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| Titel |
Imbalanced nutrients as triggers for black shale formation in a shallow shelf setting during the OAE 2 (Wunstorf, Germany) |
| VerfasserIn |
M. Blumenberg, F. Wiese |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 10 ; Nr. 9, no. 10 (2012-10-29), S.4139-4153 |
| Datensatznummer |
250007344
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| Publikation (Nr.) |
 copernicus.org/bg-9-4139-2012.pdf |
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| Zusammenfassung |
| During the oceanic anoxic event 2 (OAE 2) in the Mid-Cretaceous Period, widespread
black shale (BS) formation occurred, reflecting perturbations in major
biogeochemical cycles. Here we present geochemical and biomarker data of the
OAE 2 from a shelf setting situated at about 100–150 m water depth
(Wunstorf, Germany). Our data support that processes inducing BS deposition
were related to orbital cyclicity in Wunstorf and that they were not
restricted to the time of the OAE 2 carbon isotope excursion. Correlations
of total organic carbon (TOC) and δ15N and high relative
abundances of functionalized hopanoids (including 2-methylated structures)
suggest that BS were formed during times of imbalanced nutrients with high
phosphorus inputs and increased cyanobacterial nitrogen fixation. Periods
of BS formation were also characterized by enhanced growth of
dinoflagellates and bacteriovorous ciliates, the latter supporting the
presence of a stratified water body. The lack of biomarkers specific for
green sulfur bacteria excludes photic zone euxinia during OAE 2 in Wunstorf.
Conflicting maturities and biomarker distributions in kerogen and
extractable organic matter and, interestingly, a negative correlation of the
diagenetically resistant 2-methyl hopane hydrocarbons with TOC indicate a
complex depositional setting at Wunstorf. This might have been
induced by high continental runoff during BS formation and the accompanying
mobilisation of refractory OM from the shelves and near shore areas. |
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