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黔北凤岗硐卡拉剖面下—中奥陶统湄潭组泥岩、粉砂岩中夹含一套47.5m的连续灰岩建造,是区内迄今所测得厚度最大的“中灰岩”段。中灰岩的岩石学特征显示其成分多为分异度很高的生屑、鲕粒(豆粒)和核形石等,颗粒破碎程度偏高,丰度高时可达颗粒支撑,灰泥基质和亮晶方解石胶结均有。这些颗粒堆积形成中—高能带生屑、内碎屑浅滩,纵向上略显旋回,亦见两层较薄含瓶筐石格架的生物层。这些特征皆属浅海带暖水型沉积的标志,将该剖面的湄潭组中灰岩与之同期的大湾组和紫台组中的灰岩相比较,后者形成于偏深的相带,灰泥和泥级、粉砂级陆源碎屑含量高,也缺乏典型的暖水成因标志,故可推知扬子区陆表海的灰岩沉积相存在深度控制的海水温差分异现象。
Under the Qiacarag profile in Fenggang, northern Guizhou, the mudstone and mudstone of the Middle Ordovician Meitan Formation contain a continuous limestone of 47.5 m in thickness, which is the largest measured thickness of “limestone” in the area to date. segment. The petrological characteristics of the mid-limestone show that most of the components are chalcedges, ooids (bean grains) and nucleus-shaped stones with high degree of segregation, with high degree of particle crushing. When the abundance is high, they can reach the grain support, and the stucco matrix And brilliant crystal calcite are. These particles accumulate to form medium- to high-energy swarms, internal debris shoals, and slightly swirling longitudinally, see also the biosphere of two thinner basket-baskets of shelves. These characteristics are all indicative of shallow kelp warm water sediments. Compared with the limestones of Dawan Formation and the Purple Member of the same period, the middle reaches of the Meitan Formation in the profile are formed in the deep phase belt , Stucco and mud grade, high silt level terrigenous debris, and lack of a typical sign of the origin of warm water. Therefore, it can be deduced that there is a depth-controlled difference in seawater temperature difference between the limestone sedimentary facies in the surface sea of the Yangtze area.