Salt diapirs of the southwest Nordkapp Basin: analogue modelling

Abstract

The geometry and evolution of the salt diapirs in the southwestern segment of the Nordkapp Basin (SW NKB) were interpreted on reflection seismic data. Reflection seismic profiles were used to build a dynamically scaled model analogue to study salt tectonics of the basin. The model was prepared using lengths, densities, and sedimentary histories obtained from seismic and well data. Model results suggest that the salt structures in the SW NKB were influenced by basement faults that horizontally stretched and faulted their overburden and induced salt flow by differential loading. Model diapirs rose only where the overburden was faulted. The salt structures are aligned in two NE-SW rows that parallel the major basement faults that outline the basin. Carboniferous salt in the SW NKB formed conformable pillows in the Early Triassic (Scythian), which became diapiric during the late Early and Middle Triassic. The salt diapirs spread to form asymmetric broad overhangs at superficial levels during slow sedimentation in Late Triassic and/or Jurassic. Diapir overhangs were later reactivated because of burial by Cretaceous and Tertiary sediments. Basement faults were mapped by comparing thickness of the sediments and/or level of the reflectors on either side of the diapirs that had relatively narrow overhangs. Depth conversion and restoration of velocity pull-up of reflectors beneath salt diapirs suggest that the salt diapirs of the SW NKB have broad overhangs above narrow stems.