The Global boundary Stratotype Section and Point(GSSP)for the base of the Hirnantian Stage(the uppermost of the Ordovician System)is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangjiawan No...The Global boundary Stratotype Section and Point(GSSP)for the base of the Hirnantian Stage(the uppermost of the Ordovician System)is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangjiawan North section.The section is located near Wangjiawan village,42 km north of Yichang city(western Hubei,China),at 30°58′56″N and 111°25′10″E.The GSSP level coincides with the first appearance of the graptolite species Normalograptus extraordinarius(Sobolevskaya).Secondary markers include the onset of a positive carbon-isotope excursion,and a slightly earlier first appearance of Normalograptus ojsuensis(Koren and Mikhailova).The Wangjiawan North section possesses continuity of sedimentation and biozonation with completeness of exposures,abundant and well-preserved graptolites and shelly fossils,i.e.the Hirnantia-Dalmanitina shelly fauna which is a key element for recognition of the Hirnantian Stage.The Wangjiawan North,South and Riverside sections possess favorable facies and widespread correlation potential,are free from structure complication,metamorphism and other alteration,and have good accessibility.The Riverside section in particular possesses amenability to isotopic age determination.The beginning of the Hirnantian was followed by a global episode of a major extinction event,which happened in the Diceratograptus mirus Subzone.The proposal was voted by the International Subcommission on Ordovician Stratigraphy in October,2004,approved by the International Commission on Stratigraphy in February,2006,and ratified by the International Union of Geological Sciences in May,2006.展开更多
The Huanghuachang section near Yichang,southern China was successively approved by ISOS,recognized by ICS and then officially ratified as being the Global Stratotype Section and point(GSSP)for the base of the Middle O...The Huanghuachang section near Yichang,southern China was successively approved by ISOS,recognized by ICS and then officially ratified as being the Global Stratotype Section and point(GSSP)for the base of the Middle Ordovician Series and the Third Stage,named as Dapingian,of the Ordovician System.The conodont succession at the section is complete across the Lower to Middle Ordovician series boundary and several excellent phylogenetic lineages of Baltoniodus,Gothodus,Microzarkodina and Periodon are represented.The base of the Middle Ordovician Series and the Daping Stage is defined at a point 10.57 m above the base of the Dawan Formation at the base of Bed SHod-16 of the Huanghuachang section,22km NE of Yichang City,Hubei Province,South China.It coincides with the first appearance datum(FAD)of the conodont species Baltoniodus triangularis within the Baltoniodus lineage starting from Baltoniodus cf.B.triangularis to Baltoniodus navis.It is associated with the FAD of Periodon sp.A and followed closely by the FAD of Microzarkodina flabellum,which is taken as a reasonable proxy for the boundary.This level approxi-mates the boundary between the lower and upper Azygograptus suecicus graptolite Biozone,and nearly coincides with the base of the Belonechitina cf.henryi chitinozoan Biozone.The same faunal succession is also recorded from the Chenjiahe section,near Daping village,5 km to the north of the Huanghuachang section.展开更多
文摘The Global boundary Stratotype Section and Point(GSSP)for the base of the Hirnantian Stage(the uppermost of the Ordovician System)is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangjiawan North section.The section is located near Wangjiawan village,42 km north of Yichang city(western Hubei,China),at 30°58′56″N and 111°25′10″E.The GSSP level coincides with the first appearance of the graptolite species Normalograptus extraordinarius(Sobolevskaya).Secondary markers include the onset of a positive carbon-isotope excursion,and a slightly earlier first appearance of Normalograptus ojsuensis(Koren and Mikhailova).The Wangjiawan North section possesses continuity of sedimentation and biozonation with completeness of exposures,abundant and well-preserved graptolites and shelly fossils,i.e.the Hirnantia-Dalmanitina shelly fauna which is a key element for recognition of the Hirnantian Stage.The Wangjiawan North,South and Riverside sections possess favorable facies and widespread correlation potential,are free from structure complication,metamorphism and other alteration,and have good accessibility.The Riverside section in particular possesses amenability to isotopic age determination.The beginning of the Hirnantian was followed by a global episode of a major extinction event,which happened in the Diceratograptus mirus Subzone.The proposal was voted by the International Subcommission on Ordovician Stratigraphy in October,2004,approved by the International Commission on Stratigraphy in February,2006,and ratified by the International Union of Geological Sciences in May,2006.
基金Research on the Huanghuachang GSSP and preparation of this proposal was financially supported by the China Geological Survey(NO:200113900072)National Natural Science Foundation of China(NO:40272020)the Germany Academic exchange Centre(DAAD),Chinese Commission of Stratigraphy and Yichang Institute of Geology and Mineral Resources(YIGMR).
文摘The Huanghuachang section near Yichang,southern China was successively approved by ISOS,recognized by ICS and then officially ratified as being the Global Stratotype Section and point(GSSP)for the base of the Middle Ordovician Series and the Third Stage,named as Dapingian,of the Ordovician System.The conodont succession at the section is complete across the Lower to Middle Ordovician series boundary and several excellent phylogenetic lineages of Baltoniodus,Gothodus,Microzarkodina and Periodon are represented.The base of the Middle Ordovician Series and the Daping Stage is defined at a point 10.57 m above the base of the Dawan Formation at the base of Bed SHod-16 of the Huanghuachang section,22km NE of Yichang City,Hubei Province,South China.It coincides with the first appearance datum(FAD)of the conodont species Baltoniodus triangularis within the Baltoniodus lineage starting from Baltoniodus cf.B.triangularis to Baltoniodus navis.It is associated with the FAD of Periodon sp.A and followed closely by the FAD of Microzarkodina flabellum,which is taken as a reasonable proxy for the boundary.This level approxi-mates the boundary between the lower and upper Azygograptus suecicus graptolite Biozone,and nearly coincides with the base of the Belonechitina cf.henryi chitinozoan Biozone.The same faunal succession is also recorded from the Chenjiahe section,near Daping village,5 km to the north of the Huanghuachang section.
