MEASURED SECTIONS OF THE PENNSYLVANIAN TENSLEEP SANDSTONE, PRYOR AND BIG HORN MOUNTAINS, MONTANA D.A. Lopez, S.W. VanDelinder, M.L. Hendricks, Shawn Reddish-Kuzara, C.W. Schwartz, and D.C. Bear Claw Montana Bureau of Mines and Geology Open-File Report 553 2007
Lopez et al. MBMG Open-File Report 553 Abstract Thirteen stratigraphic sections of the Tensleep Sandstone in the Pryor and Bighorn Mountains of south-central Montana were measured and described to help understand the genesis of this regionally important oil and gas reseroir horizon. Dramatic stratigraphic changes occur in the Tensleep across south-central Montana. The upper contact is unconformable, showing topographic relief of as much as 50 ft due to a combination of erosion and the preseration of dunes at the top of the Tensleep. In the west, both upper and lower Tensleep sections are present. The lower is characterized by repeated cycles of marine, tens of feet thick, capped by ery limy to dolomitic beds 1 to 5 ft thick. The upper Tensleep is characterized by cycles of eolian dune capped by marine limy to dolomitic. Dune s can be as thick as 60 ft. The total Tensleep thickness in the western part of the area can be as much as 250 ft. In the east and central parts of the area the upper Tensleep is absent, and dune s deelop in the lower Tensleep. Vertical cycles are genetically similar to those in the western part of the region. As little as 25 ft of Tensleep is present on the east side of the Bighorn Mountains. Introduction The Permo-Pennsylanian section in the Big Horn and Powder Rier Basins is the most prolific oilproducing system in the central Rocky Mountains, haing produced more than 2 billion barrels of oil in the Bighorn Basin and 525 million barrels of oil in the Powder Rier Basin. The Permo-Pennsylanian Petroleum System includes the Permian Phosphoria Formation, which is the oil source rock, and the Pennsylanian Tensleep Sandstone, which is the main reseroir rock. Dramatic stratigraphic changes in the Tensleep occur across south-central Montana. To better understand these stratigraphic changes, 13 surface sections were measured and described in the Pryor and Bighorn Mountains. The results are summarized in the following conclusions: (1) The upper Tensleep contact is unconformable, showing topographic relief of as much as 50 ft due to a combination of erosion and the presence or absence of dunes. (2) In the west, both upper and lower Tensleep sections are present. The lower is characterized by repeated cycles of marine, tens of feet thick, capped by ery limy to dolomitic beds 1 to 5 ft thick. The upper Tensleep is characterized by cycles of eolian dune capped by marine limy to dolomitic. Dune s can be as thick as 60 ft. The total Tensleep thickness in the western part of the area can be as much as 250 ft. (3) In the east and central parts of the area the upper Tensleep is absent and dune s deelop in the lower Tensleep. The ertical cycles are similar to the ones in the west. On the east side of the Bighorn Mountains the Tensleep thins to as little as 25 ft. Most of the exposures of the Tensleep occur on the Crow Indian Reseration; the Crow Tribe gae permission to access their lands and cooperated in the project. Without their help the project could not hae been undertaken. The thirteen sections that follow were measured and described in the summer of 2005 at locali- 3
Lopez et al. MBMG Open-File Report 553 ties shown in figure 1. Relatie thicknesses are shown diagrammatically in figure 2. descriptions of samples, taken from seeral localities noted in the measured sections, were done by Hendricks and Associates, Inc. notations used in the descriptions are from the Rock Chart, 1975, Geological Society of Figure 1. Location index map of measured sections. America. 4
Lopez et al. MBMG Open-File Report 553 Figure 2. changes of Tensleep Sandstone across the project area shown diagrammatically. West is on the right, east on the left. BC, Bear Canyon; ST, Stockman Trail; 5-Mi, Fie Mile Creek; DH, Dry Head Canyon; GV, Grapeine Canyon; SC, Soap Creek; RG, Rotten Grass Creek; LG, Lodge Grass Creek. 5
Bear Canyon Location of Measured Section: SE¼ SW¼ Section 3, T. 9 S., R. 26 E. Interal s 5 5 10R6/2; pale red Base Phosphoria Formation, mostly coered, pale red to light gray limestone with red, brown and yellow chert 5 5 5YR8/1; pinkish gray Top Upper Tensleep Sandstone; sandy dolomite, uggy 15 10 N8; ery light gray fine w non light gray, cross-bedded dune 20 5 5R8/2; pink thin-bedded dolomite 23 3 5R8/2; pink fine bioturbated sandy dolomite, thickbedded 35 12 N8; ery light gray fine w non ertical light gray, cross-bedded dune ; burrowed in upper 2 ft related to oerlying marine incursion 37 2 5R8/2; pink fine w limy capping dune cycle 50 13 72 22 5Y8/1;pale yellowish gray fine w N8; ery light gray fine w non non ertical upper 3 ft light gray, cross-bedded dune Base Upper Tensleep; light gray, cross-bedded dune ; burrowed in upper 3 ft 6
