Tectono-stratigraphic development of a salt-influenced rift margin; Halten Terrace, offshore Mid-Norway

In salt-influenced rift basins the presence of a pre-rift salt layer will control the tectono-stratigraphic evolution of the rift due to the decoupling of the sub- and suprasalt faults leading to temporal and spatial variations in structural style. Lateral variations in rift flank structure will control the dispersal and volumes of sediment deposited in rifts and along rifted margins, which in turn impacts facies distributions within syn-rift stratigraphic successions. We here use 3D seismic reflection and borehole data to study the tectono-stratigraphic development of the Halten Terrace, offshore Mid-Norway, a salt-influenced rifted margin formed during Middle to Late Jurassic extension. On the eastern basin margin the rift structural style passes southwards from an unbreached extensional growth fold dissected by numerous horst and graben (Bremstein Fault Complex), into a single, through-going normal fault (Vingleia Fault Complex). This southwards change in structural style is likely related to the pinch-out of or a change of lithology (and thus rheology) within a prerift (Triassic) evaporite layer, which was thick and/or mobile enough in the north to decouple basement- and cover-involved extension, and to permit forced folding. The salt-influenced Bremstein Fault Complex underwent limited footwall uplift, with minor erosion of relatively small horsts supplying only limited volumes of sediment to the main downdip depocentre. In contrast, the more directly basement-coupled Vingleia Fault Complex experienced extensive footwall erosion, in addition to collapse of its footwall due to salt-detached gravity gliding. Our results show that where through going normal faults develop along the rift flanks, the presence of a pre-rift salt layer will suppress footwall topographic expression. The pre-rift salt layer will facilitate footwall collapse and limit the sediment supply to the basins downdip. In addition, our result shows that variable topography along the rift flanks facilitated small, localised, intra-rift flank accommodation space limiting sediment supply deeper into the rift basin.