Salt tectonics in the southern North Sea, the Netherlands

Abstract

In the Netherlands sector of the continental shelf salt structures are almost exclusively formed by Zechstein salt. Almost without exception these are related to basement faults, which have controlled the relative location of the salt structures, the triggering of salt movement, and the rate of salt movement. Differences in development of salt diapirs coincide with structural units. Dip-slip movement along basement faults enabled the upward flow of salt, because it weakened the overburden and created a differential stress field due to differential loading. Buoyancy related to density inversion alone seems insufficient to deform the overburden. Faulting is the trigger mechanism for the salt movement. The larger the throw on the fault, the further the salt structures will develop. A relationship has been proven between the timing of deformation phases and increased intensity of salt movement. It is shown that the intersection of fault systems in the basement is reflected in the geometry of the salt structures. In the study area, many hydrocarbon accumulations are related to salt structures. The hydrocarbons have been trapped in configurations, either structural or stratigraphie, that formed in response to the formation of the salt structures. Salt generally acts as a seal, but migration routes for hydrocarbons from below-salt source rocks into higher strata occur in areas of salt depletion. The study is mainly based on 2000 km of a regional 2D seismic survey (SNST83, Nopec/Geco-Prakla).