83 11 85 2 95 10 5R8/2; pink 5Y8/1; pale yellowish gray Interal N8; ery light gray fine w tabular cross Top Lower Tensleep; pale pink sandy dolomite with abundant yellow brown chert nodules and thin beds (2 3 in) hard, light yellowish gray limestone light gray, cross-bedded, limy s 98 3 5Y8/1; pale yellowish gray fine w tabular cross light gray, cross-bedded, limy to sandy limestone, lithic limestone grains 102 4 104 2 109 5 5Y8/1; pale yellowish gray 5Y8/1; pale yellowish gray fine w N8; ery light gray fine w sandy dolomite, thickbedded, abundant chert nodules throughout bed light gray, limy tabular cross light gray cross-bedded, limy 113 4 128 15 130 2 N8; ery light gray fine w 5Y8/1; pale yellowish gray fine w bioturbated massie N8; ery light gray fine w light gray, limy, friable limy, bioturbated light gray, limy, friable; platy argillaceous siltsone and at top, dolomitic 7
Interal s 133 3 5Y8/1;pale yellowish gray fine w pale yellowish gray crossbedded 136 3 142 6 157 15 168 11 175 7 N8; ery light gray fine w bioturbated bioturbated 5Y8/1;pale yellowish gray fine w ertical 5Y8/1;pale yellowish gray fine w N8; ery light gray fine w N8; ery light gray fine w cut and fill, ripple cross, tabular cross light gray, bioturbated, limy ery limy, limonitic nodules on planes (1 2cm); burrowed upper half light yellowish gray, lenticular, limy ; bed sets 1 2 ft thick light gray cross-bedded, limy ; bed sets 3 in to 1 ft thick light gray, thin-bedded limy BC-1 ery fine to finegrained, slightly quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity ~15%. 176 1 180 4 N8; ery light gray fine w brecciated N8; ery light gray fine w light gray, brecciated, limy light gray cross-bedded, limy, poorly exposed 184 4 N8; ery light gray fine w light gray cross-bedded, limy 8
Interal s 187 3 N8; ery light gray fine w light gray, thin-bedded limy, sharp basal contact, quartz grains frosted 188 1 189 1 190 1 195 5 197 2 14 14 orange fine w N8; ery light gray fine w siliceous 5GY7/2; yellow-green silt 5Y8/1;pale yellowish gray fine w 5B8/1; ery light bluish gray fine w bioturbated bioturbated 10R4/6; reddish brown friable, yellowish capped by greenish gray clay drape followed by reddish and white paleosol; clays leached out in paleosols light gray siliceous light greenish gray siltstone with ery thin cherty (1-2 inches) pale yellowish gray, thin greenish gray siltstone and dolomite (1 ft) at top Base Tensleep Sandstone; pale bluish gray, bioturbated, limy Top Amsden Formation; reddish brown mudstone interbedded with yellowish gray and pinkish gray limestone and limestone breccia; limestone beds 1 2 ft thick 9
Bear Canyon 2 Location of Measured Section: NW¼ SW¼ Section 3, T. 9 S., R. 26 E. Interal 3 3 5Y8/1 5R8/2; 13 13 pink fine w dolomite bioturbated bioturbated 5Y8/1; pale yellowish 15 2 gray fine w bioturbated bioturbated 72 57 5Y8/1; pale yellowish gray fine w Base Phosphoria Formation; light yellowish gray limestone with red chert nodules Top Tensleep Sandstone; ery dolomitic ; caps dune cycle light gray clean bioturbated top of dune below light gray, cross-bedded, dune facies 108 36 114 6 N8; ery light gray fine w 5Y8/1; pale yellowish gray fine w bioturbated massie appearing, bioturbated light gray, cross-bedded, dune facies; thin marine reworked zone at top (6 in) light gray, limy ; bioturbated causing massie appearance 125 11 N8; ery light gray fine w non planar cross Base Upper Tensleep Sandstone; light gray, cross-bedded, dune facies 134 9 5R8/2; pink Top Lower Tensleep; pale pink sandy dolomite with abundant yellow brown chert nodules and thin beds (2 3 in) 10
Crown Butte Location of Measured Section: N½ Section 10, T. 7 S., R. 26 E. Interal s N8 Base Phosphoria Formation; light gray cherty limestone (reddish brown chert nodules) 18 18 23 5 25 2 37 12 10YR7/4, orange fine w 5Y8/1, yellowish gray fine w 5YR8/1, pinkish gray fine m 5Y8/1, yellowish gray fine w non bioturbated bioturbated bedded, nodular bioturbated, destroyed bioturbated, destroyed planar steep cross beds Top Tensleep Sandstone; cherty, sandy limestone (top lower Tensleep) yellowish gray, limy pinkish gray, ery limy to sandy limestone, clastic limestone grains, stained brown from bitumen light yellowish gray, cross-bedded (dune facies) CB-1 ery fine to finegrained, slightly, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, residual dead oil, porosity ~20% 11
