engleski

Architecture and sequence stratigraphic perspectives of the Dunlin Group formations and proposal for new type- and reference wells.

The Lower Jurassic Dunlin Group is formally subdivided into the Amundsen, Johansen, Burton, Cook and Drake Formations, and these are redefined herein on basis of the well-logs and cores from the Veslefrikk Field. The Johansen sandstones are reinterpreted as a northwestward prograding delta, and the Cook Formation is broadened in stratigraphic span to include all thick sandstone bodies informally referred to as the "Intradunlin" and "Intradrake" sandstones. The Cook sandstones of the Veslefrikk Field are interpreted as tidal bars in an estuarine setting. In order to provide better correlability of the Dunlin Group formations recognized, and better match with the recent high-resolution well-logs, the new type- and reference-wells are proposed. This are the 30/3-2 (type-well) and 30/3-3, 34/10-21, 34/10-9, 34/4-3 (reference-wells). The type-well on the Veslefrikk Field is selected because it is centrally located and all of the Dunlin Group formations are developed. A large number of extensive flooding surfaces is recognized within the Amundsen, Burton and Drake Formations, and some are attributed to the maximal floodings. These are assumed horizontal and used as datum lines for the well-log correlation. Seven depositional units bounded by erosional surfaces are recognized. The erosional surfaces are bounding the incised valleys created during the sea-level lowstands and the overlying sediments are interpreted as possibly late lowstand (locally), transgressive and highstand valley-fills. These are recognized as the Cook Fm. that typically comprises fine-grained sandstones of tidal- and wave-influenced origin, followed by coarser-grained tidally-constructed sandstone bodies with the ravinement surface on the top, overlain by shales and heterolithics of the Drake Fm.

Jurassic, Dunlin Group, well logs, North Sea, Norwegian Sector

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