| The early Cenozoic
is one of the most interesting time periods for climate change research.
During this Era, the Earth’s climate changed from a greenhouse world to
an icehouse world. This dramatic change took place at the Eocene-Oligocene
boundary. This boundary marks an abrupt cooling step, which caused a drop
in eustatic sea-level and major faunal turnovers.
This cooling event has
been well documented in ocean cores, but rarely in continental sediments.
The climate conditions preceding and leading to this transition are poorly
understood and referred to as the ‘doubthouse’ period, a subject of much
debate.
The most important
climate event in this doubthouse time period is the Middle Eocene Climatic
Optimum (MECO). The MECO (44-42 Ma) is a hypothermal event of anomalous
warm temperatures in a period of general cooling. This event is found in
d18O records of the Ocean Drilling Program, but also on the northern hemisphere,
e.g. in marine limestone sections in Central Italy.
One of
the main reasons for naming it the doubthouse period is because there are
few continental records which cover this time period. The Xining
Basin is one of the few, making it unique and valuable.
The main difficulty
is how to relate them to global paleoclimate records. The key is to precisely
date features of environmental changes, and this is exactly the main aim
of this project.
|
Bas with
his back to the geology of the Xining basin(left) and sampling with Wentao
(above). |
In October 2009, the
Tiefo section (NE of Xining) was studied, and dated using magnetostratigraphy.
The section contains a 115 meter-thick and continuous sequence of red mud-gypsum
alternations ranging in age 43-37.5 Ma. The sequence covers the Late Eocene
doubthouse period, including the MECO interval. So far, the results are
very promising, but it is essential to find a section parallel to the Tiefo
section to test the recorded sedimentary features in terms of their spatial
distribution.
So far, under supervision
of Guillaume Dupont-Nivet, accompanied
by Roderic Bosboom and Hemmo
Abels, and helped by Huang Wentao,
we carried out a successful fieldwork in the Xining basin. The Tazeko
section is parallel to the Tiefo section, is studied and sampled, intended
to be dated using magnetostratigraphy, and then correlated to the existing
stratigraphic framework. This must give crucial constraints on whether
the features found in both sections are either representing local anomalies
or are a result of changes in global paleoclimate.
Tazeko
section
|
