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碳酸盐岩中燧石条带成因争鸣——以北京西山中元古界雾迷山组为例
投稿时间:2022-06-06  修订日期:2022-08-18  点此下载全文
引用本文:苏德辰,吕洪波,章雨旭,孙爱萍,朱晓青,贺静,袁效奇.2022.碳酸盐岩中燧石条带成因争鸣——以北京西山中元古界雾迷山组为例[J].地质论评,68(5):1605-1620,[DOI]:.
SU Dechen,LV Hongbo,ZHANG Yuxu,SUN Aiping,ZHU Xiaoqing,HE Jing,YUAN Xiaoqi.2022.An arguement on origin of chert bands in carbonate rocks——A case study of the Mesoproterozoic Wumishan Formation in the Western Hills of Beijing[J].Geological Review,68(5):1605-1620.
DOI:10.16509/j.georeview.2022.08.171
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作者单位E-mail
苏德辰 中国地质科学院地质研究所北京100037 sudechen@163.com 
吕洪波 中国石油大学(华东)地球科学与技术学院山东青岛266580  
章雨旭 中国地质科学院北京100037  
孙爱萍 中国地质科学院地质研究所北京100037  
朱晓青 中国地质调查局青岛海洋地质研究所山东青岛266071  
贺静 中国石油长庆油田分公司勘探开发研究院西安710018  
袁效奇 中国石油长庆油田分公司勘探开发研究院西安710018  
基金项目:本文为国家自然科学基金资助项目“华北克拉通中—新元古代古地震记录及多期裂解事件” (编号: 41772116)的成果
中文摘要:北京地区中元古界雾迷山组主要由燧石条带白云岩、燧石结核白云岩、叠层石白云岩和少量含陆源粉砂质碎屑的白云岩组成,广泛出露于北京山区,厚度2000~3500 m。以雾迷山组为代表的大量中元古代硅质沉积物的物源和形成原因,一般教科书均认为层状燧石为生物成因,结核状燧石为成岩交代成因。笔者等在北京西山等地多次野外考察发现,二维剖面上的硅质条带或硅质结核在三维实体上实际上是透镜状或席状(下一般称燧石席或硅胶席)。 燧石席内部常包裹或胶结有下伏白云岩的砾石并且因混有有机质等,表现为各种暗色或杂色。硅胶席在上覆白云质沉积物堆积之前与其周围的白云质灰泥和粒屑几乎同时形成,燧石透镜体与白云质沉积物之间存在着相互穿插、包裹的关系,但彼此之间边界清晰,无论是白云石粒屑还是燧石席都没有任何被交代痕迹。因此,笔者等认为:燧石“结核”是硅胶聚集成席,再经压实、固化的结果,其浑圆状边缘是水下硅胶与沉积介质的相变面。硅胶固化作用是北京西山中元古界雾迷山组中原生燧石的唯一成因。在成岩重力压实过程中,连续分布的原生硅质沉积物会形成布丁或“结核”构造。白云质灰泥和粒屑的胶结速度明显快于硅胶的固化速度,遇地震等外力作用,软的硅胶席会沿着弱固结的白云岩裂隙向上侵入或向下挤入,形成硅质脉。遇有后期的岩浆侵入或热变质作用的改造,硅质条带和硅质结核的成分和颜色会发生相应的变化,质地变纯,颜色由深变浅,但是仍然保留原生的层理或纹理,容易被误认为是成岩期或成岩后硅质交代碳酸盐矿物而成。
中文关键词:燧石条带  燧石结核  白云岩  硅胶席  半固结  交代作用
 
An arguement on origin of chert bands in carbonate rocks——A case study of the Mesoproterozoic Wumishan Formation in the Western Hills of Beijing
NameInstitution
SU DechenInstitute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037
LV HongboSchool of Earth Science and Technology, China University of Petroleum, Qingdao, Shandong, 266580
ZHANG YuxuChinese Academy of Geological Sciences, Beijing, 100037
SUN AipingInstitute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037
ZHU XiaoqingQingdao Institute of Marine Geology, China Geological Survey, Qingdao, Shandong, 266071
HE JingResearch Institute of Exploration and Development of PetroChina Changqing Oilfield Branch, Xi’an, 710018
YUAN XiaoqiResearch Institute of Exploration and Development of PetroChina Changqing Oilfield Branch, Xi’an, 710018
Abstract:The Mesoproterozoic Wumishan Formation in Beijing area is mainly composed of chert banded dolostone, chert nodule dolostone, stromatolite dolostone and a small amount of terrigenous silty clastic dolostone. It is widely exposed in the Beijing mountain area with a thickness of 2000~3500 meters. The provenance and cause of the formation of a large number of Mesoproterozoic siliceous sediments represented by the Wumishan Formation have been a controversial issue in the geoscience field for a long time. Most researchers believe that layered chert is biogenic and nodular chert is the diagenetic replacement. After detailed field investigations in the Western Hills of Beijing and other places, the authors have found that most of the siliceous bands or siliceous nodules (generally referred to as chert mat or siliceous gel mat in the following) occur on the sedimentary discontinuity surface, especially on the ancient erosion surface. The underlying dolostone gravels are often cemented with the siliceous material. The interior of chert mats is often mixed with impurities, especially organic matter, showing various dark and mottled colors. Chert mats were formed at the same time with surrounding dolomitic debris before the accumulation of the overlying dolomitic sediments. There is a relationship of mutual interpenetration and wrapping between chert mats and dolomitic sediments, but the boundaries between them are clear. Neither dolostone debris nor chert mat has obvious replacement trace. Therefore, the author believes that the “concretion” of chert is the result of silica gel aggregation and solidification. Silica gel solidification is the only genetic mechanism of primary chert in Wumishan Formation. Usually, the cementation rate of dolomitic mud and intraclast is obviously faster than that of silica gel mat. When an earthquake occurs or the overlying sediment is too thick, the soft silica gel will intrude upward or squeeze downward along the weakly consolidated dolostone fissure to form siliceous dykes. In the event of later magma intrusion or transformation by thermal metamorphism, the composition and color of chert strips and chert concretions will change accordingly. The texture becomes pure, and the color changes from dark to light, but the original bedding or texture is still retained, which is easily mistaken for diagenetic or post-diagenetic siliceous replacement of carbonate minerals.
keywords:chert strip  chert nodule  dolostone  silica gel mat  semi-consolidation  replacement
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