Late Jurassic plays along the western margin of the Central Graben

Abstract

The distribution of the Lower Kimmeridgian Fulmar sands along the edge of the Western Platform of the Central Graben is intimately related to Triassic halokinetic activity. Withdrawal of Zechstein evaporites resulted in the development of thick packages of Triassic Smith Bank claystones, the so-called ‘Smith Bank Pods’. The crests of the Zechstein evaporite highs were later subjected to groundwater dissolution, resulting in topographic lows, which controlled the pattern of drainage during the deposition of the Triassic Skagerrak sands. The Triassic salt movements associated with this phenomenon also exercised the underlying control on later drainage patterns in the Jurassic. The relative sea-level rise in the Early Kimmeridgian flooded the margin of the Western Platform which reworked the original valley fill and, together with erosion products from the hinterland, resulted in the deposition of the shallow marine sands of the Fulmar Formation. 3D seismic can reveal the extent of these palaeovalley systems draining into the Central Graben. The Fulmar sand packages are effectively encased in shales; a lateral seal is formed by the Smith Bank Formation and the top seal consists of Kimmeridgian shales. They represent an attractive possibility for stratigraphically trapped hydrocarbons.