Yelang Fm

Synonym: Yehlang Fm

Lithology and Thickness:

It is divided into 3 members in Northern Guizhou: Lower member (Shabuwan Member) is a yellowish-green, yellowish-gray shale with a thin layer of argillaceous limestone, and a yellowish-green montmorillonite clay or tuff layer at the bottom, with a thickness of 5-205 m. Middle member (Yulongshan Member or Huangcunba Member) is mainly composed of light grayish gray thin to medium thick layers of microcrystalline limestone, sometimes intercalated with dolomitic limestone marl shale, etc. The limestone sometimes has inclined bedding, and the top is usually stably intercalated with a layer of sparry oolitic limestone, about 20 cm thick, which is an excellent marking stratum, and the thickness of this member is 78 to 667 m. Upper member (Jiujitan Member) is dark purple, purplish red, grayish green, dark gray calcareous shale, intercalated with limestone or siltstone, with heavy sand in the lower part, 20 to 513 m thick.

Lithology-pattern: Shallow-marine marl

Relationships and Distribution:

Lower contact:

The appearance of a thin layer of yellow-green montmorillonite claystone or tuff at the bottom is delimited from the underlying Upper Permian. This Formation is in conformable contact with the underlying Upper Permian Changxing Fm (or Dalong Fm)

Upper contact:

The top is marked by the appearance of limestone in the bottom of overlying Maocaopu Fm in northern Guizhou.

Regional extent:

In addition to the north of Guizhou, the Formation also has a large area of distribution in central Guizhou and eastern Sichuan, but its lithology changes greatly. In central Guizhou, this Formation is divided into the lower Baimashao member and the upper Zhenning member: The Baimashao Member is a thin layer marl limestone with a thickness of 114 m, roughly equivalent to the Shabao Member and the lower part of the Yulongshan Member in the northern Guizhou area; the Zhenning Member is composed of yellow-green calcareous shale and thin to thick gray-black limestone with a thickness of 118 m.

The Formation in eastern Sichuan is divided into four members from bottom to top: the first member is mainly composed of thin to thick gray limestone, oolitic limestone and marl with a thickness of 122.5 m; the second member is purplish red calcareous shale interbedded with light yellow marl with a thickness of 162.7 m; the third member is mainly grey limestone with a thickness of 138.2 m; the fourth member is composed of purple shale interbedded with green shale and thin marl with a thickness of 27.3 m.

The Baima member in central Guizhou, the first and second members in eastern Sichuan are roughly equivalent to the Shabaowan member and the lower part of the Yulongshan member in northern Guizhou; The Zhenning member in central Guizhou and the 3rd and 4th members in eastern Sichuan are roughly equivalent to the upper Yulongshan member and the Jiusantan member in northern Guizhou.

GeoJSON:

Fossils:

Bivalves in Shabaowan Member: Pseudoclaraia wangi, Claraia griesbachi, Towapteria scythica; Ammonoid: Ophiceras sinense, O. demissum; Ostracoda: Hollinella tingi. Bivalves is enriched in Yulongshan Member, important ones are: Claraia stachei, C. aurita, C. guizhouensis etc. Jiujitan Member is rich in bivalve fauna (take Eumorphotis multiformis as representative).

Age:

Induan

Age span:

Beginning stage: Induan

Fraction up in beginning stage: 0.0

Beginning date (Ma):

Ending stage: Olenekian

Fraction up in ending stage: 0.15

Ending date (Ma):

Depositional setting:

It is interpreted as a mixture of shallow Marine carbonate rocks and clastic rocks.

Depositional-pattern:

Additional Information

It was firstly named after “Yelang Series”, which means common sayings of "Erqiao sandstone", "Yulongshan limestone", "Jiujitan shale", “Maocaopu limestone”, "Sanqiao limestone" named by Ding, and its age had been assigned to the late Permian. Ding Wenjiang and Gripp published "Yelang series" in 1936. After the creation of the name, the meaning has changed over and over again. Zhai Zanxun (1937) redefined the meaning of the "Yelang Series" and held the view that the "Yelang series" should be a general term that represents Early Triassic in southwest China; it only includes "YulongShan limestone", "Feixianguan Shale" and equivalent strata. Zhao Jinke et al. (1962) renamed it Yelang Group and divided it into the Shabaowan member, the Yulongshan member and the Xiacaocaopu member from bottom to top. The age was the Early Triassic. Yin Hongfu (1962) changed the “Yelang Group” to the Yelang Formation, and separated the lower Maocaopu member from the “Yelang Group”, and built another Xinglongchang Fm. Fan Jiasong et al. (1964) believed that the Yelang Fm in central Guizhou could be roughly divided into the lower Baimashao member and the upper Zhenning member; from bottom to top, it can be divided into the Shabaowan member, the Yulongshan member and the Jiusantan member in Northern Guizhou province. We follow this connotation in this book. The Shabaowan member was derived from the yellow shale of Shabaowan by Liu Zhiyuan (1942), and the named section was located in Shabaowan, 5 km northwest of Zunyi, Guizhou. The Yulong Mountain section is derived from the Yulong Mountain limestone of DingWenJiang and Gelipu (1933), and the named locality is located in Yulong Mountain about 3 km northwest of Dading County, Guizhou. Equivalent to Yu Zanxun et al. (1944) "Yulongshan construction" on the upper part of the "Huangcunba limestone member". Jiujitan Member originated from “Jiujitan series”, Lesenxun (1928), and its initial meaning was all Triassic strata and Jurassic sandstone in the suburb of Zunyi City. As redefined by Liu Zhiyuan (1942), Jiujiatan shale represents the shale between the underlying Yulongshan limestone and the overlying Maocaopu Fm limestone, which is the current use of this meaning.