GENETIC MECHANISM OF THE ALLUVIAL TERRACES ALONG THE THREE-GORGES COURSE OF THE CHANGJIANG RIVER
长江三峡阶地的成因机制

In the past, many investigators considered that the alluvial terraces in mountain areas are generally produced by the intermittent crustal uplift movement; or, it might result from a change to a more arid climate; or, from the greatly increased load derived from melting glaciers in the upstream region so that a valley floor is filled with alluvium by an aggrading stream. However, based on the field survey and the analyses of the chemical composition, mineral assemblage, pollen analysis and deposits on the alluvial iterraces distributed along the Three-Gorges course of the Changjiang River, the genetic mechanism is somewhat different from the above-mentioned sayings. (1)The three parts which constitute a terrace:the upper floodplain deposit, the middle alluvial gravel and the lower rock bench as base of terrace, were formed i n different periods.The rock bench of terrace as former river bed had been formed much earlier than the flood plain deposit.The middle gravel had been eroded before it Was covered by the floodplain deposit. (2)The upper floodplain deposit on terraces was formed under the condition of in-terglacial climate and high water level in Late Holocene.