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| Titel |
The causes of covariation between C and O isotopes in the inorganic carbonate record |
| VerfasserIn |
Peter Swart, Amanda Oehlert |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152958
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| Publikation (Nr.) |
 EGU/EGU2017-17870.pdf |
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| Zusammenfassung |
| The δ13C values of carbonate rocks are widely used as proxies for understanding the global
carbon cycle. While most workers would prefer to use δ13C values measured in oceanic
sediments, during older times the only records that exist are those found in sediments
deposited in epeiric seas or on continental margins and carbonate platforms. However,
such records are often compromised by near surface diagenesis and therefore care
must be taken to exclude altered records. One approach, which has been widely
applied, has been to examine the covariation between δ13C and δ18O values, where
a positive covariation has been suggested to indicate alteration. In order to test
this assumption we present data from a core taken in the Bahamas that has been
unequivocally subjected to both freshwater and marine diagenetic processes. Our data
suggest that the majority of the zone which has been altered by freshwater shows no
correlation between δ13C and δ18O values, with small intervals associated with
sub-aerial exposure exhibiting inverse correlations, and only the upper partially
altered portion of the core exhibiting positive relationships. The zone below the
region of freshwater alteration, previously interpreted as being the mixing-zone, is
characterized by a strong covariation between δ13C and δ18O values as a result of the upper
portion of this zone having been affected by fresh water diagenesis compared to the
lower portion. Within the marine influenced realm a variety of relationships are
produced as a result of differences in sediment origin and diagenesis. For example,
non-depositional surfaces, where marine diagenetic processes are maximized, are
typically expressed by sharp positive correlations between δ13C and δ18O values,
while changes related to different sediment sources are expressed as weak positive
covariations.
While the data set presented here may not be applicable in every situation, the study
certainly emphasizes that care must be taken when rules of thumb such as covariation of δ13C
and δ18O values suggest diagenesis. |
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