Preliminary Structural Interpretation of the Gilead Syncline and Gilead Creek Areas in the Arctic Foothills of The Northeast Brooks Range, Alaska

Garrett Speeter
University of Alaska Fairbanks, Department of Geology and Geophysics Fairbanks, Alaska; [email protected]

Geological mapping of the Gilead Creek and Gilead syncline area in the Arctic Foothills of the Northeast Brooks Range, documents two shortening directions in the Gilead sandstone (NW-SE /NE-SW). The Gilead sandstone (a potential reservoir unit) is folded into high wavelength 4° (4th order) folds at Gilead syncline and shorter wavelength 3° folds to the NW adjacent to Gilead Creek. Shorter wavelength south verging folds are present in Gilead sandstone moving up Gilead Creek north of base mark Sheck. The stratigraphic top of the Gilead sandstone is unclear and is currently under investigation. The Gilead sandstone is underlain by a detachment in the Cretaceous Kingak Shale that allows the competent Gilead sandstone to fold passively above the Triassic Shublik and Ivishak Formations, which are folded in shorter wavelengths than the Gilead sandstone. Fold axes document a dominant NE-SW shortening direction in the Ivishak and Shublik Formations in front of the Echooka anticlinorium. Back thrusts present in Triassic units and a dominant NW plunging direction suggest that the folds in Shublik and Ivishak Formations were formed then tilted as they were “bulldozed” up by the underlying Echooka and Lisburne Formations, which was possibly driven by fault bend folding at depth. The Shublik and Ivishak Formations are separated from the underlying Permian Echooka and Lisburne Formations by a detachment in the Triassic Kavik Formation. The Permian Echooka and Lisburne Formations were deformed by 2° and 3° folding and are separated from deformation in underlying units by a detachment in the Kayak Shale.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid