Shidian Fm

The Shidian Fm is derived from the Shidian Bed proposed by Brown in 1917. The type section is near Shidian City, Yunnan. The Shidian Bed had previously been referred to the Lower Ordovician in the vicinity of Shidian City, and was followed by Sun Y.C. (1942). In 1962, Zhang Wentang dated the age of the fossils from the Shidian Bed, and renamed it the Shidian Fm. In 1963, Sheng Xinfu confined the Shidian Fm to be equivalent to the D. murchisoni zone, and named the underlying strata the Bingdou Fm. During 1965-1981, when Yunnan Team of Regional Geological Survey made a regional geological survey, they discovered that the definition of the Bingdou Fm is unclear, and abandoned the stratigraphic unit. At the same time, they studied the Laojianshan section in Baoshan County, Yunnan, and divided the strata equivalent to the Bingdou Fm the Yanqing Fm, Mantang Fm and Laojianshan Fm, in ascending order, on the basis of the dating of the corresponding fossil zones (Yunnan Bureau of Geology and Mineral Resources, 1990). Considering the fact that the foundation for defining and subdividing the lithostratigraphic unit is the ages of the biozones and the unclear lithologic boundaries between the subdivided formations, the present book follows the primary definition of the Shidian Fm.

Synonym: (施甸组）

Reference Section:

The reference section is on Laojian Hill in Baoshan County, Yunnan (Yunnan Bureau of Geology and Mineral Resources, 1990).

The formation is represented by variegated medium- to fine-grained sandstone, siltstone and calcareous shale intercalated with limestone in the lower part and minor marl with developed wave bedding and trace fossil in the upper part. The Shidian Fm is 513-1787 m thick in the reference section. With a persistent lithology, the Shidian Fm is exposed on Laojian Hill in Baoshan (1787 m thick), Libala (1005 m thick) and Pupiao (513 m thick) in Shidian, Yunnan.

The lower part yields graptolites Dictyonema liaotungensis, Acanthograptus sp., and the upper part yields graptolites of Didymograptus protobifidus assemblage, U. austrodentatus assemblage, D. murchisoni assemblage, and cystoids and brachiopods.