LATE QUATERNARY RECORDS FROM THE CENTRAL PORTUGUESE COAST: GEOMORPHIC RESPONSE TO ENVIRONMENTAL CHANGE DURING OXYGEN ISOTOPE STAGES 3 AND 2

Stratigraphic sequences from central Portugal, dated by optically-stimulated luminescence, demonstrate geomorphic response to climate and sea level change during the last glacial stage (Oxygen Isotope Stages 5 through 1). These sections were investigated as part of a geoarchaeological and paleoenvironmental study of the Paleolithic in the coastal Estremadura region. Pleistocene raised beach and estuarine deposits were identified between Peniche and São Pedro de Muel, recording several relative sea level high stands between OIS 5-3 and demonstrating strong neotectonic uplift associated with active diapirs in the area. Archaeological sites in intertidal deposits at Mira Nascente and Praia Rei Cortiço provide evidence for Neanderthal occupation of the coastal zone during this period. The coastal bluffs and estuarine sequences are buried by colluvial deposits and eolian sand sheets that extend up to 15 km inland. Many of the surface sediments in the study area were previously mapped as "Pleistocene" and were presumed to be associated with severe cold/arid conditions of the glacial maximum. However, luminescence ages on the base of the eolian sands near Fanhais show they were emplaced by about 27,000 BP and were periodically active throughout late OIS 3 and OIS 2. Thick alluvial fills in coastal-draining rivers suggest high rates of upland erosion around the same time, with maximum aggradation in the Rio Tornada valley reached by about 31,000 BP. During the glacial maximum, the coastal bluffs were subject to intense colluviation, while the valley fills were reworked by eolian activity and trenched by base level lowering. Episodes of eolian, fluvial, and colluvial activity are associated with paleoclimatic events such as Heinrich Events 6, 3, 1, and the Younger Dryas, although additional dated sections are needed to demonstrate a statistically-meaningful relationship. The geomorphic episodes on the Estremadura coast were likely caused by high-frequency shifts between arid and sub-humid conditions, with corresponding reductions and expansions of forest cover that would have influenced erosion potential on hillslopes. These findings highlight significant landscape instability prior to the glacial maximum, during the critical transition between the Middle and Upper Paleolithic in Western Europe.