Late Pleistocene Southeast Amazonia Paleoenvironmental reconstruction inferred by bulk, isotopic and molecular organic matter. Saci lake-Para-Brazil

Tuesday, 16 December 2014
Gabriel Souza Martins, UFF Federal Fluminense University, Niteroi, Brazil, Renato Campello Cordeiro, Universidade Federal Fluminense, Niteroi, Brazil, Bruno Turcq, IRD, Bondy, France, Luciane Silva Moreira, Universidade Federal Fluminense, geochemistry, Niteroi, Brazil, Ioanna Bouloubassi, CNRS, Paris Cedex 16, France and Abdelfettah Sifeddine, IRD Bondy, Bondy Cedex, France
Bulk, Isotope and biolomecular analysis supported by 22 14C AMS dates, allowed the reconstruction of environmental changes during the last 35 000 years BP in the Southeast Amazonian basin. A terrestrial origin has been inferred for the odd carbon-numbered long-chain (>C27) n-alkanes. The entire n-alkane δ13C range between -31.7‰ and -36.8‰, which is the isotopic range occupied by C3 vegetation. The C29:C31 ratio shows that a gramineae contribution is higher during the Pleistocene than in Holocene. The n-alkanes concentration decrease between 32 000 – 18 000, suggesting a increase in arid conditions. The ACL index confirm this interpretation showing high values due the Pleistocene linked to more hydrological stress. A shift in the abundance of n-alkane and isotopic values are observed across the late Pleistocene glacial-Holocene interglacial climate change, suggesting a climate-induced vegetational change. During the middle Holocene the n-alcanes values decreases indicating rain forest regression accompanied by increase in the ACL values confirming the dry climate conditions. Comparison with other South American records, our record indicates regression/expansion of the rain forest linked to the South American System monsoon activity since 35 kyrs.