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This Article Figures Only Full Text Full Text (PDF) All Versions of this Article: B26305.1v1 121/11-12/1570    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Ahmad, J. Articles by Pawlowicz, J. G. GeoRef GeoRef Citation

High-resolution seismic and resistivity profiling of a buried Quaternary subglacial valley: Northern Alberta, Canada

Jawwad Ahmad¹, Douglas R. Schmitt^1,, C. Dean Rokosh^1,2 and John G. Pawlowicz²

¹ Institute for Geophysical Research, Department of Physics, Mailstop #615, University of Alberta, Edmonton, Alberta T6G 2G7, Canada
² Alberta Geological Survey, 4th Floor, Twin Atria Building, 4999-98 Ave. NW, Edmonton, Alberta T6B 2X3, Canada

Correspondence: E-mail: doug{at}phys.ualberta.ca or doug.schmitt{at}gmail.com

High-resolution seismic and resistivity profiles were acquired to assist in the delineation of a buried Quaternary subglacial valley, the existence of which was first discovered by drilling. One aspect of this valley is the glacial sediments that host substantial methane at shallow depths (~50 m or less). Geophysical well logs indicate that the glacial sediments in this area generally have lower compressional wave speeds V_P <1800 m/s and greater electrical resistivity r >10 ·m than adjacent undisturbed Cretaceous-age rocks, which have V_P >2200 m/s and r <10 ·m, respectively. Seismic-refraction velocities, seismic-reflection architecture, and electrical resistivity tomography images all indicate a deep (>300 m) valley. The reflection profile reveals a complex series of events consistent with heterogeneous deposition. One major reflection dips eastward across the valley. The reflection character changes abruptly on either side of this event, with dipping clinoform reflections beneath and nearly horizontal reflections above. These may be related to changes in deposition processes beneath a retreating ice sheet, as has been suggested by earlier workers. The buried valley's basal reflections are complex and possibly reflect glaciotectonic deformation or block plucking. The near-surface methane gas is within, but at the edge of, the valley. The methane gas–saturated zone displays anomalously high resistivities both in the well logs and in resistivity tomography.