The Eocene-Oligocene
transition (EOT, 34 Ma) is a major and dramatic change in Cenozoic climate:
this shift from greenhouse to icehouse conditions caused the first ice
caps on the Antarctic continent. It had a major impact on global climate
and involved a eustatic fall in sea-level, widespread disruption of the
global thermohaline circulation and significant floral and faunal turnovers
on the continents of which the European ‘Grande Coupure’ is the best documented
example.
The aim of this project
- which is supervised by Guillaume
Dupont-Nivet, as part of his NWO VENI project - is to understand the
tectonic-climatic interactions in the sediments of the Tarim basin |
In
cooperation with Lanzhou University, we recently showed - applying magnetostratigraphy
and cyclostratigraphy - that the EOT coincides with the aridification of
the Asian continental interior (Dupont-Nivet et al., 2007).
Other recently published
papers also report significant consequences, including the faunal turnover
known as the ‘Mongolian Remodeling’ (Meng & McKenna, 1998), change
in regional paleoenvironment and an increase in the intensity of the monsoon
(Zhang et al., 2007). |
Roderic
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The age correlation
of the EOT to changes in the Asian climate is well-established, but the
exact forcing mechanisms and processes remain a matter of strong debate.
Previous work based on general circulation models have related the observed
aridification either to the uplift of the Tibetan plateau or to the westward
retreat of the Paratethys Sea, an epicontinental sea that extended across
the Eurasian continent during the Eocene (Ramstein et al., 1997; Zhang
et al., 2007). From these studies it appears that the role of Tibetan
uplift in strengthening both the Asian monsoon system and the aridification
of central Asia by changing the regional atmospheric circulation patterns
was limited.
On the other hand,
the retreat of the Paratethys and the associated redistribution of the
thermal contrast between land and sea could have caused a significant change
in the regional pressure system and the seasonal contrast. Hence, many
studies regard the change from marine to continental conditions a far more
likely forcing mechanism of the observed change in Asian climate, particularly
when considering the simultaneous drop in global sea-level. However, significant
proof for this role of the Paratethys has only been illustrated by modeling
and not by actual field evidence. |
| Accordingly, the aim
of this project is to accurately determine the timing of the retreat of
the Paratethys by application of high-resolution magnetostratigraphy and
biostratigraphy to key sedimentary successions which have recorded this
event. The Paleogene sediments of the southwest Tarim Basin along the West
Kunlun Shan in westernmost China are characterised by a shallow marine
to continental transition and are believed to comprise the latest remnants
of the easternmost extent of the Paratethys Sea before its subsequent westward
retreat. In general, the transition is believed to be related to the uplift
of the Tibetan plateau, but this project intends to explore its association
to the global eustatic sea-level fall of the EOT by building an accurate
time framework, which should be considered an essential tool for further
research of Asian climate change during the Eocene. |
| The project included
two weeks of field work along the southwestern edge of the Tarim Basin,
together with Guillaume dupont-Nivet, Cor Langereis, Wout Krijgman and
Li Chuanxin of Peking University. It was financially supported by the Molengraaf
Fund. |
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