Interal s 65 28 10YR8/2-5Y8/1, pale orangeyellowish gray fine w flat yellowish gray mostly coered 67 2 10YR7/4, orange fine w ertical, contorted calcite-cemented nodules ~0.25 0.5 in, limy 74 7 10YR8/2, ery pale orange fine w ertical flat, thick bedded bedded limy 89 15 10YR7/4, orange fine w bioturbated bioturbated; rip-up clasts at base, calcitecemented nodules ery, orange bioturbated 92 3 10YR8/2, ery pale orange fine w bedded, flat pale orange-gray, limy 96 4 10YR7/4, orange fine w ertical bioturbated top, flat bedded rip-up clasts basal 0.5 ft, small calcite cemented nodules, limy 107 11 5Y8/1, yellowish gray fine w flat,, yellowish gray, limy, calcitecemented nodules 12
108 1 10YR6/2, pale yellowish brown Interal fine fine m flat, ery cherty, s 109 1 10YR8/2-10YR7/4, pale orangegray orange fine w, low angle with spherical calcitecemented nodules ~0.25 0.5 in Coered, base of Tensleep not exposed but Amsdent float occurs about 20 30 ft lower. 13
Dry Head Section 1 Location of Measured Section: NW¼ Ne¼ Section 11, T. 7 S., R. 28 E. Interal Base Phosphoria Formation, pink cherty limestone, coered, float only; chert brownish red and yellowish brown 5 5 5R8/2; pink fine w Top Tensleep Sandstone; cherty ery limy ; weathering produces abundant "pinpoint" ugs 35 30 36 1 37 1 40 3 N8; ery light gray fine w orange fine w orange fine w orange fine w non small ertical, rippled at top ripple ery light gray cross-bedded dune, excellent porosity, bed sets 4 to 6 ft. Rippled at top, possibly marine reworking sandy dolomite, micritic matrix ery fine limey, fines upward into siltstone ery limy 54 14 56 2 N8; ery light gray orange fine w fine to fine mod ertical top, burrowed at top 6 ft way light gray, cross-bedded dune, upper 6 ft burrowed (ophiomorpha) ery limy 14
Interal 58 2 N8; ery light gray fine to fine mod, burrowed at top 6 ft light gray, cross-bedded dune 63 5 orange fine w and laminate at top ery limy, thin sandy dolomite at the top (3 in) 78 15 orange fine w ery limy, friable, mostly coered 82 4 N8; ery light gray fine w clean, cross-bedded, light gray 88 6 10R8/2; orange-pink to light gray to way sandy limestone grading upward into sandy dolomite 110 22 112 2 117 5 N8; ery light gray fine w orange fine w N8; ery light gray fine w planar cross beds, thick bedded beds light gray, clean, cross-bedded in bed sets 4 6 ft thick, silt drapes on bed sets. ery limy clean, cross-bedded, light gray 15
Interal 124 7 orange fine w way and ripple cross yellowish gray, ery limy 126 2 N8; ery light gray fine w, flat and ripple light gray, contains clasts of dolomite breccia 138 12 10R6/2; pale red fine w Base Tensleep Sandstone; pale reddishgray, limy, brecciated at base and stained darker red at base 135 135 50 50 10R4/6-10R5/4; mod-pale red-brown 10R3/4; dark reddish brown Ranchester Member, Amsden Formation; reddish mudstone with thin interbedded light gray to mottled reddish and gray limestone; some limestones contain abundant red chert, minor amount of dolomite Horseshoe Member, Amsden Formation; mostly red mudstone with thin siltstone beds and thin yellowish muddy N7; light gray Top Madison Limestone, uggy to brecciated limestone 16
Dry Head Section 2 Location of Measured Section: NE¼ NE¼ Section 12, T. 7 S., R. 28 E. Interal s 3 3 N8, ery light gray light gray to light bluish gray, gypsiferous, cherty 24 21 10R6/6; mod reddish orange Base Chugwater Formation; reddish mudstone and thin interbedded red 3 3 10R6/2; pale red Phosphoria Foramtion; pale red, sandy, cherty limestone, brecciated in part 8 8 N8, ery light gray fine w to way Top Tensleep Sandstone; light gray to pale yellowish gray limy, thin bedded 20 12 10R6/2; pale red pale red cherty dolomite 25 5 orange fine w ertical way bedded to mega-rippled orange limy, burrowed in upper half 31 6 10R6/2; pale red pale red, sandy, silty, cherty dolomite 17
Interal s 33 2 orange fine w bioturbated planar, bedded limy, lithic limestone and quartz grains, matrix limy mud 35 2 N8, ery light gray fine w non way bedded to bedded clean cross-bedded, beds 6 in to 1 ft 39 4 orange fine w bioturbated flat bedded limy, lithic limestone and quartz grains, matrix limy mud DH2-1 ery fine to finegrained, slightly quartz, angular to subrounded, poor to fair sorting; micritic matix dolomitized and recrystallized, trace orthoclase, porosity ~14% 48 9 N8, ery light gray fine w non ertical at top only clean, cross-bedded dune, burrowed in upper 3 ft related to oerlying marine incursion 58 10 N8, ery light gray silt to fine mod rippled to way bedded light gray to greenish gray friable, silty, contains lithic limestone grains, poorly exposed 18
