PALEOSOL-BASED PALEOCLIMATE RECONSTRUCTION OF THE PALEOCENE EOCENE THERMAL MAXIMUM, NORTHERN ARGENTINA

The paleoclimatic changes during the Paleocene-Eocene Thermal Maximum (PETM) have been studied in both continental and marine strata, mostly in the Northern Hemisphere. Most studies of continental strata determined that temperature increased approximately 4-8°C above mean annual paleotemperatures. Fewer paleoclimate reconstructions have been completed on continental strata spanning the PETM in the Southern Hemisphere. In this study, paleosols in the Salta Basin, northern Argentina, were described in the field, sampled and analyzed in the laboratory to better understand the paleoclimatic changes that occurred during the PETM in the Southern Hemisphere. Paleosol samples were collected from the Maella, Maiz Gordo and Lumbrera Formations. Previous studies on these formations used palynostratigraphic, mammalian biostratigraphic and paleomagnetic data to place the Maella and Maiz Gordo Formations in the final epochs of the Paleocene, and the Lumbrera Formation in the early Eocene. Carbon isotope data from the paleosols we sampled record the globally-recognized PETM Carbon Isotope Excursion (CIE), which provides better chronostratigraphic control for these sections. Carbon isotope data from pre- and post-PETM paleosol carbonate nodules, and organic matter in PETM boundary paleosols, indicate the presence of multiple releases of isotopically light carbon into the ocean-atmosphere system before, during, and after the boundary excursion.

Various weathering indices and their associated paleoclimatic proxies were used to reconstruct paleoprecipitation rates and paleotemperatures of the Southern Hemisphere from before and after the PETM. The chemical index of alteration minus potash (CIA-K) and CALMAG were two precipitation proxies applied to determine paleoprecipitation rates. Two paleotemperature proxies were also used including the paleothermometer ratio and the paleosol weathering index (PWI). Closest to the PETM, paleoprecipitation proxies show an approximately 500 mm increase in annual precipitation rates and a temperature increase of approximately 5°C from pre-PETM values.