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

Conferencia; IAL IPA 2022 Lakes as Memories of the Landscape; 2022

The Andean North-Patagonia includes the central-SVZ and the Valdivia and Concepciónseismotectonic segments. It is under the influence of frequent explosive eruptions,megathrust earthquakes and the Liquiñe-Ofqui-Fault-Zone activity. In order to expand theknowledge of events that affected the backarc-area, one approach is to study the lacustrinesediment record. In this case, we present preliminary results about Lago Frías sedimentaryrecord (41°3’39.10752’’S; 71°47’56.10048’’W; 790 masl). This 80 m deep proglacial lakeis distal-fed by the Frias Glacier. A 98 cm gravity core was collected at the center of thebasin. Sediment characterization was performed by X-radiography, magnetic susceptibilitylogging, water and organic contents determination by weight-losson-ignition, and macro andmicroscopic components description. The core consists of a background rhythmic deposit ofolive-black silt and olive-gray clay, regarded as varves based on the bibliography, and fourevent-deposits (base to top): (1) a 32.6 cm thick masstransport-deposit at the base (olive-graymassive mud bed with fine-pebbles, sand and disperse plant remains, poorly-laminated atthe top, with a brownish-black discontinuous pyroclastic-rich sand lamina intercalated in thedeposit), preliminary associated with the 1960 Valdivia earthquake (Mw=9.5); (2) a 27.3 cmmassive turbidite deposit (sharp-base, fining-upward from a brownish-black pyroclastic-richsand to light-olive-gray clay, with plant remains), dated post-1960 main shock according tothe presence of white pumiceous and yellowish-brown obsidian vitroclasts associated to the1960 Cordón-Caulle eruption; (3) a 0.8 cm turbidite bed (grayish-black fining-upward sandwith 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. Thechronology relies on the identification of this tephra layer, supported by varve counts anddata from previous cores. These results contribute to the palaeoseismological knowledge ofthe region, further research is under development.