| Since the end of last deglaciation, the Holocene Megathermal expanded the East Asia Monsoon circulation and the continuous climate warming promoted the prosperity of the Neolithic culture. To date140Neolithic sites have been found in the Taihu-Ningshao plain, China. So the linkage between prehistoric civilization and the environmental change is of profound significance for economic development and the relation between human and nature.We obtain a core XL which is29m deep in the An’xi Town from the East Tiao river basin in Hangzhou, Zhejiang Provinces which is located on western slope of a paleo-incised vally, tending to discuss the relation between the environment change in the Hangjiahu Plain and development of the Liangzhu Civilization,. We measured the magnetic properties and particle size and identified fossil foraminifera. Results demonstrated that the core site had been coastal plain, tidal flat, estuary, tidal flat, and floodplain sequentially during the Holocene. The14C ages and elevation of sediments reflected the major control factor for the facies change is sea level change.The environmental evolution is described in detail as follows:(1)25.4-29m (early Holocene to9000cal. BP). Sediments were characterized by fine grain size, weak magnetic properties and no foraminifera fossil, indicating an environment of coastal plain.(2)21.55-25.4m (9000-8800cal. BP). Sediment lithology changed from homogeneous mud to sand-mud couples, indicating the stronger hydrodynamics of a tidal flat environment. Thermomagnetic curves showed the occurrence of Fe3S4, suggesting the deoxidized sedimentary environment influenced by seawater. Foraminifera appeared with low abundance. Species were dominated by Cribrononion, Elphidlum and Ammonia.(3)10-21.55m (8800-7500cal. BP). The lithology indicated sedimentary environment changing to estuary during this time period. The foraminifera abundance was the highest and species were mainly composed by Cribrononion, Elphidlum and Ammonia with a few Cribrononion, Florilus, Thalmann and Globigerinella. The sea level rose and water depth got deeper at the core site. Thick sediments were deposited possibly due to abundant sediment supply.(4)5-10m (7500-4300cal. BP). The top of this sediment section appeared erosional contact with the overlying section. This sediment with sand-mud couples and rich plant fragments is of typical tidal flat environment. Magnetic parameter HARD reached the highest which indicated the enhanced oxidizing environment. Declined foraminifera abundance suggested the weaken seawater influence. Species of Florilus, Cribrononion Thalmann were possibly transported by the tidal currents.(5)0-5m (from4300cal. BP). Brown yellow and grey clayey silt with rich Fe-Mn nodules occurred. It’s obviously under oxidizing environment. No foraminifera were found and grain size was coarser, reflecting a floodplain environment. The paleo-Huzhou-Hangzhou valley evolved into floodplain gradually as reflected by the comparison between sediment cores. At4.85-5m deep the avulsion deposit of coarse yellow sand was dated as4320cal. BP, inferring the migration of the East Tiao river, which possibly triggered the fall of the Liangzhu culture.The present core sediments demonstrate that the East Tiao floodplain was gradually formed since-7000cal. BP, which should be the important natural environment for the development of the Neolithic civilization in the study area. However, sediments during the Neolithic period was eroded at the core site and thus the formation time of freshwater marsh remains unknown. |
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