Tongchuan Fm
Type Locality and Naming
The type section is located at the Jinsuoguan of Qishuihe in Tongchuan City, Shaanxi. It was named by Institute of Geology, Chinese Academy of Geological Sciences in 1965. It is equivalent to the lower two members of the Yanchang Group, belonging to late Middle Triassic. Lowermost formation of the Yanchang Gr.
Synonym:
Lithology and Thickness
This formation, 596 m thick, could be divided into two parts. Lower part ("Chang 10 through 8 Members" in terminology used by hydrocarbon companies) is mainly composed of gray-green, yellowish-green and red massive coarse sandstone interbedded with grayish-green and grayish-black shale and silty mudstone at the upper unit. Upper part ("Chang 7 Member" in terminology used by hydrocarbon companies) is mainly composed of grayish-green, grayish-black and fleshy red medium-thin bedded fine sandstone, argillaceous siltstone interbedded with grayish-green and grayish-black shale with some volcanic ash horizons. There are multiple oil shale beds at the upper part and top, which becomes an important marker of this formation. The bottom boundary is located between the end of the purplish-red clastic rock and the occurrence of the thick-bedded sandstone with diagonal bedding.
Relationships and Distribution
Lower contact
The Tongchuan Fm is in conformable contact on the underlying Ermaying Fm
Upper contact
The Tongchuan Fm is conformably overlain by the Yongping Fm
Regional extent
It is widely distributed in Ordos Basin and its surrounding areas. In Fugu area, sandstones increase, purple rocks increase and their thickness decreases. There are more mudstones and shales in the southwest and south, and the grey-green and yellow-green strata are widely distributed and their thickness is gradually increasing.
GeoJSON
Fossils
This formation yields abundant fossils including plants, sporopollen, ostracods, conchostracans and bivalves. There are about more than 30 plant species including Pleuromeia, Danaeopsis, Bernoullia, Cladophlebis, Todites, Glossopteris, Tongchuanophyllum and so on. The sporopollen includes Punctatisporites, Calamospora, Podocarpidites, Protopicea, Piceaepollenites.
Age
Depositional setting
It is interpreted as a fluvial-lacustrine environment with warm humid climate.
Additional Information