STRUCTURAL EVOLUTION OF A FRONTAL RAMP SECTION OF THE WEST-SPITSBERGEN, TERTIARY FOLD-AND-THRUST BELT, NORTH OF ISFJORDEN, SPITSBERGEN

The geometry and kinematic evolution of a frontal ramp section associa ted with the Tertiary West Spitsbergen Orogenic Belt has been investig ated in a small area (Lappdalen) north of Isfjorden. The previously re cognized thrust front corresponds to a complex step or ramp in the pos ition of the sole-thrust in the area. The sole-thrust is localized to the evaporites of the Permian Gipshuken Formation to the west of the f ootwall ramp, whereas to the east it continues as a bedding-parallel t hrust in Triassic shales (Sassendalen Group). The area to the west of the footwall ramp is characterized by large scale thrusts and folds in volving the Permian Gipshuken and Kapp Starostin formations and the lo wer part of the Triassic Sassendalen Group. East of the footwall ramp both Permian and Triassic strata are sub-horizontal and apparently und eformed. Three major thrust sheets are recognized. Based on the geomet ric relationship between folds and faults in the area, both fault-bend and fault-propogation mechanisms of folding are inferred. Restoration of the Kapp Starostin Formation to its pre-deformational state indica tes a minimum of 35% shortening. Structural observations within the Sa ssendalen Group in the study area and on Dickson Land suggest that som e of this shortening is transmitted eastwards along one or more beddin g parallel thrusts in the Sassendalen Group.