Abstract
We have constructed a eustatic sea-level curve based on the stratigraphy of the tectonically stable Russian Platform. Sea-level variations measured against this reference frame were chosen as reliably representing the long-term relation of global ocean-basin volume and ocean-water volume. In constructing the curve, we backstripped stratigraphic data from numerous wells distributed across the Russian Platform and then used the present elevation of various stratigraphic horizons to tie the resulting curve to present sea level. Most strata observed represent very shallow water deposition (<25 m), and so we were able to estimate water-depth variations more reliably than would have been possible in a deep-water environment. The stratigraphy of the Russian Platform is riddled with unconformities. This is a result of the ability of even minor eustatic fluctuations to cause sea level to drop off the platform. These unconformities are important in accurately fixing sea level (0 water depth) at various times throughout the late Mesozoic-earliest Tertiary. The eustatic curve resulting from this study indicates that sea level rose by 120 m from the mid-Jurassic (60 m above present) to the mid-Cretaceous (180 m above present) and remained at about that level until the Tertiary, when it began to drop. The long-term rise was not uniform, but spasmodic, with many shorter-term eustatic rises and falls. These events had magnitudes of tens of meters over timescales of 1 to 5 m.y. The causative mechanism for these variations is not clear. The eustatic curve resulting from this study can be applied to subsiding basins and passive margins in order to quantify subsidence history.
