THE TECTONIC MOVEMENT OF QUATERNARY IN LOESS PLATEAU OF CHINA
Min Longrui (Institute of Geology, CAGS)
Prof. T. K. Huang pointed out 20 years ago that the elevating movement with large scale amplitude had been taking place from the Tertiary period in the north part of China, especially, in the Loess Plateau. On the basis of this scientific conclusion and the sedimentary and tectonic characteristics of the Quarternary period, the writer attempts to make a subdivision of the Quaternary system and tectonic stages of the Loess Plateau in China (Table 1, 2.).The first stage (Pliocene, 2.00 m. y. ): Alluval-lacustrine and proluvial-alluvial reddish soil, sand and gravel were widely accumlated within the Lo- ess Plateau as a large open inland basin during this stage. Descending movement predominated.The second stage (Late Pliocene-Early Plistocene, about 2.00 m. y.): The basement of the large open basin bent down, accompanied by development of different regions with various tectonic characteristics. In the north of the basin (socalled Liang-Mao geomorphological region), uplifting movement predominated, and in the middle and the south (so-called Yuan geomorphological region) descending movement predominated, while Sanman and Wu-cheng formations were formed.The Quaternary strata in the Loess Plateau Table 1The third stage (Middle Pleistocene-middle Late Pleistocene, 0.70-0.03 m. y.): The loess of Lishi and xifene formations and the alluvial-lacustrine of Salawusu formation were widely accumulated in the Plateau. Several fossil soil bands were found in the loess. Slow elevating movement predominated in this stage. The embryo of the Loess Plateau wasformed.The fourth stage (late Late Pleistocene-early time of Holocene, 0.03-0.008 m. y.): The loess of Malan formation was accumulated in this area. Uplifting movement predominated in this stage and the Loess Plateau was formed. Then it was characterized by Liang-Mao and Yuan geomorphological types due to erosion and washing. In short, the tectonic movemeot of Quaternary period in the Loess Plateau shows a cycle from descending, slow elevating to uplifting.It is quite evident that the uplift of plateau was closely related to tectonic movement in the Himalayan stage, and in particular, it was affected largely by tectonic movement in early Holocene-late Late Pleistocene.