Niaoge Fm

Synonym: Nuoge shale.

Lithology and Thickness:

It is mainly composed of gray thin siltstone interbedded with sandstone. Lower part is gray green calcareous mudstone, dark gray thin limestone, argillaceous limestone interbedded with brown gray shale. Upper part is gray-black calcareous shale, gray-green mica bearing sandy shale, interbedded with gray medium fine sandstone. Thickness is 398 m.

Lithology-pattern: Shallow-marine marl

Relationships and Distribution:

Lower contact:

It has a conformable contact with the underlying Tuowei Fm

Upper contact:

It has a conformable contact with the overlying Huobachong Fm

Regional extent:

The formation is mainly distributed in Kaiyuan, Jianshui, Gejiu, Yunnan, with a general thickness of 500-800 m and a thickness of about 1000 m locally. The lower part of the formation is only sporadically exposed in the area of Gejiu and Wenshan, with a wide distribution but not very stable, sometimes thin and sometimes thick, and turns into yellow shale in some areas.

GeoJSON:

Fossils:

Rich in bivalve and ammonoid fossils, mainly Protrachyceras deprati, P. costulatum, Monophyllites sp., Discotropites cf. sandlingensis, Sirenites cf. irregularis, Halobia rugosa, H. rugosoides, H. superba, H. yunnanensis, H. pleuriradia etc. There is also a small number of plant fossils Clathropteris cf. Meniscioides.

Age:

Carnian. [However, Tong et al. (2019) interpret the overlying Huobachong Fm fine sandstone as beginning in upper-mid Norian; hence, for graphic purposes, its upper boundary is put at that level for consistency.]

Age span:

Beginning stage: Ladinian

Fraction up in beginning stage: 0.8

Beginning date (Ma):

Ending stage: Norian

Fraction up in ending stage: 0.65

Ending date (Ma):

Depositional setting:

Nearshore shallow marine.

Depositional-pattern:

Additional Information

It is named as Niaogege shale, which refers to a set of shale-dominated strata distributed in the Niaoge Coalfield, Kaiyuan, Yunnan, between the underlying Qinglong limestone and the overlying Huobachong coal measures, and the age is defined as the Late Triassic. Wang and Lu (1940) divided the Triassic system of Kaiyuan Niaoge coalfield into five layers, the middle layer of which was Niaoge shale. Xu (1944) identified the fossils contained in Niaoge shale and determined that the age of Nuoge shale was Ladinian. Zhang (1947) attributed the age of Nuoge shale to the Latin period to the Ladinian to Carnian. Chen et al. (1961) renamed the Niaoge Formation and redefined it. The lower part of Niaoge shale belonging to the Ladinian was assigned to the Falang Fm, while the part representing the Carnian was still called the Niaoge Fm. In 1990, the Yunnan Geological Bureau merged the two parts and renamed it as the Bapanzhai Fm. This Lexicon maintains the meaning of the original Niaoge shale and defines its age as the Carnian.