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 paper 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 evidence of fault reactivation, are recognised and associated with the onshore part of the Lossiemouth Fault Zone (LFZ), southern-central Inner Moray Firth Basin. The basin is thought to record a history of Permian to Cenozoic deformation, but it is difficult to conclusively define the age of faulting and fault reactivation. However, structures in onshore outcrops of Permo-Triassic strata show no evidence of fault growth, and new interpretation of seismic reflection profiles in the offshore area 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 applied to characterise deformation events in other superimposed rift basins with contiguous onshore (surface)-offshore (subsurface) expressions.

Automated summary

This paper demonstrates how targeted interpretation of offshore seismic reflection data can enhance an onshore study, allowing for the separation and characterisation of different deformation events in superimposed basins. By correlating onshore and offshore data, the authors were able to determine the ages and evidence of fault reactivation in the studied area. This workflow can be applied to other rift basins with continuous onshore-offshore expressions, providing valuable insights into their deformation history.