Sedimentary and foraminiferal facies in Exmouth Gulf, in arid tropical northwestern Australia

Abstract

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.

Drone photogrammetry and KMeans point cloud filtering to create high resolution topographic and inundation models of coastal sediment archives

“…The study area has a mesotidal regime, which is amplified by the Gulf and increases southwards from an amplitude of 2.1 m at Learmonth to 2.6 m along the southernmost Gulf coast (Short, 2005). The Gulf has a maximum water depth of around 20 m (Orpin et al, 1999), and mean significant wave heights are less than 1 m, in contrast to 2-3 m along the exposed oceanic Ningaloo Reef at the western coast of the Cape. Significant wave heights exceeding 5 m and significant storm surges have been recorded from tidal and other data in the Gulf during TC conditions (Eliot et al, 2013).…”

Prograded foredunes of Western Australia's macro‐tidal coast – implications for Holocene sea‐level change and high‐energy wave impacts

“…prefer higher-energy environments; Amphistegina lobifera, which is dominant in this unit, prefers light sandy shoals just below the regular wave base (Hallock and Glenn, 1986). Ammonia parkinsoniana is abundant in shallow, marginal marine waters (Orpin et al, 1999), similar to the large, discoid Amphisorus sp. tests, which are predominantly found in water depths <10 m (Hallock and Glenn, 1986).…”

Patterns of mixed siliciclastic–carbonate sedimentation adjacent to a large dry‐tropics river on the central Great Barrier Reef shelf, Australia

“…The particle size distribution of the siliciclastic (carbonate‐free) fraction was determined after treating the bulk sample with dilute nitric acid. The particle size characteristics of the dissolved carbonate fraction were derived by subtracting each of the size classes of the siliciclastic fraction (32 in each frequency distribution) from the corresponding size class of the non‐acidified sample (Orpin et al . 1999b).…”