imprings; poor, common...... 5*0 7.Sandstone: die. yellowish brown; very fine­ grained; thin-bedded; cross-laminated; medium compound, channeled, festoon type; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 1.0 6.Siltstone: med. dark gray, silt; thinly lamina­ ted; flat-bedded; slope, smooth, yellowish brown, fissile; plant fragments, imprints, poor, common...... 11.0 5*Sandstone: grayish yellow; med .-grained;lim e; thin-bedded; cross-laminated; medium compound; channeled, festoon type; ledge, smooth, yel­ lowish gray, slabby; plant fragments, molds, poor, common...... 1.6 4.Siltstone: It. olive gray and pale yellowish orange; silt; thinly laminated; flat-bedded; slope, smooth, yellowish brown, fissile; plant fragments, imprints, poor, common...... 3.0 3.Sandstone: grayish yellow; fine-grained; con­ cretions; thin; indicates much reworking with sand-filled channels; iron concretions, common in upper portion, ovoid, yellowish red; ledge, smooth, yellowish gray, slabby; plant fragments, molds and imprints, poor, common...... 23.0 2.Carbonaceous siltstone; It. brownish gray; thin­ ly laminated; flat, slope, smooth, dark gray, fissile; plant fragments, imprints, poor, com­ mon...... 23*0 1.Sandstone: white to orange pink; med. to coarse­ grained; iron zone at 6 0 1, lime; thick-bedded; cross-laminated; medium compound; iron concre­ tions, common, ovoid, yellowish red; cliff, smooth, yellowish white, massive; plant frag­ ments, molds, poor, common...... 92.0 Total liesaverde Group . $7476 2 5 3

Feet SECTION 15, 5 MILES EAST OF RED LAKE TRADING POST (Dip, 120-6°, N 80 E)

CRETACEOUS MESAVERDE GROUP 30.Sandstone: moderate orange pink; fine-grained; thick-bedded; cross-lamina ted , medium compound, iron concretions, common, ovoid, yellowish red; cliff, smooth, white, massive; plant fragments, molds, poor, ra re ...... 34.0 29.Silstone: mod. olive brown; silt; very thin- bedded; cross-laminated; medium compound; low- angle; ledge, smooth, yellowish gray, flaggy.. 27.0 28.Claystone: mod. yellowish brown to It. olive gray; very fine-grained to clay; some hard layers of cross-laminated; thick-bedded; cross- laminated, medium compound; c lif f , smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 9-0 27.Sandstone: It. olive brown; medium-grained; iron layer at top; thick-bedded; cross-lami­ nated; medium compound; c liff , smooth, yellow­ ish gray, massive; plant fragments, molds, poor, common...... 7.0 26.Siltstone: dark yellowish orange; silt; It. very thin bedding; cross-bedded; medium com­ pound; low angle; ledge, smooth, yellowish gray, flaggy...... 12.0 25.Sandstone: grayish yellow; fine-grained; con­ cretions; thick-bedded; cross-laminated, med­ ium compound; c lif f , smooth, yellowish gray, massive; plant fragments, molds, poor, common. 9.0 24.Sandstone: dark yellowish orange; very fine­ grained; thick-bedded; cross-laminated; med­ ium compound; c lif f , smooth, yellowish gray, massive; plant fragments, molds, poor, common. 13.0 23.Siltstone: mod. yellowish brown; silt; very thin-bedded; cross-laminated; medium, low angle; ledge, smooth, yellowish gray, flaggy...... 3.0 22.3iltstone: mod. yellowish brown; silt; very thin-bedded; cross-laminated; medium, low angle; ledge, smooth, yellowish gray, flaggy...... 7.0 21.Sandstone: grayish orange; sand, fine-grained; lime; thick-bedded; cross-laminated; medium compound; c lif f , smooth, yellowish gray, mas­ sive; plant fragments, molds, poor, common.... ll-Q- 2 5 4 .

F eet 20.Sandstone: v/hite; fine-grained; thick-bedded; cross-laminated; medium compound; c liff , smooth, yellowish gray, massive; plant frag­ ments, molds, poor, ra re ...... 49.0 19.Sandstone: grayish yellow; very fine-grained; thick-bedded; cross-laminated, medium com­ pound; c lif f , smooth, yellowish gray, massive; plant fragments, molds, poor, rare ...... 17.0 18.Sandstone; mod. yellow; very fine-grained; very thin bedded; lime; cross-laminated, med­ ium; cliff, smooth, yellowish gray, massive; plant fragments, molds, poor, rare ...... 22.0 17.Sandstone; white; fine-grained; thick-bedded; cross-laminated; medium, compound; c liff, smooth, yellowish gray, massive; plant frag­ ments, molds, poor, rare ...... 50.0 l 6.Silststone-claystone: pale yellowish brown to 9 It. brown (layered) clay and silt; very thin bedded; cross-laminated; medium; low angle; shaly; ledge, smooth, yellowish g ray ...... 1 .0 l5.Siltstone: mod. yellowish brown; silt; very thin-bedded; cross-laminated; medium, low ang­ le; ledge, smooth, yellowish gray, flaggy...... 5.0 14. Siltstone: It. olive gray; silt; very thin bedded; cross-laminated; medium, low angle; ledge, smooth, yellowish gray, flaggy...... 60.0 Total Incomplete Liesaverde group 33^•0

LIAHCOS SHALE 13.Concealed...... 472.0 12. Bentonite...... 3 ll.Siltstoneidusky yellow; clay; lime; thinly laminated; f la t banded; slope; smooth, dark gray; f i s s i l e ...... *...... 19.0 lO.Siltstones: dusky yellow; clay; lime; thinly laminated; f la t banded; slope, smooth, dark gray, f is s ile ; concretions at top...... 4.0 9.Gladstone and Bentonite: dusky yellow; fine­ grained in clay...... 4 •S.Siltstones: dusky yellow; clay; lime; thinly laminated; f la t banded; slope, smooth, dark gray, f i s s i l e ...... 11.0 7 .Bentonite...... 3 Total Laneos shale 507*0 2 5 5

Feet d a k o t a C ? ) s a :i d s t o u s 6 .Claystone: dusky yellow; clay; line; thinly laminated; f la t banded; slope, smooth, dark gray; f i s s i l e ...... 13.0 5 . Coal:...... 3.0 4.Claystone: It. olive gray; claystone; thinly laminated; flat-bedded; slope, smooth, It. gray, f i s s i l e ...... 4.0 3 .Sandstone: pale yellowish orange; very fine­ grained; grades into a shale; thin-bedded; flat-bedded; ledge, smooth, yellow, slabby; plant fragments, imprints, poor, common...... 39.0 2 .Sandstone: pale yellow orange; very fine­ grained; thin-bedded; very lenticular; slope, smooth, yellowish gray; slabby...... 2.0 Total Dakota (?) sandstone r3ITo

UITC OrJF OHLIITY Erosional, 3 to 7 feet relief, filled with yellow­ ish gray medium-grained sand.

