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鄂西长阳南华系出露良好、发育完整,主要由莲沱组、南沱组构成,少数地段(长阳古城)包括古城组和大塘坡组。莲沱组为河流—河口湾相的碎屑岩组合,区域上南厚北薄,岩性三分性明显。古城组为典型的冰碛岩,对应于国际上Sturtian冰期。大塘坡组为间冰期海陆过渡相沉积。南沱组为研究区内最发育、最重要的冰碛地层,对应于国际上Marinoan冰期,区域上岩性变化不大,厚度具西南厚北东薄之趋势。长阳流溪剖面上,仅发育莲沱组和南沱组。南沱组CIA值介于52.52~55.80范围内,反映寒冷干燥气候条件、低等化学风化程度的沉积环境。莲沱组底部CIA值为68.14,为温暖湿润气候条件、中等化学风化程度的沉积;下部CIA值介于61.61~64.57之间,为温暖干燥气候条件、低等化学风化程度的沉积;上部CIA值介于55.03~59.80之间,为寒冷干燥气候条件、低等化学风化程度的沉积。莲沱组SiO2/Al2O3值介于2.13~5.10之间,变化较大,但总体明显低于南沱组SiO2/Al2O3值(4.47~5.16),莲沱组FeO/Fe2O3值介于0.16~0.49之间,远低于南沱组FeO/Fe2O3值(1.96~3.11),也就是说南沱组形成时期气候寒冷干燥、化学风化作用较弱,而莲沱组沉积时期气候相对温暖、化学风化作用相对较强。CIA值和SiO2/Al2O3、FeO/Fe2O3比值表明研究区南华系经历了“莲沱间冰期”温暖湿润—温暖干燥气候、低—中等化学风化程度,至“莲沱间冰期”寒冷干燥气候、低等化学风化程度,再到“南沱冰期”寒冷干燥气候、低等化学风化的沉积环境变化过程。
The western part of Changyang in Western Hubei Province is well exposed and well developed. It is mainly composed of the Liantuo Formation and Nantuo Formation, and a few areas (Changyang Old City) include the Ancient City Formation and Datangpo Formation. The Lintuo Formation is a combination of clastic rocks of river-estuarine facies. The upper and southern South-North thinning and lithology tricity are obvious. The ancient city group is a typical moraine rock, corresponding to the international Sturtian ice age. Datangpo Formation is the transitional facies sedimentation during the interglacial period. The Nantuo Formation is the most developed and important moraine formation in the study area, corresponding to the Marinoan Ice Age in the world. The lithology in the area has little change, and the thickness has the trend of becoming thicker in the north and easterly in the east. On the Changyang Liuxi Section, only the Liantu Formation and the Nantuo Formation are developed. The CIA value of Nantuo Formation ranges from 52.52 to 55.80, reflecting the depositional environment of cold and dry climatic conditions and low chemical weathering. The CIA value at the bottom of the Lintuo Formation was 68.14, which was a deposition of warm and humid weather and moderate chemical weathering. The lower CIA value was between 61.61 and 64.57, which was a warm and dry climatic condition with a low degree of chemical weathering. The upper CIA value Ranging from 55.03 to 59.80 for cold and dry climatic conditions, the degree of chemical weathering deposition. The values of SiO2 / Al2O3 in the Lotto Formation ranged from 2.13 to 5.10, but were generally lower than those of the Nantuo Formation (4.47-5.16). The FeO / Fe2O3 values in the Lotto Formation ranged from 0.16 to 0.49 , Which is much lower than that of Nantuo Formation (1.96 ~ 3.11). That is to say, the climate during the formation of Nantuo Formation is cold and dry with weak chemical weathering, while the relatively warm weather and the chemical weathering in the depositional phase of the Liantu Formation Strong. The CIA value and SiO2 / Al2O3, FeO / Fe2O3 ratios indicate that the South China System in the study area experienced a “warm and humid - warm and dry climate, low - moderate chemical weathering degree” to “ Dry climate, low degree of chemical weathering, and then to the ”Nantuo glacier " cold and dry climate, low chemical weathering sedimentary environment change process.