Carboniferous Productidina and Chonetidina of the Cantabrian Mountains (NW Spain): Systematics, stratigraphy and palaeoecology

The Carboniferous sediments of the thrust structures between the Porma and Bernesga rivers (map 2) and the headwaters of a tribuary of the Luna River (map 3) are described. In the lithostratigraphic chapter, the Vegamián, Alba, Escapa and San Emiliano formations are described, ranging in age from the Tournaisian to the lowermost Westfalian. The Alba and Escapa formations are subdivided into three and two members, respectively. An attempt has been made to reconstruct the palaeoecological conditions during sedimentation. The palaeoecological interpretation is based mainly on the productoids and chonetoids, but other palaeontological and lithological evidence has also been used. Many faunal assemblages have been found, which are comparable to those described by Moore (1964) from Pennsylvanian and Permian deposits in Kansas (U.S.A.). A short sedimentary history is given in chapter IV. A systematic study has been made of the Carboniferous representatives of two suborders of the phylum Brachiopoda: the Productidina and the Chonetidina. 22 Genera of the Productacea are described. They are represented by 51 species and subspecies, three of which are new. The new species are Levipustula breimeri, Karavankina rakuszi and K. wagneri. Twelve species and subspecies of seven different genera are described from the family Chonetidae. The investigation of these brachiopods resulted in a reappraisal of the Spanish Carboniferous productoids and chonetoids, combined with the description of a number of elements previously unknown in Spain. The genus Karavankina is described in some detail since only a short introductory note (Ramovs, 1966) has been published previously. A pedicle sheath is described for the first time for the genus Chonetipustula. The groove in the internal moulds of small pedicle valves of that genus are shown to be due to a groove anterior to the pedicle sheath, and not to a median septum as supposed by previous authors. A comparison of the faunas with those of other areas leads to some interesting conclusions. The fauna of the Vegamián Formation is closely comparable with German faunas of a slightly younger, distinctly Viséan age. The fauna appears to be dependent on the type of sediment deposited, viz. black shales, and not so much on the stratigraphic age. Van Ginkel (1965b) has dated the top of the Escapa Formation on the basis of fusulinids as Lower Bashkirian. The productoid assemblage of these deposits is unique and consists mainly of forms found in the Visean of north-western Europe, together with a few genera and species known from Moscovian and even younger strata elsewhere. The upper Bashkirian and the lowermost Moscovian faunas in Spain become more cosmopolitan, the Viséan and Namurian elements being replaced by new ones. In Moscovian strata, it is found that the fauna shows close relationships with the faunas described from Russia and China as well as with those found in the Westfalian marine bands of north-western Europe. The Carboniferous faunas in nord-west Spain apparently belong to the Europe Tian-Shan faunal province, because the productoid fauna as well as the fusulinid fauna agree with those described for this province (Einor et al., 1965). It seems that Karavankina should be added as another characteristic genus for this faunal province. It occurs from the Cantabrian Mountains to China. The Kasimovian productoids belong to the Moscovian genera, but differ at a specific level.