--> Synthesis of Salt Tectonics in the Southern North Sea, by M. P. Coward and S. Stewart; #90986 (1994).

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Abstract: Synthesis of Salt Tectonics in the Southern North Sea

Michael P. Coward, Simon Stewart

The role of Permian salt as a major control on structural style in the southern North Sea has long been recognized. Most published work however has been confined to specific areas within the basin and has failed to recognize the role of basin-wide gravity induced tectonics within the post-salt section.

A structural model encompassing the southern North Sea basin west of the Central Graben has been developed. This model consists of a rift system affecting the post-salt section around the margin of the basin, formed in response to basin tilt and growth of the underlying basement fault scarps from the Triassic to Paleogene. Extension across the graben systems at each side of the basin was balanced by the sum of the heaves at pre-salt (Rotliegend) level and shortening across salt-cored buckle folds ("salt pillows") in the post-salt section. The salt tectonics during this period of basin extension resulted from gravity sliding above the detachment in Permian salt. Subsequent Cretaceous and Tertiary tectonic inversion involved both basin tilt and movement on discrete faults. The post-salt sedimentary section experienced gravity spreading in response to this inversion-related uplift, resulting in syn-inversion extensional faulting where the Mesozoic section was thickest. This extension, combined with loss of fault heave in the pre-salt section was balanced by further amplification of salt-cored buckle folds in the center of the basin, so that the growth history of the folds can be balanced by the growth of the grabens over the zone of inversion.

Reactive diapiric salt walls were generated by extension of the post-salt section at the basin margins. The generation of salt walls and diapirs within the basin is recognized as the end product of a process beginning with crestal collapse of the buckle folds, followed by reactive then active diapirism, then limb collapse, forming rim synclines around central salt walls. In this model, salt pillows and walls are a passive effect of gravity driven structuration in the post-salt section.

The model is illustrated by seismic panels and analogies with other areas of salt tectonics. The model can be used to explain the structures in many other salt-bearing intracontinental rift basins.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994