2010-05-07_PERMIT FILE - C2009087 (6)

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occurrence and maturity, and hydrology (Tyler & Tremain, 1994). Coal bearing formations in the proposed PSCM permit area include the Upper Cretaceous Iles and Williams Fork Formations (see • Section 2.04.5 Figure 2.04.5 -F2. Regional Stratigraphic Column). The Wadge Coal Seam in the lower member of the Williams Fork Formation is the coal seam to be mined due to its uniform quality and thickness. The Wadge Coal Seam occupies what is termed the Middle Coal Group of the Mesa Verde Group. A local stratigraphic column is shown in Figure 2.04.6 41, PSCM Local Stratigraphic Column. Mine development within the permit area will occur in the sedimentary rock units described in the following sections. The sedimentary units described also define surface rock exposures located within the permit area. The generalized geologic setting is shown on Map 2.04.6 -M1, Surface Geology. Lewis Shale (Upper Cretaceous) — The Lewis Shale is a dark -gray homogenous marine shale deposited during a regional transgression of a historical strandline. The total thickness of the shale varies throughout the proposed PSCM permit area due to erosional thinning; the maximum thickness is approximately 500 feet in the southern part of the PSCM permit area (Robson & Stewart, 1990). The formation tends to be sandier in the upper portion of the formation and may contain few lenticular sandstone layers. Mesa Verde Group (Upper Cretaceous) — The Mesa Verde Group generally consists of interbedded sandstones, mudstones, and siltstones of varying thicknesses. These beds were deposited in a predominantly near -shore terrestrial environment, with the sedimentation influenced • by sea -level changes, indicated by the presence of both marine and non - marine rocks. The group consists of the Iles and the Williams Fork Formations and overlies the Mancos Shale. Carbonaceous rocks are present in both formations; however, in the proposed mine area of the PSCM, thick coal beds are found only in the Williams Fork Formation. Williams Fork Formation — The Williams Fork Formation-is the upper unit of the Mesa Verde Group. It ranges in thickness from approximately 1,100 feet to 2,000 feet, and includes all the rocks between the Trout Creek sandstone member of the Iles Formation and the overlying Lewis Shale. The Formation consists of interbedded layers of shale, siltstone, coal, and, massive sandstone. The Formation can be subdivided into three units: the uppermost unit or the Holderness Member, the middle unit or Twentymile Sandstone, and the lowermost unit or Mt. Harris Member. The coal beds that are of interest are part of the Mt. Harris Member. These coals are part of the Middle Coal Group of the Mesa Verde Group. Iles Formation — The Iles Formation consists of light -brown to white, fine- to medium - grained, poorly sorted calcareous sandstone interbedded with red and dark maroon sandy and silty carbonaceous shale. Thick lenticular coal beds are found in the formation. A thick sandstone unit at the top of the Iles Formation, the Trout Creek Sandstone Member, is a reliable marker horizon for drill holes in the PSCM permit area and surrounding areas. • PSCM Permit App. 2.04 -25 6/15/09