Geochemistry,Sedimentary Environment and Source Characteristics of the Lower Jurassic Sangonghe Formation in the Southern Margin of Junggar Basin
The southern margin of the Junggar Basin is an important area for oil and gas exploration.It is also an impor-tant area for studying the tectonic attributes of the basin and the evolution of the sedimentary environment.The previous research on the sedimentary environment and the characteristics of the clastic source area of the Sangonghe Formation in the southern margin is partially inadequate,which is not conducive to further exploration and development.The Sangonghe Formation of the Lower Jurassic in the southem margin is composed of the upper main body of light blue-grey to grayish green feldspathic lithic sandstone,silty mudstone,muddy siltstone,and lower soil yellow feldspathic lithic sandstone,pebbly coarse sandstone,and conglomerate.Petrological,petrographic,and geochemical studies on the upper samples show that the chemical alteration index(CIA)of the sample is 77.57,indicating that the source area has undergone mod-erate weathering;The poor grinding and sorting of detrital materials indicate that the sediment transport distance is short and the compositional maturity is low;Cu/Zn,V/Cr,V/(V+Ni),Ni/Co,and U/Th values indicate that the paleosedimentary environment is an oxygen rich oxidation environment to a oxygen poor transition environment;Sr/Cu and Al2O3/MgO values indicate warm and humid climate characteristics;Li,Sr,Sr/Ba,Th/U values indicate freshwater environment;Based on the comprehensive petrographic characteristics,it is believed that the upper part is mainly composed of shallow lake subfacies sedimentation,while the lower part is composed of braided river delta plain subfacies sedimentation.The sample con-tains rhyolite debris,and the discrimination maps of La/Th-Hf,La/Sc Co/Th,and Ni TiO2 indicate that the source rocks of the Sangonghe Formation mainly come from felsic volcanic rocks in the upper crust;The presence of a small amount of andesite debris and Th/Co,Th/Cr ratios indicates a small amount of intermediate basic rocks in the source rock.By comparing the composition of samples with different structural backgrounds of sandstone,Th Co Zr/10,La Th Sc,Th Sc Zr/10 discrimination maps,it is shown that the source area should be a continental island arc tectonic background.
Southern margin of Junggar BasinSangonghe FormationGeochemistrySedimentary environmentTec-tonic background
NETL
NSTL
万方数据
