TECTONIC REGIME AND THE PRESERVATION OF PALAEOSURFACES

Common sense, as well as the conventional scientific wisdom, suggest t hat the Earth's surface is constantly changing. The field evidence, in some areas is, however, at odds with this supposition, for firmly dat ed landscape elements of great antiquity are widely distributed. Many of these palaeoforms are of exhumed type but others are of epigene-etc h origin. Fragments of old palaeoforms are preserved in active tectoni c regions, but the chances of survival are reduced by the intense diss ection characteristic of such areas, and especially in those areas tha t have been uplifted sufficiently to induce the activity of frost and ice. Such remnants are not readily recognised and are also difficult t o date. But extensive palaeolandscape remnants are commonplace on crat ons and old orogens. Such regions are comparatively stable, and vertic al movements have dominated through much of later Phanerozoic time. Al ternations of planation and weathering on the one hand, and uplift and stripping of regoliths on the other, have produced etch surfaces. Upl ift has also induced stream dissection, but interfluves have been pres erved. Such unequal erosion and associated reinforcement effects subst antially account for the survival of palaeoforms in such cratons and o rogens, though several other factors contribute to their preservation.