--> Endicott Mountains Allochthon, Its Relation to Framework and Structural Development of Central Brooks Range, Alaska, by J. S. Kelley and W. P. Brosge; #91024 (1989)

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Endicott Mountains Allochthon, Its Relation to Framework and Structural Development of Central Brooks Range, Alaska

J. S. Kelley, W. P. Brosge

In reporting occurrences of weakly metamorphosed basement at Mount Doonerak (MD), some workers pointed out that Mississippian to Triassic strata unconformably overlying basement at MD are similar to strata in the northeastern Brooks Range, but mostly different from Devonian to Cretaceous strata exposed in the north-central Brooks Range. These workers suggested that the Devonian to Cretaceous strata in the north-central Brooks Range could be (1) a north-transported regional thrust sheet rooted south of MD, or (2) a telescoped sequence that originally lay north of MD. Subsequent authors refer to Devonian to Cretaceous strata in the north-central Brooks Range as the Endicott Mountains allochthon, a regional allochthon rooted south of MD.

A balanced cross section from recent mapping and reinterpretation of previous mapping done by various workers demonstrates the geometric possibility that the Devonian to Cretaceous strata in the north-central Brooks Range are an assemblage that was mostly deposited north of Franklinian basement rocks exposed at MD. Our cross section implies complex structural delamination and about 50% shortening within Devonian to Cretaceous strata north of MD and involvement of basement rocks in thrusting under the north-central Brooks Range. Restoration of our section infers a Devonian basin north of the restored position of MD and erosionally beveled Devonian strata south of the restored position of MD. We explain the apparent superposition of Devonian strata of the north-central Brooks Range asse blage above the Mississippian to Triassic strata at MD in terms of (1) late-stage down-to-the-south normal faults north of MD that lower the Mississippian to Triassic strata from thrust positions above the Devonian strata, and (2) thrust relations of Devonian strata south of MD not removed by the unconformity at the base of the Mississippian section. Our cross section and reconstruction suggest that Devonian strata of the north-central Brooks Range are an intensely telescoped analog of pre-Mississippian basins underlying the North Slope such as the Ikpikpuk-Umiat and possibly Meade basins.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.