Panjiazui Fm
Type Locality and Naming
The type section of Panjiazui Formation is located on the western slope of Baoshan Hill at Panjiazui, about 4 km northwest of the Jiuxi Town, 36 km northwest of Taoyuan City, Changde, Hunan Province (111°14’E, 28°12’N). In the type section, the formation is 248.5 m thick. The Panjiazui Formation was first published by Compiling Group for South-Center China Regional Stratigraphic Scale (1974). The name is derived from Panjiazui Village in Jiuxi Township, Taoyuan County, Changde City, northwestern Hunan Province. It was originally appeared in a 1973 manuscript by Liu Yiren from Hunan Regional Geological Survey Team. This formation spans the Cambrian-Ordovician boundary.
Synonym: （盘家咀组）
Lithology and Thickness
The Panjiazui Formation is a carbonate sequence. It consists of dark grey, medium-bedded limestone, striped argillaceous limestone, and greyish black, thin-bedded marlstone, intercalated with interbeds of shale. The basal part of the formation, 38.0 m thick, is composed of yellow shale or mudstone that was weathered from dark grey, thin-bedded marlstone. The thickness of the formation is slightly thinning southwestward, varying from 249 m thick at Panjiazui to 200 m thick in Jishou district.
Relationships and Distribution
Lower contact
The Panjiazui Fm is in conformable contact with underlying Shenjiawan Fm. The lower boundary of the formation is marked by lithological change from the limestone of Shenjiawan Fm to shale, which is weathered from marlstone, at the base of the Panjiazui Fm.
Upper contact
The Panjiazui Fm is in conformable contact with the overlying dolomite of the Madaoyu Fm of upper Lower Ordovician. The upper boundary is marked by lithological change from the dolomitic limestone or laminated limestone at the top of Panjiazui Fm to the marlstone bearing limestone lenses at the base of Madouyu Fm.
Regional extent
The Panjiazui Formation is exposed in the Jiangnan Slope Area of South China Region, distributed in northwestern Hunan (Cili, Taoyuan, Yunaling, Luxi counties and Jishou City).
GeoJSON
Fossils
The Panjiazui Formation is richly fossiliferous. The basal part of the formation in the type section, 21 m thick, was recognized as Onychopyge-Hysterolenus Zone by Peng (1984, 1990b), yielding trilobites Acrocephalina hunanensis, A. cf. acuta, Amzasskiella sanduensis, Brachyhipposiderus hunanensis, Conophrys changshanensis, Dichelepyge lata, Guotangia guizhouensis, Hospes guizhouensis, H. cf. sanduensis, Hunanopyge sejunct, Hysterolenus asiaticus, Leiagnostus cf. bexelli, Leiostegium constrictum, L. punctatum, Levisaspis sinensis, Macropyge angusta, Micragnostus chiushuensis, Neoagnostus cf. eckardti, Niobella bela, N. shenjiawanensis, Onychopyge austrina, Parapilekia latilus, Paraszechuanella sp., Pharostomina panjiazuiensis, Proteuloma panjiauiense, P. cf. subquadratum, Szechuanella rectangula, Taoyuania nobilis, T. xenisma, Troedssonia wiman, and T. elongate; and graptolites Callograptus dendraticus, Rhabdinopora flabeliformis, R. regularis, and R. taojiangensis. This interval equals to graptolite Rhabdinopora flabeliformis Zone (Liu, 1984), which is overlain by Callograptus taizehoensis Zone by Liu (1984). [Ordovician entry: " Additionally, graptolite Dendrograptus lotolatzensis, nautiloid Ellesmeroceras sp. and echinoderm Aristocystis sp. also have been found from the Panjiazui Fm."]
Age
Depositional setting
Additional Information