Structural Inheritance During Normal Fault Growth in Multi-Phase Rifts: A Case Study From the Northern North Sea

Abstract

In multi-phase rift systems such as the northern North Sea rift, some basement control on the nucleation, growth and linkage of rift-related normal faults is to be expected. However, our understanding of the degree of physical and kinematic linkage between basement and cover structures is limited, since deep structures are generally poorly imaged on seismic reflection data. The North Sea Rift experienced two main phases of rifting, a Permian-Triassic and a Middle Jurassic-to-Early Cretaceous phase. Moreover, prior to rifting, the area underwent multiple episodes of deformation during Ordovician-Early Devonian Caledonian contraction and Devonian extension. In this study we investigate the influence of pre-rift structures on the evolution of Permian-Triassic and Middle Jurassic-Early Cretaceous normal fault systems in the northern North Sea rift. For this purpose we utilize 2D (-9 s TWT) and 3D seismic reflection and borehole data from the North Viking Graben, the Horda Platform and the East Shetland Basin. We show that low-angle (< 30°) intrabasement reflections extend, in some areas, upward into the Triassic section. West-dipping and east-dipping intrabasement structures are identified in the Horda Platform, Stord Basin and East Shetland Basin, respectively. At depth, some of intrabasement structures terminate against a strongly reflective lower-crust. This study documents dissimilar development of intrabasement structures in the Horda Platform, Stord Basin and East Shetland Basin. In the Stord Basin and Horda Platform these structures are better developed while in the East Shetland Basin, only two sets of structures have been mapped. We also show that intrabasement structures in the Horda Platform are generally lower angle than those in the East Shetland Basin. Preliminary observations suggest a complex relationship between pre-Permian intrabasement structures and overlying Permian-Triassic rift-related normal faults, with physical linkage between the two locally occurring along strike. However, pre-existing basement structures seem to have played a significant role on the first order geometry of the North Sea rift system by controlling the location and the strike of the major younger rift-related normal faults in the basin fill.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016