Environmental changes related to the Holocene sea-level transgression and successive highstand (7–5.5 Kyr) at the NE coastal plain of Buenos Aires (Argentina)

Abstract

We present a high resolution multi-proxy study about environmental changes that occurred during the Holocene sea-level transgression and successive highstand (7–5.5 Kyr) in the central zone of Bahía Samborombón (∼35.6° S), Argentina. This study, one of the first in the area that integrates geomorphological and paleontological proxy data (pollen, non-pollen palynomorphs, foraminifera and mollusk shells), and focusing on a short time interval, offers the advantage of recognizing environmental and vegetation changes in a more comprehensive way. The aim of this work is to reconstruct the salt marsh vegetation history and paleoenvironmental changes; and to develop a model of the geomorphological evolution during the mid-Holocene sea-level transgressive phase. Between 6700 cal yr BP and 6500 cal yr BP, several rapid environmental changes took place. Those changes affected vegetation and microfauna, as well as the geomorphological features. During this period, middle to high salt marsh vegetation developed in an extensive and open tidal plain, where wide and long paleo tidal channels were flowing. Between 6500 and 6220 cal yr BP, the salt marsh transitioned into low salt marsh one as a response to a continued rise in sea level, resulting in the landward transgression of the coastline. The relative sea level reached the highstand between 6220 and 5500 cal yr BP and, consequently, extensive inundation of the coastal plain took place, except for the elevated areas such lunettes and ridges. After 5500 cal yr BP, seaward prograding beach and sand ridges formed in response to the onset of a regressive phase. Since then, the ancient tidal plain, extending ∼10 km from the present coastline, has been subjected to aeolian and pedogenetic processes.