Abstract

A. R. Wyatt writes: Algeo & Wilkinson (1991) propose 'hypsometric slope' as a measure of the rate of change of elevation with respect to fractional area. They suggest that modern continents show relatively uniform hypsometric slopes over an elevation range of –50 m to +250 m with respect to present-day sea level, and that as these slopes appear be related to continental area, the concept of hypsometric slope can be applied to past continental distributions. I show below that hypsometric slopes can vary considerably over the elevation range –50 m to +250 m. They also state that modern continental hypsometries have been employed without modification in all hypsometric studies of palaeo-eustasy known to them, implying that theirs is the first work to model past hypsometries. I do not believe that this is so, and suggest that use of the normalized hypsographic curve not only allows estimates of areal changes over greater sea-level changes than use of the hypsometric slope, but also constrains predictions rather more precisely.

Hypsometric slope. How is area to be measured for calculations of hypsometric slope? Algeo & Wilkinson take present day sea level as their base, as they are calculating the percentage area flooded for a sea-level change from 0 m to +200 m. But present-day sea level has no particular geological significance, particularly as continents show tectonic as well as eustatic sea-level changes, such as the Tertiary uplift of Africa (Bond 1978). The edge of the continental shelf may be the best marker, but this

First Page Preview

First page PDF preview
You do not currently have access to this article.