Paleoenvironmental conditions and key drivers of organic matter accumulation in the early cretaceous Talhar Shale, Lower Indus Basin, Pakistan

The Talhar Shale (early Cretaceous), a key member of the Lower Goru Formation, is notably thick (averaging 70 m) and extensively found throughout the Lower Indus Basin (LIB). Despite its geologic significance, the key factors influencing organic matter (OM) accumulation are still unknown. This study aims to address this gap by analyzing both organic and inorganic geochemical data to evaluate the source rock potential, reconstructing the early Cretaceous paleoenvironment, and identifying the primary factors controlling OM accumulation in the Talhar Shale. Our findings reveal that the Talhar Shale exhibits a high total organic carbon content (averaging 2.27 wt%) and is mainly composed of type II kerogen. The shale has reached the main stage of hydrocarbon generation, affirming its status as a thermally mature and prospective source rock for oil and gas. Additionally, the high concentration of SiO₂ classifies it as a siliceous shale, and most trace elements show their enrichment compared to the upper continental crust, signifying its elemental importance in the region. Redox-sensitive parameters of the analyzed early Cretaceous data indicate global oxic conditions towards the poles, compared to oxygen-deficient or anoxic conditions towards the equatorial regions. However, the oxic to suboxic conditions predominantly prevailed during the deposition of early Cretaceous Talhar Shale, with moderately higher paleo-bioproductivity driven by a relatively high sedimentation rate under freshwater saline conditions. Moreover, our analysis proposes paleoproductivity, paleoclimate, paleosalinity, possible high sedimentation rate, and hydrothermal activities as the key factors influencing OM accumulation, while redox conditions appear to have played a lesser role. These results justify a more comprehensive exploration of the Talhar Shale, highlighting its potential as a source rock and its broader implications for understanding global paleoenvironmental dynamics during the early Cretaceous. This study contributes to the global discourse on paleoenvironmental reconstruction and positions the Talhar Shale as a significant geological feature within the LIB and beyond.