Sea-level cycles during the growth of Atlantic-type oceans

Abstract

First-order changes in global sea level are commonly thought to be the result of short-term fluctuations in oceanic spreading rate. However, eustatic high stands have occurred only twice in Phanerozoic time, and in both cases have followed supercontinent break up by a lag period of 50–100 Ma. Therefore, if pulses in spreading rate were the primary control of eustasy, then, for some reason, rate increases would have had to have occurred with predictable periodicity with respect to major rifting events. Alternatively, we propose that the major control on first-order sea-level cycles is the formation of Atlantic-type oceans with its attendant changes in the area/age distribution of the global ocean floor and the formation of extensional passive margins. Our calculations indicate that both the approximate magnitude and relative timing of sea-level highstands relative to supercontinent break up are predicted by this mechanism. Thus, the importance of short-term spreading rate variations in eustatic cycles becomes secondary.