Study on Lithofacies Paleogeography of Daye Formation of Lower Triassic in the Middle Yangtze Region

Key words: 
• lithofacies /
• paleogeography /
• single factor analysis and comprehensice mapping method

Abstract: The study area deals with five provinces,i.e.,ichuan, Guizhou, Hubei,Hunan and Jiangxi.It is mainly in the middle Yangtze region and also include a part of the upper Yangtze region. Daye Formation of lower Triassic is widely distributed in the area and especially well outcropped in the east of Sichuan and west and east of Hubei. The biggest thickness of Daye Formation is 843.8 m and there exist various sedimentary rocks and a well potential of oil and gas. There are two kinds of different rocks in the Daye Formation,i.e.,carbonate rocks and clastic rocks. Carbonate rocks including limestone and dolomites are most widely distributed in the area. This paper has adopts “the single factor analysis and comprehensive mapping method”and the following single factors are selected:thickness, shallow-water grains content, the sedimentary thickness ratio of deep-water to shallow-water, gravity flow sediment content, the basin sedimentary content and terigenous materials content.At the same time, six fundamental single factors are drawn. On the basis of the six fundamental single factor maps,combined with other quantitative and qualitaive information and other regional geological information one piece of lithofacies paleogeographic map of Daye Age of Early Triassic in middle Yangtze region has been drawn. According to the map of the lithofacies paleogeography of Daye Age of Early Triassic,the whole area of the middle Yangtze Sea has six paleogeologic units.From northern area to southern area,there are the north deep-water basin,the northslope,the shallow-water platform,the south slope.the south deep-water basin and south－east clastic beach.From the early period to the late,sedimentary water became shallow,in the last period,the whole sea area uplifted and became carbonate platform.