Madiyi Fm
Type Locality and Naming
Northwest Hunan. The Madiyi Fm was named by the Precambrian Research Group of Hunan Bureau of Geology in 1962 and formally published on the Regional Geological Scale of Central South China in 1974. The typical section is situated south of Madiyi village of Lingyuan County, Hunan Province. Lower formation in the Banxi Gr in this location.
Synonym: （马底驿组）
Lithology and Thickness
The basal part of the Madiyi Fm is dominated by coarse clastic rocks including purple red and minor gray white massive thick-bedded metamorphic sandy conglomerate, pebbly sandstone and coarse quartzose sandstone. Upward it changes into purple red and greenish gray low-grade metamorphic medium- to thick-bedded, medium- to fine-grained quartzose sandstone, feldsphathic sandstone, lithic sandstone, siltstone, sandy slate and slate. Of which, the sequence is composed of rhythmites with a variable thickness; each rhythmite is fining-upward in clastic grain size and increase in mud. The thickness is about 200 m.
Relationships and Distribution
Lower contact
It rests unconformably on the underlying Lengjiaxi Gr
Upper contact
The top is disconformably overlain by the gray sandy conglomerate of the Wuqiangxi Fm
Regional extent
Northwest Hunan. Lingyuan County, Hunan Province.
GeoJSON
Fossils
It yields microplants of Orygmatosphaeridium exile, O. rubiginosum, Leiopsophosphaera solida, Asperatopsophosphaera baulensesis, A. umishanensis, Trachysphaeridium cultum.
Age
Depositional setting
The Madiyi Formation belongs to the shelf to continental slope transition facies based on its sedimentary feature.
Additional Information