A HIGH RESOLUTION PALEOCLIMATE RECORD DURING THE PAST 80,000 YR AT LAKE CHALCO NEAR MEXICO CITY

Paleoenvironmental conditions spanning the past ca. 80,000 yr can be established from high-resolution profiles of geochemical proxies in sediment cores taken from Lake Chalco, a closed basin lake in the Valley of Mexico near present-day Mexico City in 2008. Optical and radiographic images of the cores form a basis for stratigraphic analyses and for correlation between boreholes, which provided a composite core for the study. Geochemical profiles were produced from x-ray fluorescence (XRF) scanning on millimeter scale. Elemental data from Ca, Fe, and Si proved useful for the understanding of paleoclimatic conditions at Lake Chalco and the greater neotropics. Fe correlates with magnetic susceptibility and thus records the frequency of volcanic eruptions within the Trans-Mexican Volcanic Belt. It also allows establishment of an age model built by developing stratigraphic ties to magnetic susceptibility records in previously studied well-dated cores. Si:Ti functions as a proxy for diatom abundance and productivity throughout the record. Since Lake Chalco is essentially a closed basin, sedimentary calcite records delivery of dissolved Ca to the system with enhanced precipitation. Therefore, Ca data is evidence that the lake’s sediment record has been influenced by interstadials/stadials, as well as, millennial scale variability, such as Dansgaard Oeschger and Heinrich events.