Interal s 61 3 10YR8/2; ery pale orange cherty, sandy dolomite; chert in nodules and in 1 3 in beds, chert gray to yellowish gray 63 2 orange silt to fine mod ripple thin siltsone couplets, ery thin bedded 64 1 N8, ery light gray flat laminate sandy dolomite 67 3 orange fine to fine mod way bedded and lowangle trough cross ery limy bedsets 1 6 in 68 1 N8, ery light gray fine w bioturbated way to bioturbated ery light gray, nodular, limy, bioturbated 69 1 orange flat laminate sandy limestone 74 5 N8, ery light gray fine w ripple at top cross-bedded limy, ripple in upper 1 ft 78 4 10YR8/2; ery pale orange fine w to ripple pale yellow limy 19
Interal s 88 10 orange fine w friable, poorly exposed yellowish to orange gray 93 5 N8, ery light gray fine w light gray cross-bedded limy 97 4 102 5 105 3 107 2 orange fine w N8, ery light gray fine w orange fine w N8, ery light gray fine w way, limy, mostly coered light gray cross-bedded limy limy, mostly coered limy, lithic limestone and quartz grains, matrix limy mud 111 4 orange fine w way, limy, mostly coered 113 2 N8, ery light gray fine w limy, lithic limestone and quartz grains, matrix limy mud; poorly exposed 125 12 orange fine w way, Base Tensleep Sandstone; limy, mostly coered 20
10 10 5RP6/2 Interal Top Amsden Formation; pale red and purple mudstone, interbedded thin limestone and limestone breccia s 21
Dry Head Section 3 Location of Measured Section: NE¼ NE¼ Section 10, T. 7 S., R. 28 E. Interal Base Phosphoria Formation; sandy dolomitic limestone, cherty (reddish gray, pink, gray) 11 11 orange fine w ertical, upper 2 ft flat Top Tensleep Sandstone; beds 1 2 ft thick, limy 12 1 N8, ery light gray fine w toe of dune build up, thickens dramatically to west 22 10 orange fine w ertical limy cross-bedded, fining upward 26 4 orange fine w bioturbated bioturbated limy bioturbated 61 35 N8, ery light gray fine w non ertical, upper 2 ft cross-bedded dune, contorted from compaction and down depositional slope slumping, burrowed in upper 2 ft related to oerlying marine incursion 64 3 orange fine w bioturbated bitoturbated ery light gray to orange mottled, marine 87 23 N8, ery light gray fine w non ertical, upper 2 ft cross-bedded dune, burrowed in upper 2 ft related to oerlying marine incursion 22
Interal 93 6 orange fine w, ripple cross limy, marine 98 5 orange fine w limy cross-bedded, fining upward, rippled at top 99 1 10R8/2; orange pink, flat bedded slightly sandy dolomite 104 5 N8 to 10YR7/4, lt gray to gray orange fine w mottled limy, cross-bedded 109 5 N8, ery light gray silt platy light gray to greenish gray siltstone 110 1 N8, ery light gray fine w ripple light gray ripple cross- 111 1 orange sandy mudstone 116 5 orange fine w planar cross limy, thin bedded 23
Interal 118 2 orange flat sandy, cherty limestone; 2 in purple-gray hematitic at base 123 5 10R6/2-N8; pale red to lt gray fine w planar, lowangle cross limy, marine; stained reddish at base and light gray upward. 126 3 orange fine w flat Base Tensleep Sandstone; limy quartz and sandy limestone; lithic limestone grains Top Amsden Formation; pale purple mudstone and interbedded limestone and limestone breccia 24
Dry Head Section 4 Location of Measured Section: NE¼ NW¼ Section 10, T. 7 S., R. 28 E. 10R5/6, reddish brown claysilt Interal Base Chugwater Formation; reddish brown mudstone s 9 9 10YR7/4, orange fine w, flat, brecciated Top Tensleep Sandstone; light orange, ery limy, iron (reddish brown) stain at the top. 17 8 10YR7/4, orange fine w bioturbated sandy limestone, quartz grains and limestone clasts in micritic matrix 25 8 N8, ery light gray fine w slightly ertical, upper few ft light gray dune, burrowed top from marine incursion aboe 26 1 10YR7/4, orange fine w ertical ripple cross to bioturbated marine cut across top of underlying dune ss 32 6 N8, ery light gray fine w slightly ertical, upper few ft light gray dune, burrowed top from marine incursion aboe 33 1 10YR7/4, orange fine w ertical ripple cross to bioturbated marine cut across top of underlying dune ss 25
