|BERTRAND, S., CASTIAUX, J., & JUVIGNE, E., Tephrostratigraphy of the Late Glacial and Holocene sediments of Puyehue Lake (Southern Volcanic Zone, Chile, 40?S), Quaternary Research, in review|
In this paper, we document the mineralogical and geochemical composition of tephra layers identified in the late Quaternary sediments of Puyehue Lake (Southern Volcanic Zone of the Andes, Chile, 40?S). The mineralogical and geochemical data are used to identify the source volcanoes and to present a tephrostratigraphic model for the region. For the last millennium, the results allow us to propose a multi-criteria correlation model based on five tephra layers identified at seven coring sites. The two most recent tephras are thin fine-grained green layers composed at more than 80% by rhyodacitic glass shards. The age of these two tephras has been estimated by paralleling previously published radionuclide (210Pb, 137Cs) and varve-counting data and the comparison with historical chronicles allow us to evidence that the 2 upper tephras originate from the 1960 AD and 1921-1922 AD eruptions of the Puyehue - Cordon de Caulle volcanic complex (PCCVC). The third tephra is a sandy layer dominated by orthopyroxenes, and is related to the 1907 AD eruption of Rininahue maar. Moreover, the sediments of Lago Puyehue contain an olivine-rich tephra deposited at the end of the 16th century, and a tephra characterized by a two pyroxene association at the second half of the first millennium AD. In addition to the recent deposits, we studied the tephra succession of an 11.22 m long AMS-radiocarbon dated sediment core covering the last 17,900 years. Seventy-eight tephras have been macroscopically recognized and the fifteen thickest have been analyzed for bulk and dense mineralogy as well as geochemistry of the glass shards, when any. Tephras showing promising results for future paleoenvironmental studies in the region are detailed. These results constitute the first continuous tephrostratigraphic and tephrochronological database for the region and demonstrate that the central province of the Southern Volcanic Zone has been active throughout the last deglaciation and the Holocene.