ABSTRACT The Cretaceous petroleum system beneath the volcanic rocks in the deep offshore Indus Basin presents a challenging yet potentially significant frontier for hydrocarbon exploration. This study utilises new 2D seismic reflection data to explore the stratigraphy and structural complexities within the basin, which is predominantly influenced by extensive magmatic activity. Key findings highlight the presence of significant stratigraphic discontinuities and potential hydrocarbon reservoirs below a regionally extensive basalt unit. Through detailed seismic stratigraphy and sequence analysis, integrating data from boreholes and seismic data, this study delineates five seismic facies units grouped into Lower and Upper Cretaceous megasequences, identifies features such as saucer‐shaped sill complexes and hydrothermal vent complexes, and assesses the post‐Cretaceous depositional environments. The complex interplay between tectonics, sedimentary and magmatic processes has been mapped, providing insights into the potential hydrocarbon system. Upper Cretaceous sequences show lateral variations with a northeast to southwest fining trend and differential thickness across the volcanic units, thinning northward and thickening southeastward towards the Saurashtra High. Lower Cretaceous sequences reveal lithologic composition and thickness variability, with the Sembar and Goru formations locally exceeding 2000 m in thickness on the shelf before thinning basinwards. Quantitative thermal modelling indicates that magmatic intrusions impacted source rock maturation, raising sediment temperatures by 50°C–100°C and affecting approximately 15%–20% of the Cretaceous Sembar Formation source rock, thereby potentially generating an additional 10%–15% hydrocarbons beyond burial maturation alone. Our quantification shows magmatic heating accelerated Sembar Formation maturation by 8%–18%, facilitating hydrocarbon generation in this sub‐basalt system. The timing of this magmatism (~70–60 Ma, just before and during Deccan volcanism) was favourable, coinciding with organic‐rich shales entering the peak oil window and favouring hydrocarbon generation and migration. These findings provide insights into the geological history and hydrocarbon potential of the offshore Indus Basin's Cretaceous units and offer analogues for other volcanic passive margins worldwide.
Shahzad et al. (Thu,) studied this question.