Conférence CGC le 31 janvier 10h : Greg Brooks

Présentation (en anglais) de Greg Brooks (Geological Survey of Canada)

Mercredi 31 janvier 10h, local 2422 (490, de la Couronne)

Evidence of a major paleoearthquake interpreted from landslide deposits in a glacial lake, Ontario-Quebec, Canada

Sub-bottom acoustic profile surveys and sediment coring at Dasserat, Dufresnoy and Duparquet lakes, near Rouyn-Noranda, Quebec, reveal numerous stratigraphic occurrences of subaqueous mass transport deposits (MTDs) that are interbedded within glacial Lake Ojibway glaciolacustrine sediments.  In all three lakes, the stratigraphic level with the greatest number and most laterally extensive MTDs occurred in the identical varve year (vyr) 1483, which is the equivalent to about 9.1 ka cal BP.  These MTDs are part of a larger regional signature in W Quebec-NE Ontario, as revealed by vyr 1483 MTDs identified in: sediment cores at Chassignolle and Malartic lakes, Quebec; varve exposures near the Twin Falls and Frederick House dams; Ontario, and numerous published and unpublished logs of varve exposures from the area.  The vyr 1483 MTD signature extends at least 220 km across W Quebec-NE Ontario, and is interpreted to be best explained by shaking from a paleoearthquake.  The magnitude of the event is estimated to be about Mw ~7.3, which is indicative of a strong paleoearthquake.  The highly-precise correlation of widely-spaced MTDs provided by varves is essential to the paleoearthquake interpretation.