峡东地区震旦纪最早期风暴沉积记录及其地质意义

作为全球地质环境的重要转折期，震旦纪早期发生的全球气候巨变和海平面显著上升等事件在世界范围内留下了大量记录。报道了震旦纪早期气候剧变阶段在我国南方陡山沱组底部形成的风暴沉积。岩芯剖面的精细观察和测量分析表明，峡东地区陡山沱组底部风暴岩沉积主要集中在陡一段白云岩与陡二段底部泥页岩中，发育的沉积构造主要有冲刷侵蚀底面、搅动层、粗粒滞留沉积、粒序层理、洼状交错层理、波状层理、波痕以及水平层理等。根据风暴岩垂向上的组合特征和沉积构造差异，共识别出五种风暴沉积序列，分别指示了不同的沉积背景:潮坪浅水沉积和陆棚深水沉积。其中，陡一段主要发育浅水风暴沉积，陡二段底部主要为深水风暴沉积，随着海平面的上升，自下而上风暴作用呈现加强的趋势。另外，在陡二段还发现了风暴浪基面以下形成的具粒序层理的泥砾岩。峡东地区陡山沱组底部的风暴沉积蕴含了强烈的古地理、古气候、古地貌以及地层信息，对于恢复震旦纪早期华南地质环境及其变化具有重要意义。

Early Sinian Storm Deposits in the Eastern Yangtze Gorges Area and their Geological Significance

As an important transition period of the global geological environment, geological responses during the Early Sinian to climate catastrophes and significant sea-level rise are found in the geological record all over the world. This paper is the first report of the effect of storm deposits in the lower part of the Sinian Doushantuo Formation in South China. Detailed observation and measurement of drill cores from the eastern Yangtze Gorges area show that storm deposits mainly developed in the first member and the lower part of the second member of the Sinian Doushantuo Formation (mainly dolostone and black mudstone, respectively). Sedimentary structures recognized include erosion surfaces, stirred layers, lag deposits, graded bedding, sunken cross-bedding, wave bedding, ripple marks, and horizontal bedding. Observed combinations of vertical features and sedimentary structural differences indicate five storm sequences at times of different sedimentary background (shallow-water environment in tidal flats, or deep-water environment in the continental shelf). The deposits from storms during the first member of the Doushantuo Formation indicate a mainly shallow-water environment; in the second member, storm deposits formed mainly in deep water, with the storm action strengthening upward. Moreover, black pebbly mudstone with graded bedding was recognized under or near the storm wave base. These observations indicate that the storm deposits in the lower part of the Doushantuo Formation contain a considerable amount of information (paleogeographical, paleoclimatic, paleogeomorphological and stratigraphical), and is of great significance for recovering Early Sinian geological environmental changes in South China.