Sedimentology and dynamics of cryogenic soils in a rock glacier of the Central Andes (San Juan, Argentina)

MARTÍN MENDOZA; CARLA TAPIA BALDIS; DARIO TROMBOTTO LIAUDAT

Glasgow

Congreso; 22ND World Congress of Soil Science; 2022

International Union of Soil Science

Cryosols in the Central Andes are the result of typical periglacial processes, which involve active frost weathering, sediment transport mechanisms and freeze-thaw processes that may produce either cryoturbation or sorting phenomena (e.g., reverse gradation; patterned ground). In the study area (31°53’S - 70°11’W), permafrost-related cryoforms are located between 3400 and >4500 m a.s.l. We analyzed the sedimentological setting and thermal properties at two sites of the active layer in “El Candidato” rock glacier. The profiles were identified as turbic cryosols with no presence of vegetation or any organic horizon. Pebbles are major grain size (>50%), predominantely between 16 and 64 mm, and their main composition are lithic fragments of rhyolite. Above 15 cm depth, soil matrix is near 25% of the total mass and the silt content is around 3.1%. From 15 to 65 cm depth, pebbles and cobbles are concentrated, whereas matrix content is only 15%. Down to 90 cm depth, matrix content increases up to 28%, with a minor presence of silt (1.9%). This arrangement points to a cryogenic law that would have carried pebbles and cobbles upwards within the active layer. Concentration of silts in the top of the profile could be related with an overlapped process of frost-related extrusion in the first 65 cm of soil. As a result, the top layer shows up to 39% reduction in thermal conductivity along with an increment in matrix porosity. This distribution proves the effect of cryoturbation processes on heat fluxes within the active layer of permafrost-related cryoforms.