Structural models for the evolution of the North Sea area

Abstract

During the past decade, numerous theories on the geometry and kinematic evolution of fault systems have been expounded. Listric normal faults with shallow detachments generate roll-over anticlines. Alternatively, planar faults bounding rigid blocks, the ‘domino’ model, may be more realistic in many areas of the North Sea. From onshore analogues, relay ramps connecting en échelon extensional faults are shown to be more common than transfer faults. Recent work on fault displacement gradients has generated realistic models involving planar faults with ‘soft linkages’ for fault systems. Inversion tectonics and halokinesis are commonly observed in the Southern and Central North Sea, and their effects are sometimes difficult to separate using seismic profiles. Scaled analogue models have provided graphic illustrations of the progressive development of structures. The construction of balanced cross-sections, increasingly used in North Sea interpretations, is a technique that may be used to test the various geometric models. Links between fault system geometries at upper crustal levels and deeper crustal processes have been established using field studies, notably in the Basin and Range Province, coupled with the interpretation of COCORP and BIRPS deep seismic reflection profiles. Geometric, thermal and flexural isostatic factors are used in sophisticated modelling of lithospheric processes in the North Sea. Structural styles vary in different regions of the North Sea due to the underlying basement grain and the presence or absence of Permian and Triassic evaporites.