Analysis of a short sediment core from Lago Frías, North Patagonia, Argentina

DOMINGUEZ, LUCÍA; VILLAROSA, GUSTAVO; BEIGT, DÉBORA; COTTET, JULIETA; OUTES, VALERIA

San Carlos de Bariloche

Congreso; IAL IPA 2022. Lakes, Memories of the Landscape; 2022

International Association of Limnogeology- International Paleolimnology A ssociation

The Andean North-Patagonia includes the central-SVZ and the Valdivia and Concepción seismotectonic segments. It is under the influence of frequent explosive eruptions, megathrust earthquakes and the Liquiñe-Ofqui-Fault-Zone activity. In order to expand the knowledge of events that affected the backarc-area, one approach is to study the lacustrine sediment record. In this case, we present preliminary results about Lago Frías sedimentary record (41°3’39.10752’’S; 71°47’56.10048’’W; 790 masl). This 80 m deep proglacial lake is distal-fed by the Frias Glacier. A 98 cm gravity core was collected at the center of the basin. Sediment characterization was performed by X-radiography, magnetic susceptibility logging, water and organic contents determination by weight-losson-ignition, and macro and microscopic components description. The core consists of a background rhythmic deposit of olive-black silt and olive-gray clay, regarded as varves based on the bibliography, and four event-deposits (base to top): (1) a 32.6 cm thick masstransport-deposit at the base (olive-gray massive mud bed with fine-pebbles, sand and disperse plant remains, poorly-laminated at the top, with a brownish-black discontinuous pyroclastic-rich sand lamina intercalated in the deposit), preliminary associated with the 1960 Valdivia earthquake (Mw=9.5); (2) a 27.3 cm massive turbidite deposit (sharp-base, fining-upward from a brownish-black pyroclastic-rich sand to light-olive-gray clay, with plant remains), dated post-1960 main shock according to the presence of white pumiceous and yellowish-brown obsidian vitroclasts associated to the 1960 Cordón-Caulle eruption; (3) a 0.8 cm turbidite bed (grayish-black fining-upward sand with plant remains) which is preliminary attributed to the 2010 Maule earthquake (Mw=8.8);(4) a 0.1 cm direct fall grayish-black ash layer assigned to 2015 Calbuco eruption. The chronology relies on the identification of this tephra layer, supported by varve counts and data from previous cores. These results contribute to the palaeoseismological knowledge of the region, further research is under development.