The Mercia Mudstone Group (Trias) of the East Irish Sea Basin

SUMMARY Recent boreholes in the Fylde, Walney Island and the offshore Morecambe gas field have contributed to a greater understanding of the succession within the Triassic Mercia Mudstone Group, totalling up to 3700 m in thickness in the East Irish Sea Basin. The correlation is dependent on the distinctive colour-laminated Thornton Mudstones, now recognised in an area extending from Walney Island in the north, to Formby in the south and also probably offshore in well 110/8-2. Breccias of Triassic age are distinguished from more recent breccias. The more recent breccias contain porphyroblastic gypsum.