Stratigraphic-sedimentary reconstruction in the Permian- Triassic succession of the Central-Eastern Southern Pyrenees: a multi-disciplinary approach

The Upper Carboniferous-Lower Triassic sedimentary record in the Central- Eastern Southern Pyrenees is organized in five formal stratigraphic units, some of them bounded by angular unconformities. Due to the complex geological setting, several approaches have been used together. The adopted method was selected in order to obtain the most detailed information and reconstruct the original conditions of these basins and their later refill. The main approach followed was based on the stratigraphy and the sedimentology studies. On this basis, other approaches, such as palynology, paleopedology, isotopic analyses and clay mineralogy from claystone, were attempted in both the Erill Castell-Estac Basin and the neighbouring basins (Castejón-Laspaúles, Gramós and Castellar-Camprodón). Detailed field made it possible to define facies, facies associations and the architectural elements of the deposits. Detailed syn-sedimentary faulting was also measured with the scope to constrain the relationship between the sedimentation and the tectonics. When the stratigraphic units were clearly characterized and their vertical and lateral relations were well established, a detailed sampling was performed for the other approaches used. The stratigraphic units were then joined in sedimentary cycles (SC) bounded by angular unconformities. The sedimentary record of each SC shows significant changes in the paleoenvironmental conditions. The first sedimentary cycle (Late Carboniferous-Early Permian) is characterized by isolated sub- basins and it is strongly linked with intense volcanic activity. In the upper part of this cycle, fluvial and lacustrine sediments were deposited in a transtensive tectonic context, and again during a strong volcanic outpouring. In the second sedimentary cycle (Middle Permian), the sub-basins started to merge due to the continuation of transtensive tectonic context. The main deposits in this cycle represent playa-lake and fluvial environments with negligible volcanic influence. Finally, after a long-lasting stratigraphic gap, the third sedimentary cycle (Early-Middle Triassic) is represented by meandering fluvial systems with isolated lacustrine environments and no volcanic influence. The age of the units was constrained thanks to their newly discovered palynological content. These fossils represent an important biostratigraphic tool for correlation across the SW European basins. The age obtained by one sporomorph association found in the basal Grey Unit (SC1) was Gzhelian (Upper Carboniferous). The spores and pollen contained in the Transition Unit (SC1) indicate an Asselian age (Early Permian). The second sedimentary cycle is represented by the Lower Red Unit (LRU), which was assigned to an Artinskian age, based on palynological data. Finally, the Lower Triassic deposits contained pollen and spores too, and the age ascribed was upper-middle Anisian.