Carbonate diagenesis and paleoclimate of the Desmoinesian Lower Ismay zone, Paradox Basin, southeast Utah

The Paradox Basin is located in present day four corner area of SE Utah, USA. However, during the Desmoinesian the basin migrated from the equator to 5°N. Carbonates developed on topographic highs during late transgressive system tracts (TST) and highstand system tracts (HST). Lowstand system tracts (LST) are characterized by more than 33 evaporite cycles. Platform carbonates and basin evaporite sequences are tied by cyclic regional dolomudstones that blanket both carbonate and evaporite sediments in the early TST. Detail analyses of the Lower Ismay Zone reveals rapid sea level falls within system tracts and climate fluctuations from extreme aridity to monsoon periods.; Paleoclimate interpretation was enhanced by applying geochemical and petrographic analyses of all three depositional systems carbonate, evaporite and dolomudstone) of the Lower Ismay and Evaporite Cycle 3. Paragenetic sequences were constructed from four different horizons within the Lower Ismay Zone. These sequences identified three rapid sea level falls within the Lower Ismay. Meteoric cements in the lowest horizon indicate wetter periods in contrast to the more arid upper horizons that show well-developed sabkha fabrics and evaporite cements.; To better understand the effect climate change played on sea level fluctuations and diagenesis, climate models were run in the NCAR CSM3 program. The Late Carboniferous Earth plate configuration is the geographic base to test two obliquity extremes (21.5° and 24.5°). Results from these simulations suggest a significant shift in the Inter-tropical Convergence Zone (ITCZ) for 21.5° and 24.5° obliquities. This shift indicates that wet sediment cycles in the Desmoinesian of Wyoming are out of phase with those in the Paradox Basin. A strong seasonal shift in wind direction with cyclonic movement occurs in both models in the Paleo-Tethys, suggesting the strong monsoon climate in this region is not driven by obliquity. The maximum solar insolation latitudinal band is expanded in the January/July 24.5° obliquity model. Also, the tropical sea surface temperatures show a broader warm band at the equator in high obliquity models.