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多次黄河泛滥使现今开封城市地面以下叠置数座古城,出现“城摞城”奇观。泛滥之后的城市重建等人类活动常常扰动正常的沉积层序,给粒度旋回划分带来巨大困难,因此需要寻找其他代用指标。分别在“城摞城”中心区(ZKsz)和郊区(ZKjm)获取25 m连续岩芯,以10 cm间隔分样;用激光粒度法结合筛分开展沉积物粒度分析,用Lim法(1996)测定黑碳含量,用小波分析划分沉积旋回。结果表明:ZKjm岩芯的粒度旋回界线大多与黑碳旋回一致,表明黑碳含量可以作为划分沉积旋回的代用指标。ZKsz钻芯深度8.8~23.5 m之间的地层,粒度旋回和黑碳旋回的数量及其界限基本相同;北宋以后地层(深度0.3~8.8 m)的粒度旋回只有2个,而黑碳旋回有7个,表明黑碳含量适用于城市扰动地层的沉积旋回划分。
Several times the Yellow River flooding so that the current Kaifeng city ground below the stacking of several ancient cities, there “city of the city ” spectacle. Human activities such as urban renewal after flood often disturb the normal sedimentary sequence, which brings great difficulty to the granularity division of the cycle. Therefore, other proxy indicators need to be found. The 25 m continuous cores were obtained in ZKsz and ZKjm respectively at 10 cm intervals. The sediment particle size was analyzed by laser particle size method and sieving method. The Lim method 1996) Determination of black carbon content, using wavelet analysis of sedimentary cycle. The results show that the grain boundary of ZKjm core is mostly consistent with the black carbon cycle, indicating that the black carbon content can be used as a proxy for the division of sedimentary cycles. ZKsz core depth of 8.8 ~ 23.5 m between the strata, the size of the cycle and the number of black carbon cycles and its boundaries are basically the same; after the Northern Song Dynasty strata (depth of 0.3 ~ 8.8 m) the size of the cycle of only two, while the carbon black 7 This indicates that the black carbon content is suitable for the sedimentary cycle of the urban disturbance stratum.