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26 <br /> The Ft. Benton Formation is a 500 foot thick layer of fine <br /> grained marine deposits. The lowest part is composed of dark <br /> gray to black fossiliferous sandy shales. The middle portion is <br /> i a zone of light to dark gray argillaceous limestone and dark gray <br /> to black calcareous shales . The upper part is calcerous dark <br /> gray sandy shales. Numerous thin but laterally continuous <br /> bentonite layers are found throughout the formation. The lower, <br /> middle and upper <br /> pp parts are often referred to as the Graneros <br /> Shale, the Greenhorn Limestone, and the Carlile Shale, <br /> respectively. <br /> The Codell Sandstone is the uppermost unit in the Ft . Benton <br /> Formation. In the Dowe Flats area, it has a 15-foot total <br /> thickness and can be divided into a 7-foot gray siltstone beneath <br /> an 8-foot thick silty sandstone. This silty sandstone directly <br /> underlies the Niobrara Formation. <br /> The Niobrara Formation is traditionally separated into two units, <br /> the Fort Hays and Smoky Hill members . The Fort Hays Member is an <br /> extremely fine-grained, light gray limestone with thin <br /> interbedded shales. A section of Fort Hays Member at the south <br /> end of Dowe Flats measured 16.5 feet thick (Lowman 1911) . <br /> Limestone accounted for 13. 6 feet or 820D of the outcrop <br /> thickness. The limestone is distributed as block ranging in <br /> thickness from 0.5 to 3.1 feet and vertical joints spaced on 1 to <br /> 3 foot centers. The remaining 2 .9 feet of material is <br /> distributed as 11 thin bentonite layers having an average <br /> thickness of 6 inches. Drilling on other areas within the Dowe <br /> Flats valley has indicated an average limestone thickness of 20 <br /> feet (Masters 1951) . <br /> The overlaying Smokey Hill Member of the Niobrara Formation is <br /> generally described as a dark gray, cancerous, fossiliferous <br /> marine shale. However, characterization of the Smoky Hill Member <br /> as shale on a regional scale does not account for several <br /> separate limestone beds present in the Dowe Flats vicinity. At <br /> Dowe Fiats, limestones within the Smoky Hill Member have been <br /> described as an outcrop along the Little Thompson River and <br />