Publikationsdatum:
1992-01-01
Beschreibung:
Groundwater samples were collected from several different depths in Illinois glacial deposits at a site in east-central Illinois. Dissolved gases were extracted from many of the water samples, measured volumetrically, and analyze by gas chromatography. The DIC was precipitated as barium carbonate and analyzed for both δ13C and 14C. Due to the formation of microbial CH4, some of the DIC had unusually heavy δ13C values of −3 to −1‰. The standard groundwate 14C-age correction models were developed to account for carbonate dissolution as the primary carbon input beneath the soil zone. If the heavy δ13C values observed in this study are used in readily available groundwater dating models without accounting for the effect of microbial methane formation, many of the resultant calculated ages are negaitive (future ages) mathematically unsolvable. Isotopic and analytical result show a positive correlation (r2 = 0.90) between the δ13C of the DIC and the concentration of methane in the groundwater. With this correlation, we were able to correct the δ13C values of the DIC which were altered due to microbial CH4 formation. This adjustment of δ13C values, along with estimation of dead carbon input from the redox processes, allowed us to calculate 14C ages using standard groundwater age correction models.
Print ISSN:
0033-8222
Digitale ISSN:
1945-5755
Thema:
Klassische Archäologie
,
Energietechnik
,
Geologie und Paläontologie
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