江苏徐州赵圩剖面新元古界倪园组沉积环境演化与事件沉积

江苏徐州赵圩剖面新元古界倪园组出露完整连续,岩性组合极具代表性,沉积现象丰富,发育有大量典型的事件沉积,因其成因存在争议而长期受到关注。本研究以倪园组野外宏观岩性组合及镜下微观岩石特征为基础,依据宏观—微观对照的方法,分析了倪园组沉积环境及事件沉积特征,探讨了事件沉积频发及类型多样的成因。研究表明: (1)倪园组沉积环境自下而上依次为潟湖—缓坡中上部—缓坡中下部—缓坡中上部—潮坪+潟湖; (2)事件沉积在各段的发育情况均有所区别,其中砾屑灰岩与冲刷—充填构造在各段均有发育,但下段与中段规模较大,除此之外,中段局部见震裂角砾岩、液化底辟构造,顶部发育臼齿构造,而上段底部以臼齿构造为主,中上部见软沉积物变形构造以及交错层理,结合沉积环境分析,认为事件沉积主要发生于缓斜坡环境以及潮坪、潟湖环境; (3)综合以上研究结果,认为倪园组频发—多类型事件沉积与正常沉积构成的特殊旋回,其动力机制或与周期性的地震—风暴作用有关,即可能为Rodinia古大陆的汇聚—裂解导致的华北地台东缘伸展型区域构造运动与米兰科维奇旋回的叠加而引发的多因素耦合作用的结果。

Sedimentary environment evolution and event deposition of the Neopro-terozoic Niyuan Formation of Zhaowei section in Xuzhou,Jiangsu Province,China

The Neoproterozoic Niyuan Formation in Zhaowei, Xuzhou is exposed completely and continuously, with representative lithologic assemblages, abundant sedimentary phenomena, and a large number of typical event deposits, which has been a concern for a long time because of its controversial genesis. Based on the field macro lithologic assemblage and microscopic rock characteristics of the Niyuan Formation, and by means of macro-micro comparison, this paper analyzes the sedimentary environment and event sedimentary characteristics of the Niyuan Formation and discusses the causes of frequent occurrence and diverse types of event deposition. The results show that: (1) The sedimentary environment of the Niyuan Formation from base to top is lagoon-the middle and upper part of the gentle slope-the lower part of the gentle slope-the middle and upper part of the gentle slope-tidal flat or lagoon; (2) The development of event deposits in each section is different. Gravelly limestone and scouring filling structure are developed in each section, but the lower and middle sections are large. In addition, seismic breccia and liquefied diapir structure are seen in some parts of the middle section, molar-tooth structure is developed at the top, while molar-tooth structure is mainly seen at the bottom of the upper section, and soft sediment deformation structure and cross bedding are seen in the middle and upper part. Based on the analysis of sedimentary environment, it is considered that the event sediments mainly occurred in the gentle slope environment, tidal flat and lagoon environment; (3) Synthesizing the above research results, it is concluded that the dynamic mechanism of the special cycle composed of frequent multi-type event sedimentation and normal sedimentation of the Niyuan Formation may be related to periodic earthquake-storm action, that is, it can be the result of multi-factor coupling effect caused by the superposition of extensional regional tectonic movement on the eastern margin of North China platform and the Milankovitch cycle caused by the convergence and fragmentation of the Rodinia paleocontinent.