This phase of Project 3DGBR involved manual digitising of geomorphic map boundaries for the key seafloor features identified in the gbr100 grid, particularly for the inter-reefal area on the GBR shelf and in the Coral Sea Conservation Zone (CSCZ). See map for CSCZ boundary at: http://www.environment.gov.au/coasts/mpa/coralsea/index.html.
Methods:
GIS spatial analysis of the gbr100 grid was conducted in order to derive a number of useful background datasets for assisting in the digitising process, such as slope, aspect, hillshading, and dense contour lines.
The digitising initially focused on the deep-water (>100 m) environment to develop geomorphic maps for the continental slope, Queensland and Townsville Troughs lying within the Great Barrier Reef World Heritage Area (GBRWHA), and for the Queensland Plateau, Coral Sea Basin, Tasman Basin, and Lord Howe Rise area lying within the adjoining Coral Sea Conservation Zone (CSCZ). The project lastly focuses on the shallow-water (1° and are also greatly underestimated across the area.
coralsea_seamount.shp
Seamount is a large isolated elevation >1000 m in relief above the seafloor, characteristically of conical form. This shapefile also includes Guyot, a seamount having a comparatively smooth flat top. Seamounts and guyots were mapped mostly within the Tasmantid Seamount Chain with elevations >1000 m. This project identified several large knolls and hills close to 1000 m in height within this chain that may also be seamounts but currently lack detailed bathymetry data.
Group Layer 4. Broader-scale features:
gbr_shelf.shp
Shelf is a zone adjacent to a continent (or around an island) extending from the low water line to a depth at which there is usually a marked increase of slope towards oceanic depths. The eastern boundary of the Queensland continental shelf was mapped by closely following the change in gradient along the shelf edge. The shelf break in the north was at approximately 80 m and became deeper at about 110 m towards the south. The western boundary was clipped at the Queensland mainland coastline.
coralsea_slope.shp
Slope lies seaward from the shelf edge to the upper edge of a continental rise or the point where there is a general reduction in slope. The continental slope was mapped lying adjacent to the shelf and extending into the adjacent deep basins and troughs. The shelf feature was used to erase the western boundary of the slope and the various basins and troughs erased the eastern slope border. The slope has extensive canyons incising its surface.
coralsea_terrace.shp
Terrace is a relatively flat horizontal or gently inclined surface, sometimes long and narrow, which is bounded by a steeper ascending slope on one side and by a steeper descending slope on the opposite side. In this project, one broad-scale terrace feature was mapped lying on the slope between the Swains Reefs and Capricorn-Bunker Group of reefs, and near the Capricorn Trough.
coralsea_plateau.shp
Plateau is a flat or nearly flat area of considerable extent, dropping off abruptly on one or more sides. Extensive areas of plateaus were mapped across the Coral Sea with the largest being the Queensland Plateau. Lord Howe Rise consists of a series of plateaus separated by broad-scale valleys linking adjacent basins and troughs. Plateau boundaries were mapped around their bases where the gradient first becomes steeper. The exceptions are the Marion and Saumarez Plateaus on the Queensland continental slope, where the boundaries were mapped as the slope gradient becomes flat or nearly flat.
coralsea_valley.shp
Valley is a relatively shallow, wide depression, the bottom of which usually has a continuous gradient. This term is generally not used for features that have canyon-like characteristics for a significant portion of their extent. The shapefile includes Hole, a local depression, often steep sided, of the seafloor. Valleys and holes were mapped as long shallow depressions that often separated the numerous plateaus. These features link the basins and troughs that surround these plateaus, and in some cases can be incised with finer-scale canyons.
coralsea_trough.shp
Trough is a long depression of the seafloor characteristically flat bottomed and steep sided and normally shallower than a trench. In this project, two trough features were mapped that are essentially long basins. The larger feature is a combined Queensland and Townsville Trough lying between the continental slope and the Queensland Plateau. The smaller feature is the Bligh Trough separating the northern slope and Eastern Plateau. Both trough features feed into the Osprey Embayment and huge Bligh Canyon.
coralsea_rise.shp
Rise is a gentle slope rising from the oceanic depths towards the foot of a continental slope. For this project, an elongate rise is mapped between the Queensland Plateau and the adjacent Coral Sea Basin. The Queensland Plateau is remnant continental crust from the Gondwana breakup and so its seaward edge provides a geomorphic extension of the Australian margin, albeit at a much deeper depth than the present mainland margin. The rise was mapped where the gradient angle of the Queensland Plateau seaward edge first becomes less steep and finishes at the Coral Sea Basin abyssal plain. Another rise feature was mapped between the southern continental slope and the Tasman Basin abyssal plain.
coralsea_basin.shp
Basin is a depression, characteristically in the deep seafloor, more or less equidimensional in plan and of variable extent. Basins were mapped where their boundaries changed from generally flat to more steep gradients. Plateau or slope features were used to erase and limit the boundaries of the basin features. In the north lies the large Osprey Embayment which has smaller plateaus lying within its area. The Cato Trough is a large basin separating the southern continental slope and plateaus of the Lord Howe Rise area. On the Lord Howe Rise are shallow basins that surround the series of plateaus that lie on the Lord Howe Rise.
coralsea_abyssalplain.shp
Abyssal plain is an extensive, flat, gently sloping or nearly level region at abyssal depths. Three abyssal plains were mapped where their gradients became generally flat and at depths greater than about 4000 m. In the north are the abyssal plains of the Coral Sea Basin and Louisiade Basin, the latter being a failed arm of a rift triple junction. In the south, lies the abyssal plain of the Tasman Basin.
Group Layer 5. Background image:
gbr100_geo3.tif
This hillshade geotif image was derived from the gbr100 grid using Fledermaus 3D visualization software with a depth colour scheme configured to highlight the physiographic relief of the shallow shelf and the deeper seabed features. It is provided here to give geomorphic context to the seabed areas lying outside of the GBRWHA and CSCZ.
Funding:
Queensland Government Smart Futures Fellowship
Reef and Rainforest Research Centre
James Cook University
References:
Heap, A.D., Harris, P.T., 2008. Geomorphology of the Australian margin and adjacent seafloor. Australian Journal of Earth Sciences 55(4), 555-585. doi: 10.1080/08120090801888669
IHO, 2008. Standardization of Undersea Feature Names: Guidelines, Proposal Form, Terminology. Bathymetric Publication No.6, 4th Edition, International Hydrographic Bureau/Intergovernmental Oceanographic Commission, Monaco, pp. 32.
