黔东南下古生界碳酸盐岩台地演化

位于上扬子地块东南缘的黔东南石阡地区,下古生界地层连续发育,地质现象丰富,是研究扬子台地演化最有利的地区之一。根据野外勘查、实测剖面以及镜下薄片观察资料,识别出陆棚相、台地边缘相、台地相、潮坪相4种沉积相类型,并对扬子碳酸盐岩台地的演化过程进行精细刻画,建立其台地演化模式,研究台地由出现至成熟至衰亡的发展过程。结果表明,黔东南地区下古生界碳酸盐岩台地演化经历过建设期、发展期、逆演化期3个明显阶段。第二世早期(清虚洞组沉积期)黔南地区开始出现碳酸盐岩沉积,晚期完整的台、坡、盆格局形成;特马豆克期,碳酸盐岩沉积累计厚度达千余米,为发展期的顶峰;早奥陶世大坪期,受郁南运动影响,黔东地区由局限台地向开阔台地转变,受郁南运动的持续影响,台地逐渐向缓坡相过渡,沉积了大套的碎屑岩以及碎屑岩与碳酸盐岩混积的缓坡相岩石组合,拉开了碳酸盐岩台地逆向的序幕。晚奥陶世末,黔中隆起、雪峰隆起相继形成,毕节—遵义—石阡—铜仁一线以南抬升遭受剥蚀,五峰组、龙马溪组地层缺失,中上扬子碳酸盐岩台地的演化迎来终结。

Evolution of Lower Paleozoic Carbonate Platform in Southeast Guizhou

The Shiqian area in southeastern Guizhou, located in the southeastern margin of the Upper Yangtze Block, is one of the most advantageous areas for studying the evolution of the Yangtze Platform because of the continuous development of the Lower Paleozoic strata and abundant geological phenomena. Based on field survey, measured profiles and microscopic thin section observation data, four types of sedimentary facies were identified, including shelf facies, platform marginal facies, platform facies and tidal flat facies. In the early stage of the second period (the sedimentary period of Qingxudong formation), carbonate deposits began to appear in the south of Guizhou Province, and in the late stage, a complete platform, slope and basin pattern was formed; in the temadouk period, the cumulative thickness of carbonate deposits reached more than 1000 meters, which was the peak of the development period; in the early Ordovician Daping period, affected by the southern movement, the east of Guizhou Province changed from a limited platform to an open platform, which was continuously affected by the southern movement. The platform gradually transited to gentle slope facies, depositing a large set of clastic rocks and the gentle slope facies rock combination of clastic rocks and carbonate rocks, which opened the reverse prelude of carbonate platform. At the end of Late Ordovician, the central Guizhou Uplift and Xuefeng uplift were formed one after another, the south of Bijie Zunyi Shiqian Tongren line was uplifted and eroded, the strata of Wufeng group and Longmaxi group were missing, and the evolution of carbonate platform in the middle and upper Yangtze was coming to an end.