Yangjiagou Fm
Type Locality and Naming
The type section is located at Yangjiagou of the Pony River, Jiutai City, Jilin Province. It was named by Lu Nansheng et al., from the Group on Stratigraphy under the Changchun Geological Institute in 1975.
Lithology and Thickness
Clastics. Its basal part is composed of grey-black tuffaceous conglomerate and grey-purple siltstone, with a basal conglomerate and a thickness of 332 m. Middle part is composed of many layers of grey-green calcareous siltstones, intercalated with limestone lenses, yielding marine-facies bivalves, containing yellow-green, blue-grey and purple non-marine facies bivalve-bearing siltstones, with a thickness of 111 m. Upper part is composed of black siltstone, intercalated with grey-green carbonatized rhyolitic tuff, yielding plant fossils (phytolites) and small bivalve fossils, with a thickness of over 151 m. Total thickness ranges 500-1000 m.
Relationships and Distribution
Lower contact
Disconformable contact with the underlying Yilaxi Fm
Upper contact
Conformable continuous deposits in relation to the overlying Madatun Fm
Regional extent
The formation is lithologically stable, with the paralic facies occurring over five times in the section where the formation had been created, and in the Yangjiagou area in the south and the Zhoujiatun area in the north of the section the volcanic substance is increasing in amount. In the Batailing-Mofang-Heishanzuizi region in the northern part of the section there are found to occur the continental animal and plant fossils, with no marl intercalations having been found. The formation is extending in an approximately E-W-trend for 40 km, and is distributed in the Lujia Country, Jiutai City, with a thickness of 400 m; while in the area between Jiutai City and Shulan County the formation is 1660 m thick; and in the Jiaohe area of the eastern part it is 4138 m thick, yielding only plant fossils (phytolites), with no bivalves having been found.
GeoJSON
Fossils
Yields marine-facies Bivalves such as Liebea, Myalina, Atomodesma, Kolymia; continental-facies bivalves such as Palaeanodonta, Palaeomutela; and Plant fossils (phytolites) such as Noeggerathiopsis, Paracalamites, etc.
Age
Depositional setting
It is interpreted as a coastal river-alluvial facies.
Additional Information