2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 5
Presentation Time: 9:00 AM


GUTIERREZ, Karen, Geological Sciences, University of Michigan, 1100 N University Blvd, Ann Arbor, MI 48109 and SHELDON, Nathan D., Earth and Environmental Sciences, University of Michigan, 2534 CC Little Building, Ann Arbor, MI 48109, kagutie@umich.edu

Jurassic-aged strata of Asturias, Spain record the transition from a marine to a non-marine depositional setting, contain trace fossils including sauropod and theropod dinosaur footprints, and have been relatively unstudied. A coastally exposed continuous section at the Playa de Vega locality shows a clear transition from the marine Middle Jurassic Rodiles Formation to the non-marine Upper Jurassic Vega Formation. Within the >100 meters of Vega Formation stratigraphy that was logged there, four distinct types of paleosols were identified: 1) composite Entisols, 2) discrete Entisols, 3) Inceptisols, and 4) Vertisols. Analysis of the three types of paleosols and their associated sediments indicates a gradual drying of the paleoenvironment, and a transition between a lagoonal environment low in the section with meandering rivers upsection. Near the base of the section, sauropod tracks have been identified, indicating that a dinosaurian fauna was present at Playa de Vega during the Jurassic. The presence of Vertisols with both extensive evidence for shrink-swell behavior and dispersed pedogenic carbonate are consistent with a strongly seasonal climate. Quantitative paleoclimatic data (mean annual precipitation and temperature) will be derived from well-characterized climofunctions based on modern soils and the paleosol B horizon chemical composition of the Inceptisols and Vertisols. Values of δ13C analyses of pedogenic carbonates range from -7.23 – -8.88 ‰ and are consistent with carbon dioxide levels about eight times pre-industrial levels. Taken together, these data and additional trackways from nearby sites suggest that the sauropod and theropod dinosaurs were rather adaptable creatures capable of enduring the climatically dynamic Asturian environment while experiencing significant seasonal climatic variation.