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


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).

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