Dapingian
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The Dapingian is the third stage of the Baltoniodus triangularis which happened about 470 million years ago. The Dapingian lasted for about 2.7 million years until about 467.3 million years ago.[7]
HistoryThe Ordovician was divided into three series and six global stages in 1995; in 2005, this was amended to seven stages with the formalization of the index fossils. The conodont Baltoniodus triangularis, a species found in Baltica and China, defined the base of the regional Baltic Volkhov stage. Another conodont, Tripodus laevis, defined the base of the Whiterockian stage in western North America. T. laevis was also roughly correlated with the appearance of Isograptus v. lunatus, an abundant worldwide graptolite.[8][9]
The Whiterock Narrows section in the Ninemile Formation of Nevada was the initial suggestion for the GSSP of the third stage, but a 2001 review of the site revealed that its local conodont fauna was misaligned with wider graptolite zonation. In its place, two formal GSSP candidates were proposed. The Niquivil section of Argentina used another widespread species, Protoprioniodus (Cooperignathus) aranda, as a proxy for B. triangularis, T. laevis, and graptolites, which were absent from the section.[10] The Huanghuachang section of China hosted a more diverse fauna of index fossils, including Baltoniodus triangularis and biostratigraphically useful graptolites and chitinozoans.[9] The Huanghuachang section was approved as the GSSP for the third stage in 2006, and was ratified by the ICS in 2007.[11][12] NamingThe Dapingian is named after Daping, a village that lies near the Dapingian GSSP at Huanghuachang. Daping is very close to an outcrop with similar rocks, the "Chenjiahe section" (formerly "Daping section") in Chenjiahe.[11] The name of the Dapingian stage was introduced in 2007 and approved alongside the stage's ratification, beating out earlier suggestions such as "Volkhovian" and "Huanghuachangian".[12] GSSP  Huanghuachang section Map of China showing the GSSP location. The Global Boundary Stratotype Section and Point ( Baltoniodus triangularis in the type section. Radiometric dating has constrained the Floian-Dapingian boundary at 470 million years ago.[7] The exact boundary lies 10.57 m above the base of Dawan Formation.[9][11]
Regional stagesThe Dapingian overlaps with the upper part of the and the Castlemainian and Yapeenian stages which have been used in Australia and Scandinavia.References
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