SCHMUDE, DAVID, Texaco, Inc.; and CHRISTOPHER WEEGE*, Western Gas Resources, Inc., Denver, CO

Abstract: The Paleontology and Stratigraphy of the Lower Morrison Formation in the Como Bluff Region of Wyoming

The Morrison Formation of the Como Bluffs region has been a renowned collecting grounds of Late Jurassic dinosaurs for over 100 years. The early expeditions of Marsh in 1877 and the American Museum of Natural History in 1897 focused on collecting new and exhibition quality fossil specimens with little regard to the stratigraphy of the collection site. Recent work has discovered that most of the collections were made from the upper third of the formation with a poor sampling from the lower section. New research focuses on this portion of the section to learn how the environment changed through time and how the fauna reacted to these changes.

The Lower Morrison is a series of numerous thin limestones and sandstones interbedded with red and green mudstones deposited behind the slow retreat of the Jurassic Sundance seaway. In the Como Bluff region, this transition is expressed with wide spread deposition of numerous limestones representing the remains of large shallow alkaline lakes. These lakes were fed by seasonal streams that are manifested by fluvial sandstone bodies overlying and interbedded with the limestones. The thin continuous sand bodies suggest shallow unconfined flow over a flat alluvial plain. Calichie, desiccation features and rip-up lags suggest seasonal precipitation. Recently, several dinosaur quarries have been found in the Lower Morrison, providing new biostratigraphical information. Numerous measured sections show the regional sedimentological variations and stratigraphical positions of the fossil quarries.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana