松辽盆地南部上二叠统杨家沟组泥岩地球化学特征及地质意义

GEOCHEMICAL CHARACTERISTICS AND GEOLOGICAL SIGNIFICANCE OF YANGJIAGOU FORMATION MUDSTONE OF UPPER PERMIAN IN SOUTHERN SONGLIAO BASIN

本次研究通过对松辽盆地南部杨家沟组泥岩进行野外剖面观测、主微量元素分析测试,分析其地球化学特征,探讨杨家沟组泥岩的地质特征和沉积古环境,以期推动杨家沟组油气勘探进展。研究结果表明:杨家沟组泥岩主量元素w(SiO_(2))最高(64.18%~70.87%,平均为67.59%)其次为w(Al_(2)O_(3))(14.18%~16.71%,平均为15.67%),微量元素中U,Th,Zr和Zn元素相对于上地壳富集,Sr,Pb,Sc和Ni元素相对于上地壳亏损。样品轻稀土元素(LREE)含量为87.24×10^(-6)~187.99×10^(-6),平均为135.81×10^(-6);重稀土元素(HREE)含量为18.83×10^(-6)~27.53×10^(-6),平均为21.59×10^(-6);La_(N)/Yb_(N),La_(N)/Sm_(N)和Gd_(N)/Yb_(N)的比值分别为6.61,3.20和1.37,指示稀土元素具有轻稀土富集,重稀土亏损的特征。Eu(0.54~0.85,平均为0.65)和Ce(0.69~0.99,平均为0.89)负异常的特征。地球化学特征显示,杨家沟组泥岩物源主要为酸性岛弧物源,源岩类型为沉积岩;沉积时期为温湿的陆相或淡水环境;氧化还原条件为还原条件;构造背景主要为大陆岛弧和活动大陆边缘构造背景。

In order to promote the progress of oil and gas exploration in Yangjiagou Formation,the geochemical characteristics and sedimentary palaeoenvironment of Yangjiagou Formation mudstone in the southern Songliao Basin are studied by field profile observation and main trace element analysis.The results show that the content of w(SiO_(2))is the highest(64.18%to 70.87%,with an average of 67.59%),followed by w(Al_(2)O_(3))(14.18%to 16.71%,with an average of 15.67%).The U,Th,Zr and Zn elements are enriched in the Yangjiagou Formation mudstone relative to the upper crust while Sr,Pb,Sc and Ni are depleted relative to the upper crust.LREE contents of the samples range from 87.24×10^(-6) to 187.99×10^(-6),with an average of 135.81×10^(-6)and the contents of heavy rare earth elements(HREE)range from 18.83×10^(-6) to 27.53×10^(-6) with an average of 21.59×10^(-6).The ratios of La_(N)/Yb_(N),La_(N)/Sm_(N) and Gd_(N)/Yb_(N) are 6.61,3.20 and 1.37,respectively,indicating that LREE is enriched and HREE is depleted.Eu(0.54-0.85,average 0.65)and Ce(0.69-0.99,average 0.89)are characterized by negative anomalies.Geochemical characteristics show that the mudstone provenance of Yangjiagou Formation is mainly acidic island arc,with sedimentary rock as main source rock type.The rocks were formed under reductive conditions with warm and humid continental or fresh water environment and with a continental island arc and active continental margin tectonic setting.