Lithofacies and conodonts of Carboniferous strata in the Ivotuk Hills, western Brooks Range, Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1992

Carboniferous strata in the Ivotuk Hills, in the western Brooks Range fold and thrust belt, consist of about 45 m of dark-gray shale, mudstone, dolostone, and spiculitic chert (upper part of the Kayak Shale, Endicott Group) and at least 225 m of light- to dark-gray dolostone, chert, and minor shale (Lisburne Group). The Kayak Shale was deposited chiefly below wave base; subordinate beds of dolomitic bioclastic packstone probably formed as storm deposits. The Kayak contains conodonts of Early Mississippian (early Osagean) age. The Lisburne Group in the Ivotuk Hills can be divided into three subunits on the basis of bedding style and lithology. The lower and upper units are thin-bedded to laminated, consist chiefly of fine-grained dolostone and spiculite and subordinate dolomitized bioclastic packstone. The middle unit is massive and resistant and is made up mostly of crinoidal packstone and lesser bryozoan wackestone. The lower and middle units of the Lisburne Group yield conodonts of early Late Mississippian (late Meramecian) age; a sample from the upper unit produced latest Late Mississippian (late Chesterian) conodonts.

The Kayak Shale in the Ivotuk Hills is in general similar to the Kayak elsewhere in the Brooks Range, but also has some lithologic and faunal similarities to the Kuna Formation of the Lisburne Group. The Kayak was probably deposited in a middle to outer platform or shelf setting in somewhat deeper water than that in which most of the Kayak accumulated, but under more oxygenated conditions than those typical of Kuna environments.

Sedimentologic data and conodont biofacies indicate that the Lisburne Group in the Ivotuk Hills accumulated primarily in normal marine, middle to outer platform or shelf settings. The section correlates well in age and lithology with the Lisburne at Lisburne Ridge, about 40 km to the west. Repeated thrust panels of Carboniferous strata encountered in the Lisburne Test Well No. 1, drilled 1.5 km northeast of our study area in the Ivotuk Hills, correlate biostratigraphically and lithologically with rocks exposed at the surface, but appear to have formed, at least in part, in somewhat shallower water and more restricted depositional environments.