Lithologic Descriptions, Geophysical Logs, and Source-Rock Geochemistry of the US Geological Survey Alcova Reservoir AR–1

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Lithologic Descriptions, Geophysical Logs, and Source-Rock Geochemistry of the U.S. Geological Survey Alcova Reservoir AR–1–13 Core Hole, Natrona County, Wyoming

Scientific Investigations Report 2019–5123

U.S. Department of the Interior U.S. Geological Survey

Lithologic Descriptions, Geophysical Logs, and Source-Rock Geochemistry of the U.S. Geological Survey Alcova Reservoir AR–1–13 Core Hole, Natrona County, Wyoming

By Mark A. Kirschbaum, Thomas M. Finn, Christopher J. Schenk, and Sarah J. Hawkins

Scientific Investigations Report 2019–5123

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DAVID BERNHARDT, Secretary U.S. Geological Survey James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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Suggested citation: Kirschbaum, M.A., Finn, T.M., Schenk, C.J., and Hawkins, S.J., 2019, Lithologic descriptions, geophysical logs, and source-rock geochemistry of the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole, Natrona County, Wyoming: U.S. Geological Survey Scientific Investigations Report 2019–5123, 33 p., https://doi.org/10.3133/sir20195123.

ISSN 2328-0328 (online) iii

Contents

Abstract...... 1 Introduction...... 1 Geophysical Logs...... 6 Stratigraphy...... 6 Cloverly Formation...... 6 Thermopolis Shale...... 6 Muddy Sandstone...... 6 Mowry Shale...... 8 Frontier Formation...... 8 Geochemistry...... 8 Quantity of Organic Matter...... 9 Types of Organic Matter...... 9 Geochemistry Summary...... 13 Acknowledgments...... 13 References Cited...... 13 Appendix 1. Detailed Core Descriptions of the USGS AR–1–13 Core Hole, Natrona County, Wyoming...... 15 Appendix 2. Geophysical Logs of the USGS AR–1–13 Core Hole, Natrona County, Wyoming.....31

Figures

1. Map of southeastern part of the Wind River Basin showing location of the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole...... 2 2. Index map of the southeastern part of the Wind River Basin showing major structural elements (Finn, 2019), location of U.S. Geological Survey Alcova Reservoir AR–1–13 core hole, and location of the southeast–northwest subsurface cross section shown on figure 5...... 3 3. Stratigraphic chart of Lower and lowermost Upper Cretaceous rocks in the southeastern part of the Wind River Basin...... 4 4. Graphic log of U.S. Geological Survey Alcova Reservoir AR–1–13 core hole showing lithology, and comparison to gamma ray and conductivity logs...... 5 5. Subsurface stratigraphic cross section showing correlation of Lower Cretaceous and lowermost Upper Cretaceous strata in the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole with nearby wells in the southeastern part of the Wind River Basin...... 7 6. Gamma ray and conductivity logs of U.S. Geological Survey Alcova Reservoir AR–1–13 core hole showing relation of stratigraphic intervals to organic richness and kerogen type...... 11

7. Cross plot of S2 and total organic carbon for samples from the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole...... 12 8. Cross plot of hydrogen index and oxygen index for samples from the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole...... 12 Table

1. Total organic carbon and pyrolysis data for the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole...... 10

Lithologic Descriptions, Geophysical Logs, and Source- Rock Geochemistry of the U.S. Geological Survey Alcova Reservoir AR–1–13 Core Hole, Natrona County, Wyoming

By Mark A. Kirschbaum, Thomas M. Finn, Christopher J. Schenk, and Sarah J. Hawkins

Abstract assessments of the oil and gas potential of the Wind River Basin. Determining where to conduct such a study requires In 2013, a continuous 624-foot core hole was drilled and (1) a location along the shallow margin of the basin in order logged by the U.S. Geological Survey in Natrona County, to obtain samples that have not been subjected to the effects Wyoming, with the goal to better understand Cretaceous source of deep burial and therefore are immature with respect to rocks in the Wind River Basin. The core hole, named the Alcova hydrocarbon generation; (2) a location where little clastic input Reservoir AR–1–13, penetrated the interval extending from the during deposition would dilute the organic matter; and (3) a upper part of the Lower Cretaceous Cloverly Formation to the relatively undeformed sedimentary section. A location fulfilling lower part of the Upper Cretaceous Frontier Formation. The these criteria was identified in the southeastern part of the basin lithologies are predominantly mudrock, with minor amounts of near Alcova Reservoir (fig. 1). sandstone and altered volcanic ash beds that were deposited in A continuous core hole, the Alcova Reservoir AR–1–13, open marine, nearshore marine, and fluvial settings. was drilled and logged by the USGS in August 2013 on public Samples were collected from open marine clay-rich, land in Natrona County, Wyoming, about 30 miles southwest dark-colored mudrocks, and these were analyzed for total of Casper, Wyoming, in support of the National and Global organic carbon content and by programmed pyrolysis analysis. Assessment of Oil and Gas Resources Project. The core The results show that the lower part of the Frontier Formation, hole is located on the northeast flank of the Alcova anticline Shell Creek Shale equivalent, and the Thermopolis Shale in T. 30 N., R. 82 W., sec. 7, at lat 42.575145 degrees and contain Type III gas-prone kerogen, with poor to fair genera- long 106.70383 degrees (figs. 1 and 2). Core was recovered tive source rock potential. The upper part of the Mowry Shale between 40.5 and 623 feet (ft) below surface, an interval of has good to excellent generative potential, with organic matter 582.5 ft, of which, 94 percent of the rock was recovered. composed mainly of Type II oil-prone kerogen with some Coring began in the lower part of the Frontier Formation and mixed Type II/III kerogen capable of generating oil and gas. ended in the upper part of the Cloverly Formation (fig. 3). The core hole was drilled by personnel of the USGS during multiple days and was completed on August 8, 2013. Surface casing was set to 40.5 ft and coring began immedi- Introduction ately below. Cores were collected in 15 ft sections and boxed on location by the site geologist and a representative of the In 2005, the U.S. Geological Survey (USGS) quan- USGS Core Research Center (CRC). The core hole was titatively assessed the technically recoverable oil and gas subsequently logged by the USGS using standard geophysical resources of the Wind River Basin in Wyoming (Kirschbaum techniques including natural gamma, resistivity, conductiv- and others, 2005; Johnson and others, 2007). The assess- ity, density, sonic, and caliper with digital data collected to a ment results show high hydrocarbon potential in sandstone depth of 624 ft. reservoirs sourced from Lower and Upper Cretaceous organic- Cores were transported to the CRC located at the Denver rich mudrocks (Johnson and others, 2007). Sandstones in the Federal Center in Lakewood, Colorado, where they were Frontier-Muddy Continuous Gas Assessment Unit have high slabbed and reboxed, approximately 12 ft to a box, totaling hydrocarbon potential and are thought to be sourced from inter- 45 boxes. Butt ends were returned to the field boxes and then vening marine shales, particularly the Mowry and Thermopolis sampled for geochemical analysis. Both the slabbed and butts Shales (for example, see Burtner and Warner, 1984). There are archived at the CRC with the library number F215. are other potential source rock intervals within the assessment The core was described at several levels of detail, sam- unit; however, there are limited geologic and geochemical data pled for geochemical analysis, and photographed. The core is available for these units (Finn, 2007a). Therefore, additional portrayed as graphic logs at 1 inch (in.) = 5 ft (appendix 1) and study of other potential source rock intervals would aid future at 1.5 in. = 100 ft (fig. 4). 2 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

1052 108 10 100 103 1032

T. 32 N.

487

T. 31 N.

238

r 220 e iv USGS R e tt AR–1–13 la P North 23 T. 30 N. Alcova

Alcova Reservoir

230

T. 29 N. Pathfinder Reservoir

R. 8 W. R. 83 W. R. 82 W. R. 81 W.

ase map from U.S. epartment of the Interior National Park Service 0 1 2 3 5 MILES WYOMING

0 1 2 3 5 KILMETERS WIND RIER BASIN CASPER EXPLANATION Map Wind River asin Province boundary area USGS AR–1–13

Figure 1. Southeastern part of the Wind River Basin showing location of the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole. Introduction 3

10 1030 T. 3 35 CASPER N.

