Style and Age of Tectonism of Sadlerochit Mountains to Franklin Mountains, Arctic National Wildlife Refuge (ANWR), Alaska: ABSTRACT

Abstract

The pre-Tertiary rocks north of the Franklin Mountains and south of the coastal plain in ANWR can be subdivided into two major structural units: (1) basement--Neruokpuk Formation, Nanook Limestone, and Katakturuk Dolomite--and (2) Lower Mississippian to Upper Cretaceous sedimentary rocks. Basement rocks underwent intense deformation prior to deposition of Lower Mississippian rocks; locally the contact is structural. Crustal shortening at the structural level exposed was accommodated primarily by concentric folding. Axial planes of major folds generally strike N70°-90°E and dip 50°-80°S, indicating north vergence, and can be subdivided into two groups: east-northeast trending and east trending. Major folds plunge subhorizontally and continue laterally for up to 10 mi (15 km). Exposed reverse faults show relatively small amounts of throw (< 7,500 ft or 2.5 km). Relative shortening decreases from greater than 41% at the northern margin of the Franklin Mountains to less than 16% in the Sadlerochit Mountains, amounting to approximately 14 mi (22 km) over 39 mi (64 km) of a north-south transect. Reverse/thrust faults are interpreted to sole out along a basal decollement. This detachment probably lies between the Neruokpuk Formation and overlying basement carbonate rocks between the Franklin and Sadlerochit Mountains, and ramps upward under the coastal plain. Field structural data of the study area, and well and seismic data of the area west of ANWR, constrain the principal post-Mississippian deformation, a phase of north-south compression, to have occurred between the mid-Eocene and the present. East-trending folds suggest two deformational events. Relative timing of these events, based on field data, is equivocal. End_of_Article - Last_Page 668------------