SEDIMENTOLOGICAL ANALYSIS OF THE STONEMAN LAKE, AZ, CORE: IMPLICATIONS FOR LONG-TERM QUATERNARY CLIMATE CHANGE IN THE SOUTHWEST

Analyses of long, high-resolution lacustrine paleoclimate records preserved within lake stratigraphy of the American Southwest have the potential to illustrate long-term continental climate variability and past conditions relevant to current and projected climate changes including increased aridity and drought. AMS radiocarbon dates, tephrochronology, and paleomagnetic age constraints on two sediment cores from the hydrologically-closed Stoneman Lake in Central Arizona (STL-STL14-1A & 1B) suggest a continuous history of sedimentation from the Early Pleistocene (~1.2 Ma) to present. Thus, the core represents a rare and valuable opportunity to study long-term paleohydrological variation over many glacial cycles. Full-core sedimentological analysis was accomplished on the composite of cores 1A and 1B using CoreWall software, smear slides, and x-radiographs, and focuses on the degree of lamellae preservation as a proxy for lake depth. Sedimentologic analyses are accompanied by core scans of magnetic susceptibility, density, color reflectance, XRF elemental abundances, and a low-resolution pollen scan. Initial observations indicate a strong correlation between the preservation of laminations, spruce and fir pollen assemblages, increased planktic diatoms relative to benthic, and lower Ca:Ti_XRF ratios. As Stoneman Lake has no external drainage, these relationships are indicative of a deeper lake during colder glacial conditions due to (1) increased regional precipitation from southward deflection of the polar jet stream, and (2) decreased evaporative loss. At least ten coincidences of obviously laminated sediments with boreal pollen assemblages exist in the core that has likely experienced ~20 glacial episodes of varying intensities over its history. This suggests that not all glacial episodes were as cold and wet as the most recent glacial climate. Sediments deposited during interglacial periods are bioturbated to massive, containing pine and juniper pollen assemblages and higher Ca:Ti_XRF values. Sedimentology and stratigraphy of Stoneman Lake sediments suggest a strong link between global climate forcing and local hydrology over much of the Quaternary.