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Inversion in Other Geological Environments |
Department of Geology, Royal Hollway and Bedford New College, University of London, Egham, Surrey, TW2O OEX, UK
Department of Applied Geology, University of Strathclyde, Glasgow GI IXJ, UK
The Kechika Trough, in the western Rocky Mountains of northern Canada, is a NW-trending fold and thrust belt of Hadrynian through Mississippian strata within the telescoped passive margin of ancestral North America. The Kechika Trough underwent major crustal extension in the Mid-Late Devonian with the deposition of coarse to fine ‘Antler’ type black clastics in an asymmetrical basin consisting of a terraced half-graben system to the west and a roll-over structure to the east. Inversion and contraction of the Kechika Trough occurred during the Jurassic-Cretaceous Columbian-Laramide orogeny. The geometries of the resultant fold and thrust systems were strongly controlled by the half-graben extensional architectures and by the geometries of the synrift sediment packages. Inversion structures include contractionally reactivated extensional faults, rotated and re-utilized extensional faults, and thrust faults pinned by extensional faults as a result of buttressing against rigid sediment wedges. Inversion of the synrift sediments is associated with strongly developed chevron folding, pervasive cleavage development and imbrication by out-of-half-graben thrust faults. These thrust faults may locally climb down stratigraphic section in the direction of transport as a result of cutting through strata tilted by Mid-Late Devonian extensional faults. Major stratigraphic contrasts between adjacent thrust packages have been resolved in terms of lateral facies differences produced by extension, rather than by over-complex thrust geometries. Although syndepositional extensional faults are not preserved in the thrust belt, their position and geometry may be inferred from an analysis of structural, stratigraphic and sedimentological relationships.
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