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| Titel |
Ontong Java volcanism initiated long-term climate warming that caused substantial changes in terrestrial vegetation several tens of thousand years before 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 |
250036024
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| Zusammenfassung |
| During Cretaceous times, several intense volcanic episodes are proposed as trigger for
episodic climate warming, for changes in marine circulation patterns and for elevated marine
productivity, which 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). Volcanic outgassing results
in an increased pCO2 and should lead to a rise in global temperatures. We therefore
investigated if the volcanically-induced increase in pCO2 at the onset of OAE1a in the early
Aptian led to a temperature rise that was sufficient to affect terrestrial vegetation
assemblages.
In order to analyse changes in terrestrial palynomorph assemblages, we examined 15 samples
from 12 black shale horizons throughout the early Aptian negative C-isotope spike interval of
the Pusiano section (Maiolica Formation; N-Italy). These sediments were deposited at the
southern continental margin of the alpine Tethys Ocean and have been bio- and
magnetostratigraphically dated by Channell et al. (1995). In order to obtain a continuous
palynological record of the negative C-isotope spike interval and the base of OAE1a, we
combined this pre-OAE1a interval of Pusiano with the OAE1a interval of the nearby Cismon
section (Hochuli et al., 1999).
The sporomorph assemblages at the base of this composite succession feature abundant
bisaccate pollen, which reflects a warm-temperate climate. Rather arid conditions are inferred
from low trilete spore percentages. Several tens of thousand years before the onset of OAE1a,
C-isotope values started to decrease. Some thousand years later, bisaccate pollen began to
decrease, whereas an increase of Classopollis spp. and Araucariacites spp. percentages
indicate a rise in temperatures. Maximum temperatures (suggested by a dominance of
Classopollis spp.) were only reached after the most negative inorganic C-isotope values and
after the onset of OAE1a. Our study shows that the volcanically-induced increase in pCO2,
which ultimately led to OAE1a caused a substantial climate warming that seriously affected
terrestrial vegetation.
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.
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