JURASSIC IIQRRISON FORMATION Cow Springs sandstone member 1 .Sandstone: white; very fine-grained; thick bedding; cross-laminated; wedge, large scale; c lif f , smooth, white, massive......

SECTION 16, 5 MILES EAST OF RED LAKE (Dip 12°-40, S 75 E)

CRETACEOUS I.IESAVERDE GROUP 2 5 6

F eet 21.Sandstone: grayish yellow to mod. yellow; fine grained; lime; forms dip-slope-crest of mesa; thick-bedding; cross-laminated; medium compound; iron concretions, common, ovoid, yellowish brown; cliff, smooth, white, massive; plant fragments, molds, poor, common...... 33.0 20.Mudstone: It. olive gray; mud; laminated; flat- bedded; slope, smooth, shaley, dark gray; plant fragments, imprints, poor, abundant...... 9.0 19.Sandstone: yellowish gray; very fine-grained; thick-bedding; cross-lamination, medium com­ pound; c liff , smooth, yellow, massive; plant fragments, molds, poor, common...... 26.0 18.Sandstone: dk. yellowish orange; very fine­ grained; thick-bedding; cross-lamination, medium compound; c liff , smooth, yellowm, mas­ sive; plant fragments, molds, poor, common.... 1.0 ly.Siltstone: grayish yellow; silt; laminated; flat bedding, in places, elnticular; iron con­ cretions, common, ovoid, yellowish red; slope, smooth, yellowish gray to dark gray; shaly; plant fragments, imprints, poor, abundant...... 22.0 16.Sandstone: It. olive brown to mod. yellow; very fine-grained; thick bedding; cross-lamina­ ted, medium compound; c liff , smooth, yellow, massive; plant fragments, molds, poor, common. 18.0 15.Siltstone: It. olive gray; silt; laminated; flat-bedded in places lenticular; iron conre- tions, common, ovoid, yellowish red; slope, smooth, yellowish gray to dark gray, shaly; plant fragments, imprints, poor, abundant...... 15.0 14.Sandstone: It. olive brown; very fine-grained; thickbedding; cross-lamination, medium, com­ pound; c lif f , smooth, yellow, massive; plant fragments, molds, poor common...... 7.0 13.Siltstone: It. olive gray; silt; laminated; flat-bedded, in places lenticular; iron con­ cretions, common, ovoid, yellowish red, slope, smooth,' yellowish gray to dark gray, shaly; plant fragments, imprints, poor, abundant...... 22 .0 12.Sandstone: dk. yellowish orange; very fine­ grained; iron zone at top; thick bedding; cross-lamination, medium compound; c liff , smooth, yellow, massive; plant fragments, molds, poor, common...... 18.0 11.Claystone: It. olive brown; clay; laminated; flat-bedded, in places lenticular; iron con­ cretions, common, ovoid, yellowish red; slope; smooth, yellowish gray to dark gray, shaly; plant fragments, imprints, poor, abundant...... 35.0 2 $ 7 .

Feet 10.Sandstone: dusky yellow; very fine-grained; line; thick-bedded; cross-laminated, medium compound; c liff , smooth, yellow, massive; plant fragments, molds, poor, common...... 60.0 9.mudstone: yellowish gray, mud; laminated; flat-bedding; slope, smooth, shaley, dark gray; plant fragments, imprints, poor, abun­ dant...... 4.0 8.Sandstone: grayish yellow; very fine-grained; lime; thick-bedding; cross-lamination; large low angle; silt pellets; common, various shapes, It. gray; cliff, smooth, yellowish gray, mas­ sive; plant fragments, molds, poor, rare ...... 151.0 ■ Total mesaverde group 426.0

LkUICOS SIIiUE 7 .Concealed Claystones and S ilts to n e s ...... 395.0 C.Glaystone: It. brownish gray; concretion zone; thinly laminated ; fissile ...... 1.0 5.Claystone: It. gray; clay...... 80.0 Total Ilancos Shale 426.0

DAKOTA(? ) SAIJDSTOITE 4.Sandstone: very pale orange; fine-grained; lime; very thin bedded; slope, smooth, yel­ lowish white, flaggy; coal seams in upper 91•. 34.0 3.Sandstone: It. brownish gray; very fine sand; lime; very thin bedded; flat; slope, smooth, black, flaggy...... 11.0 2.Sandstone: It. gray; very fine-grained; thin- bedded; very lenticular, contains numerous thin coal layers; ledge, smooth, yellowish white, slabby; plant fragments, imprints, poor, common...... 6. Total Dakota (?) Sandstone 51.6 UITCOITFORLIITY Erosional, 2 to 10 inches relief, yellowish-gray sandstone. JURASSIC LIORRIS OH FORI.'all011 Cow Springs sandstone member 1.Sandstone: white to yellowish gray; fine-grained; lime; thick-bedded; cross-laminated; high-angle; slope, smooth, I t. gray, massive...... 2 5 8 .

SECTICS! 17, 3 LUXES EAST OF BED BAKE TliADIUG (Dip 100-5 ^ °S 55 E)

CRETACEOUS EESAVERDE GROUP Feet 21.Granule conglonerate: white; coarse-grained; with granules; thick-bedding; cross-lamination; medium, compound; iron concretions, common, ovoid, yellowish red; cliff, smooth, white, massive; plant fragments, molds, poor, rare... 127.0 20.Sandstone: grayish yellow: fine-grained; lime; thick-bedded; cross-laminated; medium compound, iron concretions, common, ovoid, yellowish red; c liff , smooth, white, massive; plant fragments, molds, poor, ra re ...... 10.0 19.Sandstone: grayish yellow; fine-grained; lime; thick-bedded; cross-laminated; medium compound; cliff, smooth, yellowish gray, massive; plant; fragments, molds, poor, common...... 46.0 iS.Siltstone: yellowish gray; silt; lime; 2" bentonite at S’; thinly laminated; flat-bed­ ded; slope, smooth, dark gray, fissile; plant fragments, imprints, poor, abundant...... 14.0 I?.Sandstone: grayish orange; fine-grained; lime; thick-bedded; cross-laminated; large, com­ pound; c lif f , smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 71.0 16.Siltstone: grayish orange; silt; thinly lamina­ ted; flat-bedded; slope, smooth, dk. gray, fissile; plant fragments, imprints, poor, abundant...... 9.0 15•Bentonite and claystone...... 2.0 M .Siltstone: mod. yellowish brown; silt; thinly laminated; flat-bedded; slope, smooth, dk. gray, fissile; plant fragments, imprints, poor, abundant...... 6.0 13. Carbonaceous claystone: brownish gray; clay; thinly laminated; flat-bedded; slope, smooth, dk. gray, fissile; plant fragments, imprints, poor, abundant...... 3.0 12.Coal: shows complete gradation from light gray shales to coal...... 4.0 ll.S iltsto n e : I t. gray, s i l t ...... 10.0 10.Sandstone: yellowish gray, very fine-grained; thin-bedded; cross-laminated; low angle; cliff, smooth, yellowish gray, slabby; plant frag., worm trails, imprints, poor, abundant.. 138.0 Total Ilesaverde group 436.0 259.

