INCITAP   20787
INSTITUTO DE CIENCIAS DE LA TIERRA Y AMBIENTALES DE LA PAMPA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Taphonomy of modern traces in volcaniclastic deposits: the eruption of Chaitén volcano (2008-2010) as a natural laboratory
Autor/es:
MELCHOR, R.N.; GENISE, J.; SÁNCHEZ, M.V.; SARZETTI, L.; UMAZANO, A.M.
Lugar:
Sao Leopoldo
Reunión:
Simposio; Simposio Latinoamericano de Icnología; 2010
Resumen:
Neoichnological studies on rhyolithic pyroclastic deposits of the recent plinian eruptive cycle of the Chaitén volcano (42° 50’ 10” S, 72° 39’ 15” W) were conducted during December 2009 in Chile and the west of the Chubut and Río Negro provinces of Argentina. The recognized deposits include air-fall (in soils and shallow ponds) and water-lain tephra (stream and minor mass flow), and rare reworked windblown dunes. The ash plume was directed to east and southeast of the volcano, reaching occasionally the Atlantic coast of Patagonia. After nineteen months of the start of the eruption, preservation of ash in soil profiles was patchy in the Argentine steppe. Ash thickness increased (up to 40 mm) towards the more humid western Nothophagus forest. The particular distribution of preserved air-fall tephra would be related to mean annual rainfall and vegetation or litter cover, in addition to intensity of prevalent winds, local relief and occurrence of rain or snow immediately after deposition. We found a large variety of traces in soils and ponds. The latter contained bird tracks, vertebrate swimming traces, thin invertebrate trails, and chironomid cases in water lain ash. In soils covered by grass-dominated vegetation growing on ash, insect nests and pupation chambers and earthworm, slug and rodent burrows were identified. Burrowing by earthworms in grass-covered soils produced an ichnofabric that resembles the diffuse boxwork described for Jurassic-Cretaceous rocks from Patagonia. Nesting or pupating insects (with potential equivalent to trace fossils in brackets) in ash or crossing through the ash layer were: Dichotomius torulosus (Coleoptera, Scarabaeinae) (Coprinisphaera), Frickius variolosus (Coleoptera, Geotrupinae) (Scaphichnium, Pallichnus), Diphaglossa gayi and Cadeguala albopilosa (Hymenoptera, Colletidae) (Celliforma), Corynura sp. (Hymenoptera, Halictidae) (Cellicalichnus), Augochlorini indet. (Hymenoptera, Halictidae) (Corimbatichnus), Cicadidae indet. (Auchenorrhyncha) (Feoichnus), Sphingidae indet. (Lepidoptera) (Teisseirei), Sphecidae indet. (Hymenoptera) (Rebuffoichnus) and Camponotus sp. (Hymenoptera, Formicidae) (Krausichnidae).