Permian Chronostratigraphic Framework And Sedimentary Filling Evolution In Mahu-shawan And Adjacent Area,Junggar Basin

It is very important to push the progress for the hydrocabon exploration that understand the stratigraphy and sedimentary filling characteristics of basins correctly.The previous research shows that the Mahu-Shawan area in Junggar basin was in the critical stage of tectonic change during the Carboniferous and Permian,and its environment tends to be stable in the Permian.The Permian is an important source rock and reservoir in this region,with good prospect for exploration.In addition,three major hydrocarbon-generating sag in Junggar basin are occupied in the area,so proceeding detailed sedimentology analysis has great significance.Based on a combination of the borehole,outcrop,seismic and gravity and madnetic anomaly data,and isotopic chronology and geochemical test results,this paper made an detailed analysis of the Permian stratigraphic framework,tectonic setting and sedimentary filling sequence in Mahu-Shawan.This study mainly obtained the following basic understanding:(1)There are 5 sets of strata in the Permian system of Mahu-Shawan area,including the Jiamuhe formation(~ 315-283Ma),the Fengcheng formation(~283-272Ma),the Xiazijie formation(272-265Ma),the Xiawuerhe formation(265-260Ma)and the Shangwuerhe formation(260-252 Ma)from the bottom to the top.It is worth noting that the ancient age of volcanic rocks in this region indicates that the ancient microblock may exist in the northwestern margin of Junggar.(2)There are volcanics and volcaniclastic rocks in the whole area of Jiamuhe Fm.,which can be divided into three parts from the bottom to up.Fengcheng Fm.developed volcanics and volcanic clasticrocks mainly in northern Wuxia,Kebai,and southern Mahu;and developed calcareous sand mudstone deposition in the south of Wuxia,north Mahu and the Dabasong region.From the sedimentary period of Xiazijie formation,there were gray green or reddish-brown sand conglomerate and sandy mudstone.(3)Permian developed regional unconformity between each formation,especially in the transition zone between the secondary unit.(4)The tectonic setting occurs transformation in Mahu-Shawan area from the Early Permian,indicates this study area was into the post-tectonic stretching stage,there are calc-alkaline series and tholeiitic series basalt records.