Abstract

Important changes in structural styles occur between the western Sadlerochit and Shublik Mountains in the northeastern Brooks Range of Alaska. Distinct structural variations in the Sadlerochit Mountains relative to those observed south in the Shublik Mountains is caused by the depositional pinch-out to the north of Mississippian Kayak Shale of the Endicott Group. Shortening by mechanisms of detachment folding and thrust faulting in the Shublik Mountains has been transformed to a system of small displacement, high-angle reverse and thrust faults in the Sadlerochit Mountains.

Detachment folding and thrust faulting in units above the Kayak Shale is representative of structures in the Shublik Mountains. Localized folding and faulting effecting the overlying Carboniferous Lisburne Group are not evident in the underlying Kekiktuk Conglomerate or the pre-Cambrian Katakturuk Dolomite. The Kayak Shale is structurally thinned along synclinal axes and thickened in cores of anticlines in superjacent strata.

Pinch-out of the Kayak Shale causes a significant change in the structural style of overlying Lisburne Group carbonates approximately 5 miles north in the Sadlerochit Mountains. High-angle reverse faults with little displacement propagate upward from either the pre-Cambrian Kakakturuk Dolomite or the lower Paleozoic Nanook Limestone and cross-cut the Endicott Group. The faults continue to ramp up through the basal Alapah Limestone of the Lisburne Group and eventually flatten-out and die within the Alapah Limestone. These small-scale thrust faults have caused repeated stratigraphy of the Alapah Limestone in the Sadlerochit Mountains. Strata above the faults is commonly folded.