HOLIVAR2006 Abstracts
Late Pleistocene and Holocene environmental and climatic change from Lake Tana, northern Ethiopia.
M.H. Marshall1, H.F. Lamb1, C.R. Bates2, P.V.C. Coombes1, S.J. Davies1 and M. Umer3
1Institute of Geography and Earth Sciences, University of Wales Aberystwyth, SY23 1DB, UK
2School of Geography and Geosciences Irvine Building, University of St Andrews, Fife, KY16 9AL, Scotland, UK
3Department of Earth Sciences, University of Addis Ababa, P.O. Box 1176, Addis Ababa, Ethiopia
Contact: M.H. Marshall (mhm03@aber.ac.uk)
Late Pleistocene and Holocene environmental changes are reconstructed from a 10.3 m-long sediment core from Lake Tana, the source of the Blue Nile. Diatom, X-ray fluorescence, mineral magnetic, and seismic results from core 03TL3, taken from the deepest point of the lake, indicate that the basin was shallow with a swamp-like environment persisting between 16.0 cal. kyr BP and 15.4 cal. kyr BP, recorded by a peat unit. A compacted silty-clay below the peat which prevented further recovery, also found in two littoral cores, represents a desiccation surface that is present as a high density reflector surface in the seismic data (P1). Deepening occurred post-15.4 cal. kyr BP, but diatom-inferred conductivity increased (from 700 to 3400 μS cm-1) due to evaporation from the closed-basin. Overflow into the Blue Nile occurred from about 14.7 cal. kyr BP, with a switch to inorganic lake sediment predominantly allochthonous in origin and dominated by freshwater planktonic diatoms indicative of a turbid, well-mixed lake with modern conductivity values (~145 μS cm-1). Diatom preservation becomes sporadic post-12.9 cal. kyr BP. Between 11.8 and 10.5 cal. kyr BP a shift in the magnetic assemblage indicates the input, and/or formation through oxidation, of haematite under aerobic arid conditions. This also corresponds to a seismic reflector (Z2) surface where no diatoms are preserved. Allochthonous inputs were reduced at 8.0 and 4.1 cal. kyr BP, possibly in response to catchment aridity. Clear evidence of human impact in the catchment is evident from around 1.7 cal. kyr BP.
Mike completed BSc. and MSc. degrees within the Department of Geography at the University of Liverpool before moving to Aberystwyth where he is currently writing up his PhD thesis on Late Pleistocene and Holocene palaeolimnology in the Ethiopian Highlands. His research interests include quantitative palaeoenvironmental reconstruction, specifically using diatoms, stable isotopes (particularly from diatom silica), environmental mineral magnetics, and X-ray fluorescence.