European Oligocene-Miocene

In 1997 Bruno Cahuzac and Armelle extended the LBF zonation into the Oligocene and Miocene of southern Europe, especially Mediterranean and Atlantic from Portugal to the Aquitaine. This period is characterised by a general global cooling, and a strengthening of the latitudinal temperature gradient. Since large benthic foraminifera are (sub)tropical organisms, this cooling and regional tectonic events (reduction in marine basins, increased topography in the hinterland) resulted in a deterioration in the conditions for LBF in SW Europe, and, as a result, in a reduction in diversification. The following definitions are only minimally modified from the definitions in Cahuzac and Poignant (1997).

SBZ 26 (Langhian-Tortonian)
Species diversity declines as lepidocyclinids and miogypsinids became extinct in Europe. The base of SB 26 is defined by the first occurrence (in the Mediterranean domain only) of Borelis gr. melo and the disappearance of Miogypsina. The upper limit is tentatively placed at the extinction of some groups of Heterostegina at about the Tortonian-Messinian boundary. From the Middle Miocene, a diversification can be noticed in two genera only: Heterostegina and Borelis. Neorotalia lithothamnica and Operculina are present in the Middle Miocene, and at about the base of the Tortonian Discospirina appears in Mediterranean and is still living.

SBZ 25 (Burdigalian)
The base is characterized by the appearance of Miogypsina gr. globulina, the upper limit by the extinction of Miogypsina. SB 25 closely corresponds to the Burdigalian stage. This zone includes N5 pars-N7 and NN2 pars-NN4 pars. Its top can be correlated with N7-N8 boundary.
Larger foraminifera assemblages are still rather diverse Operculina complanata, Heterostegina spp., Nephrolepidina tounioueri,Miogypsina globulina, M. intermedia, M. cushmani, M. mediterranea, Miolepidocyclina burdigalensis, M. negrii,and very rare Planolinderina.

SBZ 24 (Aquitanian)
The base is defined by the appearance of the marker Miogypsina gr. gunteri. At the upper limit bispiralled Miogypsina occur. This biozone coincides to the Aquitanian stage (Bordeaux area stratotype), but indeed the correlations of the biozones with the stages depend on the accurate limits which will be adopted for the stages. The Oligocene-Miocene boundary corresponds to the SBZ 23-SBZ 24 boundary. SBZ 24 can be correlated with N4-(N5pars?) and NN1-base of NN2. Larger foraminifera are less diverse than in older SBZ; Nummulites, Cycloclypeus, Victoriella become extinct just as the genus Praerhapydionina and most species of Spiroclypeus at the end of SBZ23. Significant taxa are: Operculina complanata, Heterostegina spp., Nephrolepidina morgani, unispiralled Miogypsina, Neorotalia lithothamnica, Planolinderina escornebovensis; the genus Miogypsinoides seems to disappear (at least in the Aquitaine basin) during SBZ 24. Miolepidocyclina occurred first with M. socini and later M. burdigalensis within this zone. The presence of Borelis and Austrotrillina is very doubtful since these genera are absent from all the Aquitanian levels whose age has been revised.

SBZ 23 (late Chattian)
The base is defined by the appearance of Miogypsinoides; the upper boundary, defined by the occurrence of Miogypsina gr. gunteri, coincides roughly with the Oligo-Miocene limit. SB 23 is of a Chattian age and is correlated with P22 and the largest part of NP25. The assemblages are fairly rich: Nummulites bouillei, Operculina complanata, Spiroclypeus blanckenhorni ornata, Heterostegina spp., Grzybowskia assilinoides, Cycloclypeus eidae, lepidocyclinids, Miogypsinoides (and its evolutional anagenetic forms from M. complanatus), Neorotalia lithothamnica and N. viennoti well known in the peri-Mediterranean area, N. verriculata, Planolinderina escornebovensis, Victoriella aquitanica, Borelis pygmaea, B. inflata, Praerhapydionina delicata, Austrotrillina spp.

SBZ 22 (late Rupelian-early Chattian)
The base is defined by the appearance of Nephrolepidina praemarginata and Eulepidina formosoides, and the upper boundary by the appearance of the first Miogypsinoides. SBZ 22 can be correlated with P20-P21 and NP23 pars-NP25 (lowermost part) zones. It corresponds to the Upper Rupelian and Lower Chattian. It can be divided into 2 subzones, SBZ 22A and SBZ 22B:
* SBZ 22A with lepidocyclinids, Nummulites and Bullalveolina; the upper boundary is marked by the occurrence of Cycloclypeus (C. mediterraneus lineage);
* SBZ 22B with lepidocyclinids, Nummulites and Cycloclypeus (C. mediterraneus lineage).

SBZ 21 (early Rupelian)
The base (correspondencing to the Eocene-Oligocene boundary) is defined by the first appearance of Nummulites fichteli and N. vascus, following the extinction of the discocyclinids. The upper limit corresponds to the first appearance of the lepidocyclinids in Europe. SBZ 21 can be correlated to P18-19 and NP21 pars – NP 23 pars zones. LBF Assemblages show high diversity: Nummulites bouillei, Operculina complanata, Spiroclypeus cf blanckenhorni ornate, Heterostegina spp., Neorotalia lithothamnica, N. verriculata, Halkyardia minima, H. maxima, Bullalveolina bulloides, Borelis sp., Praerhapydionina delicata, Austrotrillina paucialveolata, Peneroplis armorica.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith