MIDDLE AND EARLY UPPER DEVONIAN CONODONT BIOFACIES FROM THE SPANISH CENTRAL PYRENEES

The ample conodont data base, which consists of 86 taxa grouped into nine genera, from almost 450, bed by bed, samples from seven sections in the Spanish Central Pyrenees allows recognition of the geographical and biostratigraphical distribution of these taxa. As a result, a sound study on conodont biodiversity identifies 14 main biofacies. Noteworthy, the conodont radiation that took place in the Upper Givetian accounts for eight of them. The main biofacies is the Polygnathus biofacies; within it the marked change in the platform of Pa elements, narrow to wide, in the Upper Givetian stands out. During part of the Upper Givetian both type of platforms coexist, but from the upper part of the Upper disparilis Zone upwards, narrow-plaform Pa elements are not longer recorded in any Givetian rocks of all studied sections. Besides Polygnathus Biofacies, there are other four “one component biofacies”, in which the name-giver taxon accounts for over 75% of the total amount of conodont elements: Icriodus, “Ozarkodina”, Schmidtognathus and Ancyrodella biofacies. Another eight biofacies have two main components, being the first-named almost twice as abundant as the second: Polygnathus-Icriodus, Icriodus-Polygnathus, Polygnathus-Tortodus, Polygnathus-Coniforms, Polygnathus-Schmidtognathus, Schmidtognathus-Polygnathus, Polygnathus-Klapperina and Polygnathus-Ancyrodella Biofacies. The only mixed Biofacies corresponds to the Polygnathus-Ancyrodella-Klapperina.

Polygnathus is de dominant taxon from the Eifelian to Middle Givetian rocks and, consequently the Polygnathus Biofacies governs during this time span except form some spotty high abundances of Icriodus, Tortodus and coniforms that for particular time intervals and sections develop two components biofacies: Polygnathus-Icriodus, Icriodus-Polygnathus, Polygnathus-Tortodus and Polygnathus-Coniforms. The radiation of Schmidtognathus and Klapperina in the Upper Givetian counts for the Schmidtognathus, Polygnathus-Schmidtognathus, Schmidtognathus-Polygnathus and Polygnathus-Klapperina Biofacies. The innovation and subsequent radiation of Ancyrodella called for a Biofacies change in the Lower Frasnian, which is characterised by Ancyrodella, Polygnathus-Ancyrodella and Polygnathus-Ancyrodella-Klapperina Biofacies.