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GSSP for Wuliuan


Definition:

The base of the Wuliuan Stage (=basal stage of the Miaolingian Series of the Cambrian System) is defined at the base of a silty mudstone layer (within bed 9) 52.8m above the base of the Kaili Formation in the Wuliu-Zengjiayan section in Jianhe County, eastern Guizhou Province, China.
This level coincides with the first appearance of the cosmopolitan oryctocephalid trilobite Oryctocephalus indicus.
Secondary indicators near the GSSP include the ROECE negative ?13C excursion, the simultaneous appearance of acanthomorphic acritarchs, and a transgressive phase of a major eustatic event.


Location:

The Wuliu-Zengjiayan section is situated along a hill ridge which is about 0.5km northeast of Balang Village, Jianhe County, GuizhouProvince, China at a latitude of 26°44.843'N and a longitude of 108°24.830'E. The GSSP is located inside the Jianhe Natural Reserve of Paleontological Fossils and the Miaoling National Geopark.


Sedimentology:

The GSSP occurs within the Kaili Formation, which can be subdivided into three parts.
The lower part consists of thin-bedded limestones with silty mudstone interbeds (Bed 1 - 5, 23.7m thick), the middle part is dominated by silty mudstones, mudstone, calcareous mudstone and shale layers (Bed 6 - 27, 150.43m thick), and the upper part is composed of thin-bedded limestone layers and intercalated shale transitioning into grainy limestone and bioclastic limestone (Bed 28 - 30, 40.07m thick).
The GSSP level is defined at the base of a greenish-grey silty mudstone layer 52.8m above the base of the Kaili Formation.
The interval of the FAD of O. indicus is inferred to be a maximum flooding stage of a major eustatic transgression.


Primary Markers:

The GSSP coincides with the lowest occurrence of the cosmopolitan oryctocephalid trilobite Oryctocephalus indicus.

Secondary Markers:

Trilobites:
The LAD of Bathynotus kueichouensis and Ovatoryctocara sinensis at 48.8m above the base of the Kaili Formation is just below the GSSP.
Bathynotus, which occurs at the top of Cambrian Stage 4, is a guide fossil found in the western United States, Siberia, Australia and South China. Its distribution overlaps that of Olenellus and Redlichia, and this taxon has been treated as the most effective secondary tool for intercontinental correlation.

Acritarchs:
There is a turnover in acritarch assemblages just below the GSSP. The Leiomarginata simplex-Fimbriaglomerella membranacea assemblage (0 - 52 m above the base of the Kaili Formation) below the GSSP is replaced by the Cristallinium cambriense- Heliosphaeridium nodosum-Globosphaeridium cerinum assemblage (52 - 140 m above the base of the Kaili Formation).
Carbon Isotopes:

The base of the Oryctocephalus indicus Zone is marked by a distinctive peak of a rather long negative ? C excursion with minimum values of -2.7‰.

Correlation Events:

Trilobite, FAD of Oryctocephalus indicus

Other Locations around the World:

Besides South China, Oryctocephalus indicus has been identified from northern India, western USA, North Greenland, North Korea, and possibly from Siberia.
Bathynotus, which occurs at the top of Cambrian Stage 4, is a guide fossil found in the western United States, Siberia, Australia and South China. Its distribution overlaps that of Olenellus and Redlichia, and this taxon has been treated as the most effective secondary tool for intercontinental correlation.
A distinct negative excursion in the carbon isotopic composition occurs from the Bathynotus kueichouensis - Ovatoryctocara sinensis Assemblage- Zone through the Oryctocephalus indicus Zone. This excursion, near the conterminous base of the Miaolingian Series and Wuliuan Stage, can also be recognized at the Jianshan section nearby, at other localities on the Yangtze Platform, South China, in Siberia, and North America.

Notes on Derivation of Age:

The age for the base of Miaolingian Series and Wuliuan Stage is estimated at 509.1 ± 0.22 Ma.

References:

Zhao, Y., Yuan, J., Babcock, L. E., Guo, Q. J., Peng, J., Yin, L., Yang, X. L., Peng, S., Wang, C., Gaines, R. R., Esteve, J., Tai, T., Yang, R., Wang, Y., Sun, H. Yang, Y., 2019. Global Standard Stratotype Section and Point (GSSP) of the conterminous base of the Miaolingian Series and Wuliuan Stage (Cambrian)at Balang, Jianhe, Guizhou, China. Episodes 42/2, p.165-184.



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