贵州平塘甘寨剖面二叠系茅口组沉积特征与层序地层

Sedimentary characteristics and sequence stratigraphy of the Permian Maokou Formation in the Ganzhai section, Pingtang, Guizhou

关键词:  贵州平塘  黔南坳陷  茅口组  沉积特征  层序地层

Key words:  Pingtang in Guizhou  southern Guizhou depression  Maokou Formation  sedimentary characteristics  sequence stratigraphy

摘要:

本文应用沉积学手段对贵州平塘甘寨剖面中二叠统茅口组进行详细的沉积特征和层序地层的研究。研究结果显示,茅口组主要的岩石类型有亮晶-微晶生屑灰岩、生物灰岩、微晶灰岩、亮晶内碎屑灰岩、硅质岩、瘤状灰岩和含燧石灰岩等,茅口组生物种类有介形虫、腹足、腕足、三叶虫、藻类、棘屑、蜒、珊瑚、海百合茎等。岩石学特征和生物组合指示,平塘甘寨地区中二叠统茅口组为开阔碳酸盐台地沉积环境,包括台内滩和滩间两个亚相。茅口组可划分出3个Ⅲ级层序PSQ1、PSQ2和PSQ3,均由海侵体系域(TST)与高水位体系域(HST)两部分组成。层序发育受到了海平面升降变化控制,层序之间的界面P₂q/PSQ1、PSQ1/PSQ2、PSQ2/PSQ3皆为岩性-岩相转换面,层序界面P₃l/PSQ3在茅口末期受到东吴运动的影响,为构造不整合面。

Abstract:

According to the sedimentological methods, the present paper deals, in detail, with the sedimentary characteristics and sequence stratigraphy of the Permian Maokou Formation in the Ganzhai section, Pingtang, Guizhou. The rock types of the Maokou Formation mainly consist of sparry-micritic bioclastic limestone, biogenic limestone, micritic limestone, intrasparite, siliceous rocks, nodular limestone and cherty limestone. The fossil types in the Formation comprise ostracods, gastropods, brachiopods, trilobites, algae, echinoderms, fusulinids, corals and crinoids. The lithology and fossils cited above indicate the open carbonate platform sedimentary environment of the Permian Maokou Formation. Three third-order sequences have been distinguished, including PSQ1, PSQ2 and PSQ3, all of which are built up of the transgressive (TST) and highstand (HST) systems tracts. The development of these sequences may be controlled by the sea-level changes. The sequence boundaries P₂q/PSQ1, PSQ1/PSQ2 and PSQ2/PSQ3 represent lithologic-lithofacies transform surfaces. The sequence boundary P₃l/PSQ3 exhibits a tectonic unconformity due to the influence of the Dongwu movement during the latest Maokouan.