Paper No. 15
Presentation Time: 1:30 PM-5:30 PM
SEDIMENT-BORNE MAJOR AND TRACE ELEMENT GEOCHEMISTRY OF THREE TRIBUTERIES OF LAKE TANGANYIKA, EAST AFRICA
The Rusizi, Malagarasi and Lufubu rivers constitute the major external source of nutrients and solutes to Lake Tanganyika. This study uses the geochemistry of major and trace elements of bulk sediment to assess the extent of weathering in the lakes catchment basin. Fifteen samples were air-dried, ground and 0.1000g of each sample was digested overnight in a mixture of HNO3 and HF. ICP-MS was used to analyze trace and major element cocentrations in solution, while XRF was used to determine the relative abundance (%) of major oxide elements such as Al2O3, SiO2 and CaO. Chemical index of alteration was used to assess the extent of weathering, while major element ratios were used to investigate, sedimentary sorting, maturity and their combined impacts on trace element contents. Sc vs.Th/Sc, Eu/Sm vs. Eu/Ce and GdN/YbN vs. Eu/Eu* were used to study the sediment provenance. There was a strong correlation between Ca and Sr, suggesting a similarity in their origin. REEs abundance in sediemnt was deficient compared to the UCC compositions, with MREEs > LREEs > HREEs. The MREEs enrichment can be either attributed to the presence of apatite or heavy minerals. Strong relationships between TiO2 and MREEs, HREE and Y and between Th and LREEs suggest that the abundance of REEs,in Lake Tanganyika 's catchment basin, is chiefly controlled by the presence of heavy minerals such as allanite, monazite and ilmenite.A strong possitive relationship observed between Al2O3 and TiO2 suggests a high accumulation of heavy minerals and intense chemical weathering (CIA=75% to 82%) in the lake's catchment basin. It can be concluded, from this study, that the chemical weathering in the Lake Tanganyikas catchment basin is a function of lithology and the basin morphology.