The Paleocene/eocene Boundary in the Tethyan Shallow Benthic Zonation

The Paleogene shallow benthic zonation (SBZ) in the Tethyan realm was established in 1998. At that time, however, the position of the Paleocene/Eocene (P/E) boundary within this biozonation was not well constrained, as the International Commission on Stratigraphy only formalized the GSSP for the P/E boundary in 2003, defining it by the onset of the negative carbon isotope excursion (CIE) associated with the Paleocene–Eocene Thermal Maximum (PETM). Since then, the precise placement of the P/E boundary in the SBZ has been the subject of intensive study, yet it remains controversial. While some researchers advocate for placing the P/E boundary at the SBZ4/SBZ5 transition, others argue for a higher stratigraphic level ─ within the SBZ5. Here we present paleontological and isotopic evidence from southern Tibet, indicating that the P/E boundary should be placed within the SBZ 5, at least in the eastern Neo-Tethyan oceanic region of the Tibetan area. We further suggest that the incompleteness of the PETM interval from many sedimentary sections is the primary reason for the ongoing debate.