The Lower Cretaceous J sandstone of the Dakota Group (MacKenzie, 1965) is present in the Denver basin in eastern Colorado, southeastern Wyoming, and southwestern Nebraska. This informally named unit deposited during a regression of the Cretaceous epi continental sea and is composed primarily of sandstone and shale of deItaic and near-shore marine origin. The J sandstone can be divided into an upper transgressive sand, a middle marginal-marine and deltaic facies, and a lower prodelta sequence (Clark, 1978). The depth from the surface to the top of the J sandstone increases from about 4,000 ft on the gently-dipping eastern flank of the bass n to more than 8,000 ft near the steeply-dipping flank at the western boundary.
Permeability values compiled in this J sandstone study were determined from cores from 134 widely scattered boreholes. Median permeabilities, rather than average permeabilities, were used in order to minimize the effect of anomalous samples. Thirty-five oil companies and independent operators supplied core data. Core Laboratories of Denver, Colorado analyzed the core, which was submitted over a period of 25 years.
Additional publication details
|Publication Subtype||USGS Numbered Series|
|Title||Median-permeability contour maps of the J sandstone, Dakota Group, in the Denver Basin, Colorado, Nebraska, and Wyoming|
|Series title||Miscellaneous Field Studies Map|
|Publisher||U.S. Geological Survey|
|Publisher location||Reston, VA|
|Description||Plate: 35.84 x 35.35 inches|
|State||Colorado, Nebraska, Wyoming|
|Other Geospatial||Denver Basin|
|Online Only (Y/N)||N|
|Additional Online Files (Y/N)||N|