Rudistas (Hippuritida, Bivalvia) del Cenomaniense-Coniaciense (Cretácico superior) del Pirineo meridional-central. Paleontología y bioestratigrafía

Abstract

Los bivalvos rudistas están ampliamente representados entre las sucesiones de materiales carbonatados someros correspondientes al margen sur de la cuenca pirenaica durante el Cretácico superior y que hoy día afloran a lo largo del Pirineo meridional-central. Las faunas del Coniaciense superior/Santoniense inferior al Maastrichtiense son bastante bien conocidas y han sido objeto de diferentes estudios, pero no es así para las anteriores que, si se conocen, es principalmente por citas en algunos trabajos. El estudio de diferentes afloramientos correspondientes al Cenomaniense, Turoniense superior y Coniaciense, alrededor de la cuenca de Tremp (zona de Sopeira y la Sierra de Sant Gervàs, Congost d’Erinyà, Hortoneda, anticlinal de Bóixols-Abella-Sant Corneli y sinclinal de Santa Fe, y Sierra del Montsec), ha proporcionado una abundante fauna de rudistas a partir de la cual se ha podido realizar un exhaustivo estudio paleontológico que comprende descripciones detalladas y actualizadas de los diferentes taxones representados, análisis de la variabilidad intraespecífica y distribución bioestratigráfica. En total se han reconocido 35 especies correspondientes a 15 géneros de 7 familias distintas. La fauna de rudistas del Cenomaniense medio-superior está representada por Caprina adversa, Ichthyosarcolites triangularis, I. monocarinatus, I. tricarinatus, Durania blayaci, Eoradiolites sp., Sauvagesia tellensis y Sphaerulites foliaceus. Caprina adversa también se registra desde el Cenomaniense inferior. El Turoniense superior contiene una fauna formada por Hippurites resectus, Pseudovaccinites inferus, P. petrocoriensis, P. praegiganteus, P. rousseli, Praeradiolites paillettei y Sphaerulites patera. Algunas especies bien representadas en el Coniaciense se registran de forma puntual en algún afloramiento atribuido al Turoniense superior, entre ellas Biradiolites canaliculatus, Hippurites incisus, Pseudovaccinites zurcheri o P. corbaricus?. De la misma forma, Pseudovaccinites petrocoriensis y P. corbaricus? aún se reconocen en el Coniaciense inferior. El Coniaciense inferior, medio y superior se distingue en diferentes localidades. Se reconocen Bayleia sp., Hippurites incisus, H. socialis, Hippuritella sp. 1, Hippuritella sp. 2, P. corbaricus?, Pseudovaccinites giganteus, P. marticensis, P. petrocoriensis, P. zurcheri, Gyropleura? sp. 1, Gyropleura? sp. 2, Plagioptychus aguilloni, Plagioptychus cf. toucasi, Radiolites praegalloprovincialis, Radiolites sp. 1, Radiolites sp. 2, Biradiolites canaliculatus, Biradiolites cf. beaussetensis, Praeradiolites paillettei, Praeradiolites requieni y Sphaerulites sp. Algunas especies están representadas durante la mayor parte del Coniaciense, mientras que otras solamente de forma local. El momento de mayor diversidad taxonómica se produce en el Coniaciense superior, cuando se registran conjuntamente la mayoría de especies de esa edad.

Rudist bivalves are widely represented among the successions of shallow carbonate materials corresponding to the southern margin of the Pyrenean basin during the Late Cretaceous and that emerge today along the South-central Pyrenees. The upper Coniacian/lower Santonian to Maastrichtian faunas are well known and have been the subject of several studies but it is not the case for the older ones, mainly known through appointments in some works. The study of different outcrops of the Cenomanian, upper Turonian, and Coniacian around the Tremp basin (Sopeira area and the Sierra de Sant Gervàs, Congost d'Erinyà, Hortoneda, Bóixols-Abella-Sant Corneli anticline and Santa Fe syncline, and Sierra del Montsec), has provided an abundant rudists fauna on which it has been possible to perform an exhaustive paleontological study, comprising detailed and updated descriptions of the various taxa represented as well as an analysis of both their intraspecific variability and biostratigraphical distribution. In total, 35 species corresponding to 15 genera of 7 different families have been recognized. The middle-upper Cenomanian rudists fauna is represented by Caprina adversa, Ichthyosarcolites triangularis, I. monocarinatus, I. tricarinatus, Durania blayaci, Eoradiolites sp., Sauvagesia tellensis and Sphaerulites foliaceus. Caprina adversa also is recorded from the lower Cenomanian. The upper Turonian contains a rudists fauna composed of Hippurites resectus, Pseudovaccinites inferus, P. petrocoriensis, P. praegiganteus, P. rousseli, Praeradiolites paillettei and Sphaerulites patera. Species well represented in the Coniacian as Biradiolites canaliculatus, Hippurites incisus, Pseudovaccinites zurcheri or P. corbaricus?, are recorded sporadically in some outcrops attributed to the upper Turonian. At the same time, Pseudovaccinites petrocoriensis and P. corbaricus? are still recorded in the lower Coniacian. The lower, middle and upper Coniacian is identified in different locations. The following rudist taxa are recognized: Bayleia sp., Hippurites incisus, H. socialis, Hippuritella sp. 1, Hippuritella sp. 2, P. corbaricus?, Pseudovaccinites giganteus, P. marticensis, P. petrocoriensis, P. zurcheri, Gyropleura? sp. 1, Gyropleura? sp. 2, Plagioptychus aguilloni, Plagioptychus cf. toucasi, Radiolites praegalloprovincialis, Radiolites sp. 1, Radiolites sp. 2, Biradiolites canaliculatus, Biradiolites cf. beaussetensis, Praeradiolites paillettei, Praeradiolites requieni and Sphaerulites sp. Some species are represented during most of the Coniacian, while other only locally. The time of greatest taxonomic diversity occurs in the upper Coniacian, when most of that age species are recorded together.