Alice Springs town basin, review 2003
Read, R. E.
E-Publications; E-Books; PublicationNT; Report ; no. 42/2003
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Report ; no. 42/2003
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sorting. This is probably because the sediments are thinly bedded (from 150 to 300 mm thick). Test drilling has shown that the beds of sand are long, narrow bodies with a lenticular cross-section. The lenses are from 2 to 25 feet thick, and they anastomose both vertically and horizontally through the body of alluvium. This type of sediment forms about 15 per cent of the total volume of the saturated alluvium in the Town Basin. Brown and Grey Clayey Sand: The brown and grey clayey sand contains the same minerals as the brown sand, but much more matrix, and in places the proportion of silt and clay exceeds that of sand. Brown and Grey Silty Clay: Probably 80 percent of the sediment in the basin is silty clay. It consists of blue or grey silty clay, very thinly interbedded or laminated with brown clayey silt. Black carbonaceous laminae a common, and it may contain variable but appreciable quantities of very fine to medium-sized sand. The clay content is estimated to range from 10 to 40 percent. Regolith and Colluvium: The regolith overlying the Arunta Complex is a stiff blue sandy clay, with cobles and boulders of both weathered and relatively fresh metamorphic and igneous rocks. From extensive grain-size analyses Quinlan and Woolley (1969) found that the sediments in the southern end of the basin are more poorly sorted than in the northern end. 5.2.2 Basement aquifers The metamorphic rocks under the Town Basin have very low permeability and can generally be ignored. A few bores in areas of thin sediments have obtained supplies from basement rocks, but their contribution to the hydrology of the basin is negligible. 5.2.3 Aquifers outside the limits of the alluvial basin Most of the urbanised area lies outside the Town Basin. Most of this is over weathered bedrock, which would not be considered an aquifer for most purposes, but it is important in that it contains a large store of salt, which may have been mobilised by urbanisation in some cases. Groundwater of up to about 20000 mg/L is known in these rocks Little data is available for the hydraulic properties of the weathered bedrock aquifers. Permeabilities inferred from a few tests and estimated yields are shown in Appendix I. There are also a few minor alluvial aquifers associated with minor tributaries to the Todd. Springs such as that at Morris Soak flow for a time after heavy rain. These appear to be from shallow fracture systems, possibly fed by ephemeral soil aquifers. 15
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