ICHNOPEDOLOGIC ASSOCIATIONS IN THE UPPER TRIASSIC CHINLE FORMATION, STEVENS CANYON, SOUTHEASTERN UTAH: IMPLICATIONS FOR PALEOHYDROLOGY AND PALEOCLIMATE

The continental deposits of the Upper Triassic Chinle Formation in the southwest United States are interpreted as deposition during increasingly arid conditions. Ichnopedologic facies associations yield further details on the paleoclimatic, paleohydrologic, and paleoenvironmental conditions during Chinle deposition at Stevens Canyon (SC), southeastern Utah, and support this interpretation of increasing aridity. The Chinle Formation at SC is a fluvial-floodplain-lacustrine-deltaic system and consists of the Monitor Butte (MBM), Moss Back (MOM), Petrified Forest (PFM), Owl Rock (ORM), and Church Rock (CRM) members. The lateral and vertical changes within paleosols were described along with their associations with trace fossils and sedimentologic facies to synthesize ichnopedofacies. The MOM contains Rhizolith-inceptisols, the PFM contains Camborygma-Rhizolith-Therapsid Burrow-calcisols and vertisols, the ORM contains Camborygma-Naktodemasis-Rhizolith-calcisols and inceptisols and Rhizolith-inceptisols, and the CRM contains Rhizolith-inceptisols and Camborygma-Cylindricum-inceptisols. The absence of well-developed paleosols in the MOM is likely due to a limited time of stable subaerial conditions in a fluvial setting. The transition from calcisols and vertisols in the PFM, to calcisols and inceptisols in the ORM, and to inceptisols in the CRM; however, indicates that climatic conditions became drier throughout Chinle deposition. These increasingly arid conditions were punctuated by periods of wetter climate and higher water tables which supported plant life and burrowing organisms. The presence of Camborygma-Cylindricum-inceptisols in the CRM, for example, indicate that water tables could fluctuate to higher levels during more arid upper Chinle deposition, revealing a more complex climate history than an overall increase in aridity. This study shows that ichnopedofacies are an indispensable tool for correlating complex continental facies and further development of ichnopedofacies will continue to aid interpretations of the paleoclimatic, paleohydrologic, and paleoenvironmental history of the Chinle Formation and other continental deposits.