From the Mississippian to Jurassic a carbonate ramp built out to the south on the passive margin of the Arctic Alaskan Plate. The Arctic Alaskan Plate was then rifted and rotated in the Early to Mid Cretaceous. This rifting created the Barrow Arch that separates the ANS from the Canadian Basin. As the plate continued to rotate it collided with the island arch chain, initiating the Brooks Range Orogeny. As the Brooks Range uplifted subsidence dropped the carbonate ramp and created a massive amount of accommodation space in the foothills region. Sedimentation couldn't keep up with the subsidence forming a shallow anoxic sea during the Late Cretaceous to Tertiary. These sediments, along with the Mississippian to Jurassic carbonate and shallow marine deposits, form the source and reservoir rock throughout the ANS foreland basin.