Paper No. 320-21
Presentation Time: 2:00 PM
PRELMINARY REPORT ON THE ICHNOPEDOFACIES ASSOCIATIONS IN THE UPPER TRIASSIC CHINLE FORMATION, STEVENS CANYON, SOUTHEASTERN UTAH: EVALUATING INCREASING ARIDITY RECORDED DURING CHINLE DEPOSITION
Regional models for the southwest United States indicate increasingly arid conditions during deposition of the Upper Triassic Chinle Formation. Preliminary results seem to indicate that local changes in the distribution of sedimentary facies, ichnofossils, and paleosols of the Chinle Formation with respect to stratigraphic successions in the Stevens Canyon (SC) area, southeastern Utah, follow this trend. Ichnofossils, paleosols, and sedimentary facies were described from three measured stratigraphic sections and six stick sections in SC to track lateral variability. The Chinle Formation at SC is comprised of the Monitor Butte (MBM), Moss Back (MOM), Petrified Forest (PFM), Owl Rock (ORM), and Church Rock (CRM) members. The PFM is very thin in this area and is preserved as incised valley fill in the MOM. The dominant sedimentology is clay rich siltstone and mudstone in the MBM, trough cross-stratified and ripple laminated fine-grained sandstone in the MOM, angular blocky, calcareous siltstone in the PFM, angular blocky, calcareous siltstone and trough cross-stratified and massive limestone and quartz clast conglomerate in the ORM, and angular blocky, calcareous siltstone and ripple-laminated fine-grained sandstone with desiccation cracks in the CRM. Beds across SC show significant lateral discontinuity and variability. The PFM shows a lateral transition from a small lake or pond to paleosols over the course of a few dozen meters and complex channelized beds occur in the MOM. Many conglomerate and sandstone beds in the ORM and CRM respectively pinch and thicken as lenses and represent fluvial channelization. Ichnofossils described from SC include Naktodemasis, Camborygma, large therapsid? burrows, Stromatolites, enigmatic horizontal burrows, reptile tracks, and rhizoliths. Many of these traces, especially the Naktodemasis and large therapsid? burrows, are clustered in distinctive beds which can be correlated across SC. Ichnopedologic facies will be constructed from sedimentary facies, ichnofossil, and paleosol associations. Using ichnopedologic facies will help track abundance of carbonate during Chinle deposition and confirm whether or not a transition to arid conditions occurred during the Late Triassic in the SC area.