Abstract: The Meso-and Neoproterozoic section of Jixian in Tianjin, China is highly worthy of integrated research, in which the Yangzhuang Formation takes the role of linking the old and new strata. The thickness of Yangzhuang Formation is small compared with the whole Proterozoic section, but it has multiple types of rocks with special origins. The main kinds of rocks include carbonate rocks, tuffite, siliceous rocks and quartz sandstone. Carbonate rocks are predominantly composed of intra-clastic dolostone, chert dolostone and sand-bearing dolostone. Tuffite is formed by the combination of volcanic ashes and carbonate mud. The thin-bedded siliceousrocks include chert and depositional quartz with textures of oolite and pebble. The quartz sandstone appears in the upper member of Yangzhuang Formation as thin-bedded strata with double peaks of grain size distribution. The petrology reveals that the sedimentary environment of the study area is carbonate tide-flat and shallow sea which is also strongly affected by the volcanic materials and wind-brought clastics during the period of Yangzhuang. The mentioned volcanic activity in Yangzhuang Formation is expected to propel the study of the Proterozoic chronology and tectono-sedimentary evolution of North China.

Key words: North China, Mesoproterozoic Yangzhuang Formation, petrology, volcanic activity

摘要： 天津蓟县中、新元古界剖面具有极高的综合研究价值，而杨庄组在该剖面中居于承上启下的位置。杨庄组在整个中、新元古界剖面中厚度不大，但其岩石类型多样且成因特殊。主要岩石类型包括碳酸盐岩、沉积凝灰岩、硅质岩和石英砂岩。碳酸盐岩以内碎屑白云岩、燧石白云岩和含砂白云岩为主。沉积凝灰岩主要为中远源的火山灰与碳酸盐灰泥混合而成，含石英团块，显斑点构造。硅质岩包括燧石和沉积石英岩，呈薄层状产出，沉积石英岩具鲕状、砾状结构。石英砂岩呈薄层出现在杨庄组上部，具双众数结构。上述岩石特征表明，研究区在中元古代蓟县纪早期的杨庄期为浅海潮坪碳酸盐沉积环境，沉积作用受中远源火山物质和风携碎屑的强烈影响。杨庄期火山活动可能提供华北地区中元古代年代地层学和构造沉积演化研究的新证据。

关键词: 华北, 中元古界杨庄组, 岩石特征, 火山活动