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 th e type well, 7/12-3A, indicates that the age of the formation is mainl y Late Volgian to Early Ryazanian, although the lower part may extend into the Middle Volgian. Dating is based on the last occurrence of Rot osphaeropsis thula at the upper boundary of the formation and of Gloss odinium 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 equ ivalent organic-rich shales in the Bo-l well from the Danish Central G raben. The very close similarities in gamma-log patterns from the two wells, despite the considerable distance (about 180 km) between the we lls suggests that the origin of these 'hot shales' should be attribute d to regional rather than local factors. (C) 1998 Elsevier Science Ltd . All rights reserved.