This dataset was derived from well tops, seismic sections and some open file industry interpretations, utilising Petrosys mapping software.
Interpreted, compiled and edited by Brent Jensen-Schmidt. Overall supervision by Lloyd Sampson, Senior...

This dataset was derived from well tops, seismic sections and some open file industry interpretations, utilising Petrosys mapping software.

Interpreted, compiled and edited by Brent Jensen-Schmidt. Overall supervision by Lloyd Sampson, Senior Hydrogeologist, DEWNR.

Final files produced by Energy Resources Division, DMITRE. Brent Jensen-Schmidt: consulting geophysicist.
S.P. Fabjancic: imaging, archiving and application support.
Lloyd Sampson: overall supervision.


Top Cadna-owie Formation
The top 'C' is picked in the middle of a significant seismic trough. It is a fairly consistent marker horizon and is considered a reliable pick. 
The Cadna-owie regional mapping was first completed in 1996 from interpreted seismic Two-way Time data (TWT) derived from oil industry maps and direct seismic interpretation. These digital time maps were cross correlated with a 'warping' digital field derived from petroleum well depths to create depth maps. This is basically the equivalent of applying a velocity field.
Various updates and extensions were included in 2001 and 2009, derived from new drilling and seismic data.
This current dataset was completed in 2012 and incorporates all available proofed drill holes. Water well data was validated by DEWNR, however mineral well and petroleum well data was only validated where required (ie: when the data clearly appeared anomalous). Geological outcrop data and limited new seismic data were also included.
The limits of the mapped formation are defined as contiguous areas. Small patches of Cadna-owie outside the contiguous area are not included.


Base Eromanga Formation
Also referred to as the base of Jurassic sediments, this surface represents a mixture of Triassic, Permian and Basement surfaces.
The 'Aquifer' is defined here by the extent of permeable water bearing sandstones of the Cadna-owie Formation, plus lower formation layers which are part of the same aquifer system. These include the Algebuckina and Hutton Sandstones as well as minor horizons which contact the major reservoirs in some locations. 
The 'Base Aquifer' is defined as areas where the above sandstone reservoir contacts non reservoir sediments or crystalline rock.
These non reservoir layers are generally at the level of the Triassic, Permian or earlier sedimentary rock, or 'Basement' crystalline or metamorphic layers.


Surface to Top Cadna-owie Isopach
This layer is the result of subtracting an interpreted depth to the Cadna-owie horizon from the Surface elevation, to effectively create a depth to Cadna-owie map from Surface.
The ground surface elevation is derived from the 1 Second (approximately 30 Metres) Digital Elevation Model (DEM), relative to AHD as supplied by Geoscience Australia. Final grid size utilized was 200m * 200m to reduce excessive detail.
Updates and extensions were created in 2001 and 2008. Final iteration was created in 2011 for DEWNR, with the inclusion of all reliable water bore data around the western and south-western edge of the Great Artesian Basin.
These two layers (Surface & top "C") were combined to make the Surface to Cadna-owie Formation Isopach, which in this case is also equivalent to the 'Depth from Surface to Cadna-owie' map. The resultant data was smoothed to remove noise and improve the appearance of the final output map although a slight imprint from the surface elevation effects remain.
Areas where the Cadna-owie Formation is outcropping or absent, have grid values set to zero and are now defined and displayed by a zero contour.


Top Cadna-owie to Base Eromanga Isopach
The isopach between the top 'C' and Base Eromanga Formations represents what is colloquially known as the GAB aquifer (Cadna-owie Formation / Algebuckina Sandstone) in the western half of the map area. 
However, in the eastern half of the map area, the isopach represents a sequence of alternating sandstone and shale units. This region contains the Cadna-owie, Namur and Hutton units. In the Cooper Basin area this can include minor non permeable layers such as the Birkhead Formation and Murteree Shale. These minor horizons are not considered to be an absolute barrier to water flow within the gross aquifer.

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