Stratigraphic framework of Lower and Upper Cretaceous rocks in central and eastern Montana

Abstract

Large accumulations of biogenic gas are known to exist in shallow (<3,000 ft deep) Cretaceous reservoirs of the Northern Great Plains (mainly Montana) and southeastern Alberta and southwestern Saskatchewan, Canada. The 1995 USGS National oil and gas assessment made a mean estimate of 1.15-1.18 x 10 12 m 3 (41-42 trillion cubic ft) of potential additions to reserves of continuous-type (unconventional) gas in Cretaceous shallow biogenic gas plays of northern and central Montana (Rice and Spencer, 1995). About 90 percent of the 1995 gas estimate was in hypothetical plays. The controls on the boundaries of these plays were poorly understood at the time of the assessment in 1995. As a follow on to the 1995 assessment, a multidisciplinary project (Ridgley and others, 1999) was undertaken in order to better understand the controls on the gas accumulation and to better define the play boundaries. The focus of the project is on Cretaceous rocks from the top of the Mowry Shale to the base of the Judith River Formation, and within this geologic time slice the project will define the petroleum system of the shallow biogenic gas. To achieve these goals, we are integrating geologic, structural, hydrologic, and engineering studies with known and new geochemical data on the gas and co-produced water to understand the controls on the spatial distribution of potential gas accumulations and to understand the origin and time of generation and migration of the gas. An additional focus of the project is to determine the controls on the sites of shallow biogenic gas in the large southeastern Alberta gas field in Canada. This gas accumulation is in rocks age-equivalent to those that host the shallow gas in the Northern Great Plains. Over one-half of the 1995 national oil and gas assessment was based primarily on similarity of the potentially productive facies in Montana to the facies that host large shallow biogenic gas resources in southeastern Alberta and southwestern Saskatchewan. We will determine if the Canadian analog is appropriate for the Northern Great Plains shallow gas system. We plan a series of topical reports that will provide the background information required for the next assessment of the shallow biogenic gas system in the Northern Great Plains in late 2000.

A new elasmosaurid (sauropterygia, plesiosauria) from the bearpaw shale (late cretaceous, maastrichtian) of montana demonstrates multiple evolutionary reductions of neck length within elasmosauridae

“…al., 2006;Feldmann et al, 2012), although the vertical thickness at the discovery site of MOR 3072 was not measured. This westward-thinning tongue of marine shale disconformably overlies the Judith River Formation and is conformably overlain by the Fox Hills Sandstone in Montana (Feldmann et al, 1977;Condon, 2000) and the Eastend Formation in Canada (He et al, 2005). The Bearpaw Shale grades eastward into the Pierre Shale (Condon, 2000) and the outcrop similarity between the Bearpaw and Pierre shales makes these two units physically synonymous in the upper midcontinent of North America (Tourtelot, 1962;Feldmann et al, 2012).…”

A Chemostratigraphic Model for the Development of Parasequences and Its Application to Sequence Stratigraphy and Paleoceanography, Cretaceous Western Interior Basin, USA

“…In this study, the Arrow Creek and Clay Spur bentonites were identified by their stratigraphic positions at the base of the Mowry Shale (Condon, 2000) and within the base of the Belle Fourche Shale (Morath, 2007), respectively. When the Arrow Creek bentonite was not present, the Albian-Cenomanian boundary was chosen using palynological data from Scott et al (1998) (for the Bounds core) and regional trends of depletion in oxygen isotopic signatures from paleosol sphaerosiderites in the Kenyon and Bounds cores (based on the boundary pick described in White et al, 2005).…”

“…For example, the parasequences present at the base of the Northeastern Wyoming Composite section (parasequences 1-9) are not observed in the Bounds and Kenyon cores. The early Cenomanian strata in northeastern Wyoming was deposited in a wholly marine environment (Condon, 2000) in the axial portion of the KWIS (Kauffman and Caldwell, 1993), whereas the coeval strata in the Bounds and Kenyon cores were deposited in a fluvial/deltaic setting (MacFarlane et al, 1991) near the eastern paleoshoreline of the KWIS (Hamilton, 1994). Therefore, less accommodation space was available in the Kansas, precluding the deposition of parasequences 1-9 (i.e., nondeposition and/or erosion).…”

Inventory of Shale Formations in the US, Including Geologic, Geochemical, Hydrological, Mechanical, and Thermal Characteristics

“…There are a number of published isopach and structural maps of the Pierre Shale and its correlative unit, the Bearpaw, for this region (Shurr, 1977;Carlson, 1982;Smith, 1999;Condon, 2000); data from Condon (2000) for eastern Montana were used to generate GIS data for the Bearpaw (Figure 2-20). Inventory of Shale Formations in the US, Including Geologic, Geochemical, Hydrological, Mechanical, and Thermal Characteristics 24 September, 2014…”