Larger benthic foraminiferal turnover and carbon isotope excursion during the Paleocene–Eocene Thermal Maximum in the Southern Himalayan carbonate platform (Eastern Neo-Tethys Ocean, Pakistan)

Abstract The Paleocene–Eocene Thermal Maximum (PETM; ca. 56 Ma) is widely recognized as one of the most severe transient warming events during the Cenozoic Era. The investigation of shallow-marine records is crucial for comprehending the larger benthic foraminiferal (LBF) turnover and environmental changes across the PETM. Based on sedimentological, biostratigraphic, and chemostratigraphic data, this study provides the first comprehensive record of the PETM from two sections within the Baluchistan Basin (Eastern Neo-Tethys Ocean, Pakistan). A prominent negative carbon isotope excursion (CIE) of ~5.65‰ in the Jandran section and ~3.11‰ in the Sanjawi section is used to accurately characterize the PETM. This excursion indicates that the Paleocene-Eocene (P/E) boundary is located within shallow benthic Paleocene (SBP) zone 4. No significant taxonomic change is observed at the P/E boundary. The main phase of the CIE falls in the middle part of shallow benthic zone (SBZ) 5. This phase is associated with a relatively high sea level and a persistent mid-ramp depositional environment, which continues up to the top part of SBZ 5. A significant taxonomic change in the LBF assemblages is observed at the SBZ 5/SBZ 6 boundary coinciding with the CIE recovery phase of the PETM. The changes in the LBF assemblages are characterized by the disappearance of some widespread upper Paleocene genera, such as Ranikothalia, Orbitosiphon, Miscellanea, Daviesina, and Lockhartia, and the subsequent radiation of typical lower Eocene genera, such as Orbitolites, Alveolina (both genera are present in SBP 4), and Nummulites (this genus is present in SBP 3). During the CIE recovery phase, a replacement of mid-ramp sediments with shoal sediments is observed. Evidently, the primary factor influencing the LBF turnover during the CIE recovery phase of the PETM was the change in nutrient input generated by enhanced terrestrial runoff. This, in turn, was triggered by the sea-level fall.