Feet LullIGOS SHALS 9. Concealed...... 414.0 TotalLlancos Shale 434.0 DAlvOTAC?) SAilDSTONE 8. Goal...... 1.0 y.Siltstone: rned. gray; silt; laminated; flat- bedded; slope, smooth, dark gray, shaly; plantfragments, imprints,poor, common...... 4 .0 6 . Goal...... 3 .0 5 .Sandstone: med. gray; very fine-grained; thin- bedded; cross-laminated, small, compound; ledge, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 9 .0 4 .Concealed...... 20.0 3 .Sandstone: grayish yellow; very fine-grained; thin-bedded; cross-laminated, medium compound; lenticular, clay pellets, common, ovoid, It. gray; cliff, smooth, yellowish gray; slabby; plant fragments, molds, poor, common...... 17.0 2 .Sandstone: grayish yellow; fine-grained; thin- bedded; cross-laminated, medium compound; lenticular, clay pellets, common, ovoid, It. gray; cliff, smooth, yellowish gray, slabby, plant fragments, molds, poor, common...... 14.0 Total Dakota (?) Sandstone "68.0 D1TC0ITF0RLIITY Erosional, 1-3 inch relief, medium sand filling. JURASSIC MORRISON FORMATION Cow Springs Sandstone Member 1.Sandstone: It. gray; fine-grained; lime; thin- bedded; cross-laminated; slope, smooth, yellowish gray, slabby...... 260

SECTION 18, 5 NILES NORTH EAST OF RED LAKE TRADING POST (Dip 2, S 28° E) Feet

CRETACEOUS EESAVERDE GROUP 26.Sandstone: grayish yellow; med.-grained; thin-bed­ ding; cross-lamination, small compound; ledge; smooth, yellowish brown, slabby; plant frag­ ments, molds, poor, ra re ...... 18.0 25.Siltstone: grayish.orange to very It. gray; silt; laminated; flat-bedding; slope, smooth, yellowish brown, shaly; plant fragments, imprints, poor, common...... 7.0 24.Sandstone: pale yellowish brown, very fine­ grained; ; thin-bedding; cross-lamination; small, compound; ledge, smooth, yellowish brown, slabby; plant fragments, molds, poor, ra re ...... 4.0 23.Siltstone: yellowish gray; silt; changes color at 71; lime; laminated; flat-bedded; slope, smooth, yellowish brown, shaly; plant frag­ ments, imprints, poor, common...... 16.0 22.Sandstone: grayish orange; very fine-grained; lime; thick-bedding; cross-lamination, festoon type; cliff, smooth, white, massive; plant fragments, molds, poor, common...... 46.0 2l.Siltstone: yellowish gray; silt; .laminated; flat­ bedding; slope, smooth, yellowish brown, shaly, plant fragments, imprints, poor, common...... 5*0 20.Sandstone: grayish yellow; med.-grained; lime; thick-bedded; cross-laminated; festoon type; cliff, smooth, white, massive; plant fragments, molds, poor, common...... 18.0 19.Granule conglomerate; grayish yellow; granule conglomerate; thick-bedded; cross-laminated; large, compound; iron concretions, comraon, ovoid, yellowish gray;: cliff, smooth, white, massive; plant fragments, molds, poor, common. 54.0 iS.Siltstone: yellowish gray; silt; lime; lamina­ ted; flat-bedded; slope, smooth, light gray, shaly; plant fragments, imprints, poor, abund­ a n t...... 15.0 17.Sandstone: white; coarse-grained to silt; thick-bedded; cross-laminated; festoon type; cliff, smooth, white, massive; plant frag­ ments, molds, poor, common...... 57®0 2 6 1 .

F eet l 6oSandstone: grayish yellow; very fine-grained; thick-bedded; cross-lamination, medium, compound, cliff, smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 5«0 15.Siltstone: dusky yellow; silt; very thin-bedded; flat; ledge, smooth, darkbrown, slabby; plant fragments, impressions, poor, common...... 12.0 14.Sandstone; dusky yellow; med. sand; this is lower part of sandstone which has a heavy iron layer; lime; thick-bedded; cross-lamination, medium, compound; c liff , smooth, yellowish gray, massive; plant fragments, molds, poor, common...... 76.0 13.Siltstone: dusky yellow; silt; very thin bed­ ded; flat-bedding; ledge, smooth, dk. brown, slabby; plant fragments, impressions, poor, common...... 10.0 12.Siltstone: It. olive brown; silt; very thin- bedded; flat-bedded; ledge, smooth, dk. brown, slabby; plant fragments, impressions, poor, common...... '...... 3 .0 11. Burnt shale: very dusky red ...... 7 .0 10. Lignite to coal...... 4 .0 9.Siltstone: grayish orange pink; silt; laminated; flat-bedded; slope, smooth, gray, shaly; plant fragments, imprints, poor, common...... 6 .0 8 .Sandstone: grayish yellow; very fine-grained; thin-bedded; cross-laminated; low angle; . cliff, smooth, yellowish gray, slabby; plant fragments, molds, poor, common...... 63.0 Total Lesaverdegroup 426.0 M&NCOS SHALE 7.Concealed:...... 443.0 TotalLlancos Shale 443.0 DAKOTA (?) SAHDSTOIIB 6 . Coal...... 3 .0 ^.Siltstone: med. gray; silt; laminated; flat- bedded; slope, smooth, dark gray, shaly; plant fragments,imprints, poor, common...... 13.0 4.Sandstone: pale yellowish orange; very fine­ grained; thin-bedded; cross-laminated, med­ ium, compound; lenticular, channeled; clay pellets, common, ovoid, It, gray; slope, smooth, yellowish gray, slabby; plant fragments, molds, poor, ra re ...... 36.0 3 .Sandstone: med. gray; very fine-grained; thin- 2 6 2 .

