The early/middle Eocene transition at the Ésera valley (SouthCentral Pyrenees): Implications in Shallow Benthic Zones (SBZ)
Keywords:Magnetostratigraphy, Larger benthic foraminifera, Calcareous nannofossils, Ypresian – Lutetian boundary, South-Central Pyrenean Basin
An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil
biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger
foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the
calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised,
the taxa found are enough to support the chronostratigraphic attribution.
Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulites
and Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as
shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs.
These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ
13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary
occurs in SBZ 12.
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