Carboniferous Carbonate Depositional Models, Preliminary Lithofacies and Paleotectonic Maps, Arctic Alaska

Abstract

Two distinct environmental suites can be delineated for the shallow-marine Carboniferous rocks of Arctic Alaska. One is a marine transgressive suite, typified at its base by a paralic clastic sequence followed by nearshore shales and siltstones, and overlain by spiculitic carbonate rocks. This transgressive clastic-marine carbonate sequence is associated with regional Mississippian transgression. Developed above this is a carbonate platform sequence characterized by very low terrigenous clastic content and shallow-water cyclic carbonate sedimentation. The outer margins of the shelf did not support reef-forming organisms. Carboniferous sedimentation in Arctic Alaska represents a northward marine transgression over an irregular surface with residual stable positive areas. In the northeast, the Sadlerochit high was not submerged until early Chester time. In the west-central foothills region, the Nuka high is a long, linear, east-trending positive area in the subsurface; it may have been the source for the Mississippian feldspathic clastic rocks of the Nuka Formation. The Nuka high may have remained a mildly active positive element during the Mississippian. A northeast-trending negative area, the Canning sag, stretches from the Prudhoe Bay region southwest to the Sagavanirktok River region of the Brooks Range, where there is a 3,000-ft-thick accumulation of shallow-water Carboniferous carbonate rocks. The Lisburne Group, at many outcrops in the Brooks Range, was deposited as a complex of cyclic shallow-water carbonate sediments in an arid or semiarid climate. A typical cycle grades from marine ooid-crinoid grainstone to supratidal microdolomite. Composite cyclic carbonate sequences may be thousands of feet thick in outcrop. Outcrop studies indicate that thick sequences that have been dolomitized by reflux brines may have reservoir qualities in the subsurface of the north slope.