The chronostratigraphic context of the Puertollano Coalfield (Ciudad Real, Spain): new radiometric dates

The Puertollano Coalfield succession corresponds to the Late Carboniferous Stephanian Stage of the West European chronostratigraphic framework, but the position within this unit, based on megafloral biostratigraphy, has been ill-defined; attributed ages have ranged from Stephanian A (now Barruelian) to Stephanian C. During working of the Mina Emma opencast site, samples of volcanic tuff were collected from bands in the two principal coals, the Tercera (sample P173) and Segunda (sample P172) seams, separated by some 24 m. These seams lie near the middle of a total stratigraphic column of around 600 m. These samples were submitted for CA-ID-TIMS high precision U-Pb radiometric dating, which gave corresponding absolute ages: P173–303.48 Ma ± [0.44] and P172–303.19 Ma ± [0.42]. These dates correspond to the earliest Gzhelian Stage of the global chronostratigraphic timescale, close to its limit with the underlying Kasimovian. In the West European framework, constrained by radiometric dates from stratotypes in the Cantabrian Mountains, this succession falls in the earliest part of the proposed Saberian substage, closely above the contact with the preceding Barruelian substage. The Puertollano palaeobotanical record comprises a hygrophile biome related to the coal swamp environment and also, in the upper part of the succession, elements of a mesophile flora largely comprising conifer taxa. The latter have suggested the significantly younger age, in contrast to the hygrophile flora which largely corresponds to the older Saberian age. The palaeobotanical record contributes to discussion on the influence on climate as a driver of mixed floral biomes and relevance of the concept of an extrabasinal derivation of some taxa. The new dates provide the basis for on-going review of the floral dynamics and stratigraphical significance of the palaeobotanical record in the Puertollano succession, and also a framework for the unique vertebrate fauna.