Interal s 37 4 N8, ery light gray fine w slightly ertical, burrowed whole thickness light gray dune, burrowed top from marine incursion aboe 38 1 10YR7/4, orange fine w ertical ripple cross to bioturbated marine cut across top of underlying dune ss 42 4 N8, ery light gray fine w slightly ertical, burrowed whole thickness light gray dune, burrowed top from marine incursion aboe 46 4 66 20 10R5/4, pale reddish brown N8, ery light gray fine w non bioturbated top burrowed upper 4 ft sandy dolomite, pale pink at base and darkens upward dune ss, light gray to light orange in upper few ft. Upper few ft burrowed below oerlying marine incursion may be marine reworked at top DH4-8 DH4-6&7 ery fine crystalline dolomite, original micrite dolomitized and recrystallized, porosity 0 1% ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matix dolomitized and recrystallized, trace orthoclase, porosity 0 22% 26
76 10 10YR7/4, orange fine w Interal to rippled clay-rich grading upward into coarser, ery containing limestone grains (4 cycles) s 78 2 85 7 N8, ery light gray fine w 10YR7/4, orange fine w ertical beds to bioturbated toe of dune build up ery burrows 4 7 ft deep DH4-5 ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matix dolomitized and recrystallized, trace orthoclase, porosity 0 10% 86 1 N8, ery light gray fine w planar, highangle cross ery light gray crossbedded 90 4 10YR7/4, orange fine w ertical to bioturbated nodular, mottled minor thin interbedded claystone 27
Interal s 104 14 N8, ery light gray fine w non high angle planar cross light gray dune DH4-4 ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matix dolomitized and recrystallized, trace orthoclase, porosity ~24% 106 2 10YR7/4, orange fine w planar cross beds cherty, yellowish gray to gray-orange crossbedded, appears to grade upward into dune ss aboe DH4-3 ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matix dolomitized and recrystallized, trace orthoclase, porosity 0 4% 118 12 10YR7/4 to N8; grayorange to light gray fine w planar and, rippled at base dune, light gray, some contorted beds and collapsed breccia DH4-2 ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity 0 20% 124 6 N8, ery light gray fine w planar, flat light gray bedded 28
131 7 136 5 Interal 10YR7/4 to N8; grayorange to light gray fine w 10YR7/4 to N8; grayorange to light gray fine to fine w beds beds light gray cross-bedded light gray cross-bedded DH4-1 s ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity 0 20% Approximate Base Tensleep Sandstone, not exposed 29
Fie Mile Creek Location of Measured Section: Center Section 6, T. 6 S., R. 25 E. Interal s 5R5/4, mod red Base Chugwater Formation: red mudstone 4 4 9 5 11 2 14 14 17 3 28 11 N8, light gray Top Phosphoria; light gray limestone 10R7/4, mod orange, pink pink mudstone 10R8/2, pink 5YR7/4, mod yellowish gray fine w 5YR7/4, mod yellowish gray fine w N8-5YR7/1, light gray to pale yellow gray fine w ertical bioturbated, beds 1 to 2 ft thick Base Phosphoria Formation; clastic limestone to limestone breccia, some greenish rip-up clasts Top Tensleep Formation sandy limestone cherty, sandy limestone platy, thin bedded thin bedded, limy 30
36 8 5YR6/1, lt brownish gray fine w Interal ertical upper 1 ft planar and contorted beds, cross bed sets show eidence of downslope sliding 5-mi #6 s ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity ~22% 42 6 58 16 5YR7/4, mod yellowish gray fine w 5YR7/1, pale yellow gray fine to fine w ertical upper 1 ft, bidirectional (dip directions reerse through the interal) limy to sandy limestone, cherty thin bedded, bed thickness 1 4 ft, some contorted beds, looks marine 5-mi #5 ery fine to finegrained, dolomitic quatrz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity ~24% 65 7 5YR7/1, pale yellow gray fine w horizontal & ertical, partly bioturbated thin bedded 68 3 5YR7/1, pale yellow gray fine w ertical bioturbated limy, bioturbated 31
Interal s 75 7 5YR7/4, mod yellowish gray fine w planar cross, thick bedded yellowish gray limy, marine 79 4 81 2 5YR6/1, light brownish gray silt to clay N8, light gray fine w ripple in part and, some climbing ripples light brownish gray silty to sandy mudstone light gray 83 2 5YR7/1, pale yellow gray fine w planar high angle cross yellowish gray limy, some clastic limestone grains 87 4 5YR7/1, pale yellow gray fine w ertical way yellowish gray limy, burrowed 88 1 N8 fine w siliceous flat light gray silicified 98 10 5YR7/1, pale yellow gray fine to fine w yellowish gray, some limestone clastic grains 32
100 2 5YR7/1, pale yellow gray fine w Interal, flat ery fine to fine-grained quartz grading to lithic with abundant limestone grains. 5-mi #4 s ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity ~22% 103 3 107 4 10YR7/4, mod brown fine w 10YR7/4, mod brown fine w ripple, thin bedded planar highangle cross brown limy brown, crossbedded, limy 5-mi #1, #2, and #3 ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity 0 15% 113 6 N8, light gray fine to fine w ertical planar cross light gray 125 12 coered 127 2 N8 fine w dolomitic, flat sugary light gray dolomitic 33