Feet bedded; cross-lam inated, medium, compound; lenticular, channeled; clay pellets, common, ovoid, It. gray; slope, smooth, yellowish, gray, slabby; -plant fragments, molds, poor, ra re ...... 12.0 2.Sandstone: pale yellow orange; fine-grained; thin-bedded; cross-laminated, medium, compound; lenticular, channeled; clay pellets, common, ovoid; It. gray; slope, smooth, yellowish gray; slabby; plant fragments, molds, poor, rare.... 18.0 Total Dakota(?) Sandstone 82.6 UIIC OIIF ORLIIT Y Erosional, 1 to 3 feet relief; filling depres- sional; greenish gray; medium-grained;...... JURASSIC 11ORR IS Oi l F ORlvI AT I ON Cow Springs Sandstone member 1.Sandstone: greenish gray; fine-grained; lime; thin-bedded; cross-laminated; cliff; rounded; greenish gray; slabby...... 263

SECT I Oil 19, 5 LIILSS EAST OF COAL LIIiJE CANYON (Dip 2°, S 45 E)

CRETACEOUS Feet LIAI'JCOS SHALE 14.Concealed...... 22.0 13.Siltstone: dusky yellow; silt; contains many Prionotropis; beginning of sandy Maneos shale. 12.0 12.Concealed...... 270.0 11.Sandstone: yellowish gray; fine-grained; con­ tains iron zone at 8 ’; thin-bedded; cross- laminated; small scale, compound; cliff, rounded; grayish yellow; slabby; abundant pelecypods, original hard parts, excellent, abundant...... 17.0 10.Siltstone: grayish olive, silt (oysted bed) lime; thinly laminated; cross-laminated, small scale, compound; ledge, smooth, grayish black; fissile; plants and pelecypods, orig­ inal hard parts, excellent; abundant...... 7 .0 Total Incomplete Llano os Shale 328.6 DA1C0TA(?) SANDSTONE 9 .Coal: contains bone layers up to 6" in thick­ ness...... 9 .0 5. Claystone: yellowish gray; clay; thinly lamina­ ted ; flat-bedded; slope, smooth, gray, fissile; plant fragments, imprints, poor, rare ...... 4.0 7 .Sandstone: It. gray; very fine-grained; lime; very thin-bedded; concretions, rare, ovoid, yellow; ledge, smooth, gray, flaggy; plant remains, imprints, poor, abundant....*...... 21.0 6 . Coal: contains many bone layers...... 6 .0 5.Sandstone: It. olive gray; fine-grained; lime; very thin-bedded; cross-laminated, small scale, compound; ledge, smooth, flaggy; plant: imprints, excellent, abundant...... 1.0 4.Coal: very thin sandstone layers...... 2.0 3 .Sandstone: mod. dk. gray: fine-grained; very thin-bedded; flat bedded; cliff, smooth, gray, flaggy; plant impressions, imprints, excellent, common...... 3«0 2 .Sandstone: very It. gray; fine-grained; thin- bedded; gnarly bedded; c liff , rounded, gray, slabby; plant impressions, imprints, good, common...... 15.0 Total Dakota (?) Sandstone 61.0 2 6 4

Feet UITC01TF O R iJITY Erosional-0-12 feet relief, light gray, medium sand fille d . JURASSIC MORRIS 02-1 FORMATION Cow Springs sandstone member 1.Sandstone: light gray; fine-grained; lime; thick-bedded; cross-laminated; high angle, compound; c lif f , smooth, white, massive.

SECTION 20, COAL MINE CANYON (Dip 1°, N 42 E) CRETACEOUS MANGOS SHALE Total Maneos Shale 16.0 DAKOTA(?) SANDSTONE 5 .Coal...... 9.0 4.Sandstone: med. gray; very fine-grained; very thin-cross-laminated; small; ledge; smooth, yellowish gray...... 17.0 3.Sandstone: grayish yellow; very fine-grained; very thin; cross-laminated; small; ledge, smooth, yellowish gray...... 4.0 2.Sandstone: It. gray; fine-grained;; thick-bed­ ded ; cross-lam inated; medin, compound; sand­ stone, inclusions, common, irregular, white; cliff;, smooth, It. gray, massive...... 20.0 TOTAL DAK0TA(?) SANDSTONE 50.0 UNCONFORMITY Erosional, O-lo feet relief, filled sandstone conglomerate; locally sandstone breccia filled. JURASSIC MORRISON FORMATION Cow Springs Sandstone Member 1.Sandstone: white to med. gray; fine-grained; lime; thick bedded; cross-laminated; high- angle compound; cliff, smooth, white, massive. 120.0 265

SECTIOII 21, 3 HUES SOUTH OF HOVJELL LIES A, (Dip 7°, IT 50 VT)

Feet CRETACEOUS

LIAITCOS SHALE 1 0 .C oncealed...... uO.O Total i.Iancos (concealed) Shale '66.0

DMCOTA(?) SAHDSTOHE 9.Coal: containsbone layers...... 3.0 S.Siltstone: med. gray; silt; thinly laminated; slope, smooth, dark gray, fissile; plant frag- . ments, poor,common...... 6.0 7.Sandstone: It. yellowish orange; very fine­ grained; thin-bedded; cross-laminated; medium compound ledge, rough, yellowish gray, slabby; plant fragments, molds, poor, common...... 19.0 6 .Coal...... 2.0 5.Siltstone: gray, silt; thinly laminated; slope; smooth, dark gray, fissile; plant fragments, imnrints, poor, common...... 3*0 4 .Coal...... 1.0 3.Siltstone: med. gray; silt; thinly laminated; slope, .smooth, dark gray, fissile; plant frag­ ments, imprints, poor, common...... 3.0 2.Sandstone: grayish yellow; fine-grained; thick-bedded; cross-laminated; medium compound; clay pellets, common, irregular, It. gray; cliff, smooth to pitted; yellowish gray, mas­ sive; plant fragments, molds, poor, common.... 7.0 Total Dakota (?) Sandstone 49.0 UITCOUFORLIITY Erosional, 0-3 feet relief, light gray; fine­ grained; filling depressions. JURASSIC IIORRIS Oil FORLIATIOIT Cow Springs Sandstone member 1.Sandstone: white; fine-grained; lime; thin- bedded; cross-laminated; high angle compound; cliff, smooth, light gray; slabby...... 266

PARTIAL SECTION 22, GOV/ SPRINGS COAL Li INS ROAD (Ueasured along strike) Feet CRETACEOUS LIESAVSRDE GROUP 21.Sandstone: very pale orange; very fine-grained; lime; thin-bedded; cross-laminated; medium- compound ; flat-gnarly; ledge, smooth, brov/n, slabby; plant fragments, molds, poor, common.. l 6e0 20.Claystone: med. It. gray; clay; thinly lam­ inated; flat-bedded; slope, yellowish gray, fissile; plant fragments, imprints, poor, common...... 8.0 19.Sandstone: dk. yellowish orange; very fine­ grained; lime; thick-bedded; cross-laminated; medium, compound; iron concretions, abundant, ovoid yellowish red; cliff; smooth, brown, massive; ...... 6.0 iS.Siltstone and Claystone; It. olive gray; thin­ ly laminated; flat-bedded; slope, yellowish gray, fissile; plant fragments, imprints, poor, common...... 11.0 17.Sandstone: very It. gray; very fine-grained; lime; laminated; flat-bedded; slope, smooth, yellowish gray, shaly; plant fragments, im­ prints, poor, common...... 9»0 16.Siltstone: yellowish gray; silt; thinly lamina­ ted; 'flat-bedded; slope, yellowish gray, fis­ sile; plant fragments, imprints, poor, common. 13.0 15. Goal...... 3.0 14.Siltstone" and lignite; It. olive gray; silt; thinly laminated; flat-bedded; slope, yel­ lowish gray, fissile; plant fragments, im­ prints, poor, common...... 3.0 13.Claystone: It. brownish gray; clay; thinly laminated; flat-bedded; slope, yellowish gray, fissile; plant fragments, imprints, poor, common...... 5*0 12.Sandstone: grayish yellow; very fine-grained; thinly laminated; flat-bedded; slope, smooth, grayish yellow; shaly; plant fragments, im­ prints, poor, common...... 1.0 ll.Siltstone: It. olive gray; silt; thinly lam­ inated; flat-bedded; slope, yellowish gray, fissile; plant fragments, imprints, poor, com­ mon...... 2.0 10.Coal...... 3*0 9.Claystone: It. brownish gray; clay; lime; 26 ?.