ARCH

Wind

River

Basin 14–12 axis 43–16 GRANITE

MOUNTAINS T. AR–1–13 Alcova 30 N. anticline UPLIFT Alcova Pathfinder Reservoir 230 Reservoir

R. 8 W. R. 80 W.

ase from U.S. Geological Survey, 2010 1:2,000,000-scale digital data 0 5 10 MILES Lambert Conformal Conic proection Standard parallels 1 and 5 Central meridian-10 30 Latitude of origin 1, meters 0 5 10 KILMETERS North American atum of 1983 (NA 83) EXPLANATION WYOMING Frontier Formation outcrop Line of section WIND RIER BASIN Precambrian rocks Anticline CASPER Wind River asin boundary Syncline

Normal faultBar and ball 43–16 Map on downthrown block Well location area Thrust faultSawteeth on upper plate

Figure 2. Southeastern part of the Wind River Basin showing major structural elements (Finn, 2019), location of U.S. Geological Survey Alcova Reservoir AR–1–13 core hole, and location of the southeast–northwest subsurface cross section shown on figure 5.

den19-0057fig 02 4 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

Ma System Series Stage Fossil one Eastern Wind River Basin

Baculites scotti Baculites reduncus Unnamed middle member Baculites gregoryensis Baculites perplexus (late form) Parkman Sandstone Member Baculites gilberti Wallace Creek Tongue Formation Baculites perplexus (early form) Mesaverde of Cody Shale Middle Baculites sp. (smooth) Fales Sandstone Member Baculites asperiformis 80 Baculites mclearni Baculites obtusus Baculites sp. (weak flank ribs) Campanian (part) Baculites sp. (smooth) Scaphites hippocrepis III Upper sandy Scaphites hippocrepis II member Lower Scaphites hippocrepis I 83.5 Desmoscaphites bassleri Desmoscaphites erdmanni Upper 85 Clioscaphites choteauensis Cody Shale Santonian

Mid Clioscaphites vermiformis

L Clioscaphites saxitonianus 86.3 Lower shaly Scaphites depressus member Upper Inoceramus involutus Coniacian Middle Inoceramus deformis 88.7 L Inoceramus erectus Prionocyclus quadratus

Upper Cretaceous (part) Wall Creek Member Scaphites whitfieldi Prionocyclus wyomingensis 90 Upper Prionocyclus macombi Prionocyclus hyatti Emigrant Gap Prionocyclus percarinatus Member Turonian Middle Collignoniceras woollgari Mammites nodosoides Vascoceras birchbyi

Lower Pseudaspidoceras flexuosum 93.3 Nigericeras scotti Burroceras clydense Cretaceous (part) Upper

Dunveganoceras problematicum Frontier Formation 95 Plesiacanthoceras wyomingense Acanthoceras bellense Acanthoceras granerosense Belle Fourche Middle Colinoceras tarrantense Member Cenomanian Neogastroplites maclerni Lower Neogastroplites muelleri Neogastroplites haasi Mowry Shale 98.5

100 Core Muddy Sandstone interval Albian

Thermopolis Shale

113 Lower Cretaceous (part) Cloverly Formation Aptian

Figure 3. Lower and lowermost Upper Cretaceous rocks in the southeastern part of the Wind River Basin. Modified from Finn, 2007b. [Ma, million years before present] den19-0057fig 03 Introduction 5

Depth Gamma ray (in feet) Conductivity EXPLANATION 50 No recovery or missing interval Ash bed Colors approximate the actual core color, except ash beds which are shown in orange 100 Frontier Grain sie Formation C M c S F Cs G granule very coarse sand coarse sand 150 medium sand fine sand very fine sand silt clay

Clay Spur 200 Bentonite Bed

250

Upper 300 siliceous part Mowry Shale 350

400

Shell Creek Shale equivalent

450

Muddy Sandstone

500

Thermopolis Shale 550

Figure 4. U.S. Geological Survey Alcova Reservoir 600 AR–1–13 core hole showing lithology, and comparison to gamma ray and conductivity logs. Location shown on Cloverly Formation figures 1 and 2. C M c S F Cs G den19-0057fig 04 6 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

