2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 27
Presentation Time: 8:00 AM-12:00 PM

CLAY MINERALOGY AND PETROLOGY ASSOCIATED WITH A DINOSAUR LAKE (AARON SCOTT QUARRY, MORRISON FORMATION, JURASSIC), UTAH


BERTOG, Janet L.1, JEFFERY, David L.2, ROBINSON, Rath R.1, BOSWELL, Gary1, MACKEY, Dakota1, CASE, Chris3 and MCCORMICK, David3, (1)Physics and Geology, Northern Kentucky Univ, Highland Hts, KY 41099, (2)Department of Petroleum Engineering and Geology, Marietta College, 215 Fifth Street, Marietta, OH 45750, (3)Dept Petroleum Eng & Geo, Marietta College, 215 Fifth Street, Marietta, OH 45750, rathr21@aol.com

The Aaron Scott Quarry in the Morrison Formation of south-central Utah is an accumulation of vertebrate fossils representing the shoreline of a large lake during a moderate drought. Vertebrate fossils in the assemblage include largely fragmented dinosaur bones, isolated teeth and podial elements of Allosaurus, a diplodocid sauropod, a small ornithopod, and a diverse microfauna. Sequence stratigraphic analysis has shown that the fossil-bearing layer is within a forced-regression of a sequence. Within the quarry, the sediment is composed of a greenish-gray cemented siltstone with clay rip-up clasts near the base. The presence of rip-up clasts in the sediment is consistent with a drought condition, where the shoreline clays dried up, desiccated and cracked. Later, reworking of this desiccated clay produced rip-up clasts. Clay mineralogy of samples taken through the stratigraphic section of the sequence supports changing environmental conditions, with a dry period during the deposition of the fossil-bearing layer.