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Banggui Formation

Banggui Fm

Period: 
Cambrian, Ordovician

Age Interval: 
late Niuchehean through Early Ordovician (44)


Province: 
Sichuan

Type Locality and Naming

The type section is Banggui-Liuranka section in Zongza Township, Batang County, western Sichuan Province (99°23’30” E, 29°21’30” N). The section lies about 8.7 km northeast of Zongza Town and was measured by the No. 3 Brigade of Sichuan Regional Geological Survey Team in 1972. The Banggui Formation was named by the No. 2 Brigade of Sichuan Third Regional Geological Survey Team (1977). The name is derived from Banggui Village in the Zongza Township, Batang County, Ganzi Tibetan Autonomous Prefecture, western Sichuan Province.

Synonym: (邦归组)


Lithology and Thickness

The formation is mainly a carbonate sequence, composed of crystalline limestone, medium-grained crystalline dolomite, fine to coarse dolomitic marble, intercalated a few of silty slate or medium-bedded slate. In the type section, the formation is over 1477.4 m thick.


Lithology Pattern: 
Dolomitic limestone


Relationships and Distribution

Lower contact

The Banggui Fm rests conformably on the clastic Songdagou Fm

Upper contact

It is disconformably overlain by the Silurian Gezhadi Fm of multi-colored breccia limestone.

Regional extent

The Banggui Formation is exposed in Northern Qangtang-Simao Region, restricted only in the Zongza district, Batang County, western Sichuan Province.


GeoJSON

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Fossils

The basal part of the formation is non-fossiliferous. The lower part of the formation yields brachiopod Aparthophyla sp. and the middle part yields graptolites Callograptus spp., trilobite Illaenus cf. sinensis and brachiopods Finkelnburgia, Orthis, Orthambonites, and Tetraodontella.


Age 

The formation has a late Niuchehean through Early Ordovician age. It has been long regarded to be Early Ordovician in age because the fossils reported from the formation were all considered to be Early Ordovician age (Gu and Liu, 1997). However, in Utah, Great Basin, USA Finkelnburgia is known in the Finkelnburgia Zone (equivalent to conodont Cambrooistodus minutus Subzone of Cordylodus proavus Zone) Cambrian (Miller et al., 2011), which belongs certainly to upper provisional Stage 10 of Cambrian. In addition, as the formation overlies conformably on the Songdagou Formation in the Zongza district, the youngest strata of which is early Niuchehean age. Therefore the Banggui Formation should embrace strata of the latest Cambrian age (late Niuchehean). This conclusion may be further supported by the evidence that the basal interval of the formation, at least 270 m thick, is non-fossiliferous, and the “Early Ordovician fossils” are only known from younger strata of the Banggui Formation, the non-fossiliferous should be also Cambrian in age.

Age Span: 

    Beginning stage: 
Cambrian Stage 10

    Fraction up in beginning stage: 
0.5

    Beginning date (Ma): 
488.93

    Ending stage: 
Tremadocian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
477.08

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Peng Shanchi