PALEOLIMNOLOGY OF LAKE EDWARD (EAST AFRICA) FURTHER REVEALED BY XRF CORE SCANNING OF HOLOCENE SEDIMENTS

X-ray fluorescence core scans of Lake Edward sediment, collected in 1996 by a team including Mike Talbot, reveal details of processes affecting the lake during the early to mid-Holocene (11 to 6.5 ka). In this system, many geochemical proxies are affected by multiple processes, so their interpretation requires deconvolution of these signals. For example, Ca:Ti, indicates preservation of carbonate minerals. Increased Ca:Ti can reflect drier conditions and a switch to closed basin conditions, but also can may be associated with input of carbonatite-bearing ash from the nearby Katwe volcanic field, which was active in the mid-Holocene. Similarly, K:Ti and K:Rb reflect changing sediment provenance and can be interpreted to represent the combined effects of changes in erosion and weathering and in the input of ash-derived material. Major changes in Si:Ti (which resembles biogenic opal and a interpreted as a proxy for diatom productivity) appear to be linked to changes in nutrient fluxes resulting from increases increased runoff or exposure of fresh minerals to chemical weathering. Overall, the sedimentary record of the lake suggests a scenario of relatively dry conditions in the early Holocene, with maximum dryness around 8.5 ka, followed by a relatively humid period that is also characterized by an increased influence of volcanic ash.