Jushitan Fm

Lithology and Thickness:

Shale. It is divisible into three parts as follows: Lower part is composed of black shale, intercalated with black sandy limestone. Middle part is composed of grey-black and yellow-green medium- and fine-grained sandstone and shale, intercalated with sandy limestone lenses. Upper part consists of yellow-green shale, intercalated with sandy limestone lenses. Thickness is 182 m.

Lithology-pattern: Claystone

Relationships and Distribution:

Lower contact:

Conformable contact with the underlying Shuanguotang Fm.

Upper contact:

Conformable (but diachronous) with Jinta Fm volcanics

Regional extent:

Distributed in the Heishan Mt. area of Anxi County, with a thickness of 900 m; while in the area of Biyun Spring its thickness reaches as great as 400 m.

GeoJSON:

Fossils:

Ammonoids represented by Stacheoceras, Waagenoceras, Daubichites, Strigogoniatites.

Age:

Ammonoids belong to the Xiangbo’an and Kufengian Stages of the middle Permian = latest Cisuralian to mid-Guadalupian epochs

Age Span:

Beginning stage: Kungurian

Fraction up in beginning stage: 0.5

Beginning date (Ma):

Ending stage: Kungurian

Fraction up in ending stage: 1.0

Ending date (Ma):

Depositional setting:

It is interpreted as shallow-sea deposits.

Depositional-pattern:

Additional Information

Owing to the fact that no obvious boundary exists between the Jushitan Fm and the Shuangbaotang Fm in the reference section, there occurs a tendency to call the two formations jointly the Shuangbaotang Fm. But in the present Lexicon the name of the Shuangbaotang Fm is applicable strictly only to such a lithologic association which comprises mainly coarse clastic rocks and limestone, while the Jushitan Fm represents distal turbidite comprising essentially siltstone and shale.