Paleoecology significance of Late Quaternary molluscan faunas of the Bahía San Blas area, Argentina

M.P. CHARÓ, S. GORDILLO, E.E. FUCKS

QUATERNARY INTERNATIONAL

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2013 vol. 301 p. 135 - 149

1040-6182

Late Quaternary marine deposits in the San Blas Bay region (Buenos Aires, Argentina) can be seen in beach ridges and tidal plains which contain the remains of organisms, mainly mollusk shells. The main purpose of this study is the characterization of faunal assemblages existing in the region during this period, and the assessment of faunal changes related to changes over time and to local environmental factors. To this end, 26 sites were analyzed (11 Pleistocene sites, 7 Holocene sites and 8 Modern sites) and a total of 50 taxa (27 bivalves and 23 gastropods) were recorded for the area, with marine species predominant over estuarine species. Within the gastropods, epifaunal species and carnivores are predominant, with a lower proportion of herbivores and filter feeders, while bivalves are mostly infaunal and suspension feeders. Pleistocene fauna is characterized by the high quantity of mollusks in rocky environments, and is different from the fauna of the Holocene due to the presence of the warm-water Crassostrea rhizophorae, which is currently displaced to lower latitudes. Within the Modern fauna there are 4 taxa, Mesodesma mactroides, Solen tehuelchus, Barnea lamellosa and Crassostrea gigas (a species introduced by humans), which are not present as fossils, but Mesodesma mactroides is found in Holocene shell middens from the area. According to the multivariate analysis results, the sites can be divided into two groups: high energy deposits (storm ridges) and low energy deposits (tidal plains), regardless of their age. Based on these results, it was concluded that the faunal variations in the area studied are in part linked to faunal changes that took place in the Pleistocene-Holocene-Modern period, probably due to changes in temperature (e.g. Crassostrea rhizophorae); but most variations are associated with the presence of sub-environments within the area that have different energy levels; this would facilitate the presence of different taxa in accordance to the ecological requirements of each species.