The Flinders River supergroup spans the Euroka Arch a basement structure partially separating the Carpentaria Basin from the Eromanga Basin. Granite provides the basement in the northern Eromanga Basin in the southwest of the supergroup and is exposed in a very limited area by the Kevin Downs Fault. The basement of the Carpentaria Basin in the vicinity of the springs are metamorphosed sediments and these Precambrian schists outcrop in the vicinity of springs at Mt Fort Bowen, Mt Brown and Mt Little. The Gilbert River Formation forms the lower unit of the Mesozoic sedimentary sequence and is the main water-bearing aquifer for the springs in this supergroup. Some stratigraphic sequences in bores describe Hooray Sandstone, Cadna-owie Formation and Wyandra Sandstone, but these units are synonymous with facies within the Gilbert River River. This sandstone is overlain by a sequence of Cretaceous units, the Wilgunyah Formation, the Toolebuc Member and the Allaru Member that act as aquitards. The Gilbert River Formation outcrops extensively in the eastern part of the Supergroup and there are many large outcrop springs, many of which are isolated in rugged ranges, providing baseflow for major streams including the Woolgar, Norman, Clara and Yappar Rivers.

In addition to the isolated outcrops of granite and metamorphic rocks in the western edges there are important structures relating to springs. A large network of springs is aligned in the vicinity of the Woodstock Structure, a pronounced section of the Euroka Arch. Another structure clearly associated with springs is the north-south trending St Elmo Structure. Tectonic activity that created these structures during the Paleozoic has reactivated to result in minor faulting.

Additional information

• Section 4 Lake Eyre Basin Springs Assessment Final Report, DSITI 2015, Queensland Government, Brisbane.

The outcrop springs associated with the outcropping Gilbert River Formation in the eastern region of the supergroup are probably gravity-fed springs fed from higher elevation sandstone. The Gregory Range to the east of these areas is represented by a tableland of Tertiary sands overlying the sandstone. These provide recharge intake beds that store water before it percolates through the sandstone. In the south and central these springs emanate from stratigraphic weaknesses associated with side-gullies from the main streams.

In the northern areas to the south-east of Croydon large springs are associated with the footslopes of the outcropping sandstone but not necessarily in association with gullies.

The springs associated with the Woodstock Structure (Pelham, East Creek and nearby properties) are not aligned in a linear arrangement suggesting that they may be associated with braided fault structures. The springs on Bunda Bunda, Saxby Downs and nearby properties to the south may also be associated with braided minor faulting. There is no obvious evidence of faulting in the stratigraphy represented by bore logs for either of these spring clusters. These faults may be only relatively weak but the substantial artesian pressures in this region, some of the highest in the GAB, are sufficient to result in surface discharge through springs. This network of springs includes currently active springs, inactive springs and springs that were previously permanent, but are now only ephemeral. These ephemeral springs often occur in local sinkholes, but do not have obvious vents suggesting that their current groundwater source is diffuse discharge from the regolith.

Additional information

• Section 4 Lake Eyre Basin Springs Assessment Final Report, DSITI 2015, Queensland Government, Brisbane.