Comparing Carbonate and Organic AMS-14C Ages in Lake Abiyata Sediments (Ethiopia): Hydrochemistry and Paleoenvironmental Implications
Author
Gibert, ElisabethTravi, Yves
Massault, Marc
Chernet, Tesfaye
Barbecot, Florent
Laggoun-Défarge, Fatima
Issue Date
1999-01-01Keywords
paleoecologylake 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
Metadata
Show full item recordCitation
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.Journal
RadiocarbonAdditional 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
Articletext
Language
enISSN
0033-8222ae974a485f413a2113503eed53cd6c53
10.1017/S0033822200057131