关键词: 忻定盆地, 晚更新世晚期, 构造运动, 断层崖

Abstract: The Xinding basin in the north of Shanxi rift system is a normal fault-controlled extensional graben and has a strong neotectonic process during the Quaternary. Our field investigations in the Xinding basin indicate that there is a united geomorphologic surface, composed of the terrace T₂,the diluvial mesa and the top of the scarp with a height of ten to tens meters along the piedmont. The terrace T₂ and the mesa are composed of a basal gravel layer and the overlying loess deposits which can be used as dating samples for the united geomorphologic surface.As Chinese loess stratigraphy has been well studied, it favors age determination of the newest tectonic geomorphologic surfaces. Combined with the loess-paleosol time scale and some dating methods, such as radiocarbon ( ¹⁴C) and optically stimulated luminescence(OSL), the results of age dating show that the terrace T₂ and the diluvial mesa downcut at ca. 20ka BP. According to the viewpoint of climatic geomorphology, the glacial climate is helpful for river deposition. But the downcutting, which occurred in the last glacial maximum (21～18ka BP), cannot be attributed to climatic change. It shows that the Xinding basin underwent a stronger tectonic movement since later stage of late Pleistocene epoch.Statistic results of the coseismic rupture of fault events in China mainland show that a single event always has a vertical coseismic displacement with some meters. And the fault scarp that has a height of tens to tens meters along the piedmont in this paper can not be produced by only a single event. So this tectonic movement should be the product of fault activities of a period. Though some studies have shown that this tectonic movement since later stage of late Pleistocene have some evidences in the Yanqing basin and the Hubao basin, more detailed work should be done to prove that this tectonic movement is widespread in the Shanxi rift system and bigger region.

Key words: the Xinding basin, later stage of late Pleistocene epoch, tectonic movement, fault scarps