Relative Sea–level Changes in Cratonic Basins–Tectonics or Eustasy

Abstract

Large changes of the depth of water of a third order in cratonic basins, up to 100-200 m during 1-3 Ma, are commonly supposed to be of a eustatic origin. Continuous deposition took place at a depth of ≤ 10-20 m in East Siberia in the Ordovician and Silurian, East Baltic in the Cambrian and Ordovician, and in the East European Platform in the Pennsylvanian and Early Permian. Modelling of changes in the depth of water in these regions under sea-level fluctuations of a third order has shown that over the predominant part of the above epochs such fluctuations did not exceed 20-30 m. Under such circumstances, large-scale regressions and transgressions, 1-3 Ma long, in cratonic basins should be attributed to rapid vertical crustal movements. For example, the crustal uplift of ~ 200 m followed by the subsidence to the initial level occurred on the shelf in the western part of the East European Platform in the earliest Pennsylvanian. Numerous stratigraphic traps were formed due to regressions and transgressions of a third order. In each hydrocarbon basin, their prospecting requires the studies of time and space distribution of rapid vertical crustal movements in the basin and in the adjacent areas.