1.1.3 Geology


The Pedirka Basin is a largely subsurface sedimentary basin comprising Early to Late Permian sediments and coal sequences that covers an area of approximately 71,000 km2. The Pedirka Basin is centred on the SA-NT border, approximately 160 km south-east of Alice Springs.

The Pedirka Basin consists of two deep troughs that are separated by a central ridge of older rocks called the Dalhousie–McDills Ridge. A thin section of Permian sedimentary rocks over the ridge connects the two troughs. The Pedirka Basin is underlain by Early Paleozoic sedimentary rocks of the Warburton Basin and Amadeus Basin, as well as crystalline Precambrian basement rocks. Overlying the Pedirka Basin are sedimentary rocks of the Eromanga Basin (Great Artesian Basin, GAB) of Mesozoic age, as well as Cenozoic sediments.

There are two sedimentary formations within the Pedirka Basin; the Purni Formation and Crown Point Formation. The Purni Formation consists of sandstone, siltstone and claystone, as well as coal beds deposited in river and swamp-related environments. The underlying Crown Point Formation is composed of sandstone, diamictite, siltstone and shale deposited within a glacial and river environment. A well-sorted sandstone that occurs at the top of the Crown Point Formation is typically used as a marker for the end of glaciation.

Directly overlying most of the Pedirka Basin is the Eromanga Basin, which is synonymous with the GAB. In the Pedirka subregion, aquifers occur in the Winton Formation, Mackunda Formation, Cadna-owie Formation, and Algebuckina Sandstone/DeSouza Sandstone. Within deeper parts of the basin, the Triassic Simpson Basin occurs between the Eromanga Basin and Pedirka Basin strata. Overlying the Eromanga Basin are the most recent phases of sedimentation primarily deposited in episodic braided river, lake and desert environments.

The shape and structure of the Pedirka Basin formed over a series of major tectonic events that have taken place since the Proterozoic. Additionally, valleys formed by glaciers prior to the deposition of Pedirka Basin rocks may have also been important with respect to basin architecture. Deposition in the Pedirka Basin that included glacial, marine and finally terrestrial sedimentation appears to have ceased during the Late Permian. Since then, further deformation events have resulted in erosion and deposition of younger sedimentary rocks over the Pedirka Basin.

Within the Pedirka Basin, coal seams are a characteristic of the upper member of the Purni Formation, however economic coal seam gas plays may occur. Currently, there is no commercial exploitation of coal seam gas in the Pedirka Basin, although some exploration work has been undertaken. The Pedirka Basin is also the subject of conventional hydrocarbon exploration.

Last updated:
5 January 2018
Thumbnail of the Pedirka subregion

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