Crystalline basement in the Delamerian Project area is defined as Ordovician and older rocks which were affected by the Cambro-Ordovician Delamerian Orogeny and older tectonic events. It thus includes the rocks of the Adelaide Geosyncline,...
Crystalline basement in the Delamerian Project area is defined as Ordovician and older rocks which were affected by the Cambro-Ordovician Delamerian Orogeny and older tectonic events. It thus includes the rocks of the Adelaide Geosyncline, Kanmantoo Province and basement to the Murray Basin. Four data sources were combined to produce the Delamerian Basement Elevation Grid: 1. drillholes located within the project area, with stratigraphic logs, that encountered units defined as basement; 2. drillholes located within the project area, with lithological logs, that encountered lithologies considered as basement units; 3. selected drillholes located within the project area, that stopped short of entering basement units, but which provided information that assisted with the depth interpolations (N.B. these are not included in the final data package); 4. 100k mapsheet polygons of outcropping basement units. These were used to clip a 3 second SRTM Digital Elevation Model (DEM), and the DEM was converted to point data. Using Intrepid Geophysics, the variable density gridding method was applied to compute the final basement elevation (relative to sea level) grid, with a resolution of 800 m cell size. This resolution was determined to be the optimum, because of the sparsity of drillholes over the entirety of the project area. A direct comparison of the drillhole point data and the basement elevation grid, in some instances, may show divergence due to interpolation effects over large distances. For this reason it is recommended that interpretations should utilise the drillhole point data in tandem with the interpolated grid product. The cover thickness grid was calculated using the DEM, resampled to 800 m to match the resolution of the basement elevation grid. In ArcGIS, the Raster Calculator tool was used to subtract the basement elevation grid from the DEM to produce the final output. Two reliability maps are also provided. A point spacing reliability map, which provides an overview of the distances between basement data points; and a nominal grid resolution reliability map. In general terms, sparse data points produce outputs that are considered less reliable than those produced from the close-spaced data points.
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