Palynological dating of the Mandal Formation (uppermost Jurassic lowermost Cretaceous, Norwegian Central Graben) and correlation to organic-rich shales in the Danish sector

Palynological investigation of the organic rich Mandal Formation in the type well, 7\12–3A, indicates that the age of the formation is mainly Late Volgian to Early Ryazanian, although the lower part may extend into the Middle Volgian. Dating is based on the last occurrence of Rotosphaeropsis thula at the upper boundary of the formation and of Glossodinium dimorphum immediately below the lower boundary. Identification of a number of stratigraphically important bioevents has permitted a detailed correlation of the Mandal Formation in its type well with equivalent organic-rich shales in the Bo-1 well from the Danish Central Graben. The very close similarities in gamma-log patterns from the two wells, despite the considerable distance (about 180 km) between the wells suggests that the origin of these hot shales should be attributed to regional rather than local factors.