GSSP for the Cambrian - Ordovician Boundary


Definition:

The base of the Ordovician System and base of the lowest Ordovician stage (Tremadocian) is exposed in the coastal platform at Green Point, western Newfoundland, at 101.8m level, within Bed 23, in the measured section (Lower Broom Point Member, Green Point Formation), coinciding with the first appearance of the conodont Iapetognathus fluctivagus, and 4.8m below the earliest planktic graptolites.


Location:

The Green Point Section is located within the Gros Morne National Park, about 70km from Deer Lake Airport and about 10km north of the village of Rocky Harbour, western Newfoundland.
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Sedimentology:

The Green Point Section is comprised of alternating black, grey and green shales, micritic nodular and ribbon limestone and grainstone. Limestone conglomerate is largely confined to one bed (Bed 19) and a lenticular bed within Bed 25.
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Primary Markers:

First appearance of conodont species Iapetognathus fluctivagus within Bed 23.

Secondary Markers:

Graptolites:
Planktic graptolites appear 4.8m above the boundary in the Green Point Section. The earliest planktic graptolite species , Staurograptus dichotomus and Rhabdinopora praeparabola, are both present in the Green Point Section.

Carbon isotopes:
The boundary level coincides closely with the peak of a positive cycle in d13 C ( vs. PDB), representing the highest value reached in the boundary interval.

Other Locations around the World:

The Cambrian-Ordovician Boundary lies in the lower Ibex Series of North America, at the base of the Warendian Stage of north Australia, in the lower Tremadoc as used in Kazakhstan, and in the late Fengshanian of north China.

References:

Cooper, R. A., Nowlan, G. S., and Williams, S. H., 2001. Global Stratotype Section and Point for base of the Ordovician System. Episodes 24/1, p. 19-28.