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Resumen:
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We present the biostratigraphical events, ammonites and foraminifera from the Pliensbachian (Spinatum Chronozone) to the Toarcian (Bifrons Chronozone) in San Miguel de Aguayo. We sampled the profile layer by layer for ammonites (400 specimens in 86 successive levels), and we extracted 19 samples for foraminifera (4858 picked specimens). In the Spinatum Chronozone, the Amaltheidae Family dominated, with little presence of the Arieticeratinae or Harpoceratinae. The Tenuicostatum Chronozone presents a good record of Dactylioceratinae, with successive species, from Dactylioceras (Eodactylites) simplex to Dactylioceras (Orthodactylites) semicelatum. The Serpentinum Chronozone is characterised by Harpoceratinae (Eleganticeras, Cleviceras, Harpoceras), Hildoceratinae (Hildaites, Orthildaites) and by the persistence of Dactylioceras (Orthodactylites). The Bifrons Chronozone presents a good succession of Hildoceras. The foraminifera are benthic and autochthonous, and the calcareous hyaline taxa of the Lagenina Suborder, Vaginulinidae Family, are dominant. The most diverse genera are Nodosaria and Lenticulina. The most abundant species is Lenticulina toarcense, which constitutes 55.37% of the total number of specimens. Also represented, albeit as a minority, are the Textulariina, Miliolina, Spirillinina and Robertinina Suborders. The ammonites are typical of the Submediterranean Province and common to the Subboreal Province; the species of the Mediterranean Province are scarce and their record is sporadic in the Pliensbachian–Toarcian transition. The foraminifera are typical of the Atlantic Boreal Domain; two main biotic events were recognised: step-wise extinction of species between the Hawskerense and Semicelatum subchronozones, with a maximum extinction rate in the Semicelatum Subchronozone, and faunal turnover principally in the Elegantulum Subchronozone (Serpentinum Chronozone).
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