全新世中后期开封西郊黄泛沉积序列的孢粉记录

历史时期以来,黄河在开封市附近多次泛滥形成了相对完整的沉积序列。选取开封市西郊25 m岩芯（ZK_jm）为研究对象,通过孢粉分析,结合地层沉积旋回和历史文献资料,探讨了全新世中后期以来大洪水事件的孢粉记录。结果表明：黄泛地层中的孢粉含量及其组成很好地记录了大洪水事件,洪水沉积期的木本植物花粉含量高于其间断期,而人工禾本科花粉含量低于间断期。每个粒度旋回基本上都有与之对应的孢粉亚带,且其上下界限的吻合度较高,表明孢粉可作为划分沉积旋回的代用指标。岩芯孢粉亚带的数目（12个）多于粒度旋回数目（9个）,孢粉组合特征可以识别出规模较小的洪水或者一次洪水事件出现的多个短期洪水间歇期所形成的沉积,孢粉指标划分沉积旋回的精度高于粒度指标。

The middle and late Holocene pollen record from the Yellow River flooding sedimentary sequence in the western suburbs of Kaifeng City,China

The flooding of the Yellow River has occurred many times near Kaifeng City and formed a relatively complete sedimentary sequence, which provide a rare research carrier for the exploration of the stratigraphic evidence on flood events and its pollen records in the vicinity of Kaifeng. In this research, a 25-m long core was obtained from Jinming campus of Henan University (ZK_jm), which is located in the western suburbs of Kaifeng, Henan Province, China. On the basis of detailed pollen analysis, along with color identification, AMS¹⁴C dates, grain size and historical documents, sedimentary cycles in the study area were identified, and flood events and their pollen records were revealed since the middle and late Holocene. The results are as follows: According to the sand-clay ratio of grain size in the study area, ZK_jm core can be divided into nine sedimentary cycles from bottom to top, and can roughly record eight large flood events. The difference between pollen assemblages is that the percentage of arboreal pollen in flood deposition period is higher than that in neighboring hiatus period, while the percentage of planted Poaceae is lower in ZK_jm core. Except individual strata, the boundaries of sedimentary cycle are mainly consistent with the pollen subzones, suggesting pollen can be used as a reference indicator for dividing sedimentary cycles of strata. Notably, sedimentary cycles formed by smaller flood or plurality of intermittent short-term floods within one flood can be identified by pollen index. Therefore, the number of pollen subzones (12) is more than that of sedimentary cycles (9), indicating the accuracy of the cycle division of some intermittent pollen indexes is slightly higher than that of granularity. Due to seasonal changes, the variability of the flowing path of floods and the geographic scope, some floods of the Yellow River that lasted longer may have multiple intermittent short-term floods. However, the local pollen of Kaifeng City mainly deposited during the intermittent floods, which is different from the upper reaches of the Yellow River. Consequently, a pollen subzone may not indicate a specific flood event.