141 14 5YR7/1, pale yellow gray fine w Interal, flat Base Tensleep Sandstone; light yellowish gray, limy, beds 1.5 2 ft thick s 13 13 5YR6/1, light brownish gray Top Amsden, Ranchester Member; light brownish gray, cherty limestone, thin to medium bedded 23 10 N8-5YR6/1, lt gray to lt brnish gray limestone, dolomitic sandy limestone, and limestone breccia, thin bedded 28 5 5R6/6-5RP4/2, pale red-- red purple pink to pale purple mudstone and siltstone 31 3 N8 light gray dolomite 46 15 5R6/6-5RP4/2, pale red-- red purple pink to pale purple mudstone and siltstone, interbedded with thin light gray and pale pink limestone and limestone breccia 61 15 5R6/6, pale red Base Ranchester Member; mudstone with ery minor beds of limestone. 34
Interal s 67 6 10R4/6, mod reddish brown red mudstone 75 8 coered 0 Base Amsden Fomation, Horseshoe Member; coered, reddish brown soil Top Madison Group; medium gray limestone 35
Grape Vine Canyon Location of Measured Section: N½ Secton 2, S½ Section 11, T. 6 S., R. 30 E. Interal 13 13 10R6/2, pale red 5Y8/4, yellow fine w non and contorted Phosphoria (?) and Chugwater Formation: reddish cherty limestone oerlain by red mudstone Top Tensleep Sandstone; pale yellow gray fine-grained dune (?) 17 4 10R6/2, pale red fine w flat interbedded reddish mudstone and ery limy, cherty, pink-gray 20 3 5R8/2, pale pink-gray fine w ertical upper ft flat pale pinkish gray, cherty, ery limy 27 7 5R4/2, red purple fine w platy muddy, platy, beds about 0.25 in 92 55 97 5 5Y8/1, yellowish gray fine to fine w 5Y7/2, yellowish gray fine w ertical, upper 2 3 ft bed () sets 10 12 ft thick with thin muddy partings and beds, bed sets 1 2 ft thick cross-bedded thin bedded, cross-bedded 36
98 1 5P5/2, purple Interal clay silt pale purple mudstone 100 2 N8, light gray mottle, micritic limestone 102 2 10YR7/4, orange flat sandy limestone 117 15 127 10 135 8 10YR7/4, orange clay - silt platy sandy mudstone and mudstone 5YR7/2 to N8, gray orange to light gray f w 5YR7/2, orange f w calcitecemented nodules ~0.25 in, cut and fill at base, rip-up clasts cross-bedded limy cross-bedded limy, tidal channel (?) 142 7 147 5 5YR7/2 to N8, gray orange to light gray 10YR7/4, orange clay - silt mudstone mottled brecciated limestone at base and brecciated (collapse) sandy limestone at top 37
Interal 150 3 N8, light gray fine w brecciated mottled brecciated limy, cherty 153 3 N8-5YR7/2, light gray to gray orange f w planar cross beds in flat bed sets 1 2 ft thick ery limy cross-bedded 157 4 10YR7/4, orange clay - silt mudstone 159 2 161 2 5YR7/2 gray orange fine to coarse p bioturbated top 1 ft 5YR7/2 to N8, gray orange to light gray fine w brecciated, rip up clasts coarse sand with rip-up clasts at base, then thinnly muddy, oerlain by reddish gray ss and bioturbated ss at top mottled limy, light gray with reddish to pale purple 163 2 166 3 5R7/2 reddish gray reddish gray sandy nodular limestone 5YR7/2 to N8, gray orange to light gray fine w orange limy cross-bedded 167 1 N8 micritic limestone 178 11 10YR7/4, orange mudstone with thin interbedded limestones (6 in or less) 38
Interal 179 1 N8 micritic limestone 180 1 N8 fine w flat light gray ery limy 181 1 5YR8/1, pinkish gray bedded bedded, nodular chert 184 3 5YR8/1-N8, pinkish gray to light gray fine w Base Tensleep Sandstone; light gray, limy, cross-bedded 14 14 10R7/4-10R6/4, pale to pale red brown clay silt Top Amsden, Ranchester Limestone Member; mudstone interbedded with gray siltstone and limestone and minor purple siltstone 21 7 5YR8/1, pinkish gray pinkish gray limestone with reddish brown chert nodules 31 10 5YR8/1, pinkish gray mudstone, with nodular limestone near top 33 2 5YR8/1, pinkish gray mottle micritic limestone 82 49 10R7/4-10R6/4, pale to pale red brown mudstone with thin interbedded limestones (6 in or less) and limestone breccia. 39
Lodge Grass Creek Location of Measured Section: Center Section 20, T. 9 S., R. 33 E. 10R7/4 silt to clay Interal Base Chugwater Formation; red mudstone s 4 4 6 2 N8, light gray fine w 5YR7/1, pale brownish gray fine w sandy limestone ertical and ripple Top Tensleep Sandstone; light gray, limy light brownish gray, ery limy to sandy limestone LG-3 ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity 0 6% 11 5 N8, light gray fine w ertical in upper 1 ft light gray, limy 12 1 10YR6/4, light yellowish brown fine w ripple light brown, ery limy to sandy limestone 15 3 N8, light gray fine w ertical sparsely burrowed, light gray friable ; possible toe of dune 40
