Bioestratigrafía del tránsito Triásico-Jurásico en Asturiasammonoideos y bivalvos entre Avilés y Caravia. (España)

Résumé

The finding of ammonoids and bivalves in the deposits of the Triassic-Jurassic (T-J) transition in the Gijón Formation (Asturias) allowed of the biostratigraphy and chronostratigraphy of the Rhaetian and the Tettangian. Among the ammonoids, the record of an Arcestidae (Rhaetian) and several Psiloceras (Hettagian, Planorbis Zone) in the upper part of the Solís Member can be stand out. The domain Rhaetian bivalves are Isocyprima concentrica and Bakevillia praecursor. These species, together with Isocyprina ewaldi, "Pteromorphus" elongatus, Pteromya longportensis, Placunopsis cf. alpina, Modiolus minimus and Paleocardita cf. austriaca, represents a similar assemblages to that found in the Westbury and Lilstok formations (Penarth Group) in the late Rhaetian of southern England. The Hettangian bivalves are represented by the widley distributed species Pteromya tatei, which is associated to Cuneigervillia rhombica, Parallelodon hettangiensis and Eomiodos menkei. This assembalge is known in the Hettangian Planorbis Zone of France and Germany. As a consequence, the T-J- boundary has been located within the upper part of the Solís Member of the Gijón Formation.