Petrology and quartz grain microtextures of marine shoreline sands from the Punta Arenas area, southernmost Chile and King George Island, Antarctica and implications for their depositional history

Abstract

Modal composition and quartz microtextures were analyzed to investigate the provenance tectonic setting and transport mechanism in shoreline sediments from the Punta Arenas (PA) area in the southernmost part of Chile and King George Island (KGI), West Antarctica. In the sediments from both areas, volcanic rock fragments were the predominant framework grain, and a significant amount of quartz was also found in the PA area. The provenance tectonic setting of the PA area was recycled orogen, and that of the KGI area was magmatic arc. Quartz grains exhibited subangular shape, medium to high relief, and mainly mechanical microtextures, which were induced by high shear stress (>80%) and high-energy percussion (<20%). The shoreline sands of the two areas did not differ significantly in the distribution of frequency of microtextures of glacial and aqueous origins, so it is interpreted that the sand sediments from both areas had similar glacial and aqueous transport histories. The percussion microstructures, which occurred in less than 20% of the sands in both areas, may be due to the relatively short residence time in the energetic coastal conditions. The presence of weathered quartz grains fractured by glaciers indicates that they had undergone significant weathering in the preceeding warm periods. The presence of high count of pre-weathered microtextures suggests that many grains travel into glacial stream carrying the pre-weathering microfeatures, which can be recognized in the sedimentary record.