THE STONEMAN LAKE DRILLING PROJECT: PRELIMINARY RESULTS ON PALEOENVIRONMENTAL CHANGE IN CENTRAL ARIZONA OVER THE LAST ~ 1.5 MILLION YEARS

Long continuous cores of lake sediments provide enormous potential for interpreting paleoenvironmental history in the American Southwest, where few such records have been analyzed. Our research group has performed preliminary analyses from two long sediment cores, drilled in 2014, from Stoneman Lake, Arizona, totaling ~73m of record. We subsequently collected Initial Core Description data at NSFs LacCore facility. Initial sedimentary, pollen and chronologic data suggest that this record may be unique in North America. We argue that the core records a continuous paleoenvironmental change in the Southwest for the last ~1.5 Ma, covering at least 20 glacial/interglacial cycles, spanning beyond the mid Pleistocene Transition (MPT), and including one or more “superinterglacials” that may be analogs for natural future climate change. The centerpiece of our project is its innovative and collaborative approach, blending expertise in sedimentology, paleoclimatology, paleoecology, geochronology, magnetostratigraphy, stable isotopic geochemistry, organic paleothermometry, scanning XRF geochemistry, sediment biochemistry, hyperspectral analysis and climate modeling. By combining these diverse data sets, we strive to produce a long-term record of climate change. We have defined four basic facies including well-laminated diatomaceous silty clays, thinly bedded silty clays, massive clays with silt, and massive silty clays with bioturbation. Repeated alternations occur between glacial laminated facies and interglacial massive/bioturbated sections. Though our initial pollen sampling has provided a discontinuous paleovegetation framework for the entire core, we include here more detailed data for the 27 m – 43 m section, where we have identified major tephras, and which we consider documents glacial/interglacial cycles from MIS-15 – MIS-27. Spruce, fir, Douglas-fir, SW white pine, often with pelagic algae – boreal taxa – occur in most of the laminated sections of the core, and we interpret these as glacial-like conditions at the site. Combinations of lower elevation pollen types (juniper, pinyon pine, saltbush, sunflower family, etc.) are concentrated during periods we interpret as interglacials. Many of these units also contain ponderosa pine pollen, which dominates forests near the lake today.