Abstract: Franklinian Rocks Along the Alaska-Yukon Border in the Northeastern Brooks Range, Implications for Reflection Seismic Imaging Under the Arctic Coastal Plain of the Arctic National Wildlife Refuge, Alaska

John S. Kelley, Chester T. Wrucke, Larry S. Lane, Richard L. Foland

Recent mapping along the Alaska-Yukon border shows two stratigraphic successions of Franklinian rocks separated by a regional fault. The northern succession consists of Proterozoic(?) to Silurian argillite, bedded chert, limestone, and basaltic volcaniclastic rocks deposited largely below wave-base, presumably in deep water. Part of this northern succession is correlative with the Road River Formation, a succession of Early Ordovician to Early Devonian rocks widely recognized in Canada. The southern succession lies mostly south of a prominent east-striking syncline in which Ellesmerian (Mississippian to Triassic) rocks that unconformably overlie the Franklinian rocks are preserved. The southern succession consists of turbiditic argillite, limestone, and sandstone and a de ositionally overlying sandstone-dominated section previously mapped as the Neruokpuk Schist. The southern succession contains the same Proterozoic(?) to early Middle Cambrian trace fossils present in the northern succession. Rock types, indicators of depositional environments, and, age-diagnostic trace fossils common to both successions imply stratigraphic consanguinity between the two successions. A regional shallow gently south-dipping fault exposed in the north limb of the syncline emplaces the southern succession on the northern succession.

Despite the fact that rocks in the northern and southern Franklinian successions are penetratively deformed and tightly folded, low-dipping map units are also present and are likely to produce seismic reflections. Foliation and prominent cleavage surfaces in tightly folded rocks are not likely to make good reflectors because they do not separate rocks of different acoustic impedance, and beds in folds restricted to individual map units have limbs that are too appressed to produce effective seismic reflections except in narrow fold crests. However, some folds that involve multiple map units have broad crests and wave lengths that are kilometers in length and width. Likely acoustic impedance contrasts between different rock types that make up the map units in these folds could produce s ismic responses similar to the high-amplitude, shallow-dipping, concave-upward, and generally north-dipping reflectors that are as much as 5 km across in Franklinian rocks under the coastal plain in the Arctic National Wildlife Refuge.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California