Occurrence of faecal pellet-filled simple and composite burrows in cold seep carbonates: A glimpse of a complex benthic ecosystem

Ichnofossils preserved in marine sedimentary records provide unique information on various activities (feeding, dwelling, excretion etc.) of benthic organisms. Here we report faecal pellet-filled tubular (simple and composite) burrow casts from cold seep carbonate layers (16–18 mbsf) deposited at least 46–58 kyr ago in the Krishna–Godavari basin, Bay of Bengal, India. Deposition of these chemosynthetic clam bearing authigenic carbonate sediments with highly depleted carbon stable isotope ratios indicates methane expulsion that resulted in the development of a cold seep ecosystem. Although cold seep communities are extensively reported from the rock record and modern seep sites, hardly any information is available on burrowing activity of the seep biota. Our findings open up a window for future investigation of the ecological significance of such burrows.