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

Abstract

The Great Barrier Reef represents the largest modern example of a mixed siliciclastic-carbonate system. The Burdekin River is the largest source of terrigenous sediment to the lagoon and is therefore an ideal location to investigate regional patterns of mixed sedimentation. Sediments become coarser grained and more poorly sorted away from the protection of eastern headlands, with mud accumulation focused in localised 'hot spots' in the eastern portion of embayments protected from southeast trade winds. The middle shelf has a variable facies distribution but is dominated by coarse carbonate sand. North of Bowling Green Bay, modern coarse carbonate sand and relict quartzose sand occur. Shore-normal compositional changes show Ca-enrichment and Al-dilution seawards towards the reef, and shore-parallel trends show Al-dilution westwards (across bays) along a Ca-depleted mixing line. Intermediate siliciclastic-carbonate sediment compositions occur on the middle shelf due to the abundance of relict terrigenous sand, a pattern that is less developed on the narrow northern Great Barrier Reef shelf. Rates of sediment deposition from seismic evidence and radiochemical tracers suggest that despite the magnitude of riverine input, 80-90% of the Burdekin-derived sediment is effectively captured in Bowling Green Bay. Over millennial time-scales, stratigraphic controls suggest that sediment is being preferentially accreted back to the coast.

Towards a statistically valid method of textural sea floor characterization of benthic habitats

“…4. Curves of the Calinski-Harabasz (C-H) pseudo F-statistic for the following data: (a) 32-class laser-derived particle size data from the Great Barrier Reef, Australia (data from Orpin et al, 2004); (b) randomly-generated 32-class size data. For Great Barrier Reef data, the shape of the C-H curve shows the maximum C-H statistic occurs with a 2-group solution, and a progressive decrease upon successive subdivision into more groups.…”

“…General agreement with field observations of sediment textural facies has also been used as an additional semi-quantitative measure of the appropriate number of meaningful textural subdivisions (e.g., Woolfe et al, 1998a;Orpin et al, , 2004. However, as noted by Full et al (1983), with complex frequency distributions, as is the case with multimodal sediments, a complementary method for determining the optimal number of groups is required.…”

“…Typically data are archived at Wentworth arithmetic size intervals of gravel (b4 mm), sand, silt, and clay. By way of comparison, two datasets based on high resolution 32-class output from a laserparticle sizer from tropical Australia (after Orpin et al, , 2004 are also discussed. In addition, a dataset of 246 bottom grain size descriptions (8 particle size subclasses) estimated from seabed photographs (after Rumbolt and Kostylev, 2004;Fig.…”

“…To make a quantitative assessment of possible textural characterization bias resulting from different grain size resolutions, 32-class size data from the Great Barrier Reef (after Orpin et al, 2004) were reduced to 4 broad classes (clay, silt, sand, course sand) that covered the same size range as the original (4-2000 Am). Artificial (synthetic) datasets were also created to assess the ability of the grouping methodology to identify a priori known groups.…”

Facies, stratigraphy, and evolution of a middle Ediacaran carbonate ramp: Khufai Formation, Sultanate of Oman

“…A modern analog for this area is the mixed carbonate-siliciclastic deposition occurring in estuaries of the Great Barrier Reef, Australia. Here, relatively coarse quartz sands are incorporated into variably muddy to grainy shallow-marine sediments with sediment distribution controlled by local coastline and reef geometries (Orpin et al, 2004). The river system supplying siliciclastics into the underlying Masirah Bay Formation was hypothesized to be located to the north of Huqf exposures (Allen and Leather, 2006), consistent with the northern location of the Buah dome.…”