Paleoenvironmental evolution and sea-level fluctuactions along the southeastern Pampa grasslands coast of Argentina during the Holocene

VILANOVA I, PRIETO AR Y ESPINOSA M

Puerto Madryn

Simposio; Reunión Anual de Comunicaciones y Simposio del 50° Aniversario de la Asociación Paleontológica Argentina; 2005

Centro Nacional Patagónico

Holocene pollen and diatom analyses and complementary data from 18O and 13C, malacology and sedimentology have provided a detailed record of vegetation history and palaeoenvironmental change at arroyo Las Brusquitas, on the southeastern coast of the pampas of Argentina especially in relation to past sea levels. Holocene palaeosalinity trends were estimated by Detrended Correspondence Analysis and by salinity indexes based on pollen and diatom data. As a consequence of sea-level rise from the postglacial an extensive wave-cut platform formed over which Holocene infilling sequences were deposited unconformably. In these sequences, variation in pollen and diatom assemblages occurred in agreement with changes in mollusc diversity and abundance, isotope values, and sediment deposits. Between ca. 6700 and 6190 14C yr BP saline conditions predominated in an environment highly influenced by tides and salt water during the Holocene sea-level highstand. Between ca. 6200 and 3900 14C yr BP shallow brackish water bodies formed surrounded by saltmarsh vegetation that became more widespread from 5180 to 3900 14C yr BP in relation to a sea-level stabilisation period within the regression phase. Less saline conditions marked by frequent variations in salinity predominated between ca. 3900 and 2040 yr 14C BP. The intertidal saltmarsh environment changed into a brackish marsh dominated by freshwater conditions and sporadic tidal influence. Halophytic vegetation increased towards ca. 200014C yr BP indicating that saline conditions may be due to either desiccation or an unusually high tide range with rare frequency. After ca. 2000 14C yr BP the sedimentary sequences were buried by aeolian sand dunes. Changes in Holocene vegetation and environments in Las Brusquitas area are in agreement with data obtained from various southeastern coastal sites of the Pampa grasslands.