Ordovician - Dating

Dating

The Ordovician Period started at a major extinction event called the Cambrian–Ordovician extinction events some time about 485.4 ± 1.9 Mya (million years ago), and lasted for about 44.6 million years. It ended with the Ordovician–Silurian extinction event, about 443.4 ± 1.5 Mya (ICS, 2004) that wiped out 60% of marine genera.

The dates given are recent radiometric dates and vary slightly from those used in other sources. This second period of the Paleozoic era created abundant fossils and in some regions, major petroleum and gas reservoirs.

The boundary chosen for the beginning both of the Ordovician Period and the Tremadocian stage is highly useful. Since it correlates well with the occurrence of widespread graptolite, conodont, and trilobite species, the base of the Tremadocian allows scientists not only to relate these species to each other, but to species that occur with them in other areas as well. This makes it easier to place many more species in time relative to the beginning of the Ordovician Period.