The East Siberian basin in the Silurian: evidence for no large-scale sea-level changes

According to conventional ideas, numerous eustatic sea-level changes occurr ed during the Phanerozoic with amplitudes 20-100 m and periods T = 1-3 Myr (third-order cycles). At the same time, it is widely recognized that tecton ic factors have an important role in such water-depth changes. Rapid. large -scale sea-level changes have been suggested for the Silurian, for which de tailed and continuous stratigraphic successions are available in the East S iberian sedimentary basin, similar to 2X10(6) km(2) in size. These show slo w deposition at depths less than or equal to5-10 m proceeded for 10-20 Myr in many regions and enable the mathematical analysis of maximum eustatic se a-level changes, with periods of T = 1-3 Myr (third-order), that could have occurred during the Silurian. The amplitudes of such events could not exce ed similar to 20-30 m, and, for some epochs, could not be larger than 8-10 m. At the same time, rapid water-depth changes of up to similar to 100 m oc curred in some other cratonic areas. As the Silurian had a relatively stabl e sea level, these must be attributed to rapid crustal uplift and subsidenc e. The absence of third-order eustatic fluctuations with amplitudes greater than or equal to 10-20 m has also been demonstrated for the Cambrian and e arliest Ordovician. It is probable that no significant sea-level changes al so occurred at many other epochs, while rapid changes in water depth result ed from large-scale, vertical crustal movements. (C) 2001 Published by Else vier Science B,V.