元素地球化学在层序识别中的应用

Application of element geochemistry in the identification of sequence stratigraphy

为了探讨地球化学元素对层序界面及体系域识别方法的适用性,以珠江口盆地白云凹陷北坡地球化学元素为基础,讨论了在海平面变化周期内,Fe,Al,Mn及Mn/Fe,Th/U,Sr/Ca比值等参数的变化特征,它们与层序地层单元的发育有很好的对应关系。结果表明:层序界面上的Fe,Al元素含量相对较高,且以氧化物形式出现;微量元素Th/U比值很大,Sr/Ca比值则很小。Fe族元素、Th/U,Cr/V,Co/Ni,Sr/Ba及δ(Ce)等地球化学指标在低位体系域(LST)时期逐渐增高至最高,海侵体系域(TST)时期逐渐降低到最低,高位体系域时期(HST)再逐渐增高;而Mn族元素、Mn/Fe,Mn/Ti,Sr/Ca,∑REE,(La/Ce)N等地球化学指标则刚好相反,在低位体系域(LST)时期逐渐降低到最低,海侵体系域(TST)时期逐渐增高至最高,高位体系域时期(HST)再逐渐降低。

In order to discuss the suitability of identification method of sequence boundary and system tract by geo- chemical elements, this study took thegeochemical elements of the northern Baiyun depression in the Pearl River Mouth Basin as a base, and used the variation characteristics of geochemical parameters of the Fe, Al, Mn, ratios of Mn/Fe, Th/U, Sr/Ca to investigate the sea level changes. These variations can be correlated well with the development of sequence stratigraphic units. The results show that the contents of Fe and A1 are rich on the sequence boundaries, and the Fe and A1 mainly exist in oxide ; the ratio of Th/U is large, and the ratio of Sr/Ca is little. The geochemistry in- dicators of iron group,Th/U, Cr/V, Co/Ni, Sr/Ba and ^（Ce） gradually increase during the LST period until the maxi- mum, and they gradually decrease during the TST period until they get the minimum at the moment of the maximum flooding period, then they gradually increase during the HST period. The geochemistry indicators of manganese group, Mn/Fe, Mn/Ti, Sr/Ca, ∑REE and（La/Ce） N counter to those geochemistry indicators, they gradually decrease during the LST period until the minimum, and they gradually increase during the TST period until they get the maximum at the moment of the maximum flooding period, and then they gradually decrease during the HST period.