摘要
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 Nanhua System is well developed and exposed in Changyang,Hubei Province.It consists mainly of the Liantuo and Nantuo Formations,with minor sections consisting of the Gucheng and Datapo Formations.The clastic rock assemblages of Liantuo Formation forming in river or estuary environment are relatively thicker in the south area and thinner in the north,and can be divided into three lithoglical sections.The Gucheng Formation is typical tillite,which corresponds to Sturtian glaciation.The Datangpo Formation deposited in transitional facies during interglaciation.The Nantuo Formation was the most developed and important moraine stratum,which corresponds to Marinoan glaciation.Lithology has little change and thickness is gradually thinner from southwest to northeast.The Liantuo and Nantuo formations are developed only along the stream profiles at Changyang.The CIA value of 52.52~55.80 for the Nantuo Formation indicates the frigid-arid climate and low chemical weathering environment.The CIA value（68.14） for the bottom of the Liantuo Formation reflects a warm-wet climate condition and medium chemical weathering;the value of 61.61~64.57 for the lower part reflects a dry climate and low weathering environment;and value of 55.03～59.80 for the upper part indicates a warm-damp,low chemical weathering.The SiO2/Al2O3 value of the Liantuo Formation ranges between 2.13~5.10,showing a large variation,but generally lower than that（4.47~5.16） of the Nantuo Formation.The FeO/Fe2O3 value of 0.16~0.49 for the Liantuo Formation is far lower than that of Nantou Formation（1.96~3.11）.These differences demonstrate that the Nantuo Formation formed in frigid-arid and lower chemical weathering environment,but the Liantuo Formation in relatively warm and higher chemical weathering environment.Our results show that the Nanhua System in the study area experienced a series of sedimentary environmental changes,from the ＂Liantuo Interglaciation＂（warm-humid or warm-dry and low-medium chemical weathering to cold-dry,low chemical
出处
《地质学报》
EI
CAS
CSCD
北大核心
2011年第4期576-585,共10页
Acta Geologica Sinica
基金
中国地质调查局基础地质调查项目(编号1212010610709
1212010814057)资助成果
