Disturbance events recorded in the sedimentary infill of Lago Guillelmo, Parque Nacional Nahuel Huapi, Argentina

AMAT, PABLO; VILLAROSA, GUSTAVO; BEIGT, DÉBORA; OUTES, VALERIA; BARBOSA HETHERINGTON, ANDRES; COTTET, JULIETA

Bariloche

Congreso; IAL IPA 2022; 2022

International Paleolimnology Association - International Association of Limnogeology

Lago Guillelmo is a lake of glacial origin located at the eastern side of the Andean mountainrange (Northern Patagonia). This zone is frequently affected by pyroclastic falls due tothe proximity to South Andean volcanoes and also by hydrogeomorphic processes withincatchments related to heavy rains. In order to look for evidence of these natural disturbancesin the lacustrine sedimentary record, we analyze lacustrine cores and Ground PenetratingRadar (GPR) profiles, taken in the distal deltaic environment. We also analyze satelliteand historical images of the nearby catchment. The analysis of the cores (Gui-220419-1, 2 and 3) allowed us to identify different units (1) poorly laminated brownish sandy silts, with autochthonous organic matter associated to charophytes, corresponding to thenormal lacustrine sedimentation (2) tephra layers attributed to Cordón Caulle, Calbuco andOsorno Volcanoes according to pyroclast petrography and fragment morphology, and (3)sediments with terrigenous sediments and organic matter, interpreted as hyperpycnites.Especially at the bottom of Gui-220419-1 core we observed a ~9 cm thick (46 to 38 cmdepth) fining upward sequence, grading from medium sand to very fine sand, with presenceof leaves, roots and charcoal. From the GPR profiling we obtained a radargram with 1major reflector which corresponds to a tephra layer observed at Gui220419-2 at 50-51cm. We also observed another reflector corresponding to lobe-shaped morphologies thatcould be related to the hyperpycnites identified in Gui220419-1. These morphologies andits deposits are located in front of the mouth of an abandoned river course, observed insatellite and historic images. These results show the interruption of the normal lacustrinesedimentation by these disturbances and confirm the utility of this type of analysis. This workwill be extended to other zones of Northern Patagonia, linking land surface and subaqueousenvironments analyses.