Geophysical Logs the middle “muddy sandstones” as the Muddy Sandstone. Love (1948) included the upper shale unit with the overly- Geophysical logs are shown in appendix 2, and the digi- ing Mowry Shale. Sandstone beds in the lower shale have tal data are presented in Log ASCII Standard (LAS) format been referred to as the “rusty beds” by Washburne (1908) and in Finn and others (2019a). The gamma ray and conductivity Eicher (1962). The Thermopolis is Early Cretaceous Albian age based on the presence of diagnostic foraminifers in the logs are paired with the lithologic log for points of compari- upper part of the unit (Eicher, 1962); however, the lower part son (fig. 4). Core-to-log comparisons that were noted include is barren of microfossils according to Eicher (1962) so that the (1) the middle of an ash bed at 73 ft in the core corresponds lower age is indeterminate. to about 72 ft on the gamma and conductivity log; (2) the The Thermopolis is 130 ft thick in the core and is present middle of a concretion at 138.4 ft in the core corresponds to between 474.9 and 604.9 ft. The upper contact is somewhat about 138 ft on the gamma/conductivity log; (3) the middle uncertain but is picked based on the change from burrowed of a concretion at 152.2 ft in the core corresponds to about sandy siltstone below to convoluted sandstone above. The 153 ft on the gamma log; and (4) the middle of an ash bed at unit is primarily composed of dark-gray siltstone and sandy 337.5 ft in the core corresponds to about 336 ft on the gamma siltstone and contains numerous thin burrowed to laminated log. Therefore, the core-log correlation at any point is less interbeds especially in the lower part of the unit, below 537.2 ft, than a 1.5 ft difference. The geophysical logs of AR–1–13 which may be equivalent to the “rusty beds” of Eicher (1962). have been correlated to nearby wells and formation contacts This unit is called the “silt marker” in some subsurface stud- are mapped based on subsurface correlations (fig. 5). ies (Keefer, 1997; Keefer and Johnson, 1997). The laminated sandstone is mainly streaky to wavy lamination with erosional bases that are either storm or some other type of event beds. Stratigraphy The beds are highly disrupted by burrows, mainly Planolites, and by sand-filled cracks, possibly of syneresis origin. There The core includes the stratigraphic interval extending from are numerous rusty brown concretions (see appendix 1, graphic the upper part of the Lower Cretaceous Cloverly Formation log), a prominent cone-in-cone structure at 558.5 ft, and one to the lower part of the Upper Cretaceous Frontier Formation prominent altered volcanic ash between 523 and 524 ft. (figs. 3 and 4). The formation contacts are picked at lithologic changes in the core and on the basis of subsurface correlations Muddy Sandstone with nearby wells (fig. 5). In some cases, alternate contacts are discussed in the text and shown on the graphic log (appendix 1). The Thermopolis Shale is overlain by the Muddy Sand- stone. The name Muddy was first used informally by drillers Cloverly Formation for “muddy sandstones” in the lower part of the Benton Shale as described in Hintze (1915) and was called the Muddy The Cloverly Formation was named by Darton (1904) Sandstone by Love (1948). A reference section was designated for outcrops on the east side of the Bighorn Basin. The age of in the Bighorn Basin by Eicher (1960, 1962) near Greybull, the Cloverly is Early Cretaceous, probably Aptian and older Wyoming. The age of the Muddy is Early Cretaceous based (Merewether and others, 1997). Only the upper part of the on the presence of Albian age foraminifera and ammonites in Cloverly was cored in the well from 604.9 ft to the bottom adjacent units (Eicher, 1962). of the hole at 623 ft. The cored interval consists of fine- to The contacts of the Muddy with underlying and overly- medium-grained rippled to cross-laminated sandstone. There ing units are problematic because of gradational lithologies is minor greenish mudrock, mainly preserved as rip-up clasts and the inability to see lateral continuity in a core. The lower at or just above erosional surfaces. contact is placed at 474.9 ft. There are several possibilities The contact with the overlying Thermopolis Shale is for the upper contact. The main lithostratigraphic contact obscured in the core because of a lost interval, but is placed is at 460.3 ft, at the top of a clean, well-sorted laminated to above a pyrite nodule and granule bed at 604.9 ft, below which burrowed sandstone of probable nearshore marine origin. is the missing interval and then another pyritized granule layer. Log correlation to nearby wells supports this contact based on regional subsurface mapping (Finn, 2007b) (fig. 5). Using these picks, the Muddy is about 15 ft thick. The dominant Thermopolis Shale lithology is cross laminated to convoluted sandstone with minor siltstone laminations and distinct burrowing mainly The Thermopolis Shale was originally named by Lupton by Skolithos. Cross lamination is from low angle to angle (1916), which he separated into a lower shale unit, a middle of repose. The low-angle beds are interpreted as hummocky “muddy sandstone” unit, and an upper shale unit. The history cross stratification (hcs). The interpreted hcs, shows an overall of the naming of the unit is well described by Eicher (1960, decrease in radioactivity on the gamma log, and the well- 1962). Later, in the Wind River Basin, Love (1948) formally sorted nature of the sandstone indicates a nearshore marine referred to the lower shale unit as the Thermopolis Shale and origin of the unit. Laterally in the subsurface (fig. 5), the Stratigraphy 7 (part) (part) Upper Lower Jurassic Cretaceous Cretaceous 2,000 NRTHEAST (ohmm) Resistivity 2 Depth (ft) 7,000 7,500 SW 5,334 200 14–12 State API 4902520691 irkwood, W.C. sec. 12, T. 31 N., R. 82 W. sec. 12, T. (API) Gamma ray 0 (part) (part) Shale 3.2 miles Thermopolis Mowry Shale Frontier Formation Muddy Sandstone Cloverly Formation Morrison Formation 2,000 (ohmm) Resistivity 2 Depth (ft) 8,000 7,500 SW 5,546 200 43–16 State Shell Oil Co. API 4902520253 sec. 16, T. 31 N., R. 82 W. sec. 16, T. Correlation of Lower Cretaceous and lowermost Upper strata in the U.S. Geological (API)

Gamma ray 0 Figure 5. Survey Alcova Reservoir AR–1–13 core hole with nearby wells in the southeastern part of Wind River Basin. Line of section is shown on figure 2. [API, American Petroleum Institute; mmho, millimho; ohmm, ohmmeter; GL, ground elevation; KB, Kelly bushing] 5.0 miles equivalent silt marker Shell Creek Shale Upper siliceous part Clay Spur Bentonite Bed 0 and conglomerate Marker beds Unconformity Flood plain sandstone entonite Undifferentiated deposits (mmho) Conductivity 600

Depth (ft) 0 500 SW SE GL 5,460 300 EXPLANATION API 4902523875 sec. 7, T. 30 N., R. 82 W. sec. 7, T. U.S. Geological Survey Alcova Reservoir AR–1–13 (API) Gamma ray 0 SUTHWEST sandstone and siltstone Siliceous marine shale Marine shale Estuarine and fluvial sandstone Marine and marginal marine (part) Upper Lower Cretaceous Cretaceous den19-0057fig 05 den19-0057fig 8 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole sandstone has a blocky fining upward trend that has histori- The top of the Mowry Shale was originally defined from cally been interpreted as an incised valley, filled with fluvial the Powder River Basin at the top of the Clay Spur Bentonite and estuarine deposits (Dolson and others, 1991) (fig. 5) and Bed (Ruby, 1930). The upper contact of the Mowry is straight- above that are landward-stepping nearshore marine deposits forward and is placed at the top of the Clay Spur at 187.2 ft. (Gustason, 1988). This contact, somewhat disrupted by burrows of Teichichnus, Overlying the sandstone at 460.3 ft is a thin (0.1ft) altered matches the mapped contact in the subsurface. The Mowry volcanic ash that displays high gamma measurements on the contains all the early Cenomanian age ammonites of the genus log. This high gamma spike can be correlated with confidence Neogastropolites, except N. hassi (Reeside and Cobban, 1960; in nearby wells (fig. 5). Cobban and Kennedy, 1989). The Clay Spur is present in the The heterolithic strata between 429.9 ft and 460.3 ft are Wind River and adjacent basins and has been dated at about possibly of estuarine origin, or more likely are landward- 97 Ma (Obradovich, 1993). stepping nearshore marine units associated with the underlying The upper part of the Mowry is about 205 ft thick using Muddy valley fill. the lower contact of 392.35 ft in the core hole. The lithology is mainly light- to dark-gray siltstone with numerous sand- Mowry Shale stone streaks and interbedded bentonite beds. Small sand-size rounded white specks and fish bone, teeth, and fish scales are Darton (1904) named exposures of ridge-forming fos- present throughout the interval. The white specks are con- siliferous strata in the lower part of the Benton Group on the centrated in siltstone portions of graded beds. A unique sandy east side of the Bighorn Mountains, northwest of Buffalo, interval exists just below the Clay Spur and is mappable in Wyoming, the Mowrie beds. In the Wind River Basin, the the eastern Wind River Basin, eastern Green River Basin, and USGS referred to equivalent strata as the Mowry Shale (see onto the Casper arch. Below 380 ft, the facies consists of dark- for example, Love, 1948; Keefer, 1997; Keefer and John- gray siltstone with abundant Inoceramus fragments that form son, 1997; Finn, 2007b) (figs. 4 and 5). In the Wind River discrete laminations instead of the sandstone streaks present in Basin, the Mowry extends from the Clay Spur Bentonite most of the upper part. Bed down to the top of the Muddy Sandstone, and consists of two distinct units, a lower soft clay-rich shale (the upper Frontier Formation Thermopolis shale unit of Lupton, 1916), and an upper hard brittle siliceous shale (Love, 1948; Keefer, 1997; Keefer The Frontier Formation was named by Knight (1902) and Johnson, 1997). Eicher (1960, 1962) named the lower for exposures near the town of Frontier in western Wyoming. part the Shell Creek Shale for exposures at Sheep Mountain In the Wind River Basin, the name was first used by Hares anticline northwest of Greybull, Wyoming, in the Bighorn (1916). The cored interval belongs to the Belle Fourche Mem- Basin. Eicher (1962, his fig. 8) traced the Shell Creek ber and is Cenomanian age based on ammonites found in the equivalent strata into three localities in the Wind River unit on outcrop (Merewether and Cobban, 2007). Basin, including the Alcova area. The Shell Creek contains The Frontier interval is from 40.5 to 187.2 or about 147 ft two index fossils, a foraminifer Millammina manitobensis thick representing the lower part of the member, because the (Eicher, 1962) and an ammonite Neogastroplites hassi core hole was spud in the unit. In the core, the main lithol- (Reeside and Cobban, 1960) that indicate an Albian age ogy is medium- to dark-gray siltstone and sandy siltstone (Hancock and others, 1993, their table 1), but may be early with some interbedded burrowed or rippled sandstone streaks. Cenomanian age (Merewether and others, 2011, Merewether There are two prominent altered volcanic ashes in the inter- and McKinney, 2015) (fig. 3). val. The drill hole began in a sandstone that shows up on the The Shell Creek extends from the top of the Muddy gamma ray log, present from ground level to 40.5 ft. Sandstone upward to 392.35 ft at the base of an altered volcanic ash bed, below which is a gray siltstone containing glauconite. Another possible contact is at 380.25 ft, below which is a mudrock interval containing numerous Inocera- Geochemistry mus fragments. The interval between 392.35 and 460.3 ft consists of a diverse set of mudrocks with Inoceramus Thirty-nine samples were selected to evaluate the source fragments, glauconite, and burrows with some intervening rock potential of the marine shales in the cored interval as thin rippled sandstone beds. There may be several shoreface determined by total organic carbon (TOC) and programmed units genetically related to backstepping Muddy Sandstone pyrolysis analyses. Five samples are from the Frontier For- between 460.3 and 429.9 ft where lenticular to wavy- mation, 24 samples are from the upper siliceous part of the laminated sandstone is present with a highly diverse trace Mowry Shale, 4 samples are from the Shell Creek equivalent, fossil assemblage dominated by Planolites, Teichichnus, and and 6 samples are from the Thermopolis Shale (fig. 6). TOC Chondrites, overlain by heavily burrowed mudrock. This content was determined using a LECO Corporation analyzer interval is difficult to map in the subsurface so we include it by the combustion method after carbonate removal (see Jarvie, in the Shell Creek. 1991, for details), and the programmed pyrolysis analysis Geochemistry 9 was completed using a HAWK Hydrocarbon Analyzer with Four of the five samples from the lower part of the

