Fault Evolution and Structural Inheritance Over Multiple Phases of Rifting: Horda Platform, Northern North Sea

Abstract

In multi-phase rift systems, the influence of early rift structure on later rift phases is not fully understood, much since deep structures are often poorly imaged on seismic data due to great burial depths. In the North Sea Rift, which has undergone multiple phases of deformation, two main phases of rifting are recognized in i) Permo-Triassic and ii) Middle Jurassic to Early Cretaceous times. Prior to rifting, the area underwent multiple episodes of contraction and extension, notably Silurian-Devonian contraction and Devonian extensional collapse. In this study we seek to elucidate the influence of pre-existing basement structures on the development of overlying rift structures; for this purpose we utilize regional two-dimensional (2D) deep seismic reflection profiles (-9000 ms TWT) and available well data in the Horda Platform area (western flank of the Viking Graben), offshore Norway. A N-S striking, west-dipping extensional fault zone (Vette Fault Complex, VFC), which has been initiated during the Permo-Triassic rifting phase and reactivated during the Mid-Jurassic to Early-Cretaceous rifting phase, forms the focus of this study. The seismic data shows the presence of a prominent low-angle (< 30°) reflection bundle that extends into the Triassic section. This reflection bundle is interpreted as a low-angle normal fault (LANF), given i) its low angle and ii) the presence of up to 2000 ms TWT growth strata (fault-ward thickening of strata) in its hanging wall. The LANF strikes NNW-SSE over a length of more than 90 km, dipping gently towards the WSW. The nature and style of vertical linkage between the LANF and VFC are studied along three 2D seismic profiles. The study demonstrates that the LANF at depth and the VFC above are only partially vertically linked along strike. Nevertheless, preliminary work demonstrates that the structure has imparted significant controls on the localization and structural style of faults in the later rift phases. This provides new insights to the evolution of multi-phase rift systems in general, and the North Sea Rift in particular.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015