Middle Triassic evaporite sedimentation in the Catalan basin: Implications for the paleogeographic evolution in the NE Iberian platform

Abstract

The eastern sector of the epicontinental Iberian platform underwent restriction after the sedimentation of the lower Muschelkalk carbonates (Middle Triassic) under extensional regime. This resulted in the accumulation of the marine evaporites and the alluvial siliciclastics of the middle Muschelkalk facies in the Triassic Catalan basin, which varied between 100 and 120 m in thickness. This facies consists of three lithostratigraphic units sedimented at basin scale (Lower, Middle and Upper), each of which includes a distinct evaporite unit. In the Lower Unit, the evaporitic sedimentation started as a transgressive sulfate lagoon (Paüls Gypsum unit). During the Middle Unit time, a regressive evaporitic mudflat, made up of a mosaic of shallow gypsum salinas surrounded by anhydrite sabkhas (Arbolí Gypsum unit) developed; in the northeastern half of the basin, an alluvial plain was formed by siliciclastics (Guanta Sandstone unit) of a west and northwest provenance (Lleida High). During the Upper Unit time, a new transgressive sulfate lagoon occupied the southern half of the basin (Camposines Gypsum), whereas an evaporitic mudflat of red-to-variegated mudstones, marls, and lacustrine carbonates developed in the northern half. Cyclic sedimentation was mainly recorded in the evaporitic mudflat-alluvial plain complex of the Middle Unit. The sulfur isotopic values of gypsum in the three evaporite units show a decrease in δ34S with time and also a clear distinction from the values of the Keuper facies in the basin. A division of the lithostratigraphic succession into two third-order depositional sequences is proposed. The middle Muschelkalk succession in the Catalan basin is compared with the equivalent one in the subsurface of the adjacent Triassic Maestrat basin, which was filled with >600 m of marine evaporites.