ORIGINAL

Abstract Petrographic and geochemical analyses per-formed on a North Sea core from the Gryphon Field re-veal the presence of palaeo-degassing features surrounded by injected sandstones in the Eocene interval. The injected sandstones are oil-stained and poorly cemented by car-bonate and quartz. 18O isotope analyses indicate that carbonate cementation occurred during shallow burial (likely less than about 300 m). Depleted 13C (around)30 & V-PDB) carbonate cement suggests that bicar-bonate was derived from the microbial oxidation of oil and gas. Late quartz overgrowths enclose oil present in the injected units. The tubular degassing conduits are com-posed of zoned cements and have d18O and d13C isotope values similar to the injected sandstones, indicating that oil and gas seepage induced the precipitation of authigenic carbonate in the shallow subsurface. Oil inclusions in inter- and intra-crystal cement sites in both injected sandstones and degassing conduits indicate that oil seep-age was an ongoing feature at shallow burial. A proposed model involves oil and gas seepage and the formation of the degassing conduits, followed by a sand injection phase. It seems likely that oil and gas continued to leak towards the seabed by exploiting the network of permeable injected sandstones and the horizons of porous degassing features