Significant Outcrops of Cretaceous and Tertiary Rocks in Northeastern Alaska: ABSTRACT

Abstract

Cretaceous and Tertiary rocks in northeastern Alaska comprise the Neocomian part of the northerly derived Ellesmerian depositional sequence and the overlying Brookian sequence, which was derived from the ancestral Brooks Range to the south and southwest. The Ellesmerian part is less than a few hundred meters thick and consists of the upper part of the Kingak Shale and the overlying transgressive part of the pebble-shale unit and associated Kemik Sandstone Member of the Kongakut Formation. The Brookian sequence is more than 4,000 m thick and consists of, in ascending order: (1) a deep-water condensed section of organic-rich shale and bentonite with a discrete 30 to 60-m thick radioactive zone at the base; (2) a slope-and-shelf shale section with turbidites at the base; (3) a fluvial-dominated deltaic sequence that, except for one major and several minor transgressions, prograded from southwest to northeast during Albian to Eocene time; and (4) a shallow marine and nonmarine post-Eocene section. Rocks of the four facies, which represent a wide range of depositional environments, are discontinuously exposed along the coastal plain and foothills of the Brooks Range in northeastern Alaska. Certain outcrops are significant because they show critical facies relationships. Recognition of vertical and lateral facies sequences and key lithologic units, in conjunction with available paleontologic data, facilitates correlation of the Cretaceous and Tertiary rocks both across the outcrop belt and into the subsurface to the north. End_of_Article - Last_Page 670------------