SEA LEVEL IN THE ORDOVICIAN: SHARP FLUCTUATIONS IN SUBSIDENCE RATES OF THE SIBERIAN CRATON CRUST

Abstract

Most researchers relate rapid fluctuations in water depths of epicontinental sedimentary basins to eustatic sea level fluctuations. Of particular interest for oil-and-gas prospecting are third-order cycles or eustatic events 1–3 Ma long with amplitudes of 20 to 200 m. They are used as reference levels for interbasin correlation. Using the data on low sedimentation rates in extremely shallow settings (≤10 m) of the eastern Baltic and East Siberia regions, it has been shown that third-order sea level fluctuations in the terminal Cambrian–Silurian did not exceed 10–20 m. At the same time, fluctuations in water depths up to 100–200 m over periods of 1–3 Ma long were characteristic of many epiplatformal sedimentary basins on many continents. Since the sea level was almost stable, such fluctuations indicate frequent crustal uplifts and subsidences in platforms. This is a quite unexpected result, since such areas are usually considered relatively calm in terms of tectonics.