淮河支流沙河闫湾段全新世晚期古洪水事件及气候背景

Late Holocene palaeoflood events and its climatic background in the Yanwan reach of the Shahe River,Huaihe River basin

古洪水事件是水文过程对极端性气候事件的瞬时响应。通过野外实地考察,在淮河支流沙河闫湾段的河岸台地中,发现含有一套3层记录古洪水事件沉积物OFD1、OFD2和OFD3的黄土—古土壤沉积剖面,并进行了采样以及沉积物理化性质和光释光测年分析。粒度端元分析表明,OFD1、OFD2和OFD3均为水动力作用下形成的古洪水泛滥沉积物。但是OFD3、OFD1的粒度组成主要为砂级颗粒(>60%),而OFD2、古土壤(S_(0))、过渡性黄土(L_(t))和马兰黄土(L_(1))的粒度组成以粉砂为主(>70%);并且OFD3和OFD1的磁化率值和地球化学元素Na_(2)O、K_(2)O和Si O_(2)含量明显高于OFD2、S_(0)、L_(t)和L_(1),而Al_(2)O_(3)和Fe2O3含量低于OFD2、S_(0)、L_(t)和L_(1);OFD2的粒度组成、磁化率值和地球化学元素组成与S_(0)、L_(t)和L_(1)相近,与OFD3、OFD1明显不同,这可能是由于OFD2与OFD3、OFD1的物质来源不同所致。光释光测年和沉积剖面地层年代框架对比表明,该沉积剖面记录了淮河流域全新世晚期1550—1400 a的一期3次特大古洪水事件。高分辨率气候代用指标、大气环流因子以及全球平均温度的变化分析表明,沉积剖面记录的1550—1400 a一期3次特大古洪水事件,是对这一时期气候突变的响应,正好对应中国南北朝(420—589 AD)严重的气候恶化期。该研究结果对于揭示区域水文气候变化对全球变化的响应规律具有重要意义。

Palaeoflood events are instantaneous responses of hydrological processes to extreme climate.Through field investigation,a loess-paleosol sedimentary profile containing a set of overbank flood deposits(OFD1,OFD2 and OFD3)that recorded the extraordinary palaeoflood events was found on the platform scarp of the Shahe River,a tributary of the Huaihe River.The sediment samples were collected,and the physical and chemical properties and optically stimulated luminescence(OSL)dating were analyzed.The results showed that the endmembers analysis of particle size indicated that OFD1,OFD2,and OFD3 were overbank flood deposits affected by hydrodynamic forces.However,the particle size composition of OFD3 and OFD1 primarily consisted of sand(>60%),while the particle size composition of OFD2,S_(0),L(t) and L_(1) was mainly silt(>70%).The magnetic susceptibility values of OFD3 and OFD1 were significantly higher than those of S_(0),L(t) and L_(1),and the contents of Na2O,K2O and SiO2 were higher,while the contents of Al_(2)O_(3) and Fe2O3 were lower in OFD3 and OFD1.The particle size composition,magnetic susceptibility value and geochemical element composition of OFD2 were similar to those of S_(0),L(t) and L_(1),but significantly different from those of OFD1 and OFD3.These differences could be attributed to the varying material sources of OFD2,OFD3,and OFD1.OSL dating and a stratigraphic chronological framework of sedimentary profile indicated that the three extraordinary palaeoflood events were recorded during the late Holocene from 1550 to 1400 a BP in the Huaihe River basin.The analysis of high-resolution climate proxy indicators,atmospheric circulation factors,and global mean temperature demonstrated that the extreme flood events that occurred during the late Holocene from 1550 to 1400 a BP were a direct response to the abrupt climate changes,corresponding to the severe climate deterioration period of the Northern and Southern Dynasties in China.These findings are significant in understanding the regional response of hydrological climate change to global change.