57 Paleontology (Posters) I

Sunday, 16 October 2005
1:30 PM - 5:30 PM

MAPPING THE DISTRIBUTION OF EARLY JURASSIC (HETTANGIAN) DINOSAUR TRACKS IN THE WHITMORE POINT MEMBER OF THE MOENAVE FORMATION, JOHNSON FARM DINOSAUR SITE, ST. GEORGE, WASHINGTON COUNTY, UTAH

Paper number: 57-2
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Dinosaur tracks and traces, as well as bone material, are preserved in the lacustrine Whitmore Point Member of the Early Jurassic Moenave Formation at Johnson Farm within St. George, Utah city limits. Abundant dinosaur traces display a diverse array of dinosaur behaviors as preserved in mudflats and beaches surrounding ancient Lake Dixie, an oasis during deposition of the Wingate erg that occurs to the northeast. A laterally extensive three-decimeter thick fine-grained sandstone bed adjacent to ancient Lake Dixie contains the dinosaur traces. The unit is approximately 63 meters above the base of the Moenave Formation and to date has yielded more than 250 in situ theropod dinosaur tracks. Grallator tracks dominate, with only a single Eubrontes track recorded thus far. The tracked layer contains isolated fish scales and bone fragments and was extensively bioturbated by invertebrates prior to the tracking, finally it was mudcracked.

Track orientations dominantly trend southwest to southeast. Several areas of this tracked surface are heavily trampled making it difficult to distinguish individual tracks sometimes. This track-bearing layer represents a lacustrine regression where theropods were moving to and from the shoreline across a wide mudflat. This mudflat appears to be located on the south side of ancient Lake Dixie.