17 2 Interal 5YR7/1, pale brownish gray fine dolomite bedded sandy dolomite pale brownish gray to pink s 24 7 N8, light gray fine w flat, planar to way, beds 1 in to 8 in light gray, 25 1 32 7 87 55 N8, light gray fine w N8, light gray fine w N8, light gray fine w non ertical ripple to and trough cross light gray, with silty clay drapes and lenses of brownish gray limestone light gray, non, burrowed in upper 2 ft, probable dune facies Base Tensleep Sandstone; mostly coered interal, calcitecemented spherical nodules about 0.25 0.5 in. diameter, cross bed sets thin (3 in to 1 ft); appears from float that there are some interbedded thin mudstones and siltstones LG-2 ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity 0 24% 41
Interal s 18 18 10R5/4, pale reddish brown silt to clay Top Amsden Formation, Ranchester Limestone Member; red mudstone 83 65 10R5/4, pale reddish brown silt to clay mostly coered, float indicates probably interbedded red mudstone and thin limestone beds. 86 3 5YR7/1, pale brownish gray light brownish gray to pink, cherty limestone 101 15 10R5/4, pale reddish brown silt to clay coered, reddish mudstone 111 10 5YR7/1, pale brownish gray brownish gray to pink, mottled, cherty, dolomitic limestone; uggy, brecciated in part 115 4 10R5/4, pale reddish brown silt to clay red mudstone 116 1 5YR7/1, pale brownish gray mottled, sandy limestone 42
129 13 10R5/4, pale reddish brown silt to clay Interal red mudstone with interbedded thin medium gray limestone s 134 5 5YR7/1, pale brownish gray mottled limestone breccia 140 6 155 15 10R5/4, pale reddish brown N8, light gray silt to clay red mudstone, mostly coered limestone, basal 5 ft massie then remainder pale pink to light gray mottled brecciated limestone, uggy LG-1 ery fine crystalline dolomite, original micrite dolomitized and recrystallized, contains fine to coarse detrital quartz and orthoclase, porosity 0 7% 167 12 171 4 10R5/4, pale reddish brown 5YR7/1, pale brownish gray silt to clay red mudstone Base Ranchester Member; brownish gray dolomite 43
Interal s 196 25 5R4/6, moderate red Base Amsden Formation, Horseshoe Member; red mudstone Top Madison Group Limestone; medium gray, karsted, uggy limestone 44
Rotten Grass Creek Location of Measured Section: NE¼ SE¼ Section 22, T. 8 S., R. 32 E. Interal 5R5/4, mod red Triassic Chugwater Formation: red mudstone 0 2 N8, light gray flat,, med bedded Top Tensleep Sandstone: sandy limestone, cycle cap 25 23 N8, light gray ery fine well ertical, upper 1 ft platy, basal 1 ft; then remainder bedded 10 10 5R5/4-10R5/4 mod red to pale red brown Amsden Formation, Ranchester Member: red mudstone and interbedded thin micritic limestone 45
Soap Creek Location of Measured Section: N½ Section 33, T. 7 S., R. 32 E. Interal 5R5/4,mod red Base Chugwater Formation: red mudstone 1 1 N8; light gray fine w flat, Top Tensleep Sandstone; limy, cycle top 15 14 N8; light gray fine w slightly ertical, upper 2 ft bedded oil-stained (dead oil); this dune interal pinches out laterally in about 100 yards in each direction, where Chugwater rests directly on next underlying unit 21 6 5YR6/1, light brownish gray fine w way, limy to sandy limestone, top of cycle 22 1 10YR8/2, pale orange fine w flat, ery limy 34 12 N8; light gray fine w ertical, upper 1 ft bedded oil-stained, some cemented nodules as large as 0.5 in. in diameter 43 9 10YR8/2, pale orange fine w to, flat platy, some lithic carbonate clasts, some argillaceous and less resistant than. 48 5 5YR6/1, light brownish gray fine w mostly coered, light brownish gray float 46
Interal 51 3 N8; light gray fine w platy Base Tensleep Sandstone; limy, some rip-up clasts 0 2 4 2 50 46 10R7/2; mod pink Top Amsden Formation; pink mudstone 5RP7/2; pale purple dolomitic nodular limestone 10R6/2-10R7/2; pale red to mod pink reddish mudstone interbedded with thin micritic limestone 47
Spring Creek Location of Measured Section: NE¼ Section 2, T. 7 S., R. 28 E. Interal 2 2 10YR6/2, pale yellowish brown Top Tensleep Sandstone; sandy, silty, cherty dolomite 5 3 10YR6/2,p ale yellowish brown fine w ertical & horizontal ripple ery limy quartz, 5% lithic limestone grains floating mud matrix 34 29 N8, ery light gray fine w non ertical & horizontal top 1 ft trough and planar cross, burrowed upper ft ery light gray, dune, excellent porosity, some contorted from compaction and down dip slumping, burrowing related to oerlying marine incursion 38 4 orange fine cherty, sandy dolomite 43 5 orange fine w bioturbated, way to bioturbated ery limy quartz, 5% lithic limestone grains floating mud matrix 47 4 10YR6/2, pale yellowish brown yellowish brown, cherty, sandy dolomite 49 2 N8, ery light gray fine w ripple light gray, silty 48
