Composition and Origin of Buried Ferromanganese Nodules from Central Indian Ocean Basin

Five buried ferromanganese nodules were recovered at different depths of 167-169 cm (A), 172- 174 cm (B), 228-230 cm (C), 328-330 cm (D) and 418-420 cm (E) in a 5 m sediment core from the siticeous sediment of Central Indian Basin (Lat 9°00' S , Long 76°00' E) at a water depth of 5260 m. These nodules were analysed for major, trace and rare earth element(REE) concentrations to understand their genesis and compare with the surface and burled nodules in the top 1 in of the sediment column from the same basin. Nodules A, B, C are of an early diagenetic(Mn/Fe ratio between 9 3 and 15 I), nodule D IS of hydrogenetic(Mn/Fe ratio 1 6) and nodule E is of diagenetic(Mn/Fe ratio 3 0) origin. Total REE concentration ranges between 164 and 497 ppm (av-348 ppm) and is nearly 2 to 3 fold lower than the surface and burled nodules REE are conveyed from the seawater to the nodules In association with a combined phase consistnig of Fe - Ti - P. The shale (NASC) - Normalized REE pattern displays a small convex pattern with a positive Ce-anomaly indicating an oxidized environment while, the presence of positive E u-anomaly in nodules A, B and C probably suggest an aeolian dust. These burled nodules show a moderate middle and heavy REE enrichment (strong in nodules B and C) compared to light REE, but fractionation between middle and heavy REE is not very clear It appears that not much significant Post -Depositional changes have occurred in these buried nodules.