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For more than 150 yr, the Gaspé Peninsula in the northern Appalachians has generated interest for oil and gas exploration. Although oil shows and seeps are abundant, oil production has been minor. The hydrocarbon potential is restricted to Late Ordovician to Early Devonian rocks of the Gaspé belt, and different play concepts have been explored over the years. The recent discovery of the Junex-Galt natural gas field has renewed interest for onshore hydrocarbon exploration in this area of eastern Canada.

We propose a new structural model for the Middle Devonian Acadian orogeny involving development of an early foreland thrust and fold belt with deformation accommodated by folding, considerable tectonic wedging, blind north-verging thrusts, south-verging backthrusts, and a possible triangle zone followed by strike-slip faulting that partially dissected the thrust and fold belt. Previous interpretations of the tectonic evolution of the Gaspé belt during the Acadian orogeny was that of a tranpressional orogen basically characterized by folds and strike-slip faults compatible with a wrench tectonic model. Instead, new field work and seismic data that were acquired by the Ministère des Richesses Naturelles du Québec (2000–2001) and presented here suggest enough shortening during the initial compressive phase to produce south-verging folds and south-directed motion along north-dipping reverse faults.

The fold and thrust belt structural style proposed in this chapter offers a promising geological setting for potential structural traps and new hydrocarbon plays in the entire Gaspé Peninsula. Highly fractured zones are expected in domal structures above important blind thrusts and at thrust tips in areas of fault-propagation folding. Hydrocarbon migration has been documented through fractures in the Upper Ordovician to Lower Devonian Gaspé belt succession at different stages of its tectonic history. Major anticlines in the northeastern part of the Connecticut Valley-Gaspé synclinorium, i.e., Mississippi, Bald Mountain, and Holland anticlines, could be fault propagation located above blind thrusts. The Junex-Galt natural gas field is a good example of such a tectonic setting. Gas is trapped in a folded and fractured Devonian limestone that is located between two regional strike-slip faults at a depth of about 2250 m (7400 ft). Geochemical analyses from recovered oils in the area indicate a Devonian as well as an Ordovician origin very similar to oils from western Newfoundland. A large Ordovician anticline, which was imaged on old and newly acquired seismic lines, underlie the Galt area and represent deeper plays located above blind thrusts deep within the Acadian fold and thrust belt.

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