Relationships between basement faulting, salt withdrawal and Late Jurassic rifting, UK Central North Sea

Abstract

Seismic data are presented to illustrate the variety of structures found at the margins of the Central Graben and intra-graben horsts. The complexity of these structures is due to the interplay of Late Cimmerian basement extension and older salt withdrawal structures within the Zechstein–Jurassic interval. Basement extension occurred in phases from the Permian to Late Jurassic. Salt withdrawal commenced in the Triassic and continued to the Cretaceous, resulting in a network of salt withdrawal synclines and areas of salt preservation, termed ‘pods’ and ‘interpods’, respectively. During Late Jurassic extension and rifting, the interaction of basement normal faults and the overlying Zechstein–Jurassic section resulted in structures which vary according to the precise location of the basement fault beneath a pod–interpod complex. Variation in the type and complexity of structuring along basin margins results from the highly variable nature and degree of salt withdrawal prior to Late Jurassic rifting. Complex graben margin structures frequently lend themselves to be interpreted as wrench faults, with different implications for structural and stratigraphic interpretations compared to salt withdrawal interpretations. Careful evaluation of structural style at graben margins therefore has important implications for both prospect mapping and regional structural models