Idwian Regional Stage
From 439 +/- 1.8 To 437.5 Ma
Start Defined By: Graptolite, lowest occurrence of Monograptus austerus
sequens.
Start Based On: Gradstein, Ogg, Smith, _A Geologic Time Scale 2004_
-- Overlaps With --
Chinese Stage: Longmaxian (443.7 - 438)
Chinese Stage: Shinulanian (438 - 433)
North American Stage: Medinan (443.7 - 438)
North American Stage: Niagaran (438 - 421.3)
-- A Substage of --
Eon: Phanerozoic (542 - -5.5012e-005)
Era: Paleozoic (542 - 251)
Period: Silurian (443.7 - 416)
Epoch: Early Silurian (443.7 - 422.9)
Sub-Epoch: Llandovery (443.7 - 428.2)
ICS Stage: Aeronian (439 - 436)
Australian Stage: Keiloran (443.7 - 433)
Regional Stage: Alexandrian (443.7 - 436)
-- Preceeded By --
ICS Stage: Rhuddanian (443.7 - 439)
-- Followed By --
Regional Stage: Fronian (437.5 - 436)
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