The Paleozoic world; continental flooding, hypsometry, and sealevel

Absolute amplitudes of Paleozoic sea-level fluctuations are poorly known: two major curves show eustatic maxima of +300 m (Vail et al. 1977) and +600 m (Hallam 1984). Based on analysis of the flooding records of thirteen Paleozoic landmasses, the authors estimate that sea-level elevations were substantially lower than previously thought, ca. 50--220 m for most of the Paleozoic. The analysis also shows that: (1) small continents are inherently more floodable than large continents, (2) there is no difference in mean flooding of continents of a given size between the Early and Late Paleozoic, and (3) reduced global flooding during the Late Paleozoic is primarily attributable to the existence of a few large continents, rather than many small ones as during the Early Paleozoic. Global sea-level trends reflect the division of the Paleozoic into two geotectonic subcycles comprising the Cambro-Silurian (terminated by the Taconic/Caledonian Orogeny). Deviations of individual continents from the mean global curve are due to changes in hypsometry associated with tectonic/epeirogenic events. For example, a major Early Silurian regression on Laurentia resulted from the Taconic Orogeny, while large Early Ordovician and Middle-Late Devonian regressions on Gondwana are associated with rifting of the North China and South China/Indochina blocks.