Northeastern Section - 37th Annual Meeting (March 25-27, 2002)

Analyses of modernly reprocessed and reinterpreted vintage seismic reflection data provide cost-effective results and a better image of the subsurface structural architecture of the St. Lawrence platform and Appalachians of southern Quebec. A key data-set currently being evaluated is a trio of seismic reflection profiles recorded in 1978 for the Government of Quebec. The seismic lines (2001, 2002, and 2003) represent a total of 270 line-km of data. Line 2001 is the longest profile, extending across the full width of the southern Quebec Appalachians. All three lines cross the mapped surface position of the Appalachian structural front (Logan’s Line). The seismic data were recorded using a Vibroseis source, 58-12 Hz sweep, 48 channels, and 12 fold coverage. The post-stack reprocessing was carried out at the Geological Survey of Canada (Calgary), using a ProMAX^TM seismic processing system. The input digital files were original, unfiltered stack data. Processing steps applied were bandpass filter, F-X deconvolution, dip scan (slant) stack, Kirchoff time migration, and trace amplitude equalization. The enhanced reprocessed data provide new and more reliable interpretations of subsurface geology. New observations include: 1) thrust and fold structures northwest of the mapped structural front, within the St. Lawrence platform. For example; a possible incipient triangle zone structure located above a footwall ramp of the principal Appalachian décollement; 2) ramp-associated folds and detached thrust sheets, and tectonic wedges; 3) presence of both extensional and compressional structures within the platform, including southeast- and northwest-dipping faults, forming half-graben., and possible platform overlap features, related to fault inversion?; 4) shallow sub-horizontal décollement beneath thrust nappes; 5) steep dipping margins delineating the anticlinorium of the hinterland, including NW-dipping back thrusts on the NW limb, and SE-dipping normal faults on the SE limb; 6) the sub-surface geometry of the hinterland dominated by stacked thrust wedges. The seismic reprocessing and ensuing interpretation and integration with other geoscience data may provide a new impetus for oil and gas exploration along the St Lawrence Lowlands and Appalachians of southern Quebec.