Towards a late Quaternary tephrochronological framework for the southernmost part of South America - the Laguna Potrok Aike tephra record

摘要

A total of 18 tephra samples have been analysed from the composite sediment sequence from Site 2 of the Laguna Potrok Aike ICDP expedition 5022 from southern Patagonia, Argentina, which extends back to ca 51kacalBP. Analyses of the volcanic glass show that all layers but one are rhyolitic in composition, with SiO_2 contents ranging between ca 74.5 and 78wt% and suggest an origin in the Austral Andean Volcanic Zone (AVZ; 49-55°S). Nonetheless, two main data clusters occur, one group with K_2O contents between ca 1.5 and 2.0wt%, indicating an origin in the Mt. Burney volcanic area, and one group with K_2O contents between ca 2.7 and 3.9wt%, tentatively correlated with Viedma/Lautaro and the Aguilera volcanoes in the northern part of the AVZ. The early Holocene Tephra, MB_1 and the late Pleistocene Reclus R_1 tephra occur in the upper part of the sequence. Periods with significant tephra deposition occurred between ca 51-44kacalBP, and ca 31-25kacalBP, with a decrease in tephra layer frequency between these two periods.