汝河全新世古洪水沉积学与光释光测年研究

Sedimentology and OSL Dating Study of the Holocene Palaeoflood on the Ruhe River

汝河流域曾发生过堪称世界之最的"1975·8河南驻马店特大洪水垮坝事件",其洪水规模之大,受灾面积之广,受灾及死亡人数之多,震惊世界。因此探究汝河特大洪水事件的发生规律及其气候背景具有极其重要的科学价值。通过对汝河流域开展广泛细致的野外考察,在驻马店-遂平段第一级河流阶地前沿发现多处全新世古洪水滞流沉积物剖面,记录了流域发生的气候水文事件信息。最终选取汝河诸市乡地点(ZSX)全新世黄土土壤剖面进行系统采样,结合沉积学指标研究,准确鉴别出汝河ZSX黄土古土壤剖面中所夹三组古洪水滞流沉积物(slackwater deposits,SWD),为典型河流洪水悬移质泥沙沉积物。结合地球化学特征分析,确认三组古洪水SWD的物质是汝河上游流域发生特大暴雨洪水期间,流域地表土壤侵蚀与水土流失的产物。这三组古洪水滞流沉积物记录了末次冰消期和全新世发生在汝河流域的三期古洪水事件。结合典型剖面地层对比和应用SAR法对剖面关键沉积层位进行光释光测年(optical stimulated luminescence dating,OSL),建立了准确的地层年代框架。这三期古洪水事件分别发生在12000~11200aBP、4200~4000aBP、3200~3000aBP,皆发生在全球性气候突变或者转折时期,表明在这些时段季风气候变化异常,变率增大,洪水和干旱事件皆有发生。本研究对于淮河防洪减灾、水土保持及水资源开发利用,对于揭示区域气候水文变化与全球变化的响应规律,具有十分重要的科学意义和实践价值。

Notorious flood collapse event occurred in Zhumadian of Hunan province on August 1975, and shocked the world with its flood scale, huge stricken area and high death toll. Therefore, studying its occurrence regularity and climate background will be of great scientific significance. Through paleo- hydrological investigations carried out in Ruhe River, the Holocene loess-soil profiles with interbedded flood slackwater deposits （SWDs） were found in terrace I in the Zhumadian-Suiping section of the Ruhe River, which records the climate hydrological events in Ruhe River. Systematic sampling was carried out in the Holocene loess-soil profiles at ZSX site in the Reaches of Ruhe River. Combined with particle sedimentary features, three sets of slackwater deposits （SWD） were identified within the Holocene loess- soil profiles, which are typical of suspended sediment load in the floodwater. Analysis of geochemical characteristics confirms the paleoflood slackwater deposits were the results of loess and soil on both sides of the Ruhe River during storm flood. The three palaeo-flood sediments record three palaeo-flood events occurring the last deglaciation and Holocene. By contrast of type stratigraphic profiles and optically stimulated luminescence （OSL） dating, precise stratigraphic chronology framework was constructed. Three palaeofloods were dated to 12000 - 11200 a BP, 4200 - 4000 a BP and 3200 - 3000 a BP, respectively, all occurring in globally climate change or transforming periods. This study shows that the monsoonal climate was highly variable with both droughts and floods occurring in the Huai River. Our results are of great significance to mitigate flood disasters and exploit water resources, as well as to understand hydrological response to global climatic change.