A six-week geological cruise of the West German research vesselSonne, under the auspices of the Australian-German Science Agreement, hasyielded a considerable amount of information about the Exmouth Plateau, theWallaby Plateau, and the intervening Cuvier Abyssal Plain. The main aim ofthe cruise was to sample pre-Quaternary strata cropping out on the plateaumargins; subsidiary aims were to sample the Quaternary sequence from conti-nental shelf to abyssal plain on two representative profiles, to obtainQuaternary cores for gas analysis, and to search for manganese modules. Allfour aims Were successfully accomplished.
During the cruise 31 single-channel seismic profiles were run tohelp select sampling targets. On the Exmouth Plateau and adjacent areas 102stations were successfully occupied, 31 yielding pre-Quaternary rocks. On the Wallaby Plateau and adjacent areas 18 stations were successfully occupied,13 yielding pre-Quaternary rocks. Samples were obtained from depths rangingfrom 100 m to 5200 m.
The sampling of pre-Quaternary strata has shed new light on thearea, On the northern Exmouth Plateau thick sequences of Early Jurassicshelf carbonates and Middle Jurassic coal measures were found beneath themain (?Late Jurassic) unconformity. Cretaceous shelf and pelagic sedimentswere also shown to exist. Above the main unconformity there is a condensedsequence of Cainozoic pelagic carbonates. On the northern margin of theWombat Plateau there is a volcanic sequence at least 300 m thick beneaththe main unconformity. On the northwestern Exmouth Plateau Albian andMiocene carbonates were sampled. On the southern margin results were disa-ppointing, but Mesozoic sandstone and shale and Tertiary pelagic carbonateswere sampled.
The layered sequence below the main (?Neocomian) unconformity,both on the eastern Wallaby Plateau and on the "Sonne Ridge", which extends northward from the plateau into the Cuvier Abyssal Plain, was shown to consistof interbedded weathered "basalts", tuffs, breccias, and volcaniclasticsediments. This suggests that a thick volcanic pile of Early Cretaceous ageforms much of the Wallaby Plateau.
A variety of Quaternary cores, almost all of biogenic carbonates,were obtained on profiles from Rowley Shoals to the Argo Abyssal Plain, andfrom southwest of Barrow Island to the Cuvier Abyssal Plain. Quaternarycores in the central Exmouth Plateau were sampled for gas analysis; pre-liminary results indicate that methane is generally present, but in verylow amounts. Manganese nodules were obtained from the southern and easternmargins of the Wallaby Plateau, and preliminary determinations of contentsof nickel and copper suggest that they are above Indian Ocean averages, butwell below a grade of economic interest.
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