Abstract:

In this study, the authors made use of the most valuable chance of salvage excavation of the cultural relics in the Three Gorges Project to do environmental archaeology research in two typical archaeological sites: the Zhongba Site in Zhongxian County and the Yuxi Site in Fengdu County of Chongqing City, and one natural peat profile, the Dajiuhu peat of Shennongjia Mountain. Chronology, sedimentology, component and morphology of heavy minerals, micromorphology of zircon, geochemistry and environmental magnetics were used to distinguish the paleoflood deposits in archaeological sites. In addition, the sporopollenclimate conversion function was set up and used to study the Dajiuhu peat, and the authors raveled the environmental evolution background since the Holocene out and made the comparison between the environmental evaluation records of natural sedimentary strata and the paleoflood events in the typical archaeological sites. The study of the temporalspatial distribution of the archaeological sites shows that the 677 archaeological sites from the Paleolithic Age to the Tang and Song Dynasties in the Three Gorges reservoir of Chongqing area distributed more and more densely from west to east and from high land to low land. Most of the sites were distributed along the river and aggregated at the confluence. Obviously, the altitudes of archaeological sites in the Paleolithic Age and the Neolithic Age are much higher than those of historical sites. The human beings of each generation would like to choose the first or the second river terraces as living sites, which are nearer to the water sources and easier to withstand floods. Our research indicates that the reason for the Zhongba Site being able to stand over five thousand years was related to the salt industry and the favorable ecologic environment. The research indicates that since 76 ka BP, at least 16 times of paleoflood with water level above Wusong Elevation 147024 m (a.s.l.) left deposits in the Neolithic layers of unit T0403 from the Yuxi Site. Pollen analysis of the 148 samples and 10 AMS14C dating data from the peat core with depth of 297 cm in the Dajiuhu Basin offered good information of natural environment background during the Holocene, especially the 82 ka BP cold event, which might be a representative in the globe. Then, multiproxy records were relatively stable during 6742 ka BP, which shows the best water and thermal condition in the Holocene Optimum. Around 42 ka BP, the climate and environment transformed from warm and wet to cool and dry. During 3509 ka BP, precipitation amount was low. After 09 ka BP, the climate turned cool and wet. According to our study, ten paleoflood layers appeared during 8267 ka BP, eight during the Holocene Optimum (6742 ka BP) and only two (the layer 371 during the West Zhou Dynasty and the layer 21 during the Warring States) during 3509 ka BP when precipitation reduced. During the rather much precipitation period since 09 ka BP, three flood layers (the layer 11C1 in the middle Song Dynasty, the layer 51 in the Qing Dynasty and the layer 2B2 of 1981) existed in the Zhongba Site. The results indicate that flood frequency was the highest during 8267 ka BP and the second high during 6742 ka BP. This paleoflood rule in the Three Gorges reservoir area may be able to explain why the archaeological sites lacked during 7851 ka BP in the Jianghan Plain of the middle reaches of the Yangtze River.

Key words: Three Gorges reservoir area of the Yangtze River, environmental evolution during the Holocene, environmental archaeology, paleoflood events, study process