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This work focuses on the Olenekian-Anisian (Early-Middle Triassic) continental record of the Central-Eastern Pyrenean basin (NE Spain), a near-equator (10°-14°N) basin located in the western peri-Tethys margin, inside the Variscan fold-belt. Due to the mass mortality of the end-Permian and the subsequent Smithian-Spathian Boundary (SSB) crisis, the Early Triassic and its transition to the Middle Triassic was a time period with intermittent stages of environmental instability that affected fauna and flora intensely. Compared to other crisis, a remarkable feature is the longer time required to achive life recovery during this time-interval and the fact that continental environments have been less globally studied than their marine counterparts. Furthermore, in SW Europe there is almost no sedimentary continental record from the beginning of the Triassic. This multidisciplinary study, embracing sedimentology, mineralogy, palaeontology, palaeopedology and palaeogeography, of 10 complete and well dated Early-Middle Triassic field sections has allowed (1) the location and characterization of the oldest Mesozoic sedimentary record in the basin, which is of late Smithian age and overlies the late-middle Permian continental rocks and of (2) the Smithian-Spathian transition (SST), (3) the timing of life recovery during the late Spathian-Anisian, (4) the characterization of the first incursion of the Tethys sea into the basin, and (5) the comparison of the evolution of this basin with other basins of the same age in SW Europe. The SST coincides with hyper-arid climate conditions, evolving to semi-arid in the late Spathian and semi-arid to semi-humid in Anisian times. Poorly sorted breccias and conglomerate alluvial sheets with aeolian reworking dominate the SST, as a result of these environmental changes and tectonicsA broader comparison, based on stratigraphic studies by other authors, indicates less aridity in the basin studied compared to other SW Europe basins in the same period, maybe due to its greater proximity to the equator. Sedimentary characteristics changed during the late Spathian, when sandy braided fluvial systems developed and the first dispersed plants, pollen assemblages and paleosols appeared. Well-developed floodplains and associated paleosols and plants developed during the early Anisian, when more humid conditions prevailed. The occurrence of aluminium phosphate-sulphate (APS) minerals might be considered as evidence of environmental acidification during the Olenekian with an amelioration during the early Anisian, as described in neighboring basins, although in the Pyrenean basin this acidification was probably less intensive. The first incursion of the Tethys sea reached the Central-Eastern Pyrenean basin during the Anisian-Ladinian transition, about 3 My later than in neighbouring Southwestern Europe basins. General comparison with other Early-Middle Triassic continental records of Western Europe basins indicates contrasting trends of climate and sedimentary evolution, probably related to the still prevailing great paleorelief of the Variscan foldbelt, where part of the study basin could constitute an elevated area during some time-intervals, possibly related to the so-called Ebro High.

The Pyrenean-Cantabrian Orogen arose through the collision of the Iberian and Eurasian plates, mostly in Cenozoic times. This orogen comprises two main mountain ranges, the Pyrenees to the east, and the Cantabrian Mountains to the west. To date, the early Alpine tectono-sedimentary phases preserved in the Cantabrian Mountains, of Permian and Triassic age, have been considered independently from the same phases in neighbouring basins of SW Europe, and even from the eastern part of the same orogeny (the Pyrenean orogeny). In consequence, the beginning of the Alpine cycle in the Cantabrian Mountains has been interpreted within a specific geodynamic context, far from the general evolutionary phases of the western Peri-Tethys basins. Through detailed field work, including geological mapping, sedimentology, lithostratigraphy and petrology of volcanic rocks, and new palaeontological data, here we define several new lithostratigraphical formations and five new tectono-sedimentary cycles (TS I-V) for the initial phases of evolution of the Mesozoic Basque-Cantabrian Basin, interrupted by periods of tectonic stability. To complete this information, we include data from an onshore borehole (Villabona Mine) and two offshore boreholes constrained by 2D reflection seismic profiles acquired in the North Iberian continental platform. The main tectono-sedimentary cycles, related to the deposition of five major identified lithostratigraphic units, can be described as follows: TS I (late Gzelian-early Asselian), relating to the late Variscan deformation and preserved in a single outcrop in all the Cantabrian Mountains (San Tirso Formation). This formation is constituted by medium-distal alluvial fan deposits in which humid intervals predominate, forming some thin coal beds. TS II (Asselian-Sakmarian), a post-Variscan extensional phase with associated calc-alkaline magmatism, represented by profuse volcanic and volcanosedimentary intercalations in the early Permian sedimentary basins (Acebal Formation) and small plutons in surrounding areas. TS III (Kungurian), or reactivation of the post-Variscan extension leading to alluvial and lacustrine carbonate sedimentation in arid climate conditions, which do not change during the rest of the Permian and Triassic periods (Sotres Formation). A generalized karstification in the basin represents the end of Permian deposition, followed by an interruption in sedimentation longer than 30 Myr. The Permian tectono-sedimentary cycles (TS II and TS III) are contemporary with Variscan belt collapse and the basins are controlled by extensional reactivation of NE-SW and E-W Variscan structures, and NW-SE late Variscan structures. TS IV (late Anisian–middle Carnian), renewed sedimentation in more extensive basins, precursors of the great Mesozoic Basque-Cantabrian Basin. This cycle is represented by fluvial deposits (Cicera Formation, or Buntsandstein facies), which are interrupted by the first Mesozoic marine ingression (Rueda Formation, or Muschelkalk facies). TS V (Norian-Rhaetian), or shallow marine carbonate deposits (Transición Formation) related to increasingly compartmentalized sub-basins, controlled by normal faults. This final TS is broadly connected with different basins of the western Peri-Tethys domain. The identification of units TS I-V in the Cantabrian Mountains along with the volcanic character of TS II, all indicate the development of a common post-Variscan to early Alpine tectono-sedimentary evolution for the whole Pyrenean-Cantabrian realm., This work was funded by projects CGL2014-52699P and CGL2015-70970-P (Spanish Ministry of Economy and Competitiveness and FEDER Funds of the European Union), as well as projects: >Sistemas Sedimentarios y Variabilidad Climática> (642853) of the CSIC, Basin Analysis (910429), and Palaeoclimatology and Global Change (910198) of the Universidad Complutense de Madrid. The authors thank Luis Villa Iglesias and José Antonio Marín Barcaíztegui (MINERSA GROUP) for providing all the required borehole data from the Villabona Mine (Asturias) and for facilitating access to the mines for sampling. We thank both anonymous referees and Editor Andre Strasser for improving the final version with their comments, and A. Burton for reviewing the English.