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Identification of Pedogenic Carbonates using Stable Carbon Isotope and Microfabric Analyses
Author(s) -
Rabenhorst M. C.,
Wilding L. P.,
West L. T.
Publication year - 1984
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1984.03615995004800010023x
Subject(s) - pedogenesis , carbonate , geology , geochemistry , soil water , stable isotope ratio , organic matter , cretaceous , isotope analysis , isotopes of carbon , mineralogy , paleontology , chemistry , soil science , total organic carbon , environmental chemistry , physics , oceanography , organic chemistry , quantum mechanics
In soils formed from limestone, it is often difficult to distinguish between inherited and pedogenic carbonate. In nature, both thermodynamic and kinetic factors have caused fractionation of C isotopes. While marine carbonates usually have δ 13 C values near zero, the processes of pedogenic carbonate formation result in considerably lower values, which are dependent only on the δ 13 C of the soil CO 2 gas. Therefore, a simple proportionality may be employed to quantitatively estimate pedogenic carbonates in the soil. Seven pedons formed over Cretaceous limestone in Central and West Texas were studied. The δ 13 C values were determined for the parent carbonates, soil organic matter, and for the various carbonate‐enriched horizons. Both finely disseminated carbonates in A horizons and massive indurated petrocalcic materials were confirmed by isotopic analyses to be primarily of pedogenic origin. Characteristic microfabrics were correlated with isotopic assay of massive petrocalcic materials which may be diagnostic for identification. Although generally useful, isotopic analysis underestimates the pedogenic component in certain carbonate forms, including laminar caps and some concretions and pendants. It is postulated that a different mode or environment of formation for these forms is responsible for discrepancies with theoretical values.