GSA Connects 2021 in Portland, Oregon

Paper No. 131-2
Presentation Time: 8:20 AM


HAYES, Robert, Geosciences, University of Arizona, 1040 E 4th St, #1, Tucson, AZ 85719 and DECELLES, Peter G., Geosciences, University of Arizona, 1040 E 4th St, Tucson, AZ 85721

The Shinarump Conglomerate (and equivalents in the Gartra Member and Temple Mountain Member) comprises the basal member of the Upper Triassic Chinle Formation, cropping out widely across the Colorado Plateau. The Shinarump Member is composed of mixed sandy and gravelly fluvial sediments and displays abundant cross-stratification. Previous studies have concluded, based on sedimentological and geochronological data, that the Shinarump represents a series of mixed alluvial-bedrock palaeovalley fill deposits, but there exist limited attempts to quantify statistically the nature of the fluvial system which deposited the member. This study therefore combines data collected from outcrops across Utah, including measurements of over 4000 trough cross-sets, macro-scale fluvial structures mapped using photomosaics, and sandstone petrologic data. Results obtained show a strong NW trend in palaeoflow, in agreement with coarser resolution studies in the literature, and additionally allow for quantitative estimation of sinuosity of the system ranging between 1.16 and 1.57. Application of the fulcrum approach of source-to-sink calculations allows for first-order estimation of the sediment load of the fluvial system in comparison to the volume of the sink, finding that the estimates of lifetime source volume generally exceed those for the sink, but are of the same order (e.g. 6.07 x105 km3 vs 4.17 x105 km3), though wide uncertainty exists in estimating climatological parameters. Applying this methodology highlights the challenges in examining systems deeper in geologic time, and the importance of clearly defined paleogeographies to characterizing fluvial load.