Seismic Expression of the Canyon Fill Facies and its Geological Significance------A Case Study from Ariyalur-Pondicherry Subbasin, Cauvery Basin, India

Roy Moulik, S.K""¹, Dr. G.K. Prasad² (1) BSG, KDMIPE, Oil and Natural Gas Corporation Limited, Dehradun, India (2) Oil and Natural Gas Corporation Limited, Dehradun, India

Two-way time contour mapping at the top of Cretaceous-Tertiary boundary (K/T boundary) and the isochronopach of Sequence K3C reveal a canyon network at the K/T surface of Aryalur-Pondicherry Sub-basin, Cauvery basin, located at the southeast coast of India. At the end of Cretaceous period there was tectonic reorganization resulting uplift causing marine regression throughout the basin. This caused incision of exposed shelf and the formation of submarine canyon at the shelf edge. Subsequently canyon was filled during Late Paleocene times. Five different types of canyon fill facies have been identified based on the seismic expressions of the canyon fill. Integrating the available well data with seismic, lithological interpretation of different types of canyon fill facies have been made and presented diagrammatically in this paper. Somewhere it is sand rich, at some places shale rich and sometimes consists of alternate sand and shale facies. The porosities and permeabilities of the sands are quite good as evidenced by the testing data. A conceptualized depositional model of these sands has been postulated. This model shows that sands were deposited in submarine canyon set up under the influence of gravity driven mass transport processes like slumps/slides and debris flow. Key Words: K/T boundary, canyon fill, slumps/slides, debris flow