Rare earth elements as indicators of the provenance of near- and offshore sediments

  • Kezia Lim

    Student thesis: Other thesis - CDU

    Abstract

    The rare earth elements have similar properties, which mean they tend to be transported in nature together, so they are able to retain their abundance patterns during erosion and transportation. However, it is the small systematic differences between the rare earth elements and their relative stability and immobility during weathering, which also enables them to be useful as provenance indicators.

    This study determined the rare earth element composition of the surface sediments of the Adelaide River, Daly River, Bynoe River, Norman River and the Norman River Offshore in northern Australia to determine if rare earth elements could be used as provenance indicators for these rivers and coastal areas.

    In this study it was determined that the most suitable method for the analysis of REEs for the use in provenance studies was digestion with perchloric/nitric acid digest and analysis of digests using inductively coupled plasma mass spectrometer. Using this method, the REE profiles show that the bulk of the rare earth elements were located in the finer-grained clay and silts fraction of sediments.

    The particular phases in which the rare earth elements were generally located was also determine by sequential extraction. The results from this found that the non-residual forms of the rare earth elements were generally bound to the carbonates, Fe-Mn oxides and the bound to organic matter. However, depending on the type of sediment the bulk of the rare earth elements were distributed mainly in the residual phase for sandy sediments and the residual and the bound to organic matter for the clay-rich sediments. The concentrations of the rare earth elements in the different sediment phases were in the order: residual>bound to organic matter>bound to Fe-Mn oxides>bound to carbonates>.exchangeable.

    Differences between the rivers/area could be seen in the rare earth element profiles with variations in the relative enrichment of LREEs, MREEs and HREEs as well as in the europium anomalies. Therefore, statistical analysis was performed to determine the significant differences between the rivers and grainsize fractions of the sediment.

    The results of ANOVA and Tukey HSD test showed using the finer-grainsize fractions and the ∑LREE/∑MREE and ∑LREE/∑HREE it was possible to determine significant differences between the catchment areas. Therefore, for the north Australian rivers and areas there were differences between the Bynoe River and the Norman River when the variable ∑LREE/∑MREE was applied. When the variable ∑LREE/∑HREE was applied, there were differences between the Daly River, Bynoe River and the Norman River from all the other areas.
    Date of AwardNov 2001
    Original languageEnglish
    SupervisorNiels Munksgaard (Supervisor) & David Parry (Supervisor)

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