Microstructural analysis and geochemical vein characterization of the Salinic event and Acadian Orogeny: evaluation of the hydrocarbon reservoir potential in eastern Gaspe

For the past century, eastern Gaspe Peninsula has generated an interest in oil and gas exploration. This paper examines the fractured reservoir play i n the Upper Ordovician to Lower Silurian limestones of the White Head Forma tion. The White Head Formation is strategically important for play concepts in eastern Gaspe because of its stratigraphic position, overlying potentia l source rocks of Cambrian and Ordovician age, and underlying Silurian and Devonian rocks that host oil seeps. Combined microstructural and petrograph ic evidence, as well as isotope geochemistry, helped in proposing a genetic link between fracture sets and the Salinic event and Acadian Orogeny. The proposed tectonic model involves three distinct events beginning with shall ow to moderate burial, followed by fracturing and uplift as a result of nor mal faulting during the Salinic disturbance, and deeper burial, fracturing, folding and strike-slip faulting during the Acadian Orogeny. Fractures tha t developed within the White Head limestones during the Salinic event and t he Acadian Orogeny contributed to enhance porosity and permeability to some extent at different stages during the entire tectonic history of the rocks . The presence of liquid hydrocarbon inclusions in Salinic veins and methan e inclusions in the Acadian veins indicates that hydrocarbon-rich fluids mi grated through the fracture network. The Salinic fracture network could the refore have provided a pathway for expulsion of liquid hydrocarbons from so urce rocks before they became overmature.