Origin of Jurassic Carbonate Nodules in Southeastern Wyoming

摘要: The Morrison Formation of the Western United States is famous for dinosaurs and other fossils that have been excavated from its beds. It was deposited during Late Jurassic in a semi-arid, savannah-like environment. remarkably extensive, with outcrops across eight states; however attempts to correlate between Wyoming Colorado Plateau proven difficult. goal this research determine origin carbonate rocks beds exposed on Spring Creek Preserve southeastern Wyoming, assess their potential lithostratigphic correlations. A wide range techniques were employed, ranging macroscopic observations field geochemical isotopic analyses. Field relationships macro- microtextures nodular calcareous units are consistent mineral deposition freshwater lacustrine muds development palustrine limestones, nodules calcrete as micritic desiccated. Strontium isotope data suggest developed alteration nearby carbonates little exogenous input. thickness level below mid-Morrison unconformity at 42 m observed localities suggests an extended period subaerial exposure desiccation study area middle time. If presence these found throughout result synchronous regional lake-level lowstand, it plausible horizon correlates Mid-Morrison paleosol identified Utah Colorado. strontium composition belemnite underlying Sundance corresponds Oxfordian age (161-157 million years ago) unit places maximum Reserve area.