The effect of cover composition on extensional faulting above re-activated basement faults: results from analogue modelling

Abstract

Analogue models were used to investigate differences in deformation between sedimentary cover sequences of contrasting composition above reactivated basement faults during extension. Two types of model arrangements were used. The first represented clastic sediments directly overlying faulted basement, and the second represented a basal ductile layer in an overburden overlying the same faulted basement. The basement configuration consisted of faults both oblique and orthogonal to the bulk extension direction. Particular attention was paid to the resulting map-view fault patterns.In experiments without a basal ductile layer in the overburden, grabens only developed in areas directly above basement faults. In section, cover faults above oblique basement faults curved in profile and, in places, exhibited reverse movement at shallow depth. In experiments involving a ductile layer at the base of the overburden, faults developed oblique to both the bulk extension direction and the basement faults. The resulting fault pattern was influenced by both bulk extension and basement fault reactivation.The results indicate that cover sequences that include thick basal ductile layers above reactivated basement faults are more likely to develop faults with strikes perpendicular to the regional extension direction, compared to those without. Faulting in an overburden lacking a basal ductile sequence is more likely to be directly influenced by the underlying reactivated basement faults.