Abstract: Alaska Peninsula Late Cretaceous Fore-Arc Deposition

Ernest A. Mancini, Thomas M. Deeter

Upper Cretaceous deposition on the Alaska Peninsula was controlled by convergent-plate tectonics. The Late Cretaceous arc front was along the northern margin of the present Peninsula, whereas the trench was seaward of the present Kodiak and Shumagin Islands. The Upper Cretaceous Kodiak and Shumagin Formations represent slope-basin and accretionary-prism accumulation; the Campanian Coal Valley, Chignik, and Hoodoo Formations of the Alaska Peninsula represent fore-arc deposition landward of the trench-slope break. The Campanian age of the formations is based on palynomorphs, ammonites and inoceramids, and foraminifers respectively.

The preceding formations consist of approximately correlative sediments deposited in different environments. The nonmarine conglomerates, sandstones, and coals of the Coal Valley Formation accumulated as alluvial-fan and braided-stream deposits, the inner neritic sandstones and siltstones of the Chignik Formation as upper and lower shoreface deposits, and the outer neritic and bathyal siltstones and shales of the Hoodoo Formation as offshore deposits. The Hoodoo conglomerates and sandstones accumulated as turbidites.

The petrographic similarity of the Coal Valley, Chignik, and Hoodoo Formations also indicates that these formations are facies equivalents chiefly comprised of plutonic rock fragments, feldspars, and quartz, suggesting derivation from the eroding Late Cretaceous arc front.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC