It is commonly accepted that the major control on long-term eustasy is variation in sea-floor spreading rate. The middle Cretaceous sea-level highstand, in particular, has been correlated with a postulated pulse of rapid spreading in the Pacific basin. This inferred event took place during the Cretaceous normal superchron (CNS) and has also been used as evidence for the existence of superplumes from the deep mantle, giving a causative link between core-mantle interactions and the record of sea-level change. There are reasons, however, to question the foundation upon which this linkage is based. Recent studies of marine geochemistry show no evidence for large hydrothermal fluxes during middle Cretaceous time that require major increases in oceanic spreading rates. Plate reorganizations in the Pacific during the CNS show evidence of ridge jumps, indicating that more of the sea floor of this age may be preserved than has been presumed. Improvements in the Mesozoic time scale indicate that the CNS was longer than previously assumed, reducing the need for rapid spreading rates in the Pacific basin. Middle Cretaceous rapid plate generation rates are not needed to explain the history of sea-level change. Long-term eustasy can easily be accounted for by supercontinent breakup, variations in the distribution of crust consumed at subduction zones, and other effects. Because the inferred pulse of spreading was, in part, used to argue for the existence of a superplume, the basis for this hypothesis is diminished. The phenomena attributed to deep mantle plumes can be accounted for by plate tectonic forces and plate reorganization. Hence, we question the basis and need for the Cretaceous pulse of rapid sea-floor spreading.
- Geological Society of America