PRELIMINARY CHEMOSTRATIGRAPHY OF CAVE DEPOSITS IN THE PANTANAL WETLANDS (BRAZIL): INSIGHTS INTO LATE QUATERNARY ENVIRONMENTAL CHANGE

The Pantanal wetlands of lowland west-central Brazil form one of the largest tropical wetland ecosystems on Earth. The wetlands are important from both global and regional perspectives, through their contributions to the carbon cycle and the valuable ecosystem services they provide to local inhabitants. Yet the response of the wetlands to climate change in the Quaternary remains unclear, in part because lake sediment archives have been either temporally short, punctuated by unconformities, or time averaged such that only low resolution paleoenvironmental reconstructions were feasible. The exploration of cave systems on the southeastern margin of the Pantanal has uncovered new archives of environmental change in the form of speleothems and sediment deposits. In this study, we present a novel chemostratigraphy of cave deposits from Jaraguá cave near Bonito in Mato Grosso do Sul state. Cave deposits were trenched in situ, revealing distinct stratification of dominantly red and brown siliciclastic sediments. Organic matter in the deposits was dated using radiocarbon, which revealed that the last glacial maximum, deglacial, and much of the Holocene are captured in the sequence. Cave sediment chemistry was assessed using ED-XRF for major and minor elements, LECO and carbonate coulometry for carbon content, and elemental analysis isotope ratio mass spectrometry for C/N, δ¹³C_ORG and δ¹⁵N_ORG. Preliminary results indicate a continuous record marked by strong variability in major element proxies for mineralogy, organic/inorganic carbon content, and stable isotopic composition of organic matter. These first results indicate that important millennial-scale chemical transitions occur in the record, potentially driven by changes in precipitation, vegetation structure, soil stability, and hillslope erosion. Ongoing work centers on refining the radiocarbon age model and comparison of the preliminary chemostratigraphic data with coeval speleothem results from Jaraguá cave as well as lake sediment-derived proxy records of hydroclimate from other sites in southern and central Pantanal.