全新世中后期开封西郊地层大洪水事件及其孢粉记录

发布时间：2018-03-19 14:48

  本文选题：全新世中后期　切入点：黄泛地层　出处：《河南大学》2015年硕士论文　论文类型：学位论文

【摘要】：黄河流域是中华文明的发源地之一,尤其是黄河中下游地区,在相当长时期内一直是我国的政治、经济和文化中心。开封作为八朝古都,其城市兴衰与黄河密切相关。目前关于黄河对开封城市影响的研究多限于黄河泛滥危害开封的次数和重大河患入城后的影响,而对于开封究竟经历了多少次黄河决溢和泥沙堆积、每次洪水的强度及等级划分标准等问题尚没有科学定论。传统的孢粉学研究多用于揭示区域古环境变化,关于洪水泛滥期与沉积间断期孢粉组合差异的研究较少。然而,开封市附近的多次黄河泛滥形成了相对完整的沉积序列,为我们探索开封地区大洪水事件的地层学证据及其孢粉记录提供了难得的研究载体。本研究选取开封市西郊河南大学金明校区内25 m钻孔(ZKjm)为研究对象,通过颜色、粒度和孢粉分析,结合AMS14C测年和历史文献资料,对全新世中后期开封西郊地层沉积旋回划分、大洪水事件及其孢粉记录进行系统的研究,结论如下:(1)开封市西郊ZKjm岩芯根据粒度(砂黏比)自下而上可以划分出9个沉积旋回:深度20.5~24 m(旋回1)、17.5~20.5 m(旋回2)、14.5~17.5 m(旋回3)、11.8~14.5m(旋回4)、9.8~11.8 m(旋回5)、7.8~9.8 m(旋回6)、4.2~7.8 m(旋回7)、2.5~4.2 m(旋回8)和0.5~2.5 m(旋回9)。深度14.5 m左右为战国时期大梁城古地面,13~14 m左右的地层应该是在公元前225年沉积物基础上发育的秦、汉、隋、唐、北宋等朝代的文化层。(2)开封市西郊ZKjm岩芯大致记录了八次大洪水事件,发生时间分别为4000 a BP前后、3500~3300 a BP、3100 a BP前后、公元前225年、1387年、1461年、1642年和1841年。气候突变(变冷)、黄河两岸的水土流失、政府治理不力以及人为决堤等是黄河水患的主要原因。(3)选取跃移质线段的斜率、砂黏比、推移质与跃移质的交切点Ф值和沉积厚度作为评价指标,定量的进行大洪水等级划分。根据洪泛总指数(TFI),建立了洪水等级标准:TFI0.16,弱(Ⅰ级);0.16≤TFI0.36,中等(Ⅱ级);0.36≤TFI0.56,强(Ⅲ级);TFI≥0.56,极强(Ⅳ级)。洪水强度属于Ⅱ级的分别是1841年、1461年和1387年的洪水,属于Ⅲ级的分别是1642年、3100 a BP前后和3500~3300 a BP的洪水,属于Ⅰ级和Ⅳ级的分别是公元前225年和4000 a BP前后的洪水事件。除水动力条件外,洪水的破坏程度还与洪水持续时间、人为防御程度、洪水发生时的气象条件、房屋结构等因素有关。(4)除个别地层沉积旋回和孢粉亚带的下界差别稍大外,其他旋回基本上都有与之对应的孢粉亚带,可见地层孢粉可以作为划分沉积旋回的代用指标。孢粉亚带的数目多于旋回数目,说明在某些层段旋回划分上孢粉指标的精度稍高于粒度;也可能是由于有些黄河泛滥历时较长,期间因季节变化、洪水流路和波及范围多变等原因,导致一次洪水事件可能出现多个短期洪水间歇期造成的。洪水间歇期间沉积的孢粉多为开封当地源,与洪水泛滥期间从中上游带来的孢粉类组合必然存在一定差别。因此,有些孢粉亚带可能并不指示特定的大洪水事件。(5)开封市西郊ZKjm岩芯洪水泛滥沉积期和沉积间断期孢粉组合的差异主要表现为沉积期木本植物花粉含量几乎均高于临近的沉积间断期,而沉积间断期人工禾本科花粉含量大都高于沉积期,主要与洪水对花粉的分选作用、花粉源范围和人类活动等因素有关。但是受气候条件、人类活动、沉积间断时间长短等因素的影响,旋回3和旋回7沉积间断期木本植物花粉含量显著高于沉积期;由于岩芯周围无农田存在和“崇祯大旱”事件,分别导致旋回4和旋回7沉积间断期人工禾本科花粉含量低于沉积期。
[Abstract]:The Yellow River basin is one of the birthplace of Chinese civilization, especially the middle and lower reaches of the Yellow River, in a quite long period of time has been China's political, economic and cultural center. It is the capital of eight dynasties, the rise and fall of the city and the Yellow River are closely related. The current research on the influence of the Yellow River city Kaifeng limited to the Yellow River flood hazards it and the number of major flood into the city after the impact, and for opening through how many times the accumulation of the Yellow River dike and sediment, every flood intensity and grading standards and other issues is no scientific conclusion. Research for revealing regional paleoenvironmental changes traditional palynology, research on the flood period and the hiatus period of pollen the difference between the less. However, opened near the city of the Yellow River flooding repeatedly formed a relatively complete sedimentary sequence, we explore the flood event stratigraphy and evidence Kaifengs The pollen record provides the carrier rare. This study selected the city west of Henan University Jinming campus 25 m drilling (ZKjm) as the research object, through the analysis of color, grain size and pollen, and combined with the historical literature of the late Holocene AMS14C, in the western suburbs of Kaifeng sedimentary cycle division, flood events and palynological records system research, conclusions are as follows: (1) Kaifeng City West of ZKjm core based on the grain size (sand clay) from top to bottom can be divided into 9 sedimentary cycles: m (cycle 1) depth of 20.5~24, 17.5~20.5 m, 14.5~17.5 m (cycle 2) (cycle 3), 11.8~14.5m (4 cycles), 9.8~11.8 m (5 cycles), 7.8~9.8 m (4.2~7.8 m (6 cycles), 7 cycles (8 cycles), 2.5~4.2 m) and 0.5~2.5 m (9 cycles). The depth of about 14.5 m for the Warring States period, the ancient city of 13~14 beam ground, about M formation should be developed in 225 BC sediments on the basis of qin, 姹，

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