ABSTRACT: Bedrock Geology of the Northernmost "Bulge" of the Rocky Mountain Cordillera

Arthur C. Banet, Jr.

Analyses of LANDSAT imagery of the northernmost part of the Rocky Mountain Cordillera shows that rocks along the Alaska-Yukon border crop out in areally extensive predominantly curvilinear patterns. This area is a distinct and unique "bulge" in the mountain system where Upper Proterozoic sediments comprise most of the bedrock. At least two distinct and separate sedimentary successions are represented.

The predominantly clastic Neruokpuk Group of the Inuvikian Sequence spans the international border. It exceeds 13,000 m of south-southwest-dipping, mildly metamorphosed slatey argillites, quartz arenites, argillitic limestones, and chert. Correlations indicate that there are eight units which crop out in elongate arcs.

Coeval, south-dipping, predominantly carbonate rocks crop out in the Sadlerochit and Shublik Mountains and at Kikiktak Mountain. The Katakturak Formation is up to 2400 m of dolomite, silicified dolomite, and stromatolitic limestone of Upper Proterozoic age. It is unconformably overlain by the massive limestones and shale of the Nanook Formation (U. Cambrian-U. Devonian). Undivided, the Nanook is 1800 m thick with some sections removed by pre-Devonian erosion.

As yet, the nature of the sedimentological relationships of these two successions is still unclear. CDP seismic shows two suites of pre-Ellesmerian, north-dipping and south-dipping reflectors beneath the Arctic Coastal Plain, north of the Sadlerochit Mountains. However, resolution deteriorates north of the Neruokpuk exposures, precluding attempts to tie seismically interpreted suites to outcrops. Also, exploration drilling has penetrated the north-dipping reflectors, but recovery and testing of interbedded argillites and limestones fails to resolve this enigmatic stratigraphic relationship.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990