Niobrara formation

Dean W. E. and Arthur M. A. (1998) Geochemical expression of cychcity in Cretaceous pelagic hmestone sequences Niobrara Formation, Western Interior Seaway. In Stratigraphy and Paleoenvironments of the Cretaceous Western Interior Seaway USA. Concepts in Sedimentology and Paleontology, no 6 (eds. W. E. Dean and M. A. Arthur). Society Economic Paleontologists Minerologists, Tulsa, pp. 227-255. 

Sandstone has been found to contain selenium in varying concentrations, but most probably contains <1 mg/kg (Rosenfeld and Beath 1964). However, sandstone in Wyoming has been found to contain >100 mg/kg (Beath et al. 1946). Generally, the selenium concentration of limestone is low however, shales of the Niobrara formation in South Dakota have been found to contain over 40 mg/kg. The range of selenium concentrations in phosphate rocks is <1-300 mg/kg (NAS 1976a). 

Subsidence modeling was used to evaluate the thermal maturity profile of the source beds. The subsidence model developed for this area is presented by Pittman (1988). A 107-m core in the Niobrara Formation and Carlile Shale provided consistent vitrinite reflectance data to calibrate the subsidence curves. An Ro of 1.41% corresponds to the base of the Niobrara Formation. This value was used as a control on the development of the subsidence profile that is, a match of 1.41% was obtained for the base of the Niobrara. 

Fig. 2. Columnar section for the Wattenberg area of the Denver Basin. The primary source rocks are the shales and limestones of the Dakota Group, Benton Group, and Niobrara Formation. The most important hydrocarbon reservoirs are the Dakota J Sandstone and the Hygiene and Terry sandstones of the Middle Pierre Shale. The Lyons Sandstone, Codell Sandstone of the Benton Group, and limestone of the Niobrara Formation also produce hydrocarbons...

Source rock analyses were made for the Niobrara Formation and the Carlile Shale because of the paucity of data available in public domain literature. The Niobrara in the Wattenberg area is a black shaley limestone and is the richest source rock in the basin. Source rock data used in calculations presented later in this chapter are shown in Table 1. Only analyses made on core samples were used except for the Pierre Shale where a lack of cores necessitated the use of data derived from outcrops and drill cuttings. 

Driscoll, P.L., Bowen, J.G., and Roberts, M.A. "Oil Base Foam Fracturing Applied to the Niobrara Shale Formation," 1980 SPE Annual Fall Technical Conference and Exhibition of AIME, Dallas, September 21-24. 

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