Yilaxi Fm
(20), mid-Middle Permian
Type Locality and Naming
The type section is located in the Chajiagou area of Yilaxi region, Yongji County, Jilin Province, and the reference section is situated in the Batailing-Mofang-Heishanzuizi region of Jiutai City, Jilin Province. It was named by the Jilin Regional Survey Party under the Changchun Geological Institute in 1960, and was cited officially by Tao Nansheng et al. (1975).
Lithology and Thickness
Volcanics and Clastics. Composed mainly of intermediate-acidic volcanic rocks and clastic rocks, with its lower part consisting of dark-grey andesite; with its middle part consisting of grey-green rhyolite and its tuff; and with its upper part consisting of grey-green and grey-purple tuffaceous slate, sandstone, sandy conglomerate, black slate and cherty banded limestone. Total thickness is over 3900 m.
Relationships and Distribution
Lower contact
Disconformable contact with the underlying Fanjiatun Fm in the mining limestone deposit of the Fanjiatun Village of the Dashuihe region
Upper contact
Disconformable contact with the overlying Yangjiagou Fm in the mining limestone deposit of the Fanjiatun Village of the Dashuihe region
Regional extent
Distributed in the areas of Dasuihe and Yilaxi of Yongji County, the Bonihe and Batailing areas of Jiutai City. In the Daheshen area of Huadian City the formation is 1300 m-thick, in the Longtanshan of Jilin City it is 890 m thick, in the Jiaohe area it is 338 m thick. The intermediate volcanic rock in lower part of the formation is the thickest, and is thinning to both the south and north. The marine fossiliferous limestones in the middle part of the formation are well developed in the Batailing and Lishuyuan areas in Jiutai City, yet they are very rare in the Yilaxi and Fanjiatun areas. The intermediate volcanic rocks and volcaniclastic rocks in middle part of the formation are increasing in amount northeasterly from the Nuanquanzi area, and are decreasing in amount southwesterly and are thinning out till the Yilaxi and Fanjiatun areas.
GeoJSON
Fossils
The limestone layer yields bryozoan fossils such as Girtypora, Stenopora.
Age
Depositional setting
It is interpreted as chiefly an intermediate-acidic volcanic-rock formation
Additional Information