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Ashfield Shale is part of the Wiannamatta group of sedimentary rocks in the Sydney Basin. It lies directly on contemporaneously eroded Hawkesbury sandstone or the Mittagong formation. These rock types were formed in the Triassic Period. It is named after the Sydney suburb of Ashfield. Some of the early research was performed at the old Ashfield Brickworks Quarry. This rock type is often associated with the Inner West and North Shore of the city. However, it has also been recorded at Penrith, Revesby, Bilpin and Mount Irvine. == Description == Ashfield Shale comprises black mudstones and grey silty shales with frequent sideritic clay ironstone bands. The depth ranges between 45 and 64 metres.〔 Though it is recorded at 20 metres thick at the Sydney Olympic Site. The chemistry of the rock is typical of shales, with high iron levels, and some iron sulphide and low calcium levels. The geology of the shale lenses within the Hawkesbury Sandstone is chemically similar to the Ashfield Shale.〔 Small scale bedding is abundant. The shales are sandy at the top of the sequence. There are up to ten bands in a fifteen-metre section. The fine grained silty sediments were laid down in a low energy, south-east flowing deltaic setting, near the shores of a shallow sea. There is no natural selection in which the Ashfield Shale is completely exposed. However, it can be seen at railway and roadside cuttings, as well as old quarries. With weathering and exposure, the shale becomes a paler colour. Weathering of the shale units produces a reddish/brown podsolic soil, often with poor drainage, such as that in the Cumberland Plain. These clay soils are recognised as being reactive with an appreciable shrink-swell capacity. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ashfield Shale」の詳細全文を読む スポンサード リンク
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