Lateral variation in structural style along an evaporite-influenced rift fault system in the Halten Terrace, Norway: Influence of basement structure and evaporite facies

Abstract

The Halten Terrace is underlain by a Triassic evaporitic package, resulting in vertically decoupled normal fault systems following subsequent extension. Four structural domains are identified along the eastern margin of the Halten Terrace, characterised by: i) thick-skinned normal faults affecting both sub-salt and supra-salt cover, ii) basement-restricted normal faults associated with fault-propagation folds, iii) thick-skinned, distributed normal faults, and iv) thick-skinned, localised normal faults. A fault domain boundary associated with an NE–SW striking basement fault corresponds to an abrupt change in style in the north of the Halten Terrace. Summed throw and estimated strain measurements show that throw and strain accommodated by the fault system increase southward, corresponding to a transition from distributed to localised faulting. The evaporite package is variable in thickness, but those variations do not correspond spatially to variations in structural style. Wells that penetrate the evaporite package, and volume attribute analysis of 3D seismic data, suggest variable evaporite facies. A change in seismic attributes from high-amplitude, low variance to low-amplitude, high variance corresponds to a change from decoupled to thick-skinned faulting. The sub-evaporite fault template, amount of strain accommodated across the fault system, and facies variations in the evaporite package are key influences on structural style.