AU-WA
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No abstract available
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The Albany Canyon complex off southwest Australia extends 700 km from Cape Leeuwin to east of Esperance. The Canyons head on the uppermost continental slope and extend up to 90 km offshore, to the lowermost slope and onto the abyssal plain. The largest have cut down 1500-2000 m in places. In general, on the upper slope they have cut down into harder, older rocks: Canyon walls are steep, thalwegs slope at up to 15?, and ancient structures control their orientation. On the lower slope the Canyons generally have not reached harder rocks, Canyon walls are less steep, thalweg slopes are less, and they are generally oriented down slope. The Canyons have exposed Jurassic and younger sequences: their nature and information from seismic profiles, have helped us build an understanding of Canyon history. Flood plain deposition rather than erosion occurred during Australia-Antarctic rifting in the Late Jurassic, not supporting cutting of river Canyons. Shallow marine sedimentation characterised the Early Cretaceous, when gradients were low and Canyon cutting unlikely. Deep river Canyons were probably cut during uplift and erosion immediately before the Santonian break-up from Antarctica, and their paths controlled later marine Canyons. Only with the onset of rapid seafloor spreading and subsidence in the Middle Eocene (~43 Ma) did gradients steepen and major marine Canyon cutting become possible. The major sea level fall at the Middle/Late Eocene boundary (~40 Ma) brought sediment to the edge of the continental shelf, which may have initiated the Canyons. Carbonate sedimentation replaced siliciclastic sedimentation in the Late Middle Eocene, but carbonate grains from the outer shelf could cut the Canyons, largely during periods of low sea level.
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25% coverage sth east 22-1/F50-2/3
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to follow
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22-1/F50-15/3