Abstract
Well-characterised tephra horizons deposited in various sedimentary environments provide a means of synchronising sedimentary archives. The use of tephra as a chronological tool is however still widely underutilised in southern Chile and Argentina. In this study we develop a postglacial tephrochronological model for the Chilean Lake District (ca. 38 to 42°S) by integrating terrestrial and lacustrine records. Tephra deposits preserved in lake sediments record discrete events even if they do not correspond to primary fallout. By combining terrestrial with lacustrine records we obtain the most complete tephrostratigraphic record for the area to date. We present glass geochemical and chronological data for key marker horizons that may be used to synchronise sedimentary archives used for palaeoenvironmental, palaeoclimatological and palaeoseismological purposes. Most volcanoes in the studied segment of the Southern Volcanic Zone, between Llaima and Calbuco, have produced at least one regional marker deposit resulting from a large explosive eruption (magnitude ≥ 4), some of which now have a significantly improved age estimate (e.g., the 10.5 ka Llaima Pumice eruption from Llaima volcano). Others, including several units from Puyehue-Cordón Caulle, are newly described here. We also find tephra related to the Cha1 eruption from Chaitén volcano in lake sediments up to 400 km north from source. Several clear marker horizons are now identified that should help refine age model reconstructions for various sedimentary archives. Our chronological model suggests three distinct phases of eruptive activity impacting the area, with an early-to-mid-Holocene period of relative quiescence. Extending our tephrochronological framework further south into Patagonia will allow a more detailed evaluation of the controls on the occurrence and magnitude of explosive eruptions throughout the postglacial.
Highlights
Widespread tephra horizons, typically representing ash fallout from large volcanic eruptions, have the potential to form excellent isochronous marker horizons across diverse depositional environments
This results in the definition of 25 well-characterised and precisely dated tephra marker horizons, from large explosive eruptions which can be used to integrate various records and extend the tephrochronological framework further south
Some of the key marker horizons that were previously known from the literature have well-defined chemical compositions and improved age estimates
Summary
Widespread tephra horizons, typically representing ash fallout from large volcanic eruptions, have the potential to form excellent isochronous marker horizons across diverse depositional environments. In addition to radiocarbon dating of bulk sedimentary organic matter or macrofossil remains, tephra deposits incorporated within lacustrine sediments may be used as a chronological tool. If the chemical composition and relative stratigraphic position of a tephra deposit incorporated in lake sediments can be matched with proximal terrestrial records, the known age of the deposit can be transferred between sections and used to construct precise sedimentary age models and synchronise records with various applications (e.g., Blockley et al, 2012; Davies et al, 2012; Moernaut et al, 2014; Ponomareva et al, 2015; Van Daele et al, 2014, 2015). Precise chronological reconstructions of records containing tephra deposits are essential to investigate possible feedbacks between volcanism and climate or the local environment (e.g., Henríquez et al, 2015; Huybers and Langmuir, 2009; Jara and Moreno, 2014; Maclennan et al, 2002; Watt et al, 2013a), and causal links between volcanism and tectonic earthquakes (e.g., Eggert and Walter, 2009; Lemarchand and Grasso, 2007; Watt et al, 2009)
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