Feet thinly laminated; flat-bedded; slope, yellow­ ish gray; fissile; plant fragments, imprints, poor, common...... 2.0 S.Claystone: yellowish gray; clay; some bentonite; lime; thinly laminated; flat-bedded; slope, yellowish gray, fissile; plant fragments, imprints, poor, common...... 5»0 7.Sandstone: grayish orange; very fine; laminated; flat-bedded; slope, smooth, grayish yellow, shaly; plant fragments, imprints, poor, com­ mon...... 18,0 b.Siltstone: yellowish gray; silt; thinly lam­ inated; flat-bedded; slope, yellowish gray, fissile; plant fragments, imprints, poor, common...... 15.0 5.Sandstone: grayish yellow; very grained fine; lime; laminated; flat; slope, smooth, grayish yellow; shaly; plant fragments, imprints, poor, common...... 29.0 4.Sandstone: yellowish gray, very fine-grained; laminated; flat-bedded; slope, smooth, grayish yellow; shaly; plant fragments, imprints, poor, common...... 10.0 3.Sandstone: grayish orange; fine-grained; lime; thin-bedded; cross-laminated; medium, compound; ledge, smooth, yellowish gray; slabby; plant fragments, molds, poor, common...... 2.0 2.Siltstone: yellowish gray; silt; thinly lam­ inated; flat-bedded; slope, yellowish gray, fissile; plant fragments, imprints, poor, com­ mon...... 8.0 1.Sandstone: yellowish gray; fine-grained; line; thick-bedded; cross-laminated, large compound; iron concretions, common, ovoid, yellowish brown; cliff, smooth,yellowish gray, massive.. 1.0 Total Incomplete Llesaverde Group 170.0

PARTIAL SECTION 23, CO>7 SPRINGS GOAL IJINE (measured along strike) CRETACEOUS MESAVERDE GROUP . 24. Concealed...... 73*0 23.Sandstone: yellowish gray; fine-grained; lime; thick-bedded-cross-laminated; large, compound; 2 6 8 .

Feet iron concretions, common, ovoid, yellowish red; cliff, white, massive; plant fragments, imprint, poor,common...... 24.0 22. Concealed...... 20.0 21.Sandstone: grayish yellow; fine-grained; lam­ inated; ledge, smooth, yellowish brown, platy; plant fragments,imprints, poor, common...... 33<>0 20. Concealed...... 24.0 19.Sandstone: grayish orange pink; very fine­ grained; laminated; ledge, smooth, yellowish brown, platy; plant fragments, imprints, poor, common...... 8 .0 18. Concealed...... 30.0 17. Concealed...... 12.0 16.Sandstone: yellowish gray, fine-graine; lamina­ ted; ledge, smooth, yellowish brown, platy, plant fragments, imprints, poor, common...... 7*0 15. Concealed...... 9 .0 14.Sandstone: mod. yellowish brown to pale yel­ lowish orange; very fine-graine; lime; lam­ inated; ledge, smooth, yellowish brown, platy; plant fragments, imprints, poor, common...... 4 .0 13.Sandstone: It. olive gray; very fine-grained; laminated; ledge, smooth, yellowish brown, platy; plant fragments, imprints, poor, common. • 1.0 12. Concealed...... 12.0 ll.Siltstone: me. gray; silt; very thin; flat- bedded; slope, smooth, dark gray, flaggy; plant fragments, imprints, poor, common...... 6.0 10. Coal...... 4 .0 9.3iltstone: med. gray; silt; very thin; flat- bedded; slope, smooth, dark gray, flaggy; plant fragments, imprints, poor, common...... 17.0 8 .Sandstone: grayish orange; very fine-grained; lime; thick-bedded; cross-laminated; large compound; c lif f , smooth, yellowish white, massive; plant fragments, molds, poor, common. 2 .0 7 .3 iltsto n e s: has 3* ss. at l o v...... 36*0 6.’.'feathered lignite; shows gradation sequence.... 4.0 7 *Coal...... 7.0 4 .Coal...... 8.0 3 .Sandstone: grayish yellow; very fine-grained; thickebedded; cross-laminated; large-compound; cliff, smooth, yellowish white, massive; plant fragments, molds, poor, common...... 37*0 2 . Coal...... 1.0 1. Lignite...... 2.0 Total Incomplete ilesaverde Group 379*0 2 6 9 . .

Bibliography

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Plate 11

Fig. 1 Trenching to obtain good exposures, in the Maneos shale, one mile south of Cow Springs Trading Post.

Fig. 2 Continuous recording-density-settling device. Plate 11

Fig. 2 2 7 6 ,

Plate 12

Fig. 1 Cretaceous section, Lolomai Point, northernmost point of Black Mesa. Jm, Morrison formation; Kd, Dakota (?) sandstone* Km^oMahcos shale; Kmv, Mesaverde group. Elevation, 8,000 fe e t.

Fig. 2 Badland topography resulting from weathering of the Mane03 shale in Blue Canyon. Kd, Dakota (?) sandstone; Km, Mane os shale; Kmv, Mesaverde group. Plate 12

Fig. 1

F ig. 2 2 7 7

Plate 13 Fig. 1 Demoiselles, as seen in Marsh Pass, showing earlier surface of deposition with* present erosion removing the fine material. Fig. 2 Coal-bearing member (Mvcb) of the Mesaverde group (Kmv) con­ taining slope-froming siltstone and claystone with sandstone ledges.

Fig.3 Lower escarpment of Black Mesa capped by Dakota (?) sandstone, (Kd): slope-forming Maneos shale (Km) and upper escarpment (Kmv). Comb Ridge monocline in background. Looking Northeast toward Marsh Pass. Fi.g. 1 Pig. 2

Fig. 3 2 7 8

Plate 14 Fig. 1 Toreva block, five miles east of Red Lake. Mesaverde group, (Kmv) slumped down due to incompetent Mancos shale(Km).

Fig. 2 Contact of upper pediment and Mancos shale (Km), one mile north of Blue Canyon.

Fig. 3 Rounded gravels which comprise the lower pediment. P la te 14. § 7 9 .

Plate 15

Fig. 1 Vertical c lif f formed by the upper sandstone member (Uss) of the Mesaverde group (Kmv). North end of Marsh Pass.

