Laserfiche WebLink
unconformably overlying overturned sedimentary shales and sandstone units of the Cretaceous <br />age. Three units are of significance in the area: the Pierre Shale, the Trinidad Sandstone, and the <br />Vermejo Formation (these are illustrated in Figure 3 of the PAP). <br />The Pierre Shale outcrops approximately 1.5 miles east of the mine area. The shale unit consists <br />of 3,900 feet of olive -gray clay and silt layers that contain bentonite and marine fossils. It is a <br />non - coal - bearing unit that exhibits very low hydraulic conductivity, and thus is considered to be <br />a relatively impermeable unit. At the top of the Pierre is a sequence of thin, inter - bedded <br />sandstones and mudstones. <br />The Trinidad Sandstone, directly above the Pierre Shale, outcrops approximately one mile east of <br />the mine site and is composed of massive buff to yellow sandstones ranging from 40 to 90 feet in <br />thickness. The base of the Trinidad Sandstone is marked by the transitional change from the <br />prodeltaic sediments (Pierre Shale) to delta front deposits. The Trinidad Sandstone is composed <br />of delta front deposits (Lower Trinidad) and Tributary channel sand deposits (Upper Trinidad), <br />the change in depositional environments indicates the delta front was transgressing east. <br />The Vermejo Formation overlies the Trinidad Sandstone and is the coal - bearing unit of mining <br />interest to the Southfield operation. The Vermejo Formation consists of a complex network of <br />mudstones, siltstones, sandstones and eleven coal seams, all indicative of a vast fluvial delta and <br />plain sequence. The coals developed in the backwater swamp areas of the river delta. The coal <br />seams of economic importance in the area are Monarch, Red Arrow, Jack O'Lantern, Vento, <br />Manley and Rex Carbon. Total thickness for the Vermejo sequence is approximately 925 feet. <br />The coal seams mined at the Southfield Mine are two of the six principal seams present in the <br />Vermejo Formation — the Red Arrow and the Jack O'Lantern. The Red Arrow seam ranges in <br />thickness from 4 to 7 feet and is a moderate to high sulfur coal with three recognizable units <br />separated by bony layers of ash. The Jack O'Lantern seam is a low sulfur coal that ranges in <br />thickness from 4 to 8 feet and also consists of three recognizable units separated by boney ash <br />layers. The permittee has provided a complete coal, roof, and floor analysis in the permit. For <br />further information refer to Section 2.04.6 of the permit. <br />Ascending upward on the stratigraphic column from the Vermejo Formation is the Raton <br />Formation, a unit consisting of two members: a basal sandstone and an upper muddy -sandy <br />layer. The Raton averages 650 feet in thickness. The erosional base of this unit marks the top of <br />the Vermejo Formation in the Southfield mine area. There are no coal- bearing units found in the <br />Raton, since its character indicates that a period of increased uplift and subsequent erosion in the <br />area followed that of the depositional low- energy environment found in the Vermejo. <br />Unconformably overlying the Raton Formation are the sediments of the Poison Canyon <br />Formation. Similar in composition and character to the Raton, the Poison Canyon Formation is <br />coal barren and is approximately 200 feet in thickness of alternating beds of mudstone and <br />sandstone. <br />Covering most of the topographic ridges in the Southfield mine area are a series of Pleistocene <br />boulder /colluvial/alluvial deposits. Most of the boulders consist of gneiss, schist and sandstones <br />D <br />