Abstract
Optical and geochemical techniques were applied to organic matter of Late Quaternary sediments from Lakes Victoria and Rukwa, East Africa. Variations in total organic carbon (TOC) and hydrogen content (expressed as Hydrogen Index, HI) can be related to known changes in lake level and used to identify periods of very low water or subaerial exposure in basinal sequences. TOC and HI both decline as an exposure surface is approached, mainly due to the selective removal of unstable components by bacterial respiration and inorganic oxidation. Inert organic material of very low HI is typically concentrated at the overlying transgression surface. The carbon isotopic composition of the particulate organic matter tends to be less negative in sediments associated with exposure surfaces. Although weathering may be partially responsible, isotopic variations are mainly due to changes in the relative importance of material from plants using C4 photosynthesis, such as grasses and sedges, growing around the shore and on the exposed lake muds, and of material from planktonic algae and terrestrial C3 plants.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 121-137 |
| Number of pages | 17 |
| Journal | Palaeogeography, Palaeoclimatology, Palaeoecology |
| Volume | 70 |
| Issue number | 1-3 |
| DOIs | |
| State | Published - Apr 1989 |
Bibliographical note
Funding Information:We acknowledgfein ancials upportf rom the Royal NorwegianR esearchC ouncil (NAVF), the GuggenheimFo undationa ndthe National Science Foundatono f the U.S.A. Dr. J. L. RichardsonD, r. G. Kitaka and the late Capt. Illugasona ssistedw ith coring,a ndDr. E. Lind, then Professoor f Botanya t MakerereC ollege, Dr. John Okedi, then Director of EAFFRO, Jinja, and Mr. John Bousefielda t Lake Rukwa, providedl aboratorya nd workshop facilities, vesselsa, nd many other courtesies. Pyrolysisa ndTOC analysews erec arriedo ut at the Norsk Hydro ResearchC entre,B ergen, and the Geolab, Statoil, StavangerT. he help and cooperatioonf Birger Dahl (Norsk Hydro), Hilary Irwin (Statoil) and their respective staffs is gratefully acknowledgedT. he National GMS LaboratoryU, niversityo f Bergen, wheret hei sotopica nalysews erec arriedo ut,is supportebdy NAVF. Sturla Rolfseni s thanked for his assistanceT.h e isotopics tudyreported here forms part of a projectf undedi n part by VISTA (Den norske stats oljeselskapsb asic researchp rogramme)W. e are gratefult o Dr. David Burney for his pollen analysesa nd to Drs. Kurt Haberyan, Kerry Kelts, Alayne Street-Perrotatn d Bjorn Buchardtf or reviewing earlier drafts of the paper.
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Copyright 2014 Elsevier B.V., All rights reserved.
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