Print this pageClimate Variability in Desmoinesian Carbonate Cycles Identified by Stable Isotope Trends, Variable Paleosols, Diagenetic Patterns, and Stratigraphic Modeling
SMITH-ROUCH, LINDA S.
Climate variability among glacial periods of Desmoinesian high-frequency platform carbonate cycles may be preserved in paleosols, stable isotope trends, and vadose diagenesis. The study evaluated lower Ismay Stage, Paradox Basin, SE Utah, outcrop sections near the Goosenecks area along the San Juan River. Within the Ismay Stage silcretes and calcretes alternately form on subaerial exposure surfaces. Subaerial exposure surfaces develop during the same system tract (LST) as basin evaporites precipitate, thus evaporite cycles should mimic the similar climate variations as platform silcretes or calcretes (relative humidity, air temperature, length of seasons, and etc.). Silcrete formation may indicate different relative humidity and pH values among glacial cycles from calcrete horizons. The depth of vadose zone diagenesis from each subaerial exposure surface provides a close proxy to minimum sea-level fall for each glacial period (LST). Stable isotope excursions from microcomponents identify indiscrete exposure surfaces that show little diagenetic overprinting with a negative carbon shift and small positive shift in oxygen. All cycles do not show the same shift, this may be due to variable microbial activity in soils, subsequent diagenetic overprinting, or climate. Stratigraphic modeling provides a dynamic tool to quantify and test values and assumptions obtained from collaborative studies (e.g. variations in sea-level amplitudes, time duration of systems tracts, evaporite precipitation rates, track platform margin/sea-level position (onlap) to monitor vadose zone depth and diagenetic overprinting from all cycles).