Oblique rifting and sequential faulting in the Jurassic development of the northern North Sea

Abstract

Jurassic structural development of the northern North Sea has characteristics of oblique rifting. This is interpreted to result from an obliquity between Jurassic NW-SE-to WNW-ESE-directed extension and a preexisting N-S-trending zone of deformation related to Permo-Triassic rifting and thinning of the crust. The zone of maximum Jurassic extension i.e. the Viking and Sogn grabens, defines a narrow (25–40 km) depression which trends diagonally (NNE-SSW) across a broader (130–150 km) Permo-Triassic basin. The Jurassic rift zone consists of a system of ene´chelon rift segments, with changing symmetry along strike, bounded by faults oblique to the overall graben envelope.Sequential Jurassic fault development as well as the interference between N-S- and NE-SW-striking faults are explained within the context of oblique rifting. The early (Late Bajocian-Oxfordian) rift stage was dominated by reactivation of N-S-striking major faults, whereas a number of coeval but smaller faults have a NE-SW orientation. NE-SW-striking faults show increasing importance during the Jurassic stretching phase, and major faults defining this orientation accommodated most of the Kimmeridgian-Volgian extension. Faults striking NESW ] are observed to cross-cut earlier N-S-trending faults; they interfere with N-S-trending faults to define faultblocks with rhombohedral shape; and they are associated with partial collapse of crestal areas of N-S-oriented fault-blocks to form structural terraces.