Abstract

Isolated, lens-shaped accumulations of fi sh bones, scales, teeth, and coprolites in a sandy matrix occur along a few bedding planes within the Cretaceous Mowry Shale in an outcrop along Highway 191 north of Vernal, Utah. These accumulations have previously been interpreted to be large coprolites or regurgitate material, but are actually storm lag deposits in a sediment-starved basin. Accumulations (lenses) vary in size: the largest measured is 15 × 10 cm in plan view and 2 cm thick. Matrix in these lenses consist of fi ne-grained, well-rounded quartz grains that are absent in the surrounding shale layers. The disarticulated fossil material is the size of coarse sand, with some bone fragments and fi sh scales over 1 cm. The material is compacted, but poorly cemented. Jaw fragments, teeth, and vertebrae found within the lenses are mostly from teleost fi sh, commonly from the genus Enchodus, an alepisauroid. Teeth from Carcharias amonensis, a lamniform shark, are also present. Phosphatic pebbles (1-5 mm), which are likely teleost microcoprolites, are also found in these lenses. The lenses were deposited by bottom, winnowing storm currents and trapped in bottom scours in an area of limited coarse sediment supply on a gently sloping shelf.