Paleomagnetism of the Yuanmou Basin near the southeastern margin of the Tibetan Plateau and its constraints on late Neogene sedimentation and tectonic rotation

New paleomagnetic investigation was carried out on the late Neogene fluviolacustrine sequence of the Yuanmou Basin, located near the southeastern margin of the Tibetan Plateau. Magnetostratigraphic results indicate nine reverse magnetozones (R1 to R9) and eight normal magnetozones (NI to N8) in the sedimentary profile, which can be correlated to the geomagnetic polarity timescale from C3n.3r to C1 r.1r. The age of the sedimentary sequence of the Yuanmou Basin can thus be paleomagnetically constrained to an interval from early Pliocene to Pleistocene, with sedimentation rates varying from 12.5 to 55 cm/kyr. In addition to its highly resolved rnagnetostratigraphic sequence, the Yuanmou Basin provides a record of Plio-Pleistocene tectono- and climato-sedimentary processes. The mean declinations of the seventeen polarity units (excluding samples with transitional directions) can be grouped into three distinct directional intervals, Group I (2.58-1.37 Ma), Group II (4.29-2.58 Ma) and Group III(4.91-4.29 Ma). These directions indicate that the Yuanmou Basin has probably experienced vertical-axis clockwise rotation of about 12 degrees from 1.4 Ma to 4.9 Ma, which may be related to slip activity of the Red River fault to the southwest and the Xianshuihe-Xiaojiang fault to the east. (C) 2008 Elsevier B.V. All rights reserved.