Shizipu Fm
Type Locality and Naming
The type section is at Shizipu 5 km north of Zunyi, Guizhou. The Shizipu Fm is derived from the Shizipu Shale proposed by Yoh S.S in 1928. In 1948, Liu Zhiyuan named it the Shizipu Bed, which was called the Shizipu Series by Lu Yanhao in 1959. In 1962, Zhang Wentang renamed it the Shizipu Fm. Subsequently, Zhang Wentang confined the Shizipu Fm to be between the oolitic limestone and the limestone with polygonal crack of the Baota Fm, i.e. the middle-upper part of the previously defined Shizipu Fm. In 1974, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, restricted further the Shizipu Fm to only the upper part of the previously defined Shizipu Shale.
Synonym: (十字铺组）
Lithology and Thickness
The Shizipu Fm is composed of gray, grayish green thin- to medium-bedded calcareous and silty mudstone, argillaceous limestone and clay marl.
Relationships and Distribution
Lower contact
It rests conformably on the shelly limestone of the Guniutan Fm (Ordov column 43) or conformably on the Laozhai Fm (Ordov column 42). The Shizipu Shale had previously been thought to be in fault contact with the underlying strata, and to be composed of lower shale, middle shale and oolitic limestone and upper shale.
Upper contact
It is conformably overlain by the “limestone with polygonal cracks” of the Baota Fm (Pagoda Fm; Ordov column 43), or has the next younger regional unit as the Mutong Fm (Ordov column 42). The Shizipu Shale had previously been thought to be in fault contact with the overlying strata, and to be composed of lower shale, middle shale and oolitic limestone and upper shale.
Regional extent
With a persistent lithology, the Shizipu Fm is seen in northern Guizhou (8-30 m thick), Southeastern Guizhou (several meters to more than 30 m thick), Tanjiagou in Guangyuan (66.1 m thick) and Dalianghui in Wangcang (3.4 m thick) of Sichuan and northeastern Yunnan (8-18 m thick). At Tanjiagou in Guangyuan, Sichuan, the strata equivalent to the Shizipu Fm was previously defined as the Tanjiagou Fm (Sichuan Bureau of Geology and Mineral Resources, 1991). At Lengshuigou in Wenshan, Yunnan, the Shizipu Fm, previously defined as the Lengshuigou Fm, is composed of 102-190 m thick yellowish green, yellowish gray marl, argillaceous limestone and calcareous siltstone intercalated with minor shale, and yields trilobite Reedocalymene, graptolites Orthograptus aff. disjunctus, Pseudoclimacograptus aff. scharenbergi and brachiopod and cystoid (Yunnan Bureau of Geology and Mineral Resources, 1990).
GeoJSON
Fossils
In Zunyi, the Shizipu Fm yields graptolites of Gymnograptus linnarssoni assemblage, brachiopod and cystoid.
Age
Depositional setting
Additional Information