Litho- and biostratigraphy and hydrocarbon source-rock potential of the Jurassic-Paleogene strata in the Kala Chitta Range, northwestern Himalayas, Pakistan

In this study Jurassic-Paleogene strata were investigated to understand the litho- and biostratigraphic framework and hydrocarbon source-rock potential of various stratal packages. Biostratigraphic controls were used to establish the chronostratigraphic framework of Jurassic-Paleogene strata in the area. The Lower Jurassic (Hettangian) clastics saw an unconformity during the Sinemurian-Pliensbachian, while the Lower Jurassic (Toarcian)-Middle Jurassic (Bajocian) clastic-carbonate mixed strata is also separated by a Bathonian unconformity from the Middle Jurassic (Callovian) to the Upper Jurassic (Tithonian) carbonate sequence. The Upper Jurassic Oxfordian strata are missing, while the Upper Jurassic (Kimmeridgian)-Lower Cretaceous (Valanginian) glauconitic sandstone and clays are the conformable sequences. The Lower Cretaceous (Hauterivian)-Upper Cretaceous (Turonian) clastics is a conformable sequence that is separated by a Coniacian-Santonian unconformity from the Upper Cretaceous (Campanian) pelagic carbonates. The Cretaceous-Tertiary boundary is marked by laterites, while the Paleocene (Thanetian) sequence is represented by a shale- and sandstone-dominated sequence. The Paleocene (Thanetian)-Early Eocene (Ilerdian) siliciclastic-carbonate mixed sequence marks the last episode of Tethyan sedimentation. Total organic content (TOC), organic petrography and Rock-Eval pyrolysis (REP) techniques were used to evaluate the hydrocarbon source-rock potential, kerogen type and level of maturity of the hydrocarbons. The majority of studied samples show the occurrence of type IV kerogen. However, the Middle Jurassic (Callovian)-Upper Jurassic (Tithonian) carbonate sequence of the Samana Suk Formation, the Kimmeridgian-Valanginian Chichali Formation, the Paleocene (Thanetian) sequence of the Hangu Formation and the Paleocene (Thanetian)-Early Eocene (Ilerdian) Patala Formation confirms the Type III kerogen, poor-fair source-rock quality, immature-mature, gas- and oil-prone indigenous hydrocarbon occurrence in the region.