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    Comparing Carbonate and Organic AMS-14C Ages in Lake Abiyata Sediments (Ethiopia): Hydrochemistry and Paleoenvironmental Implications

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    Author
    Gibert, Elisabeth
    Travi, Yves
    Massault, Marc
    Chernet, Tesfaye
    Barbecot, Florent
    Laggoun-Défarge, Fatima
    Issue Date
    1999-01-01
    Keywords
    paleoecology
    lake sediments
    pore water
    East Africa
    crystallization
    Ethiopia
    Lake Abiyata
    lacustrine environment
    applications
    accuracy
    mass spectra
    spectra
    Africa
    Holocene
    last glacial maximum
    paleoclimatology
    Pleistocene
    sediments
    Cenozoic
    Quaternary
    C 14
    carbon
    isotopes
    radioactive isotopes
    geochemistry
    carbonates
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    Citation
    Gibert, E., Travi, Y., Massault, M., Chernet, T., Barbecot, F., & Laggoun-Défarge, F. (1999). Comparing carbonate and organic AMS-14 C ages in Lake Abiyata sediments (Ethiopia): Hydrochemistry and paleoenvironmental implications. Radiocarbon, 41(3), 271-286.
    Publisher
    Department of Geosciences, The University of Arizona
    Journal
    Radiocarbon
    URI
    http://hdl.handle.net/10150/654471
    DOI
    10.1017/S0033822200057131
    Additional Links
    http://radiocarbon.webhost.uits.arizona.edu/
    Abstract
    We studied a 12.6-m-long sequence from Lake Abiyata (Central Ethiopia) to establish a reliable and accurate chronology for use in global paleoclimatic reconstructions. The 26 accelerator mass spectrometry radiocarbon (AMS 14C) ages, performed on carbonates and organic matter, define 2 parallel chronologies, representing the complete Holocene period. However, these chronologies show a significant discrepancy from 500 to 900 BP in depth; ages obtained on carbonates were always older than those on organic matter. The hydrogeological and geochemical behavior of the Lake Abiyata basin has shed light on this discrepancy. We found that the carbonate crystallization is due mainly to the mixing of lake waters with ground-waters from the multi-layered aquifer contained in the 600-m-thick basement of the lake. The 14C activity of total dissolved inorganic carbon (TDIC) measured by AMS from bottom and surface lake waters (111.4 and 111.8 pMC, respectively) confirms that the mixing occurs at the water-sediment interface. This evidence of groundwater participation in the carbonate crystallization calls into question the current paleoclimatic reconstructions based on inorganic carbonates in lakes. Specific attention should thus be given to the respective proportions of each end-member in the mixing for the quantitative estimation of the groundwater input. This will help to validate the paleoenvironmental reconstructions and to highlight an eventual diagenetical evolution of inorganic carbonates during burial, via the study of pore waters.
    Type
    Article
    text
    Language
    en
    ISSN
    0033-8222
    ae974a485f413a2113503eed53cd6c53
    10.1017/S0033822200057131
    Scopus Count
    Collections
    Radiocarbon, Volume 41, Number 3 (1999)

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