Abstract

The northeastern Gaspé Peninsula is divided into two distinct tectono-stratigraphic domains: Cambro–Ordovician rocks of the Humber and Dunnage zones, to the north, and Siluro–Devonian rocks of the Gaspé Belt, to the south. The northeastern part of the Gaspé Belt is being investigated for its hydrocarbon potential. This area is dissected by major NW-trending faults that divide the study area into three tectonic domains: the northern, central and southern blocks. During the Late Silurian-Early Devonian Salinic disturbance, the faults were active as synsedimentary normal faults. Faults were reactivated as dextral strike-slip faults during the Middle Devonian Acadian Orogeny. Regional Acadian folds are ENE- to E-trending. Locally, NW-trending folds related to the Salinic disturbance occur close to the faults.

Because of their total organic carbon content (TOC), the Cambro-Ordovician rocks were considered to be more likely source rocks than rocks of the Siluro-Devonian Gaspé Belt before maturation.

Good source rock intervals are locally present in the York River Formation, in all the tectonic blocks of the study area. These beds are rich in organic matter, are marginally mature and of limited extent. Based on TOC and Rock-Eval analyses, the Indian Point and Forillon formations show significant thicknesses of fair source rocks in some wells of the central block where most oil indications and seeps occur. Our results indicate that these source rocks have the highest hydrocarbon potential.

A new calibration is proposed between the reflectance of collotelinite (standard vitrinite) and that of chitinozoans and solid bitumen, which are more common than vitrinite in marine successions of the Gaspé Belt. Interpretation of reflectance analysis indicates that thermal maturation in the Gaspé Belt succession is primarily related to burial and occurred during deposition of the Gaspé Sandstones. Maximum burial is contemporaneous with Acadian ENE- to E- trending folding and pre-dates strike-slip faulting. Oil and condensate in Indian Point and Forillon formations were mostly produced before the Acadian deformation, but after the Salinic disturbance. Potential source rocks of the York River Formation generated some oil during and after Acadian deformation.

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