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Journal of the Geological Society; 1997; v. 154; issue.2; p. 311-319;
DOI: 10.1144/gsjgs.154.2.0311
© 1997 Geological Society of London

Article

Holocene palaeolimnology of Kajemamm Oasis, Northern Nigeria: an isotopic study of ostracodes, bulk carbonate and organic carbon

J. A. HOLMES1, F. A. STREET-PERROTT2, M. J. ALLEN1, P. A. FOTHERGILL3, D. D. HARKNESS4, D. KROON5 & R. A. PERROTT2

1 School of Geography, Kingston University, Penrhyn Road, Kingston upon Thames, Surrey KT1 2EE, UK
2 Department of Geography, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK
3 Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
4 NERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, Glasgow G75 0QF, UK
5 Department of Geology and Geophysics, University of Edinburgh, Edinburgh EH9 3JW, UK

A high-resolution 5500 year palaeolimnological record from Kajemarum Oasis, a closed basin in the Manga Grasslands of northern Nigeria, provides evidence of environmental change in Subsaharan Africa during the Holocene. Palaeohydrological variations, mainly changes in the balance between precipitation and evaporation, are recorded by stable oxygen isotope ratios in bulk carbonate and ostracod calcite and by the Sr/Ca ratio in ostracode shells. Variations in the carbon isotope ratios in carbonates indicate changes in primary productivity in the lake, whereas the carbon isotope composition of organic carbon reflects ecophysiological processes within the lake and its surrounding catchment. Results indicate that there have been marked environmental changes in the Manga Grasslands over the last 5500 years. A more variable climate set in around 1500 cal. a BP. A prolonged drought between 1200 and 1000 cal. a BP, with reduced aquatic productivity, was followed by a switch to a wetter, but still unstable climate: moist conditions prevailed during the Little Ice Age. The results indicate that drought has affected the Sahel episodically over the last 1500 years and is not solely a twentieth-century phenomenon.


Keywords: Holocene, Ostracoda, Sahel, stable isotopes, trace elements.




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