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Abstract


Devonian of the World: Proceedings of the 2nd International Symposium on the Devonian System — Memoir 14, Volume III: Paleontology, Paleoecology and Biostratigraphy, 1988
Pages 257-264
Paleoecology and Biostratigraphy

Devonian Faunas and Major Depositional Events in the Southern Alexander Terrane, Southeastern Alaska

N. M. Savage

Abstract

The Alexander Terrane of southeastern Alaska has the most complete Paleozoic stratigraphic sequences of any known Alaskan suspect terrane, and within these Paleozoic sequences those of Devonian age are particularly important. Early, Middle and Late Devonian fossils occur, principally on the western side of Prince of Wales Island and on smaller nearby islands. Good faunas of conodonts, brachiopods, corals and graptolites have been collected, with most of the shelly fossils coming from limestones. Limestones occur widely in early to late Pragian, middle to late Eifelian, middle Givetian, middle to late Frasnian and middle Famennian times. These limestones are occasionally interlayered with a variety of lava flows and pyroclastics, possibly indicating a volcanic arc origin. Infrequent graptolitic and plant-bearing shales of Early Devonian age may represent pelagic deposits. The earliest Lower Devonian limestone that forms the north end of Lulu Island has yielded early Lochkovian conodonts and brachiopods. Pragian brachiopods and conodonts have been recovered from several localities. Late Pragian to early Emsian graptolites occur on northeast Noyes Island and at Port St. Nicholas and Klakas Inlet on Prince of Wales Island. Emsian conodonts and brachiopods occur on Wadleigh and Kasaan Islands, just west and east of Prince of Wales Island, respectively. The earliest known Middle Devonian occurs on Alberto Island and also just north of Staney Creek on Prince of Wales Island. At both localities middle to late Eifelian conodonts, brachiopods and corals occur in the Wadleigh Limestone. Givetian conodonts and brachiopods are known from Coronados Island and the easternmost of the Alberto Islands. The earliest Late Devonian so far recognized consists of the upper parts of the Wadleigh Limestone. This has yielded good Frasnian conodonts, brachiopods and corals on Wadleigh Island and also on one of the Coronados Islands several kilometres to the south. A middle Famennian brachiopod fauna has been described from the Port Refugio Formation on Suemez Island. In general the Alexander terrane faunas have most affinity with coeval faunas in Nevada, East-central Alaska, and the Northwest Territories (Canada).


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