A LONG PLEISTOCENE PALEOCLIMATIC AND PALEOENVIRONMENTAL RECORD FROM STONEMAN LAKE, ARIZONA

We present here results from a multi-proxy analysis providing a long paleoclimatic record from Stoneman Lake, Arizona that shows significant glacial and interglacial variability over the last million years. Stoneman Lake is a small, circular depression on the southern Colorado Plateau in central Arizona that formed by a collapse in late Cenozoic basalts. Two parallel lacustrine sediment cores (80 m and 35 m deep) drilled 20 m apart are combined to form a composite core. A Bayesian age model for the core is derived from 15 radiocarbon dates and tephrochronology of ashes from the Lava Creek B and multiple Long Valley, California, volcanic eruptions including the Bishop Tuff. Middle to late Pleistocene glacial maxima are represented by deep lake deposits with well-preserved bedding, boreal pollen taxa (i.e., Picea), and lower density and MS. Interglacial periods are associated with shallow-water deposits characterized by banded-to-massive siliciclastic material, some authigenic calcite, the alga Phacotus, and higher density and MS. Prior to the mid-Pleistocene transition (MPT), smaller-amplitude changes in the lake environment suggest milder glacial conditions compared to those of the middle and late Pleistocene. This suggests that southwestern North America saw a significant intensification of glacial conditions (colder, wetter) following the MPT. A detailed pollen analysis correlated with sedimentary facies analysis shows significant climate and ecosystem variability between glacial and interglacial periods and also shows significant variability within post-MPT glacial periods and post-MPT interglacial periods. Glacial periods are characterized by higher percentages of arboreal pollen and interglacials by higher percentages of non-arboreal pollen and more abundant charcoal, however, the individual taxa that make up these sums vary from glacial (interglacial) stage to glacial (interglacial) stage. This variability is likely due to a combination of different climatic forcing factors (local insolation variability, atmospheric CO₂) and antecedent plant community conditions.