A FINAL REPORT ON THE GLOBAL STRATOTYPE SECTION AND POINT(GSSP) FOR THE HIRNANTIAN STAGE (UPPER ORDOVICIAN)

The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage (Upper Ordovician) 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, 42km north of Yichang city (western Hubei, China), at 30°58′56″N and 111°25′10″E on the east flank of the Huangling Anticline. 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 Mikhailova). The beginning of the Hirnantian was followed by a global episode of major extinction event, which happened in the Diceratograptus mirus Subbiozone. The Wangjia- wan North Section possesses continuity of sedimentation and biozonation with completeness of exposures, abundant and well-preserved graptolites and shelly fossils. The Wangjia- wan North and South sections as well as the Wangjiawan Riverside section possess favorable facies and widespread correlation potential, free from structure complication, metamorphism and other alteration and good accessibility. The Wangjiawan Riverside section in particular possesses amenability to isotopic age determination.The proposal approved by the International Subcommission on Ordovician Stratigraphy in October of 2004, by International Commission on Stratigraphy in February of 2006, and ratified by International Union of Geological Sciences in May of 2006.