Xinyuan Fm
Type Locality and Naming
The named section is located at Tunshang, about 3 km east of Zisong Town, Wangmo County, Guizhou, from Xinyuan to Jiangdonggou. The Xinyuan Formation was first established by Wang Yu et al in 1959 at the National Stratigraphic Conference and the Field Conference on Stratigraphy of the Southern Guizhou, and was later cited by Zhao Jinke et al. (1962) and Yin Hongfu (1962). In 1963, Wang Yu et al. officially published the named section of Xinyuan Fm. The formation is named to represent the Middle Triassic Anisian shale interbedded with fine sand rocks near Ziyun County, southern Guizhou. In 1976, the Stratigraphical Group of Guizhou Stratigraphy and Palaeontology (Chen Longzhi) assigned the 125m sandy shale containing bivalve Daonella moussoni in the upper part of the formation to the Bianyang Fm.
Synonym:
Lithology and Thickness
The Xinyuan Formation is mainly composed of gray, gray-green, yellow-gray clay shale and calcareous shale, interbedded with gray thin to medium thick calcareous sandstone, siltstone, micrite, muddy limestone. The upper part contains more sandy components, and the bottom is often marked by crystal and vitric tuff (commonly known as "mung bean rock" or "Green Bean" horizon).
Relationships and Distribution
Lower contact
Xinyuan Fm is in conformable contact to the underlying Ziyun Fm of the Lower Triassic. Gan Xiuming (1983) first proposed that a stable layer of yellowish-green montmorillonite vitric tuff (commonly known as "mung bean rock" or "Green Bean" volcanic ash horizon) was used as the lower boundary of Xinyuan Formation.
Upper contact
It is in conformable contact to the overlying Bianyang Formation of the Middle Triassic.
Regional extent
It is mainly distributed in the vast northeastern area of the line from Liangtian Town, Zhenning County to Wangmo County, Guizhou Province. The lithology is stable and the thickness varies greatly from tens of meters to more than 1576 m
GeoJSON
Fossils
The Daonella guizhouensis zone, the Daonella americana - D. producta - D. ignobilis assemblage and the Daonella pseudomoussoni - D. obtusa assemblage could be established from bottom to top. Ammonoids: Balatonites multisulcatus, Paraceratites cf. binodosus, Huishuites cf. bifidus, Hollandites sp., Acrochordiceras sp., Paracrochordiceras sp., Danubites sp., Judicarites sp., etc.
Age
Depositional setting
It is interpreted as the shallow sea sediments.
Additional Information