User:Bonehart/SouthwestBrooksridge/Structural Geology of Brooks Range

Through field and seismic investigation it is found that the key features of the northern Brooks Range was formed by two superposed north directed deformation belts:
 * 1) A thin skinned fold and Thrust Belt formed in late Jurassic to Early Cretacious (Neocomian)
 * 2) A thin to thick skinned fold and Thrust Belt that developed in the early Tertiary following sedimentary burial beneath the Colville basin.

First Thrusting Episode
The first episode of thrusting in northern Alaska was related to the Late Jurassic and Early Cretaceous north facing arc-continental collision which put the Endicott Mountains and higher allochthons beneath a Jurassic oceanic arc. During the deformation, allocthons of distal facies sequences were internally deformed and detached from their continental substrate and assembled by northward thrusting into shingled, north-thinning deformational wedges. Evidence shows that deformational wedges were put onto south-dipping autochthon in two major phases, with the higher allocthons being emplaced during early Neocomian (140 Ma) and the Endicott Mountains allocthon being emplaced in the late Neocomian (120 Ma).
 * This thrusting resulted in the construction of a topographically high-standing region that borders the south edge of the Colville basin.
 * High tectonic loading produced by the thrusting caused subsidence of the basin.
 * After this first period of thrusting there was a time of “quiet” from late Early Cretaceous and Late Cretaceous where approximately 8 km of deposition took place in the Colville basin from strata of the south and west. Most of the deposition appears to be from slumping and normal faulting.

Second Thrusting Episode
The second episode of north-directed thrusting occurred approximately 60 Ma to 45 Ma which was probably generated by a plate interaction in southern Alaska. Thrusting occurred very deep under the southern portion of Brooks Range and angled up beneath the northern portion. This thrusting event formed reverse faults that truncated older deformational wedges and the mid-Cretaceous deposits that overlie the wedge.

Oil Exploration
National Petroleum Reserve, Alaska (NPRA) have found that only dolomitized carbonate rocks contain sufficient porosity to form major reservoirs in the area. The first episode of north directed, thin-skinned thrusting and thrust related folding followed by refolding by normal faults after the second thrusting event provided ideal closures for oil and gas reservoirs.