The Barremian to Aptian formations outcropping in the Gorgo a Cerbara Section, Umbria-Marche basin, Italy, centred around the 'Selli Level' (OAE1a) were studied for their micropalaeontological content, with particular emphasis on the agglutinated foraminifera. Faunal variations are observed that are in phase with the lithological variations. Foraminiferal assemblages display an overall increase in diversity and abundance upsection. A low-diversity Barremian benthic foraminiferal assemblage is replaced by a more diverse assemblage during a faunal turnover identified -5 m below the base of the black shale corresponding to the OAE I a. From 40 to 20 cm below the base of the anoxic layers, an acme of Verneuilinoides cf. neocomiensis is closely followed by the LO of this species (the last specimens of which are all pyritised). At 20 cm below the base of the Selli Level the turnover rate peaks, with the first occurrence of a lituolid assemblage that continues above the Selli Level, representing the benthic microfacies characteristic of the greenish-grey cherty member of the Marne a Fucoidi. Above the calcareous-free, radiolarian-bearing anoxic levels, foraminifera start to appear in the assemblages at ca. +50 cm above the top of the Selli Level. From that point upward, the trend is an overall increase in benthic foraminiferal diversity, particularly accelerated at +3.5 m above the Selli Level where the first red beds occur, peaking in the uppermost samples collected from the section. A local zonal scheme based on agglutinated foraminifera is proposed, with a stratigraphic resolution twice greater than the standard planktonic zonation.

Agglutinated foraminifera from the proposed GSSP stratotype for the Barremian/Aptian boundary (Gorgo a Cerbara, Umbria-Marche basin, Italy)

COCCIONI, RODOLFO
2011-01-01

Abstract

The Barremian to Aptian formations outcropping in the Gorgo a Cerbara Section, Umbria-Marche basin, Italy, centred around the 'Selli Level' (OAE1a) were studied for their micropalaeontological content, with particular emphasis on the agglutinated foraminifera. Faunal variations are observed that are in phase with the lithological variations. Foraminiferal assemblages display an overall increase in diversity and abundance upsection. A low-diversity Barremian benthic foraminiferal assemblage is replaced by a more diverse assemblage during a faunal turnover identified -5 m below the base of the black shale corresponding to the OAE I a. From 40 to 20 cm below the base of the anoxic layers, an acme of Verneuilinoides cf. neocomiensis is closely followed by the LO of this species (the last specimens of which are all pyritised). At 20 cm below the base of the Selli Level the turnover rate peaks, with the first occurrence of a lituolid assemblage that continues above the Selli Level, representing the benthic microfacies characteristic of the greenish-grey cherty member of the Marne a Fucoidi. Above the calcareous-free, radiolarian-bearing anoxic levels, foraminifera start to appear in the assemblages at ca. +50 cm above the top of the Selli Level. From that point upward, the trend is an overall increase in benthic foraminiferal diversity, particularly accelerated at +3.5 m above the Selli Level where the first red beds occur, peaking in the uppermost samples collected from the section. A local zonal scheme based on agglutinated foraminifera is proposed, with a stratigraphic resolution twice greater than the standard planktonic zonation.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11576/2506904
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