DEVONIAN BRACHIOPODS FROM ALASKA'S ACCRETED TERRANES AND THEIR PALEOBIOGEOGRAPHIC RELATIONSHIPS WITH FAUNAS FROM ARCTIC REGIONS OF EURASIA AND ADJOINING PARTS OF LAURENTIA (WESTERN & ARCTIC NORTH AMERICA)

Biogeographically distinctive Devonian brachiopods occur in many of Alaska’s accreted terranes and provide critical data regarding their paleogeographic origins. We are involved in a taxonomic study and biogeographic assessment of Devonian brachiopods from these terranes. In the Alexander terrane, the Wadleigh Limestone includes an early Pragian fauna from Heceta Island which is most similar to NE Asia and the Farewell terrane. Eifelian age Wadleigh Ls. brachiopods and gastropods are essentially identical to those of the Farewell terrane. Givetian brachiopods (dominated by stringocephalids) occur in both the Wadleigh Ls. and Coronados Volcanics. The latter unit contains Stringocephalus axius and Geranocephalus cf. inopinus. The upper limestone member of Cedar Cove Fm. on Chichagof Island contains Warrenella praekirki indicative of an early Eifelian age (though we cannot yet rule out a late Emsian age) and widespread throughout western and northern Laurentia.

The Farewell terrane contains a highly diverse early Pragian brachiopod fauna in the Soda Creek Ls. which is most closely related to coeval faunas from NE Asia, Taimyr, and the Alexander terrane. The Eifelian Cheeneetnuk Ls. (Farewell terrane) shares several species with the Denay Ls. of Nevada, but also contains some distinctive elements showing Eurasian affinities. Distinctive brachiopod faunas from the western Brooks Range (western part of the Arctic Alaska terrane) include abundant stringocephaloid brachiopods (Omolonia antiqua Alekseeva and Geranocephalus inopinus) indicating similarities both with NE Asia and western Laurentia. Frasnian brachiopods from the Kugururok River valley show their strongest affinities to the Russian Arctic (including forms related to Mucrospirifer novosibiricusToll).

In summation, Pragian brachiopods of S. Alaska clearly show strong linkage with NE Asia and Taimyr, with no species co-occurring in western Laurentia. During the Eifelian, both Eurasian and Laurentian species are observed in the southern Alaskan terranes. Givetian brachiopods of the Alexander and Arctic Alaska terranes include stringocephalids which suggest a strong faunal alliance between W. Laurentia, Alaska, and NE Asia. The lack of Baltica Devonian brachiopod elements precludes derivation of these terranes from that paleocontinent.