Paleozoic Brine and Gas Seeps on Anticosti Island: Impacts for Developing Unconventional Hydrocarbon Resources

English Abstract:

The Upper Ordovician Macasty shale on Anticosti Island hosts hydrocarbon potential currently being evaluated for non-conventional extraction. This study focuses on groundwaters in the region for evidence of deep groundwater discharge to shallow aquifers and at surface. Of particular interest is the high salinity spring, Source-de-Saumure-de-la-Chaloupe, situated near the Chaloupe River on Anticosti Island. At this spring, water is discharging at about 0.05 L s^–1 with salinity of 3x seawater and accompanying gas ebullition at a rate of roughly 10 cc s^–1. The water precipitates calcite, forming a mound measuring about 1 m in height and 30 m in diameter around the main vent. Stable isotopes and geochemistry of the waters indicate them to be a mixture between shallow, meteoric waters and basin brines of evaporated seawater origin. The gas is dominated by methane with δ¹³C values from –57.7‰ (June 2014) to –44.3‰ (July 2013) that suggests a mixture between biogenic and thermocatalytic methane. The dissolved inorganic carbon has an enriched δ¹³C signature (+9.2‰) indicating that the DIC is affected by biogenic methanogenesis. Preliminary DNA sequencing results of biofilms growing in the brine suggest that bacteria and archaea likely play a role in carbon cycling. Our current hypothesis in this evolving study holds that shallowly circulating, methanogenic groundwater in the karstic aquifers of Anticosti Island acquires contributions of basin brine with thermocatalytic methane from the deep Paleozoic strata via a system of fracture permeability associated with the adjacent Jupiter fault. Ongoing research focuses on noble gases and ¹⁴C with stable isotopes of the carbon pool to resolve the origins of the mixing fractions.