Shore platform development on an uplifting limestone island over multiple sea-level cycles, Niue, South Pacific
Niue is an uplifted limestone island, which preserves an atoll morphology with a sequence of terraces aroundits outer margin. A modern terrace fringes much of the island and this paper examines the extent to whichthis terrace can be considered accretionary and constructed by coral and coralline algae, or erosional andtruncated by those processes that form shore platforms. The occurrence of Pleistocene limestone outcroppingacross this terrace and the continuation of caves and other karst features, dissecting the sub-aerial limestones,onto the forereef indicate the overall significance of erosion. At present live coral cover is restrictedto isolated colonies growing in grooves, potholes and karstic channels eroded into the modern terrace surface.Coralline algae coat the outer margin of this terrace, and also veneer prominent surf benches that occur on thewindward shore, 1¿2 m above the terrace surface. Terrace evolution on Niue therefore appears to be primarilyerosional in origin. There is little accommodation space for reef growth and, as a result, accretional fringingreefs are absent around most of the island. Erosional processes have also dominated landscape evolution for atleast the past few eustatic cycles. Fringing reef growth is absent or severely restricted during the last interglacialand occurs as sporadic small reefs on the seaward margin of an erosional terrace during the penultimate interglacial.The development of terrace features in uplifting reef settings does not necessarily originate through accretionalreef processes and may in fact be entirely erosional. Although reef terraces are frequently depositional inother settings, those present on Niue indicate a predominance of erosion, indicating the need to discriminateemergent terraces in terms of the extent to which they are erosional or accretionary when using such featuresto reconstruct island palaeoenvironments.
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