Cretaceous-Tertiary Boundary Events: The Fossil Vertebrate, Palaeomagnetic and Radiometric Evidence from Peninsular India

Recent data based on microvertebrates and associated microfossils suggest that the Lameta and coeval formations of Peninsular India are younger (Maestrichtian) than ages previously assigned to them (Cenomanian-Turonian). Similarly, the Takli and their intertrappean correlatives in several localities have yielded dinosaurian elements indicating thereby a Cretaceous rather than Tertiary age. Furthermore, no exclusively Tertiary taxa has been recorded from these beds at Nagpur, Asifabad, Kachchh and adjoining areas. Samples collected for palaeomagnetic studies with reference to vertebrate-bearing horizons suggest that the Deccan basaltic activity was initiated in the Late Maestrichtian at the end of Lameta times. The major part of the eruption took place during the reversed magnetic chron, 29R, which encompasses the Cretaceous-Tertiary Boundary. Radiometric dates (K/Ar, ⁴⁰Ar/³⁹Ar) tend to cluster in a 60 m.y. 70 m.y. interval. The Deccan traps have been cited as a possible alternative source of Ir enrichment in comparison to the hypothesis which ascribes the anomalously high values of this element at the KTB to an extra-terrestrial impact. The gradual decline of dinosaurs as well as other marine plankton and benthos towards the close of the Cretaceous favours hypotheses that do not advocate 'instantaneous' global mass extinctions.