Eustacy during the Cretaceous: Its implications and importance

Abstract

Evidence for eustatic fluctuations in mean sea level during the Cretaceous is provided, with the dating of thirteen transgressive episodes between late Valanginian and early Maastrichtian time, separated by intervals of eustatic regression. The assumption of a direct genetic link between mean sea level and volumetric changes in the mid-oceanic ridge systems would, in turn, imply that plate motion was strongly episodic, with individual movements probably having a time span of the order of one to two million years, and being separated by several million years of subdued plate motion. The concept of marine cycles of strongly diachronous transgression is rejected and episodes of eustatic transgression are considered to be short-lived, rarely extending beyond two million years duration and, in general, probably much less. The relationship between the major Cretaceous transgressions and regressions and contemporary magnetic polarity reversals, orogeny and continental volcanism are discussed. An interpretation is also presented of the effects of eustatic fluctuations on Cretaceous oceanic sedimentation and the input of nutrients into the marine environment, as well as on palaeoclimate and such biological phenomena as species diversification, population “explosions”, mass faunal extinctions and evolutionary theory.