Mineralogical and elemental geochemical characteristics of Taodonggou Group in Taibei Sag , Turpan-Hami Basin: Implication for Source sink system and evolution history of lake basin

Abstract. The Middle Permian is an important basin-forming period in the Turpan-Hami Basin. Based on mineral characteristics and elemental geochemistry of the Taodonggou Group mudstone we analyze the parent rock type, source area location, sedimentary environment and source area tectonic background for this mudstone. On this basis we are able to reconstruct the source-sink system and lake basin evolution of the Taodonggou Group. We find the following: (1) Taodonggou Group mudstone minerals are mainly clay and quartz, and can be classified into four petrographic types according to mineral fraction. (2) The Taodonggou Group mudstone was deposited in a warm, humid and hot paleoclimate, with strong weathering. The parent rocks of the Taodonggou Group mudstone are two types of felsic volcanic rocks and andesites, with weak sedimentary sorting and recycling and with well-preserved source information. (3) The Taodonggou Group mudstone were deposited in dyoxic freshwater-brackish water in intermediate-depth or deep lakes with stable inputs of terrigenous debris but at slower deposition rates. Deposition of the middle of Taodonggou Group was influenced by hydrothermal activity; the tectonic setting of the Taodonggou Group source area was a continental island arc and an oceanic island arc. (4) The evolution of the Middle Permian Lake basin in the Turpan-Hami Basin can be divided into three stages: In the early part of the deposition of Taodonggou Group the depocenter was in the Bogda area. At this time the area that became Mt Bogda was not exposed and a succession of high-quality type-III source rocks was widely deposited in the basin. In the middle of the deposition of the Taodonggou Group the depocenter gradually migrated to the Taibei Sag. At this time the Mt Bogda area underwent uplift, and, together with hydrothermal activity, a succession of type-II source rocks was widely deposited in the basin. In the late part of the Taodonggou Group, uplift of the Mt Bogda area ceased and the depocenter transferred entirely to the Taibei Sag.