Geomorphological Evolution of Lord Howe Island and Carbonate Production at the Latitudinal Limit to Reef Growth

Lord Howe Island is a volcanic island, rising to over 800 m, draped with Late Quaternary submarine and subaerial carbonate sediments. The island and neighbouring islets lie within a chain of seamounts and is presently at or close to the latitudinal limit to coral reef growth. Lord Howe Island and adjacent Balls Pyramid, composed of the basalts erupted around 6 million years ago, sit near the middle of broad shelves on separate peaks of one major volcanic edifice. The central part of the Lord Howe Island is covered by calcarenite that was deposited primarily as dunes (eolianite), but with isolated beach units. Uranium-series, amino acid racemisation, and thermoluminescence dating indicate that many of these were deposited during marine oxygen isotope stage 5. Eolianite units stratigraphically below the beach deposits are of penultimate interglacial, or in places perhaps older, age. Different suites of erosional landforms are associated with different lithologies. Towering plunging cliffs characterise the resistant Mount Lidgbird Basalt, in some cases fringed with large talus slopes. On less resistant lithologies or where nearshore topography means greater wave force as a result of waves breaking, there are shore platforms. Slumping cliffs abut broad erosional platforms on the poorly lithified calcarenite. A fringing reef on the western side of Lord Howe Island, the southernmost coral reef in the Pacific, is dominated by coral and coralline algae.Carbonate sediments veneering the shelf around the islands contain a more temperate biota. Located at the southern limit of reef-forming seas, but apparently having undergone erosion for much of its history outside of reef seas, Lord Howe Island provides insights into marine planation of volcanic islands close to what has been termed the Darwin Point. It represents the initial stages of fringing reef development on a volcanic island.

豪勋爵岛（Lord Howe Island）是一座火山岛，海拔超过800米，被晚第四纪海底与陆上碳酸盐沉积物所覆盖。该岛及邻近小岛坐落于海山链之中，目前处于或接近珊瑚礁生长的纬度极限。由约600万年前喷发的玄武岩构成的豪勋爵岛与相邻的巴尔斯金字塔（Balls Pyramid），位于一座大型火山构造的不同峰体的宽阔陆架中部附近。豪勋爵岛的中部被钙结岩（calcarenite）覆盖，这些沉积物主要以沙丘（风成岩，eolianite）形式沉积，同时也存在孤立的海滩单元。铀系、氨基酸外消旋作用（amino acid racemisation）及热释光（thermoluminescence）测年结果显示，其中多数沉积体形成于海洋氧同位素5期（marine oxygen isotope stage 5）。位于海滩沉积物地层之下的风成岩单元，形成于倒数第二次间冰期，部分区域的年代可能更为久远。不同类型的侵蚀地貌与不同岩性相对应：抗蚀性较强的利德伯德山玄武岩（Mount Lidgbird Basalt）常发育高耸的悬垂陡崖，部分区域覆有大型塌积坡；在岩性较弱或因近岸地形导致破波浪力更强的区域，则分布有海蚀平台；在固结成岩程度较差的钙结岩区域，崩塌崖壁与宽阔的侵蚀平台相接。豪勋爵岛西侧的岸礁是太平洋最南端的珊瑚礁，以珊瑚和珊瑚藻为主要优势类群。环绕岛屿陆架的碳酸盐沉积物蕴含更为温带的生物群落。该岛地处造礁海域的南部极限，但在其大部分历史时期似乎都处于非造礁海域并遭受侵蚀，为研究接近所谓达尔文点（Darwin Point）的火山岛海洋夷平作用提供了研究视角。它代表了火山岛岸礁发育的初始阶段。