Strike-slip relay ramps

Abstract

Areas of reorientated bedding at contractional oversteps between strike-slip faults are here called strike-slip relay ramps. Metre-scale examples are described from the Jurassic sediments at East Quantoxhead, Somerset U.K. Larger strike-slip relay ramps occur in the Rio de Peixe Basin, NE Brazil, along the Newport-Inglewood Trend, California, and in the Bovey Basin, SW England. Although the geometry and development of strike-slip relay ramps are similar to those of relay ramps in normal fault systems, there are differences in the structures which accommodate the transfer of displacement between the overstepping faults. Whereas strike-slip relay ramps are typically transpressional, with pressure solution often occurring, relay ramps in normal fault systems are dominated by extension or transtension. Care needs to be taken when interpreting areas of reorientated bedding between overstepping faults, particularly when displacement directions are unknown, for example when using seismic data. This is because relay ramps can occur in both strike-slip and normal fault zones.