Biogeographic and Stratigraphic Evidence for the Siberian Origins of the Arctic Alaska Plate

By

R.B. Blodgett (Oregon State University), J.G. Clough (Alaska Division of Geological & Geophysical Surveys), and M.R. Sandy (University of Dayton)

The Arctic Alaska plate (or terrane) contains a number of biogeographically distinctive fossil faunas and floras that are closely allied with those of the Siberian paleocontinent. Examples are given from the Middle Cambrian (trilobites), Upper Ordovician (brachiopods, gastropods, ostracodes), Lower and Middle Devonian (brachiopods, calcareous green algae), Mississippian (lycopod plants), and Upper Triassic (halobiid and monotid bivalves, brachiopods) that suggest that this region showed closer affinities with Siberia, rather than to western or northern North America. These close biogeographic affinities and similar lithologic associations with Siberia suggest that Arctic Alaska was part of that continent at least until Late Triassic time. The timing of rifting from Siberia is still speculative, but definitely post-Late Triassic. Strong biogeographic links are also present with pre-Mississippian faunas of the Farewell terrane of southwestern Alaska, most notably during the Late Ordovician (Ashgillian), when their macrofaunas are essentially identical. Similarities between Arctic Alaska and the Farewell terrane cease after the Devonian, suggesting that the latter was also derived from Siberia during an earlier rifting episode.

Pre-Carboniferous unconformity-bounded megasequences on the Arctic Alaska plate represent unique depositional episodes in the history of northern Alaska that are distinct from the northern Cordillera. Direct stratigraphic evidence from the northeastern Brooks Range suggest that a Neoproterozoic rifting event (~780 Ma) resulted in a carbonate-dominated passive margin that persisted into late Early Devonian time. This thick succession of over 4000 m of carbonate rocks is unparalleled in the Canadian Arctic and requires reexamination of tectonic models for northern Alaska.  

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.