摘要
扬子地块主体在中三叠世晚期出现了一次大规模的海退(即著名的拉丁期大海退),但是位于扬子地块西南缘的黔西南地区在同期却出现了一次大规模的海侵,与之对应的沉积岩相也由以杨柳井组为代表的浅水碳酸盐岩沉积变为以竹竿坡组为代表的一套富含大量浮游生物和游泳生物的深水瘤状暗色灰泥岩和代表最大海泛面的瓦窑组黑色页岩和深海灰岩沉积。之后,扬子台地被一套深水陆源硅质碎屑浊积岩和一套巨厚的陆相含煤碎屑沉积岩覆盖,从此结束了其自晚元古代以来长达630Ma的碳酸盐岩台地生长演化历史。对比分析表明,黔西南地区这次大规模海侵与全球海平面变化同步,相当于全球海平面变化曲线的一级旋回UpperAbsaroka旋回(megacycle)的第三个二级超级旋回中的第一个三级旋回,具有全球对比性。
There was a large regression of sealevel in the later Middle Triassic in the Yangtz Block (the famous Ladinian large regression in China). But a large transgression of sealevel was took place in the southwest corner of the Yangtz Block at the southwest region of Guizhou Province during the same period. The Yangtz carbonate platform was drawn by the seawater during this transgression. Sedimentary facies also changed sharply from shallow water carbonates (Yangliujing formation) such as peloidal packstone and grainstone with dolomitic lime mudstone and laminated dolostone contained burrows and fenestral voids to deepsea deposits (Zhuganpo Formation) such as nodular muddy limestone with pellets contained Neogondolella Polunathifornis and condensed section (Wayao Formation) with black shale and thin bedded (several cm) lime mudstone. After the LadinianCarnian, terrigenous clastic sediments including turbidite of the Laishike Formation covered the Yangtze carbonate platform. The Yangtze Block, with a long evolution history of 630 Ma since late Proterozoic, stopped growing. It is proposed that the LadinianCarnian transgression in southwestern Guizhou province was synchronous with the global sealevel changes. The LadinianCarnian transgression was the first third circle of the third second supper circle in the Upper Absaroka megacycle of the global sealevel change curve established by Haq B U in 1987 and 1988.
基金
国家自然科学基金项目(40173005)
关键词
黔西南地区
海侵
海平面变化
三叠纪
扬子地块
transgression
sea-level changes
Triassic Ladinian-Carnian
Yangtze block
