AEOLIAN PALEOSOILS RELATED TO ARCHAEOLOGICAL RECORD AT LAKE ARTURO, NORTH OF TIERRA DEL FUEGO

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

La Plata

Congreso; IV Congreso Argentino de Cuaternario y Geomorfología; 2009

AACG - UNLP - ABEQUA

A sequence of aeolian deposits and paleosoils of 46 m in thickness located at the southeast margin of Lake Arturo (53º 43´S/68º 18´W) is reported. It is a permanent lake with salty and turbid waters but its depth is still unknown; 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 the top, 50 m above the present shoreline. The studied aeolian deposits lie over a silty-clay bed of probable glacial origin, which overlies on rounded, medium to coarse, sandy matrix gravel and sandstones of Middle Miocene age. On top of them, seven silty-clay edaphic levels are interbedded with non-edaphic levels of similar texture.  Edaphic beds vary in color, the deepest are 10Y/R, the medium are 2.5 and the most surficial are 5 YR.  Organic matter content varies between 0.74 to 3.02%. FDOM, charcoal, spots, white precipitate, voids, pellets and clay skins are present. Structure is blocky to granular. A 3 cm ash layer is present in between one of the non-edaphic layers; overlying it, three edaphic and four non-edaphic beds are developed. Lama guanicoe long bones and skulls are abundant within the edaphic beds. The thickness of the fine deposits besides the lake show that aeolian processes have been more intensive than in the surroundings. We support that the lake would have acted as a deflation source during low precipitation and high evaporation climatic periods, being the lake partially dried. The alternance of edaphic and non-edaphic silty-clays levels is interpreted as the occurrence of humid-dry or stable-unstable cyclicity. While the more favorable periods would allow the growth of vegetation, dry periods would favor its burial. This cycle would has been repeated three times before a regional eruption of unknown source took place, after  that, the cycle continued twice developing  new edaphic beds up to the uppermost deposits forming the present silty-clay dune. The sequence is interpreted as a repeated paleosoils formation process, but there is not an available chronological frame yet. Radiocarbon dating on bones and volcanic ash geochemistry being performed as well as other palaeopedological and palaeoenvironmental studies will allow us to establish the chronology of this pedogenetic cycle. Lithic and faunal archaeological materials are being exposed by the present aeolian erosion visible not only in the exposure but also on deflation hollows, generating palimpsests that make difficult to understand its origin. Paleoclimate and past climatic variability is a key for the reconstruction of environments exploited by hunting-gatherers and to build a chronological sequence of human occupation in this rough area.