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| Titel |
Upper Campanian-Maastrichtian stable isotopes and calcareous nannofossil palaeoecology in the Boreal Realm (Stevns-1 well, Danish Basin Chalks) : implications for climate change |
| VerfasserIn |
N. Thibault, N. Schovsbo, L. Stemmerik  , F. Surlyk |
| 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 |
250028730
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| Zusammenfassung |
| The Stevns-1 borehole, drilled in eastern Denmark close to the famous K-Pg boundary
section of Stevns Klint, recovered 456 m of upper Campanian to basal Danian chalks with
~100% recovery. A nearly complete nannofossil biozonation was documented for this
core (Sheldon, 2008). Stevns-1 represents the first complete section throughout the
uppermost Cretaceous chalk of NW Europe and the most expanded Maastrichtian section
worldwide. Because these chalks lack extensive burial diagenetic overprinting and
are composed of more of 70% of calcareous nannofossils in volume, they likely
reflect conditions of past sea-surface waters, thus making this site highly suitable for
the study of past environments and climates of the Boreal realm in the uppermost
Cretaceous. Here, we present the results obtained on the long-term evolution of
calcareous nannofossil assemblages and bulk carbon- and oxygen-stable isotopes on
this site. In the nannofossil assemblage, the main significant changes are observed
within the distribution of Watznaueria barnesiae (considered in the Boreal realm as a
warm-water index), of the cool-water taxa and of the fertility indices. The neat
opposition between the relative abundance of the sum of cool-water taxa and that of
Watznaueria barnesiae allowed us to build a nannofossil temperature index (NTI). The
NTI and the bulk δ18O show the same evolution and have a high coefficient of
correlation (R2=0.73), thus suggesting that oxygen stable isotopes could be used
here to estimate past variations of sea-surface temperatures (SST) in the Boreal
realm. These two proxies suggest the following climate evolution : SST were quite
stable and warm in the upper Campanian, and are estimated at around 19-C. A
4-C cooling is recorded between the uppermost Campanian and the lowermost
Maastrichtian. An expanded mid-Maastrichtian warming episode of 1.5-C is recorded and
followed by a second cooling event of 1.5-C in the upper Maastrichtian. The end
of the Maastrichtian is characterized by the well-documented Deccan warming
which is here expressed by a 2.2-C rise. This climate evolution is similar to that
shown in the tropical South Atlantic, Pacific and Indian oceans (Barrera and Savin,
1999). As already suggested by these authors, the two cooling events seem to match
well two third-order regressions of the sea-level as nicely expressed in the recently
updated sea-level curve of Miller (detailed in Kominz et al., 2008), indicative of a
possible glacio-eustatic control. Moreover, we show that changes in the abundances
of nannofossil fertility index taxa occured at the time of remarkable shifts in the
δ13C curve. This suggests a competition for trophic resources through time among
nannofossil taxa, indicative of surface-water fertility changes which are associated with
the distinct climatic modes, with more fertile and/or more stable environmental
conditions during the Campanian and the mid-Maastrichtian warming modes. The
evolution of species richness and the record of first appearance and last appearance
datums also suggest significant changes in the stability of the nannofossil community,
with more severe environmental conditions coincident with minimum or sharply
decreasing δ13C values during the two cooling events of the Campanian-Maastrichtian
interval.
References
Barrera, E. and Savin, S.M. In: Barrera, E., and Johnson, C.C., Eds., Evolution of the
Cretaceous Ocean-Climate System: Boulder, Colorado, Geological Society of America
Special Paper 332, 1999, pp. 245–282.
Kominz, M.A., Browning, J.V., Miller, K.G., Sugarman, P.J., Mizintseva, S., Scotese, C.R.,
2008. Basin Research 20: 211-226.
Sheldon, E., 2008. Upper Campanian – Maastrichtian calcareous nannofossil biostratigraphy
of the Stevns-1 borehole, Denmark. Journal of Nannoplankton Research 30(1): 39-49. |
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