Tephrostratigraphy of a deep-sea sediment sequence off the south Chilean margin: New insight into the Hudson volcanic activity since the last glacial period

A detailed tephrostratigraphy study supported by Accelerator Mass Spectrometry (AMS) 14C dating, stable isotope (δ18O) and geochemical analyses has been carried out from a deep-sea core collected offshore the Chonos–Taitao archipelago (southern Chile), close to the main Andean volcanic centres of the Southern Volcanic Zone (SVZ). Counting of glass-shards in the drill core revealed the occurrence of twelve ash layers over the last 22 ka BP. Their provenance was determined by comparing the 14C age and major-element geochemistry of glass shards with tephra recovered in terrestrial fallout deposits from the Southern South Volcanic Zone (SSVZ). Four cryptotephra layers in the uppermost part of the studied core (1.9–16.1 ka BP) can be confidently correlated to the corresponding Cerro Hudson volcanic eruptive events HW7, HW3, HW2 and HW1. For the eight remaining tephra layers deposited between 16.1 ka and 20 ka BP, no direct correlation is possible with onland volcanic products; however the major-element geochemistry of the glass shards strongly suggests the Cerro Hudson as the volcanic source for these tephra. On the other hand, the lack of two of the largest Hudson Holocene eruptions (3.6 and 7.5 ka BP) in the uppermost part of deep-sea core may be linked to changes in the position of the Southern Westerlies Wind belt (SWW) as a response to the climate variability in Northern Patagonia during the Holocene.