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| Titel |
Evolution of volcanically-induced palaeoenvironmental changes leading to the onset of OAE1a (early Aptian, Cretaceous) |
| VerfasserIn |
Christina E. Keller, Peter A. Hochuli, Martino Giorgioni, Therese I. Garcia, Stefano M. Bernasconi, Helmut Weissert |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036049
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| Zusammenfassung |
| During the Cretaceous, several major volcanic events occurred that initiated climate warming,
altered marine circulation and increased marine productivity, which in turn often resulted in
the widespread black shale deposits of the Oceanic Anoxic Events (OAE). In the sediments
underlying the early Aptian OAE1a black shales, a prominent negative carbon isotope
excursion is recorded. Its origin had long been controversial (e.g. Arthur, 2000; Jahren et al.,
2001) before recent studies attributed it to the Ontong Java volcanism (Méhay et al., 2009;
Tejada et al., 2009).
Therefore the negative C-isotope excursion covers the interval between the time, when
volcanic activity became important enough to be recorded in the C-isotope composition of the
oceans to the onset of widespread anoxic conditions (OAE1a). We chose this interval
at the locality of Pusiano (N-Italy) to study the effect of a volcanically-induced
increase in pCO2 on the marine palaeoenvironment and to observe the evolving
palaeoenvironmental conditions that finally led to OAE1a. The Pusiano section (Maiolica
Formation) was deposited at the southern continental margin of the alpine Tethys Ocean
and has been bio- and magnetostratigraphically dated by Channell et al. (1995).
We selected 18 samples from 12 black shale horizons for palynofacies analyses.
Palynofacies assemblages consist of several types of particulate organic matter,
providing information on the origin of the organic matter (terrestrial/marine) and
conditions during deposition (oxic/anoxic). We then linked the palynofacies results to
high-resolution inorganic and organic C-isotope values and total organic carbon content
measurements.
The pelagic Pusiano section consists of repeated limestone-black shale couplets, which are
interpreted to be the result of changes in oxygenation of bottom waters. Towards the end of
the negative C-isotope excursion we observe enhanced preservation of the fragile amorphous
organic matter resulting in increased total organic carbon values in the black shale as well as
in the limestone intervals. This shows how a rising pCO2 triggered changes in climate and
oceanography and resulted in an increasing oxygen-deficiency of the bottom waters that
persisted even during the “limestone intervals” before oxygen-depletion finally became a
global phenomenon.
References:
Arthur, M.A., 2000, Volcanic contributions to the carbon and sulfur geochemical cycles and
global change, in Sigurdsson, H., Houghton, B., McNutt, S.R., Rymer, H., and Stix, J., eds.,
Encyclopedia of Volcanoes, Academic Press, p. 1045–1056.
Channell, J.E.T., Cecca, F., and Erba, E., 1995, Correlations of Hauterivian and Barremian
(Early Cretaceous) stage boundaries to polarity chrons: Earth and Planetary Science Letters,
v. 134, p. 125-140.
Jahren, A.H., Arens, N.C., Sarmiento, G., Guerrero, J., and Amundson, R., 2001, Terrestrial
record of methane hydrate dissociation in the Early Cretaceous: Geology, v. 29, p.
159-162.
Méhay, S., Keller, C.E., Bernasconi, S.M., Weissert, H., Erba, E., Bottini, C., and Hochuli,
P.A., 2009, A volcanic CO2 pulse triggered the Cretaceous Oceanic Anoxic Event 1a and a
biocalcification crisis: Geology, v. 37, p. 819-822.
Tejada, M.L.G., Suzuki, K., Junichiro, K., Rodolfo, C., J., M.J., Naohiko, O., Tatsuhiko, S.,
and Yoshiyuki, T., 2009, Ontong Java Plateau eruption as a trigger for the early Aptian
oceanic anoxic event: Geology, v. 37, p. 855-858. |
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