USING PALEOSOLS OF PATAGONIA TO RECONSTRUCT MID-CRETACEOUS TO EARLY PALEOGENE CLIMATES (Invited Presentation)

Although the mid Cretaceous-Paleogene is one of the best-documented global “hothouse” intervals in Earth’s history, few continental climate histories exist for this time in the Southern Hemisphere, and fewer still for Patagonia (southern Argentina). In this synthesis, we used paleosols of central-south Patagonia in order to document terrestrial climates at mid-high paleolatitudes for three crucial periods in the past: the mid-Cretaceous, the latest Cretaceous, and the early Paleogene. Following this aim, we performed a paleopedological study of six units, which included macro- and micromorphology, bulk paleosol geochemistry, clay mineralogy, organic carbon concentrations and stable isotope compositions. Also, we use paleobotanical data, including palynology and/or phytoliths, as biotic proxies.

The first period corresponds to the Cenomanian Mata Amarilla and Puesto El Moro formations (⁓55º paleo SL), which are composed mainly of stacked fluvial deposits with intercalated paleosols. These are mainly Vertisols with minor Histosols, Inceptisols and Alfisols, which indicated subtropical temperate and seasonally humid conditions. The second period corresponds to the Maastrichtian Chorrillo Formation (⁓54º paleo SL) that is a pedogenically modified fluvial succession dominated by Vertisols with minor Histosols. These indicate temperate and seasonally humid conditions. The third period corresponds to the early-middle Eocene Las Flores (LFF) and Koluel-Kaike (KKF) formations (~52º paleo SL) and the mid-Eocene Cañadón Vaca Member (CVM) (~51º paleo SL). The LFF is a fluvial succession pedogenically modified with Ultisols that suggest their formation under a tropical and humid climate. The KKF and the CVM are volcaniclastic fluvio-eolian successions bearing Ultisols and Alfisols/Ultisols (KKF), and Aridisols, Inceptisols and Alfisols (CVM). The KKF paleosols indicated temperate and seasonal subhumid/humid conditions, while the CVM ones attest to temperate and seasonally semiarid-subhumid conditions. Biotic proxies are in agreement with interpreted climates and environments for these three studied periods.

Overall, this multiproxy record provide some of the first insights into long-term terrestrial climates during the Cenomanian, Maastrichtian, and early-mid Eocene in the mid-high paleolatitudes of the Southern Hemisphere.