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| Titel |
Mesozoic black shales, source mixing and carbon isotopes |
| VerfasserIn |
Guillaume Suan |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132402
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| Publikation (Nr.) |
 EGU/EGU2016-12910.pdf |
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| Zusammenfassung |
| Over the last decades, considerable attention has been devoted to the paleoenvironmental and
biogeochemical significance of Mesozoic black shales. Black shale-bearing successions
indeed often display marked changes in the organic carbon isotope composition (δ13Corg),
which have been commonly interpreted as evidence for dramatic perturbations of global
carbon budgets and CO2 levels. Arguably the majority of these studies have discarded some
more “local” explanations when interpreting δ13Corg profiles, most often because
comparable profiles occur on geographically large and distant areas. Based on newly
acquired data and selected examples from the literature, I will show that the changing
contribution of organic components with distinct δ13C signatures exerts a major but
overlooked influence of Mesozoic δ13Corg profiles. Such a bias occurs across a wide
spectrum of sedimentological settings and ages, as shown by the good correlation
between δ13Corg values and proxies of kerogen proportions (such as rock-eval,
biomarker, palynofacies and palynological data) recorded in Mesozoic marginal
to deep marine successions of Triassic, Jurassic and Cretaceous age. In most of
these successions, labile, 12C-enriched amorphous organic matter of marine origin
dominates strata deposited under anoxic conditions, while oxidation-resistant, 13C-rich
terrestrial particles dominate strata deposited under well-oxygenated conditions. This
influence is further illustrated by weathering profiles of Toarcian (Lower Jurassic)
black shales from France, where weathered areas dominated by refractory organic
matter show dramatic 13C-enrichment (and decreased total organic carbon and
pyrite contents) compared to non-weathered portions of the same horizon. The
implications of these results for chemostratigraphic correlations and pCO2 reconstructions
of Mesozoic will be discussed, as well as strategies to overcome this major bias. |
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