Datasets relating to samples collected from the Lagoon physiographic zone on Wistari Reef

Researchers: Opdyke, Bradley, Dr (collaborator) ,  Ryan, David (principalInvestigator)

Brief description Wistari Reef is a lagoonal platform reef, situated on the Tropic of Capricorn, within the Capricorn and Bunker region of the southern Great Barrier Reef. Surface samples were taken from the lagoon area to determine the mean grainsize and the sorting coefficient and also the proportion of aragonite to calcite within the samples. Within the lagoon area the average mean grainsize is ~1.25phi, with an average sorting coefficient of 1.04phi. Individual samples exhibited much variation in grainsize and sorting. The 'lagoon' physiographic zone needs to be sub-divided into 'deep-lagoon' samples (eg S16) and 'patch-reef dominated' samples (eg S11). The sediments of the 'deep-lagoon' are poorly sorted medium to fine sands, with little contribution from in situ patch reef growth. The 'patch-reef dominated' sediment is a poorly sorted medium sand, and contains a high proportion of coarser grains derived from patch reefs within the lagoon. There was a higher proportion of Aragonite in the samples compared to calcite.

Lineage Statement: GRAINSIZE & SORTING COEFFICIENT - Surface samples were collected on reef walks or on boat transects across Wistari Reef. Deeper samples were obtained by diving. Samples were collected using a hand-held scoop and 600ml plastic bottles. Sediment samples were sieved in order to determine modal particle diameters, and sorting data. Samples were first dry sieved. Sieves of sizes -1.0phi to 2.5phi were stacked and installed on a sieving shaker. Samples were weighed out to approximately 250g, and each sample was sieved for 15 mins to ensure correct separation of size fractions. Each fraction was then removed from the sieve and weighed. The size fractions 2.5phi, 3.0phi, 3.5phi and 4.0phi were pre-weighed, and wet sieved separately using a low pressure water hose, through smaller micropalaeontological sieves. Sediment textures are expressed in terms of mean grainsize, and sorting coefficient, represented by standard deviation. XRD ANALYSIS - Surface samples were collected on reef walks or on boat transects across Wistari Reef. Deeper samples were obtained by diving. Samples were collected using a hand-held scoop and 600ml plastic bottles. XRD analysis was performed at Australian National University using a Siemens D501-K710 Diffractometer, with CuK alpha radiation at 40kV and 40mA and a graphite monochromator. Approx. 1.0g of sample was milled in an agate mortar and pestle with acetone as a cooling and lubricating agent, until a grain size of <10µm was acheived. Sample then spiked with 20% ZnO, and mixed. The dried sample was loosely packed onto a slide, with the surface temporarily covered with a rough-surfaced frosted glass, ensuring random orientation. A scanning range of 6 to 70 degrees was used, with a step size of 0.02 degrees, at a rate of 1 degree/min.

Lineage Statement: Although this data shows the mean average grainsize of the nine surface samples collected within the lagoon, much variation in grainsize and sorting was seen within the sediments. It may be better to sub-divide the samples into those that were collected from the 'Deep-Lagoon', and those that were collected from the 'Patch Reef Dominated' areas. Scanned histograms are used to highlight the percentage of sediments within each grainsize bracket. The exact percentage figures are not available. Aragonite and calcite percentages are provided for three samples. Mean grainsize of surface samples parameters: Average mean grainsize (phi), average sorting coefficient (phi), dominant coarse biota, dominant fine biota. Grainsize of surface samples parameters: Sample, latitude (d,m,s), longitude (d,m,s), grainsize brackets (phi), percentage of sediments in grainsize brackets (%). XRD analysis parameters: Sample site, latitude (decimal degrees), longitude (decimal degrees), percentage aragonite (%), percentage calcite (%).

Notes Credit
Funded by The Australian Research Council (ARC)

Notes Credit
The Australian National University (ANU)

Notes Purpose
To provide an overview of the sedimentary zones of Wistari Reef. Conducted as part of a broader study looking at Holocene production and accumulation of sediments on Wistari Reef.

Data time period: 1998 to 1998

151.87416,-23.48148 151.89686,-23.47539 151.89976,-23.45741 151.87906,-23.46323 151.87344,-23.4769 151.87416,-23.48148

151.8866,-23.469445

153,-23 153,-24.5 151.5,-24.5 151.5,-23 153,-23

152.25,-23.75

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