Exmouth Gulf is a major U-shaped embayment on the northwestern coast of Western Australia, at a latitude of 22°S. Water temperatures are 18-31°C and normal oceanic salinity is maintained by strong tidal currents despite the hot, arid climate. A series of sediment grab samples were collected and analysed for particle-size and foraminiferal diversity. Samples contained mud, quartzose fine sand and coarse carbonate sand fractions. The muddiest facies are located in the most sheltered areas of the gulf: mangrove channels, tidal flats, southwestern flanks and the deeper axial region. Quartzose fine sands probably have mixed origins which might include: southern aeolian dunes; cyclone-related reworking of beach and near-shore deposits; and reworked relict shelf alluvium. The shallow-water fair-weather wave climate may play a significant role in localised sediment dispersal and sorting along the eastern margin of the gulf. Sediment distributions within the gulf are complicated by low sedimentation rates through much of the central and western areas of the gulf, significant mixing, and possible inheritance of pre-Holocene alluvium. The Holocene foraminiferal assemblage recorded from Exmouth Gulf is overwhelmingly dominated by benthic species: agglutinated, calcitic-porcellaneous, and calcitic-hyaline groups. The distribution of individual foraminiferal species shows relatively simple patterns, governed by environmental parameters. Live individuals are rare.
Along the south-eastern coast of New Zealand's South Island, observations and characterisations of shelf geology are complicated by numerous possibly active faults (e.g. the coast-parallel Akatore and coast-perpendicular Waihemo and Castle Hill faults), a Miocene-aged volcanic edifice (i.e. the Dunedin volcano) and incision from an extensive submarine canyon system. Conventional marine seismic data do not adequately image the basin beneath the shallow shelf here. However, six recently digitised high-frequency single-channel boomer seismic surveys have enabled the investigation of unique local geological structures and their relationships to the tectonic and sedimentary development of the region. These structures have significant control on active processes such as: (1) the localisation of sedimentation and submarine erosion; (2) the instigation of canyon channel incision; and (3) the distribution of fluid migration pathways on the shallow shelf. Future data acquisition will further constrain these processes and help to evaluate earthquake risk in this region.
In broad terms, fluvial systems can be considered as comprising two basic geomorphologic features, a channel and its floodplain (overbank), each of which may accumulate sediment or undergo erosion. The sedimentary relationships between channels and floodplains, the resultant sedimentary architecture and the form of the dependent landscape may all be considered in terms of the relative rates of channel and floodplain aggradation and/or erosion. Using this approach, the Herbert River in north Queensland can be divided into seven 'fluvial fields'. By considering the likely migration directions of field boundaries in the lower floodplain we conclude that, contrary to many sequencestratigraphic models, lowering sea-level would drive a general aggradation of the system on the Great Barrier Reef shelf, whereas a sea-level rise would cause further incision of the modern coastal plain.
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