History of Ordovician

	Revision 4 . . August 30, 2001 6:29 pm by Don Kenney [Added Faunal stages*]
	Revision 3 . . (edit) April 7, 2001 5:58 pm by Don Kenney

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Difference (from prior major revision) (no other diffs)

Changed: 3c3

The Ordovician period started at a (apparently minor?) extinction event sometime around 500 million years ago and lasted for about 50-80 million years. It ended with a major extinction event that wiped out 60% of marine genera. It is unusual to find any two sources that agree exactly on the absolute time of the start and end of the period.

The Ordovician period started at a (apparently minor?) extinction event sometime around 490 million years ago and lasted for about 50-80 million years. It ended with a major extinction event that wiped out 60% of marine genera. It is unusual to find any two sources that agree exactly on the absolute time of the start and end of the period.

Changed: 5c5,26

Ordovician rocks contained abundant life and contain major oil and gas resevoirs in some regions.

Ordovician rocks contained abundant life and contain major oil and gas reservoirs in some regions. The Ordovician is usually broken into Lower (Tremadoc and Arenig), Middle (Caradoc, Llanvirn, Llandeilo) and Upper (Ashgill) subdivisions. The Faunal stages from youngest to oldest are: Hirnantian/Gamach? (Upper-Ashgill) Rawtheyan/Richmond? (Upper-Ashgill) Cautleyan/Richmond? (Upper-Ashgill) Pusgillian/Maysville?/Richmond? (Upper-Ashgill) Trenton (Middle-Caradoc) Onnian/Maysville?/Eden? (Middle-Caradoc) Actonian/Eden? (Middle-Caradoc) Marshbrookian/Sherman? (Middle-Caradoc) Longvillian/Sherman? (Middle-Caradoc) Soundleyan/Kirkfield? (Middle-Caradoc) Harnagian/Rockland? (Middle-Caradoc) Costonian/Black? River (Middle-Caradoc) Chazy (Middle-Llandeilo) Llandeilo (Middle-Llandeilo) Whiterock (Middle-Llanvirn) Llanvirn (Middle-Llanvirn) Cassinian (Lower-Arenig) Arenig/Jefferson?/Castleman? (Lower-Arenig) Tremadoc/Deming?/Gaconadian? (Lower-Tremadoc)