期刊
LETHAIA
卷 45, 期 2, 页码 227-237出版社
WILEY-BLACKWELL
DOI: 10.1111/j.1502-3931.2011.00275.x
关键词
Boundary; Cambrian; conodont; Global boundary; Stratotype Section Point; Iapetognathus; Ordovician.
类别
资金
- Swedish Research Council
In 2000, the International Union of Geological Sciences ( IUGS) ratified the decision from the International Working Group on the Cambrian- Ordovician Boundary ( COBWG) to place the Global boundary Stratotype Section and Point ( GSSP) for the base of the Ordovician System in the Green Point section, Newfoundland, Canada, at a point coinciding with the first appearance of the conodont Iapetognathus fluctivagus. However, a restudy of the conodont successions from Green Point shows that this species is not present at the boundary interval, and as a consequence the section does not fulfil the biostratigraphical requirements of a GSSP. The GSSP horizon as now defined is based on a level part- way through the range of I. preaengensis - a species with lower first appearance datum ( FAD). The true FAD of I. fluctivagus is above the FAD of planktonic graptolites and well above the FAD of I. preaengensis. As a consequence of these problems, a restudy of the GSSP section and the other sections in the Cow Head Group is necessary. A redefinition of the GSSP horizon is suggested. The following four alternative horizons have potential as new horizons for the GSSP level: the FAD of Cordylodus intermedius; the FAD of Cordylodus andresi; the FAD of Eoconodontus notchpeakensis; and the FAD of the agnostoid Lotagnostus americanus.
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