Paleomagnetism of upper Cretaceous rocks from South China

Paleomagnetic study of upper Cretaceous redbeds from two areas in South China was undertaken in an effort to constrain better the history of tectonic movements in southeastern Asia. From the Nanjing area (32°N, 119°E), high-temperature characteristic directions which pass a fold test were obtained from ten sites (43 samples) in the upper Cretaceous Puko and Yanzijing Formations. The paleomagnetic pole position (76.3°N, 172.6°E; A₉₅ = 10.3°) agrees well with a late Cretaceous reference pole for Eurasia and thus confirms that this part of South China was fully sutured to Eurasia by the end of the Cretaceous with no paleomagnetically resolvable subsequent relative rotation. In western Sichuan (26.5°N, 102.3°E), high-temperature characteristic directions of normal and reverse polarity were obtained from twelve samples (48 specimens) in the upper Cretaceous to lower Paleocene Xiaoba and Leidashu Formations. A provisional paleomagnetic pole position (80.9°N, 296.8°E; A₉₅ = 7.7°) differs significantly from a late Cretaceous Eurasia reference pole. In terms of apparent tectonic movement, the difference in paleopole positions would indicate a 13 ± 10.3° northward translation and 22 ± 11.2° counterclockwise rotation of western Sichuan relative to Eurasia. Confirmation of this reconnaisance result, which would suggest that western Sichuan was pushed ahead of an impinging India, is needed.