Bridging the gap between Quebec and Newfoundland: new insights on the protracted and diachronic history of the Anticosti foreland basin

Abstract

The offshore part of the Anticosti foreland basin between Gaspé Peninsula (Quebec) and western Newfoundland has been investigated for its petroleum potential, mainly in the 1980s, but its geometry and evolution remain poorly documented. In this study, short-wavelength magnetic markers associated with intra-sedimentary magnetic susceptibility contrasts are interpreted in conjunction with high-resolution seismic data to map the distribution of rock units. Magnetic markers associated with igneous dykes are distinguished from those associated with sedimentary units by their higher amplitude and geometry. Conjunct interpretation of magnetic and seismic datasets provides new insight on the geometry of the Anticosti Basin and indicates that: i) a relatively thick (~ 2 km) post-Llandovery (post- Jupiter Formation) sedimentary succession occurs in the core of two regional synclines where youngest preserved sediments are interpreted as correlative with the Upper Gaspé Sandstone Group - Red Island Road Formation (Emsian–Eifelian); ii) post-Eifelian (Acadian) deformation consists of a series of folds, 2–10 km in wavelength in the Honguedo Strait, north of the Gaspé Peninsula, and to a single greater wavelength fold in the Strait of Belle Isle; iii) newly recognized NW-striking faults that parallel the eastern Gaspé Peninsula shoreline exhibit significant syn- to post-Middle Mississippian movements; iv) the southern boundary of the Anticosti Basin corresponds either to the unconformity at the base of the Carboniferous–Permian Magdalen Basin or to previously poorly documented ESE to NE-striking faults; v) a series of dykes trend from N90° near Gaspé Peninsula to N170° between Anticosti and Newfoundland islands. These new findings are integrated in an evolution model that enhances the stratigraphic and tectonic along-strike variability of the Anticosti foreland basin.