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EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Cratonic Sequences of North American EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Queenston Clastic Wedge EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Millburg Volcanic Ashes - Pennsylvania EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Subduction initiated on west coast NA Greywackes and volcanics accumulate EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Other Tectonic Events Ouachita Trough EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Other Tectonic Events Williston Basin EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Other Tectonic Events Williston Basin EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Other Tectonic Events Williston Basin EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Other Tectonic Events Williston Basin EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY Other Tectonic Events Williston Basin Evaporites Red River Formation EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOGEOGRAPHY EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOCLIMATE EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOCLIMATE EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOCLIMATE EARLY PALEOZOIC EVENTS ORDOVICIAN PALEOCLIMATE From the Early to Middle Ordovician, the earth experienced a milder climate in which the weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana finally settled on the South Pole during the Late Ordovician, massive glaciers formed causing shallow seas to drain and sea levels to drop. This likely caused the mass extinctions that characterize the end of the Ordovician, in which 60% of all marine invertebrate genera and 25% of all families went extinct.