Evolution of the Late Cretaceous orbitoidal foraminifera and implications for the taxonomy and biostratigraphy in the Eastern Neo-Tethys, Lower Indus Basin, Pakistan: A biometric approach

Abstract

In the eastern Neo-Tethys realm, the Late Cretaceous larger benthic foraminifera (LBF) Orbitoides and Omphalocyclus are poorly known. Herein, Orbitoides and Omphalocyclus populations from the Fort Munro Formation in Rakhi Nala Section, Lower Indus Basin, Pakistan are investigated. This work documents the most primitive evolutionary stages of these genera in the eastern Neo-Tethys. In Orbitoides, the average values of the size of embryon (Li + li) for the 18 investigated samples range between 477 and 516 µm and the average E values range between 4.2 and 4.7. In Omphalocyclus, the embryons are always trilocular and their sizes range between 112 and 485 μm, with an average between 153 and 287 μm. The E values range between 2 and 3, with an average of 2.3. Based on the average values of E and size of the embryon (Li + li), the populations of Orbitoides and Omphalocyclus have been attributed to the O. media and O. omanensis species, respectively. A late Campanian age is assigned to the Fort Munro Formation based on the recognition of O. media and O. omanensis. The detailed biometric study reveals primitive species of Orbitoides and Omphalocyclus from Pakistan (a part of eastern Neo-Tethys) in the Asian biogeographic province (ASP) during the late Campanian.