Diagrammatic cross section of the Gregory Karst
The strongly developed karrenfields on the Supplejack member show a zonation which results from progressively longer periods of exposure at the surface. This starts with incipient karren development on recently exposed surfaces adjacent to the contact with the overlying Skull Creek Formation and continues through progressively deeper dissected karren to a final stage of "ruined cities" of isolated pinnacles at the outer edge (Zones 1 to 4 on cross-section below). Microkarren are abundant and extremely well developed - expecially on the thin dolomite slabs of the upper Skull Creek formation ("cu" on diagram).
Diagrammatic cross section of the Gregory Karst
Extensive horizontal maze caves underlie the dissected surface, being best developed under karren zones 2 & 3. The largest, Bullita Cave, is an extensive horizontal, multi-level, joint-controlled, maze system with a total passage length of 103 km(± 5) in 2005. Its overall extent is 4-5 km. The nearby Dingo Cave has about 50 km of passages. Passage junctions are typically every 15-30 m. Bullita Cave is divisible into sectors, separated by narrow connections (often a single tight passage). The individual sectors have distinctive properties.
A theory of speleogenesis is being evolved by members of the Gregory Karst Special Interest Group of the ASF - who have been mapping the system for 15 years. A preliminary report appeared in 1995 and that model is being developed further. This will probably involve progressive exposure of the Supplejack Member by slope retreat and broad-scale water input via the karrenfield. Lithological control by a shale bed that is easily eroded by flood waters is part of the story. Wet season flooding may be significant. One suggestion is that this is a type of epikarst cave.