Holocene molluscan variations and palaeoclimate in the coastal area of Argentina
by
Marina Aguirre
Facultad de Ciencias Naturales y Museo, Paseo del Bosque 1900, La Plata, Argentina
Coauthors: Mariano Donato (LASBE, Museo de La Plata, La Plata, Argentina)and Enrique Fucks (INGEA; Facultad de Ciencias Naturales y Museo; La Plata, Argentina)

In Argentina variations in Quaternary molluscan assemblages are recorded between the Río de La Plata and Tierra del Fuego (Buenos Aires, Río Negro, Chubut, Santa Cruz provinces) where several sea-level highstands were preserved (MOIS11/9 to MOIS1) testified by abundant shell concentrations (mainly bivalve and gastropod benthic taxa). The Holocene coastal deposits, ridges and marine terraces (at + 3-12m a m.s.l., 3-8 ka B.P.) and estuarine facies poorer in molluscan content, are better preserved and dated. Their molluscs are potentially useful to reconstruct palaeoenvironments and palaeoclimates, palaeobiodiversity, evolutive and palaeobiogeographic histories, complementing geological and geochronological approaches. A review and update, including more than 120 taxa from 28 localities, and results from quantitative comparisons (Cluster Analysis, Principal Component Analysis, Parsimony Analysis of Endemism), reinforce that most taxonomic and distributional differences biotic responses to rapid climate changes. Some examples are: 1) retractions or extinction from the modern Agentine Sea of several taxa (Triphora sp., Urosalpinx rushi, Anachis avara; Noetia bisulcata, Crassostrea rhizophorae, Anomalocardia brasiliana); 2) the northern assemblages (Mar Chiquita, Bahía Blanca, Puerto Lobos) are richer and more diverse than southwards (Camarones, Bahía Bustamante, Golfo San Jorge, Patagonia), but less diverse than in southern Brazil or Surinam; 3) in addition to the latitudinal trend, the palaeobiodiversity was lower in assemblages younger than ca. 4.5 ka B.P. (post-Hypsithermal cooling effect). This together with stable isotope variations of selected shells (where available) reinforce SST and precipitation levels as the main controlling factors for the differences observed. Overall most probably linked to shifts in oceanic and atmospheric circulation patterns (South Atlantic Anticyclonic Centre, shallow water currents, precipitation patterns) with consequences for the palaeobiogeographic history of many taxa since ca. 7-6 ka B. P. (Bonaerensian area) or 8-7 ka B. P. (Patagonia). Intraspecific morphological variations of several abundant taxa (Mactra, Littoridina; Brachidontes) most probably respond to local environmental changes (substrate, energy, salinity, and secondarily temperature fluctuations).

Date received: November 26, 2004

Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caod-55.