Recent studies indicate that the bulk (80%) of the Deccan trap
eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r
spanning the Cretaceous-Tertiary (K-T) boundary. Determining where
within this major eruptive phase the K-T mass extinction occurred has
remained problematic. For this reason, models estimating the biotic and
environmental consequences have generally underestimated the rate and
quantity of Deccan gas emissions by orders of magnitude leading to
conclusions that volcanism could not have been one of the major causes
for the K-T mass extinction. In this study we report that the most
massive Deccan trap eruption occurred near the K-T mass extinction.
These results are based on sedimentologic, microfacies and
biostratigraphic data of 4-9 m thick intertrappean sediments in four
quarry outcrops in the Rajahmundry area of the Krishna-Godavari Basin of
southeastern India. In this area two Deccan basalt flows, known as the
Rajahmundry traps, mark the longest lava flows extending 1500 km across
the Indian continent and into the Bay of Bengal. The sediments directly
overlying the lower Rajahmundry trap contain early Danian planktic
foraminiferal assemblages of zone P1a, which mark the evolution in the
aftermath of the K-T mass extinction. The upper Rujahmundry trap was
deposited in magnetic polarity C29n, preceding full biotic recovery.
These results suggest that volcanism may have played critical roles in
both the K-T mass extinction and the delayed biotic recovery. (c) 2008
Elsevier B.V. All rights reserved.