上扬子地台南缘早志留世埃隆期碳酸盐岩岩石学特征及沉积环境

Petrological characteristics and sedimentary environment of carbonate during Aeronlian stage of Early Silurian in the southern margin of Yangtze Craton

上扬子地台南缘早志留世埃隆期发育的碳酸盐岩,近期揭示具有较好的油气勘探前景,但有关该套岩层的岩石学特征及其沉积环境研究需要进一步深入。论文以野外地质剖面和室内薄片鉴定为基础,对上扬子地台南缘早志留世埃隆期碳酸盐岩开展系统的岩石颗粒组分、岩石类型和沉积环境分析。发现早志留世埃隆期碳酸盐岩颗粒类型主要为生物碎屑,含少量内碎屑与鲕粒;根据曾允孚先生等的碳酸盐岩结构成因分类方案,该地区碳酸盐岩主要有7种类型:包括亮晶鲕粒灰岩、亮晶生物屑灰岩、珊瑚礁灰岩、亮晶砂屑灰岩、砂屑-生物屑微晶灰岩、微晶砂屑灰岩和微晶灰岩。根据岩石学特征和野外露头分析,认为在早志留世埃隆期研究区从早期到晚期沉积环境经历了碳酸盐缓坡到碳酸盐台地的转变,并发育了外缓坡、内缓坡、台地边缘斜坡、台地边缘滩、台地边缘生物礁、开阔台地等亚相。以三级层序为编图单元,揭示了礁滩沉积区域展布特征,生物礁滩体主要发育于SQ2层序,具有环带状展布的特征。

The carbonate rocks which developed in the southern margin of upper Yangtze Craton during Aeronlian stage of Early Silurian had a huge potential of oil and gas exploration, but its rock components, petrological types and sedimentary environment are not clear. Combined with the profile measurements in the field and thin section identification in the indoor, this paper conducts rock components, petrological types and sedimentary environment analysis of carbonate rocks in the southern margin of Upper Yangtze Craton during Aeronlian stage of Early Silurian. The study shows that rock components of carbonate rocks are mainly bioclastic, intraclasts and ooide less. According to Mr. Zeng Yunfu＇s classification scheme carbonate about rock structural genesis, carbonate rocks in this area are mainly seven types, includes sparry oolitic limestone, sparite bioclast limestone, coral reef limestone, sparry intraclastic calcarenite, intra-biomicrite, microcrystalline calcarenite, micrite. According to the analysis of the characteristics of petrology and outcrops, during the early stage of Aeronlian, Shiniulan Formation in the southern margin of Upper Yangtze Craton mainly consisted of carbonate ramp, further divided into the sedimentary facies zones includes inner ramp and outer ramp; during the later stage of Aeronlian, Shiniulan Formation in the southern margin of Upper Yangtze Craton mainly consisted of carbonate platform, which developed open platform, platform margin beach, platform margin reef, platform foreslope and so on. Based on the three order sequence, the regional distribution characteristics of the high energy reef flat facies are revealed, and the reef beach bodies are mainly developed in the SQ2 sequence, which is characterized by the zonal distribution.