Dazhuang Fm
Type Locality and Naming
Southeast Shaanxi (east of Xian). The Dazhuang Fm was named by the Lingkou Subteam of Geology Department of Northwest University and the No. 713 Team of Shaanxi Bureau of Metallurgy in 1977. The typical section is located in Dazhuang (Fengfeng Mountain) in Shangsidian, Luonan County, Shaanxi Province.
Synonym: （大庄组）
Lithology and Thickness
The Dazhuang Fm consists of yellowish gray muddy and silty dolomite bearing stromatolites, It is dominantly composed of dolomicrite, chert and siliceous slate, which is subdivided into two members by a disconformable surface (ferruginous sediment). Lower member is a carbonate facies composed of pelitic and sandy dolomite intercalated with siliceous slate. Upper member consists of microclastic rock, dominantly pelitic slate, carbonaceous slate and siliceous slate, which belongs to the neritic facies. The total thickness is about 400 m.
Relationships and Distribution
Lower contact
The Dazhuang Fm disconformably overlies the underlying Fengjiawan Fm (upper Guandaokou Gr ; Jixian, mid Mesoproterozoic)
Upper contact
It is unconformably overlain by the Luoquan Fm with a layer of gray pelitic slate.
Regional extent
Southeast Shaanxi (east of Xian). With a persistent lithology, the Dazhuang Fm considerably varies in thickness along outcrop length, on west of Wujiagou in Luonan it is absent, eastward to Zhifang, it is gradually increasing, in Shibeigou with 20 m, in Sangpingchuan with 138 m, in Poxianggou with 155 m and around Gaogou-Shijiwan with 508 m, showing a trend of thicker in east and thinner in west.
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Fossils
Age
Depositional setting
Additional Information