Character and controls of fold-and-thrust deformation from pre-orogenic to foreland basin deposits: an example from the Gilead creek region of the Northeastern Brooks Range, Alaska

Abstract

"The character of structures in the Gilead Creek region is influenced by the mechanical stratigraphy in the area. Shortening is distributed throughout the mechanical stratigraphy along detachments in the incompetent Kayak, Kavik, Kingak, and Hue Shales. Detachment intervals separate competent Lisburne Group, Echooka Formation, Ledge Sandstone/Shublik Formation, Gilead sandstone, and moderately competent Seabee Formation from each other and allow the competent units to fold at distinct wavelengths according to their mechanical properties. Thick, competent units tend to form long-wavelength folds. Thin, competent units form relatively short-wavelength folds. Thin, competent units that are structurally bound to a thicker, structurally more dominant unit, adhere to the structural style of the dominant unit unless there is some detachment between them. Strain is distributed through shale intervals in the moderately competent units, allowing short-wavelength folds in the thin competent beds. The dominant trend of structures in the area is northeast overprinted on east. East-trending structures formed during the ~60 Ma event that formed the main axis of the Brooks Range and its foothills. Northeast-trending structures formed during the formation of the northeastern Brooks Range dated at ~45 Ma, ~35 Ma, and ~27 Ma, manifest locally by the compressional uplift of the Echooka anticlinorium southeast of Gilead Creek"--Leaf iii.