Imaging of Niobrara Formation and Mowry Shale samples from a range of thermal maturities provided observations and data on pore systems, organic matter (OM) types and associations with mineralogy and fabric, wettability, and microporosity associated with both diagenetic and detrital clays. Imaging techniques included scanning electron microscopy, organic petrography and correlative scanning electron microscopy, and mapping of mineralogy through energy dispersive spectroscopy.

This Data Release contains data associated with the journal article "Geochemistry of the Cretaceous Mowry Shale in the Wind River Basin, Wyoming". Data include bulk organic geochemistry, major and trace element geochemistry, mineralogy, extractable organic matter composition, extractable biomarkers, and organic stable carbon isotope analyses.

This Data Release contains data associated with the journal article "Geochemistry of the Cretaceous Mowry Shale in the Wind River Basin, Wyoming". Data include bulk organic geochemistry, major and trace element geochemistry, mineralogy, extractable organic matter composition, extractable biomarkers, and organic stable carbon isotope analyses.

In 2019 the U.S. Geological Survey (USGS) quantitively assessed the potential for undiscovered, technically recoverable continuous (unconventional) oil and gas resources in the Niobrara interval of the Cody Shale in the Bighorn Basin Province (Finn and others, 2019). Leading up to the assessment, in 2017, the USGS collected samples from the Niobrara and underlying Sage Breaks intervals (Finn, 2019) to better characterize the source rock potential of the Niobrara interval. Eighty-two samples from 31 wells were collected from the well cuttings collection stored at the USGS Core Research Center in Lakewood, Colorado. The selected wells are located near the outcrop belt along the shallow margins of the basin to obtain samples that were not subjected to the effects of deep burial and subsequent organic carbon loss due to thermal maturation as described by Daly and Edman (1987) (fig. 1). Sixty samples are from the Niobrara interval, and 22 from the Sage Breaks interval (fig. 2).

In 2019 the U.S. Geological Survey (USGS) quantitively assessed the potential for undiscovered, technically recoverable continuous (unconventional) oil and gas resources in the Niobrara interval of the Cody Shale in the Bighorn Basin Province (Finn and others, 2019). Leading up to the assessment, in 2017, the USGS collected samples from the Niobrara and underlying Sage Breaks intervals (Finn, 2019) to better characterize the source rock potential of the Niobrara interval. Eighty-two samples from 31 wells were collected from the well cuttings collection stored at the USGS Core Research Center in Lakewood, Colorado. The selected wells are located near the outcrop belt along the shallow margins of the basin to obtain samples that were not subjected to the effects of deep burial and subsequent organic carbon loss due to thermal maturation as described by Daly and Edman (1987) (fig. 1). Sixty samples are from the Niobrara interval, and 22 from the Sage Breaks interval (fig. 2).

For sample mounting, organic petrology laboratories typically use cold-setting epoxy-resin (e.g., 40°C, used by Oklahoma Geological Survey, OGS) or heat-setting plastic (e.g., 180°C, used by U.S. Geological Survey, USGS). Previous workers have suggested a systematic vitrinite reflectance (VRo) increase was associated with the thermoplastic preparation process, relative to epoxy mounting, which was attributed to moisture loss from the transient high temperatures of plastic mounting. In this study, we evaluated thermal effects to low maturity organic matter from transient exposure to elevated temperatures. A subbituminous coal sample was subjected to long-term (4 to 38 weeks) exposure to temperatures of 85 to 120°C and afterward evaluated by multiple approaches to test thermal advance [elemental analyses, Rock-Eval pyrolysis, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), pyrolysis gas chromatography, and petrographic analyses, including vitrinite reflectance and spectral fluorescence], all of which showed no detectable systematic changes between the original sample and its heat-treated products. We also compared vitrinite reflectance of six low maturity samples (those most likely to react to transient heating) mounted via both cold-setting epoxyresin and heat-setting thermoplastic. Results indicate measured VRo of a sample prepared by one mounting process was within the standard deviation of reflectance for the same sample prepared via the other process. Moreover, VRo results were not systematically higher in thermoset mounts. Contrary to previous work, these results suggest thermoplastic mounting or other transient exposure to elevated temperatures does not impact thermal maturity estimates from reflectance measurement for low maturity organic samples. Furthermore, the average interlaboratory difference in measured VRo (between OGS and USGS) for the same sample prepared by either epoxy-resin or thermoset mounting was 0.038%, about double the average difference between VRo for the same sample prepared via epoxy-resin versus thermoset in a single laboratory (0.024%). This result indicates interlaboratory variability impacts interlaboratory VRo measurement reproducibility to the extent that systematic differences could not be observed between thermoplastic and cold-setting sample preparation approaches, even if such differences were present.

