EVOLUTION OF THE TIMAN-PECHORA AND SOUTH BARENTS SEA BASINS

Abstract

We have analysed 129 stratigraphic sections from the Timan-Pechora basin, from its adjacent continental shelf and from the South Barents Sea basin, in order to determine whether existing models of extensional sedimentary basin formation can be applied to these intracratonic basins or whether new mechanisms of formation need to be invoked. The subsidence history of each section has been calculated using standard backstripping techniques. An inverse model, based on finite-duration lithospheric stretching, has then been used to calculate the distribution of strain rate as a function of time required to fit each subsidence profile. Results demonstrate an excellent fit between theory and observation. By combining our analysis with independent field-based and geophysical observations, we show that the Timan-Pechora basin underwent at least four phases of mild lithospheric stretching during the Phanerozoic (β<1.2). These phases occurred in Ordovician, Late Ordovician-Silurian, Middle-Late Devonian and Permian-Early Triassic times. Growth on normal faults, episodes of volcanic activity and regional considerations provide corroborative support for the existence of all four phases. Although less well constrained, subsidence data from the South Barents Sea basin are consistent with a similar Early-Middle Palaeozoic history. The main difference is that Permian-Early Triassic extension is substantially greater than that seen onshore. This similarity implies structural connectivity throughout their respective evolutions. Finally, subsidence modelling demonstrates that rapid foreland basin formation, associated with the Uralian Orogeny, was initiated in Permo-Triassic times and is confined to the eastern margin of the Timan-Pechora basin. Coeval foreland subsidence does not occur on the eastern margin of the South Barents Sea basin, supporting the allochthonous nature of Novaya Zemlya. The most puzzling result is the existence of simultaneous lithospheric extension and foreland loading in Permian-Early Triassic times. This juxtaposition is most clearly seen within the Timan-Pechora basin itself and suggests that convective drawdown may play a role in foreland basin formation.