Lithostratigraphic analysis and palaeoenvironmental Interpretation of the late tertiary and quaternary sediments of The Nakuru, Elmentaita and Naivasha basins.

Abstract

The objective of this thesis is to provide a better understanding and correlation of the lacustrine palaeoenvironments of the late Tertiary and Quaternary rift sediments within the basins of Lakes Nakuru, Elmentaita and Naivasha. The study involved both field and laboratory investigations. In the field, detailed geological mapping, description, stratigraphic measurements and interpratation of rock outcrops were undertaken. Collected samples were subsequently subjected to petrographic and geochemical laboratory analyses. Both the field data and laboratory results were further subjected to computer analysis and results presented as maps, stratigraphic sections, tables, graphics, triangular plots and correlation fence diagrams. A survey of the strata within these basins yielded localised composite fluviatile deposits of mainly alluvio-Iacustrine stratified tuffs and relatively thin diatomaceous beds. Over 50m thick diatomaceous lacustrine deposits at Kariandusi diatomite mine formed in an extensive lake on the rift floor and is an obvious evidence of an extensive old lake formation on the rift floor. The lake beds formed thick tabular sediments on unstable faulted rift floor and were later incised by rivers which are then infilled by high energy polymictic volcaniclastics fluviatile conglomerates. The erosional contact separating the fluviatile and lacustrine lithofacies provide useful marker for intra-basinal correlations. Stratigraphic sections of thick diatomaceous beds at Soysambu mine document another extensive