Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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Multi-Proxy Paleolake Reconstruction Of Summer Lake, Oregon

Abstract

The unique sensitivity to changes in temperature and precipitation recorded in the lakes of the Great Basin can be used to reconstruct regional paleoclimate, which can be tied to global changes in climate. For example, shallow lake levels in the western Great Basin are hypothesized to coincide with colder regional air temperatures because of lack of evaporation from oceanic sources. Such colder temperatures are evident in distinct sediment intervals in a core from Summer Lake, OR predicting low lake levels in those intervals. Cold water Ostracode species Cytherissa lacustris appears in multiple sections in the BB3-I sediment core from Summer Lake, OR. This interval had previously been attributed to stadial events in between interstadial events IS#8, #7, and #6 occuring during the Late Pleistocene throughout the northern hemisphere from ∼42-32 ka, as defined by the Greenland ice core stratigraphy. This interval of core was continuously sampled from ∼9-13 meters for grain size, carbon-nitrogen ratios, and inorganic carbon analyses to infer paleoclimate through lake level reconstructions. This interval was chosen because it includes a characteristic low intensity feature in the Earth's magnetic field that can be correlated to a similar feature in the Greenland Ice Core Project (GRIP) through cosmogenic nuclide concentrations. As predicted, the appearance of the cold water species, C. lacustris, coincides with low lake indicators including an increase in grain size, a decrease in carbon-nitrogen ratios (i.e., infrequent high discharge events), and an increase in total inorganic carbon.