Lower Devonian Carbonate Facies and Platform Margin Development, East-Central Alaska and Yukon Territory: ABSTRACT

Abstract

Pragian to Emsian (mid-late Early Devonian) sedimentation on the southwestern portion of the Yukon stable block, east-central Alaska and Yukon Territory, is represented by a package of intergradational carbonate facies, each characteristic of its relative position on or off the carbonate platform and the platform's stage of development. End_Page 658------------------------------ In Pragian time, crinoid thickets were extensive across the platform. By Emsian time, an east-west-trending rugosan coral-stromatoporoid reef complex, cored by Renalcis-bound mudstone, had developed along the platform margin. This reef complex was composed of large colonial corals, often capped by stromatoporoids, with framework cavities filled with skeletal wackestone to rudstone matrix. A pelletal and intraclastic wackestone to packstone facies was deposited in the slightly protected back-reef environment to the north. Concurrently, sediments and blocks were shed from the fore reef southward into the foreslope environment dominated by a Thamnopora-crinoid floatstone to rudstone facies. Slope failures produced bioclastic debris flow and turbidite sedimentation of shelf-carbonate detr tus into the coeval shale of the adjacent basin situated to the south and west. Pelagic sedimentation of clay-size carbonate material also deposited thin, dark, lime mudstone beds within this basin. Toward the end of Emsian time, a rapid marine transgression inundated the shallow shelf area, and deeper water open marine carbonate sedimentation occurred, represented by a tentaculitid-rich whole-fossil bioclastic wackestone to mudstone facies. As the waters continued to deepen, basinal siliceous oozes and clays were deposited over the entire region through the Middle Devonian. End_of_Article - Last_Page 659------------