PRELIMINARY RESULTS OF A PALEOCLIMATE-PALEOFIRE RECORD FROM THE EARLY PLEISTOCENE OF THE UNCOMPAHGRE PLATEAU (ROCKY MOUNTAINS, COLORADO)

Many recognize that ongoing climate warming affects hydroclimate and, by extension, fire regimes, especially in arid regions of, e.g. the western U.S. Accordingly, an increasing number of studies have reported paleofire records from, in particular, Holocene and late Pleistocene archives across various regions of the arid West. Here, we report on an effort to investigate paleoclimate and paleofire from a time and region rarely preserved—an upland lake of the early Pleistocene, prior to the Mid-Pleistocene Transition. We recovered core from an early Pleistocene (~1.4-1.3 Ma) lake buried within the subsurface of Unaweep Canyon, an upland system of the Uncompahgre Plateau in western Colorado. After spudding at 1921 m elevation and destructively drilling to 200 m subsurface (1721 m elevation above sea level), we cored nearly 150m of a paleo lacustrine system. The age (~1.4-1.3 Ma) is based on cosmogenic-nuclide dating of a previous, correlative section. The sediment comprises predominantly mass flow deposits with grain sizes ranging from sand to mud. Over the ~147m of the lacustrine section, prominent color variations occur, from vibrant reds and ochres (oxidized) to drab olives and dark gray (reduced). These color variations correspond to changes in palynological assemblages that indicate two cold-warm variations-- probable glacial-interglacial cycles—with warm represented by the drab colors, and cold by the oxidized colors. Although charcoal particles occur throughout the cored section, charcoal abundance and frequency increases in the olive-grey intervals, seemingly recording increased wildfire activity and associated mass flow events during interglacials. We will integrate additional palynological analyses with analyses of charcoal, carbon-nitrogen-sulfur, organic biomarkers (glycerol dialkyl glycerol tetraethers), x-ray fluorescence (XRF) elemental geochemistry, and magnetic susceptibility to more comprehensively reconstruct the early Pleistocene climatic and paleofire history of this region of the Rocky Mountains.