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Dating recent sediments from the subaqueous Yangtze Delta and adjacent continental shelf, China

机译:对中国长江三角洲及邻近大陆架最近的沉积物进行测年

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Abstract In this study we analyzed sediment lithology, fallout of 210Pb and 137Cs, and spheroidal carbonaceous particles (SCPs) for two short cores, {YZE} and CX38, obtained by gravity corer from the Yangtze River mouth offshore and adjacent continental shelf, to compare geochronological methods on the recent sediments of this area. Lithology and grain size changes in {YZE} suggested the re-discharging of the North Channel of the Yangtze River mouth by flood events during 1949–1954 and associated accretion in the offshore area. This event was validated by a remarkable zone of declination in both 137Cs and 210Pb activities and the absolute ages derived from the 137Cs and SCPs. In contrast, 210Pb results show obvious disturbance of grain size by sediment mixing and cannot be interpreted above 100 cm. In CX38, absolute ages for the early- and mid-1950s were derived by the 137Cs and the {SCP} profile respectively, which occurred in a reasonable sequence. The excess 210Pb distribution shows exponentially decreasing activities with depth, and the mean sedimentation rate agrees roughly with the one inferred from the {SCP} profile. We suggest that the limitation of the 210Pb method needs consideration while the {SCP} profile has the potential to provide a useful and independent dating method for recent Yangtze offshore and adjacent shelf sediments.
机译:摘要在本研究中,我们分析了重力核芯仪从长江口近海和邻近大陆架获得的两个短岩芯{YZE}和CX38的沉积物岩性,210Pb和137Cs的沉降以及球形碳质颗粒(SCP),以进行比较对该地区最近沉积物的地质年代学方法。 {YZE}的岩性和粒度变化表明,1949-1954年期间的洪灾事件和相关海域沉积物的增加使长江口北航道重新排泄。 137Cs和210Pb活动中有明显的偏角区以及137Cs和SCPs得出的绝对年龄,证实了这一事件。相反,210Pb的结果表明,沉积物混合明显干扰了晶粒尺寸,在100 cm以上无法解释。在CX38中,1950年代早期和中期的绝对年龄分别由137Cs和{SCP}剖面得出,它们以合理的顺序出现。过量的210Pb分布表明活动随深度呈指数下降,平均沉降速率与{SCP}剖面推断的沉降速率大致相符。我们建议210Pb方法的局限性需要考虑,而{SCP}剖面有可能为近期的扬子江近海和邻近陆架沉积物提供一种有用且独立的定年方法。

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