HEADING WEST ON THE MOAB MEGATRACKSITE: A 300 KM MID JURASSIC CORRELATION OF TOP-ENTRADA THEROPOD DINOSAUR TRACKSITES

Correlation of Mesozoic terrestrial sequences using vertebrate body and trace fossils is problematic. However in recent years it has become evident that there are a number of widespread dinosaur track zones associated with the top of various well-defined stratigraphic units. These are either single-surface megatracksites or thin stratigraphic zones that can be understood in terms of the local sequence stratigraphy. In the western United States we recognize at least seven such Mesozoic zones, or megatracksites (also called dinosaur freeways) that crop out from Utah and Colorado, through Arizona and New Mexico and into Texas. Three are Cretaceous and not mentioned here, but four from the Upper Triassic through Middle Jurassic have interesting implications for correlation in the Colorado Plateau region The oldest example is an Upper Triassic, upper Chinle Group (Rock Point Fm and equivalents) zone containing almost all known Chinle Group tracks. The top of the Lower Jurassic Springdale Sandstone in southern Utah and northern Arizona was also recently identified as a probable megatracksite, as was a track rich zone at the top of the Kayenta Formation in much of southern Utah. Herein, is presented the first statement that the Moab Megatracksite, associated with a single surface at the top of the Entrada Formation in eastern Utah, may be correlated to three tracksites in a well defined top-Entrada zone in south central Utah and near Page, Arizona. These sites are up to 300 km southwest of the most northeasterly known sites. This significantly increases our concept of the geographical area previously named the Moab megatracksite. The strength of this correlation is strongly supported by the similarity in theropod tracks (ichnogenus Megalosauripus) at all three of these southwesterly sites, discovered in or near the canyons of the Escalante, Good Hope Bay and Lone Rock.