Kinetics instrument (see Espitalie and others, 1977; Tissot and Frontier Formation, have S2 values ranging from 2.5 to 2.65, Welte, 1978; Peters, 1986; and Hunt, 1996, for detailed discus- indicating that the Frontier has fair generative potential sions of the pyrolysis method). (fig. 7). The remaining Frontier sample has poor potential with

an S2 value near 1. The S2 values from the upper siliceous part of the Mowry Shale show a range from 1.88 to 21.09 (fig. 7) Quantity of Organic Matter indicating good to excellent source rock. S2 values from the lower part of the Mowry Shale (Shell Creek equivalent) are According to Jarvie (1991), the quantity of organic matter less than 1.0 and are considered to have poor potential for in a rock measured as weight percent TOC is an indicator of generating hydrocarbons (fig. 7). Three of the six samples the organic richness and hydrocarbon generative potential. from the Thermopolis Shale have S values ranging from 2.59 Rocks with less than 0.5 weight percent TOC have poor gen- 2 to 4.52 indicating a fair potential to generate hydrocarbons. erative potential, rocks with 0.5 to 1 weight percent TOC are The remaining three samples have values less than 2.5 and are considered fair, rocks with 1–2 weight percent TOC are con- considered poor source rocks (fig. 7). sidered good, rocks with 2–4 weight percent TOC are considered very good, and rocks with greater than 4 weight percent TOC are considered to have excellent generative potential Types of Organic Matter (Peters and Casa, 1994). TOC measurements for the Frontier Formation, the upper siliceous part of the Mowry Shale, the According to Jacobson (1991) and Peters and Cassa Shell Creek equivalent, and Thermopolis Shale are presented (1994), there are four main types of kerogen in sedimentary in table 1, figures 6 and 7, and Finn and others (2019a). rocks: Type I, composed of oil-prone hydrogen-rich organic The five samples from the lower part of the Frontier matter is generally from lacustrine and some marine sedi- Formation have TOC contents that range from 1.02 to ments; Type II, also composed of oil-prone hydrogen-rich 1.74 weight percent (average 1.54 weight percent), indicating organic matter that is mainly in marine sediments; Type III, good generative potential (fig. 7). TOC content for samples composed of terrestrial organic matter derived mainly from from the upper siliceous part of the Mowry Shale range from woody plant material that is low in hydrogen content and 1.04 to 4.53 weight percent, with an average of 2.87 weight generates mainly gas; and Type IV, composed of dead or inert percent (fig. 7). All but two samples have greater than carbon that has little or no generating capacity. Using the 2 weight percent TOC indicating good to excellent genera- results of pyrolysis analysis, the type of kerogen present in a tive potential. Samples from the lower part of the Mowry source rock can be determined by the hydrogen index and the

Shale (Shell Creek equivalent) have TOC contents that range oxygen index, defined as (S2/TOC) ×100 (mg-HC/g-TOC), from 0.63 to 1.22 weight percent (average 0.97 weight per- and (S3/TOC) ×100 (mg-CO2/g-TOC), respectively (Espitalie cent) indicating fair to good generative potential. TOC con- and others, 1977; Tissot and Welte, 1978; and Hunt, 1996). tents for the Thermopolis Shale samples range from 1.07 to According to Hunt (1996), the type of hydrocarbons (oil or 2.85 weight percent (average 1.62 weight percent), indicating gas) generated from a source rock depends on the hydrogen good to very good generative potential. content of the organic matter. The results from pyrolysis Peters and Cassa (1994) suggest that TOC is not always analysis of the samples collected for the lower part of the a good indicator of source rock potential because measure- Frontier Formation, upper part of the Mowry Shale, Shell ments may include inert carbon that has little or no generating Creek equivalent, and the Thermopolis Shale are shown on potential. Peters and Cassa (1994) stated that the S2 measure- table 1 and plotted in figures 6 and 8. ment derived from pyrolysis analysis is a better indicator of The five samples from the lower part of the Frontier generative potential of source rocks. The S2 value, expressed Formation indicate that it is composed of Type III gas-prone as milligrams of hydrocarbons per gram of rock, represents kerogen (fig. 8). All but one sample from the upper sili- the fraction of original kerogen in a source rock capable of ceous part of the Mowry Shale indicate that it is composed generating hydrocarbons that have not yet been converted of Type II oil-prone kerogen with lesser amounts of mixed to oil or gas or both (Tissot and Welte, 1978). According to Type II/III kerogen (fig. 8). Three samples from the lower part

Peters and Cassa (1994), rocks with S2 values less than 2.5 of the Mowry Shale (Shell Creek equivalent) are composed of have poor generative potential, rocks with S2 values between Type IV kerogen with little or no generative potential (fig. 8).

2.5 and 5 have fair generative potential, rocks with S2 values The remaining sample from the Shell Creek is marginal ranging from 5 to 10 have good generative potential, rocks Type III with some capacity to generate gas. Results from the with S2 values from 10 to 20 are considered to have very good Thermopolis Shale show it is composed mainly of Type III generative potential, and rocks with S2 values greater than and Type IV kerogen with some mixed Type II/III kerogen

20 have excellent generative potential. S2 measurements for indicating that it is a potential source rock mainly for gas and the Frontier Formation, upper part of the Mowry Shale, Shell marginal for oil (fig. 8). Creek equivalent, and the Thermopolis Shale are presented in table 1 and shown in figures 6 and 7. 10 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

Table 1. Total organic carbon and pyrolysis data for the U.S. Geological Survey Alcova Reservoir AR–1–13 core hole, American Petroleum Institute well 4902523875, latitude 42.575145, longitude 106.70383, Township 30 N., Range 82 W., sec. 7, SW1/4, SE1/4, Sixth Principal Meridian, Elevation 5,460 feet.

