The onset of the post-glacial transgression in the northern Argentine Continental Margin: new insights based on paleontological evidence

CECILIA LAPRIDA; GERMAN DIAZ; NATALIA GARCÍA CHAPORI; GRACIELA BRESSAN; JUAN PABLO GRANT; NORA MAIDANA; ROBERTO A. VIOLANTE

Punta del Este

Congreso; COLACMAR - XV Congreso Latinoamericano de Ciencias del Mar; 2013

During Late Glacial Maximum, the Argentine shelf was widely subaerially exposed. Here we present the record of the first phase of the late-glacial flooding of the Argentine northern shelf. Sediment core SHN-T392 (90 m water depth, ~40°S-57°W) was co llected by vessel Puerto Deseado during 2012. Based on a preliminary description, we identified a sequence of fine-grained siliciclastic inner shelf deposits, fine-grained marine lagoons, and coarse-grained bioclastic deposits from the base of a transgressive system (Violante et al. 2012). New AMS radiocarbon dates confirm that the succession was deposited between ~16 kyr BP and 10 kyr BP, during the earliest sedimentation associated with the postglacial marine transgression into the shelf. More detailed examination employing foraminifer, ostracod and diatom analysis, has revealed that the basal unit is barren on diatoms but incorporated broken and corroded foraminifera, together with oligohaline ostracods of more pristine appearance, and has therefore been reinterpreted as fluvial estuarine facies developed on an ancient foredune. The change to transitional a fluvio-marine environment, such as estuarine brackish-water lagoonal facies related to receding coastlines, occurred at ~15 kyr BP; while at ~13.5kyr BP diatoms indicate that a well vegetated mixohaline estuarine lagoon was established. Soon after the 12.5kyrBP, ostracods and foraminifera indicate marine-dominated facies associated with a gradual increase of sea level. Around 11-10 kyr BP a thick transgressive bioclastic bed overlaid by fine siliciclastic shelf facies indicate fully marine conditions in a wave dominated-environment. This shell bed is interpreted as deposited during storms probably in foreshore settings. In conclusion, core SHN-T392 represents the early evolution of a wave-dominated estuarine system related to the Late Glacial sea-level rise.