Biochrono and Tectonic Framework for the Origin of KTB Canyon in Nagapattinam Subbasin, Cauvery Basin

Abstract

There is a prominent canyon feature across Cretaceous – Tertiary boundary (KTB) in the Nagapattinam sub basin.
Foraminiferal data from 34 well sections reveal that the sedimentary processes were disrupted 0.5-1 Ma before KTB and
0.5 to 1 Ma post KTB with intervening erosional process. The hiatus across KTB is diachronous and is 7-9 Ma along the
axis, 3-4 Ma along the flanks and 1.8 Ma along the periphery and beyond the canyon.
A credible correlation exists between timing of relative sea level fall and KTB canyon formation in the Cauvery Basin and
the Deccan volcanism in west central India. The reunion hot mantle plume above which India was gliding over during Late
Maastrichtian lifted west, central and peninsular India into a dome like feature. This has caused upliftment and east ward
tilt of the Cauvery Basin. Relative sea level fall is recorded on top of the Kallankurichhi Formation in the outcrops (CF6-
CF5 zones, Phase-1 Deccan volcanism, ~70 Ma). Destabilization of shelf edge and slope sediments began around this time.
The coastline receded and the areas west of Orathanadu got exposed (CF4 zone; ~68 Ma). Doming continued till the base
of CF3 zone (~67 Ma). The critical point of instability was around ~66.4 Ma (CF2-CF1 zones; Phase - 2 Deccan
volcanism). This triggered a chain of sedimentary processes involving shelf edge collapse, slumping, sliding and debris
flows. Vast amounts of Middle – Late Maastrichtian sediments were removed creating the canyon. Post Deccan volcanism,
there was a transgression beginning from P1b planktic zone (~ 65 Ma) as a response to thermal cooling and subsidence.
Thus it is evident that canyon development was largely restrained to upper- middle slope regions within a chronostratigraphic
framework of 70-66.4Ma.