PALEONTOLOGICAL SURVEY OF UPPER JURASSIC AND LOWER CRETACEOUS DEPOSITS IN GUNNISON GORGE NATIONAL CONSERVATION AREA, COLORADO, USA FOR A GEOCORPS AMERICA INTERNSHIP

GeoCorps America offers temporary, paid internships to geoscientists at National Parks, National Forests, and the Bureau of Land Management to provide participants with experience in the field of geology. Over the course of ten weeks during the summer of 2012, three localities, covering a total of 228 acres, within the Gunnison Gorge NCA were surveyed for paleontologic remains through the BLM office in Montrose, Colorado. Solitary field surveys were conducted and involved use of a 4-wheel drive vehicle to access sites to hike through rough terrain in a hot, dry climate. During the internship, additional paleontological opportunities were offered to help broaden the experience.

The geologic exposures within the Gunnison Gorge NCA are Precambrian basement rock overlain by Mesozoic sedimentary rocks. The focus of this study was on Mesozoic sedimentary exposures of the Late Jurassic Saltwash and Brushy Basin Members of the Morrison Formation and the Early Cretaceous Burro Canyon and Dakota Formations.

Paleontological resources in the Uncompahgre Field Office area include therapods, ornithopods, and sauropods from the Morrison. The Burro Canyon includes dinosaur bones and tracks, impressions of limonitic wood, seedpods, and leaves. Regionally the Dakota contains abundant plant fossils, including fern trees. The Dakota is known for its pervasive invertebrate ichnofossils and for its vertebrate ichnofossils, including ornithopod and therapod trackways, crocodile tracks and swim tracks, and pterosaur swim tracks.

This study resulted in the discovery of vertebrate material, trackways, invertebrates, invertebrate ichnofossils, and plant material within the study area. Thirty-five waypoints of interest were taken. Of these waypoints, seventeen were sites of ichnofossils (including dinosaur and crocodile trackways and invertebrate burrows), thirteen sites contained plant material, three contained vertebrate material, one site contained invertebrate body fossils, and one site contained archeological material. The most intriguing finds were the ornithopod dinosaur trackways. These tracks were found as the positive relief of a print preserved in fine-grained sandstone of floodplain deposits towards the base of the Dakota.