METALS AS INDICATORS OF DETRITAL PROVENANCE IN PALEO-LAKE MABABE, BOTSWANA

The Mababe Depression is an arid basin located within the Okavango rifting zone in Northern Botswana. Lacustrine features of the depression indicate that it once supported an expansive lake throughout much of the Holocene. Stratigraphy within the Mababe Depression has resulted from the accumulation of sediment from both local and distant sources. Presently, however, this area is dominated by the arid climate of the Kalahari Desert and receives limited in-flow from four rivers: the Savuti, the Ngwezumba, the Mababe, and the Guatumbi.

This research focuses on identifying metal concentrations from two trenches in the Southeastern region of the depression, MAB6 and MABX, which may provide clues about the origin of the detrital sediment. This study in combination with previous research on detailed phosphorus geochemistry and future research into biogenic silica concentrations will aid in building a history of the paleoclimate of this region. In particular, we are interested in understanding how paleoclimate and tectonic activity influenced lake processes in the region.

Metal concentrations were determined following microwave assisted acid digestion of 132 sediment samples via ICP-OES. Results from this study show increases in metal concentrations, particularly Mn, Fe, and Ti with a decreases in Al at depths of ~250 cm. At this depth, metal ratios, such as Fe/Al and Fe/Ti increase by a factor of 20 while average Al/Ti ratios decrease suggesting a significant change in detrital provenance occurred during this time interval. This interval also corresponds to the depth where mineral P increased significantly at the expense of organic and oxide-associated P. Together these results suggest a major environmental change occurred during this time interval that altered detrital provenance and impacted lake biological productivity.