14 Geochemistry, Sediments, and Structure

Tuesday, 17 March 2009
1:30 PM - 3:30 PM

PRELIMINARY REPORT ON THE PALEOECOLOGY OF THE CRETACEOUS (CENOMANIAN) WOODBINE FORMATION AT THE ARLINGTON ARCHOSAUR SITE, NORTH TEXAS

Paper number: 14-7
Program: Technical Sessions
Time: 3:00 PM – 3:15 PM

Authors

Abstract

The Arlington Archosaur Site is a prolific North Texas fossil locality that preserves a Mid –Cretaceous ecosystem along a low lying coastal plain. The site lies within the Cenomanian (95 Mya) rocks of the Woodbine Formation in North Arlington, Tarrant County. Typically the Woodbine is known for scattered remains of vertebrates in variable states of preservation. The Arlington Archosaur Site is unique for producing numerous fossils in a relatively good state of preservation. The depositional environment of the Arlington Archosaur Site is a near shore coastal embayment and Gyttja style channel fill; fine grained sediments (mud and clay), rich with organic material; wood and coal. The 1st of three fossil horizons occurs within an organic rich oxbow lake at the base of the section. Overlying the oxbow deposits, fossil horizon 2 occurs within the muds and clays of the 1st of 2 channel fills. Fossil Horizon 3 occurs above a channel lag conglomerate bed associated with the base of channel fill 2. Stratigraphically, these horizons represent phases of deposition from a meandering river system along a coastal plain.

Among the fossils recovered to date are: dinosaur; ornithopod (Protohadros) and theropod, crocodile (Woodbinesuchus), turtle, shark (Hybodont & Cretodus), fish (dipnoan and pycnodont), coprolite, plant, wood and coal. The wood deposits consist of large (>2m) logs deposited at the base of section in association with the Oxbow deposits. The ornithopod material recovered from fossil horizon 1 includes a nearly complete post cranial skeleton; a scapula, coracoid, radius, ilium, ischium and pubis, cervical, dorsal and caudal vertebrae. This ornithopod post crania is to date the most recovered from the Woodbine. Teeth, vertebrae, a femur, phalange and a claw of a new theropod have been recovered from the channel lag deposits. These fossils represent a new theropod dinosaur from the Woodbine Formation. Coprolites, fossil wood, plant material and charcoal found at the site offer data on the ecology and environment. A dense charcoal conglomerate bed in mid-section is interpreted as evidence of a regional forest fire. The Arlington Archosaur Site represents a unique window into the Cenomanian ecosystems of North America and is an ongoing research project at UT-Arlington.