Correlating deformation events onshore and offshore in superimposed rift basins: the Lossiemouth Fault Zone, Inner Moray Firth Basin, Scotland

The separation and characterisation of different deformation events in superimposed basins can be challenging due to the effects of overprinting and/or fault reactivation, combined with a lack of detailed geological or geophysical data. This study shows how an onshore study can be enhanced using a targeted interpretation of contiguous structures offshore imaged by seismic reflection data.

Two deformation events, including unambiguous evidence of fault reactivation, are recognised in the onshore part of the Lossiemouth Fault Zone (LFZ), southern-central Inner Moray Firth Basin. The basin is thought to record a history of (possibly) Permian to Cenozoic deformation, but it is commonly difficult to conclusively define the age of faulting and fault reactivation. However, structures in Permo-Triassic strata onshore outcrops show no evidence of growth geometries and new interpretation of seismic reflection profiles offshore reveals that Permo-Triassic fills are widely characterised by subsidence and passive infill of post-Variscan palaeotopography. We propose that sequences of reactivated faulting observed onshore and offshore can be correlated and can be shown in the latter domain to be early Jurassic-late Cretaceous, followed by localised Cenozoic reactivation. The workflow used here can be adapted to characterise deformation events in other superimposed rift basins with contiguous onshore surface-offshore subsurface expressions.