Bed-parallel slip associated with normal fault systems

Stretching of the Earth's upper crust is commonly accommodated by normal faulting, fault-related folding and/or fracturing such as veins and joints. However, an increasing number of outcrop-scale studies highlight that extension is also accompanied by bed-parallel slip (BPS). The identification of BPS surfaces is, however, challenging due to their localised nature within bedded host rock sequences, the absence of suitable slip markers, and the scale and resolution of both outcrop and seismic reflection data. Here, we present examples of BPS identified within extensional fault systems in sedimentary sequences and outline the nature, magnitude, segmentation, and spatiotemporal distribution of BPS surfaces. These constraints provide a basis for defining the principal structural controls on BPS development and its geometric and kinematic relationship to normal faulting. We conclude that BPS is a common feature within multi-layered host rock sequences, irrespective of their lithological and mechanical properties, and is kinematically associated with a broad range of fault-related deformation, including bed rotations, flexural-slip folding, and both tectonic and gravity-driven sliding. The presence of BPS within normal fault systems can increase the complexity of the host rock volumes and fracture arrays with potential implications on subsurface fluid flow and seismicity.