Relationship between chemical composition and magnetic susceptibility in sediment cores from Central Indian Ocean Basin

摘要

Three sediment cores in a north-south transect (3°N to 13°S) from different sediment types of the Central Indian Ocean Basin (CIOB) are studied to understand the possible relationship between magnetic susceptibility (χ) and Al, Fe, Ti and Mn concentrations. The calcareous ooze core exhibit lowest χ (12.32 × 10~(-7) m~3 kg~(-1)), Al (2.84%), Fe (1.63%) and Ti (0.14%), terrigenous clay core with moderate χ (29.93 × 10~(-7) m~3 kg~(-1)) but highest Al (6.84%), Fe (5,20%) and Ti (0.44%), and siliceous ooze core with highest χ (38.06 × 10~(-7) m~3 kg~(-1)) but moderate Al (4.49%), Fe (2.80%) and Ti (0.19%) contents. The distribution of χ and detrital proxy elements (Al, Fe, and Ti) are identical in both calcareous and siliceous ooze. Interestingly, in terrigenous core, the behaviour of χ is identical to only Ti content but not with Al and Fe suggesting possibility of Al and Fe having a non-detrital source. The occurrence of phillipsite in terrigenous clay is evident by the Al-K scatter plot where trend line intersects K axis at more than 50% of total K suggesting excess K in the form of phillipsite. Therefore, the presence of phillipsite might be responsible for negative correlation between χ and Al (r = -0.52). In siliceous ooze the strong positive correlations among χ, Al_(exc) and Fe_(exc) suggest the presence of authigenic Fe-rich smectite. High Mn content (0.5%) probably in the form of manganese micronodules is also contributing to χ in both calcareous and siliceous ooze but not in the terrigenous core where mean Mn content (0.1%) is similar to crustal abundance. Thus, χ systematically records the terrigenous variation in both the biogenic sediments but in terrigenous clay it indirectly suggests the presence of authigenic minerals.