Megafossil Evidence for Siberian and Uralian Connections of the Arctic Alaska-Chukotka, Farewell and Alexander Terranes: Implications for the Early Evolutionary History of the Amerasian Basin
James Clough1 and R. B. Blodgett2
1Alaska Divisionof Geological & Geophysical Surveys, Fairbanks, AK.
2Consulting Geologist, Anchorage, AK.
Three Alaskan tectonic terranes contain a number of biogeographically distinctive megafossils for select intervals of Paleozoic through Triassic time that are non-North American and shed light on the early evolutionary history of the Amerasian basin. These data are part of a growing body of evidence, including detrital zircon provenance and ages of magmatism, that indicate a paleogeographic position of the Alaska-Chukotka, Farewell and Alexander terranes distinct and separate from the northern Cordillera and Canadian Arctic Islands through at least Triassic time.
The Arctic Alaska-Chukotka terrane includes strictly Siberian affinities of Middle Cambrian trilobites; and Late Ordovician trilobites, brachiopods, gastropods, and ostracodes (NE Brooks Range and York Mountains of the Seward Peninsula) that are exclusively confined to the Siberian platform and southern Taimyr. Late Early Devonian and Middle Devonian brachiopods and calcareous green algae are similarly non-Laurentian and linked to Siberia. Late Mississippian brachiopod fauna from the upper part of the Lisburne Group, exposed throughout the Brooks Range, contain many brachiopods of strictly Eurasian affinities which are unknown in Laurentia, but widespread across Eurasia and North Africa. Late Mississippian lycopods from Arctic Alaska-Chukotka demonstrate strong Angaran affinities. Permian faunas show strong affinities as well with the Siberian platform, virtually lacking any fusulinids and reefal buildups (both of which are commonly found in the Canadian Arctic Islands). Richly diverse Upper Triassic bivalves and brachiopods show closer affinities with northeast Siberia rather than to NW Laurentia.
Middle Cambrian trilobites of the Farewell terrane are strictly of Siberian aspect, most notably to the eastern part of the Siberian Platform. During Late Silurian-Lochkovian time a distinctive algal barrier reef complex characterizes the outer margin of the Nixon Fork subterrane of the Farewell terrane during Late Silurian-Lochkovian time. Associated with these reef complexes are aphrosalpingid sponges that are known only from the Alexander terrane and in the Ural Mountains and Kuznetsk Basin of Russia.
These megafossil data indicate that during the Paleozoic and probably up through Triassic time; these terranes were NOT closely connected to North America, but instead were more likely attached to or juxtaposed to Siberia, Taimyr, Kolyma, the Urals and Eurasia.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia