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Silurian rocks in Alaska have been identified in 12 accreted terranes and in the Tatonduk-Nation River area of east-central Alaska, which represents part of autochthonous North America. Most of the terranes are in situ or structurally imbricated portions of the North American (or Siberian) continental margin. An exception is the Alexander terrane of southeastern Alaska, which originated as an offshore island arc. Discontinuously exposed and (or) highly altered sequences have precluded detailed investigations of Silurian rocks in most parts of Alaska, but reconnaissance-level studies reveal that graptolitic shales of turbidite or hemipelagic origin record deep-water or “shale out” conditions west or north of the ancient continental margin of North America. Platform carbonates are also exposed in many areas and are particularly well represented in southwestern (Nixon Fork subterrane of Farewell terrane) and southeastern (Alexander terrane) Alaska, indicating that much of Alaska resided close to the paleoequator in the Silurian. Subtidal stromatolite reefs in southwestern and southeastern Alaska that are similar to those in Salair and the Ural Mountains, Russia, indicate a paleobiogeographic connection between these two parts of Alaska, Siberia, and eastern Baltica via the Uralian Seaway in the Late Silurian. Deposition of vast accumulations of red beds and other siliciclastic rocks beginning in the Late Silurian suggests that parts of Alaska may have been affected by late stages in Cale-donian orogenesis and (or) early stages in the Ellesmere orogeny during formation of the Laurussian landmass.

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