Sediment accumulation and Holocene - OzCoasts

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Sediment accumulation and Holocene evolution of the Fitzroy River lower floodplain Figure 5: Digital elevation model of the Fitzroy River estuary. 10
Sediment accumulation and Holocene evolution of the Fitzroy River lower floodplain Methods and data Field work Laboratory work Several field surveys were undertaken to collect sediment surface samples and cores from the different study areas. A geoprobe percussion coring system (Qld DNRMW drill rig) was used to collect cores from the floodplain in 2003 (Ryan and Brooke, 2003; Skene et al., 2004). This kind of coring system is ideal for the floodplain clay rich sediments. Sample sites were constrained, to some degree by accessibility, but were chosen to provide a good spatial coverage and insight into the historical and geological evolution of the floodplain. Samples were also collected for analyses from river bank exposures and floodplain pit samples along the Fitzroy River. These eroded banks and other exposures reveal examples of the sediment facies observed in floodplain cores. To build a more comprehensive stratigraphy for the lower floodplain these data are combined with borehole logs previously compiled for Queensland Geological Survey and Department of Mines. Push cores were also acquired from Crescent Lagoon, Frogmore Lagoon, Casuarina Creek and Kamiesh Passage during September 2003 and August 2004, to gain an insight into some of the historical changes in the catchment and and sediment accumulation rates in different estuarine environments. The lagoons were chosen as they were the only lagoons that have not dried out, but are inundated by large floods (Figure 2). One of the cores from Crescent Lagoon was studied by Mio Kuhnen for her honours thesis (Kuhnen, 2004). The tidal creeks, Casuarina Creek and Kamiesh Passage, were chosen for coring due to their proximity to the termination of a feeder channel with relatively low tidal currents. These core sites are therefore more likely to be depositional environments. The tidal range in both tidal creek locations was approximately 3– 5 m. Sediments In order to characterise the facies identified in the geoprobe and push cores, sub-samples from cores were analysed in the lab for grainsize using the Malvern laser grainsize analyser. The data was converted to ratios of sand:silt:clay using Gradistat software (Blott and Pye, 2001). Stable isotope analyses As a means of characterising the organic sediment component, total organic carbon, total nitrogen and stable isotopes were measured on the bulk sediment, 11
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