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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 528

Last Page: 528

Title: Sedimentology of Cretaceous Kuskokwim Group, Southwestern Alaska: A Borderland Complex: ABSTRACT

Author(s): J. A. Pacht, W. K. Wallace

Article Type: Meeting abstract


The southern portion of the Albian to Coniacian Kuskokwim Group was deposited in a continental borderland setting formed during accretion of exotic terranes to continental Alaska. This borderland was characterized by a broad, deep shelf with local highlands and confined basins. The Kuskokwim Group includes braided stream, marginal-marine, shelf turbidite, and borderland basin depositional facies. These facies are analogous to those of rocks deposited on the Neogene continental borderland of southern California.

The detritus which makes up the Kuskokwim Group was at least partly derived from highlands within the continental borderland, perhaps including islands. Sediment was transported by braided streams and deposited along shorelines. The detritus was then redeposited on the borderland shelf in submarine fans. Middle fan, outer fan, and basin plain facies have been recognized. Some fan turbidites may have been reworked by wave action during major storms, as suggested by the presence locally of sandstone beds with hummocky cross-stratification. Much of the Kuskokwim Group is characterized by thin-bedded TCDE siltstone-shale turbidites. These may represent deposition in areas of the borderland which were far from a sediment source. Detritus was also deposited in borderland basins, efined by submarine channel complexes composed of sandstone, conglomerate, and classic turbidites.

The Kuskokwim Group depositionally overlies diverse tectono-stratigraphic terranes of continental, magmatic arc, and oceanic affinity, indicating that those terranes were juxtaposed by the time of deposition. The continental borderland character of the Kuskokwim Group indicates that deposition occurred in a tectonically active environment. This may have been a fore-arc environment analogous to the present Kodiak-Shumagin shelf, or a transform environment analogous to the Neogene southern California borderland.

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