Provenance and tectonic setting of Early Eocene Sohnari Member of Laki Formation from southern Indus Basin of Pakistan

Abstract

The current study is carried out the bulk mineralogical and geochemical investigation of the Early Eocene Sohnari coal‐bearing sedimentary rocks from the southern Indus Basin in Pakistan. The sediments of the Sohnari Member of Laki Formation are composed of shale and sandstone. Their provenance and tectonic setting can well constrain the evolution of the Indus Basin and help solve the controversy regarding the timing of the India–Eurasia collision. X‐ray diffraction results confirm the existence of abundant quartz, zircon, and hematite. The assemblages of hematite, calcite, halite, and gypsum indicate the depositional history of Early Eocene time of southern Indus Basin had with dry, low temperature, and high salinity conditions. The geochemical results demonstrate that the Sohnari sediments are dominated by mature sublitharenites derived predominantly from quartz sedimentary and felsic rocks with minor arc‐related mafic inputs. The chemical index of alteration and plagioclase index of alteration of the Sohnari Member indicate the sediments experienced low to high weathering conditions in the southern Indus Basin during Early Eocene time. The provenance characteristics suggest that the Early Eocene sediments were deposited in a passive margin, instead of a foreland basin. Therefore, we propose that India might still have not collided with Eurasia in the Ypresian of Early Eocene (56–47.8 Ma).

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

“…The lithology and mineralogy of Sohnari Member have been discussed in detail by Hakro et al (2017). The Chat Member of Laki Formation is about 111 m thick in this section (Figure 3).…”

“…Integrated age dating and palaeo-bathymetric demarcations reveal significant basin uplift and erosion at the end of the Cretaceous and end of Eocene times, the latter coinciding with the closure of the Neo-Tethys (Wakefield & Monteil, 2002). However, in a recent study in the Lower Indus Basin, Hakro et al (2017) suggested that the Indian-Asian collision had not occurred at the SW margin during Early Eocene time. The different ideas are due to the different episodes of collision at various geographic positions.…”

“…The studied sections are in Thatta and Jamshoro districts of Sindh Province, Pakistan (Figure 2b). The region is mainly occupied by the Lakhra Anticline, which was previously referred to as the Hyderabad anticlinorium or Hyderabad Arc (Hakro et al, 2017;HSC, 1961). The Lakhra Anticline is a gentle doubly plunging anticline.…”

“…Kureshy (1984) studied the Laki Formation in Pakistan for LBF and recognized three species of Alveolina (A. oblonga, A. ovicula, and A. subpyrenaica). The Lower Eocene succession of the Lower Indus Basin, Laki Range mostly represents a carbonate platform (Hakro et al, 2016;Hakro et al, 2017;Khokhar et al, 2016;Shah, 2009), which shows favourable palaeoenvironmental conditions for the survival of Alveolina. Therefore, this succession offers an excellent opportunity to study Alveolina in detail.…”

Energy Dispersive X-Ray Spectroscopy of the Sohnari Member of Laki Formation from Southern Indus Basin of Pakistan

“…The Sohnari member of the Laki Formation (K 2 O) concentration ranges from 0.51% to 0.80%, with a mean value of 0.51% and 0.21%. As compared to other cations (calcium and magnesium), the lattices of montmorillonite often contain small amounts of potassium and sodium oxides [20], and [28]…”