The Neotectonics in the Niushou Mountains, the Northeastern Margin of the Tibetan Plateau, China and Its Impact on the Evolution of the Yellow River
摘要
The Yinchuan Basin and the arc-form ranges that are adjacent to the south of the basin are of great importance to the study of the neotectonic and paleoenvironmental changes of the northeastern margin of the Tibetan Plateau.The Niushou Mountains,the northernmost one of the ranges,is cut by the Yellow River(segment from Zhongning to the Qingtong Gorge) forming terraces on Tertiary strata along the western of the mountains,which has recorded the neotectonic evolution in this region.The Pliocene Ganhegou Formation on the east of the Niushou Mountains is composed of basin-marginal facies and fluvial facies that represent an abandoned channel.This abandoned channel was dextral displaced by an active fault on the west of the mountains during the Pleistocene.Beside the slip strike,enormous vertical offset occurred,overlaying large acreage of piedmont deposit.On the basis of the deformation in Tertiary strata,the spatial distribution of piedmont and fluvial deposit and previous dating on certain terraces,a reasonable interpretation is presented in this paper.The segment of the Yellow River aforesaid was actually a tributary of a large river on the east side of the Niushou Mountains in the Pliocene.By uplifting of research area in the Pleistocene,the large river shrank and shifted westward,leaving behind an abandoned channel and a tributary that enlarged into the current segment of Yellow River.