A multi‐proxy based high‐resolution stratigraphical analysis of the possible Palaeocene–Eocene boundary interval, Salt Range, Pakistan

Abstract

The Palaeocene–Eocene boundary (PEB) interval has been recognized in the Patala Formation, Nammal Gorge Section, Pakistan using lithostratigraphy, stable carbon isotope stratigraphy and integrated biostratigraphy. Four distinct lithological units are identified in the Patala Formation in stratigraphic order from bottom to top; unit‐1 to unit‐4. The top of unit‐3 hosts three closely spaced unconformities demarcated as U1, U2, and U3. The PEB interval is represented by a negative shift of 1.61‰ in δ13CV‐PDB representing the carbon isotopic excursion (CIE) in unit‐2. Based on the encountered foraminifera, dinocysts, and calcareous nannoplanktons, the following biozones are identified across the PEB; two larger benthonic foraminiferal (LBF) zones (SBZ4 and SBZ5), the zonal boundary slightly postdating the CIE, two smaller benthonic foraminiferal zones (BB1 and BB2), three planktonic foraminiferal zones (P4/P5 + E1), four dinocysts zones (Pak‐DV, Pak‐DVI, Pak‐DVII, Pak‐DVIII), and two calcareous nannoplankton subzones (NP9a and NP9b). The following protist, dinocyst and calcareous nannoplanktons encountered in the studied interval advocates for the placement of the possible PEB at the level between samples NAM‐SH‐07 and 08; 1—presence of the smaller benthonic foraminifera Angulogavelinella avnimelechi diagnostic of the base of the CIE and the benthonic extinction event (BEE) Tethys wide, 2—presence of the cosmopolitan and the PEB diagnostic dinocyst species ‘Axiodinium augustum’, 3—presence of the PEB diagnostic Rhomboaster‐Discoaster calcareous nannoplankton assemblage. The LBF species Alveolina vredenburgi [a marker species of the Larger Foraminiferal Turnover (LFT) associated with the Palaeocene Eocene Thermal Maximum (PETM) and PEB in western Tethys] occurs slightly above the onset of the CIE. Previously reported compositional change in the LBF assemblage from the Salt Range [i.e. the replacement of the Palaeocene orbitoidiform LBF (Setia and Orbitosiphon) by the Eocene LBF (Orthophragminids, Alveolina, Nummulites and Assilina)] also postdates the PEB interval here. The late appearance of Alveolina vredenburgi and the compositional change in the LBF after the onset of the CIE are attributed to the facies variation across the PEB reflecting fluctuating depositional environment due to the active tectonic across this interval. This fluctuation is evident from the smaller benthonic and planktonic foraminiferal dominating assemblages in unit‐2 representing bathyal settings followed by LBF dominating unit‐3 representing shallow carbonate platform settings. The change in LBF assemblage closely resembles the well‐known LFT associated with the PETM as well as the carbonate platform stage III and the PEB reported from other Tethyan sections.

Origin and Evolution of Eocene Rock Salts in Pakistan and Implications for Paleoclimate Studies: Insights From Chemistry and Cl Stable Isotopes

“…In this basin, the onset of the carbon and oxygen stable isotope excursion has proved that it's associated with the PETM (Hanif, 2011). Besides isotopic evidences, paleontological ones also support that the PTEM impacted the area neighboring the Salt Range (Afzal et al, 2011;Hanif et al, 2020) and indicate that the environment fluctuated (bathyal -shallow carbonate platform; Hanif et al, 2020). Still, to our knowledge, the studies about the PTEM effects in this region are still scarce, therefore arising the need for further investigations based on petrographic (e.g.…”

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

“…Hanif et al (2014) focused on dinocysts (Axiodinium; Williams et al, 2015;Fensome et al, 2009, previously as Apectodinum) abundance and its correlation to the Palaeocene-Eocene boundary with the help of carbon isotopic excursion (CIE). Whereas the latest findings of Hanif et al (2020) did place the possible P-E boundary based on CIE and RD-assemblages but the interval contains the signature of dissolution caused by the ecological artefact. This dissolution affected the quality so that the boundary remained less precisely marked.…”

“…However, the exact location of the PETM has not precisely been located yet. Recently, Hanif et al (2020) have reported detailed stratigraphical analysis of the P-E boundary interval from the Salt Range, Upper Indus Basin. They used a multi-proxy approach such as lithostratigraphy, stable isotopes, foraminifera, organic dinoflagellates, as well as calcareous nanno-plankton, for better understanding the P-E interval, according to the latest available literature, references therein in Hanif et al (2020).…”

“…Recently, Hanif et al (2020) have reported detailed stratigraphical analysis of the P-E boundary interval from the Salt Range, Upper Indus Basin. They used a multi-proxy approach such as lithostratigraphy, stable isotopes, foraminifera, organic dinoflagellates, as well as calcareous nanno-plankton, for better understanding the P-E interval, according to the latest available literature, references therein in Hanif et al (2020). They introduced the possible P-E boundary, based on Carbon Isotopic Excursion (CIE) with support of the Nitrogen-Carbon (N/C) ratio, and Rhomboaster-Discoaster (RD)-assemblages.…”

Alveolinids from the Lower Indus Basin, Pakistan (Eastern Neo‐Tethys): Systematic and biostratigraphic implications

“…Larger benthic foraminifera (LBF) are a useful tool for biostratigraphical and palaeoenvironmental interpretations (Gary, 1991;Hallock & Glenn, 1986;Hanif et al, 2021;Papazzoni et al, 2017;Serra-Kiel et al, 1998;Zoeram et al, 2015). The LBF are significant contributors to shallow marine sediments in the tropical and subtropical regions during the Early Palaeogene, and occasionally they formed prolific accumulations along the western, central, and eastern regions of Neo-Tethys (e.g., Drobne, 1977;Hӧttinger, 1960;Özcan, 2002;Racey, 2001;Schaub, 1981).…”