This project will involve a detailed mineralogical and chemical analysis of the clay minerals in numerous long sediment-cores (up to 12m in length) which have been collected recently from Lake Malawi and Lake Turkana in East Africa. By analyzing carefully the vertical changes in the clay assemblages and correlating these with changes in diatom contents, physical stratigraphy and interstitial-water chemistry, we will a) document the timing and degree of paleosalinity fluctuations of these lakes during the last several thousand years and b) examine the detailed processes of clay-mineral diagenesis in alkaline lakes, especially the uptake of Mg in smectite phases and the transformation of smectite into illite under variable chemical conditions. The data will be correlated with other proxy climatic indicators from these lake basins and with previous studies elsewhere in East Africa to help document patterns of global climate change in the Holocene. Furthermore, since both rift-valleys and alkaline lakes are now recognized as important depositional environments in the geological record, an understanding of the behavior of clay minerals in these modern settings will help evaluate the role of burial diagenetic reactions for the generation and migration of petroleum in non-marine settings.
