通过野外考古调查研究,利用对钟桥遗址疑似古洪水层和研究区现代洪水沉积物的锆石微形态、粒度、磁化率、Rb/Sr等地球化学指标的比较、AMS14C技术和考古器物断代,发现钟桥遗址在4800~4597 cal. a BP、4479~4367 cal. a BP和4168~3850 cal. a BP分别经历了三次古洪水事件并相应堆积了古洪水沉积层;结合江汉平原及其周边地区众多遗址的古洪水沉积层时代对比证据,揭示了屈家岭文化中晚期(4900~4600 cal. a BP)和石家河文化末期至夏代(4100~ 3800 cal. a BP)两次大洪水事件在江汉平原地区非常普遍。对史前洪水发生环境背景的进一步分析,反映江汉平原在5000~4500 a BP及4000 a BP前后的时段气候表现得不稳定,古洪水事件与气候环境变化驱动的江汉平原湖群扩张存在一定的联系,并影响区域新石器文化兴衰过程。同时,其它证据也表明该区社会发展过程和环境变化过程特别是古水文过程的矛盾在石家河文化末期已特别突出,发现具有全球意义的4000 a BP前后气候异常引起的大洪水事件是江汉平原地区石家河文化消亡的重要环境因素;而石家河文化末期该区内部或同中原以及其它地区间的冲突,都加速了石家河文化的崩溃。这些研究成果,提供了可靠的大禹时代史前洪水证据来说明其对新石器文化兴衰的社会影响,对于揭示4000 a BP气候事件中区域气候水文变化的响应规律,亦具有重要的科学意义。
英文摘要:
Field archaeological investigations were carried out in the Jianghan Plain in the middle reaches of the Changjiang River. Based on the integrated study with a comparative analysis for characteristics of the modern flood sediments, multidisciplinary approaches such as the AMS14C and archaeological dating, micromorphology of zircon, grain size, magnetic susceptibility and geochemistry are conducted to identify paleoflood sediments archived at the Zhongqiao Site. The results indicate that three paleoflood events (i.e. 4800- 4597 cal. a BP, 4479-4367 cal. a BP & 4168-3850 cal. a BP) occurred at the Zhongqiao Site. Comparisons of paleoflood deposit layers at numerous Neolithic sites show that two Holocene extraordinary paleoflood events occurred over the Jianghan Plain area at approximately 4900-4600 cal. a BP (i.e. mid-late Qujialing cultural period) and 4100-3800 cal. a BP (i.e. from late Shijiahe cultural period to the Xia Dynasty). Further analysis of the environmental background for the paleoflood occurrences suggested that there was great climate variability between approximately 5000-4500 a BP and ca 4000 a BP. These two paleoflood events were closely related with the expansion of Jianghan lakes driven by the climatic change, and influenced the rise and fall of regional Neolithic Culture. Other evidences also suggested that intensified discrepancy between social development and environmental change processes (especially the hydrological process) in the end of Shijiahe cultural period might be the key factor leading to the collapse of Shijiahe Culture. The severe extraordinary floods related to the climatic anomaly at ca 4000 a BP and political conflicts from internal or other cultural areas all accelerated the collapse of the Shijiahe Culture. These results gave us a better understanding of the climate change at ca 4000 a BP, and also provide evidence for the prehistoric flood events in the Great Yu age, which is considered to be the turning point from the Neolithic Age to the Bronze Age in China.