[Depths are in feet; Tmax, temperature (°C [degrees Celsius]) corresponding to S2 peak; S1, milligrams of hydrocarbons per gram of rock; S2, milligrams of

hydrocarbons per gram of rock; S3, milligrams of carbon dioxide (CO2) per gram of rock; PI, production index [S1/S1+S2]; TOC, total organic carbon in weight percent; TC, total carbon in weight percent; HI, hydrogen index; OI, oxygen index]

Depth Tmax S1 S2 S1+S2 S3 PI S2/S3 TOC TC HI OI S1/TOC Frontier Formation 44.40 440 0.02 1.14 1.16 0.2 0.02 6 1.02 1.11 111 20 2 64.25 440 0.05 2.65 2.70 0.24 0.02 11 1.67 1.71 159 14 3 94.70 440 0.05 2.58 2.63 0.19 0.02 14 1.59 1.63 162 12 3 149.80 440 0.05 2.50 2.55 0.19 0.02 13 1.74 1.79 143 11 3 173.55 441 0.04 2.64 2.68 0.3 0.01 9 1.66 1.8 159 18 2 Mowry Shale 192.70 433 0.06 1.88 1.94 0.24 0.03 8 1.04 1.14 181 23 6 198.60 431 0.21 6.90 7.11 0.18 0.03 38 2.48 2.58 278 7 8 212.55 430 0.23 5.74 5.97 0.29 0.04 20 2.00 2.09 287 14 11 220.25 427 0.39 10.93 11.32 0.35 0.03 31 2.68 2.82 408 13 15 235.50 428 0.40 9.64 10.04 0.28 0.04 34 2.58 2.78 373 11 15 241.15 429 0.38 9.63 10.01 0.21 0.04 46 2.50 2.82 386 8 15 250.10 427 0.34 9.67 10.01 0.42 0.03 23 2.79 2.81 304 13 11 263.20 427 0.62 16.61 17.23 0.27 0.04 62 3.61 3.74 427 7 16 272.15 424 0.69 17.34 18.03 0.33 0.04 53 3.68 3.93 472 9 19 282.80 422 0.87 14.30 15.17 0.33 0.06 43 3.74 3.82 368 8 22 288.55 422 0.66 21.09 21.75 0.35 0.03 60 4.53 4.81 466 8 15 292.35 424 0.54 15.48 16.02 0.34 0.03 46 3.89 4.32 398 9 14 294.30 424 0.55 13.37 13.92 0.19 0.04 70 3.23 3.36 414 6 17 307.15 422 0.72 20.50 21.22 0.34 0.03 60 3.86 4.49 531 9 19 313.05 427 0.54 12.09 12.63 0.25 0.04 48 2.88 3.2 420 9 19 318.00 424 0.58 15.13 15.71 0.27 0.04 56 3.39 3.92 446 8 17 327.80 423 0.58 12.12 12.70 0.21 0.05 58 3.10 3.57 390 7 19 342.55 428 0.51 9.76 10.27 0.25 0.05 39 2.72 3.21 358 9 19 346.50 427 0.46 8.67 9.13 0.27 0.05 32 2.50 2.94 347 11 18 350.35 426 0.25 7.01 7.26 0.23 0.03 30 2.15 2.46 326 11 12 351.85 424 0.19 5.05 5.24 0.21 0.04 24 1.80 1.97 281 12 11 358.25 426 0.30 7.66 7.96 0.24 0.04 32 2.82 3.2 272 9 11 373.50 427 0.32 6.53 6.85 0.4 0.05 16 2.00 2.38 327 20 16 385.30 426 0.40 8.38 8.78 0.27 0.05 31 2.86 3.56 293 9 14 Shell Creek Shale equivalent 396.90 431 0.05 0.31 0.36 0.31 0.14 1 0.63 0.69 49 49 8 411.20 438 0.05 0.70 0.75 0.18 0.07 4 1.22 1.27 57 15 4 423.50 436 0.03 0.47 0.50 0.29 0.06 2 0.96 1.08 49 30 3 431.70 436 0.14 0.38 0.52 0.19 0.27 2 1.08 1.09 31 16 12 Thermopolis Shale 479.40 441 0.07 4.11 4.18 0.31 0.02 13 2.85 2.85 144 11 2 497.20 442 0.09 4.52 4.61 0.31 0.02 15 1.99 2.1 227 16 5 513.10 442 0.03 2.59 2.62 0.22 0.01 12 1.44 1.44 180 15 2 541.40 438 0.04 0.83 0.87 0.22 0.05 4 1.10 1.23 76 20 4 559.55 438 0.00 0.49 0.49 0.23 0.00 2 1.07 1.04 46 22 0 600.60 441 0.04 1.29 1.33 0.18 0.03 7 1.25 1.73 103 14 3 Geochemistry 11

API 4902523875 U.S. Geological Survey Alcova Reservoir AR–1–13 SW SE sec. 7, T. 30 N., R. 82 W. GL 5,460 Depth (feet)

Gamma ray Conductivity Total organic carbon Hydrogen index Tmax (ºC) (weight percent) S2 (mg HC/g rock) 0 300 600 0 (API) (mmho) 1 2 3 4 5 10 15 20 100 200 300 400 500 430 450 470

Frontier Formation (part) 100

Clay Spur Bentonite Bed 200

Upper siliceous part 300 Mowry Shale

Shell Creek 400 Shale equivalent

Muddy Sandstone

500

silt Thermopolis Shale marker

600 Cloverly Formation

EXPLANATION

Marine shale Estuarine and fluvial entonite sandstone Siliceous marine shale Unconformity Flood plain sandstone Sample and conglomerate

Figure 6. U.S. Geological Survey Alcova Reservoir AR–1–13 core hole showing relation of stratigraphic intervals to organic richness and kerogen type. [API, American Petroleum Institute units; mmho, millimho; mgHC/g rock, milligrams of hydrocarbons per gram of rock; ºC, degrees Celsius]

den19-0057fig 06 12 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

100 1,000 EXPLANATION Frontier Formation EXPLANATION Mowry Shale 900 Type I Frontier Formation Shell Creek Shale euivalent Mowry Shale Excellent Thermopolis Shale Shell Creek Shale euivalent 800 Thermopolis Shale ery good 700 10 Type II

Good 600

Fair 500 (mg HC/g rock) 2 S

400 Hydrogen index (mg-HC/g-TOC) 1

300 Poor 200

Type III 100

ery Type I Poor Fair Good good Excellent 0.1 0.1 1 10 0 Total organic carbon, in weight percent 0 50 100 150 200 Oxygen index (mg-CO2/g-TOC) Figure 7. Cross plot of S and total organic carbon for samples 2 Figure 8. Cross plot of hydrogen index and oxygen index for from the U.S. Geological Survey Alcova Reservoir AR–1–13 core samples from the U.S. Geological Survey Alcova Reservoir hole. Parameters describing source rock generative potential AR–1–13 core hole. [mg-HC/g-TOC, milligrams of hydrocarbons per are from Peters and Cassa (1994). [mg HC/g rock, milligrams of gram of total organic carbon; mg-CO2/g-TOC, milligrams of carbon hydrocarbons per gram of rock] dioxide per gram of total organic carbon]

