Organic chemistry and magnetic susceptibility to characterize Late Mesolithic (ca. 8400-7000 cal BP) palaeoenvironmental conditions in the Sado Estuary, Portugal.

Abstract

Late Mesolithic hunter-gatherer communities (ca. 8400-7000 cal BP; ca. 6450-5050 cal BC) occupied the inner areas of the Tagus and Sado rivers (Portugal) during the Early-Middle Holocene transition. At that time both river valleys were flooded by marine ingression due tom the rapid Holocene sea-level rise that occurred until ca. 7000 cal BP, forming large estuarine areas with favourable conditions for occurrence of marine/estuarine species. The palaeoenvironmental characterization of the Tagus estuarine system shows that, during the Mesolithic occupation, shell middens were placed in the proximity of saltmarsh environments and near the upstream limit of tidal influence. The deceleration of the sea-level rise at ca. 7000 cal BP led to a relative increase in the fluvial sediment supply. However, despite the fluvial influence, estuarine conditions prevailed in the area of the Tagus that was occupied during the Late Mesolithic (e.g. Muge tributary) until ca. 6000 cal BP, long after the disappearance of these hunter-gatherer communities.