NEW DATA ON THE LATE PALEOZOIC OF THE ALEXANDER TERRANE AND WRANGELLIA

Wrangellia and Alexander occupy the west coast from Vancouver Island up to the southern interior of Alaska. Convergent geologic histories have been proposed for these terranes at various times from the Pennsylvanian through the Jurassic. Interpretation of Late Paleozoic position is important to these interpretations and provides control on Triassic position, though detailed Late Paleozoic data are absent. Additionally, while tectonostratigraphic histories define terranes, a reconstruction of general stratigraphy or paleontology for the Alexander terrane is lacking.

The Late Paleozoic of Vancouver Island (Wrangellia) overlies Early Paleozoic volcanics and comprises Mississippian through Early Permian deeper-water shales, cherts, and carbonate debris flows, and shallower-water carbonate grainstone and rare packstone/wackestone. Brachiopod, bryozoan, crinoid, and conodont faunas indicate generally cool water conditions for this time interval.

To contrast, the Late Paleozoic of the Alexander terrane overlies extensive Proterozoic to Early Paleozoic igneous and sedimentary rocks that are commonly eroded and re-deposited into Late Paleozoic and Triassic units. The Pennsylvanian through Early Permian in southeast Alaska (Keku Strait) comprises deeper-water silty, bioturbated carbonates, shallow-water fusulinacean-dominated shoals, coral bioherms, clastic-dominated shallow-water carbonates, and rooted tidal deposits with plant fossils. The corals and fusulinaceans indicate warmer water conditions for these units, but they are overlain by Early? Permian carbonates dominated by distinctly cool-water brachiopods. Unlike the tectonically quiescent Late Paleozoic units on Vancouver Island, episodes of volcanism and massive conglomerates with Early Paleozoic clasts indicate more tectonic activity for the Alexander terrane.

Despite interpretations of similarity between Alexander and Wrangellia, a reconstruction of Alexander's stratigraphy demonstrates dissimilarity between the two terranes. Paleontologic, tectonic, and climatologic differences further support differentiation. Additional work on the Late Paleozoic of Alaskan Wrangellia is required as it appears different from both southern Wrangellia (Vancouver Island) and the Alexander terrane.