Sucesión de asociaciones de foraminíferos en el tránsito Pliensbachiense-Toarciense en Almonacid de la Cuba (Zaragoza, España)

Abstract

[Foraminiferal biostratigraphy from the Pliensbachian-Toarcian transition in Almonacid de la Cuba (Zaragoza, Spain)]. The foraminiferal assemblages are rich and diversified along the Pliensbachian/Toarcian transition. 8,694 specimens have been found and 75 taxa have been recorded, most of them belonging to the Lagenina Suborder, although species of Textulariina, Miliolina, Spirillinina and Robertinina have been also identified. The stratigraphic ranges of the species show no significant changes at the Pliensbachian/Toarcian boundary. The Last Occurrence of typical Pliensbachian taxa, like Planularia inaequistriata (Terquem), Prodentalina terquemi (D�Orbigny), Marginulina prima (D�Orbigny), Ichthyolaria sulcata (Bornemann), I. intumescens (Bornemann) or Saracenella sublaevis (Franke), takes place in the Tenuicostatum Zone. Besides, the Tenuicostatum Zone can be partially characterized by the presence of Planularia obonensis (Ruget) and Saracenella aragonensis (Ruget), that are no longer present in Serpentinus Zone. This last Zone, Serpentinus, can be recognized by the first record of the genus Citharina, with the spe-cies Citharina cf. colliezi (Terquem) and Citharina cf. clathrata (Terquem). Besides, the last appearance of Paralingulina tenera (Bornemann) takes place in the base of Serpentinus Zone in Almonacid de la Cuba as it occurs in other sections of the Central Sector of the Aragonese Branch; outside this Sector P. tenera appears for last time in the Tenuicostatum Zone, Semicelatum Subzone.