High resolution geomorphic map of a submerged marginal plateau, northern Lord Howe Rise, east Australian margin

Abstract

High resolution multibeam bathymetry is used to map and interpret seabed geomorphology for part of the northern Lord Howe Rise plateau in the Tasman Sea. A mapping system of geomorphic units and elements is used, extending the previous hierarchy of geomorphic provinces and features used for the Australian margin. The mapped area covers ∼25,500 km 2 and incorporates broad ridges, valleys and plateaus. Superimposed on these features are clusters of volcanic peaks, smaller ridges, holes, scarps and aprons. An additional characteristic of the seabed in this area is an extensive network of polygonal furrows that covers the plateau and the lower slopes of larger ridges. These furrows are formed in stiff, unconsolidated carbonate ooze that forms a near-continuous sediment cover across the area. Peaks are the only geomorphic feature not fully draped in pelagic ooze. The distribution of geomorphic units suggests strong controls from underlying geological structures. In water depths of 1400 to 1600 m some peaks occur in clusters on ridges that sit above acoustic basement highs and volcanic intrusions. Elsewhere, broad plateaus and valleys slope to the southwest following the regional dip of the Lord Howe Rise plateau. In contrast, localised geomorphic elements such as moats and holes have likely explanation in terms of spatial variations in sedimentation rates in relation to bathymetric highs. Polygonal furrows are attributed to dewatering processes. The geomorphology of the seabed mapped in this study incorporates examples of forms that have not been previously mapped in such detail on the Australian margin. These are unlikely to be unique to the mapped area of the Lord Howe Rise and can be expected to occur elsewhere on the Rise and presumably on other parts of the Australian margin with a similar geological history.