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Pushuiqiao Formation

Pushuiqiao Fm

Period: 
Triassic

Age Interval: 
Early Early Triassic (TJ34)


Province: 
Xizang (Tibet)

Type Locality and Naming

Sichuan geological bureau third area survey team named in 1974. The named section is located at Pushui Bridge, east of Jiangda County, Tibet Autonomous Region. The Pushuiqiao Formation represents a set of clastic and pyroclastic strata mainly distributed in the middle and late Indian of the Early Triassic in the Jiangda area

Synonym:


Lithology and Thickness

It is mainly composed of clastic rocks and pyroclastic rocks, which can be divided into upper and lower members. Lower member (purplish red rock member) consists of purplish red massive tuffaceous conglomerate and purplish red thick siltstone and pebbled sandstone lens. Upper member (grey-green member) consists of medium-thick grey-green to massive dacitic tuff, tuff breccia, tuff lava, argillaceous siltstone with gray thin layers of sandy limestone, gravel limestone and a small amount of purplish red dacitic tuff breccia. The total thickness is about 600 meters.


Lithology Pattern: 
Volcanic ash


Relationships and Distribution

Lower contact

At the bottom, the purplish red conglomerate is unconformable to the Paleozoic granites in different horizons or the Warrissian granites.

Upper contact

At the top, the grey-green tuff has conformable contact with the overlying Serongsi Fm

Regional extent


GeoJSON

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Fossils

It contains bivalve fossils Eumorphotis multiformis-Claraia clarai assemblage and gastropod fossils Natiria cf. costata.


Age 

In 1987, Rao Rongbiao et al. discovered Late Triassic ammonoids Hauerites sp., Cryptenerites sp. Styrites sp. in the limestone of the named site of the Serongsi Fm (overlaying the Pushuiqiao Fm). Therefore, it is suggested that the Silongsi Fm should be abandoned and the limestone stratum should be regarded as the seventh member of the Pushuiqiao Fm, and the age of the Pushuiqiao Fm should be revised from the Early Triassic Indian to the Olenekian. Tong et al. (2019, Triassic integrated stratigraphy and timescale in China, Science China: Earth Sciences, v. 62, no. 1) assign it as spanning the Induan, only.

Age Span: 

    Beginning stage: 
Induan

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
251.90

    Ending stage: 
Induan

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
249.88

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Zhang Shunxin, Xiong Feng and Tong Jinnan.