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There are several levels of terraces in the Three Gorge Valley of the Yangtze River.Based on field survey,chemical and mineral analyses,archaeological data,radiocarbon dates,and pollen diagram,a hypothesis is presented that the rock planes of terraces and their overlying gravels and fine flood sediments were developed in different environmental conditions of different stages.The rock planes were the old channel beds and were developed in underwater conditions.The coarse gravel layers between bedrocks and fine flood sediments are the relics from erosion.The fine flood sediments overlying the gravels were deposited in high waterlevel periods of the Yangtze River in the past interglacial periods or in the middle Holocene.Thus,the genetic mechanism of terrace deposits in the mountainous region may be very different from that of the binary structure of terrace deposits in the plain region.
There are several levels of terraces in the Three Gorge Valley of the Yangtze River. Based on field survey, chemical and mineral analyzes, archaeological data, radiocarbon dates, and pollen diagram, a hypothesis is presented that the rock planes of terraces and their overlying gravels and fine flood sediments were developed in different environmental conditions of different stages.The rock planes were the old channel beds and were developed in underwater conditions. coarse gravel layers between bedrocks and fine flood sediments are the relics from erosion. fine flood sediments overlying the gravels were deposited in high waterlevel periods of the Yangtze River in the past interglacial periods or in the middle Holocene. Thus, the genetic mechanism of terrace deposits in the mountainous region may be very different from that of the binary structure of terrace deposits in the plain region.