Cenomanian-Turonian sea-level transgression and OAE2 deposition in the Western Narmada Basin, India

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

Major geologic events of the Cauvery Basin, India and their correlation with global signatures – A review

The present review is aimed at correlating major geologic events of the Cauvery Basin with analogous global episodes. The Cauvery Basin came into existence due to Gondwana break up during Late Jurassic–Early Cretaceous by taphrogenic rift process. The first marine transgression close to Aptian/Albian boundary at the western margin of the basin terminates the syn-rift tectonic phase, which is also precise in adjoining Krishna-Godavari (KG) Basin. Two regional tectonic episodes are well documented in the basin which have global significance viz. (1) A major basinal uplift during late Turonian caused by Marion hot mantle plume resulted in widespread subaqueous volcanism in the southern part of the Cauvery Basin. This uplift also led to relative sea level (RSL) fall of about 100 m in Cauvery and KG Basins and an unconformity of a magnitude of 2.3 Ma. The RSL fall closely correlates with global sea level fall. This volcanic episode also resulted in Madagascar detachment from India. (2) The reunion hot mantle plume that led to Deccan volcanism in central India resulted in E–SE tilt of the Cauvery Basin during upper Maastrichtian (CF1-CF3 zones). This tilt caused a sea level fall of about 80 m and lateral withdrawal of sea by about 50 km developing a major erosional unconformity ranging in magnitude of ∼1.8–30 My. The magnitude of RSL correlates well with global sea level fall. This sea level fall caused widespread development of canyon features in the Cauvery Basin resulting in differential subaqueous erosion. The globally significant ocean anoxic events viz. OAE-1b, OAE-1d, OAE-2 and OAE-3 are fairly discernible in the Cauvery Basin. The new isotopic palaeotemperature data suggests that southern India and Madagascar were located apparently in middle latitudes within the tropical-subtropical climatic zone during Albian and early Maastrichtian. The magnitude of hiatus across K–Pg boundary varying from 0 to 30 Ma is estimated based on planktic foraminifera for subsurface sections. The magnetostratigraphy of outcrop sediments with rich fossil evidences reveals that magnetic polarity reversals consist of 13 magnetozones in the Late Cretaceous sedimentary strata