Elusive Ridge, Brooks Range, Northern Foothills, Structural and Stratigraphic Relationships Between Allochthon and Parautochthon

Elusive Ridge has both general and regional scientific significance because it exposes a record of the geometry and evolution of the leading edge of an orogenic wedge across the transition from allochthonous synorogenic deposits to parautochthonous foreland basin fill. Elusive ridge is a northwest trending ridge located in the Brooks Range, Alaska. In the northern foothills of the range, Elusive Ridge is at the junction of the east-west trending Central Brooks Range and the northeast trending Philip Smith Mountains. It is one of the few locations along the Brooks Range mountain front where the base of the allochthonous wedge is exposed over the parautochthon. The ridge provides exposures across this transition that are unusually good and continuous for the clastic rocks north of the mountain front. Exposures on Elusive Ridge are primarily comprised of Berriasian – Valanginian Okpikruak formation and Aptian(?) – Albian Fortress Mountain Formation. The northwest extent of the ridge includes shale and sandstone units. This study of the area provides insight into the stratigraphic and structural relations among the main elements at this transition, including: synorogenic deposits at the toe of the Endicott Mountains allochthon (Okpikruak Formation), parautochthonous late-tectonic wedgetop deposits (Fortress Mt./Cobblestone Formations), late- to post-tectonic foredeep fill (Torok and Nanushuk Formations).