Late Quaternary Sedimentation Processes and Sediment Accumulation Changes off Portugal

Abstract

A multiproxy analysis was carried out on sediments from the Portuguese margin to evaluate the timing and character of environmental changes during the past 10000 years. The Portuguese shelf combines inputs from marine and continental sources and furthermore allows the acquisition of sediments records with various temporal resolutions, thus allowing a synoptic reconstruction of environmental changes on different timescales.Surface samples show, that continental input is limited to very close to the source, e.g. a river mouth. ROV- and echosound data reveal a very high textural variability of sea floor sediments. High-resolution data from a gravity core from the Tagus Prodelta (GeoB 8903) shows changes in sediment supply and transport mechanisms around 2000yrs BP and 600yrs BP. Grain-size has a dominating effect on other sediment proxies, allowing further conclusions on the interaction between environmental processes and sediment properties. On a long term, shelf sediments are mainly affected by the postglacial sea level rise. The effect of frequent tsunamis varies spatially and is not clearly evident in the sediments.