The pedosedimentary evolution and chronology of Tortugas, a Late Quaternary type-site of the northern Pampa, Argentina

Abstract

New micromorphological, magnetic susceptibility, geochemical and geochronological data have been collected from Tortugas, a key Late Quaternary type-site of the northern Pampa (Argentina), thus enabling the detailed reconstruction of the pedogenic and sedimentary history of this loess–paleosol sequence. Paleosols developed in the Ceres Formation and the overlying lower member of the Tezanos Pinto Formation retain evidence for leaching, bioturbation and particularly clay translocation processes being dominant. Both paleosols are truncated: evidence for water sorting and sediment reworking, as well as continued bioturbation and redistribution of carbonates, suggests that intervening depositional phases were complex. The previously recorded ‘Hypsithermal Soil’ developed in the upper member of the Tezanos Pinto Formation has similar characteristics to the buried paleosols, yet does not appear to have been truncated at this site and is only covered by a thin layer of sediment (San Guillermo Formation). This latter unit has been pedogenically welded onto the ‘Hypsithermal Soil’, thus creating the present-day surface soil (complex). A series of optically stimulated luminescence dates from throughout the sequence provide a stratigraphically consistent chronological framework (ca. 1–150 ka) for the pedosedimentary reconstruction, yet conflict with the previously reported thermoluminescence-based chronology for the site and region (ca. 1–90 ka).