Micropaleontological Records Of Holocene Environmental Changes And Human Activities In The Ning Shao Coastal Plain,South Hangzhou Bay Coast

Since the last deglaciation,great changes have taken place in the distribution pattern of land and sea resulting from polar ice melting and sea-level rise with gradual global warming.Since the Early mid-Holocene,with the stabilization of sea level,a great amount of terrigenous materials have been transported to the sea,and then the embryo of the present coastal zone has formed.In this process,human successively occupied the coastal area of south Hangzhou Bay(SHB),forming the Neolithic civilization sequence of Kuahuqiao Culture(7.8-7.4 cal kyr BP),Hemudu culture(7.0-5.3 cal kyr BP)and Liangzhu Culture(5.3-4.0 cal kyr BP).The existing literature shows that the earliest rice cultivation and domestication occurred in the Kuahuqiao area on the apex of Hangzhou Bay in the Early mid-Holocene,but no such imprints of earlier rice domestication to date has been found in other areas of SHB.Is rice cultivation and domestication synchronous in SHB?What are the relationships among Neolithic human activities,cultivation and domestication of rice and the evolution of geomorphic environment?It has become a hot issue for researchers.It is of great scientific and humanistic significance to carry out relevant research on these question for a comprehensive understanding of the environmental background and the emergence and development of Neolithic civilization in SHB.Here,sedimentological,environmental magnetism and micropaleontological(phytolith,pollen and foraminifera)analysis were carried out on core YJ1503 of Jingtoushan site and core TJA of Tongjia'ao site in SHB.Based on the chronology framed by high-precision accelerator mass spectrometry(AMS¹⁴C)dating,the sequence of Holocene environment changes and the corresponding human occupations at these two sites were established,respectively.This combined with other geological and archaeological records in the region aimed to demonstrate the geomorphological process of Ningshao Plain of SHB,the features of Neolithic human activities including rice domestication and the response-mechanism between human and nature since the Holocene.The main conclusions are as follows:(1)A terrestrial process prevailed at the Jingtoushan area prior to ca.8600 cal yr BP.The occurrence of foraminiferal at ca.8600-8400 cal yr BP indicated that the environment was affected by transgression.This was then followed by a brackish water setting as more freshwater algae appeared at ca.8400-7600 cal yr BP.After ca.7600cal yr BP,rice bulliform phytoliths began to appear significantly,indicating that the environment had changed from the brackish water to a fresh water environment.Notably,a large number of rice bulliform phytoliths and fresh water herbaceous pollen appeared after ca.6600 cal yr BP,indicating that the region evolved into a freshwater wetland environment eventually.(2)The occurrence of foraminifera in core TJA showed that Tongjiaao site was affected by transgression at least 7700 years ago with rice phytoliths rarely seen.Then rice bulliform phytoliths increased with diminishing foraminifera,indicating a desalinized process to freshwater setting,but the magnetic features of sediments showed that the environment was still fluctuated at ca.7600-6700 cal yr BP.During ca.6700-5400 cal yr BP,the appearance of peat layers,relatively stable magnetic parameters and the presence of abundant rice phytoliths indicated that a freshwater wetland environment had prevailed.(3)The phytolith evidence of rice from Jingtoushan and Tongjiaao suggested that rice domestication in Yaojiang Valley started no later than 7600 cal yr BP and continued to Hemudu culture period intermittently.This indicated that rice domestication in Yaojiang Valley was synchronous with Kuahuqiao area.This new finding filled the gap of archaeological connotation between Kuahuqiao Culture and Hemudu culture.The difference between Jingtoushan and Tongjiaao was that the rice bulliform phytolith of TJA appeared after 7600 cal yr BP,but it did not show the clear traits of domestication.Phytolith records from sediment cores at both sites showed that relatively intensive rice domestication and planting occurred after ca.6700-6600 cal yr BP.(4)The sea level change since the early Holocene has pronounced influence on the geomorphological process and rice domestication and cultivation in SHB coast.The sedimentary records of Jingtoushan,Tongjiaao and other cores in SHB show that?7600and?6600 cal yr BP are the key time for the transformation of geomorphological environment.The former responds to the initial regression in SHB about 7600 years ago which promotes the formation of coastal plain and provides material basis for the utilization and domestication of rice.While since ca.6700-6600 cal yr BP,the formation of vast freshwater wetland environment greatly accelerated the domestication of rice and the development of rice farming in SHB.It should be noted that the geological,biological and archaeological evidence shows that there are obvious differences in the development of rice domestication and rice farming in different areas of SHB,which may be related to the varied geomorphological processes caused by the inherited paleotopography and material transportation and deposition in different places under the condition of relatively stable sea level since the middle to late Holocene.