Paleoecology and Geochronology of Uruguayan Coastal Marine Pleistocene Deposits

Abstract

Minimum radiocarbon ages of marine Pleistocene molluscs from Uruguay range from 29,500±600 to 35,500±1900 14C yr B.P. Because knowledge of the marine Quaternary stratigraphy of Uruguay remains inadequate, no attempt is made to correlate between these deposits and recognized lithostratigraphic units. Analysis of the temperature and salinity ranges of the various molluscs suggests the establishment of a poly-euhaline fauna that inhabited waters warmer than present at the same latitude. This is supported by a northward retreat in the recent distribution of Chrysallida cf. C. gemmulosa, Nioche subrostrata, and probably Anomalocardia brasiliana. These marine Pleistocene deposits can probably be correlated with the last interglaciation (oxygen-isotopic substage 5e). At that time the fluvial-marine front of the Rio de la Plata was displaced much further northwestward than previously supposed. Chrysallida cf. C. gemmulosa and Limaria sp. are recorded in Uruguayan Quaternary deposits for the first time.

Late Quaternary continental and marine sediments of northeastern Buenos Aires province (Argentina): Fossil content and paleoenvironmental interpretation

“…and mid-Holocene, the mixing of oceanic and fluvial waters increased the salinity gradient, which caused a northward displacement of the horizontal zonation of the Río de la Plata in comparison with the modern pattern. This claim is supported by the forams and ostracods recovered and in agreement with similar evidence documented for Uruguay and La Plata-Samborombón Bay (Sprechmann, 1978;Aguirre, 1993a;Martínez et al, 2001).…”

“…They also correlate with the Chuy Formation recognized in Uruguay (Nueva Palmira, La Coronilla; Martínez et al, 2001) and the Late Pleistocene transgression studied in Brazil (Suguio and Martin, 1978).…”

“…The SST cannot be assumed to have been much warmer; there is no evidence of latitudinal displacements in comparison with the modern geographical ranges, like those documented for other deposits with similar minimum 14 C ages (e.g. Nueva Palmira and La Coronilla, Uruguay; Magdalena and Bahía Blanca, Bonaerensian area) (Weiler et al, 1988;Chaar et al, 1992;Martínez et al, 2001). No such displacement was documented for the Holocene transgression either.…”

Causes and contrasts in current and past distribution of the white shark (Lamniformes: Carcharodon carcharias) off southeastern South America

“…Attacks to pinnipeds are rare in the San Francisco Bay and attribute it to the low salinity of the bay which may deter the presence of white sharks therein. During the late Pleistocene and Holocene transgre-ssions, salinity was much higher in the Río de la Plata area (Cavallotto et al, 1999;Martínez et al, 2000) what explains the presence of C. carcharias in the present coast of the freshwater sector of the Río de la Plata (Cione & Torno, 1988).…”

Late Quaternary molluscan assemblages from the coastal area of Bahía Bustamante (Patagonia, Argentina): Paleoecology and paleoenvironments

“…Studies performed on similar deposits of the SW Atlantic margin are available for the Bonaerensian littoral (Aguirre, 1993a(Aguirre, ,b, 1996, some areas along the Patagonian coasts (Feruglio, 1932;Aguirre and Codignotto, 1998;Gordillo, 1998;Pastorino, 2000;Aguirre, 2002Aguirre, , 2003, and other coastal deposits in South America, such as Guyana (Altena, 1971(Altena, , 1975, Uruguay (Martínez et al, 2001), andBrazil (Forti Esteves, 1974). Along the Pacific South American coast, most detailed work has been devoted to Peru (e.g.…”