den19-0057fig 07 References Cited 13

Geochemistry Summary Dolson, J., Muller, D., Evetts, M.J., and Stein, J.A., 1991, Regional paleotopographic trends and production, Muddy Results of total organic carbon and programmed pyrolysis Sandstone (Lower Cretaceous), central and northern Rocky analyses of potential hydrocarbon source rocks in the Alcova Mountains: American Association of Petroleum Geologists Reservoir AR-1-13 core hole in Natrona County, Wyoming, in Bulletin v. 75, no. 3 p. 409–435. the southeastern part of the Wind River Basin are summarized Eicher, D.L., 1960, Stratigraphy and micropaleontology of the as follows: Thermopolis Shale: Peabody Museum of Natural History, 1. The lower part of the Frontier Formation contains Type III Yale University, Bulletin 15, 126 p. gas-prone kerogen, with poor to fair generative potential. Eicher, D.L., 1962, Biostratigraphy of the Thermopolis, 2. The upper part of the Mowry Shale has good to excel- Muddy, and Shell Creek Formations, in Enyert, R.L., and lent generative potential, with organic matter composed Curry, W.H., eds., Symposium on Early Cretaceous rocks of mainly of Type II oil-prone kerogen with some mixed Wyoming and adjacent areas: Wyoming Geological Asso- Type II/III kerogen capable of generating oil and gas. ciation 17th Annual Field Conference Guidebook, p. 72–93. 3. The kerogen in the Shell Creek equivalent is marginal Espitalie, J., Madec, J.M., Tissot, B., Mennig, J.J., and Leplat, Type III and mainly Type IV kerogen with poor genera- P., 1977, Source rock characterization method for petroleum tive potential. exploration: Offshore Technology Conference, v. 3, no. 9, p. 439–444. 4. The Thermopolis Shale has poor to fair generative potential, with mainly Type III gas-prone kerogen. Finn, T.M., 2007a, Source rock potential of Upper Cretaceous marine shales in the Wind River Basin, Wyoming, in USGS Wind River Basin Province Assessment Team, Petroleum systems and geologic assessment of oil and gas in the Wind Acknowledgments River Basin Province, Wyoming: U.S. Geological Survey Digital Data Series DDS–69–J, ch. 8, 24 p. The authors thank the U.S. Geological Survey (USGS) Finn, T.M., 2007b, Subsurface stratigraphic cross sections drilling group, especially Art Clark, the staff of the USGS of Cretaceous and lower Tertiary rocks in the Wind River Core Research Center including John Rhoades, Terry Huber, Basin, central Wyoming, in USGS Wind River Basin Dawn Ivis, and Josh Hicks; and the staff of the Central Energy Assessment Team, Petroleum systems and geologic assess- Resources Science Center Petroleum Geochemistry Research ment of oil and gas resources in the Wind River Basin Laboratory including Augusta Warden, Mark Dreier, and Province, Wyoming: U.S. Geological Survey Digital Data Tom Oliver. The manuscript benefitted from reviews by Ron Series DDS–69–J, ch. 9, 28 p. Johnson, Justin Birdwell, and Ofori Pearson of the USGS and their suggestions and comments are greatly appreciated. Finn, T.M., 2019, Structure contour and overburden maps of the Niobrara interval of the Upper Cretaceous Cody Shale in the Wind River Basin, Wyoming: U.S. Geological Survey Scientific Investigations Map 3427, pamphlet 9 p., 2 sheets, References Cited scale 1:500,000, accessed March 2019, at https://doi.org/10.3133/sim3427. Burtner, R.L., and Warner, M.A., 1984, Hydrocarbon genera- Finn, T.M., Kirschbaum, M.A., and Schenk, C.J., 2019a, LAS dig- tion in Lower Cretaceous Mowry and Skull Creek Shales of ital data files for the U.S. Geological Survey Alcova AR–1–13 the northern Rocky Mountain area, in Woodward, J., Meiss- core hole, Natrona County, Wyoming: U.S. Geological Survey ner, F.F., and Clayton, J.L., eds., Hydrocarbon source rocks data release, https://doi.org/10.5066/P9J7FJQU. of the greater Rocky Mountain region: Rocky Mountain Association of Geologists Guidebook, p. 449–467. Finn, T.M., Kirschbaum, M.A., and Schenk, C.J., 2019b, Total organic carbon and pyrolysis analysis data for the U.S. Cobban, W.A., and Kennedy, W.J., 1989, The ammonite Geological Survey Alcova AR–1–13 core hole, Natrona Metengonoceras Hyatt, 1903, from the Mowry Shale County, Wyoming: U.S. Geological Survey data release, (Cretaceous) of Montana and Wyoming: U.S. Geological https://doi.org/10.5066/P9VLAKVG. Survey Bulletin 1787–L, 11 p. Gustason, E.R., 1988, Depositional and tectonic history of the Darton, N.H., 1904, Comparison of the stratigraphy of the Lower Cretaceous Muddy Sandstone, Lazy B Field, Powder Black Hills, Bighorn Mountains, and Rocky Mountain River Basin, Wyoming in Diedrich, R.P., Dyka, M.A.K., Front Range: Geological Society of America Bulletin, Miller, W.R. eds., Eastern Powder River Basin-Black Hills: v. 15, p. 379–448. Wyoming Geological Association 39th Annual Field Con- ference, p. 129–146. 14 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

