10. PLIOCENE AND PLEISTOCENE BIOSTRATIGRAPHY OF BACHMAYERELLA TENUIS AND INCERTAE SEDIS, FORMA A, EASTERN MEDITERRANEAN, HOLES 965A, 966A, 967A, AND 969A1Silvia Spezzaferri2 and Dorothee Spiegler3 |
ABSTRACTThe range of Bachmayerella tenuis and Incertae sedis, forma A, allows a remarkable improvement of the stratigraphic resolution of the Pleistocene interval spanning the Globigerina cariacoensis and Truncorotalia truncatulinoides excelsa Zones. Bachmayerella tenuis last occurs in the lower part of the calcareous nannofossil Zone NMNN19a. Incertae sedis, forma A, last occurs in the lower part of Zone MNN19f. An informal zonation incorporating planktonic foraminifer bioevents and the last occurrence (LO) of these two forms, probably belonging to the calcdinocyst group, is proposed as follows: Subzone A (Bachmayerella tenuis) spans the interval from the increasing abundance of N. pachyderma sinistral to the LO of B. tenuis. Subzone B (Incertae sedis, forma A) spans the interval from the LO of Bachmayerella tenuis and the LO of the Incertae sedis, forma A. Subzone C (T. truncatulinoides excelsa) spans the interval from the LO of the Incertae sedis, forma A, and the modern seafloor. The new form, Incertae sedis, forma A, is informally described. The isotopic composition of the Incertae sedis, forma A, tests is similar to the isotopic composition of the benthic foraminifer Oridorsalis stellatus. Further studies, including a light optical investigation on the wall texture, are currently underway to clarify its taxonomic position. |
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