Late Quaternary environmental changes in San Matías Gulf (Patagonia, Argentina): a multi-proxy approach based on Amiantis purpurata (Lamarck) (Bivalvia)

BAYER, M.S.; GORDILLO, S.; MORSAN, E.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

International Paleontological Association

intensified in the last few years because such interdisciplinary research provides strong evidence for environmental reconstructions and interpretations. In this work several proxies, including taphonomy, paleoecology, paleobiogeography, morphometry and sclerochronology, were used simultaneously to evaluate whether Amiantis purpurata from the San Matías Gulf (northern atagonia, Argentina) records environmental changes during the late Quaternary. Extant and fossil A. purpurata shells from different localities from Pleistocene MIS5e, mid-Holocene and modern times were analyzed by integrating the above proxies. Different taphonomic attributes (articulation, R-L valves ratio, fragmentation, abrasion and teeth preservation), size and shape, historical-geographical, and stable isotopes (δ18O and δ13C) were considered in this interdisciplinary analysis. Our data indicated that the southernmost fossil record of A. purpurata was that of the San Matías Gulf, being also the most abundant taxon in Pleistocene, Holocene and modern molluscan assemblages. Pleistocene shells were smaller and exhibited different shape with respect to Holocene and modern shells,probably due to changes in primary productivity (i.e., variation of quality and nutrient availability)through the Late Quaternary within this gulf. Valves were well preserved (100% original aragonite), but they showed variations in intensity of the taphonomic attributes which was associated with local conditions of each site. Oxygen and carbon isotope profiles suggest climate seasonality, which also was variable over the time period considered; this variation could be associated with changes in sea surface temperature, salinity and/or water circulation. This multi-disciplinary approach showed that A. purpurata exhibited variations between modern and fossil shells mainly associated with changes in substrate, seasonality and water paleocirculation, although local and global events such as the Last Glacial Maximum, San Matías Gulf´s configuration (12,000 yrs. BP) and Holocene Climatic Optimum may also have played a role. Therefore, A. purpurata is a good indicator to reconstruct the late Quaternary paleoenvironment of San Matías Gulf. The strategy of multi-proxy analysis was very useful to strengthen the interpretation of taphonomic, paleobiogeographical,paleoecological, paleoclimatic, and morphometric variations recorded in mollusks shells in relation to environmental changes that occurred during the Quaternary. [Part of the Doctoral Thesis of S.B.].