Coal in National Petroleum Reserve in Alaska (NPRA): Framework Geology and Resources: ABSTRACT

Abstract

The North Slope of Alaska contains huge resources of coal, much of which lies within NPRA. The main coal-bearing units, the Corwin and Chandler Formations of the Nanushuk Group (Lower and Upper Cretaceous), underlie about 20,000 mi2 (51,800 km2) of NPRA. They contain low-sulfur, low-ash, and probable coking-quality coal in gently dipping beds as thick as 20 ft (6.1 m) within stratigraphic intervals as thick as 4,500 ft (1,370 m). Lesser coal potential occurs in other Upper Cretaceous units and in Lower Mississippian and Tertiary strata. The river-dominated Corwin and Umiat deltas controlled the distribution of Nanushuk Group coal-forming environments. Most organic deposits formed on delta plains; fewer formed in alluvial plain or delta-front environments. Most NPRA coal beds are expected to be lenticular and irregular, as they probably accumulated in interdistributary basins, infilled bays, or inland flood basins, whereas some blanket beds may have formed on broad, slowly sinking, delta lobes. The major controls of coal rank and degree of deformation were depth of burial and subsequent tectonism. Nanushuk Group coal resources in NPRA are estimated to be as much as 2.75 trillion short tons. This value is the sum of 1.42 trillion short tons of near-surface (< 500 ft or 150 m of overburden) bituminous coal, 1.25 trillion short tons of near-surface subbituminous coal, and 0.08 trillion short tons of more deeply buried subbituminous coal. These estimates indicate that the North Slope may contain as much as one-third of the United States coal potential. End_of_Article - Last_Page 677------------