Temporal evolution of the sand-spit between Torreira and Furadouro (NW Portugal)

Abstract

Dune systems comprise about 60% of the Portuguese coast but they arc best developed in northern areas, where they form an extensive sand plain. The dunes display several stratigraphic evidences for a long period of sand accumulation during the Holocene, related with sea level rise. Morphological aspects have shown that coastal systems progradated to the shelf but it is not clear if they migrated great distances prior to doing so. Between Torreira and Furadouro beach, three main genetic units have been recognised which are separated by major surfaces. The first unit, unit A, defines the top of a depositional cycle that marks a period of estuarine lagoonal condition stabilities and the inversion of the depositional trend. Radiocarbon data suggests that the lagoon was formed before 1997 years BP (calibrated ages). The sedimentation of unit B favoured the development of sand ridge systems. Unit C marks a new period that leads to the reworking of coastal sediments by wave and wind action in a landward direction. The evolution of this sector may be attributed to sea level fluctuations induced by local factors such as periods of intense supply of sediments to the shelf.