CLIMATE HISTORY IN THE ALTIPLANO BASIN: A REFLECTION OF SURFACE UPLIFT OR CLIMATE CHANGE?

The δ¹⁸O values of sedimentary carbonate have been used to reconstruct the paleoelevation of the Andean plateau. Recent climate modeling studies have questioned the extent to which surface uplift history based on stable isotopes in the Andes are a reflection of regional climate change. The relative roles of climate change and surface uplift in generating the δ¹⁸O values of sedimentary carbonate in intermontane basins can be evaluated using approaches aimed at teasing out the climate signal. Specifically, records of surface paleotemperature allow for paleoelevation reconstruction independent of the δ¹⁸O values of carbonate, and records of paleo-aridity allow for reconstruction of climate that can affect the δ¹⁸O values of carbonate. We use C-O clumped isotope thermometry to estimate paleoelevation of the northern and southern Bolivian Altiplano to show that rapid, large magnitude surface uplift occurred in the late Miocene in the north and middle Miocene in the south (Smith et al., this session). We then compare these elevation histories to the record of local aridification, based on the δ¹³C values of paleosol carbonate and fossil tooth enamel. The δ¹³C values of fossil teeth provide insight into the vegetation type that can be related to the δ¹³C values of paleosol carbonate to quantify plant respiration rates and, by extension, water-stress conditions. By comparing elevation history to the aridification history, we examine whether δ¹⁸O records better reflect inferred paleoelevation or the amount of rainfall in the northern and southern Altiplano. We find that surface uplift histories, based on paleotemperature estimates, correspond with pronounced aridification, despite the unique timing of surface uplift recorded in the north versus the south. In the northern Altiplano, δ¹⁸O values of paleosols agree with paleoelevations based on paleotemperatures. In the southern Altiplano, relatively positive δ¹⁸O values for paleosol carbonate result in lower paleoelevation estimates than paleotemperature-based elevation estimates, which can be ascribed to greater aridity in this region. The observation of concomitant surface uplift and aridification, despite the different timing of surface uplift between the north and south, suggests that climate change resulted from surface uplift.