Upper-flow-regime deposits related to glacio-volcanic interactions in Patagonia: Insights from the Pleistocene record in Southern Andes

Abstract

Supercritical flows and their associated upper-flow-regime bedforms have been increasingly recognized in several contrasting depositional environments around the world, including volcano-sedimentary settings. In recent years, there have been significant advances in flow modelling, architecture and depositional dynamics in upper-flow-regime bedforms related to glacio-volcanic interaction, however most of these works come from specific volcanic landscapes. Examples of other regions with different tectonic and volcanic settings are needed in order to gain a more global perspective regarding the generation and preservation of upper-flow-regime glacio-volcanic bedforms. This study presents a detailed analysis of Pleistocene volcaniclastic deposits accumulated in alluvial to lacustrine deltaic environments in the Southern Andes within the Southern Volcanic Zone. Six facies were defined and related to distinctive bedforms by examining sedimentary features, including textural characteristics, sedimentary structures, architecture and composition. Among these facies, five are distinguished by deposition from supercritical flows and upper-flow-regime bedforms, such as cyclic steps, chutes and pools, and antidunes. The stratigraphic succession reveals a predominance of repeated supercritical flows, which appear to be influenced by the availability of detritus for removal along with sudden water discharges. Compositional analyses indicate that explosive volcanism was the primary source of detritus, occurring synchronously with sedimentation. Additionally, the widespread occurrence of Pleistocene glacial conditions in this region suggests that volcanic-induced melting ice or snow may have been an important source of water supply. Regarding the Southern Andes, the presence of local depressions, such as volcano-tectonic calderas plays an essential role in the generation and preservation of the upper-flow-regime bedforms related to glacio-volcanism. Furthermore, the importance of carrying out detailed and multidisciplinary studies seems to be critical for the recognition of these deposits in the record of the Andes.