PHOSPHATIC NODULES IN THE OUTER CONTINENTAL-SHELF OFF MADRAS, BAY OF BENGAL

Phosphatic nodules and rock pieces were collected from the outer continental shelf off Madras at 150-200m depth. They are associated with biogenous clayey sand. Polished sections of nodules exhibit alternate brownish grey phosphatic and creamy white calcitic laminae. XRD analysis indicates that carbonate fluorapatite and calcite are the dominant minerals. P2O5 content of the nodules and rock pieces is 17.54% and 19.98% respectively. SEM studies of the phosphatic nodule revealed the presence of colonised phosphatic cell structures resembling bacteria. Fossiliferous phosphatic rocks belonging to upper Cretaceous - lower Eocene age are possibly exposed at the continental shelf edge. Studies suggest that phosphorous from the older phosphatic rocks are dissolved and later assimilated by bacteria and colonised within the cavities of the nodules. Formation of these phosphatic nodules due to microbial activity probably took place during upper Pleistocene lowered sea level period.