Compressional Salt Tectonics and Exploration Plays in the Kosyu–Rogov Trough, the Timan–Pechora Basin

Abstract

This study aims to investigate the structure and petroleum habitat of salt-related structures in the Kosyu–Rogov Trough, which is a part of the Uralian fold-and-thrust belt in the Timan–Pechora Basin. The structures produced by the upper Ordovician salt are thought to have a much wider distribution in the Kosyu–Rogov Trough and the adjacent Chernyshev Swell than was previously believed. The sedimentary cover of the Kosyu–Rogov Trough is decoupled along the salt layer, resulting in the long-distance transfer of contraction in the post-salt deposits. Based on an integrated interpretation of subsurface data, including 2D and 3D seismic surveys, two types of salt structures are recognised: (1) salt pillows and (2) squeezed diapirs. The salt pillows are distributed in the mildly disturbed central part of the Kosyu–Rogov Trough above the layer-parallel flat of the salt detachment. The squeezed diapirs are clustered within the external part of the study area in the highly disturbed Chernyshev Swell, where the salt layer is passing into basin margin carbonate equivalents. The squeezing of the massive salt diapirs of the Chernyshev Swell has produced large, salt-detached backthrusts in the external part of the Kosyu–Rogov Trough. The horizontal displacement of the backthrust can reach 15 km. Stratigraphic thinning over diapirs and angular unconformities indicate that the initiation of the salt tectonics preceded the onset of the Uralian collision shortening in the late Artinskian. Salt diapirism episodically influenced the facies distribution in the post-salt deposits, predetermining the location of carbonate banks, reefs, oolitic shoals and karstified areas. The large thickness of the sedimentary cover has resulted in early hydrocarbon migration, peaking before the Uralian shortening. This explains why previous exploration projects targeting thrust-related traps that postdated the main migration were largely unsuccessful. It is proposed that traps associated with long-lived salt structures, which were able to receive a hydrocarbon charge during the peak of hydrocarbon migration, are of primary exploration interest.