Late Paleozoic Stratigraphic History and Provenance of the Farewell Terrane, Southwestern Alaska
Michigan State University, Department of Geological Sciences East Lansing, Michigan, USA
Alaska’s Farewell terrane resides in the western Alaska Range, and represents the northernmost position of the North American Cordillera. Exposed both north and south of the Denali fault, the Farewell terrane is primarily composed of three subterranes: (1) the Upper Paleozoic and dominantly siliciclastic Mystic subterrane, (2) Lower Paleozoic siliciclastic and carbonate units of the Dillinger subterrane, and (3) Lower Paleozoic carbonate strata of the Nixon Fork subterrane. New geologic mapping, measured stratigraphic section, and provenance data of Devonian–Permian strata of the Mystic subterrane reveal a continuous record of siliciclastic sedimentation. Strata consist largely of interbedded, fine- to coarse-grained sandstone and mudstone, which are laterally extensive (>100 m) and exhibit tabular geometries. Individual units are 0.02–1.0 m thick and sandstone facies are characterized by plane beds, ripple cross- stratification and massive beds. Mudstone rip-up clasts are common at the base of beds. Matrix-supported conglomerate occurs sporadically throughout this unit with individual clasts that are rounded to subrounded and range from 1–10 cm in diameter. Preliminary provenance reveals clasts and grains consisting of lithic sedimentary fragments, mono- and polycrystalline quartz, and abundant chert. Overall, this unit appears to coarsen upward and may grade stratigraphically into overlying marginal-marine to non-marine strata of the Permian Mt. Dall conglomerate. Continued study of the stratigraphic history and provenance of these strata will provide a basis for understanding the early stages of orogenesis along the northernmost exposure of the North American Cordillera.
AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid