Distribution of major, trace and rare-earth elements in surface sediments of the Wharton Basin, Indian Ocean

Abstract

Bulk chemical analyses of eighteen surface sediments taken on an east-west transect (lat. 15°40′S) in the Wharton Basin, Indian Ocean, were analysed for major, trace and rare-earth elements (REE) by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The relationship between Al and K suggests in situ formation of authigenic phillipsite. The relationship between P and Ca suggests accumulation of biogenic apatite/fish bone debris from high biological productivity waters, which is confirmed by the linear relationship with P and Cu. A strong positive correlation among redox sensitive metals (Mn, Fe, Cu, Ni and Zn) suggests that they are incorporated into a ferromanganese oxide phase, probably micronodules. Calcareous oozes from the transect have low REE abundance (La ∼ 8 ppm) with a very strong negative Ce Ce ★ value (0.41), siliceous oozes have high REE abundance (La ∼ 28 ppm) with moderate positive Ce Ce ★ (1.24) and red clays have highest REE abundance (La ∼ 66 ppm) with a weak positive (1.05) to moderate negative Ce Ce ★ (0.73). Shale-normalized REE patterns and ( La Yb ) n ratios record similar enrichment of heavy REE (HREE) relative to light REE (LREE) in all sediment types. This might be due to retention of the bottom water REE pattern and the presence of fish bone debris. Correlation coefficient and R-mode factor analyses suggest a very strong positive association ( R 2 > 0.9) of REE with P, and thus most likely with biogenic apatite/fish bone debris. As P is directly associated with biological activity it is thus related to surface primary productivity. REE in the Wharton Basin sediments appear to reflect a combination of surface water effects and diagenetic processes.