Modelling the effect of Pliocene-Quaternary changes in sea level on stable and tectonically active land masses

摘要

A mathematical model was used to examine the effect of Pliocene and Quaternary changes in sea level on the development of tectonically active and inactive rock coasts. The model calculated rates of mechanical wave erosion according to such factors as the deep water wave regime, bottom topography and surface roughness, and the resistance of the rocks. Subaerial terraces were truncated or eliminated by subsequent terrace formation at lower elevations, especially on steeply sloping landmasses experiencing slow rates of uplift. Submarine terraces formed during glacial stillstands were best preserved when rapid subsidence quickly carried them below the level of wave action. On slowly subsiding landmasses, submarine terraces formed during interglacials and glacial periods experienced repeated erosional modification during subsequent periods of rising and falling sea level and were generally less distinctive. On rapidly rising or subsiding (>5mmyr~(-1)) landmasses, terraces that formed during interglacial stages alternated, above and below present sea level, with terraces formed during glacial stages. Despite some differences in terrace occurrence and elevational distribution, it may be difficult to distinguish profiles cut during accelerating or decelerating uplift. The amount of erosion during sea level oscillations increases with oscillation amplitude and the larger oscillations in the middle to late Quaternary were therefore more conducive to erosion than the smaller oscillations of the Pliocene and early Quaternary. The effect of oscillation amplitude may have been countered during the earlier stages of profile development, however, by steeper submarine gradients and reduced rates of wave attenuation.