GSSP for Guzhangian Stage
Definition:
The base of the Guzhangian Stage is defined at the base of a limestone (calcisiltite) layer, 121.3 m above the base of the Huaqiao Formation in the Louyixi section along the Youshui River in northwestern Hunan, China. This level coincides with the lowest occurrence of the agnostoid trilobite Lejopyge laevigata. The horizon corresponding to the FAD of Lejopyge laevigata is near the peak of a rather long negative δ13C excursion of up to 0.58‰.
Location:
The Louyixi Section is situated along the south bank of the Youshui River (Fengtan Reservoir), about 4 km northwest of Luoyixi (4 km southeast of Wangcun), in northwestern Hunan, China at a latitude of 28°43.20’ N and a longitude of 109º57.88’ E.
In the Luuoyixi Section the Huaqiao Formation consists of dark, thin-bedded, thinly laminated lime mudstones, argillaceous limestones, and fossiliferous limestone lenses. Light-colored ribbbon limestones are present in places. The GSSP occurs in a succession of dark gray to black limestones (lime mudstones, or calcimicrites and calcisiltites) and fine-grained argillaceous limestones interbedded with lenses of fossil rich limestone (calcisiltie). Lejopyge laevigata first appears in the lower part of a 82 cm thick layer of dark gray, thinly laminated calcisiltite, overlying another layer of thinly laminated, dark gray calcisiltite.
Primary Markers:
Trilobites: The GSSP coincides with the lowest occurrence of the cosmopolitan agnostoid trilobite Lejopyge laevigata at a level 121.3 m above the base of the Huaqiao Formation.
Secondary Markers:
Trilobites:The last occurrence of Lejopyge calva is below the GSSP. Just above the GSSP is the highest occurrence of agnostoid trilobite Ptychagnostus atavus.
Conodonts: Conodont Laiwugnathus laiwuensis occurs immediately below the FAD of trilobite Lejopyge laevigata.
Carbon Isotopes: The FAD of Lejopyge laevigata is near the peak of a long negative δ13C excursion.
Correlation Events:
Trilobite FAD Lejopyge laevigata
Other Locations around the World:
The first occurrence of Lejopyge laevigata has been recognized worldwide. This species has been identified from rocks in Argentina, Australia, China, Denmark, England, Germany, Norway, Sweden, North Greenland, India, Kyrgyzstan, Turkestan, Uzbekistan, Kazakhstan, northern Poland, Russia, and the USA.
Notes on Derivation of Age:
Estimated from trilobite-zone scalings