Harris, E. E.1, C. G. Mull2, P. R. Peapples1,
D. L. LePain3
(1) Alaska Division of Geological and Geophysical Surveys, Fairbanks, AK
(2) Alaska Division of Oil and Gas, Anchorage, AK
(3) Wisconsin Geological & Natural History Survey, Madison, WI
ABSTRACT: New Detailed (1:63,360-scale) Mapping of the Brooks Range Northern Foothills and Rangefront, Kanayut River Area, Alaska
Rocks of the Endicott Mountains allochthon form the mountain front and include the clastic Devonian Endicott Group, platform carbonates of the Pennsylvanian-Mississippian Lisburne Group, the Permian Siksikpuk Formation, and Jurassic-Triassic Otuk Formation. A broadly plunging anticline exposes progressively younger rocks and shallower thrust blocks to the west; folded thrusts also plunge to the west. In the eastern part of the map area, a major north-vergent detachment along the Hunt Fork shale overrides the Kanayut Conglomerate and joins the Mississippian Kayak shale detachment above. To the west, the thrust cuts upsection into the Lisburne Group. At least four horses are exposed within the range front map area and represent uplift occurring from mid-Aptian to mid-Cretaceous. Anomalously high porosity within vuggy dolomitized Lisburne Limestone appears to be associated with thrusting. In the southern foothills the structurally higher Ipnavik River allochthon consist of turbidites of the Neocomian Okpikruak Formation with scattered mafic bodies emplaced during deposition, and isolated exotic blocks of Permian to Triassic chert shed northward from, and deformed by, the advancing thrust sheets. In the foothills to the north are rocks of the Brookian sequence that record progressive infilling of the Colville basin with sediment sourced from the ancestral Brooks Range. In the southern foothills syndepositional deformation related to north-vergent thrusting and uplift during mid- to late-Aptian form complex fold and thrust relationships of early Brookian strata. In the northern foothills regional shortening (post-Albian?) of younger Brookian strata forms broad regional synclines separated by thrust-fault-breached anticlines, with evidence of south-vergent backthrusting.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.