The beginning of the Buntsandstein cycle (Early-Middle Triassic) in the Catalan Ranges, NE Spain: Sedimentary and palaeogeographic implications

The Early-Middle Triassic siliciclastic deposits of the Catalan Ranges, NE Spain, are dominated by aeolian sediments indicating a predominance of arid climate during this time span, in sharp contrast with the coeval fluvial sediments found in the Castilian Branch of the Iberian Ranges, 300 km to the SW. The NE-SW-oriented Catalan Basin evolved during the Middle-Late Permian as the result of widespread extension in the Iberian plate. This rift basin was bounded by the Pyrenees, Ebro and Montalban-Oropesa highs. The Permian-Early Triassic-age sediments of the Catalan Basin were deposited in three isolated subbasins (Montseny, Garraf, Prades), separated by intrabasinal highs, but linked by transversal NW-SE oriented faults. The three subbasins show evidence of diachronic evolution with different subsidence rates and differences in their sedimentary records. The Buntsandstein sedimentary cycle started in the late Early Triassic (Smithian-Spathian) in the central and southern domains (Garraf and Prades), with conglomerates of alluvial fan origin followed by fluvial and aeolian sandstones. Source area of the fluvial sediments was nearby Paleozoic highs to the north and west in contrast with the far-away source areas of the fluvial sediments in the Iberian Ranges, to the SW. These fluvial systems were interacting with migrating aeolian dune fields located towards the S, which developed in the shadow areas behind the barriers formed by the Paleozoic highs. These highs were separating the subbasins under arid and semi-arid climate conditions. The dominating winds came from the east where the westernmost coast of the Tethys Sea was located, and periods of water run-off and fields of aeolian dunes development alternated. Some of the fluvial systems were probably evaporating as they were mixed into the interdune areas, never reaching the sea. From the end of the Smithian to the Spathian, the Catalan Basin and neighbour peri-Tethys basins of the present-day southern France, Sardinia and Minorca islands constituted a geographical arch where arid and semi-arid conditions represented an extension of the prevailed arid and hyper-arid conditions in surrounding areas of the Variscan Belt. Harsh climatic conditions in this area prevented the life recovery in the aftermath of the Permian-Triassic extinction event until the early Anisian, when more humid climate allowed for the colonisation of the area by plants, amphibians and reptiles. The boundary between desert areas and semi-arid and/or seasonal climate domains during the Smithian-Spathian in SW Europe can be precisely established in NE Iberia, between the Catalan-Ebro region and the Castilian Branch of the Iberian Ranges, to the SW. (C) 2013 Elsevier B.V. All rights reserved.