The Paleogene sediments
of the Central Asian basins include the remnants of the easternmost extent
of a large epicontinental sea. This shallow marine sea once extended across
the Eurasian continent before it retreated westward and became known as
the Paratethys Sea.
Despite the common
notion that the formation of the Tibetan Plateau primarily governed paleoenvironmental
changes in Asia, climate modeling experiments suggest this sea served as
a major moisture contributor governing Asian monsoons and aridification
of the Asian continental interior.
Paleogeographic
map showing the extent of marine conditions after the last major sea retreat
from the Tarim Basin, time equivalent with a major aridification phase
in the Xining Basin at 36.6 Ma
The age and paleogeography
of the sea retreat in Central Asia remain poorly constrained, however,
hampering our understanding of its paleoenvironmental impacts and its controlling
mechanisms, which are generally interpreted to be related either to eustatic
sea-level fall or to sedimentary overfilling resulting from initial uplift
of the surrounding mountain ranges in the Indo-Asia collision system. |
| Accordingly,
our research is twofold.
(1) In the southwest
Tarim Basin in west-China and in the Alay Valley and Ferghana Basin in
Kyrgyzstan we focus on the transgression-regression cycles recorded by
the shallow marine sediments of Paleogene age.
(2) In the Xining Basin
along the northeastern margin of the Tibetan Plateau we study sedimentary
successions which have recorded the major step-wise aridification in the
so-called doubthouse period preceding the Eocene-Oligocene transition from
global greenhouse to icehouse conditions. |
Interval
of the Shuiwan section in the Xining Basin with small scale cycle numbers.
Black-white
bar represents 5 m in stratigraphy. White arrow is the location of the
first lithofacies and paleoenvironmental change at 36.6 Ma correlative
to the sea retreat in the Tarim Basin. |
By using multiple litho-,
magneto- and biostratigraphic constraints from these key sedimentary successions,
an extensive regional stratigraphic framework will be constructed in both
areas, which helps to improve understanding of the link between the sea
retreat and contemporaneous paleoenvironmental changes in Asia.
Field
view of the Aertashi section in the southwest Tarim Basin (west China)
|
So far, our research
on the Paleogene marine-continental records in the southwest Tarim Basin
confirms that the last major sea retreat from the paleo-depocentre coincides
with a significant aridification step in the Xining Basin in the early
Priabonian (36.6 Ma). Furthermore, the sea retreat clearly pre-dates major
events which were usually held responsible for the sea retreat:
-
Oligocene-Miocene regional
uplift of the Pamir mountains, Tian Shan and Kunlun Shan, and
-
Major eustatic sea-level
falls of the Eocene-Oligocene Transition (~34 Ma) and mid-Oligocene (~30
Ma).
The
Tarim Basin team in our base camp
Clearly, higher resolution
age control is required to better constrain the paleoenviron- mental impacts
(i.e. aridification, regional biotic reorganizations) and controlling mechanisms
(i.e. tectonically-induced early stage basin infilling vs. eustatic sea-level
fall) of this significant retreat and to provide valuable insight into
the regional tectonic and paleogeographic evolution of Central Asia.
|
|
2011
-
Abels, H.A.,
Dupont-Nivet, G., Xiao, G., Bosboom, R.E. and Krijgsman, W. (2011). Step-wise
change of Asian interior climate preceding the Eocene–Oligocene Transition
(EOT). Palaeogeography, Palaeoclimatology, Palaeoecology,
299,
399-412.
-
Bosboom,
R.E., Dupont-Nivet, G., Houben, A.J.P., Brinkhuis, H., Villa, G., Mandic,
O., Stoica, M., Zachariasse, W.J., Guo, Z., Li, C. and Krijgsman, W. (2011).
Late Eocene sea retreat from the Tarim Basin (west China) and concomitant
Asian paleoenvironmental change, Palaeogeography, Palaeoclimatology,
Palaeoecology, 299, 385-398.
|
