Fault‐Controlled Thermal Maturity of Organic Matter in the Upper Jurassic Jhuran Formation, Kutch Basin, Gujarat, Western India

ABSTRACT The Upper Jurassic Jhuran Formation of the pericratonic Kutch basin, western India, is generally considered to consist of a poor‐to‐moderate‐source rock, and its relatively high thermal maturity has largely been attributed to widespread igneous activity associated with the Deccan volcanism. However, the role of fault‐controlled structural processes in modifying the thermal evolution of organic matter (OM) remains unexplored. This study evaluates source‐rock properties of carbonaceous shales across the kodki normal fault (KNF) and investigates the origin of thermal‐maturity variations between the footwall (FW) and hangingwall (HW). Samples were analyzed using Rock‐Eval pyrolysis, vitrinite reflectance, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and outcrop‐based structural and fracture studies. The analyzed samples have moderate carbon content and poor hydrocarbon generation potential. Thermal maturity proxies consistently indicate higher maturity in the HW than the FW. VR‐derived paleotemperatures suggest that the HW experienced temperatures approximately 18–28°C higher than the FW, supported by lower AD1/AG ratios, lower G‐full width at half maximum (FWHM) values, and reduced hydroxyl‐band intensities. FTIR spectra indicate no systematic mineralogical differences between the two fault blocks. Field observations reveal a higher fracture density and abundant vein‐filled fractures in the HW. Thermal maturity difference across the KNF is attributed to fracture‐controlled uneven fluid flux, which locally enhanced thermal maturity in the HW compared to FW. These results demonstrate that fault‐related structural processes can locally modify the regional thermal evolution established by magmatic activity and should be considered when evaluating thermal maturity variations in tectonically active sedimentary basins.