Soft‐sediment deformation structures induced by cyclic stress of storm waves in tempestites (Miocene, Guadalquivir Basin, Spain)

Abstract

The identification of triggering agents for soft‐sedimentation structures is an enigmatic geological problem. Mainly seismic‐induced soft‐sediment structures have been recognized in ancient sediments, rather than those resulting from storm waves. We analyse soft‐sediment deformation structures in Upper Miocene calcarenitic tempestites of the Guadalquivir Basin (Southern Spain). The most common structures are load‐casts which vary in height and width from 10 centimetres to several metres. The structures are always restricted to a small part of the stratigraphic sections, in exclusive association with tempestites. The analysed soft‐deformation structures are interpreted to be the result of liquidization processes. Chiefly from their inferred depositional environment, and subordinately from the deformation style, we have devised basic criteria to identify the trigger mechanism. In these soft‐sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves.