Abstract

Three structural/stratigraphic provinces were defined in the Marsh Creek area. Complexly deformed Upper Cretaceous rocks locally overlain by a NE trending klippe defines the Coastal Plain Province (CPP). The klippe consists of a duplex with north-vergent thrust faults and short wavelength folds within Jurassic and younger rocks. Fault bend folds are the dominant fold type. Significant lateral structural variations result from branching and rejoining splays and loss of displacement in folds. A northern topographic salient with respect to the main Sadlerochit Mountains defines the Marsh Creek Province (MCP), south of the CPP. This salient is an ENE trending, north vergent asymmetric anticline of pre-Mississippian to Lower Cretaceous rocks formed above a major detachment which ramps northward out of the pre-Mississippian sequence. Both the forelimb and backlimb show significant variation along strike. Mountain front, forelimb, structure changes from a duplex in the east to a backthrust in the west. Two orders of folding modify the gently dipping backlimb. First order E trending monoclinal steps are interpreted to reflect changes in attitude of the underlying detachment. Second order, ENE trending chevron folds formed by fault propagation from the basal detachment. The Sadlerochit Mountains Province (SMP) is defined by the main E-W trend of the range. One large fold/fault block of the whole stratigraphic section defines the regional strike and structural style of the province. A thrust fault bounds the block on the north. This fault is interpreted as having segmented a once continuous structure composed of the SMP and MCP. Two dominant structural trends, E and ENE, are observed. E trends are observed in pre-Mississippian cored structures and are interpreted to reflect preexisting trends. ENE trends formed in Mississippian and younger rocks normal to the tectonic transport direction.

Truncation, from north to south, of each province's trend by the adjacent province constrains the relative timing of deformation. The duplex in the CPP developed first and was isolated as a klippe by development of the MCP. This is a forward propagating sequence involving progressively deeper stratigraphic levels. The fault on the northern boundary of the SMP developed most recently and is out of sequence with respect to the other major structures.