Post–glacial tephrochronology record off the Chilean continental margin (∼41° S)

Abstract

The Southern Volcanic Zone of the Andes (∼33–46° S) is a very active volcanic zone with several volcanic centers recording recurrent historical activity (e.g. Llaima, Villarrica, Puyehue-Cordón Caulle, Osorno, Calbuco and Hudson). Tephrochronology is a valuable tool to help better understand the eruptive history of volcanic centers, essential for producing volcanic hazard maps. Additionally, tephrochronology can also be very useful to synchronize stratigraphic records of different nature such as paleoclimatological, paleoceanographical and archaeological records on land, lakes, ice and the ocean. Here we present a (crypto) tephrochronological record from two marine sediment cores retrieved in the Chilean continental margin at ∼41° S and ∼41.6° S. The records display continuous sedimentation since the late glacial, as robustly constrained by planktonic foraminifera δ18O and 14C dates. During this period, twenty three cryptotephras were identified as glass shard peaks together with two ∼25–30 cm–thick visible tephras (one in each core). The source of the (crypto) tephras was mainly constrained by major and trace element geochemistry of individual glass shards together with their stratigraphic position, since it is not possible to observe physical characteristics, such as color and grain size, when analyzing cryptotephras. From these, one cryptotephra was robustly correlated with the HW7 eruption from the Hudson volcano occurring in the Late Holocene at ∼1.5 cal ka BP; and the two visible tephra layers were identified as distant correlatives of the Lepué tephra originating from Michinmahuida volcano and occurring in the Deglaciation/Holocene transition at around 11 cal ka BP. Additionally, eight cryptotephra occurring at ∼3.6, 6.2, 7.0, 8.5, 9.6, 14.2, 15.9 and 18.2 cal ka BP were robustly identified as sourced from Michinmahuida volcano but where otherwise not correlated, providing novel evidence of pre Holocene activity of this volcanic center.