Foraminíferos del tránsito Pliensbachiense-Toarciense en la sección de Ariño (Teruel, España)

Resumo

The foraminiferal assemblages of the Pliensbachian- Toarcian transition at the Ariño Section (Central Sector, Iberian Range) are rich and diversified. A total of 6,389 specimens have been retrieved and 72 taxa identified. The assemblages are dominated in number of specimens and species by the Suborder Lagenina, Superfamily Nodosarioidea, Family Vaginulinidae. Other fossil groups also typical of marine shelf waters were found with the foraminifera in the samples; that is bivalves, brachiopods, bryozooans, crinoids, crabs, echinoids, gastropods, holothurians, ophiuroids, ostracods, serpulids, ammonites and fish teeth. Taphonomic processes were evaluated; infilling and cementation, recrystallization and calcite crusts, and biostratinomic transports are the most common features. Foraminifera are mainly resedimentated, only one single specimen has been found with signals of reelaboration. The stratigraphic range chart of the foraminifera shows that no significant events occurred at the Pliensbachian-Toarcian boundary. The step-wise extinction of typical long-ranging Pliensbachian takes place along the Pliensbachian-Toarcian transition with the highest extinction rate within the Semicelatum Subzone (Tenuicostatum Zone) of the Toarcian. The most significant renewal event also occurs within the Toarcian, in the Elegantulum Subzone (Serpentinum Zone) with the first appearance of the genus Citharina. The acmé of Ammobaculites barrowensis Tappan in the uppermost Semicelatum Subzone can be considered as a regional ecostratigraphic event in the Iberian Range.