Vertical motion of Australia in the Cretaceous: A mantle dynamics perspective

Abstract

The marine inundation of Australia during the Early Cretaceous, and its subsequent exposure during the generally Late Cretaceous global sea-level high, form an example of continental epeirogeny. Epeirogeny is relative vertical motion of a continent or part of a continent with respect to other continents when this motion is unaccompanied by folding or faulting. The general features of the Cretaceous history have long been recognized by Australian geologists. Over the years, John Veevers of Macquarie University has published extensively on the Phanerozoic history of Australia, and most recently has placed the Cretaceous vertical motion into context of the plate-tectonic evolution of the region (Veevers et al., 1991 ). Understanding the cause of epeirogeny has always been difficult, since vertical motion, particularly vertical motion on a regional scale, is not a direct consequence of plate tectonics. The Mesozoic and Cenozoic vertical motion of Australia is of interest to geodynamics for two reasons. First, the vertical motion is not only simple in its spatial and temporal character, but it is also relatively “easy” (at least in comparison to other regions around the world) to infer quantitatively. Second, the vertical motion occurred not so far back in geologic time, so there is the prospect of relating this motion to plate-tectonic evolution and present day bathymetry, geoid, and lateral mantle structure. The time has now come to reassess the Cretaceous motion in the context of recent advances in mantle dynamics. Broad-scale vertical motions of the Earth's surface can be predicted from geodynamic models - models which can be tested with bathymetry, gravity, and seismology.