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First evidence of triserial planktonic foraminifera Jenkinsina columbiana in Paleocene (Palmyride, Syria)

Taxonomic determination, phylogenetic relationships and stratigraphic ranges of triserial taxa are often misinterpreted due to their small size, dissolution susceptibility and patchy distributions in open sea environments. Based on differences in wall-structure, triserial planktonic foraminifera have been grouped into three genera, Guembelitria, Jenkinsina and Gallitellia, which all have different stratigraphic ranges. The Cretaceous genus Guembelitria has pore mounds with a central pore, while the test of Eocene and Oligocene Jenkinsina columbiana is covered by pustules, with pores between them. Gallitellia vivans is the only recent representative of the triserial planktonic foraminifera. Molecular studies indicate that G. vivans is not related to the Cretaceous-Paleogene triserial species, but instead they represent a separate lineage of planktonic foraminifera that branches close to the benthic rotaliids (Ujiié et al., 2008). A significant stratigraphic gap from Guembelitria to Jenkinsina has been reported from the middle Paleocene to lower Eocene (Kroon and Nederbragt, 1990 ; Huber et al., 2006). Detailed micropaleontological analyses of the small size fraction of Paleogene hemipelagic marls in boreholes in Palmiride area in Syria, has revealed the presence of triserial planktonic foraminifera. The first evidence of Jenkinsina in the Paleocene is in the upper part of Zone P2 together with Subbotina triloculinoides, S. cancellata, Morozovella praeangulata, Globanomalina compressa, Praemurica inconstans and Rectoguembelina cretacea. In Zone P3a, which is documented by a rich and very well preserved association of planktonic foraminiferal species such as Morozovella angulata, Acarinina strabocella, Igorina pusilla, Globanomalina ehrenbergi, and G. imitata, Jenkinsina columbiana becomes more frequent. Biostratigraphic determinations are also supported by the presence of the calcareous nannoplankton species Toweius selandianus, Toweius pertusus, Toweius eminens, Coccolithus pelagicus, Prinsius bisulcus, Cruciplacolithus primus, Calciosolenia aperta, Calciosolenia fossilis, which indicate the NP5 Zone. From lower Paleocene Zone P2, Jenkinsina columbiana is present in the small size fraction in all samples from the upper Paleocene, Eocene and Oligocene in the Palmiride area of Syria. Additional investigations of the small size fraction from lower Paleocene sediments is needed to determine if the gap between the highest occurrence (HO) of Guembelitria in Zone P1b and the lowest occurrence (LO) of Jenkinsina in Zone P2 can be closed.

planktonic foraminifera, nannoplankton, paleocene, Syria,

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