Fig. 2 Channel on Morrison-Dakota contact between the Dakota (?) sandstone and the Westwater Canyon sandstone member of the Morrison fm. as seen in Marsh Pass. Kd, Dakota (?) sandstone; ' Jwc, Westwater Canyon sandstone. 1

- Fig. 3 Channel on Morrison-Dakota contact as seen in Blue Canyon be­ tween Cow Springs sandstone (Jcs) and Dakota (?) sandstone (M)e Plate 15

Fig. 1

Fig. 2 F i g . 3 2 8 0 .

P l a t e 1 6

Fig. 1 Channels on Morrison-Dakota contact as seen in Coal Mine Can­ yon, Jcs, Cow Springs sandstone member of the Morrison; Kd, Dakota (?) sandstone; Km, Mancos shale.

Fig. 2 Channels on Morrison-Dakota contact near the mouth of Coal Mine Canyon, showing lenticular nature of coal seams. Jcs, Cow Springs sandstone; Kd, Dakota (?) sandstone; Km, Mancos shale. Plate 16

Fig. 2 2 8 1

P l a t e 1 7

Conglomerate lenses in the Conglomerate member of the Dakota(?)5 sandstone, Columnar Section 8. ‘

Fig. 2 Close-up of above gravels showing bedded nature.

Fig. 3 Contact of Cow Springs sandstone member (Jcs) and Dakota(?) sandstone (Kd) showing thin conglomerate lens. Columnar. Section 2.

Fig. 4 Gravels distributed throughout in the conglomerate member of the Dakota (?) sandstone. Columnar Section 5. P la te 17

Fig. 3 Fig. 4

. 1 2 8 2 .

P l a t e 1 9

Fig. 1 Contact Cow Springs sandstone member (Jcs), Dakota (?) sand­ stone (kd), Blue Canyon.

Fig. 2 Contact Cow Springs sandstone member (Jcs), Dakota (?) sand­ stone (Kd). showing coal resting directly on Cow Springs sand­ stone, 5 miles east of Red Lake.

Fig. 3 Mud pellets in the Dakota (?) sandstone, note long axis orientation. Plate 19 2 8 3

P l a t e 2 1

Fig. 1 Contact Dakota (?) sandstone (Kd) and basal sandstone member (Km) of the Mancos shale. Note thin coal seam.

Fig. 2 Sulphurous sublimate resulting from burning coal beds, Coal Mine Canyon. -

Fig. 3 Coal Mine, Coal Mine Canyon. Plate 21 2 8 4 .

P l a t e 2 2

Fig. 1 Plant fragments from bone in Dakota (?) sandstone coal seam (unidentified).

Fig. 2 Cross-section of rippled bedding from Dakota (?) sandstone. Three feet below coal seam in Longhouse Valley.

2 8 5 .

P l a t e 2 3

Fig. 1 Slumped area resulting from burning coal seams.

Fig. 2 Erosional remnant of burned area white layer is ash from burned coal. Note crumpled area above ash.

Fig. 3 Natural slag. Bow work structure resulting from melting of shale and filling cracks in underlying material. Slag with white ash in contact. J mm Plate 23 Fig. Fig. 1 F ig . 3 Fig. 2 mm 2 8 6 .

P l a t e 2 4

Fig. 1 Sandstone dike in black shale and coal of the Dakota(?) sandstone in Longhouse Valley.

Fig. 2 Medial escarpment resulting from siltstone layers at the base of the siltstone member of the Mancos shale. Horizontal line below cliffs are footprints when tracing bentonite layers. Blue Canyon.

Fig. 3 Fossiliferous nature of basal sandstone member of the Mancos shale. Plate 24

Fig. 2 28?

P l a t e 2 5

Fig. 1 Cephalopod impressions in siltstone member of the Mane os shale. Note fragmental nature.

Fig. 2 Ripple marks from underside of sandstone layers in alternating siltstone-sandstone member of the Maneos. Cow Springs at Col­ umnar Section 2.

Fig. 3 Worm trails on the underside of sandstone layers in the alter­ nating siltstone-sandstone member of the Maneos shale. Cow Springs at Columnar Section 2, P la te 25 288

Plate 26

F ig .l Worm tr a il in underside of sandstone layer in the alternating siltstone-sandstone member of the Mancos shale. Note the pitted nature of the side walls of the worm trail.

Fig. 2 Protuberances from the sandstone layers of the alternating siltstone-sandstone member of the Mancos shale. One-tenth normal size.

Fig. 3 Cross-section of a septeria from the Mancos shale. Siltstone Member,

2 8 9

P l a t e 2 7

Fig. 1 Large concretion in the siItstone member of the Mancos shale. Columnar Section 2.

Fig.’: 2 Cone-in-cone from siItstone layers in the siltstone member of the Mancos shale. Blue Canyon.

F ig.3 Cone-in-cone showing manner in which the layers part. Mancos shale in Blue Canyon. P la te 27

Fig.' 3 2 9 0 . P l a t e 2 8

Fig. 1 Concretion layer showing cone-in-cone in the outer layers. Cow Springs Coal Mine road.

Fig. 2 Melikarian structures. One showing surface markings and the other showing a geode-like hollow center that is crystal lined.

2 9 1

Plate 29

Fig. 1 Maneos shale, black shale variety, showing the bentonite layers. Blue Canyon.

Fig. 2 Bentonite and gypsum capping the ledges in Blue Canyon. Note the handle of a pick sticking down into the bentonite.

F ig .-3. Note the vegetation growing along the bentonite beds. Columnar Section 5 Xonghouse valley. P la te 29

Flg. 1 Fig. 2

F l g . 3 292. P l a t e 3 0

Fig. 1 Contact of the Maneos shale and the overlying Mesaverde group. Lower part of the sandstone is the basal sandstone member of the Mesaverde group.

Fig. 2 Alternating siltstone-sandstone member of the Maneos shale'showing the contact of the Maneos and the Mesaverde group. P la te 30

Fig. 2 2 9 3 . P l a t e 3 1

F ig .l Black shales and coals overlying the basal member of the Mesaverde group. Note the sandstone lenses that split the siltstone and coals. Columnar Section 5 Longhouse valley.

Fig. 2 Surface markings on the basal sandstone member of the Mesaverde group. Fucoids on laminae of beach sand­ stone.

Fig. 3 Surface markings on laminae of the beach sandstone. Small circles are believed to be bore holes and the large object is believed to be a sh ell impres­ sion. P la te 31

Fig. 2 2 9 4 .

Plate 32

Fig. 2 Cross-section of a specimen of the basal sandstone member of the Mesaverde group showing the laminae which are believed to have originated in a beach.

Fig. 1 Scollop-like structures which are believed to be beach cusps. Basal member of the Mesaverde'group.

Fig. 3 Laminae in the basal sandstone member of the Mesaverde group believed to be beach laminae. Columnar Section 10. P la te 32

Fig. 2 P l a t e 3 3

Fig. 1 Quartz grains from the basal sandstone member of the Mesaverde group. Note somewhat rounded beach sand grains. 25X

Fig. 2 Thin section of same sandstone as that above. Cross ed Nicols. Minor small feldspar. P la te 33

Fig. 1

Fig. 2 2 9 6 .

P l a t e 3 4

Fig. 1 . Thin section of laminated part of the basal sand­ stone member of the Mesaverde group. Note the very fine grain nature of this specimen.

Fig. 2 Cross-lamination of the basal sandstone member of the Mesaverde group. Long,low angle sets believed to be part of the upper foreshore of a beach deposit.

Fig. 3 Continuation of the same sets illustrated above.(Fig.2). P la te 34

Fig. 1-

Fig. 2 F i g . 3 2 9 7 .

P l a t e 35

i’igv-.l Cross-lamination in the- tipper foreshore of the beach deposits of the basal sandstone member of the Mesaverde group; Note truncating surface.

Fig. 2 Continuation of the above laminae. Columnar Section

2 . ■

Fig. 3 %per foreshore cross-lamination in the basal sand­ stone member of the Mesaverde group. Columnar Sect­ ion 13.

Fig. 4 Lower contact of the upper foreshore deposits. Columnar Section 13. P la te 35

‘Pig. 3 F ig . 4 2 9 8 . * P l a t e 36

Fig. 1 Upper foreshore cross-lamination in the basal sand­ stone member of the Mesaverde group. Note the low angle of the individual liminaa. Columnar section 16.

‘ Fig. 2. Alternating "torrential" and horizontal cross-lam ination. Foreset type on a very small scale. Arkosic sandstone member of the Mesaverde group.

Fig. 3 Alternating "torrential" and horizontal cross- lam­ ination. Arkosic sandstone member.

Fig. 4 Low-angle compound cross-lamination in the arkosic member of the Mesaverde group. Columnar section P l a t e 36

Fig.»3 Fig. 4 2 9 9 .

P l a t e 3 7

Fig. 1

Individual grains by oblique light of the arkosic sandstone member of the Mesaverde group. Part of grains are feldspar. lOx

. Fig. 1 Individual grains by oblique light of the lower portion of the arkosic sandstone member of the Mesaverde group. Grains somewhat equant. I2x Fig. 2 300.

P l a t e 3 8

Fig. 1 Thin-section of Arkosic sandstone member. Note large unal­ tered feldspar (fid) grains. Ground mass medium-grained. Columnar section 2. 25x

Fig. 2 Thin-section of arkosic sandstone member. Shows unaltered feldspar (Fid). Ground mass coarse-grained. Conglomeratic nature. Columnar section 12. 2£>x Fig. 1 ^ 9 t e 39

'= sasSSSSH

::: cross-laminatioa.

eacn 8 Prominent. F ig .•1

Fig. 3 3 0 2 .

P l a t e 4 0

Fig. 1 Thin, sandy siltstone beds which occur in the arkosic sand­ stone. Note irregularity of deposition surfaces. Columnar Section- 17.

Fig. 2 Low-angle compound, large-scale cross-lamination. Arkosic sandstone member. Section 6.

Fig. 3 Low-angle compound, cross-lamination. Normal festoon channel f i l l in arkosic member. Columnar Section 4.

Fig. 4 Alternating "torrential" and horizontal cross-lamination with low-angle compound in arkosic sandstone. Columnar Section 5*

Plate 41

Fig. 1 Iron concretions showing spongy, limonite which make up concentric circles with hollow centers. Arkosic sandstone member.

Fig. 2 Iron cemented sandstone concretion with hollow center Arkosic sandstone member. P la te 41

Fig. 1

• Fig. 2 3 0 4 .

Plate 42 Fig. 1 Small-scale foreset bedding alternating "torrential** and horizontal in the coal-bearing member of the Mesaverde group. Columnar Section 4.

Fig. 2 Intricate bedding and cross-lamination as shown by the weath­ ering of the sandstone layers in the coal-bearing member. Columnar Section 4.

Fig. 3 Weathering along bedding planes indicates the intricate bed­ ding found in the sandstone layers of the coal-bearing member of the Mesaverde group.

Fig. 4 Plunging festoon cross-lamination, some low-angle compound. Columnar Section 4. Fig. 4 3 0 5 .

P l a t e 4 3

Fig. 1 Pseudo-cross-lamination as a result of ripples on a horizontal surface. Columnar section 15

Fig. 2 Large iron concretions in sandstone layer of the arkosic sandstone member. Columnar section 10.

Fig. 3 Crumpled bedding in sandstone layer of the coal-bearing member due to some form of soft rock deformation. Columnar section 2.

Fig. 4 Crumpled bedding believed due to shrinkage subsequent to deposition. Sandstone layer in coal-bearing member at Columnar section 4. F ig . 1

F ig . 3 306

Plate 44

Fig. 1 Cow Springs Coal Mine loading chute. Note coal seam at foot of loading chute.

Fig. 2 MBrazilanut concretions-note concentric rings of lam­ inated material. Upper sandstone member of Mesaverde.

3 0 7

Plate 45

Fig. 1 Sandstone concretions in upper sandstone member Mesa- verde group. Columnar section 11.

Fig. 2 Examples of the above sandston concretions. Cigar shaped concretion believed to have originated in ripple trough. Note circular cross-section of con­ cretions. Inoceramus. sp. Lends support to near­ shore intrepretation for this sandstone. Upper sand­ stone member of the Mesaverde group. Columnar Section 11. P la te 45

F i g . 1 PLATE -36045'

EXPLANATI ON X SEDIMENTARY ROCKS ..>c T f / ;

I u v i u m

Mesaverde formation

AZ Mancos shale \J m V 'O - ' " ' z . i X / h / £ • x ^ o o r M \ Dakota(?)Sandstone Z o Z - ■ < / \ V \ ) f f V " UNCONFORMITY y . / 7 1 / \j ; V

Km > •

Morrison formation \ V \

Note:- Areal projection of Dakota (?) \ Sandstone is exaggerated / K \ X / N z \ , ; / . l y - ;r ^ z x ( y

\ / z / : x. / \ \ / \ . • U J s N fr y X \ K-v "\ _* \ \

Kmv/^

KAYENTA COAL MINE 3 6 °3 0 J V

V.

Kmv %\COW SPRINGS " COAL MINE X Kmv z \ ' z "X X (/ xX~==- - i ' ' SECT / 12 -SCOC Z

A 1 z Profile Section A-A1 - z 7 ox : xx *:i - \ A:: y \ \

r S' / j

...S' V

Kmv

c Z \

Z'

V

Compiled from aerial mosaic maps Fairchild Aerial Surveys, 1934 and Geologic map of Black Mesa , Ariz. by J.W Horshbarger. AREAL GEOLOGIC MAP OF CRETACEOUS ROCKS Geology by George A. Williams BLACK MESA, ARIZONA

SCALE 4 Miles

NORTHERN PORTION PLATE I PLATE II Je " „»c>

t t fi­x' 3

V y '-x

EXPLANATION

SEDIMENTARY ROCKS \

z r UJ o v LU cr Alluviu m z V Kmv z

K#Pv 'N X )X Km r \ B' SECT.

