Geophysical and geological characteristics of cross-cutting reflectors in the East Irish Sea: implications for glacial gas-hydrate formation and weathering fronts

Indicators of fluid migration and pressure-temperature changes in glaciated settings provide constraints on past ice-thickness, subglacial hydrology, and subsurface fluid behaviour. The East Irish Sea is a glaciated shelf area hosting hydrocarbon fields, wind farms, potential sites for Carbon-Capture and Storage and Hydrogen storage, and nuclear-waste sequestration. Two cross-cutting reflections (CCR) have been identified 80 m and 170 m below sea-level on seismic data acquired in 20 m of water in the EIS. The CCRs are imaged where they cross-cut normal seismic-stratigraphic reflections. An exploratory borehole provides petro-physical wireline data. The CCRs resemble gas-hydrate or diagenetic Bottom Simulating Reflectors (BSRs) representing palaeo-hydrate BSRs, formed during the last glacial maximum when conditions for a Gas-Hydrate Stability Zone (GHSZ) existed beneath thick ice accumulations. However an oxidation weathering front, in the presence of freshwater infiltration at sea-level low-stands during glacial periods, represents an equally plausible model. In the palaeo-BSR scenario, depth of the CCRs below basal Quaternary could be used to calculate ice-thickness required for establishment of a GHSZ. The weathering scenario would provide constraints on fresh-water flushing during glaciation. Both scenarios inform possible future conditions at the site, which is close to present and planned energy and waste facilities.