Comparación de aspectos tafonómicos y paleoecológicos de bivalvos dominantes en depósitos litorales del Cuaternario tardío del noreste y sudeste bonaerense (Argentina).

AGUIRRE M.L., RICHIANO S., FARINATI E. FUCKS E.

La Plata

Congreso; IV Congreso Argentino de Cuaternario y Geomorfología, XII Congresso Da Asociacao Brasileira de Estudos Do Quaternario, II Reunión sobre el Cuaternario de América del Sur; 2009

Asoc. Arg. de Cuaternario y Geomorfología, Univ. La Plata, Asoc. Brasilera de estudios del Cuaternario

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES; mso-fareast-language:ES;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Marine Late Quaternary skeletal deposits between Bahía Samborombón and Bahía Blanca (Buenos Aires Province) provide excellent examples of molluscan parautochthonous concentrations. Taphonomical and palaeoecological aspects of dominant bivalves, Mactra isabelleana d´Orb. and Brachidontes rodriguezi (d´Orb.), with different shell structure, habitats and life habits, represent useful palaeoenvironmental tools, allowing to compare the timing of removal from the taphonomically active zone (TAZ) and some physical parameters prevalent at the time of deposition. About 5,400 molluscan shells were sampled in supratidal, intertidal to shallow-subtidal beach deposits: beach ridge sands and tidal flat facies of Pascua Formation (Late Pleistocene; MIS, Marine Isotope Stage, 5e ?), Las Escobas Formation and Destacamento Río Salado Formation (Mid-Holocene; MIS1) in Bahía Samborombón and from sand shell ridges of the Holocene transgression at Bahía Blanca estuary. The main taphonomical attributes (articulation, fragmentation, abrasion, colour, encrustation, bioerosion) classified as three alteration grades (0, good; 1, fair; 2, poor; for articulation only two grades were disntinguised), quantified and plotted as bar plots and ternary taphograms, allow repeatable regional comparisons. The taphonomical results of both taxa, owing to differences in their morphology, ecological requirements and life modes/habits, are able to provide reliable palaeoenvironmental information both in high and low energetic facies. Transport and time of exposure are the main controlling factors for the distinction between shells of Mactra from tidal flat facies (Bahía Samborombón) regarding Mactra and Brachidontes from beach ridge facies (Bahía Samborombón and Bahía Blanca), where the taphonomic signatures confirm typical littoral environments characterized by moderate to high wave energy, with eventual multi-episodic extraordinary storm events. These are responsible for the transport and accumulation of bioclasts and lithic material at different short distances, from their original position. Our results confirm that the samples from different units are separated owing to differences both in extrinsic (environmental) and intrinsic (shell structure, size, mineralogy) factors.