Miocene sedimentary sequences of the Sardinian Graben System as possible analogue for the Upper Jurassic Rogn Formation of the Norwegian Continental Shelf

The Rogn Fm is an Oxfordian to Volgian (Late Jurassic) sand-rich interval recognised in the offshore subsurface of the Norwegian Continental Shelf (Gjelberg et al., 1987, Dalland et al., 1988). In its type well the formation is up to 60 m thick and exhibits a coarsening-upward trend (Provan 1992) (Fig. 1). The Rogn Fm, which has found encased in shelf fines or adjacent to the flanks of structural highs, consists of well-sorted coarse-grained sandstones, made up of sub-angular clasts, diffusely cross laminated, and also including siltstones and shales (e.g., Elliott et al., 2015) (Fig. 1). The Rogn Fm has become even more renowned thanks to its good reservoir properties (P=29%; K=8 Darcy; N/G=0.7) and because it provided promising oil discoveries in the last twenty years. The more accepted interpretation on the depositional genesis of the Rogn Fm is the derivation from the erosion of several hundred of meters of pre-Permian to Upper Jurassic successions from the uplifted Frøya High, and the subsequent accumulation in sheltered coastal zones and/or in more distal ‘shelf ’ environments, tectonically shaped into narrow-elongate depocenters (Provan 1992). The recurrent motif of cross-bedding observable in the Rogn sandstones point out towards a general control exerted by tractional flows, whose strength was possibly influenced by lateral constrictions, generating a series of current-influenced subaqueous bedforms (i.e. in the southern-east Frøan Basin) or transported towards further to north on the Halten Terrace. However, a number of uncertainties related to the sub-seismic depositional architectures or lateral facies changes of the Rogn Fm call for evaluable outcropanalogue studies, useful to constrain or revise preliminary interpretations and, thus, to increase the exploitation potential of the Rogn Fm.