The timing of oceanic anoxic events in the Cretaceous succession of Cauvery Basin: Constraints from ⁴⁰Ar/³⁹Ar ages of glauconite in the Karai Shale Formation

This study presents 40 Ar/ 39 Ar ages of autochthonous glauconites from the lower segment of the onshore Karai Shale Formation of the Cauvery Basin that constrain its age from 100.3 ± 0.7 to 92.6 ± 0.6 Ma. The 40 Ar/ 39 Ar plateau ages of the 3 glauconite samples are consistent with the existing biostratigraphic age of Late Albian to Middle Turonian of the Karai Shale Formation. These ages are significant because of the occurrences of oceanic anoxic event (OAE)1d and oceanic anoxic event (OAE)2 in contemporaneous offshore deposits, the Sattapadi Shale and Bhuvanagiri Formation, respectively. Although in the onshore deposits, the glauconite ages mark condensed deposits of the transgressive Karai Shale. As onshore glauconitic deposits may be transitional to organic‐rich black shale deposits offshore in modern and ancient sedimentary settings, the 40 Ar/ 39 Ar ages precisely constrains the timing of Cretaceous oceanic anoxic events reported in the Cauvery Basin.