Larger Foraminiferal Extinction and Origination Event during the Paleocene-Eocene Thermal Maximum in the Potwar Basin (Eastern Neotethys)

In the Potwar Basin (Pakistan, Eastern Neotethys), the Paleocene-Eocene transition has been investigated and the changes in larger benthic foraminiferal (LBF) assemblages have been compared with the carbon isotope excursion (CIE). The ~5‰ negative CIE is here used to place the exact position of the Paleocene-Eocene boundary that falls in the base of the Shallow Benthic Zone (SBZ) 5. The boundary between the SBZ 5 and 6 corresponds to the early stages of the CIE recovery phase, which is characterized by the disappearance of the some typical Paleocene lamellar-perforate LBF genera such as Miscellanea, Kathina, and possibly Ranikothalia. In the Potwar Basin, some species of Daviesina and Glomalveolina also disappeared at the base of SBZ 6. At the same time, the genus Orbitolites and some species of Alveolina, Nummulites, miliolids, and Assilina appeared and led to the larger foraminiferal extinction and origination (LFEO) event.

The LFEO event represents the late response of the LBF to the abrupt environmental perturbation induced by the Paleocene-Eocene Thermal Maximum (PETM). At the Duleram section (Potwar Basin), the pre-PETM phase is characterized by highly stable and oligotrophic conditions, as revealed by the dominance of large, K-strategists LBF genera (e.g., Miscellanea, Ranikothalia, and Daviesina). At the onset of the PETM, an increased nutrient supply led to establishment of more eutrophic conditions and a collapse of the oligotrophic LBF with the rise of more nutrient-tolerant, small-sized LBF (e.g., glomalveolinids). At the post-PETM phase, stable oligotrophic conditions were re-established, as revealed by the dominance of new K-strategists LBF genera (Alveolina, Nummulites, and Assilina).

As the changes in the LBF assemblages match well with the CIE changes, we can use them as proxies to infer the variations from stable oligotrophic to eutrophic marine conditions during the PETM event in the Eastern Neotethys.