Fossil chironomids and ostracods from a 5000 years- sediment sequence of Laguna El Chaltel, Southern Patagonia, Argentina

MASSAFERRO, J., LAPRIDA, C ORPELLA, G. AND RAMÓN MERCAU, J.

La Plata, Argentina

Congreso; X Congreso Argentino de Paleontología y Bioestratigrafía y el VII Congreso Latinoamericano de Paleontología; 2010

Lakes are excellent sensors of environmental change, including climate change. Chironomids (Insecta, Diptera) and ostracods (Crustacea) are among the most useful biological indicators for paleoenvironmental reconstruction found in lake sediments, due to their sensitiveness to environmental variables. However, the use of these microfossils in quaternary studies for southern Patagonia is still limited and poorly understood because of the paucity of regional taxonomic and palaeonvironmental knowledge. The multi-proxy study of lacustrine sediments from Laguna El Chaltel presented here aims to partially fill this gap. Laguna El Chaltel is a permanent lake located at 49° 58` 25``, 71° 06’ 53’’ in Southern Patagonia, Argentina, in the semidesert steppe East of the Andes. A 60.8-cm short sediment core has been analysed in order to obtain information about the paleoenvironmental evolution of the lake during the last ca. 5000 yr BP. The 210Pb/237C dating gave an age of 4685 cal yr BP for the base of the core. The presence and abundance of littoral chironomids of the genus Polypedilum Kieffer suggests oscillations in the lake level during the timespan of the core, while variations in the relative abundance of the ostracod Limnocythere rionegroensis Cusminsky & Whatley indicates the onset of periods of evaporative concentration. Some geochemical and physical parameters such as TIC, TOC and magnetic susceptibility show similar patterns evidencing important variations in lake dynamics.