| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
* Chevron Energy Technology Company, 6001 Bollinger Canyon Road, San Ramon, California 94583
** Chevron North America Exploration and Production Company, 9525 Camino Media, Bakersfield, California 93311
*** Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115
Institut fuer Geowissenschaften, Universitaet Potsdam, Karl-Liebknecht-Strasse 24, 14476 Golm, Germany
TNO B&O National Geological Survey, P.O. Box 80015, NL 3508 TA Utrecht, The Netherlands
Department of Geology, 1475 Jayhawk Blvd., University of Kansas, Lawrence, Kansas 66045
BradleyRitts{at}chevron.com
Approximately 1300 m of Oligocene-Miocene clastic strata are exposed along the Miran River in the southeastern Tarim basin, where the adjacent Altun Shan form the topographic escarpment of the northern Tibetan Plateau. The sedimentary section is faulted against Proterozoic rocks of the Altun Shan in the footwall of the south-dipping, oblique reverse Northern Altyn Tagh fault. Oligocene-Lower Miocene strata consist of fine-grained rocks that record low-gradient depositional systems. Mid-Miocene and younger rocks consist of coarse conglomerate, derived from the Altun Shan and deposited by high-gradient depositional systems. The change to coarse, high-gradient depositional systems with detrital source areas coincident with the modern Miran River drainage is interpreted to mark the onset of uplift of the Altun Shan on the Northern Altyn Tagh fault and its erosional exhumation. The age of the change from pre-orogenic to synorogenic sedimentation is constrained by a foraminifera assemblage at the base of the conglomeratic section that includes Early-Middle Miocene planktonic foraminifera. This interpretation is also supported by apatite fission track and (U-Th)/He ages and thermal models that indicate rapid Miocene cooling, and hence, rapid exhumation of the Altun Shan. In addition to defining the age of the synorogenic section, the foraminifera assemblage contains planktonic taxa, indicating a connection to open marine waters, and benthic assemblages typical of brackish to near-sea level paleobathymetry. Thus, micropaleontologic evidence demonstrates that the Miran River locality, now at
1400 m elevation, was at sea level approximately 15 million years ago. Thus, in addition to constraining the age of surface uplift and exhumation of the Altun Shan, the principal mountain range of the Tibetan Plateau in this region, as 15 to 16 Ma, the foraminifera assemblage indicates that the SE Tarim basin, off the northern edge of the plateau, had an average surface uplift rate of nearly 100 m/m.y. for the past 15 million years. These results suggest that shortening in the Altun Shan and uplift of the range significantly post-dated the initiation of large-scale strike-slip on the Altyn Tagh fault, and that regional surface uplift mechanisms operated in the Tarim basin, beyond the margins of the Tibetan Plateau.
This article has been cited by other articles:
|
|
 |
|
  P. M. Bovet, B. D. Ritts, G. Gehrels, A. O. Abbink, B. Darby, and J. Hourigan Evidence of Miocene crustal shortening in the North Qilian Shan from Cenozoic stratigraphy of the western Hexi Corridor, Gansu Province, China Am J Sci, April 1, 2009; 309(4): 290 - 329. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
