惠州凹陷HZ21钻孔珠江组地球化学特征及其沉积环境

Geochemical characteristics and sedimentary environments of the Zhujiang Formation in well HZ21 at Huizhou depression

根据21件碎屑岩样品的常量元素和微量元素相关关系、组分含量及某些元素的比值特征,探讨了珠江口盆地惠州凹陷HZ21钻孔的元素地球化学特征与古环境意义。研究表明:Al2O3、Fe2O3、K2O、TiO2、V、Cr、Rb相互间呈明显的正相关关系;SiO2与Al2O3、Fe2O3、TiO2呈明显负相关,与K2O呈弱相关关系;Sr与CaO呈明显正相关关系;P2O5与Al2O3、Fe2O3、K2O、TiO2呈明显的正相关,与SiO2呈明显的负相关,且与CaO呈弱相关关系。据锶钙比值103(Sr/Ca)和V/Cr值分析,HZ21井珠江组从下往上水体有逐渐加深的趋势,与单井沉积相分析结果一致。据镁铝比值102(MgO/Al2O3)和Sr/Ba值分析,珠江组从下往上沉积环境的水体盐度变化不太大,但到上部略有下降。古气候指示剂Rb/Sr值和MgO/CaO值显示,NSQ1和NSQ2层序时期气候干燥寒冷,而NSQ3和NSQ4这两个层序时期气候湿热。总之,地球化学特征所反映的沉积环境与沉积相分析的结果相一致,说明元素地球化学与沉积环境关系密切,可作为沉积相判别的标志。

This study discussed the sedimentary geochemistry characteristics and the palaeosedimentary environ- mental significance of the Zhujiang Formation in well HZ21 at Huizhou depression, Pearl River Mouth basin, on the basis of geochemical analyses of 21 rock samples. The results indicated： A1203, Fe203, K20, TiO2, V, Cr and Rb remarkably were positively correlated with each other; SiOz was apparently negatively correlated with A1203, Fe203 and TiO2,and weakly negatively correlated with I〈20; Sr and CaO positively correlated with each other; P205 positively correlated with A1203, Fe203, K20 and TiO2, and negatively correlated with SiO2, and weakly negatively correlated with CaO. The analytic result of the value of 103（Sr/Ca） and V/Cr revealed that the depth of sedimentary water increased from bottom to top in the Zhujiang Formation of well HZ21, and the variation regularities were consistent with the conclusions of sedimentary facies. The analytic result of the value of 102 （MgO/A1203） and V/Cr revealed that the salinity was similar from the bottom to the top of Zhujiang Formation, but decreased slightly in the top of Zhujiang Formation. Based on the characters of Rb/Sr and MgO/CaO, NSQ1 and NSQ2 were deposited in cool-dry climate condition, NSQ3 and NSQ4 were deposited in warm-wet climate condition. In summary, the geochemical characteristics and the sedimentary environment are closely correlated, and the geochemical charac- teristics can be regarded as a mark in the sedimentary facies recognition.