Paleomagnetic and Fission-Track Dating of a Late Cenozoic Red Earth Section in the Liupan Shan and Associated Tectonic Implications

【摘要】 The north-trending Liupan Shan (六盘山) is an important tectonic boundary between the Tibetan Plateau and the Ordos platform. The Late Cenozoic red earth deposits of the Liupan Shan record its tectonic history and environmental effects. In this article we report a new Late Cenozoic red earth section from an intermontane basin in the southern part of the Liupan Shan. Lithofacies analysis, paleomagnetic and fission-track chronologies, and paleocurrent analysis have been employed to identify the tectonic uplift events of the Liupan Shan. Based on the age constraints of mammal fossils, the pa-leomagnetic polarity zones of the Huating (华亭) Section can be approximately correlated with the standard polarity zones that lie between C3An.2n and C5n.1n of the Geomagnetic Polarity Timescale; the bottom age of this section is approximately 10 Ma. Based on this and the previous studies, we infer that a tectonic event commenced in the southern Liupan Shan in this interval between 8.3 and 8.7 Ma, accompanied by a remarkable increase in sediment accumulation rate. Field observations, fission-track dating, determinations of grain-size frequency distributions and the vertebrate fossils found there suggest that the red earth deposits were reworked by water and mainly transported by fluvial-alluvial processes from the adjacent area.更多还原

【Abstract】 The north-trending Liupan Shan (六盘山) is an important tectonic boundary between the Tibetan Plateau and the Ordos platform. The Late Cenozoic red earth deposits of the Liupan Shan record its tectonic history and environmental effects. In this article we report a new Late Cenozoic red earth section from an intermontane basin in the southern part of the Liupan Shan. Lithofacies analysis, paleomagnetic and fission-track chronologies, and paleocurrent analysis have been employed to identify the tectonic uplift events of the Liupan Shan. Based on the age constraints of mammal fossils, the pa-leomagnetic polarity zones of the Huating (华亭) Section can be approximately correlated with the standard polarity zones that lie between C3An.2n and C5n.1n of the Geomagnetic Polarity Timescale; the bottom age of this section is approximately 10 Ma. Based on this and the previous studies, we infer that a tectonic event commenced in the southern Liupan Shan in this interval between 8.3 and 8.7 Ma, accompanied by a remarkable increase in sediment accumulation rate. Field observations, fission-track dating, determinations of grain-size frequency distributions and the vertebrate fossils found there suggest that the red earth deposits were reworked by water and mainly transported by fluvial-alluvial processes from the adjacent area.更多还原