MONSOON AND ARID CLIMATE FLUCTUATIONS FROM THE UPPER PENNSYLVANIAN PARADOX BASIN, SE UTAH

Desmoinesian carbonate-evaporite sediment cycles from the Paradox Basin, SE Utah record three scales of climate change, 1) less than 10 ky, 2) precession, and 3) maximum obliquity. High frequency cycles were identified from four paragenetic sequences in the Lower Ismay Zone and changes in the % silt within platform carbonates (Akah, Desert Creek, Ismay, and Honaker Trail Zones) from the Honaker Trail outcrop. Variations in bromide concentrations within halite beds from the Gibson Dome core evaporite cycles recorded precession scale climate change. Obliquity and lower order cycles were recorded by TOC, HI and OI values from dolomudstone shales covering both carbonate and evaporite cycles.

Four Lower Ismay micro-profiles segregate into four basic types by fabric, texture and cements (inferred climate). 1) Marine oolitic grainstone cemented by shallow meteroic mosaic spars. 2) Lagoonal micrite clasts by meteroic dissolution breccia and late blocky spar cements. 3) Wackestone to packstone with a 1 to 1.5 m section of discontinuous karst lenses with geopedal sediment, botryodial and meniscus cements. 4) Intertidal packstone with spar filled fenestral vugs, capped by a thin caliche with some quartz cements overlain by a thin silcrete dominated by red angular rip up breccia and micrite clasts. The percent silt calculated within platform carbonates identified periods of high aeolian input signifying drier climates. Aeolian quartz silt was derived from large sand ergs in Utah and Wyoming. During short monsoon periods feldspathic silts were sourced from the Uncompahgre Uplift and delivered into the basin by rivers and runoff from the northeast. Bromine concentrations in basin halite beds identify periods of monsoon development (low %), sea level transgression (med. high %), and basin drawdown (high %). Shales from Gibson Dome core record HI > 300 in cycles 3,4,7,15 indicating algal lacustrine environments. High TOC wt % indicate cycles with stronger terrestrial organic matter sourced from wetter periods as runoff from surrounding highlands.