Laserfiche WebLink
• member of the Iles Formation and the Twenty-mile sandstone member of the Williams Fork <br />Formation. The upper coal group includes the coal horizons of the Williams Fork Formation <br />above the Twenty-mile sandstone member. It is the coal horizons of the middle coal group <br />that are of economical interest in the Yoast Area. <br />Middle Coal <br />The middle coal group of the Mesaverde Group occurs in a 400-foot sequence of sandstone, <br />sandy shale, and shale between the Trout Creek and Twenty-mile sandstone members. Within <br />this group, in ascending order, is the Wolf Creek, Sage Creek, Wadge, and Lennox coal <br />seams (Figure 2). The lowermost seam, the Wolf Creek, varies in thickness from 13.0 to <br />22.0 feet and, in places, exhibits a shale parting caused by an increase in water velocity <br />into the paludal environment. Above the Wolf Creek coal seam is a sequence of sandstone, <br />sandy shale, and shale approximately 100 feet thick. Overlying this interval is the Sage <br />Creek coal seam. The Sage Creek coal ranges in thickness from about five feet to one foot <br />or less. Separating the Sage Creek and Wadge coal seams is a sequence of predominantly <br />sandstone interbedded with sandy shale, shale, and thin coal beds. This 50-foot thick <br />. strata, although dominated by sandstone, exhibits some facies change, lensing, and <br />interbedding due to variations in depositional environments. The Wadge coal seam <br />possesses the most uniform lateral continuity and quality of the four coal seams in the <br />middle coal group. The Wadge seam varies from about 7.5 to 13.0 feet in thickness and, <br />like the Wolf Creek seam, may contain a shale parting. The Wadge coal seam is separated <br />from the uppermost coal, the Lennox, by a 50-foot thick sequence consisting of sandstone <br />interbedded with sandy shale and shale. This strata is very similar to that underlying <br />the Wadge seam; however, the shales and sandy shales appear to comprise more of the strata <br />above than below the Wadge. The Lennox coal seam varies from 2.0 to 6.0 feet thick, but <br />may be absent due to erosion. The material above the Lennox coal seam consists of <br />sequences of sandstone, sandy shale, and shale. <br /> <br />4 <br />