滇黔桂盆地及其邻区二叠系与三叠系之交的淹没不整合面

THE DROWNED UNCONFORMITIES BETWEEN PERMIAN AND TRIASSIC IN THE DIANQIANGUI BASIN AND ITS ADJACENT AREAS

滇黔桂盆地及其邻区在晚二叠世长兴晚期发生快速海侵,导致了第Ⅰ幕淹没事件,研究区内的连陆台地大部分被淹没,形成大隆组硅质泥页岩系凝缩段地层和其下相对局限发育的第Ⅰ幕淹没不整合面;在早三叠世印度初期发生更大规模的快速海侵,导致更大的第Ⅱ幕淹没事件,研究区内的连陆台地和孤立台地均被淹没,形成罗楼组、马脚岭组等同时异相沉积地层底部的钙质泥页岩系凝缩段地层和其下全区普遍发育的较为典型的第Ⅱ幕淹没不整合面。这两幕淹没不整合面合称二叠系与三叠系之交的淹没不整合面,它们是三级层序SQ26的底界面,具有明显的穿时性;凝缩段是它们的主要标志。中二叠世冷坞末期和晚二叠世吴家坪末期的两幕东吴运动导致的研究区古地理背景的重大改变对淹没不整合面的发育有重要的影响。淹没不整合面的形成与二叠纪末期发生的全球淹没事件基本同步,是全球海平面急剧上升的结果,它对研究区的石油勘探具有积极的地质意义。

The attached platforms drowned for the most part and the condensed section (siliceous mudstone and shale of the Dalong Formation) forming, the First-Episode Drowned Unconformity under the condensed section developed when the First-Episode Drowned Event was caused by the rapid transgression in the Late Changhsingian of the Late Permian in the Dianqiangui Basin and its adjacent areas; the attached platforms and the isolated platforms all drowned and the condensed section (calcareous mudstone and shale of the Luolou Formation and the Maojiaoling Formation) forming, the Second-Episode Drowned Unconformity, under the condensed section which is more typical, developed when the Second-Episode Drowned Event was caused by the more rapid and larger transgression in the earliest Induan of the Early Triassic. As the third-order sequence boundaries under SQ_(26), the two drowned unconformities, whose main symbols are the condensed sections, combine the drowned Unconformities with remarkable diachronism in the transitional period from Permian to Triassic. Being influenced considerably by the important changes of paleogeographic background resulting from the two Dongwu Revolutions in the latest Lengwuan of the Middle Permian and the latest Wujiapingian of the Late Permian, The drowned unconformities, developed roughly in the same time with the global drowned Events leading from the rapid rise of the global sea-level from the latest Permian to the earliest Triassic, have positive geologic value to the oil exploration in our work areas.