Ngalia Basin hydrogeological inventory

This Ngalia Basin dataset contains descriptive attribute information for the areas bounded by the relevant spatial groundwater feature in the associated Hydrogeology Index map. Descriptive topics are grouped into the following themes: Location and administration; Demographics; Physical geography; Surface water; Geology; Hydrogeology; Groundwater; Groundwater management and use; Environment; Land use and industry types; and Scientific stimulus. The Ngalia Basin is an elongate, east-trending basin over 500 km long and 90 km wide. It occurs mostly in the Northern Territory, with limited occurrence in Western Australia. The Ngalia Basin is an intra-cratonic sedimentary basin in a structural downwarp formed by a faulted asymmetrical syncline. The basin began to form about 850 Ma, and contains a Neoproterozoic to Carboniferous sedimentary succession. Sedimentation ceased in response to the 450 to 300 Ma Alice Springs Orogeny. The maximum stratigraphic thickness of the Ngalia Basin is about 5000 m. The basin contains mainly arenaceous sedimentary rocks, with lesser fine-grained rock types and some carbonates. Fining upwards sedimentary cycles are commonly preserved and capped by calcite-cemented fine-grained sandstone and siltstone. Tectonic events disrupted deposition during basin evolution and led to at least ten unconformities. There are many disconformable contacts, with angular unconformities common in areas with abundant faulting. The upper-most arkosic sandstone formations in the Ngalia Basin are the Mount Eclipse Sandstone and the Kerridy Sandstone. These units have an aggregate thickness of several hundreds of metres and are the main aquifers within the Ngalia Basin sequence. There is some interstitial porosity, especially in the Mount Eclipse Sandstone, although joints and fissures associated with faulting provide significant secondary permeability. These aquifers provide good supplies of potable to brackish groundwater, and supply the community borefield at Yuendumu. The Ngalia Basin is almost entirely concealed by Cenozoic cover, including Palaeogene-Neogene palaeovalley, lake and alluvial fan sediment systems and Quaternary aeolian sands. Shallow aquifers with brackish to potable water occur in many palaeovalleys sediments overlying the basin.