Microbial origin of the phosphorites of the Western continental shelf of India

Abstract

Phosphatised algal nodules were recovered by dredging from the western continental shelf off Goa at depths ranging from 70 to 150 m. Energy dispersive X-ray analysis indicates that the phosphorus present in the algal nodules is confined to brownish grains and occurs as cavity fillings. Phosphate grains are predominantly distributed in the outer layers and become less abundant towards the centre of the nodule P₂O₅ and fluorine contents are higher (9.5 and 1.25%, respectively) in the outer laminations while they are lower (5.4 and 0.78%) in the inner layers. SEM studies have revealed that the phosphate grains comprise endolithic filamentous fungi. Phosphatised cellular structures resembling bacteria are also present. It is thus envisaged that the direct role of upwelling compared to the microbial influence is probably of less significance in the phosphatisation of these limestones.