Geology of Caves

The geology of caves and karst (Karst is the term for limestone areas that contain caves – not all Limestone is cave bearing) is a subject of fascination for many cavers with a scientific bent.

Limestone

Most caves, including those in Buchan and other parts of Victoria, form in limestone. Limestone is a rock that contains more than 50% calcium carbonate, and this is usually present as calcite, a mineral. Calcium carbonate forms the skeletons of the majority of marine animals such as corals and shells. Limestone can also contain lime mud from other sources.

Limestone is a sedimentary rock, in that it is formed by the deposition of material, in this case the little sea creatures I have mentioned. The solubility of limestone in water and weak acid solutions eats way the limestone over millions of years to form caves.

Take a closer look!

So – what you are climbing around in is the compressed and ancient remains of millions and millions of sea creatures, hardened and condensed into rock. The limestone around Buchan contains many fossils such as corals, gastropods and brachiopods. Have a close look at the rock when you are underground – you’ll see them all over the place. The rocks around ‘Baby Pierre’ cave in Buchan have some nice crinoids.
Much of the ‘decoration’ in caves are formed by calcite, including straws, stalactites, stalagmites, columns, shawls, helictites and flowstone.

Fossils in Devonian Limestone, in Murrindal (Near Buchan, East Victoria)

Fossils in Devonian Limestone, in Murrindal (Near Buchan, East Victoria)

Most of Buchan’s caves are in ‘Lower Devonian’ limestone, and is somewhere in the vicinity of ~416 – 397 (+ 2.5) Million years old. The limestone is dark in colour and quite hard. This is in dramatic contrast to the young limestone found in the West of Victoria which is lighter in colour and more sandy and soft in texture. The main cave area in Western Victoria, known as Bats Ridge, is a late mid Pleistocene limestone. The main dune has been dated at 290 + 34 Ka (thousand years). Scroll down to see a table detailing the type of rock in our Victorian caving areas.

Victoria is blessed with all of Limestone Caves, Volcanic Caves, and Granite caves. Pretty incredible for one small state. If you are interested in finding out more about cave and karst related geology, send an email to me Tom Aberdeen (See the contact us link on the main page) and I will put you in touch with some experts in the field. Cave geology is fascinating and adds further depth of appreciation into this hobby.

More fossils in Devonian Limestone, Murrindal (Near Buchan), Eastern Victoria

More fossils in Devonian Limestone, Murrindal (Near Buchan), Eastern Victoria

A suggestion for interstate cavers planning a trip to Victoria would be to visit both the deeper older Limestone in and around Buchan, and then drive West to the volcanic caves as well, which are one of only 2 areas of significant Volcanic caves in the whole of Australia – and even going further West to the caves described in the ‘Western and Limestone Coast’ menu. Three distinctly different areas all with individual merit.

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