关键词: 葫芦河流域, 中全新世, 环境演变, 古人类活动

Abstract: Hulu River drainage area is located in eastern Gansu and southern Ningxia, which is west of Lupan Mountain in middle Loess Plateau. The middle Holocene strata were well developed on the first terrace of the Hulu River and its tributaries. The paleoenvironment is established by the analyses of sedimentary characteristics, clay minerals, carbonates and pollens in the deposits ors the terrace. The climate changes remarkablly affected the ancient civilization in the region.The early Holocene stratum can be seen at the bottom of the first terrace, which mainly consists of alluvial loessic deposits. The clay minerals are mainly illites and the pollens are mainly herbs,which shows a relatively dry and cool paleoclimate. There was no ancient civilization during this period in this region.The early-middle Holocene stratum lies in the lower part of the first terrace, which is mainly composed of alluvial and lacustrine silts and clay. The alluvial gravels can also be found in some places, which indicates a warm and humid paleoclimate. A climate change is found by the sedimentary analyses. It was the warmest and the most humid from 8 000 to 6 000 aBP. The contents of kaolinite and montmorillonite are high. The pollens indicates a wooded grassland or a forest flora of coniferous and broadleaf trees. The favourable natural conditions resulted in the appearances andrapidly development of ancient civilizations. The first stage of Dadiwan civilization (7 800- 7 300aBP) shows some relatively advanced characteristics with big ancient communities (based on the size of the sites), appearances of colourful pottery and agriculture. The early Yangshao civilization (6 800- 6 000 aBP) shows some developmental features. The communities were still big and the number of communities was increased. From 6 000- 5 000 aBP the clay mineral association and the pollen spectrum indicate a slighty dry and cool paleoclimate. The technology of production and pottery making of the middle and late Yangshao civilization during this period had some development, the number of ancient communities were also increased but the size of communities was not increased and some were even decreased.The late middle Holocene (about 5 000- 3 000 aBP) stratum mainly consisting of alluvial loessic silts lies in the upper part of the first terrace, representing a distinguish aggradation of loessic silts.The fact that the content of illite increased and the contents of the kaolinite and montmorillonite decreased and the pollen is mainly herbs indicates a drier and cooler paleoclimate. The number and the size of the communities of the Changshan civilization(4 800-4 200 aBP) decreased. Thete were some cave like residences. The technology of pottery makinghad some retrogradation. The communities of Qijia civilization(4 400-3 900 aBP) were widely distributed but the size of them were very small indicating that the civilized area increased but the production of per unit area decreased, and also the proportion of animal husbandry increased. The ancient civilization from 3 900-3 300 aBP has not been found out yet. The Shiwa civilization(about 3 000 aBP) was also very limited in scale. All of these are because of the deterioration of the paleoenvironments during this period.

Key words: Hulu River area, middle Holoocene, paleoenvironment, human activity