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| Titel |
The Campanian - Maastrichtian (Late Cretaceous) climate transition linked to a global carbon cycle perturbation |
| VerfasserIn |
S. Voigt, O. Friedrich, A. S. Gale |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025072
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| Zusammenfassung |
| The Late Cretaceous was a period of long-term climate cooling succeeding the extreme
warmth of the mid-Cretaceous greenhouse world. The cooling is mainly considered
as a result of changes in ocean circulation due to plate movements resulting in
progressive deep-water exchange between the deep oceanic basins and a parallel drop in
atmospheric carbon dioxide concentrations. In Campanian – Maastrichtian times,
pronounced climate cooling is documented between 71 - 69 Ma, when distinct changes in
foraminiferal oxygen and carbon isotope data at a global scale indicate substantial
deep-water cooling and reduced rates of organic carbon burial. The causal mechanisms of
this cooling period, however, are poorly understood to date. While some authors
suggest mainly oceanographic changes, others supposed an ephemeral glaciation
related to a eustatic sea-level fall. Mainly, the relative timing of oceanic oxygen and
carbon isotope changes to eustatic sea-level changes is not proven yet. Likewise, the
influence of plate tectonic changes as the opening of gateways or the subduction of
mid-ocean ridges and/or of orbital forcing is poorly understood. A principle objection
beside the sparse available data is the low temporal resolution of biostratigraphic
zonations.
Here, we present carbon isotope stratigraphies from Campanian-Maastrichtian Boundary sites
in the Boreal and Tethyan shelf seas of Europe and from Shatsky Rise in the tropical Pacific
in order to improve the resolution of stratigraphic correlation. Prominent features at that time
are two negative carbon isotope excursions (CIEs) in the late Campanian and earliest
Maastrichtian, which are well documented in the Lägerdorf-Kronsmoor section in
N-Germany and the Campanian-Maastrichtian Boundary Stratotype at Tercis in SW France.
These new carbon isotope records correlate well with the carbon isotope reference curve from
the English Chalk (Jarvis et al., 2002, 2006).
The new carbon isotope record at Site 305 in the tropical Pacific shows the prominent
negative CIE in the early Maastrichtian, which perfectly resembles the carbon isotope data of
planktonic and benthic foraminifers (Barrera and Savin, 1999). Numerous stratigraphic
details, represented only by single points in the foraminiferal record, are clearly resolved in
the bulk-carbonate carbon isotope signal. Of special importance are several positive
excursions, which are superimposed on the CIE. These detailed carbon isotope features can
be correlated to the shelf-sea carbon isotope curves of Europe (Lägerdorf-Kronsmoor) in a
surprisingly good precision supported by calcareous nannoplankton stratigraphy (Lees
& Bown 2005). The possibility to correlate small-scale carbon isotope variations
proves their robustness as significant signals. The carbon isotope variations seem
to reflect minor changes in the global carbon cycle, possibly triggered by orbital
forcing.
The negative CIEs in the Campanian-Maastrichtian lasted about 0.8-1 million years
and are associated with major regressions on epicontinental shelves. Intensified
ventilation of the 12C enriched deep-water reservoir, lowering of the CCD and
increased rates of terrestrial and marine organic matter oxidation during the sea-level
fall could have caused an increase of 12C in the inorganic carbon reservoir. The
associated change in the slope of seawater strontium isotopes possibly suggests an
increased continental weathering flux as result of long-term (first order) sea-level
fall and widespread continental shelf exposure. Activation of silicate weathering
could have triggered enhanced atmospheric CO2 reduction, which again became a
positive feedback for ongoing climate cooling at the end of the Cretaceous greenhouse
climate. |
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