MEXIDRILL, THE BASIN OF MEXICO DRILLING PROJECT: OVERVIEW AND INITIAL GEOCHEMICAL RESULTS

MexiDrill, the Basin of Mexico Drilling Program recovered a ~400 kyr lacustrine record of subtropical North American environmental change at a site adjacent to Mexico City. This record has societal relevance as it provides context for consideration of changing water balance in a densely populated, water-stressed region. Paleoclimatic reconstructions will enhance our knowledge of long-term natural climate variability in the North American subtropics, and its relationship to changes at higher latitudes. The site lies at the northern margin of the Intertropical Convergence Zone (ITCZ) where modern precipitation amounts are influenced by sea surface temperatures in the Pacific and Atlantic Basins. In addition, its sediments have recorded pre-Holocene volcanic history; knowledge of the magnitude and frequency relationships of the area’s explosive volcanic eruptions will improve risk assessments of future activity. Explosive eruption deposits will also be used to provide the backbone of a robust chronology necessary for full exploitation of the paleoclimate record. Here we will provide an overview of the project, and some initial results. We have completed XRF core scanning of a 350 m composite section of core from four holes, which provides data on the major element inorganic composition of the sediments. XRF scanning allows us to delineate aridity (Ca from preservation of calcium carbonate); estimate diatom productivity (Si/Ti); characterize tephras; evaluate changing sediment provenance (K/Ti); and estimate accumulation rates of terrigenous materials (Al and Ti). Our preliminary interpretation indicates that glacial intervals (MIS 2, 6, and 8) are periods of wetter conditions, but that humid conditions were less marked during MIS 2 than earlier glacial periods.