Detachment Tectonics in Sadlerochit and Shublik Mountains and Applications for Exploration Beneath Coastal Plain, Arctic National Wildlife Range, Alaska: ABSTRACT

Preliminary field investigations suggest three detachments in the Sadlerochit and Shublik Mountains: (1) the Kingak Shale, (2) along the pre-Mississippian unconformity, and (3) within the pre-Mississippian basement. The Kingak Shale decollement is the sole thrust for divergently branching subsidiary thrusts that repeat the Cretaceous Kemik Sandstone Member and overlying section. Well-exposed footwall and hanging-wall cutoffs together with multiple repetitions of Jurassic and Cretaceous over short distances demonstrate the detachment and provide permissive evidence of large-scale shortening. The detachment along the pre-Mississippian unconformity is not a sole thrust for subsidiary thrust faults. It is marked by cleavage development and folding of the overlying Mississippi n and younger rocks in marked disharmony with the underlying homoclinal pre-Mississippian strata. Detachment within the pre-Mississippian basement is not exposed but is interpreted from cumulative shortening across thrust faults observed and inferred in the Sadlerochit and Shublik Mountains. As envisioned, it would be a shallow south-dipping floor thrust for subsidiary faults largely controlled by the basement infrastructure. Thrust faults that cut the overlying Mississippian and younger section have horizontal displacements of 5-8 km and emplace pre-Mississippian rocks on Cretaceous strata. A large number of smaller thrust faults, responsible for deformation of the pre-Mississippian surface contribute to shortening. Structures involving the pre-Mississippian section trend east-west whereas earlier formed structures related to the Kingak Shale decollement trend east-northeast to west-southwest. Possible exploration leads beneath the coastal plain include: (1) large, broad, basement-involved structural culminations that may have subtle seismic expressions and (2) pre-Mississippian potential reservoirs thrust over Cretaceous source beds. Possible applications for regional seismic interpretation include: (1) means of discriminating basement-involved structures from preexisting basement-detached structures and (2) suggestion that two broadly different structural patterns exist under the coastal plain. End_of_Article - Last_Page 667------------