Great Artesian Basin - Paleogene-Neogene Cover - Thickness and Extent

## **Abstract** 

This dataset and its metadata were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied.



The Paleogene-Neogene Cover - Thickness and Extent dataset, is one of a set that represents the hydrostratigraphic units of the Great Artesian Basin, which include five major aquifers, four intervening aquitards, and the Paleogene/Neogene cover. The alluvium cover has not been included as it is considered to be transparent to movement of water. There are six layers in the Paleogene-Neogene cover data set. A: Cover extent B: Paleogene/Neogene Volcanics cover extent C: Outcrop extent D: Isopach raster E: Isopach contours F: Location of data points The datasets have been derived from the lithostratigraphic intercepts in drillhole data from petroleum exploration wells, water bores, and stratigraphic wells. Seismic correlation and assessment of hydrogeological character based on electrofacies have not been used. The working datasets for this study has been derived primarily from the following databases: 1. Using data from http://www.ga.gov.au/scientific-topics/water/groundwater/gabwra/data/technical-reports 2. PEPS-SA (Petroleum Exploration and Production System - South Australia) (Department of Primary Industries and Regions SA, 2011) 3. WaterConnect Groundwater database (Govt. of SA, 2011) 4. QPED (Queensland Petroleum exploration database) (Geological Survey of Queensland, 2010). 5. GABLOG (Great Artesian Basin Well Log Dataset) (Habermehl, 2001) 6. Additional supplementary information was derived from published reports listed in the references section below. 7. In the Carpentaria, especially offshore, data derived from seismic interpretation. This is a regional interpretation for mapping at approximately 1:1 000 000 to produce a broad scale overview, and examination of small areas by collecting extra data is most likely to produce results that differ from this regional interpretation. This dataset and associated metadata can be obtained from www.ga.gov.au, using catalogue number 81675. Associated report reference: Ransley, T., Radke, B., Feitz, A., Kellett, J., Owens, R., Bell, J. and Stewart, G., 2015. Hydrogeological Atlas of the Great Artesian Basin. Geoscience Australia. Canberra. \[available from www.ga.gov.au using catalogue number 79790\]

## **Dataset History** 

METHOD: Cover Extents Extents are taken from the dataset Thickness of Paleogene-Neogene sequence overlying the Great Artesian Basin (Geoscience Australia, 2013) and modified using: 1. Additional Cenozoic intercepts in drilling (Govt. of SA, 2011) in South Australia 2. Paleogene-Neogene volcanics from Surface Geology of Australia 1:1 million scale dataset 2012 edition (Raymond et al. 2012) 3. Palaeovalleys from Groundwater. Salinity investigations using airborne geophysics in the Lower Balonne area Southern Queensland. National Action Plan for Salinity and Water Quality (Kellet et al. 2004) 4. Hydraulic connectivity between the Quaternary alluvium and GAB aquifers in the Surat Basin (GAB Atlas, 2014) Extent lines were adjusted to envelop all intercepts of the Hydrostratigraphic unit. This produced some varied and irregular shapes, some patchy regions, and required some interpretation to establish the most likely extent boundary. Outcrop Extent Outcrop extents are taken from the dataset Thickness of Paleogene-Neogene sequence overlying the Great Artesian Basin (Geoscience Australia, 2013), but modified in South Australia from additional Cenozoic drill log data (Govt. of SA, 2011). Isopach Raster Source point thickness values calculated from Drillhole intercepts as well as isopach line data were extrapolated using the ESRI ANUDEM Topo-To-Raster surface modeller to produce thickness grid surface. Zero thickness constraints were applied at the known extent of the aquifer/aquitard, except in cases where the formation extends beyond the GAB boundary (for example the Precipice formation on the eastern side of the GAB, where the formation is quite thick and is exposed as a cliff). In these cases, constraints were not applied and the software was allowed to model a thickness right up to the GAB boundary. Resulting grids were modified using the ESRI Grid Calculator to set the minimum thickness to 0, and clipped to the aquifer/aquitard extent. Isopach Contours Quaternary units and known thicknesses are not included; therefore this cover is essentially of the Paleogene-Neogene sequence only. In the south-western Eromanga Basin, stratigraphy from water bore and drillhole documentation (see References) does not always differentiate between tertiary (T) and quaternary (Q) units, so the quaternary component is unknown. If there is no distinction of a surficial component above these combined Cenozoic units and the unit thickness is less than 20m, the unit has been ignored on the assumption that it has a high probability of a dominant Quaternary component. Combined Cenozoic thicknesses recorded under a surface Quaternary unit have been taken as given. In the Gulf of Carpentaria, thickness interpretation used off-shore seismic surveys (see Seismic References). In this area, the entire Cenozoic interval is assumed to be the Paleogene-Neogene thickness after water depth has been subtracted. In this seismic profiling, the Cenozoic appears uniform in character and no subdivision into tertiary and quaternary units was possible. Lake Eyre Basin thicknesses are from contours from Tertiary stratigraphy and tectonics, Eromanga Basin region (Moussavi-Harami & Alexander, 1998) and Surface Geology of Australia 1:1 million scale dataset (Raymond et. al. 2012). Isopach contours were calculated from the Paleogene-Neogene thickness grid using the ESRI Contour Tool. These were calculated at 50m intervals. In most cases the zero contour lines generated by the tool were replaced by the extent of the aquifer due to the erratic nature of the generated lines. In cases where the aquifer/aquitard is thick at the extent, the zero isoline is outside the extent and is not mapped in that area. Isopachs were clipped to the aquifer/aquitard extent.

## **Dataset Citation** 

Geoscience Australia (2015) Great Artesian Basin - Paleogene-Neogene Cover - Thickness and Extent. Bioregional Assessment Source Dataset. Viewed 07 December 2018, http://data.bioregionalassessments.gov.au/dataset/26335d25-e904-462b-b075-50cfe5dc9b31.

Tags: Australia, Galilee subregion, geoscientificInformation
Organization: Bioregional Assessment Program