Evolution and composition of cliff-top barriers at the northern shore of San Matías Gulf, Patagonia, Argentina.

Patagonia is a key place to analyze the climatic trends (waves and winds) of the Southern Hemisphere. The northern coast of the San Matías Gulf (" Bahía Sin fondo " for the original Spanish descriptions) is characterized by an attached sand barrier developed on top of former cliffs. Morphological features are indicating changes in the regional slope when the sea level drowned the depression of the gulf. An original eastern slope was progressively replaced by slopes towards the south. The availability of sand during the transgression and maximum sea level was directed to the east due to the dominant westerly winds. Sand dunes accumulated on top of former cliffs and today –due to coastal erosion-, remain as cliff-top dunes. A conceptual model for the formation of these cliff-top barriers is described in relation to the fluctuation of the sea level and the sand migration, which was studied through mineralogical analysis comparing the different environments: cliff, beach, and dunes. Their composition explains the sediment transport shift and is locally associated to the Río Negro Formation deposits and regionally to Andean Cordillera volcanic sources. • Clifftop dunes are dominant along the northern shore of San Matías Gulf, Río Negro, Argentina. • Mineral provenance indicates the erosion of the cliffs and the westerlies transport. • Although the gulf was flooded during the Holocene transgression, the successions preserved indicate a sea-level drop since then. [ABSTRACT FROM AUTHOR]