Woods Hole Oceanographic Institution

Sebastien Bertrand

»Sequence mapping of Holocene coastal lowlands. The application of the Streif?s classification system in the Belgian coastal plain
»Temporal evolution of sediment supply in Lago Puyehue (Southern Chile) during the last 600 years and its climatic significance
»Climate variability of Southern Chile since the Last Glacial Maximum: a continuous sedimentological record from Lago Puyehue (40°S)
»Reconstruction of the Holocene seismotectonic activity of the Southern Andes from seismites recorded in Lago Icalma, Chile, 39°S
»Nature, origin, transport and deposition of andosol parent material in south-central Chile (36-42?S)
»Tephrostratigraphy of the Late Glacial and Holocene sediments of Puyehue Lake (Southern Volcanic Zone, Chile, 40?S)

BERTRAND, S., & FAGEL, N., Nature, origin, transport and deposition of andosol parent material in south-central Chile (36-42?S), Catena, in press. DOI 10.1016/j.catena.2007.08.003

The andosols of south-central Chile (36-42?S) are developed on yellow-brown loams that cover the region with a thickness of several meters. In the literature, several hypotheses concerning the nature, origin, mode of transport and deposition of the andosol parent material have been advanced but no general agreement has been found. In this paper, we test these hypotheses by analyzing new representative outcrops located around Icalma (38?50?S) and Puyehue (40?40?S) lakes by a pluri-methodological approach. Our data demonstrate that the andosol parent material has the typical mineralogical and geochemical signature of the regional volcanism and that these deposits are post-glacial in age. The grain size of the deposits and the morphology of the coarse grains evidence that most of these particles haven?t been re-transported by wind but are direct volcanic ash falls deposited throughout the Late Glacial and Holocene. Because of the prevailing westerly winds, most of them have been transported to the East. Following the deposition of the volcanic particles, weathering and pedogenetic processes have transformed part of the volcanic glasses and plagioclases into allophane and have wiped out the original layering. This work demonstrates that most of the andosols that occur in the Andes and in the eastern part of the Intermediate Depression of south-central Chile are developed on volcanic ashes directly deposited by successive volcanic eruptions throughout the Late Glacial and Holocene.

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