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Galiwinku Groundwater Resource and Evaluation DLH-492



Galiwinku Groundwater Resource and Evaluation DLH-492


Yin Foo, Des


E-Publications; E-Books; PublicationNT; Report ; 6/1984




Made available via the Publications (Legal Deposit) Act 2004 (NT).





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Dept. of Transport and Works

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Report ; 6/1984

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Technical Report WRD84006 Viewed at 14:07:13 on 29/07/2010 Page 24 of 60. 2.5 Regional Hydrogeology The Wessel Group of rocks contains the Carr~rian depositional seauence of the Arafura Basin. The group has been divided into four distinct formations Elcho Island Formation, Marchinbar Sancstone, Raiwalla Shale and Buckingham Bay Sandstone. The extent of each formation is shown on Figure 2.5. The Buckingham Bay Sandstone has not been investigated by drilling. Bores, have entered the overlying sequence, the Raiwalla Shales and proven the shales to be unfavourable as ,.,rater bearing strata. Both units are estimated to be in excess of 600 m thick and cover a considerable area in the Arafura Basin. (Ref 5) Conformably overlying the Raiwalla Shale is the Marchinbar Sandstone. It is described as a flaggy to massive thin bedded quartz sandstone. Outcrops exist extensively throughout the Wessel Islands. Prospects for water supplies within the formation are known to be good with !?upplies in excess of 10 L/ s intersected at both Maningrida and Raminginning. The uppermost unit of the Wessel Group the Elcho Island Formation, is predominant in the coastal regions of north Arnhem Land. Bores have intersected the formation at several locations along the coast. Outstation drilling both on Howard Island and to the east of the Glyde River at Dhipidi intersected small supplies in the sandstone at shallow depth. The overlying strata consisted partly of remnant shales. Apart from those bores at Galiwinku, several others drilled further north on the island have intersected the shaly unit. In three of these, the bores were drilled deep enough to intersect the supply at the sandstone interface. Of these, t~lO produced saline water. Examination of the lithological logs for outstation bores RN 20957, RN 20958 (Gulumarri); RN 20959, RN 20920 (Ganpurra) and RN 8500, RN 8501 (Gitan) (see Appendix A, Table A.I) has enabled a strike and dip of the Elcho Island Formation in this area to be estimated. This result indicates the geological mapping of the area is inconsistent and implies a discrepancy in the differentiation between the basal sandstone of the Elcho Island Formation and the Marchinbar Sandstone. That is, in some parts, the basal sandstone of the Elcho Island Formation has been incorrectly mapped as Marchinbar Sandstone or vice versa. The similarity in strata intersected by bores drilled at outstations throughout the region tends to support the latter alternative. As a consequence, the formation contact could be placed along the spine of the island and regionally, the delineated contact as shmvn on Figure 2.5, further north. Table 2.5 is a summary of the Wessel Group lithology.

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