New onshore insights into the role of structural inheritance during Mesozoic opening of the Inner Moray Firth Basin, Scotland

Abstract

The Inner Moray Firth Basin (IMFB) forms the western arm of the North Sea trilete rift system that initiated mainly during the Late Jurassic-Early Cretaceous with the widespread development of major NE-SW-trending dip-slip growth faults. The IMFB is superimposed over the southern part of the older Devonian Orcadian Basin. The potential influence of older rift-related faults on the kinematics of later Mesozoic basin opening has received little attention, partly owing to the poor resolution of offshore seismic reflection data at depth. New field observations augmented by drone photography and photogrammetry, coupled with U-Pb geochronology, have been used to explore the kinematic history of faulting in onshore exposures along the southern IMFB margin. Dip-slip north-south- to NNE-SSW-striking Devonian growth faults are recognized that have undergone later dextral reactivation during NNW-SSE extension. The U-Pb calcite dating of a sample from the synkinematic calcite veins associated with this later episode shows that the age of fault reactivation is 130.99 +/- 4.60 Ma (Hauterivian). The recognition of dextral-oblique Early Cretaceous reactivation of faults related to the underlying and older Orcadian Basin highlights the importance of structural inheritance in controlling basin- to sub-basin-scale architectures and how this influences the kinematics of IMFB rifting.