Fanning River Karst (Queensland)

Background

The Fanning River Karst is an area of tropical sub-humid karst that lies southwest of Townsville, and is developed on a 1 km wide belt of the Devonian Burdekin Formation. The formation comprises alternating narrow zones of thick bedded reef limestones with good karst development, thinner bedded limestone with poor karst development, and poorly exposed belts of interbedded limestone, sandstone and shale with no karst features. This could be an example of "Stripe Karst".

The surface karst comprises locally fluted outcrops, some well developed griked limestone pavements which dip at the angle of the bedding, and scattered dolines.

The 25 known caves are scattered and generally small. Two areas of denser cave development occur: in the northern and central areas. This latter area is the most significant and contains the largest caves. The caves are thought to have formed below a higher water table during the mid Tertiary; and were drained, with occasional reflooding, during the late Tertiary and Quaternary. Paleokarst features include speleothem deposits which predate the latest phreatic sculpturing of the walls.

Rope Ladder Cave (FR-2) is the largest and most complex cave in the area. It may have the best detailed exposure of a fossil reef in Australia, and is an important educational and scientific resource. The Maternity Cave (FR-1) is biologically significant as it is a bat maternity site.

The climate is tropical monsoon, with pronounced wet and dry seasons.

Further reading

  • K.G. Grimes, 1990: Fanning River Karst Area: Notes on the Geology and Geomorphology, Department of Resource Industries, Queensland, Record 1990/7 (unpublished) - (PDF version)

    Selected photographs and diagrams

    To view full size images, click on the displayed image.
    Dipping limestone pavement with minimal karren development. This is following the dip of the bedding at the contact between a thick-bedded reef facies, and an overlying thin-bedded muddy limestone that has been removed by erosion.
    S89FR03s.jpg
    Devonian Limestone - dipping back reef lagoon facies - a thin-bedded muddy unit exposed in the cave wall.
    S880133.jpg
    Devonian Limestone - reef facies. A massive unit composed of fossil stromatoporoids, corals etc...
    S880120.jpg
    Detail of fossil stromatoporoid and other beasties exposed in the cave wall.
    S880114s.jpg
    Map of Rope Ladder Cave (4FR-2) the largest cave in the area. This is a phreatic system with large sculptured chambers in the east (where most of the photos were taken) and a maze of smaller joint-controlled passages to the west.
    4FR-Fig06.png
    Phreatic sculptured limestone in 4FR-2. An area of solution-sculptured paleokarst speleothem can be seen beneath the right-hand man.
    S89FR04.jpg
    Detail of a cave wall with a paleokarst speleothem (right) sculptured in continuity with the rest of the limestone.
    S880119s.jpg
    A smaller joint-controlled cave passage in 4FR-2. The floor is a partly undermined old speleothem layer.
    The caves are hot and humid !
    S89FR02.jpg
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