Abstract: Xinding Basin is a typical Cenozoic graben-type basin in the northern Fenwei graben system,which is surrounded by mountains of 2000 to 3000m high above sea level. Downward from the peak to the piedmont on the basin side are respectively peneplanes of Beitai stage and Dianziliang stage in Paleogene,peneplane of Tangxian stage in Neogene,and seven-level river terraces and six-level pediments in Quaternary. Loess and paleosol sequences on the landforms are correlative to typical loess section,which is an advantage for landform dating.A study has been made of the paragenetic relations of the pediments and river terraces on the northern piedmonts of Wutai Mountains and Xizhou Mountains via geomorphologic mapping on 1:10000 scale,and an analysis on the role of tectonic,climatic,and drainage factors in the parageneses. The Quaternary pediments and river terraces on the north piedmont of Wutai Mountains are united to constitute six steps of geomorphic surfaces. The episodic uplifting of fault blocks is deemed to be the dominant factor in the formation of the unified surfaces.Episodic uplifts result in longitudinal profiles of riverbeds alternated by cascade and gentle reaches one in mountainous areas. Terraces disappear upstream near the vertex of cascade reach. Cascade reaches represent quickly uplifting stages,and gentle ones represent stable stages. On condition that waterfalls between adjacent terraces recede at same speed,durations of active or stable stages can be estimated by ages of terraces and relative length of cascade reach and gentle one,and then ages of uplifting stages since 1.20Ma are estimated. The four quickly uplifting stages are from 1200 to 1059ka BP,from 600 to 501ka BP,from 130 to 103ka BP,and from 20ka BP to present. Other intervals are stable stages.

Key words: Xinding Basin, river terrace, pediment, uplift, loess

摘要： 忻定盆地位于汾渭地堑系北段,是一个典型的新生代张性断陷盆地,其周缘由持续隆升的断块山地围绕。断块山地的阶段性隆升在山麓地带形成了由山麓剥蚀面与河流阶地构成的6级联合地貌面,并在山区河段形成了由急流段与缓流段相间分布的河流纵剖面形态,急流河段的最高点对应阶地在上游方向上的消失点。急流段由多级跌水组成,是断层多期地表错动的结果,代表了山地快速隆升时期,而缓流河段代表了山地相对稳定期。根据河流阶地的断代以及急流河段与缓流河段的相对长度估算了山地阶段性隆升的时代,4个快速隆升期分别距今1200～1059ka,600～501ka,130～103ka,20～0ka,其间为3个相对稳定期。

关键词: 忻定盆地, 河流阶地, 山麓剥蚀面, 隆升, 黄土