Early Eocene orthophragminids from the Lower Indus Basin, Pakistan, and their biostratigraphic implication

Abstract

Orthophragminids are a key biostratigraphic proxy for Paleocene–Eocene sequences in western Tethys, but poorly known in eastern Tethys. The orthophragminids were previously misinterpreted as Paleocene's orbitoidiform foraminifera in the Indus Basin, Pakistan. This study focuses on detailed taxonomy and biostratigraphy of orthophragminids. Nine species/subspecies of orthophragminids are identified, including Discocyclina ranikotensis, D. archiaci bakhchisaraiensis, D. a. ex. interc. staroseliensis bakhchisaraiensis, D. dispansa hungarica, D. d. taurica, D. d. broennimanni and Orbitoclypeus schopeni ramaraoi, and two new species Discocyclina pseudoranikotensis n. sp. and Discocyclina debalensis n. sp. are described. The identified orthophragminid taxa represent the orthophragminid zones OZ2-3, corresponding to the shallow benthic zones SBZ5-7 of early Ypresian (early Eocene), which are correlated with those in western Tethys. However, we found that the first appearances of D. d. hungarica and D. d. taurica occur in the OZ3 or SBZ7 in this study instead of the OZ5 or SBZ10 as in western Tethys. The possible paleoecological setting for the occurrences of recognized species is interpreted as inner to middle shelf.