Laserfiche WebLink
Wet Mountain Fault to the west. Strata on the northeast limb of the syncline dip gently <br />to the west at approximately 5 degrees. The southwest limb of the syncline dips very <br />steeply and in some cases strata on this limb are overturned. Dips in the southwest <br />limb range from 45 degrees NW to 85 degrees overturned. The Wet Mountain Fault is <br />comprised of pre-Cambrian granitic rocks uncomfortably overlying overturned <br />sedimentary shales and sandstone units of the Cretaceous age. Three units are of <br />significance in the area - the Pierre Shale, the Trinidad Sandstone and the Vermejo <br />Formation (see Figure 3). <br />The Pierre Shale outcrops approximately 1.5 east of the mine area. The shale unit <br />consists of 3,900 feet of olive-gray clay and silt layers that contain bentonite and marine <br />fossils. It is a non-coal-bearing unit that exhibits very low hydraulic conductivity and <br />thus is considered to be a relatively impermeable unit. At the top of the Pierre is a <br />sequence of thin, inter-bedded sandstones and mudstones. <br />The Trinidad Sandstone, directly above the Pierre Shale, outcrops about 1.0 miles east <br />of the mine site and is composed of massive buff to yellow sandstones ranging from 40 <br />to 90 feet in thickness. The Trinidad Sandstone is indicative of a prodeltaic depositional <br />environment. <br />The Vermejo Formation overlies the Trinidad Sandstone and is the coal-bearing unit of <br />mining interest to the Southfield operation. The Vermejo Formation consists of a <br />complex network of mudstones, siltstones, sandstones and eleven coal seams, all <br />indicative of a vast fluvial delta and plain sequence. The coals developed in the <br />backwater swamp areas of the river delta. The coal seams of economic importance in <br />the area are Monarch, Red Arrow, Jack O'Lantern, Vento, Manley and Rex Carbon. <br />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 <br />in the Vermejo Formation - the Red Arrow and the Jack O'Lantern. The Red Arrow <br />seam ranges in thickness from 4 to 7 feet and is a moderate to high sulfur coal with 3 <br />recognizable units separated by bony layers of ash. The Jack O'Lantern seam is a low <br />sulfur coal that ranges in thickness from 4 to 8 feet and also consists of 3 recognizable <br />units separated by boney ash layers. The permittee has provided a complete coal, roof <br />and floor analysis in the permit. For further information refer to Section 2.04.6 of the <br />permit. <br />Ascending upward on the stratigraphic column from the Vermejo Formation is the <br />Raton Formation, a unit consisting of two members- a basal sandstone and muddy- <br />sandy layer. The Raton averages 650 feet in thickness. The erosional base of this unit <br />marks the top of the Vermejo Formation in the Southfield mine area. There are no <br />coal-bearing units found in the Raton, since its character indicates that a period of <br />increased uplift and subsequent erosion in the area followed that of the depositional <br />low-energy environment found in the Vermejo. <br />Uncomfortably overlying the Raton Formation are the sediments of the Poison Canyon <br />Formation. Similar in composition and character to the Raton, the Poison Canyon <br />Page 6 of 36