Quantifying sources and transport pathways of Surface sediments in the Gulf of San Jorge, Central Patagonia (Argentina)

Abstract

The Gulf of San Jorge (GSJ) is a semicircular basin, approximately 160 km long and 250 km wide, located in the central part of Patagonia between 45°S and 47°S, lacking any present-day major perennial tributaries. The grain size and bulk and clay mineralogical compositions as well as major and minor elements of 75 surface sed¬iment samples from the GSJ and the adjacent continental shelf were investigated to define the spatial distribution, transport pathways, and potential sources of terrige¬nous material. To better constrain the origins of GSJ sediments, analyses were also performed on 14 terrestrial, riverine, and marine samples from potential source areas around the gulf and Patagonia. The mineral assemblage of surface sediments in the gulf, dominated by plagioclase, quartz, and clays, is a function of the primary continen¬tal volcanic geology of Patagonia. The significant concentration of volcaniclastic parti¬cles indicated by mineralogical signatures and scanning electron microscope images of sediments suggests a substantial contribution from rhyolitic volcanism to the modern sedimentation in the gulf. High amounts of smectite are carried into the GSJ by dust transport, whereas inputs of chlorite and illite seem to be associated with continental shelf current transport from southern Patagonia. Finally, our results suggest that 50% of the surface sediment in the GSJ is derived from external/oceanic inputs, 40% from inner gulf shores (i.e., erosion and runoff), and 10% from dust (i.e., aeolian transport).