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Sanhedong Formation

Sanhedong Fm

Period: 
Triassic

Age Interval: 
Early-Middle Late Triassic (TJ49)


Province: 
Yunnan

Type Locality and Naming

The original Sanhedong Fm is divided into lower limestone section and upper black shale section, representing the Late Triassic Carnian-Norian deposits distributed in the Weishan area of Yunnan. The named section is located in Sanhe Cave near Waigu Village, Ma'anshan Township, Weishan, Yunnan.

Synonym:


Lithology and Thickness

It is mainly light to dark gray thick limestone with a small amount of argillaceous limestone, marl and sandstone, with flint clumps or flint nodules on the top. It is 276 m thick.


Lithology Pattern: 
Limestone


Relationships and Distribution

Lower contact

Its bottom is conformable in contact with the coral limestone on the top of the underlying Waigucun Fm

Upper contact

It has a conformable contact with the overlying Waluba Fm

Regional extent

It is exposed from Weishan Mountain in Yunnan via Eryuan, Jianchuan, Weixi to Deqin County in the north. The thickness of Weishan Mountain is the largest, with a thickness of 274 to 296 m; The area from the north to the Hetaoshu area is 80-100 m; it also becomes thinner to the east and west.


GeoJSON

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Fossils

Bivalves Halobia pluriradiata, H. cf. yunnanensis, Modiolus cf. pygmaeus, Jianchuania sp. etc. At the Baijizu Mountain in Jianchuan County, this formation contains bivalves Halobia ganziensis, H. yandongensis, H. yunnanensis, H. pluriradiata, Cassianella cf. angusta, Angustella cf. rugosa; Ammonoid Rhacopyllites sp., Thisbites sp., Anatibetites sp., Partibetites sp. etc.


Age 

In 1975, the first area survey team of Yunnan geological bureau determined the age of the group as the middle of late Triassic. In 1984, Liu Huaizhi further defined the age of the group as from the late Carnian to the early Norian in the Late Triassic. In 1990, Yunnan Bureau of Geology and Mineral Resources revised the definition of Sanhe Dong Formation and defined it as the lower limestone section of the named Sanhe Dong Fm, and the age was defined as the late Carnian period. The black shale section on it is named as the Eight Dailu Fm. This lexicon follows the last meaning and holds that this group may extend to the early Norian in some areas. Schematic stratigraphic section suggests span of late Carnian.

Age Span: 

    Beginning stage: 
Carnian

    Fraction up in beginning stage: 
0.5

    Beginning date (Ma): 
232.15

    Ending stage: 
Carnian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
227.30

Depositional setting

This group is a shallow sea deposit with stable lithology and a wide distribution.


Depositional pattern:  


Additional Information


Compiler:  

Zhang Shunxin, Xiong Feng and Tong Jinnan.