Growth of salt-induced structures in the Norwegian-Danish basin

Abstract

Five relatively deep-seated salt plugs, situated in the Norwegian-Danish Basin, have been investigated. The Zechstein salt has pierced the Triassic and probably also the Jurassic strata in the area. In two of the structures salt has also intruded Lower Cretaceous strata. Otherwise, however, the relative upward movement of the salt has only resulted in the formation of salt-induced dome-shaped structures in the Lower Cretaceous and younger sediments overlying the salt plugs. Isopach maps, based on seismic reflection data, show that, as a rule, relative upward movement of the salt plugs has occurred during sedimentation. Such movements find their expression in local thinning of the interval, superimposed, as a rule, on a regional thickening. Using on-structure and off-structure thickness data, a quantity called the “convergence” can be calculated which numerically measures the proportional thinning of an interval over a given structure. The convergence values, thus calculated, show that there was continuous structural growth in all four structures that can be investigated in this way in Lower Cretaceous and later times except in Eocene times when there possibly was no growth at all in any of the four investigated structures. It is also found that a typical time-rate of growth during the post-Jurassic for these salt-induced structures is 1 mm per 1000 years (1 · 10 −3 mm/year) except for the Eocene where the rate of growth was possibly zero.