Hancock, J.M., Kennedy, W.J., and Cobban, W.A., 1993, A Merewether, E.A., Dolson, J.C., Hanson, W.B., Keefer, W.R., correlation of upper Albian to basal Coniacian sequences Law, B.E., Mueller, R.E., Ryer, T.A., Smith, A.C., Stilwell, of northwest Europe, Texas and the United States Western D.P., and Wheeler, D.M., 1997, Cretaceous stratigraphy Interior, in Caldwell, W.G.E., and Kauffman, E.G., eds., in a northeast-trending transect, northern Utah to south- Evolution of the Western Interior Basin: Geological Asso- central South Dakota: U.S. Geological Survey Map I-2609, ciation of Canada Special Paper 39, p. 453–476. 2 sheets, pamphlet, 10 p. Hares, C.J., 1916, Anticlines in central Wyoming: U.S. Geo- Merewether, E.A., and Cobban, W.A., 2007, Outcrop descrip- logical Survey Bulletin 641–I, p. 233–279. tions and fossils from the Upper Cretaceous Frontier Hintze, F.F., 1915, The Basin and Greybull oil and gas fields: Formation, Wind River Basin and adjacent areas, Wyoming, Wyoming Geological Survey Bulletin 10, 62 p. in U.S. Geological Survey Wind River Basin Assessment Team, eds., Petroleum systems and geologic assessment Hunt, J.M., 1996, Petroleum geochemistry and geology: New of oil and gas resources in the Wind River Basin Province, York, W.H. Freeman and Company, 743 p. Wyoming: U.S. Geological Survey Digital Data Series Jacobson, S.R., 1991, Petroleum source rocks and organic DDS–69–J, Chapter 11, 95 p. facies, in Merrill, R.K., ed., Source and migration processes Merewether, E.A., Cobban, W.A., and Obradovich, J.D., 2011, and evaluation techniques: American Association of Petro- Biostratigraphic data from Upper Cretaceous Formation— leum Geologists Handbook of Petroleum Geology, p. 1–11. eastern Wyoming, central Colorado, and northeastern New Jarvie, D.M., 1991, Total organic carbon (TOC) analysis, Mexico: U.S. Geological Survey Scientific Investigations in Merrill, R.K., ed., Source and migration processes and Map 3175, 2 sheets, pamphlet, 10 p. evaluation techniques: American Association of Petroleum Merewether, E.A., and McKinney, K.C., 2015, Chronostrati- Geologists Handbook of Petroleum Geology, p. 113–118. graphic cross section of Cretaceous formations in western Johnson, R.C., Finn, T.M., Kirschbaum, M.A., Roberts, S.B., Montana, western Wyoming, eastern Utah, northeastern Roberts, L.N.R., Cook, Troy, and Taylor, D.J, 2007, The Arizona, and northwestern New Mexico, U.S.A.: U.S. Geo- Cretaceous-Lower Tertiary Composite Total Petroleum logical Survey Open-File Report 2015–1087, 10 p., 1 sheet, System, Wind River Basin, Wyoming in USGS Wind River accessed February 2018, at https://dx.doi.org/10.3133/ Basin Province Assessment Team, Petroleum systems and ofr20151087. geologic assessment of oil and gas in the Wind River Basin Province, Wyoming: U.S. Geological Survey Digital Data Obradovich, J.D., 1993, A Cretaceous time scale, in Caldwell, Series DDS–69–J, ch. 4, DDS–69–J, 96 p. W.G.E., and Kauffman, E.G., eds., Evolution of the Western Interior Basin: Geological Association of Canada Special Keefer, W.R., 1997, Stratigraphy and correlation of Cretaceous Paper 39, p. 379–396. and Paleocene rocks, northern Wind River Basin, Wyoming: U.S. Geological Survey Oil and Gas Investigations Chart Peters, K.E., 1986, Guidelines for evaluating petroleum source OC–146–A. rock using programmed pyrolysis: American Association of Petroleum Geologists Bulletin, v. 70, no. 3, p. 318–329. Keefer, W.R., and Johnson, R.C., 1997, Stratigraphy and correlation of Cretaceous and Paleocene rocks, west-central Peters, K.E., and Cassa, M.R., 1994, Applied source rock Wind River Basin, Wyoming: U.S. Geological Survey Oil geochemistry, in Magoon, L.B., and Dow, W.G., eds., The and Gas Investigations Chart OC–146–B. petroleum system—From source to trap: American Associa- tion of Petroleum Geologists Memoir 60, p. 93–120. Kirschbaum, M.A., Finn T.M., Johnson, R.C., Kibler, J., Lillis, P.G., Nelson, P.H., Roberts, L.N.R., Roberts, S.B., Reeside, J.B., Jr., and Cobban, W.A., 1960, Studies of the Charpentier, R.R, Cook, T., Klett, T.R., Pollastro, R.M., Mowry Shale (Cretaceous) and contemporary formations and Schenk, C.J., 2005, Assessment of undiscovered oil in the United States and Canada: U.S. Geological Survey and gas resources of the Wind River Basin Province: U.S. Professional Paper 355, 126 p. Geological Survey Fact Sheet FS–2005–3141, 2 p. Ruby, W.W., 1930, Lithologic studies of the fine-grained Upper Knight, W.C., 1902, The petroleum fields of Wyoming—III: Cretaceous sedimentary rocks of the Black Hills region: U.S. Engineering and Mining Journal, v. 73, no. 21, p. 720–723. Geological Survey Professional Paper 165, 54 p. Love, J.D., 1948, Mesozoic stratigraphy of the Wind River Tissot, B.P., and Welte, D.H., 1978, Petroleum formation and Basin, central Wyoming in Maebius, J.B., and Netterstrom, occurrence: New York, Springer-Verlag, 538 p. P.W., eds., Wind River Basin, Wyoming: Wyoming Geologi- cal Association 3rd Annual Field Conference, p. 96–111. Washburne, C.W., 1908, Gas fields of the Bighorn Basin, Wyo- ming: U.S. Geological Survey Bulletin 340–F, p. 348–363. Lupton, C.T., 1916, Oil and gas near Basin, Big Horn County, Wyoming: U.S. Geological Survey Bulletin 621, p. 157–190. Appendix 1 15

Appendix 1. Detailed Core Descriptions of the USGS AR–1–13 Core Hole, Natrona County, Wyoming 16 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 0 Top of core at 40.5 feet

Bone fragment

Frontier 0 Formation

0.5 feet

80 C S F M Cs c G

den19-0057Appendix01-Mark measured section 40 FT to 80 FT Appendix 1 17

epth (in feet) 80

Frontier 100 Formation

0.25 feet 0.30 feet 105

0.06 feet 0.03 feet

0.01 feet 0.03 feet

110

115

120 C S F M Cs c G

den19-0057Appendix01-Mark measured section 80 FT to 120 FT 18 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 120

125

0.1 feet

130

135

Frontier Formation 10 0.1 feet Pl

150

155

10 C S F M Cs c G

den19-0057Appendix01-Mark measured section 120 FT to 160 FT Appendix 1 19

epth (in feet) 10

Frontier Formation

180

185

187.2 feet Te

Clay Spur Bentonite Bed 3.4 feet 190

Sch Sch

Sch Upper Mowry Shale 195 siliceous part 0.01 ft

Thin ash 200 C S F M Cs c G

den19-0057Appendix01-Mark measured section 160 FT to 200 FT 20 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 200

0.2 feet

205

210

215

Bone

Upper siliceous 220 Thin ash part Mowry Shale

225 Probably ash (see log, appendix 1)

Bone

0.1 feet 0.2 feet 230 0.2 feet 0.7 feet 0.2 feet

235

Fish bone 20 C S F M Cs c G

den19-0057Appendix 1 Mark measured section 200 FT to 240 FT Appendix 1 21

epth (in feet) 20

0.15 feet

25 0.25 feet

2.60 feet

Bone 250 Thin ash

0.05 feet Inoceramus

255

0.20 feet 0.05 feet Thin ash

0.20 feet Upper siliceous 20 0.10 feet part 0.05 feet Mowry Shale

Bone

20 Compacted burrow () filled with sand and bone Fish scale Bone

25 Dispersed ash 1.0 feet

0.1 feet

280 C S F M Cs c G

den19-0057Appendix01-Mark measured section 240 FT to 280 FT 22 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 280

285 0.06 feet With Inoceramus fragment Thin ash

290 0.05 feet

Thin ash

295

0.15 feet Thin ash Upper siliceous 300 part Mowry Shale

305

0.15 feet

Bone fragment 310 0.30 feet

Thin ash; pyritied

0.06 feet

Thin ash 0.03 feet 315

Inoceramus; bone fragments 320 C S F M Cs c G

den19-0057Appendix01-Mark measured section 280 FT to 320 FT Appendix 1 23

epth (in feet) 320

0.30 feet

Thin ash 325

Thin ash 0.30 feet 330

0.15 feet

335

1.40 feet

Upper siliceous 30 part Mowry Shale 0.15 ft; contains Inoceramus

35 Thin missing interval Thin ash

350 0.25 feet

1.25 feet Thin ash

355

30 0.2 feet C S F M Cs c G

den19-0057Appendix1 Mark measured section 320 FT to 360 FT 24 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 30 Thin ash

Fish scales

Fish scales and bone

Thin ash streaks

35 Upper 0.75 feet siliceous part

0.06 feet 380 0.10 feet Mowry Shale 0.15 feet

385

390

392.35 feet 0.50 feet Glauconite

0.50 feet Te; Sch 395 0.03 feet Shell Creek 0.20 feet Shale equivalent

0.06 feet Glauconite 00 0.06 feet C S F M Cs c G

den19-0057Appendix 1 Mark measured section 360 FT to 400 FT Appendix 1 25

epth (in feet) 00 Sch; Te

0.20 feet

05 0.55 feet 0.20 feet Sch Sch

15 Chambered fossils; bone; teeth 1.00 feet

Shell Creek Shale 20 0.90 feet equivalent 0.04 feet Mowry Shale

Pl; Th possible Muddy top 30 at 429.9 feet Pl; Pa

0.07 feet Pl; Te 35

ertical mud lined 0 burrows C S F M Cs c G

den19-0057Appendix 1 Mark measured section 400 FT to 440 FT 26 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 0

