Abstract

MARTINEZ, Sergio et al. Molluscan assemblages from the marine Holocene of Uruguay: composition, geochronology, and paleoenvironmental signals. Ameghiniana [online]. 2006, vol.43, n.2, pp.385-397. ISSN 1851-8044.

Dates of marine Holocene molluscs from Uruguay (Villa Soriano Formation) range from 6849 to 1858 cal. years BP. There are no significative gaps among the different ages obtained, with the exception of the interval 2276-2830 calculated years BP. Two kinds of concentrations are distinguished: autochthonous, for which a low energy depositional environment is inferred, and parautochthonous, deposited in foreshore and nearshore high-energy environments. Results of different types of multivariate analyses on presence-absence and abundance data show that only three localities are clearly differentiated from the others. The discrimination of two of them (Arazatí, Las Cañas) is explained by the presence of only one or two species, but the third (Punta Rasa) is the only one where characteristic species of rocky or hard substrates are undoubtedly represented . Analyses of salinity and temperature ranges of the various mollusc assemblages suggest a displacement of the Rio de la Plata estuary about 300 km westwards along the Uruguayan coast from its present position, and the presence of warmer waters than those found today at the same latitude. With the exception of the currently northwards displaced Anomalocardia brasiliana (Gmelin), Marshallora nigrocincta (C.B. Adams), Nioche subrostrata (Lamarck), Bulla striata Bruguìere and Miralda sp., all species are present today at the Uruguayan coast.

Keywords : Uruguay; Holocene; Paleoecology; Shell-beds; Mollusca; Bivalvia; Gastropoda.