Cryptotephra deposition and preservation in four sub-Arctic lakes in Yukon, Canada

Abstract

Cryptotephra research is one of the fastest growing subfields of tephrochronology. Here the extraction, processing, and analytical techniques required for cryptotephra studies are reviewed and assessed in detail. A workflow is suggested depending on the site’s characteristics to improve the quality of data. The debate surrounding acid digestion procedures and their potential to alter glass geochemistry is specifically addressed, eliminating the concern for glass alteration if methods are correctly followed. Guidelines for tephra identification, shard profile interpretation, and analytical procedures such as the use of secondary standards and time- dependent intensity corrections are presented. The result is a detailed protocol that acts as a guide through the methods of cryptotephra research in lake and peat cores for new researchers to the field while simultaneously improving interlaboratory comparability. Further, four Yukon lakes were processed for cryptotephra to refine their chronologies and support the paleoenvironmental studies at each site. The full Holocene record at Hanging Lake was examined, the Holocene to late Pleistocene at Gravel Lake, and the Pleistocene to Holocene transition at Barlow Lake. Surface cores of Chapman Lake and Gravel Lake were also fully assessed. Multiple limiting factors were found at these lakes, obstructing the preservation and identification of primary cryptotephra deposits. Reworking, secondary deposition, and presence of nearby loess deposits all complicated shard profiles. However, evidence of multiple Holocene eruptions from Mt. Churchill, Augustine, and Aniakchak, and the identification of Redoubt 1989/90, Katmai 1912, Ruppert tephra, Ksudach KS2, and eight unknown glass shard populations reinforce the potential of cryptotephra research on Yukon Lakes.