Sedimentary environment and tectonic setting of the Middle Jurassic Xiufeng Formation in the Upper Heilongjiang River basin

The petrological characteristics and major element,trace element,REE and C and O isotope quantitative analyses of sandstones of the Middle Jurassic Xiufeng Formation in the Upper Heilongjiang River basin indicate that:the major elements are characterized by higher K2O/Na2O and SiO2 and lower SiO2/Al2O3 and Fe2O3+MgO,showing the nature of the active continental margin;the trace elements are featured by lower B and Sr/Ba,higher Fe/Mn and lower Z values of C and O isotopes,indicating the features of inland fresh-water sediments;and REE are characterized by enrichment in LREE,good fractionation and weak Eu depletion and the REE patterns are similar to those of the active continental margin and Paleozoic granites on the southern margin of the Upper Heilongjiang River basin.An integrated analysis of the petrological and geochemical characteristics of the Xiufeng Formation suggests that Xiufeng Formation formed in a fresh-water river environment and that its materials mainly came from the Late Carboniferous Talin superunit and Mesoproterozoic-Lower Cambrian Dawangzi Formation-complex.The formation of the Upper Heilongjiang River basin is related to the Mongolia-Okhotsk orogeny,and this basin is an active continental-margin basin.