PALEOECOLOGY AND PALEOENVIRONMENTS OF THE UPPER CRETACEOUS (CENOMANIAN) WOODBINE FORMATION AT LAKE GRAPEVINE; DENTON COUNTY, TEXAS

A facies analysis of Upper Cretaceous (Cenomanian)exposures of the Woodbine Formation at Lake Grapevine in southern Denton County, Texas was conducted. This study was instigated in order to develop an understanding of regional depositional environments in relation to paleoecosystems along the eastern shores of the Western Interior Seaway. The study consisted of measured sections taken from exposures along the northern shore of Lake Grapevine, from Rock Ledge Park, westward through Murrell Park. The depositional environments grade from prodelta mudstones at Rock Ledge Park, to brackish water, lagoonal silts and clays in Murrell Park. Stratigraphically, the Woodbine exposures at Lake Grapevine represent a marginal marine regressive sequence with the marine environments of the Lewisville Member being overlain by the fluvial sands of the Arlington Member.

Fossil sites found along the northern shore at Murrell Park are indicative of brackish water, lagoonal environments. The fossil fauna includes brackish water brachiopods along with rostral teeth from ganopristid sawfishes. The ganopristid teeth are found in a dense microvertebrate hash that includes shark teeth and turtle remains. Overlying the brackish water microvertebrate bed, are terrestrial vertebrates and plants preserved in a heavily oxidized sandstone. Hadrosaurid (Dinosauria:Ornithischia) post cranial material was recovered along with plant leaf material and fossil wood. The hadrosaurid material is principally from the axial skeleton with a few minor appendicular elements. The fossil leaves are in a congested fossil hash, with overlapping elements. The fossil wood occurs in equally dense accumulations, with evidence of burrows from wood burrowing molluscs. This unique accumulation of fossils offers a brief window view into Cenomanian paleoecosystems.