Past environmental changes during the late Holocene sea-level fall (last 2.7 Ka) at the NE coastal plain of Argentina

MARIEL LUENGO; ISABEL VILANOVA; ENRIQUE FUCKS

Utrecht

Workshop; INQUA-PAGES ECR workshop: Impacts of sea-level rise from past to present (iSLR); 2018

PAGES-INQUA Utrecht University

Here we present a reconstruction of vegetation history and environmental changes at thecentral zone of Bahia Samborombon during the Late Holocene sea-level regressive phase(last 2.7 Ka) corresponding to MIS 1. This study is an integrative approach based on thecombination of geomorphological and micropaleontological (pollen, non-pollenpalynomorphs and foraminifera) proxy data. We found agreement among theenvironmental inferences from each proxy, which clearly show the evolution of theestuarine saltmarsh from an intertidal environment under significant marine influencetowards a supratidal brackish-freshwater environment as sea-level was falling. Theevidence of this evolution is (1) coastal progradation encompassing at least 5.7 km asrevealed by relict shorelines. Saltmarsh elevation is evidenced as a result of accretion dueto fine sediments accumulation of at least 1.2 m thick. We posit based on these values, asignificant progradation and accumulation processes. (2) Plant succession, characterizedby the replacement of low saltmarsh vegetation by that typical of high saltmarsh; whichthen is associated to brackish-freshwaters plant communities in shallow water-bodiesenvironments. (3) A gradual decrease of dinocysts and foraminifera assemblages, thelatter absent during the last millennium indicating a decrease in marine influence and theconsequent lower salinity values. Bahia Samborombon coastal plains became a regionalscale character during the last 2.7 Ka due to its surface increase, turning into one of themost extensive southeastern-South America saltmarshes, currently constituting abiosphere reserve.