Phreatic drainage conduits within quartz sandstone: evidence from the Jurassic precipice sandstone, Carnarvon Range, Queensland, Australia
Discrete underground drainage conduits in quartz sandstones are far less common than in limestones. This paper provides field evidence from the quartzose Precipice Sandstone in the Carnarvon Range of south-central Queensland, Australia, for tubular underground drainage networks similar inmanyways to limestone conduits. Diameters range from less than 1 or 2 cm to over 1.5 m, most display a near-circular to oval cross-section that seems to suggest phreatic or epiphreatic development, and the internal surfaces of many are case-hardened by secondary silica deposits. A number of the region's perennial springs appear to be fed by such tubes. The dominant vertical jointing of the quartz sandstone and relatively high permeability of the sandstone are important controls on tube formation. Solutionalweathering of the sandstone is widespread, and is followed by the removal of loosened sand grains by flowing underground water, the process of ‘arenisation’. Tube developmentwould appear to have been happening for a very long time, and maystill be occurring. A model for tube network formation is proposed. These findings highlight our potentially poor understanding of groundwater flow within some quartz sandstones, and may have important groundwater management implications.