Geometry and kinematics of the Yakataga anticline, Icy Bay, Alaska

Abstract

The Yakataga incline is a well-exposed asymmetrical fold with a ramp tip beneath the forelimb. Uncomformities in the backlimb and forelimb indicate that both limbs rotated during fold growth. The stratigraphic character and evidence for deformation before full lithification suggest non-parallel folding by distributed strain rather than flexural slip. These characteristics of the natural fold do not fit existing models for thrust-related folds and I suggest two models for the Yakataga anticline's growth: 1) the fold formed as a non-parallel detachment fold modified by fault-propagation folding in the forelimb; and 2) the fold formed as a rotating-limb fault-propagation fold. The first of these models seems to fit the natural fold better because: 1) this model accounts for the subsidiary fold in the forelimb; and 2) rotation of the backlimb in the fault-propagation fold model requires a fanning of the bedding, a feature not observed in the natural fold.