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| Titel |
Clumped isotope geochemistry of mid-Cretaceous (Barremian-Aptian) rudist shells: paleoclimatic and paleoenvironmental implications |
| VerfasserIn |
S. Huck, T. Steuber, S. Bernasconi, H. Weissert |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067959
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| Zusammenfassung |
| The Cretaceous period is generally considered to have been a time of climate warmth, but
there is an ongoing dispute about the existence of Cretaceous cool episodes - including the
short-termed installation of polar ice caps. The Late Barremian-Early Aptian represents a
Cretaceous key interval in terms of paleoclimate and paleoceanography, as it provides
evidence for (i) a cooler climate (Pucéat et al., 2003) and (ii) a considerable seasonality of sea
surface temperatures (SSTs) at low latitudes (Steuber et al., 2005). The timing and
significance of these cool episodes, however, are not well constrained. Recently published
TEX86 data, in contrast to oxygen isotope paleotemperature estimates, now are in support of
a climate scenario with equable hot (~30Ë C) tropical SSTs from the Early Cretaceous
onwards.
The aim of this project is to reconstruct the evolution of Barremian-Aptian sea-surface
temperatures (SSTs) in the tropical Tethyan realm by use of a combined geochemical
approach including oxygen isotope analysis and carbonate clumped-isotope thermometry.
Paleotemperature proxies are based on the isotope geochemistry of low-Mg calcite of pristine
rudist bivalve shells (Toucasia, Requienia) collected from different carbonate platform
settings, including the Provence platform in SE France and the Adriatic Carbonate platform
in Croatia.
Carbonate clumped-isotope geochemistry deals with the state of ordering of rare isotopes
in molecules, in particular with their tendency to form bonds with other rare isotopes
(13C-18O) rather than with the most abundant ones. Carbonate clumped-isotope
thermometry has been shown to allow for reconstructing (i) the temperature of carbonate
mineral formation and calculating (ii) the isotopic composition of the water from
which carbonate minerals were formed (by using the δ18O of the analysed carbonate
sample).
Our approach seeks to provide insights into possible biases in temperature estimates of
different paleothermometers. Carbonate clumped isotope geochemistry (thermometry) is not
only a robust new tool for reconstructing changes in temperature, but also enables
paleoclimatic and paleoenvironmental implications, e.g. estimates about freshwater influx or
evaporation intensity at ancient tropical shallow-water settings. In combination with
high-resolution δ18O, clumped isotope analysis has the potential to differentiate between
temperature and salinity changes and this may help to evaluate the significance of meridional
temperature gradients. The assumed strong seasonality of low-latitudinal mid-Cretaceous
temperatures, based on intra-shell δ18O variations in sclerochronological sections of rudist
bivalves (Steuber et al., 2005), is going to become verified or falsified during the current
study.
References
PUCéAT, E., LéCUYER, C., SHEPPARD, S.M.F., DROMART, G., REBOULET, S., AND
GRANDJEAN, P., (2003): Thermal evolution of Cretaceous Tethyan marine waters inferred
from oxygen isotope composition of fish tooth enamels Paleoceanography, 18,
7_1-12.
STEUBER, T., RAUCH, M., MASSE, J.-P., GRAAF, J., AND MALKOÄ, M. (2005):
Low-latitude seasonality of Cretaceous temperatures in warm and cold episodes. Nature, 437,
1341-1344. |
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