Xialoucun Fm
Type Locality and Naming
No type section was assigned when the unit was erected. An auxiliary section, the Lugou section, was selected by Ma (1998) as representative section of the formation. The section, measured by Yang et al. (1991), lies at Lugou gully in Baoluo Township, about 3.5 km north of the junction of Lugou stream and Luohe River, or about 7 km north of Luonan County, Shangluo City, Shaanxi Province (110°46’02”E, 34°08’26”N). It is the lower portion of the same section shared with overlying Shangloucun and Wangyu formations. In this section, the Xialoucun Formation is 204.1 m thick. The formation was named by Regional Geological Survey Team of Geological Bureau of Northwest China (1965). The name is derived from Xialoucun Village in Shimen Township, Luonan County, Shangluo City, southeastern Shaanxi Province.
Synonym: （下楼村组）
Lithology and Thickness
The Xialoucun Formation is mainly a metamorphic clastic sequence, consisting of greyish green sandy, silty, and calcareous phyllite and chloritized muscovite-biotite schist, intercalated with thin- to thick-bedded dolomitic marble, calcite marble, and minor oolitic limestone or lenses of oolitic limestone.
Extending southward to Hancun and Shahe villages of the Luonan County, the formation is dominated merely by silty phyllite and chloritized muscovite-biotite schist with minor pelitic-banded calcite mylonite in the base and the thickness is increased to 381 m; further extending westward to Wangyu of Yaoshi Township, Shangzhou District of Shangluo City, the formation becomes 150 m thick and consists of thin-platy limestone merely with minor calcareous phyllite; extending even further westward to Dajing of Shangzhou District, Shangluo City, the formation consists of carbonate rock in the lower part and sericitic chloritic schist in the upper part with a total thickness of 110 to 130 m; and to Tieluzhi of Shangzhou District, the most west to the type area of the formation, the facies changed completely into calcareous phyllite and the thickness sharply decreases down to 0~40 m.
Relationships and Distribution
Lower contact
The Xialoucun Fm is in disconformable contact with underlying Chushatung Fm. The lower boundary is marked by disappearance of the dark grey, thick-bedded dolomite or marble of the Chushatung Fm
Upper contact
The Xialoucun Fm is in conformable contact with overlying Shangloucun Fm. The upper boundary is defined by the disappearance of the phyllite of Xialoucun Fm or appearance of the oolitic limestone at the base of the Shangloucun Fm.
Regional extent
The Xialoucun Formation is exposed in the Kunlun-Qinling Region, restricted to the northern Shangluo City, southeastern Shaanxi Province (south half of Luonan County and Shangzhou District of the City). The thickness of the formation ranges from 30 to 381 m.
GeoJSON
Fossils
No fossil is known from the formation.
Age
Depositional setting
Additional Information