ABSTRACT: Structural Inversion in the North Urals Foreland, U.S.S.R.

SCHAMEL, STEVEN, University of South Carolina, Columbia, SC, and NIKOLAI A. MALYSHEV and VIKTOR V. YUDIN, Institute of Geology, USSR Academy of Science, Syktyvkar, U.S.S.R.

The Pechora basin, the foreland depression west of the North Urals and Pay-Khoy thrust belts, is partitioned structurally by a series of large northwest-trending anticlinoria, which locally have amplitudes in excess of 1000 m. The principal belt of anticlinoria, the Pechora-Kolva zone, marks the limits of an early Paleozoic rift system formed during, or shortly after, the development of the passive margin of northeast Europe. The individual anticlinoria within this zone are inverted half-grabens; reverse movement on original normal faults has given rise to large fault propagation folds. A long history of growth of the inversion structures from the mid-Carboniferous through the Early Jurassic is recorded in nested unconformities, stratigraphic thinning, and/or facies changes across the anticlinoria. The foreland anticlinoria are oblique to the north-south-trending North Urals thrust belt. The thrust belt intersects the Pechora-Kolva zone in a region of complex overstepping frontal thrusts.

Structural inversion within the Pechora basin spans the same period of time as the development of the North Urals orogen by plate collision. The inversion structures are thought to have formed by left-lateral transpression reactivating deep-seated normal faults several hundreds of kilometers in front of the nascent North Urals orogenic front. The closing of the Urals seaway and collision of northeast Europe with the Kazhak-Kirghiz plate in the mid-Paleozoic resulted in transfer of compressive stress far back onto the Russian Platform. The Pechora basin anticlinoria are analogous to structural inversions now recognized in the Alpine foreland of Western Europe, the sub-Andean basins of northern South America, and elsewhere.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)