碳酸盐台地淹没过程的微相响应——以陕西铜川桃曲坡奥陶系剖面为例  

Microfacies Response to the Drowning Process of the Carbonate Platform:A Case Study on the Ordovician Succession at the Taoqupo Section,Tongchuan City,Shannxi Province,North China Block

作　　者：刘采[1] 秦松[2] 苏文博[1] 傅力浦[3] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]四川省地勘局区调队,四川双流610213 [3]中国地质调查局西安地质矿产研究所,陕西西安710054

出　　处：《地质调查与研究》2013年第1期23-38,共16页Geological Survey and Research

基　　金：国家自然科学基金项目(40772076;41272046);国家科技部973项目:若干重大地质环境突变的地球生物学过程(2011CB808800)

摘　　要：晚奥陶世早期,位于华北板块西南缘的鄂尔多斯盆地南缘发生了一次台地淹没事件,致使鄂尔多斯南缘台地由镶边碳酸盐台地转变为远端变深的缓坡台地。作为这个台地边缘的代表性剖面─陕西铜川桃曲坡中上奥陶统剖面保存了此次碳酸盐台地淹没过程的完整记录。野外观测和室内微相分析表明,这一淹没过程可划分为淹没前阶段、淹没阶段及后淹没阶段三个不同的沉积阶段。淹没界面位于泾河组与金粟山组之间,沉积相由台地边缘礁相突变为陆棚边缘相。(1)淹没前阶段:其建造为泾河组上部沉积,微相主要包括生屑亮晶灰岩、球粒亮晶灰岩、被包壳的生屑亮晶灰岩、内碎屑亮晶砂屑灰岩,台地边缘礁相沉积,指示一种正常浅海台地环境;(2)淹没阶段:其建造为泾河组-金粟山组交界处及金粟山组下部沉积,微相主要为泥晶灰岩、含生屑泥晶灰岩,代表了深水陆棚沉积环境;(3)后淹没阶段:代表性建造为金粟山组中上部及桃曲坡组沉积,主要微相有含生屑泥晶灰岩、稀少的生屑泥晶灰岩和骨针泥灰岩,呈现深水陆棚-斜坡沉积环境。区域资料表明,该台地淹没的主要原因是鄂尔多斯南缘镶边碳酸盐台地受扬子板块向华北板块俯冲消减作用的影响发生阶梯状断裂,造成了台地的最终淹没。桃曲坡剖面自泾河组上部到金粟山组下部的微相组合是对这一宏观过程的微观响应。During the Late Ordovician Period, the carbonate platform at the south margin of the Ordos region, North China Block, had been drowned. This drowning caused the earlier rimmed-carbonate platform into the later distal steepened-ramp ones. As the most representative section at the south margin of this platform, the Taoqupo section in Tongchuan City, Shaanxi Province, entirely recorded this drowning process. Based on the observation at the outcrop and the microfacies analysis under the thin-sections, three phases of the drowning process of the carbonate platform can be distinguished, including the pre-drowning phase, the drowning phase and the post-drowning phase. At this section, the drowning surface is the litho-stratigraphical boundary between the Jinhe Formation and the Jinsushan Formation, which indicates an abrupt change of the depositional environment from the typical reef-shoal-dominated platform into the much deeper water facies around the offshore shelf area. The pre-drowning phase is the upper part of the Jinhe Formation, which is characterized by the typical platform-marginal biohermal facies with the bio-sparite microfacies, the pelmicsparite microfacies, and the coated bioclastic grainstone microfacies, as well as the intra-spararenite microfacies; The drowning phase is a condensed depositional interval at the base of the Jinsushan Formation, mainly represented by the micrite and fossiliferous micrite in microfacies, which suggests a deeper water offshore shelf environment; The post-drowning phase is the middle and upper part of the Jinsushan Formation and the lower of the Taoqupo Formation, which was shown by the off- shore shelf to the slope of the platform-margin facies with the fossiliferous micrite, the sparse biomicrite and the spiculite marlstone in microfacies. Combining with the regional data of the stratigraphic and the tectonic research, it can be concluded that this drowning event should be triggered by the ladder-shape faults developed at the margin of the Ordos carbonate platform, caused

关 键 词：台地淹没 碳酸盐微相 奥陶纪 桃曲坡剖面 鄂尔多斯南缘 

分 类 号：P543.63[天文地球—构造地质学]