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Title: Early chemical diagenesis and sedimentology in a high energy sublittoral marine environment, Swansea Bay
Author: Rees, A. W. G. R.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1988
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The sedimentological and geochemical processes occurring in 30cm long sediment cores taken over an 18-month period from Swansea Bay, South Wales have been examined. Sedimentological analysis included a detailed determination of sediment grain size and the interpretation of box core X-radiographs. Geochemical analyses included carbonate, organic carbon, organic nitrogen and various phosphorus fractions in the solid phase, and sulphate, alkalinity, ammonium, phosphate, silica, iron, manganese and pH in the pore water. Sedimentological results confirm the high energy dynamic nature of deposition in the Bay. Storm processes resulted in the formation of multiple layers of varying proportions of gravel, sand, silt and/or mud. Pore water chemistry data, and the results of stoichiometric modelling demonstrate that organic matter decomposition via sulphate reduction was the dominant diagenetic process. Modelled nutrient ratios and decomposition rate constants were consistent with the metabolisable organic matter fraction being predominantly composed of plankton detritus. Results indicate that the concentration of metabolisable organic matter was relatively low, limiting the extent of sulphate reduction and resulting in the build-up of unusually high concentrations of ferrous iron. Pore waters were predominantly saturated with respect to siderite and rhodochrosite, but mainly undersaturated with respect to vivianite and reddingite. Pore water silica concentrations generally increased exponentially with depth as a result of biogenic silica dissolution. Despite the variability in sediment compositon, many of the pore water profiles exhibited an approximately steady state appearance. A pseudo-steady state was justified for the purposes of modelling because in many cores fluctuations may have been smoothed out by diffusion and concentrations of reactive organic matter and biogenic silica per unit volume of pore water may have been approximately constant. Potential diffusive nutrient fluxes and the enhanced release of nutrients during sediment resuspension have been quantified.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available