Prediction of Paleoclimate of Eocene Salt, Kohat Basin, Khyber Pakhtunkhwa, Pakistan

Fluid inclusion analysis is a significant tool to evaluate the paleoclimate reconstruction of ancient evaporite precipitation. The current study is a significant research to evaluate the ancient climate of Eocene salt. The thin sections petrography, XRD, SEM, Laser raman spectroscopy, and Microthermometric analysis have been used to evaluate the prediction of paleoclimate of Eocene salt. Two sections were measured and samples were collected for thin sections analysis. Under thin section, halite is mainly cubic shape euhedral form and also consists of other minerals like gypsum, anhydrite, polyhalite, sylvite, and dolomite. Geochemical data obtained from XRD, indicates the presence of Na and Cl as major ions, with subordinate Ca, SO4, Mg, etc. Laser raman spectroscopy analysis reveals that water and CO2 fluids are trapped within the inclusions. Generally, fluid inclusion analysis and geochemistry are useful tools to evaluate the origin and paleoclimate of Eocene Salt. Geochemical data shows that the Eocene salt is not a product of marine water but it also consists of meteoric and surface water. Low concentration of Br- and presence of SO4 shows that halite is precipitated from SO4 type water. Homogenization temperature (Th) ranges from 14°C to 43°C. Microthermometric data shows that fluids were entrapped during and after salt precipitation. Histogram of fluid inclusions also shows that primary and secondary inclusions have discontinuous behavior that shows inclusions were not trapped at the same time of deposition. Some are formed at the time of precipitation and some are formed after precipitation. The presence of impurities like Fe, Mg, Ca, and other ions within the halite show that halite was exposed to the atmosphere by tectonic activities and meteoric water/surface water percolates through fractures and is trapped as inclusion along with the micro fractures. So the Th variation indicates that fluid was trapped at various seasons. Low temperature show inclusions were trapped in winter/spring seasons and high temperatures indicates inclusions were trapped in the summer season. The maximum homogenization temperature of fluid inclusions in halite is 43°C which is closed to the maximum climatical temperature of the present summer. The result shows that Eocene salt has been deposited in hot, arid, and dry conditions during Eocene time. The alternating period of desalination and evaporation is responsible for the formation of soluble halite.