We report the Narmada Seaway began in India during the largest global sea-level transgression and Oceanic Anoxic Event 2 (OAE2) δ¹³C excursion during the late Cenomanian to early Turonian. The transgression progressed eastward during the Turonian-Coniacian and reached Jhilmili by the end of the Maastrichtian. During this time the Narmada and Godavari Seaways may have joined via the Narmada-Tapti rift and formed a Trans-India Seaway. The history of this major seaway is entombed in a fossil-rich marine transgression of the tectonically active Narmada rift zone. We examined this transgression in the western Narmada Basin, Gujarat, to improve age control based on planktic foraminifera and ostracods and evaluate paleoenvironmental changes based on the Cenomanian-Turonian OAE2 δ¹³C excursion, δ¹⁸O records, and mercury concentrations in sediments as index for volcanic eruptions.

Results reveal the onset of the OAE2 δ¹³C excursion began in the western Narmada Basin during the late Cenomanian coeval with the sea-level transgression and first influx of planktic and benthic foraminifera in the Nimar Sandstone that overlies Archean rocks. The OAE2 δ¹³C excursion peak was recorded in oyster biostromes followed by fluctuating values of the δ¹³C plateau in the overlying Limestone with oysters beds, and gradual decrease to background values by the early Turonian. We tested the age of the transgression and δ¹³C excursion based on planktic foraminifera and ostracod biostratigraphy and successfully compared the results with the Pueblo, Colorado, Global Section and Stratotype Point (GSSP), and the eastern Sinai Wadi El Ghaib section of Egypt. PDF