Interal 50 1 N8, ery light gray ery light gray to pale pink cherty, sandy dolomite 56 6 N8, ery light gray rippled to platy silty to sandy mudstone 57 1 orange fine w ertical way and lowangle trough cross limy,, marine 61 4 orange fine w bioturbated bioturbated bioturbated, limy, some limestone lithic grains 62 1 orange fine w limy, ; chert nodules 65 3 N8, ery light gray silty claystone with chert beds 1 to 4 in thick 69 4 N8, ery light gray fine w light gray to greenish gray limy 73 4 N8, ery light gray fine w light gray ery limy ; cross bedded 75 2 orange, flat bedded sandy dolomitic limestone 49
Interal 95 20 N8, ery light gray fine w to non trough and planar cross dune, ery light gray, stained yellowish gray in part (30%), at base 96 1 101 5 orange fine w platy platy, muddy N8, ery light gray fine w non ery light gray, cross-bedded dune 103 2 orange fine to fine mod platy clay-rich 112 9 N8, ery light gray fine w ery light gray, cross-bedded dune 116 4 orange fine w ertical basal 1 ft, then trough cross-bedded orange cross-bedded limy 127 11 orange fine w ertical basal 1 ft, then trough cross-bedded Base Tensleep Sandstone; as aboe but mostly coered, orange cross-bedded limy Top Amsden Formation; mostly float, purple-gray mudstone 50
Stockman Trail Location of Measured Section: SW¼ Section 32, T. 8 S., R. 26 E. Interal s Base Phosphoria Formation; medium gray limestone cherty (reddish brown) 15 15 N8, ery light gray fine to fine w ertical, top 1 ft Top Tensleep Sandstone; light gray, cross-bedded, dune ss 25 10 N7, light gray fine limestone ertical, top 1 ft flat, partly bioturbated sandy limestone to ery limy 67 42 N8, ery light gray fine to fine w ertical, top 2 ft High angle trough and planar cross light gray, crossbedded, dune ss 73 6 N8, ery light gray light gray limestone, caps cycle 85 12 N8, ery light gray fine to fine w light gray, crossbedded, dune ss 89 4 N8, ery light gray light gray, sandy, cherty, dolomitic limestone 51
93 4 10YR8/2, ery pale orange fine to fine Interal w ertical bioturbated yellowish gray, bioturbated limy ST-2 s ery fine to finegrained, dolomitic quartz, angular to subrounded, poor to fair sorting; micritic matrix dolomitized and recrystallized, trace orthoclase, porosity 0 12% 98 5 N8, ery light gray fine w cross-bedded and way light gray, 103 6 N8, ery light gray fine w ertical and partly bioturbated, light gray bioturbated 112 9 N8, ery light gray fine w ertical & horizontal and partly bioturbated light gray, bioturbated limy 113 1 N8, ery light gray fine w light gray 117 4 5Y8/4, yellow fine w and ripple cross sandy limestone to ery limy, contains clastic limestone grains 52
Interal s 121 4 5Y8/4, yellow fine w and ripple cross ery limy 127 6 5Y8/4, yellow fine to ery fine w yellowish gray, fine upward grading into oerlying bed 143 15 5Y8/4-N8, gray-yellow to light gray fine w planar cross yellowish gray to light gray, dune (?) 145 2 155 10 N8, ery light gray fine dolomite 5Y8/4, yellow fine to fine w way laminations sandy dolomite cut and fill structure at base, trough cross, bidirectional 1 3 in bed sets, marine, tidal ss (?) ST-1 ery fine to finegrained, slightly quartz, angular to subrounded, poor to fair sorting, algal fragments present, micritic matrix dolomitized and recrystallized, trace orthoclase, porosity ~17% 164 9 5Y8/4, yellow fine w limestone to ss platy, sandy limestone to lime 53
Interal s 172 8 N8, ery light gray fine to fine w non ertical planar tabular cross, steep light gray cross-bedded grades upward into massie 174 2 10R4/6 reddish brown mudstone, top few inches greenish gray claystone 186 12 N8, ery light gray fine w climbing ripples Base Tensleep Sandstone; light gray, locally stained reddish gray at basal contact, sharp basal contact 23 23 10R6/2, pale red Top Amsden, Ranchester Limestone Member; reddish gray mudstone interbedded with light gray limestone and limestone breccias in beds 1 ft thick or less, much less abundant than mudstone (20 30%) 40 17 N8, ery light gray cherty limestone, some chert bedded in 3 6 in beds, reddish gray chert 54
Interal s 128 88 129 1 68 68 10R6/2, pale red N8, ery light gray 10R4/6 reddish brown reddish gray mudstone and interbedded limestone breccia and nodular limestone in beds 1 2 ft thick; mudstone about 60 70% Base Ranchester Limestone Member; light gray limestone Base Amsden, Horseshoe Member; reddish brown mudstone and siltstone Top Madison Group; medium gray uggy to karsted limestone 55