Longjiayuan Fm
Type Locality and Naming
Northeast Shaanxi. The Longjiayuan Fm was named by the Party of Qinling Geological Regional Survey, Ministry of Geology in 1959. The type section is near Longjiayuan Village, Luonan County, Shaanxi Province. It is in the lower-middle part of the Guandaokou Gr.
Synonym: （龙家园组）
Lithology and Thickness
The Longjiayuan Fm is composed of neritic magnesium-carbonate rock, sandwiched with clastic rock in lower part. It consists of greyish, dark-grey, medium-to very thick-bedded silty, fine-crystalline dolomite with chert bands. There is an unstable pebbly sandstone or a conglomerate in the base, and hematite lenticules are seen locally. The Longjiayuan Fm is 800 m thick
Relationships and Distribution
Lower contact
The Longjiayuan Fm is in regional conformable contact onto the underlying Gaoshanhe Fm (the lowermost formation of the Guandaokou Gr). And unconformable basal contacts are seen locally.
Upper contact
It has a conformable contact with Xunjiansi Fm
Regional extent
Longjiayuan Fm is distributed in Luonan, Longxian, Lantian counties, Shaanxi Province. To the east it extends to Lingbao, Lushi, Luanchuan and Luoning counties, Henan Province. It is laterally stable in lithologic character, but changeable in thickness, for example, in Shipo-Xiyuhe, Luonan County, but to west in Bayuan, Lantian County it decreased to 385 m thick only, to east it decreased to 740-897 m around Lingbao and Lushi, 180-360 m in Luanchuan, Luoning, Henan Province. It is 1000-1200 m thick.
GeoJSON
Fossils
The formation bears diverse stromatolites, for example, in Luonan District are Pseudogymnosolen mopanyuensis, Luoyukouella luoyukouensis, Xiaoqinlingella xiaoqinlingensis, Longicolumella formosus, Microstylusexiguas, Lochmecolumella f. and Conophyton cf. concellsum, C. shanpolingensis. The typical microplants are Asperatopsophosphaera, Pseudozonosphaera etc.
Age
Depositional setting
Additional Information