Leikoupo Fm
Type Locality and Naming
The type section is located at Leikoupo, near Xinchang, Weiyuan County, Sichuan province. It was named by Xu Deyou in 1939. It was firstly named as “Leikoupo series”, which was regarded as the upper part of “Jialingjiang limestone”. And then it was revised as Leikoupo Fm in 《China Regional Stratigraphic charts (Draft) 》 in 1956..
Synonym:
Lithology and Thickness
From bottom to top, there are four Members: First Member is dominated by gray limestone and dolomitic limestone interbedded with a few shales, and its bottom is a layer of green illite claystone (commonly known as “Green bean rock” or "mung bean") with a thickness of about 40 m; Second Member is dominated by the gray, Yellow-green, a little purple, thin to medium-thick dolomitic limestone interbedded with some argillaceous dolomites, or mainly argillaceous dolomite, intercalated with dolomitic mudstone, dolomite, dolomitic limestone, evaporite solution breccia and a few siltstones, 80-170 m thick; Third Member is dominated by light gray, dark gray thin to thick limestone, argillaceous limestone, intercalated with dolomitic limestone, oolitic limestone, bioclastic limestone, and dolomite, anhydrite and halite, the surface is breccia, 150-250 m thick; Fourth Member is dominated by light gray, gray-yellow thin to medium-thick dolomite and argillaceous dolomite, intercalated with anhydrite, and sometimes dolomite and hard gypsum interbeds, anhydrite weathered into gypsum breccia on the surface, and the disappearance of the anhydrite layer is a sign of the top boundary, with a thickness of 25 to 188 m.
Relationships and Distribution
Lower contact
It is conformable in contact to the underlying Jialingjiang Fm
Upper contact
Usually, disconformable contact with overlying formations. It is well-developed and conformable in contact to overlying formations only in Guangyuan, Jiangyou and Wangcang of Sichuan.
Regional extent
It is mainly distributed in Sichuan basin but also in the northeastern of Yunnan province. This formation is generally subjected to different degrees of erosion, the sequence is mostly incomplete, and the residual thickness varies greatly. The formation from Chongqing to Luzhou was completely eroded; in the Weiyuan-Junlian area and east of Huaying Mountain, with a residual thickness of 75 to 373 m; in the north of Guang’an to the front edge of Micang Mountain and Emei Muchuan area, with a thickness of 300 to 362 m; the thickest area near Nanchong and Wutong Bridge in Leshan can reach 500-1000 meters. The lithology of this formation in the northern and middle sections of Longmen Mountain varies greatly, dominated by large sets of thick layers to massive dolomites, with a thickness of 572 to 635 m; in the northeastern Yunnan area, it is composed of limestone, dolomite, and dolomitic limestone intercalated shale. The rock is composed of 71 to 447 m thick.
GeoJSON
Fossils
Ammonoids, bivalves and conodonts. From the first to third members: Asoella illyrica assemblage, Noetlingites-Semiornites assemblage, Progonoceratites-Beyrichites assemblage. In the third Member, there are some conodonts, such as Neospathodus germanicus and N. kockeli.
Age
Depositional setting
Restricted carbonate platform. The gypsum and salt deposits in this group represent a saline water environment.
Additional Information