Origin and Significance of Subsurface Lime Mud in the Outer Shelf off Visakhapatnam, Central East Coast of India

Lime mud occurs within 100-225 in isobath in the outer shelf along the East Coast of India, Bay of Bengal off Kakinada-Bheemunipatnam coast. A thin capping of Non-Carbonate clay/mud varying from 10-200 cm overlies the lime mud. The capping is thicker in the peripheral zone Lime mud is greyish white to creamy white resembling plaster of Pans and comprises minor ooids, pelloids, mud aggregates, foraminiferal tests and few terrigenous detrials. The maximum thickness of lime mud probed is 2 89 m.

Texturally, lime mud is sandy silt within top one meter subsurface level followed by silt up to 2 83 m subsurface depth. Chemical data show a maximum concentration of CaO -52 08% (CaCO₃ - 92 95%), Sr 0 66% and Li- 500 ppm. The XRD data show that the major constituent mineral is aragonite (85-90%) followed by Mg - calcite/calcite together with or without halite. The aragonite crystals are typically stubby and bladed with irregular outline and pointed terminations under SEM Textural, mineralogical and chemical parameters and coarse fraction studies suggest that lime mud might have been formed in shallow water environment as chemical precipitate during late Pleistocene/early Holocene and subsequently transported to deeper parts of the shelf.