New age controls on the tephrochronology of the southernmost Andean Southern Volcanic Zone, Chile

Abstract

The chronology of over 50 tephra layers preserved in a lake sediment core from Laguna La Trapananda (LLT) in the southern portion of the Andean Southern Volcanic Zone (SSVZ), Chile, is constrained by new radiocarbon age determinations, which span the period from late Pleistocene glacial retreat to the late Holocene. The tephra are correlative with tephra previously described from other lake cores in the region and are attributed to explosive eruptions of the SSVZ volcanoes Mentolat, Hudson, Macá, and potentially Cay. The new age determinations are used to estimate the ages of the >50 tephra in the LLT core, as well as those from the other previously described lake cores in the area, by a Bayesian statistical method. The results constrain the frequency of explosive eruptions of the volcanic centers in the southernmost SSVZ. They indicate that there was essentially no increase in the rate of eruptions from late-glacial to recent times due to deglaciation. They also provide isochrones used to constrain the depositional histories of the small lacustrine systems within which they were deposited and they provide a tephrochronologic tool for other paleoclimatic, paleoecologic, archaeologic and tephrochronologic studies in central Patagonia.

Holocene environmental and climate evolution of central west Patagonia as reconstructed from lacustrine sediments of Meseta Chile Chico (46.5° S, Chile)

“…For Volcán Cay, no large regional events are documented. It is suggested that Volcán Cay had no important activity during the Holocene at all (Weller et al, 2019(Weller et al, , 2015.…”

Current practices in building and reporting age-depth models

“…Although 84% of the papers in our literature sample showed uncertainties on a plot of the age model, none made explicit use of the uncertainties in their paleoenvironmental reconstructions. Weller et al (2019) was the only paper to use uncertainty estimates in a tangible way i.e., in the assignment of ages to poorly-dated tephras. Consideration of age model uncertainties will need to be incorporated into paleoenvironmental reconstructions for the advances provided by Bayesian age models to be fully realized.…”

Evidence for distal transport of reworked Andean tephra: Extending the cryptotephra framework from the Austral volcanic zone

“…ii) Alternatively, tephra abundance could indicate changes in eruption frequency from the SVZ and AVZ. Several studies have discussed a link between deglaciation and increasing volcanism (Watt et al, 2013;Fontijn et al, 2016;Weller et al, 2018); however, the low Na 2 O and high SiO 2 values in detrital tephra from Hooker's Point suggest that the glass has been subjected to extensive weathering prior to deposition. This weathering indicates a lag between the eruptive event and final burial of the glass at Hooker's Point.…”