松辽盆地北部上二叠统林西组古生物年代学、地球化学特征及地质意义

对松辽盆地北部地区黑富地l井钻遇的上二叠统林西组碎屑岩样品进行微体化石以及主量元素、微量元素和稀土元素测试分析,进而探讨该区林西组时代、地球化学特征、沉积环境及构造背景.获得的Protohaploxypinus fertilis-Piceaepollenites opimus-Alisporites communis孢...

Paleochronology,Geochemical Characteristics,and Geological Significance of the Upper Permian Linxi Formation in the Northern Songliao Basin

The paleontological fossils, major and trace elements (including rare earth elements (REEs)) of the Upper Permian Linxi Formation (Fm.) clastic rocks in well Heifudi 1 in the northern Songliao Basin were analyzed, in order to explore the age, geochemical characteristics, sedimentary environment, and tectonic background of the Linxi Formation. The Protohaploxypinus fertilis, Piceaepollenites opimus, and Alisporites communis palynological fossil assemblages obtained in this study indicate that the stratigraphic age is Late Permian. The average content of major elements is SiO₂=60.41%, CaO=3.65%, Al₂O₃=16.36%, K₂O=2.69%, Na₂O=3.25%, K₂O/Na₂O=0.40-7.01, and A1₂O₃/(CaO+Na₂O)=0.92-6.89. The total REE (ΣREE) contents are of 63.20×10^-6-208.05×10^-6(average 147.56×10^-6), with mainly negative Eu anomalies (δEu) of 0.56-1.34 (average 0.73) and weakly-negative Ce anomalies (δCe=0.90-0.98). The clastic rocks are characterized by LREE enrichments and HREE depletions. The trace element contents are characterized by depletions in Nb, Ta, and Sr, and enrichments in Rb, Ba, La, Sm, Pb, and Nd. Geochemical features of the clastic rocks and the discrimination diagrams of La/Th-Hf and TiO₂- Ni show that the Linxi Formation has diverse sediment sources, mainly from upper-crustal felsic rocks and minor from mafic rocks. The primitive-mantle normalized multi-element and chondrite-normalized REE diagrams, K₂O/Na₂O-SiO₂ plot, together with tectonic discrimination functions (F₁, F₂) and geochemical parameters indicate that the northern Songliao basin provenance source region was largely in an active continental margin and continental island arc setting, whilst the sedimentary facies was transitioned from marine-terrestrial to terrestrial.