Triassic evaporites of Iberia: Sedimentological and palaeogeographical implications for the western Neotethys evolution during the Middle Triassic–Earliest Jurassic

This paper deals with the Middle Triassic-to-earliest Jurassic evaporite sedimentation in the epicontinental, eastern Iberian platform. This deposition occurred under extensional regime during the westwards migration of the Neotethys Ocean at the start of the Pangea break-up. Although attention is focused on the evaporitic episodes recorded in the Epicontinental (Germanic) Triassic of the platform, the evaporite units in the carbonatic Alpine Triassic are also considered. In the Epicontinental Triassic, up to six evaporitic episodes, which alternated with three carbonatic episodes and a siliciclastic one, occurred between the Anisian and the Lower Hettangian. The evaporitic episodes may be divided into two groups. The stratigraphic units of the older group have similar characteristics in salinity and facies, and were formed in chloride-rich, evaporitic mudflats. In the younger group, the salinity and depositional features display considerable differences and the environments evolved from evaporitic mudflats to extensive salterns. The different evolutive trends in the evaporites of the two groups suggest major re-structuration of the platform after the sedimentation of the siliciclastic units of the middle Keuper (Carnian Humide Episode). Progressive marine influence in the assemblage of the six evaporitic episodes is deduced from the changing nature of the evaporites and their host sediment. All the evaporite units accumulated as transgressive and highstand systems tracts. The close relationship between evaporite units and thick accumulation suggests that the structural control played a major role in the sedimentation. In the Alpine Triassic, the presence of evaporites interbedded in the allochthonous carbonate units is documented. Lateral correlation of the evaporite units of the Epicontinental and the Alpine types of Triassic allows us to reconstruct the facies continuum across the original Iberian platform. Such a west-to-east transect illustrates the palaeogeography, structural evolution, and major depositional controls in the platform during the period under study. The deduced evaporitic pattern could be applied to other Triassic platforms which acted as epeiric seaways for the westward advance of the Neotethys.