MAGNETOSTRATIGRAPHY OF THE MIDDLE-JURASSIC-BRENT-GROUP IN THE OSEBERGOIL-FIELD, NORTHERN NORTH-SEA

Magnetopolarity stratigraphy of the Brent Group and the uppermost part of the Dunlin Group has been established in two well cores from the O seberg Field (well 30/6-7 and well 30/9-2), northern North Sea. Palaeo magnetic analysis of thermal demagnetization results defines a series of normal and reverse magnetozones in both wells. Remanent coercivity analysis of these Middle Jurassic clastic sediments indicates a magnet omineralogy independent of grain size interpreted to be of diagenetic origin, thus suggesting that the magnetization is of early post-deposi tional origin. Integration with the existing palynostratigraphic frame work results in the establishment of several isochronous horizons, esp ecially in the Ness Formation, which suggests lateral continuity of ma gnetostratigraphic datum planes between the two wells at the Oseberg F ield. Although the exact dating of the magnetozones is not established , the combined application of magnetopolarity and biostratigraphy prov ides a stratigraphic framework of improved resolution for these rock f ormations.