Josep Maria Puig Lopez, Miquel Poyatos-Moré, John Howell

Thin, condensed coarse-grained shallow-marine successions can be difficult to describe and interpret, especially in the subsurface because they commonly lack finer grained intervals which are typically associated with sequence stratigraphic surfaces. This lack of mudstones and siltstones means that they also typically make excellent reservoir intervals. The Oxfordian to Volgian intra-Draupne Formation sandstones in the Johan Sverdrup Field, southern Utsira High, represent such a system. This study presents a new, basinwide sequence stratigraphic model that unravels the detailed depositional history of the succession and places its formation within a regional Late Jurassic tectonostratigraphic framework. The succession is comprised of four parasequences deposited following a regional Kimmeridgian marine flooding event. Sediments were mainly supplied through Haugaland sourced fan deltas and longshore currents reworking the Avaldsnes High. The first parasequence shows a distinctive suite of facies consisting of fine-grained and mud-rich bioturbated sandstones deposited in a protected back-barrier lagoon. Subsequent parasequences lack fine grained sediments and are dominated by bidirectional cross stratified, coarse-to-very coarse sandstones and gravels deposited in a tidal strait. A progressive reduction of fault related subsidence in the Middle Volgian along with Late Volgian-Ryazanian sea level rise and inversion of pre-existing structures, promoted backstepping of the feeder systems, sediment starvation and the progressive deposition of the black and green-red shales of the Draupne and Asgard formations. This study accounts for features previously unidentified in the basin and which have implications for understanding the deposition of coarse-grained shallow marine successions around the Utsira High and other transgressed basement highs.