Dapo Fm
Type Locality and Naming
The Dapo Formation was erected by the Guangxi Regional Geological Survey Team in 1962. The section for the designation is at Dapoyu of the Pingnan county of Guangxi. The Dapo Formation represents the strata between the Xinlong Fm and the Shuangyuzui Fm in the Dapoyu of Pingnan County, Guangxi, which was assigned to Early Cretaceous. The formation is the second rock formation of the Yongfu Gr.
Lithology and Thickness
The Dapo Formation is composed primarily of purple red clastic sedimentary rocks. Its basal part is represented by purple red massive conglomerate and gravel-bearing sandstone. Lower part is sandstone and mudstone. Upper part is siltstone and mudstone. The formation is 760 m thick.
Relationships and Distribution
Lower contact
Its base is separated from the clayey siltstone of the underlying Xinlong Fm by massive conglomerate.
Upper contact
Its top is separated from the gravel-bearing sandstone of the Shuangyuzui Fm by sandy mudstone.
Regional extent
The formation mainly occurs in the Dazhou, Shuiwen and Shiwandashan basins of southeast Guangxi. It varies considerably in thickness. In the Dazhou basin, the basal conglomerate commonly contains purple red clayey lumps; its lower part is built up by sandstone and argillite, while its upper part siltstone and mudstone. In the Shuiwen basin, the basal conglomerate is generally thick; the upper part of the formation contains a relatively large amount of calcareous siltstone and mudstone in the east section of the basin. In the Shiwandashan basin, sediments are quite coarse in the eastern part with the thickness increasing from west to east. The formation is 1851-1618 m thick in the Shuiwen basin, 760 m in the Dazhou basin and 511 m in the Shiwandashan basin.
GeoJSON
Fossils
It yields ostracods Lycopterocypris debilis, Cypridea sp.; bivalves Trigonioides kodairai, Nakamuranaia chingshanensis, Nippononaia yunnanensis; and gastropods Hydrobia sp.
Age
Depositional setting
It is of fluvial-lacustrine sedimentation.
Additional Information