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Summary

The Permian marks an important, yet poorly understood, tectonic transition in the Tian Shan region of northwestern China between Devonian-Carboniferous continental amalgamation and recurrent Mesozoic-Cenozoic intracontinental orogenic reactivation. The Turpan-Hami basin accommodated up to 3000 m sediment and is ideally positioned to provide constraints on this transition. New stratigraphic data and mapping indicate that extension dominated Early Permian tectonics in the region, whereas flexural, foreland subsidence controlled Late Permian basin evolution.

Lower Permian strata in the northwestern Turpan-Hami basin consist of coarse-grained debris flow and alluvial fan deposits interbedded with mafic to intermediate volcanic sills and flows. In contrast, Lower Permian rocks in the north-central and northeastern Turpan-Hami basin unconformably overlie an Upper Carboniferous volcanic arc sequence. These Lower Permian strata include possible shallow marine carbonate, and thick volcanic and volcaniclastic rocks which are in turn followed by littoral to profundal lacustrine facies. Following a regional Lower-Upper Permian unconformity, regional sedimentation patterns record the development of a more integrated sedimentary basin. The Upper Permian is entirely nonmarine and can be correlated along the west-east depositional strike of the basin. The lower Upper Permian consists of a broad belt of braided fluvial deposits shed northward. This is followed by fluctuating littoral-profundal lacustrine and associated fluvial facies. The uppermost Permian is characterized by shallow lake-plain and fluvial environments.

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image: China map

Location map of the Junggar and Turpan-Hami basins, showing maximum known extent of Upper Permian lake deposits.


image: map, photo of fault

Geologic map and satellite image of the Taoshuyuan fault, southern Bogdashan. The Taoshuyuan fault is interpreted to be a reactivated Early Permian normal fault (Wartes et al., in press).

image: photo, mountainside

Organic-rich Upper Permian oil shales of the Lucaogou Formation, southern Junggar basin (photo: Alan Carroll).


image: photo, mountain

Upper Permian Tarlong Formation in the western-most Turpan basin (photo: Alan Carroll).

image: photo mountainside

Early Permian lacustrine mudstone and volanic rocks in the eastern Hami basin near Tianshanxiang (northeast of Hami), with Upper Permian Tarlong Formation on skyline (photo: Alan Carroll).


Researchers

This project represents the recently completed M.S. thesis of Marwan Wartes. We also collaborated with Todd Greene of Stanford University (now at Anadarko Petroleum).

Acknowledgements

Financial support was provided by the Donors of the Petroleum Research Fund, American Chemical Society, and by Conoco and Texaco.


page created December 5, 2001