Abstract
The distal deposition of tephra from explosive volcanism has the potential to geochronologically constrain sedimentary archives and landforms. With this technique, we constrain a Late Glacial glacier re-advance on Svalbard and suggest that glacioisostatic emergence rates during the Younger Dryas chronozone were at least three times greater than previous estimates. The identification of cryptotephra (i.e., non-visible) horizons, outside the extent of visible fallout, has greatly expanded the field of application of tephrochronology. While the cryptotephra revolution has triggered a burst of investigations using low-concentration tephra to constrain distal sedimentary sequences, as of yet, few investigations have used this tool to constrain the age of glacial landforms. Here we constrain a moraine formed during a glacier re-advance (12.8–12.2 cal ka BP) into a high relative sea level during the early Younger Dryas chronozone, with the first identified occurrence of the Icelandic Vedde Ash on Svalbard. Low concentrations (∼63 shards/g dried sediment) of the bimodal Vedde Ash (rhyolitic long axis c. 30–90 μm; basaltic c. 35–100 μm) were identified in a lake sediment sequence collected from the Heftyebreen glacier foreland, in a tributary valley to Grønfjorden, western Spitsbergen. Given that the cryptotephra was deposited within a lacustrine isolation basin, we further reconstruct a minimum rate of glacio-isostatic emergence during the end of the Late Glacial. Strong and longstanding evidence suggests Svalbard's west-coast cirque glaciers were less extensive during the Late Glacial than the Late Holocene. However, the Late Glacial Heftyebreen moraine suggests Svalbard glacier dynamics during this period may have been more complex.
Highlights
The distal deposition of tephra in far-field locations resulting from explosive volcanism is revolutionizing how we correlate and precisely date sedimentary archives and landforms (Lowe, 2011; Davies, 2015)
This study demonstrates that cryptotephra on Svalbard can provide reliable new age constraints for lacustrine sedimentary archives, glacial landforms and raised marine deposits
We successfully extend the tool of crypto-tephrochronology from beyond sedimentary sequences to landforms and processes
Summary
The distal deposition of tephra in far-field locations resulting from explosive volcanism is revolutionizing how we correlate and precisely date sedimentary archives and landforms (Lowe, 2011; Davies, 2015). Visible tephra beds are most often used to constrain stratigraphic sequences (Lowe, 2011), but have been correlated to glacial land forms (e.g., Schomacker et al, 2003; Benediktsson et al, 2015) as well as relative sea level (Rundgren et al, 1997; Brader et al, 2017). While cryptotephra investigations have most commonly been used to constrain marine and lacustrine stratigraphic sequences (Zamelczyk et al, 2012; Wastegård et al, 2018; van der Bilt and Lane, 2019), as of yet, little focus has been placed on dating landforms or linking non-visible tephra to relative sea level. Cryptotephra has global potential in aiding regions with poorly constrained glacial and sea level histories, in regions like the Arctic, where other forms of geochronology can be problematic (i.e. lack of organic material for 14C dating, coal or car bonate rocks affecting radiocarbon ages; Wolfe et al, 2004; Timms et al, 2017)
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