Northern Territory - Surface karst

Introduction

The Katherine area is at the northern end of the Daly Basin, a broad area of flat-lying early Palaeozoic limestone that has an extensive cover of Cretaceous sandstone and claystone and younger alluvium. Karst features are mainly restricted to the exposed limestones at the northern and western margins of the basin.

Most outcropping limestone forms pavements of grikes and clints or, in more strongly dissected areas, widening and deepening of the grikes has converted the clints to pinnacles and small towers that are typically 1-3 m high, but up to 30 m in places. The surfaces of the pinnacles and towers are sculptured by deep "rainpits" and rillenkarren grading to spitzkarren in the more dissected areas. Locally the pitting becomes very intense to form a sharp fretted surface analogous to coastal phytokarst. Kamenitza up to two metres across are also common and some have outlet channels. Beneath the sandy cover there is a well-developed epikarst surface of narrow smooth-surfaced pinnacles and deep shafts, which is exposed within the occasional soil-subsidence doline.

Further south, the rainfall is lower, and outcrops around the edge of the basin have only hackly surfaces with deep "rain-pits" ranging in width from 3 mm to 20 mm.

The caves are horizontal systems, dominantly phreatic-sculptured joint-directed mazes of fisssure passages, or more linear gently sinuous passages. Paleokarst fills and other features are common and might date back to before the Cretaceous. Phreatic features such as spongework and ceiling cupolas are common. They are typically hot and humid.

Further reading

Karp, D., 2002: Land degradation associated with sinkhole development in the Katherine region. Department of Infrastructure, Planning and Environment, NT. Technical Report 11/2002

Lauritzen, S.E., and Karp, D., 1993: Speleological assessment of karst aquifers developed within the Tindall Limestone, Katherine, N.T., Power and Water Authority, NT. Report 63/1993.

Selected photographs and diagrams

To view full size images, click on the displayed thumbnail image.
C020616.jpg Katherine karst area, Daly Basin, NT
Pinnacle. It is full of holes
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C020619.jpg Katherine karst area, Daly Basin, NT
Close-up of a pinnacle, showing cavernous horizon.
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C020630.jpg Katherine karst area, Daly Basin, NT
Epikarst pinnacles and shafts exposed by soil subsidence.
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C020637.jpg Katherine karst area, Daly Basin, NT
Recent subsidence pit beside the Stewart Highway. Epikarst pinnacles and shafts have been exposed.
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C020608.jpg Katherine karst area, Daly Basin, NT
Lake Hickey (in background) is a "polje" that floods during major wet seasons. In the forground is a marginal ponor that leads to a small cave.

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C020612.jpg Katherine karst area, Daly Basin, NT
Paleokarst fill in an old fissure cave unroofed at the top of a limestone ridge.
Calcrete pisoliths from an old soil fill - or are they cave pearls?
File: C020612.jpg
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