TOWARDS A CRYPTOTEPHRA FRAMEWORK FOR NORTHERN NORTH AMERICA: CHRONOLOGICAL AND STRATIGRAPHIC IMPLICATIONS FOR SEDIMENTARY SEQUENCES

Cryptotephra studies, utilizing non-visible layers of far travelled volcanic ash produced from explosive eruptions, have expanded rapidly since the 1990s. Cryptotephra have fundamental applications for stratigraphy and chronology as they produce isochronous horizons in sedimentary records over wide geographical areas. If cryptotephra layers are well characterized then their identification within a sedimentary record can be used as tie points to correlate between records locally, regionally, and across continental scales. Additionally, if a tephra has been dated this age can be imported to the age model for the site, or used to test an existing age model.

The recent discovery of distal cryptotephra, including beds from Alaska and the Cascades, in eastern North America (Pyne-O’Donnell et al., 2012) indicates a cryptotephra framework likely exists for much of North America. In this study, we are developing a framework for northern North America, primarily recording eruptions from Kamchatka and southern Alaska. Key layers identified so far during the Holocene include several from Augustine (~2200 BP), Anaiakchak (~3600 BP), and Fisher (~9400 BP) in the Aleutians; the White River North (~1650 BP) and East (~1150 BP) tephras from eastern Alaska; and the Mazama (~7600 BP) and Mt St Helens W (~520 BP) tephras from the Cascades.

This project discusses current knowledge of cryptotephra records in northern North America, with a particular focus on geographical distributions and best age estimates produced using Bayesian modelling techniques. This results in an assessment of the potential for cryptotephra to be utilized by researchers in a wide range of sedimentary records for both stratigraphical and chronological purposes.