X \ X

\ ✓

\ ~

X -A

Kmv J

\

"X--

\. J6' -S' •_y

Km Xr /

Kmv 5 > -v-

Kmv 'V? . ■ ... 'Y-Z;.T s tf" - mr Krr.v v N \ j y ) I > ’ A , x : ;

Km s.~ Ool

\ w w

X ,N x V > X si* ' * * • X X iX X/Z-Z ( r V

h \ Qal A -A S>N, A XN* » 'X Nv II \ 'V X II

-

f X X x r \ y v

\

'i

X Km \ X / \ ■y ./•- aZ

Qal

\ X

r

'

4 Miles

PORTION

PLATF ? FEET Sect. Sect. Sect. Sect Sect Sect. Sect Sect. Sect. Sect Sect.

160 2 13 4 8 6 7 5 11 SW 20 10 NE

2 2 mi 5 mi mi 7 mi 4 mi 6 mi 2 mi mi 4m i 6 mi 140

.co (Z)

CD 120 oO c II mK a y e n fit o Id 1 / U) 3 V 's : o 100 0) o o CD CD c V- o O “OV) c o CO CD CL CL z> o JC o Q

Conglomerate member

co co O Km Mancos shale Sandstone S hale Coal jcs - Cow Springs Sandstone CORRELATION CHART 3V- for "3 <9 O ° or^o QO Concretions 6 o o o Conglomerate Concealed jwc - Westwater Canyon Sandstone •0 » o o DAKOTAS) SANDSTONE. Western Portion Block Mesa Area, Arizona KAYENTA to COW SPRINGS PLATE 3

Sect. Sect. Sect. Sect Sect. Sect

160 2 IS 17 16 15 9 S -4 mi 3mi -3m i -3m h -3m^

140 - O CO CO o Tuba 120 o co

CO D o 100 0) o O § o CDc o o * E Q) £ _ L_ o ■D S S § 1 ! Cv 0_ S CD o Q. CL Qo a)w Km Mancos shale Z) jO E

... V) T3 Sandstone C o V) >.0 ° o ° Conglomerate ^ C P

Jcs Cow Springs Sandstone

'O) t P II cn 2 E CORRELATION CHART cn O for DL. —D DAKOTA (?) SANDSTONE Western Portion Black Mesa Area, Arizona

COW SPRINGS to BLUE CANYON

PLATE 4 f

> 5 '

L ‘______FEET

Sect. Sect. Sect. 160 W 20 19 21 E

3m i 4 mi 140

120

100

U) 3 O 0) o o O sz 2 CL CL

BLUE CANYON to COAL MINE CANYON

PLATE 5

FEET

Sect Sect Sect 800 2 13 5 sw NE CDl O 5 mi 21 mi 700 0) •ov. O CO m ® U CD - - 6 0 0 ' _5 g.^ 5- to D o Q) 500 O e cn b e ' o n e S > " 5' 0 CD o 400

CD CL o Kmv Mesaverde formation, CL JC CO 500 CO o Mancos shale C_> c o C l a y s t o n e mem b e r Sandstone 200

Concretions

100 Concealed

------— 2 _B g_so_t____ 5 o_n d_s_t o_n_e____ m_e m_b_§ 1------i- •• «. -i.•.• ••• •• I. B entonite Dakota (?) SS CD CD CORRELATION CHART o for o o MANCOS SHALE Q Western Portion Black Mesa Area. Arizona

COW SPRINGS to MARSH PASS

P I A T F R

FEET Sect Sect

800 2 9 CL N S 3O V- cn < 16 mi 0) "O 700 L_ CD > 0)S 2 CO AJ tern 60 0 D o Q) O O

500 CD L_ Si Its to o mem be

4 0 0

Kmv Mesaverde formation

3 0 0 2 Mancos shale

Sandstone 200

Concretions

100 Concealed

Dakota (?) SB Benton i te 0 Dakota (?) SB

CORRELATION CHART o for Q MANCOS SHALE Western Portion Block Mesa Area, Arizona

COW SPRINGS to BLUE CANYON

I PLATE 7

Sect. Sect. Sect. Sect. Sect. Sect. Sect. Sect. Sect. Sect. Sect. Sect. 3 2 14 13 4 12 8 6 5 10

FEET I _ • mi 3om i Imi m i 5 m i 4 mi 6 mi 3m i 4 m i ■6m i I20Q.

Q) 1100 Cl Cl 3

1000

9 0 0

800

700 (/) 3 o 0) 600 3CL u O o Q) Q) v. 500 O 0)L_ > (0o 0) CD CL 4 0 0 CL Z)

30 0

200

100

■“BosaT - Sandstone _ jnemoflr _

t--" CORRELATION CHART Concealed K m Mancos shale Sandstone Shale Coal for MESAVERDE GROUP Western Portion Black Mesa Area, Arizona COW SPRINGS to MARSH PASS

PLATE 8

Sect. Sect. Sect. Sect. Sect. Sect

2 18 17 16 15 9

FEET

4mi- ■3m i- 3m i ■3m i -3m i

1200

iio o w n a T3 6 Q. c

1000 i- ■.

9 0 0 0) :V/4v;

jO E 0) 8 0 0 E

•V. CO 7 00 o D c —==—~^=r O -TT^l •'rV.y.v.; Sandstone 0) o u 0) n 60 0 CL o ZJ Coal o

a> "O o Shale o 500 0) T'jy 3-'''■< > o o CO K m Mancos shale CD

• - • ;•* ...... •

300 ■V: a> :::

xi ;.-.T E " !V.

V-r:.-"- : in *• *v; ■ • • O .x 100 [/'Vv^vr-r;

,v: — —* 'K- - .•** - - • • •. ■ .. i'.. - •- ---::: " v Basal ...... > Sandstone __m£mb£r_ K m CORRELATION CHART for MESAVERDE GROUP Western Portion Black Mesa Area, Arizona COW SPRINGS to BLUE CANYON

PLATE 9

S Santa Rita U Pinedale V Clifton W Deer Creek fTTl Sandstone A A Kayento I | Marine Shale BB Cow Springs (Hi Continental Deposits C Rinconoda Canyon BS tea g y o n D Alamosa creek t E Koiporow its Region Lava Flows E San Ignacio F Casa Salazar G Cabezon H Gallma J Pagosa Spring K Durango L Tijeros M Cernllos N Las Vegas 0 Raton P Carthage Q White Mountains R San Andre's Mountains

0 10 20 30 40 Miles

THREE-DIMENSIONAE CORRELATION Dl AG RAM (AFTER PIKE, 1947) PLATE 10