Hanxia Fm
Type Locality and Naming
It was named Hanxia System by Wang Shangwen in 1945 and first quoted by Yu Changming in 1956. The Gansu Geological Bureau revised the name to Hanxia Group in 1976, and Hanxia Formation in 1997. The type section is at Hanxiagou, west of Yumen County, Gansu Province. Coordinate: 39°49′N, 97°08′E.
Synonym: （旱峡组）
Lithology and Thickness
It is dominated by purplish red thick-bedded siltstone and sandstone intercalated with conglomerate. It bears raindrop prints and ripple marks. Fossils are rarely found. The thickness is 1903 m in the type section.
Relationships and Distribution
Lower contact
Conformable contact with the underlying Quannaogoushan Fm
Upper contact
Unconformable with the overlying Laojunshan Fm of Devonian (not in Dev lexicon entries); elsewhere the schematic strat column indicates overlain by the Xueshan Gr of early Devonian.
Regional extent
The formation is widely exposed from Hongkouzi of Anxi County in the west, to Songdaban of Sunan County via Changma of Yumen County in the east; further eastwards to Haiyuan County and Tongxin County of the Ningxia Hui Zizhiqu. It gets thinner and thinner in thickness towards its eastern and western ends in the distribution area: 169 m thick at Hongkouzi of Anxi County, 1903 m thick at the type section locality in Hanxiagou of Yumen, eastwards 10000 m thick at Hongshuiba River of Sunan County, 1579 m at Haihe, and 421 m at Tongxin of Ningxia.
GeoJSON
Fossils
The fossils are rare in this formation. The corals such as Palaeofavosites hanhsiensis, Favosites sp., Syringopora sp., Tryplasma cf. princeps, and trilobite Scutellum (Thysanopeltella) sp., are occasionally found in the formation.
Age
Depositional setting
The formation belongs to littoral-neritic facies. The Silurian sequence demonstrated a large-scale regression sequence from deep-sea turbidite deposits at the lower part to the neritic-littoral deposits at the top.
Additional Information