Lithological control on the elevation of shore platforms in a microtidal setting

Abstract

The shore platforms on Shag Point, southern New Zealand, are quasi-horizontal surfaces and are developed between supratidal and low water spring levels. A range of morphologies occur, with more exposed platforms having a distinct low-tide cliff, in contrast to low-tide surfaces where the seaward edge is buried beneath rubble and macro-algal growth. The platforms range in width from 20 to 80 m and are eroded into Late Cretaceous/Early Tertiary fine marine sandstones and mudstones. Shore platforms have formed in two principal lithological units: a homogeneous unit that is characterized by few discontinuities, and a fractured unit with joints spaced about 0.5 m apart. Rock hardness is low in bo..