Ziyun Fm
Type Locality and Naming
Guizhou Geological Bureau 108 team named in 1966. The named section is located in Xinyuan to Bandang in the suburb of Ziyun County, Guizhou.
Synonym:
Lithology and Thickness
It is mainly composed of gray medium thick breccia clastic limestone and micritic limestone, calcareous and siliceous claystone with unequal thickness interbedded. It can be divided into two lithologic units: Lower unit is mainly composed of thick gray and purplish red layers, massive brecciate calcareous limestone, medium and thin micritic limestone, grey-green and purplish red shale and siliceous shale, often with gradation characteristics and catchment structure, sliding flexure structure. Upper unit is mainly gray and dark gray thin lamellar argillaceous banded micrite (and silty) limestone, with siliceous shale and calcareous shale. Thickness 20 to 210 m.
Relationships and Distribution
Lower contact
At the bottom, the thick, massive breccia-rich calcareous limestone is conformable with the underlying thin micrite limestone of the Chayeshao Fm (Guizhou) or with the Luolou Gr (Guangxi).
Upper contact
Ziyun Fm is in conformably overlain by the Xinyuan Fm. Gan Xiuming (1983) first proposed that a stable layer of yellowish-green montmorillonite vitric tuff (commonly known as "mung bean rock" or "Green Bean" volcanic ash horizon) was used as the lower boundary of Xinyuan Fm.
Regional extent
GeoJSON
Fossils
Ammonoids: Owenites-Meekoceras zone and Tirolites-Procarnites zone. Bivalves: Claraia aurita
Age
Depositional setting
The Yuanziyun Formation represents the Early Triassic Olenekian sedimentary facies of the broad sea basin in the Ziyun area of Guizhou. According to Guizhou Bureau of Geology and Mineral Resources (1987), the Ziyun Formation represents the slope facies calcareous gravity flow deposits of this age in southern Guizhou.
Additional Information