| 11. | These fast-moving nektonic carnivores lived in the Ordovician period.
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| 12. | It is overlain by the Eau Claire Formation or Ordovician strata.
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| 13. | The caldera itself is located on the Precambrian-Ordovician basement.
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| 14. | Fossil spores from land plants have been identified in uppermost Ordovician sediments.
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| 15. | Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids.
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| 16. | The eastern side of the gap has Ordovician Martinsburg shale.
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| 17. | The underlying Ordovician rocks are overlain by disturbed Devonian and Mississippian rocks.
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| 18. | In the Early and Middle Ordovician the nautiloids underwent an evolutionary radiation.
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| 19. | The ignimbrite contains Ordovician lithic fragments and 1020 % pumice.
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| 20. | The Carboniferous rocks were deposited metamorphosed in late Ordovician times.
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