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?.04.6 <br />• Stratigraphy <br />The sedimentary units exposed in the report area are of <br />lurasaic to Quaternary age. They are described below in ascending <br />order. <br />Morrison Formation (Jurassic) <br />Brushy Basin Member U er Jurassic) <br />The Brushy Basin Member (approx. 400 feet thick) is the <br />oldest stratigraphic unit exposed adjacent to the permit area. It <br />is a slope-forming unit that consists dominantly of flood-plain <br />mudstones and bentonitic shales with minor lacustrine limestones <br />beds and rusty-red interlayed lenses of sandstone and conglomer- <br />ate. The shale and mudstone vary from white to pastel tints of <br />red, blue and green. Random throughout are thin beds of hard <br />finegrained sandstone. The beds of chert pebble conglomerate <br />range from a few inches to about 25 feet thick. This member is <br />well known for a great abundance of petrified caood and bone. <br />Burro Canyon Formation Lower Cretaceous) <br />The Burro Canyon Formation (approx. 150 feet thick) of <br />early Cretaceous age overlies the Morrison, and forms either <br />mesa-capping resistant units or ledgy outcrops above the less <br />resistant Morrison shales. The formation generally consists of <br />two conglomeratic sandstone beds 10-40 feet thick separated by <br />light green mudstone and shale. Irregular, dense, pink to gray <br />limestone nodules are locally present in the mudstone. The <br />sandstone is poorly sorted and consists mostly of quarts with <br />some c~ert g sins. The conglomerate consists of pebbles of <br />chert, quarts limestone,]quartzite and sandstone. <br />The Burro Canyon Formation is interpreted as an alluvi- <br />al system deposited across a broad, relatively even surface on <br />top of the Morrison Formation. In many respects, the formation <br />appears to represent a continuation of Morrison deposition. The <br />sandstone and conglomeratic sandstone were deposited from a <br />relatively high energy transport medium and is a distinctly <br />fluvial deposit formed by meandering or sinous streams. <br />• 2.04-5 May 1991 <br />