Extending the late Holocene White River ash distribution, northwestern Canada

Peatlands are a particularly good medium for trapping and preserving tephra , as their surfaces are wet and well vegetated. The extent of tephra-deposi ting events can often be greatly expanded through the observation of ash in peatlands. This paper uses the presence of the White River tephra layer (1 200 B.P.) in peatlands to extend the known distribution of this late Holoce ne tephra into the Mackenzie Valley, northwestern Canada. The ash has been noted almost to the western shore of Great Slave Lake, over 1300 km from th e source in southeastern Alaska. This new distribution covers approximately 540 000 km(2) with a tephra volume of 27 km(3). The short time span and co nstrained timing of volcanic ash deposition, combined with unique physical and chemical parameters, make tephra layers ideal for use as chronostratigr aphic markers.