30 years on - Arctic Upper Palaeozoic stratigraphy, depositional evolution and hydrocarbon prospectivity

The southern Norwegian Barents Sea - Svalbard - North Greenland area formed the central portion of the east-west oriented northern Pangaean shelf during Carboniferous and Permian times. Integration of onshore geological data and offshore, mainly geophysical data, has greatly improved our understanding of the evolution of this part of the shelf during Late Palaeozoic time. The four-fold lithostratigraphic division of the succession reflects long, 15-30 Myr periods of relatively stable depositional conditions separated, at the group boundaries, by abrupt changes which can be linked to ongoing rifting of the area and the northward drift of Pangaea. Deposition of the dominantly non-marine Billefjorden Group started onshore in the Late Famennian (in the offshore areas during the Early Viséan) and continued into the Early Serpukhovian. Following regional uplift, sedimentation resumed diachronously during mid-Serpukhovian - Early Moscovian times. The climate changed from humid to arid during the latest Serpukhovian, and the bulk of the Gipsdalen Group is characterised by warm-water carbonates and evaporites. The Upper Sakmarian -Artinskian (?lower most Kungurian) Bjarmeland Group reflects deposition on a cool-water carbonate shelf. The mid-Sakmarian shift from warm-to cool-water carbonates seems to predate a comparable transition in the Sverdrup Basin which is dated to have taken place 5-8 Myr later, in the Early Artinskian. During Kungurian and younger Permian time the central Pangaean shelf was dominated by deposition of deeper water spiculites and shale, and sandstones and cold water carbonates were restricted to isolated highs and the southern shelf margin. Moscovian-Asselian exposure-capped shelf carbonates and Palaeoaplysina - phylloid algal buildups of the Gipsdalen Group form the most prospective reservoir rocks in the region. The top of the main reservoir interval is defined by a major, Early Sakmarian, flooding surface which forms a regional seismic mapping horizon. Post-depositional fresh-water modification of the carbonates took place locally due to Artinskian and younger Permian uplift and subaerial exposure. Mapping of Permian karst systems is a major task for better reservoir predictions.