Criteria for Distinguishing Primary Evaporite Features from Deformation Features in Sulfate Evaporites

摘要

In many tectonized regions, evaporites, which served as décollement zones, are brought to the surface, where they are studied as part of the normal sedimentary succession and their internal structures are commonly treated as the primary products of deposition and synsedimentary deformation. Evaporites, however, respond to tectonism in a manner that is vastly different from other rocks in the succession. Associated limestone, dolostone, and siliciclastic beds may remain virtually unaffected by the same degree of deformation that significantly alters evaporites. Even modest differential stresses, with geologically reasonable strain rates applied at low temperatures (20–200°C), result in significant recrystallization, foliation, and flow in evaporites, whereas other rocks (non-evaporites) in the same succession may show little apparent change. The large differences in physical properties between evaporites and both carbonate and siliciclastic lithologies in such tectonized sections result in evaporites that no longer reflect their original sedimentary environment because of recrystallization and plastic deformation. Yet, because their structures and fabrics may not be recognized as secondary, they can be misinterpreted as original features indicative of primary depositional environments.