Buenos Aires Mid-Holocene highstand revisited: beaches lie, estuaries do not

ISLA, FEDERICO IGNACIO; ESPINOSA, MARCELA ALCIRA; DE FRANCESCO, CLAUDIO GERMÁN

Cairns, Australia

Congreso; 17th INQUA Congress; 2007

INQUA

The mid-Holocene highstand affected the coastal plains of Buenos Aires Province, Argentina. As this coast has also been affected by storms, the beach-ridge plains are reflecting these episodic processes as discrete sequences attached, but dominantly recording the regression after the maximum level reached. In fact, sea level curves have been proposed from mollusc shells sampled within these beaches, overestimating their real ages (shells are older than the sedimentary deposit) and their altitudes (storm level) in relation to mean sea level (MSL), assuming similar tidal ranges and wave setups. On the other hand, several estuaries began to be filled during the sea level rise, and were definitively filled during the sea level drop. The paleoenvironmental history of these estuarine sequences has been recorded by diatom assemblages, which indicated progressive changes from marine to freshwater habitats from the Mid to Late Holocene. Estuaries ended as tidal flats where, if there was a connection to open water, it is possible to recognize their reworking into cheniers. The taphonomic and paleoecological analysis of mollusc shells, particularly those of the genus Heleobia, helped to discriminate these processes. In the present paper different C14 datings performed on different facies were plotted in order to discriminate the storminess record from the MSL record.