Pleistocene and Holocene interglacial molluscan assemblages from Patagonian and Bonaerensian littoral (Argentina: SW Atlantic): Paleobiodiversity and Paleobiogeography

AGUIRRE M; DNATO M.; RICHIANO S.; FARINATI E.

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2011 vol. 308 p. 277 - 292

0031-0182

Our analysis of palaeobiodiversity and palaeobiogeography of Quaternary molluscan assemblages provide information on the last coastal scenarios in the SW Atlantic. We present patterns of species richness, areas of endemismand between areas relationships based on records (721 taxa) fromArgentina and northwards in South America (Surinam, Brazil, Uruguay), including Pleistocene, Holocene and modern sites (48 localities). In Argentina, our data since the Mid-Late Pleistocene (MIS11-1; ca. 400 ka B.P. to present) suggest environmental changes linked to sea-level and climatic fluctuations, large enough to alter benthic associations (compositional, geographical variations, including a few extinctions). The southwards decreasing diversity trend for modernbivalves (mostly infaunal taxa) and gastropods (mostly epifaunal taxa), from Surinam to Tierra del Fuego, responds mainly to latitudinal SST, salinity barriers, hydrodynamic forces (rivers and shallowcurrents):minima peaks fit with local estuarine and marginal marine sites influenced by the Río de la Plata plume; highest peaks with fully marine, warmer waters influenced by the Brazilian Current (Bonaerensian sector); a similar trend applies for the Holocene; Pleistocenemaxima peaks in Patagonia belong toMIS11 andMIS5 highstands (warmer than today).Multivariate (Cluster Analysis, CA;MinimumSpanning Trees superimposed to Principal Coordinates Analysis, PCO) and cladistic (Parsimony Analysis of Endemicity, PAE) methods showed congruent relationshipsbetween localities, discriminating marginal from open marine environments, but PCO combined with PAE was most advantageous for our area and dataset (382 gastropods, 339 bivalves; 29 Pleistocene, 28 Holocene and 35 modern sites) allowing objective, quick comparisons. Shifts of areas of endemism during the Holocene and Pleistocene relatewith SST and salinity changes; amore homogeneousMid-Holocene (ca. 7?5 kaB.P.) scenario, of regionally increased salinity and higher (ca. 2 °C) SST, defined the Bonaerensian and northern Patagonian sectors, facilitating southwards shifts of bivalve and gastropod taxa; for Patagonia a colder Pleistocene scenario south of SAO is documented by Tegula atra (exclusive Pleistocene coldwater species extinct in the SWA), probably a signal of post-LGM palaeoceanographical changes in the Mar Argentino.