The Xiaoyangqiao section, Dayangcha, North China: the new global Auxiliary Boundary Stratotype Section and Point (ASSP) for the base of the Ordovician System
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In 2019 the Sub-Commission on the Ordovician System approved the Xiaoyangqiao section, North China as a new ASSP section for the base of the Ordovician System. The sedimentary succession of the section is exposed in a natural outcrop near the Dayangcha Village at a position of 42 degrees 3'24 '' N, 126 degrees 42'21 '' E. It has a well-preserved, abun-dant and diverse fossil record across the boundary with key markers (conodonts and graptolites), which provide improved intercontinental correlation of the Cambrian- Ordovician boundary. The appearance of the first plank -tonic graptolites is immediately below the base of the Cordy-lodus lindstromi Conodont Zone. Other fossils, including acritarchs, brachiopods and trilobites are also present in the Xiaoyangqiao ASSP section. Non-biotic secondary global markers near the base of the Ordovician System include a positive carbon isotopic excursion with the maximum peak (named HSS) below the boundary, a prominent unnamed negative peak immediately below the boundary and a prominent carbon isotope excursion with positive peaks above the boundary. The latter excursion is associated with the appearance of the planktonic graptolites in the Ordo-vician. The strength of the Xiaoyangqiao ASSP section is the correlation between the conodonts and graptolites, correspondence of sea-level lowstands, and the matches of geochemical parameters.
Originalsprog | Engelsk |
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Tidsskrift | Episodes |
Vol/bind | 44 |
Udgave nummer | 4 |
Sider (fra-til) | 359-383 |
Antal sider | 25 |
ISSN | 0705-3797 |
DOI | |
Status | Udgivet - 2021 |
ID: 287066738