Abstract
The Kohat Basin (KB) lies on the Himalayan Foothills and is of scientific importance as it directly recorded the closure of the Tethys Sea and the Himalayan collision between India, Asia, and a number of other small plates. During the Eocene, after the collision between the Indian and Eurasian plates terminated the Tethys Sea, thick-bedded marine evaporite sequences developed in the KB. In this study, we combined mineralogy, geochemistry, fluid inclusion and chlorine stable isotope compositions to discuss the origin and evolution of the KB Eocene halite deposits with the ultimate objective of defining the paleoclimate that was prevailing in Asia during the Eocene. Our results showed that halite samples were SO42− rich (225–370.103 ppm) and Br− poor (<3 ppm). Cl−, B+, Mg2+, K+, SO42− and very low Br concentrations as well as the (Br/Cl) ratios indicated that halite resulted of a mixture of solutions with variable compositions and that dissolution, recrystallization and a progressive decrease in dolomitization were the mechanisms leading to the formation of these evaporites. A Br/Cl vs Cl plot revealed that the end members involved were: seawater (sw), saline waters and/or freshwaters. The recrystallization process prevented identifying the primary structures and primary fluid-inclusions. Most of Cl isotope compositions (−0.54‰<δ37Cl < 0.83‰) were within the usual range (0 ± 0.5‰) associated to seawater as the initial source for the halite. The higher isotope compositions (δ37Cl ≥ 0.83‰) comforted the hypothesis of the genesis by mixing of solutions of different origins as well as the involvement of recrystallization. Based on our results, we are proposing the following to explain the regional paleoclimate sequence: 1) shallow water conditions; 2) halite precipitation induced by evaporation, 3) unstable paleoclimatic conditions that resulted in the morphing from an evaporite basin into a terrestrial foreland basin. All these events were controlled by regional tectonic and linked to both the overall uplift times of the NW Indian Craton and the Eocene thermal maximum one during the Eocene-Oligocene period.
Highlights
The collision tectonic events leading to the final closure of the Tethys Sea during the Cenozoic formed mountain chains that prolong from the Mediterranean region to Asia (Potter and Szatmari, 2009)
All samples yielded higher SO42− concentrations compared to Ca2+, which confirmed that halite precipitated from SO42−-type waters
The high Mg2+ contents in the halite samples compared to the Eocene seawater supported a global decrease in the dolomitization process
Summary
The collision tectonic events leading to the final closure of the Tethys Sea during the Cenozoic formed mountain chains that prolong from the Mediterranean region to Asia (Potter and Szatmari, 2009) These events were recorded by the Paleocene–Pleistocene sedimentary rocks present in India, Nepal and Pakistan (Najman et al, 2017). Records of marine sedimentation ranging from the Paleocene to younger ages can be observed at the Kohat Plateau (KP; NW Pakistan), known as the Kohat Fold and Thrust Belt (KFTB) (Hussain and Zhang, 2018) These sedimentary rocks are mainly constituted of complex groups of sulfate, evaporite, shale/ sandstone, and conglomerates (Meissner et al, 1975). The Indus River and the Kurram Fault mark (Figure 1) its eastern and western boundaries (Kazmi and Rana, 1982)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
