| 天津蓟县晚元古代冰碛岩的发现 |
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| 引用本文： | 史书婷,王金艺,郭芪恒,金振奎,朱小二,王昕尧,李阳,李硕,任奕霖,王凌.天津蓟县晚元古代冰碛岩的发现[J].沉积学报,2019,37(6):1181-1192. |
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| 作者姓名： | 史书婷 王金艺 郭芪恒 金振奎 朱小二 王昕尧 李阳 李硕 任奕霖 王凌 |
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| 作者单位： | 中国石油大学 (北京) 地球科学学院, 北京 102249 |
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| 基金项目： | 国家重点基础研究发展计划（973计划）项目（2006CB202300） |
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| 摘 要： | 在对华北板块中北部天津蓟县中、新元古界的研究中发现,在新元古界青白口系景儿峪组之上、早寒武世府君山组之下,发育一套角砾岩,其究竟属于晚元古代还是早寒武世,并没有确切证据。由此推测为晚元古代并将这套地层命名为“西井峪组”。通过对西井峪组角砾岩的野外实测、薄片观察,对角砾岩的沉积特征做了详细的描述,并对其成因及物源进行了分析。结果表明:西井峪组为一套厚155 m的角砾岩,并可根据角砾成分和大小的变化分为九段。这套角砾岩中角砾的成分主要为白云岩,还有少量的燧石及石灰岩;整体呈块状,无层理,无层面;角砾含量80%~90%,杂乱排列,大小混杂,分选差,磨圆差,普遍为棱角状和次棱角状,填隙物主要为白云石泥和粉砂,结构成熟度极低。角砾的母岩主要是中元古界蓟县系雾迷山组,少量来自铁岭组。这套角砾岩属于冰川成因,为典型的冰碛岩。这套冰碛岩的发现对恢复晚元古代地球气候特征具有重要意义,其出现或许与“雪球地球”有关。
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| 关 键 词： | 蓟县 晚元古代 西井峪组 冰碛岩 冰川 |
| 收稿时间： | 2019-08-27 |
Discovery of Tillite in the Late Proterozoic at Jixian County of Tianjin,North China |
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| Institution: | College of Geosciences, China University of Petroleum(Beijing), Beijing 102249, China |
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| Abstract: | In the Middle and Neoproterozoic in Jixian county,Tianjin in the north-central part of the North China Plate,a set of breccia was developed above the Jingeryu Formation of the QingBaikou system and the Fujunshan Formation of the Early Cambrian. There is no definitive evidence of whether it belongs to the Late Proterozoic or Early Cambrian. The author speculates that it is the Late Proterozoic and named the formation the "Xijingyu Formation." The sedimentary characteristics of the breccia in the Xijingyu Formation are described in detail through field measurements and thin slice observation,and its genesis and provenance were analyzed. The results show that the Xijingyu Formation is 155 m thick and can be divided into 9 sections according to the change of breccia composition and size. The composition of the breccia is mainly dolomite,with a small amount of chert and limestone; the formation is blockshaped,without bedding or layering;the breccia content is 80%-90%,disorderly arranged,and mixed in size,The sorting and roundness are poor,and it is generally angular and sub-angular. The interstitial is mainly dolomite mud and silt,and the structural maturity is extremely low. The parent rock of the breccia is mainly the Wumishan Formation from the Middle Proterozoic,and a small amount is from the Tieling Formation. This breccia is glacial in nature and is a typical tillite. The discovery of the tillite is of great significance for restoring the characteristics of the Late Proterozoic Earth's climate, and its emergence may be related to the "Snowball Earth". |
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