Xiawuna Fm
Type Locality and Naming
The type section is located at Dangduogou, 24 km northwest of Diebu County of Gansu Province.
It was named by Zhang Yan in 1961 and was published in 1976 by Regional Stratigraphic Scale, Volume Gansu.
Lithology and Thickness
The Formation, 300-400 m thick, is composed of two sedimentary cyclic sequences.
Calcareous sandstone. The lower part of the first cycle consists of gray medium- to thick-bedded calcareous quartz sandstone, clayey siltstone and shale; and the upper part is gray thick-bedded to massive sandstone and bioclastic limestone
Sandstone, limestone. The second cycle consists of a lower part of light-brownish-gray medium- to thick-bedded iron-bearing quartz sandstone and silty limestone with sandy shale, and an upper part of gray medium- to thick- bedded microcrystalline limestone, bioclastic limestone and stromatoporoid-bearing limestone with a few siltstone layers.
Relationships and Distribution
Lower contact
It conformably overlies the Lure Fm limestone or the coeval Lubagou Fm dolomite
Upper contact
It conformably underlies the Pulai Fm.
Regional extent
The Formation is widely distributed in the western Qinling Mts. with relatively persistent lithology and thickness of 300-400 m.
GeoJSON
Fossils
The upper part of the first cycle contains coral Dendrostella trigemma-Fasciphyllum crassithecum Assemblage Zone.
The upper part of the second cycle contains brachiopoda Geranocephalus xiawunaensis-Scharkovaelites sinensis Assemblage Zone, Strigocephalus Acme Zone, and conodont Icriodus arkoeensis in the upper part.
Age
Depositional setting
The upward trend of sedimentary environments of each cyclic deposit shows a shallowing from shallow shelf to a carbonate platform.
Additional Information