Tops file for the Niobrara interval of the Upper Cretaceous Cody Shale and associated strata in the Bighorn Basin, Wyoming

The Bighorn Basin is a large Laramide structural and sedimentary basin that encompasses about 10,400 square miles in north-central Wyoming and south-central Montana (fig. 1). The basin is bounded on the northeast by the Pryor uplift, on the east by the Bighorn uplift and on the south by the Owl Creek uplift. The northern margin is formed by a zone of faulting and folding referred to as the Nye-Bowler lineament. The western and northwestern margins are formed by the Absaroka volcanics and Beartooth uplift, respectively. Commercial hydrocarbon production was first established in the Bighorn Basin when oil was discovered from Cretaceous reservoirs at Garland field in 1906 (Biggs and Espach, 1960). Since then, many important conventional oil and gas resources have been discovered and produced from reservoirs ranging from Cambrian through Tertiary in age (De Bruin, 1993; Fox and Dolton, 1989,1996). In addition, a potential basin-centered gas accumulation may be present in Cretaceous reservoirs in the deeper parts of the basin (Spencer, 1987; Ryder, 1987; Surdam and others, 1997; Johnson and Finn, 1998; Johnson and others, 1999; and Finn and others, 2010). It has been suggested that various Upper Cretaceous marine shales are the principal hydrocarbon source rocks for many of these accumulations (Geis, 1923; Burtner and Warner, 1984; Hagen and Surdam, 1984; Meissner and others, 1984; Ryder, 1987). With new drilling and well completion technologies, equivalent marine source rock intervals, in particular the Niobrara Formation, are now important continuous (unconventional) shale gas and shale oil objectives in other Rocky Mountain basins (Matthews, 2011; Sonnenberg, 2011; Williams and Lyle, 2011; Durham, 2012a,b, 2013; Taylor and Sonnenberg, 2014; and Hawkins, 2016). In the Bighorn Basin the Niobrara is represented by shales, calcareous shales, marls, siltstones, and sandstones in the lower part of the Upper Cretaceous Cody Shale (Finn, 2014) (fig. 2). Please see supplemental information for associated references. Selected figures have also been included to help describe this data release. These figures are provided in pdf and jpg format. These include: Fig. 1_Rocky Mountain basins.pdf/jpg. Map of Rocky Mountain region showing locations of Laramide sedimentary and structural basins and intervening uplifts. Fig. 2_Xsection.pdf/jpg. Regional east-west stratigraphic cross section of Cretaceous rocks in the Wind River Basin. Each modified from Finn (2014). Please see data dictionary sheet in the excel file for detailed table column/attribute information.