Facies Stacking of a Deep Sea Depositional Lobe: Case Study from Palaeogene Andaman Flysch, South Andaman Islands, India

Abstract

This study presents an architectural element analysis of submarine fan deposits based on facies analysis in excellent outcrops of the Andaman Flysch in South Point section at the eastern margin of South Andaman Islands. The 292 m thick section of the Andaman Flysch consists of four facies viz. thick-bedded sandstone, thin-bedded sandstone, heterolithics and shale. Greater part of the section, particularly towards the top and bottom is dominated by amalgamated, laterally persistent thick-bedded sandstone. A detailed analysis of 78 m thick section at the central part of the section reveals vertical stacking of dominantly thin-bedded sandstones, heterolithics and shale encased within amalgamated thick-bedded sandstone. The vertical stacking of facies corresponds to dominantly lobe fringe and inter-lobe elements at the central part and lobe axis and lobe flank elements at the top and bottom of the section. The occurrence of coarse-grained clastic equivalents of Andaman Flysch with erosional bases of sandstones in north and middle Andaman Islands and very fine-grained clastics in Great Nicobar Island, along with present investigation in South Andaman Islands reveals an arc-parallel transformation of architectural elements from channel, channel-lobe transition zone and lobes from north to south.