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

Abstract

Experimental data of the major elements, trace elements and rare earth elements of the dark argillaceous slate from the Upper Permian Linxi Formation in Well Heifudi 1 of the northern Songliao basin were examined so as to discuss the geochemical characteristics, sedimentary environment and tectonic background of the Linxi Formation. The average content of major elements is SiO2=65.05%, Al2O3=17.23%, CaO=2.58%, Na2O=2.84%, and K2O=3.29%. K2O/Na2O is 0.20-3.48, and A12O3/(CaO+Na2O) is 0.41-8.01. The ΣREE is between 80.68×10-6 and 215.59×10-6 (average 173.41×10-6), the δEu negative anomaly is between 0.61 and 0.88 (average 0.70), and the Ce negative anomaly is between 0.91×10-6 and 1.01×10-6, relatively weak. The clastic rocks are characterized by LREE enrichment and HREE depletion. The trace elements are characterized by a loss of Nb, Ta, and Sr, and are relatively rich in Rb, Ba, La, Ce, Pb, Nd, and Sm. The elemental analysis of core samples and the results of w(TiO2)-w(Ni)and La/Th-w(Hf)indicate that the sediment source of Linxi Formation is diverse, mainly from felsic rock of the upper crust with a minority of intermediate-basic igneous provenance. The results of trace element standardized spider web map, rare earth element chondrite standardized partition pattern,diagrams of K2O/Na2O-w(SiO2), Th-Co-Zr/10, F2-F1 structural background discrimination,and geochemical parameters comparison indicate that the provenance of Linxi Formation in Well Heifudi 1 is mainly from active continental margin and continental island arc,which would like be formed in the marine-terrestrial transitional to terrestrial environment.