Normal fault growth and fault-related folding in a salt-influenced rift basin: South Viking Graben, offshore Norway

Three-dimensional seismic data were analysed to reconstruct the structural and stratigraphical development of a salt-influenced rift basin and thus gain an understanding of the relationships between normal fault growth, salt tectonics and the evolution of syn-rift depocentres. The Sleipner Basin, South Viking Graben, northern North Sea, is ca. 30 km long by 8 km wide and is bound to the east by a major extensional fault zone (Sleipner Fault Zone). Two types of fault-related fold are identified within the basin: (1) A fault-parallel monocline, interpreted as an extensional forced-fold, which formed through the upward propagation of the Sleipner Fault Zone through ductile evaporites of the Zechstein Supergroup and (2) three fault-perpendicular, salt-cored anticlines that compartmentalise the basin into four sub-basins and are related to displacement gradients along-strike of the Sleipner Fault Zone. Detailed seismic-stratigraphic analysis of pre- and syn-rift stratal units reveals a complex interplay between fault growth and salt movement which strongly controlled the evolution of syn-rift depocentres. During the early syn-rift, a series of depocentres, separated along-strike by the fault-perpendicular folds, were offset into the axis of the basin (ca. 3–4.5 km to the west of the Sleipner Fault Zone) by the fault-propagation fold. Later in the rift event, the influence of the fault-perpendicular folds depleted, resulting in a larger, interconnected depocentre that shifted into the immediate hangingwall of the fault as the surface of the fault-propagation fold was breached. The results of this study have implications for normal fault growth and sedimentary depocentre development in salt-influenced rift basins, and contribute to the general understanding of the controls on salt migration.