洛阳盆地龙山文化晚期大洪水地球化学特征及其社会影响研究

GEOCHEMICAL CHARACTERISTICS AND SOCIAL INFLUENCE OF PALEOFLOOD EVENTS IN THE LATE LONGSHAN CULTURE WITHIN THE LUOYANG BASIN

洛阳盆地位于黄河中游,属中原腹地,史前资料丰富,是揭示河流水文系统对于季风气候变化响应规律以及研究史前大洪水事件对中国古代文化发展演变影响的理想区域。鉴于此,我们在洛阳盆地洛河流域开展广泛的野外考察,在其下游发现了全新世古洪水沉积剖面——太学村(TXC)剖面。对其进行细致的观察与地层划分,并重点结合地球化学元素指标,对剖面中三组古洪水泛滥沉积层(overbank flood deposits,OFD)与黄土层、古土壤层不同的地球化学特征进行了对比研究,结果表明:(1)在近代黄土层(L_(0))和古土壤层(S_(0))内,常量元素地球化学参数(残积系数、淋溶系数、退碱系数)、微量元素(Zr、Zn、Mn、Rb、Sr)含量及Rb/Sr比值的变化,受到全新世气候变化及风化成壤环境的影响;在古洪水泛滥沉积层中,常量元素地球化学参数、微量元素含量和Rb/Sr比值的变化,深受沉积物物质来源原始特征的影响;(2)古洪水泛滥沉积层的地球化学特征显著区别于近代黄土层、古土壤层,其中Zn、Mn、Rb含量及残积系数、Rb/Sr比值表现为OFD3/OFD1>S_(0)>L_(0)>OFD2;而淋溶系数、退碱系数及Zr、Sr含量则表现为OFD3/OFD1<S_(0)<L_(0)<OFD2。其中,古洪水OFD2记录的古洪水事件发生时间为4000-3800 a B.P.。这期大洪水事件对河谷平原区龙山文化晚期人们的生产生活造成了严重威胁,并使得新石器时代龙山文化晚期向青铜器时代二里头文化转折变化期间出现长达几百年的文化断层。

The Luoyang Basin is located in the middle reaches of the Yellow River,which is the hinterland of the Central Plains and rich in prehistoric cultural sites.It is an ideal area to study the regional hydrological response to monsoon climate change and the impact of paleoflood events on prehistoric cultural evolution.In this study,fieldwork investigations were carried out along the Luo River within the Luoyang Basin.Combined with the geochemical elements,the different geochemical characteristics of three paleoflood OFD units,loess and paleosol in the TXC profile were studied.The main conclusions are as follows:(1)In the Holocene aeolian loess(L_(0))and paleosol(S_(0)),the changes of eluvial coefficient,eluviation coefficient,dealkalization coefficient,trace elements(Zr,Zn,Mn,Rb,Sr)concentration and Rb/Sr ratio are deeply affected by the climate change and the intensity of weathering and pedogenic modification in the Holocene.In the OFD units,the change of these related geochemical parameters,trace elements concentration and Rb/Sr ratio are deeply influenced by the original characteristics of sediment provenance.(2)In the profile,the geochemical characteristics of the OFD units are significantly different from those of L_(0)and S_(0).On the one hand,trace elements(Zn,Mn,Rb)concentration,eluvial coefficient and Rb/Sr ratio are OFD3/OFD1>S_(0)>L_(0)>OFD2,while eluviation coefficient,dealkalization coefficient and trace elements(Zr,Sr)concentration are OFD3/OFD1<S_(0)<L_(0)<OFD2.The paleoflood event recorded by the second paleoflood OFD unit occurred in 4000-3800 a B.P.,which posed a serious threat to people’s lives in the late Longshan culture in the alluvial plain of the Luo River.The cultural missing for several hundred years occurred during the transition from the late Neolithic Longshan culture to the Bronze Age Erlitou culture may be closely related to the frequent paleoflood events in this period.The results are of great significance for improving the research methods of paleoflood hydrology and deeply understanding the prehistoric environmental change and human adaptation.