The final lithospheric breakup of the Australian-Antarctic rift system remains controversial due to sparse geological constraints on the nature of the basement along the ocean-continent transition zones. We present new interpretations of multichannel seismic reflection transects, as well as new petrological data of dredged mantle rocks along the East Antarctic margin (Seamount B, offshore Terre Adélie). By combining both datasets, we show that a 50–100 km wide domain of cold (900°C), fertile subcontinental mantle was exhumed along the non-volcanic Antarctic margin. The dredged peridotites preserve characteristics similar to mantle xenoliths found in syn- to post-rift volcanism at the eastern end of the Australian margin (Victoria and Tasmania), indicating the sampling of a common fertile subcontinental mantle during rifting between Australia and Antarctica. Seamount B represents the initial stages of exhumation of cold subcontinental lithosphere along an ocean-continent transition during rifting. This thick mantle domain was likely affected by syn-rift melt impregnation at high-pressure (8 kbar), leading to the formation of plagioclase-pyroxenites. Overall, the combination of continental rifted blocks, a 50-100 km wide domain of volcanic-poor subcontinental mantle and (ultra)-slow spreading implies that ocean-continent transition zones along the Australian-Antarctic margins represent a recent analogue to ocean continent transition zones from the Jurassic Western Tethys. Additionally, evidence of syn-rift melt stagnation at high pressure suggests that magmatism along the Australian-Antarctic rifted margins was sufficient to form magnetic anomalies that can be used as isochrons despite their formation in lithosphere other than mature, steady-state ocean crust.

Dredge rocks were recovered on scientific voyage SS2011_06 on the MNF RV Southern Surveyor, from the Perth Abyssal Plain, offshore Western Australia. Continental rocks (gneiss, granite, sandstone) were dredged from both the Batavia Knoll and the Gulden Draak Ridge (dredge sites 1, 2, and 3). A small amount of high weathered basalt was recovered from the Gulden Draak Ridge (dredge site 4). Three successful dredges were undertaken along the Dirck Hartog Ridge recovering predominantly gabbro (dredge 5) and basalts (dredge sites 6 and 7).

The Petrel Sub-basin Marine Environmental Survey GA-0335, (SOL5463) was undertaken by the RV Solander during May 2012 as part of the Commonwealth Government's National Low Emission Coal Initiative (NLECI). The survey was undertaken as a collaboration between the Australian Institute of Marine Science (AIMS) and GA. The purpose was to acquire geophysical and biophysical data on shallow (less then 100m water depth) seabed environments within two targeted areas in the Petrel Sub-basin to support investigation for CO2 storage potential in these areas. This dataset comprises an interpreted geomorphic map. Interpreted local-scale geomorphic maps were produced for each survey area in the Petrel Sub-basin using multibeam bathymetry and backscatter grids at 2 m resolution and bathymetric derivatives (e.g. slope; 1-m contours). Five geomorphic units; bank, plain, ridge, terrace and valley, were identified and mapped using definitions suitable for interpretation at the local scale (nominally 1:10 000). Maps and polygons were manual digitised in ArcGIS using the spatial analyst and 3D analyst toolboxes.

The Oceanic Shoals survey (SOL5650, GA survey 339) was conducted on the R.V. Solander in collaboration with Geoscience Australia, the Australian Institute of Marine Science (AIMS), University of Western Australia and the Museum and Art Gallery of the Northern Territory between 12 September - 5 October, 2012. This dataset comprises an interpreted geomorphic map. Interpreted local-scale geomorphic maps were produced for each survey area in the Oceanic Shoals Commonwealth Marine Reserve (CMR) using multibeam bathymetry and backscatter grids at 2 m resolution and bathymetric derivatives (e.g. slope; 1-m contours). Six geomorphic units; bank, depression, mound, plain, scarp and terrace were identified and mapped using definitions suitable for interpretation at the local scale (nominally 1:10 000). Maps and polygons were manual digitised in ArcGIS using the spatial analyst and 3D analyst toolboxes. For further information on the geomorphic mapping methods please refer to Appendix N of the post-survey report, published as Geoscience Australia Record 2013/38: Nichol, S.L., Howard, F.J.F., Kool, J., Stowar, M., Bouchet, P., Radke, L., Siwabessy, J., Przeslawski, R., Picard, K., Alvarez de Glasby, B., Colquhoun, J., Letessier, T. & Heyward, A. 2013. Oceanic Shoals Commonwealth Marine Reserve (Timor Sea) Biodiversity Survey: GA0339/SOL5650 Post Survey Report. Record 2013/38. Geoscience Australia: Canberra. (GEOCAT #76658).

Ocean currents are strongly controlled by seafloor topography. Recent studies have shown that small-scale features with slopes steeper than 0.05° significantly affect subsurface eddy velocities and the vertical structure of ocean circulation patterns. Such slope gradients represent the majority of the present-day oceanic basins. Modeling past oceanographic conditions for key climate stages requires similarly detailed paleo seafloor topography grids, in order to capture ocean currents accurately, especially for ocean models with sufficient resolution (<0.1°) to resolve eddies. However, existing paleobathymetry reconstructions use either a forward modeling approach, resulting in global grids lacking detailed seafloor roughness, or a backward modeling technique based on sediment backstripping, capturing realistic slope gradients, but for a spatially restricted area. Both approaches produce insufficient boundary conditions for high-resolution global paleo models. Here, we compute high-resolution global paleobathymetry grids, with detailed focus on the Southern Ocean, for key Cretaceous and early Cenozoic climate stages. We backstrip sediments from the modern global bathymetry, allowing the preservation of present-day seafloor slope gradients. Sediment isopach data are compiled from existing seismo-stratigraphic interpretations along the Southern Ocean margins, and expanded globally using total sediment thickness information and constant sedimentation rates. We also consider the effect of mantle flow on long-wavelength topography. The resulting grids contain realistic seafloor slope gradients and continental slopes across the continent-ocean transition zones that are similar to present-day observations. Using these detailed paleobathymetry grids for high-resolution global paleo models will help to accurately reconstruct oceanographic conditions of key climate stages and their interaction with the evolving seafloor.

Rocky reefs form an important habitat on the continental shelf and one subject to disproportionate fishing pressure given the high productivity of this habitat relative to adjacent sandy seabed. Despite this, little is known of the extent and nature of these systems beyond their value to the fishing industry. This project collated all known mapping data from government and industry (including data acquired during CERF and NERP Hubs) to provide an updated map of this key habitat around Australia. A geomorphological classification system is also being developed for these reefs, and associated cross-shelf habitats with the aim of it being accepted and adopted nationally, and it is being tested and refined for biological applicability. This record describes the national habitat map data product generated from multiple datasets collated as part of NESP MBH Project D3. The individual habitat mapping datasets collected as part of the data collation process have also been published and are linked to this record.