For sample mounting, organic petrology laboratories typically use cold-setting epoxy-resin (e.g., 40°C, used by Oklahoma Geological Survey, OGS) or heat-setting plastic (e.g., 180°C, used by U.S. Geological Survey, USGS). Previous workers have suggested a systematic vitrinite reflectance (VRo) increase was associated with the thermoplastic preparation process, relative to epoxy mounting, which was attributed to moisture loss from the transient high temperatures of plastic mounting. In this study, we evaluated thermal effects to low maturity organic matter from transient exposure to elevated temperatures. A subbituminous coal sample was subjected to long-term (4 to 38 weeks) exposure to temperatures of 85 to 120°C and afterward evaluated by multiple approaches to test thermal advance [elemental analyses, Rock-Eval pyrolysis, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), pyrolysis gas chromatography, and petrographic analyses, including vitrinite reflectance and spectral fluorescence], all of which showed no detectable systematic changes between the original sample and its heat-treated products. We also compared vitrinite reflectance of six low maturity samples (those most likely to react to transient heating) mounted via both cold-setting epoxyresin and heat-setting thermoplastic. Results indicate measured VRo of a sample prepared by one mounting process was within the standard deviation of reflectance for the same sample prepared via the other process. Moreover, VRo results were not systematically higher in thermoset mounts. Contrary to previous work, these results suggest thermoplastic mounting or other transient exposure to elevated temperatures does not impact thermal maturity estimates from reflectance measurement for low maturity organic samples. Furthermore, the average interlaboratory difference in measured VRo (between OGS and USGS) for the same sample prepared by either epoxy-resin or thermoset mounting was 0.038%, about double the average difference between VRo for the same sample prepared via epoxy-resin versus thermoset in a single laboratory (0.024%). This result indicates interlaboratory variability impacts interlaboratory VRo measurement reproducibility to the extent that systematic differences could not be observed between thermoplastic and cold-setting sample preparation approaches, even if such differences were present.

In 2021 the United States Geological Survey (USGS) sampled the lower part of the Upper Cretaceous Lewis Shale in the eastern part of the Southwestern Wyoming Province to better characterize its petroleum source rock potential for an upcoming resource assessment. Ninety-five samples from 24 wells were collected from well cuttings of the lower part of the Lewis Shale stored at the U.S. Geological Survey Core Research Center in Lakewood, Colorado. The selected wells are located near the shallow margins of the basin to obtain samples that were not subjected to the effects of deep burial and subsequent organic carbon loss due to thermal maturation as described by Daly and Edman (1987) (fig, 1). The sample intervals were selected based on high gamma ray responses that Pyles and Slatt (2007) interpreted to be organic-rich condensed sections. Special emphasis was given to the Asquith marker bed which represents the maximum transgression of the Lewis Shale (Pasternack, 2005) (fig. 2).

In 2021 the United States Geological Survey (USGS) sampled the lower part of the Upper Cretaceous Lewis Shale in the eastern part of the Southwestern Wyoming Province to better characterize its petroleum source rock potential for an upcoming resource assessment. Ninety-five samples from 24 wells were collected from well cuttings of the lower part of the Lewis Shale stored at the U.S. Geological Survey Core Research Center in Lakewood, Colorado. The selected wells are located near the shallow margins of the basin to obtain samples that were not subjected to the effects of deep burial and subsequent organic carbon loss due to thermal maturation as described by Daly and Edman (1987) (fig, 1). The sample intervals were selected based on high gamma ray responses that Pyles and Slatt (2007) interpreted to be organic-rich condensed sections. Special emphasis was given to the Asquith marker bed which represents the maximum transgression of the Lewis Shale (Pasternack, 2005) (fig. 2).

This digital data release contains previously published contours on the tops of the Mowry Shale, Morrison Formation, and Minnelusa Formation. The maps are from a series of U.S. Geological Survey Miscellaneous Field Studies (MF) showing computer-generated structure contours, isopachs, and cross sections of selected formations in the Powder River basin, Wyoming and Montana (Crysdale 1990, 1991a, 1991b). The maps were constructed from information stored in a U.S. Geological Survey Evolution of Sedimentary Basins data base. This data base contains picks of geologic formation and (or) unit tops and bases determined from electric resistivity and gamma-ray logs of 8,592 wells penetrating Tertiary and older rocks in the Powder River basin. Well completion cards (scout tickets) were reviewed and compared with copies of all logs, and formation or unit contacts determined by N. M. Denson, D.L. Macke, R. R. Schumann and others. These maps are based on information from 2,429 of these wells that penetrate the Minnelusa Formation and equivalents.