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Time-Structure Maps of the St. Lawrence Lowlands Platform, Southern Québec – Tool for the Identification of Structural Sags and Potential Hydrothermal Dolomite (HTD) Hydrocarbon Reservoirs

Robert Thériault, and Jean-Yves Laliberté, Québec Ministry of Natural Resources, Hydrocarbon Branch, Québec, QC, G1H 6R1

Regional time-structure maps of the Precambrian basement and top of Trenton Group have been produced using over 400 seismic profiles and 120 wells from the St. Lawrence Lowlands. These new maps show the presence of N-S to NE-SW basement faults that parallel the St. Lawrence River, and which are interpreted to have formed during the Cambrian rifting event of Laurentia. A second system of orthogonal E-W oriented faults are interpreted to be related to the Ottawa-Bonnechère graben and to transform faults associated with the drift phase of Iapetus. This structural pattern is also observed on the top of Trenton time-structure map, which implies that these two fault systems were active from the Cambrian to at least the Late Ordovician. Hence fault reactivation may have taken place during the Taconian Orogeny, with a possible strike-slip component in the form of wrench faults. Such structures represent elsewhere prime targets for the formation of HTD reservoirs.

The time-structure maps reveal the presence of several structural sags originating at the top of the Trenton Group. These occur in the Lac St. Pierre and Lotbinière areas, forming linear depressions measuring approximately one km in width by up to 50 km in length. A number of hydrocarbon discoveries have been made along very similar structures in the United States (Albion-Scipio, Lima-Indiana, Finger Lakes) and Ontario (Dover, Lakeshore), within HTD reservoirs associated with the Trenton-Black River interval. However, although these rock formations occur throughout the St. Lawrence Platform in Québec, the HTD play remains to be tested.

AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York