Extensive Occurrence of Fe–Mn Crusts and Nodules on Seamounts in the Southern Andaman Sea, India

A reconnaissance survey for Fe–Mn crusts and nodules from West Sewell Ridge (WSR) and Sewell Rise (SR) in the Andaman Sea revealed their widespread occurrence along the summit of the ridge and on the slopes. Remotely operated vehicle (ROV) dive observations illustrate that the crusts are more concentrated on massive exposures at water depth of 800– 900 m and nodules swamped in foraminiferal ooze at water depth from 600 to 1100 m. During the ROV dives, massive, smooth, macro-botryoidal, flat, granular, gritty, coarse and knobby nature of Fe–Mn crusts and nodules have been observed. Nodules and crusts collected onboard were mostly black, brownish-black and pitch black in colour. Nodules show rough, botryoidal and granular/sacchoroidal texture. The diameter of the nodules increased up to 13 cm. They showed distinctly arranged concentric layers. The recovered crusts were mostly detached pieces without substrate.