Modern and ancient continental hypsometries

Controls on coastal hypsometries of modern continents and oceanic islands may be used to estimate palaco-continental area-elevation distributions. The most important controls on coastal hypsometry are landmass area and coastal gradient, increases in which result in steeper area-elevation distributions. Thus, any change in sea level will flood or expose a smaller fractional area of continents which are large or have steep coastal gradients than of those which are small or have gentle coastal gradients. Coastal gradients are dictated primarily by the tectonic setting and age of continental margins. While active and transform margins generally have steep coasts, mean coastal gradients for passive margins decrease exponentially with increasing margin age. Consequently, continents comprised mostly of mature passive margins are generally more 'floodable'.
These observations are applicable to a variety of palaeo-eustatic problems. Hypsometries corrected for changes in landmass area reduce variance in flooding records between different Palaeozoic continents by more than 50%. Assuming minimum-variance superimposition of flooding curves for different Palaeozoic continents permits identification of possible hypsometric anomalies. Calculated Palaeozoic sea level maxima are between +200 m and +400 m with respect to present sea level, substantially lower than previous estimates to +600 m.
Modelling evolution of coastal hypsometries due to changes in length and age of passive margins suggests that hypsometry varies cyclically in response to continental rifting and collision. Coastal hypsometries are steepest during rifting events and decrease by a factor of two to three as passive margins age. Coastal hypsometries in a 'sutured' world are steeper than those of a 'rifted' world due to increased continent size and decreased passive margin length. Thus, sea level highstands associated with times of continent dispersal may result in part from the enhanced 'floodability' of rifted continents.