Modern depositional environment in Lake Bosumtwi, mapped by the spatial relationships of bulk sediment and magnetic mineral grain size.

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A study of the modern depositional environment mapped by the spatial relationships of bulk sediment and magnetic mineral grain size has been conducted at Lake Bosumtwi. A total of 134 sediment samples were collected from specific locations over the entire lake with sampling depths ranging from 2 cm to 8 cm using the Ekman dredge. Sample measurements include magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, saturation isothermal remanent magnetization, loss- on-ignition as well as the determination of magnetic hysteretic parameters such as coercive force (Hc) and the remanent coercivity (Hcr). In addition, grain size analysis was performed on selected samples using the Rotap sieving method. The analysis of the measured results shows an increase in the magnetic concentration of the samples with increasing lake water depth. Coercivity values measured reveals that samples contain high proportions of magnetic minerals with low coercivity. The magnetic mineral grain size analyzed shows a decrease in size as lake water depth increases and bulk sediment grain size decreases with increasing water depth. The ratio of saturation remanent magnetization to saturation magnetization (Mrs/Ms) for selected samples were calculated. This ratio was observed to lie in the range of values, 0.21 – 0.31 indicating the presence of pseudo – single domain magnetic mineral grain size. Similarly, the percentage of organic content of the samples was found to increase with increasing lake water depth. From the results above, it can be concluded that, the uppermost 8 cm of surface sediment possibly accumulated under wet climatic conditions, which allowed the settling of sediments of reduced dust flux. The magnetic minerals present in the lake could be more of an authigenic and diagenetic origin than from allogenic origin.
A Thesis Submitted to the Kwame Nkrumah University Science and Technology, for the degree of Master of Science in Geophysics.