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Abstract

R. Swennen, F. Roure, and J. W. Granath, eds., Deformation, fluid flow, and reservoir appraisal in foreland fold and thrust belts: AAPG Hedberg Series, no. 1, p. 412-430.

Copyright © 2004 by The American Association of Petroleum Geologists.

DOI:10.1306/1025703H13127

Structural Style and Hydrocarbon Potential in the Acadian Foreland Thrust and Fold Belt, Gaspeacute Appalachians, Canada

D. Kirkwood,1 M. Lavoie,2 J. S. Marcil3

1Deacutepartement de Geacuteologie et de Geacutenie Geacuteologique, Universiteacute Laval, Queacutebec, Canada
2Deacutepartement de Geacuteologie et de Geacutenie Geacuteologique, Universiteacute Laval, Queacutebec, Canada
3Junex Inc., Queacutebec, Canada

ACKNOWLEDGMENTS

The model presented in this chapter is the result of detailed field work conducted by the coauthors in northeastern Gaspeacute. Our ideas evolved because of numerous discussions with colleagues who have worked for many years in the Gaspeacute and have seen almost every outcrop. Special thanks go to Michel Malo, Pierre-Andreacute Bourque, Daniel Brisebois, and Rudolf Bertrand, who unselfishly shared all of their unpublished results. We would like to acknowledge C. Morin and J.-Y. Laliberteacute from the Ministegravere des Ressources Naturelles du Queacutebec for permission to publish their seismic line. We are also indebted to Junex, Inc., for their continued financial and logistical support of our research projects in eastern Gaspeacute, and particularly to Jean-Yves Lavoie, for his relentless and aggressive exploration of the Gaspeacute Peninsula over the years and his support of new ideas. Thanks to the Geological Survey of Canada, Queacutebec Office (National Mapping Project [NATMAP]–Geological Bridges of eastern Canada) for financial and logistical support during the 2001 field season. Additional field work and scholarships to M. Lavoie were funded by a Natural Sciences and Engineering Research Council individual research grant to D. Kirkwood. M. Lavoie acknowledges financial support from the Fonds pour la Formation de Chercheurs et l'Aide aacute la recherche. This chapter was substantially improved because of AAPG Bulletin reviewers, A. Bally, R. Price, and G. Stockmal. Their comments helped improve the organization of the chapter and made the final version more easily accessible to a sophisticated worldwide audience.

ABSTRACT

For more than 150 yr, the Gaspeacute 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 Gaspeacute 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 Gaspeacute 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 Ministegravere des Richesses Naturelles du Queacutebec (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 Gaspeacute 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 Gaspeacute belt succession at different stages of its tectonic history. Major anticlines in the northeastern part of the Connecticut Valley–Gaspeacute 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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