Lithofacies Paleogeography Of The Guanwushan Period In The Middle Devonian In Western Sichuan

The thesis comprehensively is applied the theories of structural geology,sedimentology,paleontology and geophysics to reconstruct the layers and lithofacies palaeogeography characteristics on the basis of outcrops,drilling data,logging data and seismic data.Restore the original location of the outcrops and drillings.The three profiles,i.e.,the north profile,the central profile and the south profile,of Longmenshan Fault Belt are quantitatively restored based on the balanced section technique,so as to create the function relationship between current location and initial location of outcrops and restore the nappe distance of outcrops.The research shows that decken distance of the central profile is higher than the north and south profile.The data show that central profile is 30-45km,while south and north profile is 10-30km.And the Shuangyushi area barely moves.Depending on plenty of outcrops,drilling and logging data,identify Guanwushan Fornation top and bottom boundary.The researching has shown that the thickness of Guanwushan Formation is in 0-500m.Generally,the Middle Devonian Guanwushan Formation is thicker in the west,on the contrary,thinner in the east and thicker in the north while thinner in the south.So there are two subsidence centers,i.e.,Guixi and Jiguanshan area.And the thickness are 511m and 350m.On the whole,the thickness is thinning to the east,north and south.Even the area of Xibeixiang is 150m.And the region in the east of Qingfeng gorge,Guangyuan city-Shuangtan2-Jiangkou Town,Jiange County-Jinhua village,Jiangyou City-Tashan Town,Santai County-Jianping Town,Santai County-Longquan Village,Deyang City-Shuangqiao Village,Deyang City-Guihua Town,Pengzhou City-Wenjinjiang Village,Chongzhou city-Dafeishui Village,Dayi county-Lushan county-Gaojiachang Village,Baoxing County is absent from Guanwushan Formation.According to lithologic,paleontologic,logging response characteristics and structural settings,two main sedimentary facies types can be identified,including open platform facies and restricted platform facies on the basis of restoring initial location of the outcrops.The main sedimentary face of the north profile is open platform,while central and south profile tends to be restricted platform facies due to Pengguan and Baoxing Palaeo-island.Restoring initial location of the outcrops,recruiting lithofacies palaeogeography characteristics of the Middle Devonian Guanwushan Formation in West Sichuan Basin.On the basis of balanced section technique.The finding indicates that the rock types of the Middle Devonian Guanwushan Formation in the north profile are dominated by dolomite(crystalline,brecciated and bioclastic dolomite)and limestone(micrite,bioclastic and biogenic limestone).While,the central and south profile are mainly made up of limestone(micrite,bioclastic and biogenic limestone)and less dolomite.It should be noticed that there are reefs between central and south profile of the Guanwushan Formation,and rock types are brecciated dolomite,bioclastic dolomite and reef limestone.The study shows that sedimentary facies types are basin-slope,plateform-margin,open platform,restricted platform,shoreland and palaeo-island from the west to east on the basis of restored lithofacies of palaeogeography.And the region in the west of Pingwu-Baiyang-Jianshe is basin-slope;the area in the west of PingwuguchenYinchanggou is plateform-margin;the zone in the west of K3-Shuigentou-BeichuanMaoxian-Chuandongzi-Longdong is an open platform.The restricted platform is in open platform's east,palaeo-island's east.At the last,the sedimentary patterns are put forward on the basis of restoring geography.