Aeolian paleosols and the archaeological record at Lake Arturo, Northern Tierra del Fuego, Argentina

CORONATO, ANDREA; FANNING, PATRICIA; SALEMME, MÓNICA; ORÍA, JIMENA; PICKARD, JOHN

La Plata

Congreso; IV Congreso Argentino de Cuaternario y Geomorfología; 2009

Facultad de Ciencias Naturales y Museo de La Plata

A sequence of aeolian deposits and paleosols, 46 m thick, located at the southeast margin of Lake Arturo (53º 43´S/68º 18´W) is reported. It is a permanent lake of salty and turbid waters with still unknown depth; lightly oval in shape, its longest axis is oriented N-S and its perimeter is about 6 km. The lake is placed in the semiarid Fuegian cold steppe where westerlies blown daily with a monthly median velocity of 25 km/h-1. Wave erosion over sedimentary rocks forms cliffs along the south and east coasts. An active dune is placed on top, 50 m above the present shoreline. The deposits overlie a silty-clay bed of probable glacial origin, capping rounded, medium to coarse, sandy matrix gravel and sandstones of Middle Miocene age. A sequence of at least seven paleosols has been identified within the silty clay sedimentary units.  The paleosols are identified on the basis of their colour (10Y/R to 5 YR) and organic matter content (0.74 to 3.02%). Charcoal, voids, pellets and clay skins, all indicative of soil development, are also present. A 3 cm thick layer of white, fine grained material, tentatively identified as volcanic ash, is located at approximately  21 m depth. Lama guanicoe long bones and Ctenomys sp. remains are abundant within the paleosols. The most likely source of the sediments making up this sequence is deflation from the dry bed of Lake Arturo during past periods of relatively low precipitation and high evaporation. The presence of paleosols within the aeolian sequence suggests the alternation of more humid with drier, or relatively stable with less stable, periods. While the more humid periods would allow the growth of vegetation, and hence additions to soil organic matter, dry periods would favor its burial. A chronology for the sequence is yet to be determined. Radiocarbon dating on bones, volcanic ash geochemistry and Optically Stimulate Luminescence dating of the aeolian sediments, as well as other palaeopedological and palaeoenvironmental studies, will allow a chronology to be established that may also inform on human occupation of the area in the past. Lithic and faunal archaeological materials, formerly buried within the sediments, are being exposed and conflated by contemporary aeolian erosion generating palimpsests that are challenging to interpret in terms of human behaviour in the past. However, the sedimentary sequence provides a unique opportunity to use past climatic variability to reconstruct the environments exploited by hunter-gatherers and to build a chronological sequence of human occupation of interior Tierra del Fuego.