PERMFILE132410 - Laserfiche WebLink

Home Browse Search

West E(k Mine Rollins Sandstone Member The Rollins Sandstone Member is conspicuous white to buff, well sorted, fine to medium grained, massive cliff=forming sandstone of marginal marine origin, ranging in thickness from 150 to 300 feet in the azea. Although this sandstone forms a good local subsurface mazker, it is a poor regional marker because of lateral facies changes and intertonguing with shale. The Rollins Sandstone forms conspicuous cliffs in the area and is generally easily recognizable in cores. It has poor permeability and a few miles to the north has been given "tight gas sand" designation by the Colorado Oil & Gas Conservation Commission. Lower Coal Member The Lower Coal Member consists of interbedded sandstones, siltstones, shales, and coal. The unit averages 270 feet in thickness and contains three recognized persistent potentially minable coals in its lower part; The A, B, and C-Seams. The Lower Coal Member is almost always capped by massive sandstone units which range in thickness from 20 to 225 feet (informally designated as the "Upper and Lower Marine Sandstones"). These sandstones appeaz similar in nature to the Rollins sandstone, but show much more variation in thickness. The top of this sandstone marks the base of the Upper Coal Member. Upper Coa! Member The Upper Coal Member contains approximately 220 feet of shales, mdstones, siltstones, sandstones, and three persistent and potentially minable coals recognized as the D, E, and F-Seams. The D and E Coal Seams locally merge to form a single minably thick coal body. The Upper Coal Member displays sequences of disturbed bedding (attributed to compaction and bioturbation) in the non-coal units. The shale to sandstone ratio increases relative to the Lower Coal Member, and the sandstones appeaz to be less continuous than those in the Lower Coal Member. This is probably due to a greater fluvial influence in the depositional regime of the Upper Coal Member. Barren Member The Barren Member of the Mesaverde Group lies above the F-Seam and is approximately 1000 feet thick in the West Elk Mine coal lease azea. This member consists of interbedded sandstone, siltstone, and shale with a few thin and discontinuous coals of no commercial importance. The Barren Member caps the highlands in the western, central, and southern portions of the mine property. The lenticular sandstones commonly form the uppermost cliffs in outcrop. Beneath the highest mesas occurring in the easternmost portions of the West Elk Mine coal lease azea, the Barren Member is overlain by the Ohio Creek Member and the Wasatch Formation. Ohio Creek Member The Ohio Creek Member is the uppermost member of the Mesaverde Group. This unit is approximately 700 feet in thickness and consists primarily of interbedded sandstone, mudstone, and shale. The sandstones range from a few feet to more than 100 feet in thickness and are generally •1 2.04-24 RevitedJun. 1995 PR06; Revised Jan. 1998 PR08