Late Palaeocene to Early Eocene biostratigraphic framework from Upper Indus Basin, Pakistan, Eastern Tethys

Abstract

This investigation resulted in the biostratigraphic framework of the Upper Palaeocene–Lower Eocene rocks from the Upper Indus Basin, Pakistan, Eastern Tethys. The Patala Formation of the Chinjana Nala, Surghar Range of the Upper Indus Basin, was selected for this purpose. Lithologically, the Patala Formation is composed of shale and limestone interbeds. Three different fossil groups – smaller benthic foraminifera, planktic foraminifera, and calcareous nanno‐planktons – are used to establish a biostratigraphic framework for the Patala Formation. The biozones recognized in this study include: (a) bathyal benthic biozones, BB1 and BB2 of the Late Palaeocene and Early Eocene, respectively; (b) planktic biozones, P4 and P5 of the Late Palaeocene, while E1 and E2 of the Early Eocene; and (c) Calcareous Nanno‐planktons biozones: the NP9, which is further divided into NP9a and NP9b of the Late Palaeocene and Early Eocene, respectively. These biozones have been integrated to identify the Palaeocene–Eocene (P–E) boundary interval by applying widely used biostratigraphic criteria (i.e.,Rhomboaster‐Discoaster[RD]‐assemblage of calcareous nanno‐planktons). In this study, we have considered the lithological interval between ChN/TP‐16 and ChN/TP‐17 as a marker horizon for the P–E boundary interval, which provided a basis for the correlation of locally established biozones with those established Tethys wide, that is, Pak‐DIV to part of Pak‐DVI correlated to SRX‐1 and SRX‐2, which are equivalent to BB1, P4, P5, and NP9a. Similarly, parts of the Pak‐DVI and Pak‐DVII are correlated to SRX‐3, which are equivalent to BB2, E1, E2, and NP9b within the study.