Raised Reef-Capped Terraces and Plio-Pleistocene Sea Level Changes, North Malekula, New Hebrides

Abstract

In the west of northern Malekula, Pliocene sediments rest with angular unconformity on lower Miocene volcaniclastic rocks. Six tilted, reef-capped terraces overlie benches cut in the Pliocene succession. Facies analysis shows the Pliocene sequence to be transgressive, indicating a relative sea level rise of at least 400 feet. Analysis of the terrace deposits shows that they resulted from the cycle: transgression-slow regression-rapid regression, repeated at least six times. These cycles can most simply be explained by sea level oscillations combined with continuous tectonic uplift, and probably represent major Pleistocene eustatic oscillations. Correlation with similar reef-capped terraces elsewhere cannot be made on elevation alone. The number of terraces present depends partly on the rate of uplift. The ratio of the elevations of terraces which formed during the same eustatic oscillations in different areas will only be the same if uplift in all areas was at a steady rate.