Pl dominated S Te 5 Te, Pl, Pa Te, Pl

Pl, Pa; Te Shale Creek 0.10 feet Shale 50 Pl, Te equivalent

Mowry Shale Te, Pl

55 Ch, S

0.10 feet

0 0.05 feet 460.3 feet 0.10 feet Teredolites Pl

Muddy Sandstone S

S, Pl

474.9 feet 5 Pl

Pl Thermopolis Shale

80 C S F M Cs c G

den19-0057Appendix1-Mark measured section 440 FT to 480 FT Appendix 1 27

epth (in feet) 80

Plant fragments Pl

90 Plant fragments

Pl Thermopolis 500 Shale

505

510

515

520 C S F M Cs c G

den19-0057Append 1 Mark measured section 480 FT to 520 FT 28 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 520

Pl dominated

0.6 feet; greenish

525

530

535 Pl

silt marker at 537.2 feet, top Pl dominated of rusty beds As

Thermopolis Pl, Pa 50 Shale Pl

550

555 Pl

Cone-in-cone

50 C S F M Cs c G

den19-0057Appendix01-Mark measured section 520 FT to 560 FT Appendix 1 29

epth (in feet) 50

Micro hcs

Thermopolis 580 Shale Pl

585

590

Pl dominated

595

Pl concentration

00 C S F M Cs c G

den19-0057fig 01-Mark measured section 560 FT to 600 FT 30 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

epth (in feet) 00 Pl

EXPLANATION Thermopolis Shale No recovery

Pl Ash bed 604.9 feet 05 Pyrite nodule Disbursed ash Colors approximate the actual core color, except ashPyrite beds nodulewhich are shown in orange

Isolated sand streak

Continuous sand streak or graded bed

10 Lenticular bedding

Asymmetrical ripple

Wavy bedding EXPLANATION Cloverly Cross stratification Formation No recovery 15 Hummocky cross stratification hcs Ash bed Silt lamina Disbursed ash Convoluted bedding Colors approximate the actual core color, Rip ups except ash beds which are shown in orange Carbonate bed

Isolated sand streak Concretion 20 Continuous sand streak or graded bed Cracks

Lenticular bedding Inoceramus prisms Bottom of core Rip ups at 623 feet Asymmetrical ripple Coal or plant fragments

Wavy bedding Rip ups

25 Cross stratification Silt lamina with horiontal C S F M Cs c G burrow Hummocky cross stratification hcs Horiontal burrows Silt lamina ertical burrows EXPLANATION EXPLANATIONConvoluted bedding

Carbonate bed No recovery Trace fossils As Asterosoma Concretion Ash bed Ch Chondrites Pa Palaeophycus Cracks Disbursed ash Pl Planolites Colors approximate the actual core color, Inoceramus prisms Sch Schaubcylindrichnus except ash beds which are shown in orange S Skolithos Coal or plant fragments Te Teichichnus Isolated sand streak Th Thalassinoides Rip ups Continuous sand streak or graded bed Silt lamina with horiontal Grain sie Lenticular bedding burrow Horiontal burrows C S F M Cs c G Asymmetrical ripple granule very coarse sand Wavy bedding ertical burrows coarse sand medium sand Cross stratification fine sand Trace fossils very fine sand Hummocky cross stratification hcs As Asterosoma silt Ch Chondrites clay Silt lamina Pa Palaeophycus Pl Planolites den19-0057Appendix1Convoluted bedding Mark measured section 600 FT to 625 FT Sch Schaubcylindrichnus Carbonate bed S Skolithos Te Teichichnus Concretion Th Thalassinoides

Cracks den19-0057Appenidix01-explanation of symbols Grain sie Inoceramus prisms C S F M Cs c G Coal or plant fragments granule very coarse sand Rip ups coarse sand medium sand Silt lamina with horiontal fine sand burrow very fine sand Horiontal burrows silt clay

ertical burrows

Trace fossils As Asterosoma Ch Chondrites den19-0057Appenidix01-explanationPa Palaeophycus of symbols Pl Planolites Sch Schaubcylindrichnus S Skolithos Te Teichichnus Th Thalassinoides

Grain sie

C S F M Cs c G granule very coarse sand coarse sand medium sand fine sand very fine sand silt clay

den19-0057Appenidix01-explanation of symbols Appendix 2 31

Appendix 2. Geophysical Logs of the USGS AR–1–13 Core Hole, Natrona County, Wyoming 32 Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole

Company U.S. Geological Survey Company U.S. Geological Survey Company U.S. Geological Survey Company U.S. Geological Survey Date August 8, 2013 Company U.S. Geological Survey Date August 8, 2013 Date August 8, 2013 Date August 8, 2013 API 4902523875 Well ID Alcova Reservoir AR–1–13 Date August 8, 2013 API 4902523875 Well ID Alcova Reservoir AR–1–13 API 4902523875 Well ID Alcova Reservoir AR–1–13 API 4902523875 Well ID Alcova Reservoir AR–1–13 State Wyoming County Natrona API 4902523875 Well ID Alcova Reservoir AR–1–13 State Wyoming County Natrona State Wyoming County Natrona State Wyoming County Natrona Location Latitude N 42.575145 Longitude W 106.70383 State Wyoming County Natrona Location Latitude N 42.575145 Longitude W 106.70383 Location Latitude N 42.575145 Longitude W 106.70383 Location Latitude N 42.575145 Longitude W 106.70383 Township 30 N Range 82 W section 7 Location Latitude N 42.575145 Longitude W 106.70383 Township 30 N Range 82 W section 7 Township 30 N Range 82 W section 7 Township 30 N Range 82 W section 7 Logs run gamma, sonic Township 30 N Range 82 W section 7 Logs run gamma, caliper, density Logs run gamma, induction Logs run gamma, resistivity Depth driller 624 ft Logs run gamma, caliper Depth driller 624 ft Depth driller 624 ft Depth driller 624 ft Depth logger 620 ft Depth driller 624 ft Depth logger 622 ft Depth logger 620 ft Depth logger 621 ft Logged by A. Clark, C. Schenk Depth logger 620 ft Logged by A. Clark, C. Schenk Logged by A. Clark, C. Schenk Logged by A. Clark, C. Schenk Logged by A. Clark, C. Schenk

NATURAL GAMMA DELTA T AMP(N) POR(SON) 0 API 300 -0 µSEC/FT 0 M 5000-0 PERCENT 50 NATURAL GAMMA CALIPER DEN/LS NATURAL GAMMA COND NATURAL GAMMA RES(16N) TIME(N) AMP(F) 0 API 300 3 INCH 7 1 G/CC 3 0 API 300 600 MMHO 0 0 API 300 0 OHM-M 50 200 µSEC 700 0 M 5000 Depth NATURAL GAMMA CALIPER Depth DEN/SS Depth AP-COND Depth RES(64N) Depth TIME(F) (feet) 0 API 300 2 INCH 8 (feet) 1 G/CC 3 (feet) 600 MMHO 0 (feet) 0 OHM-M 50 (feet) 200 µSEC 700 0 0 0 0 0

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620 620 620 620 620 Publishing support provided by the Science Publishing Network, Denver Publishing Service Center

For more information concerning the research in this report, contact the Center Director, USGS Central Energy Resources Science Center Box 25046, Mail Stop 939 Denver, CO 80225 (303) 236-1647

Or visit the Central Energy Resources Science Center website at https://www.usgs.gov/energy-and-minerals/energy-resources-program/

Kirschbaum and others—Lithologic Descriptions, Geophysical Logs, Source-Rock Geochemistry of Alcova Reservoir AR–1–13 Core Hole—SIR 2019–5123 ISSN 2328-0328 (online) https://doi.org/10.3133/sir20195123