Boletín de la RSEHN. Sección Geológica

Los datos obtenidos a partir de colecciones paleontológicas que se encuentran en los museos pueden ser útiles para hacer una estimación de la diversidad así como para estudios paleobiogeográficos. Suárez Vega en su Tesis Doctoral sobre el Jurásico de Asturias citó un número importante de especies de bivalvos y su contexto estratigráfico. En 2007, una parte importante de este material fue depositado en el Museo del Jurásico de Asturias. En este trabajo se presentan los resultados de la revisión taxonómica de la colección de bivalvos del Jurásico Inferior de este autor, procedentes de diecisiete afloramientos distribuidos por toda la Cuenca Asturiana y que corresponden a intervalos estratigráficos diferentes. El mayor número de ejemplares se ha recogido en los acantilados de la Playa de Peñarrubia, Gijón (33%). En conjunto, se han revisado más de 250 ejemplares y alrededor de 200 se han podido determinar específicamente debido a su buen estado de conservación. Corresponden al intervalo Sinemuriense Superior (Cronozona Obtusum)-Toarciense Superior (Cronozona Aalensis), repartiéndose la mayoría entre las cronozonas Obtusum, Oxynotum e Ibex. Con anterioridad a este trabajo la diversidad estaba subestimada y con este estudio se ha ampliado a veintinueve géneros, pertenecientes a once órdenes y veintidós familias. Los géneros mejor representados, en relación con el número total de ejemplares analizados, son Gryphaea (18%), Pholadomya (15%), Semuridia (13%), Pseudopecten (10%) y Pleuromya (7%). Se cita, por primera vez, el género Anningella, que hasta el momento, sólo se había reconocido en Gran Bretaña y, destaca la presencia de otros nuevos taxones para Asturias como son Dacryomya, Palaeoneilo, Modiolus (Cyranus) entre los protobranchios, Semuridia y Meleagrinella entre los pteriomorphios, y Mesomiltha y Unicardium entre los heteroconchios.

Data from museum palaeontological collections can contribute to estimates of diversity as well as to palaeobiogeographical studies. Linkages between species occurrence and descriptive information from the field can also be useful to verify taxa and species association occurrences in a space-temporal analysis. This can be especially valuable when data reflect stratigraphically well-constrained sampling intervals. Part of the scientific research of Suárez Vega was dedicated to the Jurassic stratigraphy of Asturias (N Iberian Peninsula). He made a diverse and extensive palaeontological collection of material between the late 1960s and early 1970s, leading to his PhD thesis publication in 1974, “Estratigrafía del Jurásico en Asturias”. In that work he refers to some significant bivalve occurrences observed and cited in their stratigraphical context. In 2007 Suárez Vega donated his collections to the Museo del Jurásico de Asturias (MUJA), where it was incorporated and has been held and curated ever since. A re-evaluation study was carried out on the Suárez Vega Lower Jurassic bivalve specimens at MUJA. Twenty-eight fossil sites were analysed, providing bivalve material from several sections showing distinct space-temporal resolution of the Asturian basin. The localities range from E to W, from Ribadesella to Playa de Peñarrubia (Gijón) respectively, on the coast and with others provenances from inner parts of Asturias such as Borines (Piloña). Most sections represent short chronostratigraphies with the exception of the coastal cliff sections, although these are almost impossible to sample in good conditions or they are completely inaccessible due to urban development. The major bivalve material comes from Playa de Peñarrubia (33%), Santa Mera (8%), Villaviciosa (8%), and Péon (10%) sections, but there are fourteen other localities with less abundance. The collected material corresponds and reflects well exposed sections with abundant strata surfaces or shell concentrations in exceptionally preserved conditions as in Peón. The Lower Jurassic bivalve analysed material comprises more than 250 specimens; the large majority of them (ca 200) were indentified to species level because of their well preserved nature. They span from the Upper Sinemurian (Obtusum Chronozone) to the Upper Toarcian (Aalensis Chronozone) and most of the specimens are equally represented in the Obtusum, Oxynotum and Ibex chronozones. The apparent diversity is equitable distributed in these chronozones too. The diversity of bivalve taxa cited for all the time intervals in Asturias in previous publications were underestimated and our re-evaluation suggest 31 genera and 39 species, representing 24 families and 12 orders. The most represented genera, in terms of total number of specimens, are Gryphaea (18%), Pholadomya (15%), Semuridia (13%), Pseudopecten (10%) and Pleuromya (7%). These data are reflected at family level with Gryphaeidae (17%), Pectinidae (15%), Pholadomyidae (15%) and Pergamidiidae (13%). Therefore the major represented orders are: Ostreida (33%), Pectinida (33%) and Pholadomyida (16%). The occurrence of pectinoid Anningella outside of Great Britain is recognized for the first time. We also record new occurrences for Asturias for the protobranchs Dacryomya, Palaeoneilo, Modiolus (Cyranus), the pteriomorphs Semuridia and Meleagrinella, and the heteroconchs Mesomiltha and Unicardium. Although the Suárez Vega collection was biased by field collecting methodology, these precise data are important for palaeobiogeographical analysis on the same interval in NW European Provinces. This revision provides and updated bivalve biodiversity data set allowing the comparison between Asturias with other nearby basins like Lusitanian (Portugal), Basque-Cantabrian basin and Iberian Ranges (NE to E of Spain). In future studies this information will be integrated in palaeontological analysis with newly collected material from the same time and space intervals in order to better understand the palaeoceanographic dynamics of these faunas.