ABSTRACT

The middle-late Miocene Utsira sandstone of the North Sea Basin contains a fully preserved, regional marine sand deposit that records a stable paleogeographic setting of shelf sand transport and accumulation within an epeiric shelf sea which persisted for ca. 8 Myr. The sediment dispersal system was defined by (1) sediment input through a prograding strandplain platform, coast-to-shelf bypass, and regional basin-centered transport and deposition within an elongate seaway; (2) a high-energy marine regime; (3) very low rates of sediment supply and accumulation in the accommodation-dominated seaway; (4) high sediment reworking ratio and consequent abundance of autochthonous sediment; (5) regional along-strike sediment transport; and (6) local to subregional landward sediment transport. Shelf systems were primarily nourished by sediment reworked from the Shetland strandplain, which prograded eastward into the central Viking Trough. The Viking strait lay between the constructional platform and the nondepositional Horda Platform. Southward longshore transport on the high-energy shoreface and shallow shelf platform constructed the mounded south Viking shelf shoal. Southward-building sandy banner banks that formed along the recurved arc of the platform margin nourished the shoal system. Low-angle sigmoid clinoforms with downstepping, aggradational tops are distinctive architectures of the strike-fed sand bodies. The combination of strong marine currents and slow but continual sand supply from the Shetland strandplain created regional, sandy shelf depositional systems that individually covered 3500 to 6000 sq. km. of basin floor. Defining elements of the shelf shoal systems include their location within the basin axis, mounded morphology, stratal architecture, and construction by amalgamated marine sand facies.