Micromorphological characteristics of Andean cryogenic deposits produced by landslides in Erizos valley, San Juan, Argentina

DARIO TROMBOTTO LIAUDAT; CARLA TAPIA BALDIS; MARTÍN MENDOZA

Glasgow

Congreso; 22ND World Congress of Soil Science; 2022

International Union of Soil Science

Erizos valley in the Andes of San Juan (31.707149 ° S, 70.275189 ° W), Argentina, is covered by geoforms produced by catastrophic processes with different dynamics and genesis. The study area is surrounded by the Santa Cruz Mountain Range, which exceeds 4700 m asl., with a periglacial environment (>3700 m asl) and mountain permafrost in an unstable condition. A tongue-like landslide, which has already appeared in images since 1985, clearly comes from a root of the process located in the level with permafrost, verifiedthrough perennial snow patches and nearby rock glaciers. The distal part of the landslide shows a typical randomly distributed molard field. Along the landslide however, it is possible to detect aligned cones. The lithology in the studied profiles (at 3100 m appr.) are from the Late Cretaceous, which are conglomerates and red-purple sandstones. Angular gravels immersed in fine sand and silt predominate in the deposit. The residual cones result from the landslide erosion, apparently associated to the ice-dynamics, ice amount and freezing thickness. The 60 cm sedimentological cover of the profile is chaotic and disaggregated. Today the molards are thawed, dry and shrunken. The thin sections of the samples portray indicators of their past Andean tundra environment with freezing and ice through a meta-fragmoidic fabric, c/f= close porfiric, without organic indicators, broken lithics, sedimentary vesicles connected with irregular, curved planes of variable diameter, silt cappings, fine sediment rings around angular lithics indicating illuviation, conglomeric sectors of fine sediments and brown to blackish globules of iron hydroxides