GENERAL43393 - Laserfiche WebLink

Home Browse Search

-13- Geologic units exposed in the North Fork Urainaye Basin consist of Late Cretaceous to Early Tertiary Aye sedimentary strata, Tertiary Aye igneous intrusive s, and 4uaternary Aye alluvial and cblluvial deposits. A generalized stratiyraphic colwnn of Late Cretaceous units can be found in Figure 3. The units are described below in ascending order. The i~lancos Shale is the oldest strata exposed in the region, and is of Late Cretaceous Aye. This unit is composed of over 4,000 feet of gray marine snales and minor interbedded buff colored sandstones. This unit is highly erodible and unstable. Erosion and oversteepeniny of slopes in this formation produce the numerous rock falls and landslides observed in the lower rJorth Fork Urainaye Basin (Junye, 1974). The Mesaverde Formation is of Late Cretaceous Nye and conformably overlies the Mancos Shale. This formation consists of approximately 2,3UO feet of marine and terrestrial deltaic sedimentary rocks. The Mesaverde Formation is the coal-bearing formation in the region and is divided into five main members; the Rollins sandstone, the Lower Coal Bearing (Bowie) member, the Upper Coal Bearing (Paonia) member, and the Barren (Undifferentiated) member and the Uhio Creek Conylo~nerate (Johnson, 1943; Wellborn, 1942; and Johnson and play, 19B0). The rtollins sandstone member is a 12U to 2UU foot thick, massive, cross-bedded, mediurn to fine-grained, buff to white colored sandstone. This sandstone is regionally extensive and resistant in outcrop and forms prominent cliffs. This member is used regionally as a ~narKer horizon to define the tdp of the 14ancos Shale and the oottom of the coal-bearing horizons. The Lower Coal bearing (Howie) member consists of 26U to 35U feet of interbedded gray shales, thin to thick lenticular beds of buff-colored, fine- td medium-grained sandstones, and coals. Tne top of the member is usually capped by a massive buff-co;ored sandstone up to 9U feet in thickness. This sandstone, however; appears not to oe a single persistent oed, but is actually several thick lenticular sandstones occurring at progressively lower stratiyraphic horizons fran east to west. Three coal horizons exist in the Lower Coal-Hearing ~meinber; the "A" (Uld King) horizon, the "d" (Somerset) horizon, and the "C" (Bear) horizon. The "A" horizon is i~runediately above the kollins sandstone and is nut currently mined. The "B" horizon contains two coal seams and occurs about 2U to 12U feet above the Rollins sandstone. Tnis horizon is presently mined at the Somerset Mine and may be :pined at the h1t. Gunnison Mine. The "C" horizon contains one coal sewn that occurs 5U to lUU feet auove file "H" horizon. This horizon has been mined at U.S. Steel's Elk Creek Mine and the Bear IVO. 1 and 2 Mines, and is currently mined at the Hear No. 3 Mine. !t may be mined at the Mt. Gwuiison Kline in the future.