Abstract:

The paleosedimentary environment during the preservation of volcanic materials is one of the key factors influencing the volcanic oil-gas reservoir. During the interval of volcanic eruption, the deposited thin sedimentary lithologic layer has sedimentary characteristics. The trace elemental characteristics in the thin sedimentary layers are closed related to the paleosedimentary oxide-reductive environment and are important parameters for paleoenvironment identification. Thus, the paleosedimentary environment can be identified indirectly based on the trace element analysis on cores of the thin sedimentary layers during volcanic eruption intervals. Thin sedimentary lithologic layers, including mudstone and siltstone, had deposited during the interval of volcanic eruption in the Upper Carboniferous Haerjiawu Formation of Malang sag, Santanghu basin, Xinjiang. Eleven types of trace element ratios of these fine sediments, including U/Th, authigenic U, V/Cr, Ni/Co, V/Sc, V/(V+Ni), Cu/Zn, Fe3+/Fe2+, Sr/Ba, V/Zr, and B/Ga are used to trace the oxide-reductive paleoenvironment during the interval of volcanic eruption. Seven kinds of parameters, V/(V+Ni), V/Sc, Sr/Ba, V/Cr, V/Zr, Cu/Zn and B/Ga of mudstone, carbon mudstone, and siltstone indicate an underwater reduction environment and the coastal shallow sea environment with frequent water-land transition; It is concluded that the volcanic rocks of the Haerjiawu Formation are mainly deposited by eruption and preserved in underwater environment, and the complex sedimentary genetic environment of frequent water-land transition also exists.

Key words: eruption interval, sedimentary interbeds, paleosedimentary environment； trace elements, geochemistuy parameter； Malang sag