Molluscs, palaeoenvironmental variations and biotic responses during Pleistocene and Mid-Holocene highstands along Bonaerensian and Patagonian litoral areas (Argentina)

AGUIRRE, MARINA L.; RICHIANO, SEBASTIÁN; NEGRO SIRCH, Y.; FUCKS, E.

Congreso; IX Congreso Abequa, II CQPLI; 2003

Late Quaternary molluscs from coastal deposits (beach ridges, marine terraces, estuarine facies) of Argentina arepotentially useful to reconstruct palaeoenvironments and palaeoclimates linked to oceanic and atmospheric changes,evolutive and palaeobiogeographic histories, which complement geological studies. Bivalves and gastropods from shellconcentrations suggest differences with modern conditions: 1) salinity displacements (Pleistocene, Holocene;Boaerensian); 2) temperature fluctuations (Pleistocene, Holocene); 3) biotic responses to the Hypsithermal (Holocene).Dominant/exclusive taxa characterize the main areas sampled: 1) Bonaerensian: Conus, Thais, Crassostrea,Anomalocardia, Erodona, Mactra, Pitar (Pleistocene); Littoridina, Diodora, Mactra, Corbula, Tagelus, Raeta, Pitar(Holocene); Patagonian: Tegula, Buccinanops, Protothaca, Clausinella (Pleistocene), Fissurella, Nacella, Pareuthria,Adelomelon, Brachidontes, Aulacomya, Protothaca, Eurhomalea, Mulinia (Holocene). Quantitative variations andlatitudinal shifts are likely responses to climatic cycles and their effects on the marine biotas. The last impact of coldmolluscan taxa from southernmost Atlantic Ocean, initiated through the Malvinas (Falkland) current, probablyestablished the modern biogeographical pattern after ca. 4.5 ka B.P., shown by extinction or retraction of taxa from theAgentine Sea (Triphora, U.rushi, A.avara; N.bisulcata, C.rhizophorae, A.brasiliana). The excellent preservation andlarge amounts of shells reveal intraspecific morphological variability (i.e., Mactra, Littoridina; Brachidontes, Nacella,Tegula) most probably associated with environmental changes (substrate, energy, salinity, temperature).