Chemical and mineralogical composition of marine sediments, and relation to their source and transport, Gulf of Carpentaria, Northern Australia

The Gulf of Carpentaria is an epicontinental sea, deeply indented in the north of the Australian continent. A selection of 100 samples of the surficial marine sediments collected on a regional grid were analysed for major chemical elements and mineral phases using wet chemistry, X-ray diffraction, optical and electronic microscopy.The surficial sediments of the Gulf are highly heterogenous and consist of both young and relict mineral and carbonate components. The terrigenous fraction is fluvial in origin and consists mainly of quartz (16–68%), minor feldspars (0–9%) and traces of siderite. The clay species determined include kaolinite, mixed layers of smectite–illite and illite; clays range up to 15% and do not present a clear pattern of distribution. Biologically productive areas of the Gulf, mainly in shallower parts, supply the carbonate component of the sediment. The carbonate material is comprised of aragonite (7–30%), low-Mg (5–30%) and high-Mg calcite (7–28%), and has variable degrees of alteration caused by sediment transport and/or diagenesis. Such processes are partly reflected in the regional distribution of mineral and chemical components throughout the Gulf. The interpretation of the data set was further refined by cluster analysis (Ward's method), which separated eight clusters (provinces) of sedimentary material. The eastern side appears to be the main source of both terrigenous and carbonate sediment, which is inferred to be transported clockwise. During this dispersion, physicochemical and mineralogical changes take place; the sediments become finer grained and characterised by more stable species of carbonates. As a consequence, the center and the northwest sections are clay-rich and contain dominantly low-Mg calcite.Ooids are relict components that have been identified in areas in which they were not mentioned by previous studies, notably in the southeast. These carbonate particles consist of concentric layers of aragonite deposited around a nucleus of angular quartz, most likely of fluvial origin.This study indicates a complex history over a short time frame with sediment supply, biological production and current patterns being the main factors that control the sediment character and its regional distribution within the Gulf.