Limestone, caves

A current 1.00-g sample of carbon shows 921 disintegrations per hour. If 1.00 g of charcoal from an archaeological dig in a limestone cave in Slovenia shows 5.50 X 103 disintegrations in 24.0 h, what is the age of the charcoal sample ... 

The story does not end with cavern formation. Many limestone caves, such as Carlsbad Caverns, contain spectacuiar formations that inciude staiagmites, stalactites, and limestone columns. We need to examine the equiiibria more cioseiy to understand how these structures form. 

Acids and bases are found throughout nature. In fact, acids and bases are used as a defense mechanism by insects and can produce beautiful limestone cave formations. If not monitored carefully, however, acids and bases in the environment can cause a lot of harm. 

The formations inside limestone caves are made up of limestone, too. Water that drains through the cracks in rock and into a limestone cave often contains dissolved limestone. As the drop of water hangs from the ceiling, some of the carbon dioxide trapped... 

Bubbles of carbon dioxide gas form when the vinegar hits the chalk. A piece of chalk covered in vinegar and left for a couple of days will completely dissolve. Limestone rocks dissolve in carbonic acid to form limestone caves, and marble buildings and statues will eventually dissolve in acidic rain, too. 

A These downward-growing, icicle-shaped structures called stalactites and the upward-growing columns called stalagmites are formed in limestone caves by the slow precipitation of calcium carbonate from dripping water. 

The effect of pH on the solubility of CaC03 has important environmental consequences. For instance, the formation of limestone caves, such as Mammoth Cave in Kentucky, is due to the slow dissolution of limestone (CaC03) in the slightly acidic natural water of underground streams. Marble, another form of CaC03, also dissolves in acid, which accounts for the deterioration of marble monuments on exposure to acid rain (Interlude, pages 650-651). 

Stalactites hang from the ceiling of limestone caves. They look like icicles and occur at cracks where water flows through the limestone and into the cave. Sometimes water containing some dissolved calcium carbonate will drip off the tip of a stalactite and onto the floor of the cave. In these places, stalagmites will form on the cave floor. Sometimes a stalactite and a stalagmite will connect and make a column. 

Figure 6.1 An example of stalagmites and stalactites in a limestone cave.

This process and its reverse account for the formation of limestone caves and the stalactites and stalagmites found there. The acidic water (containing carbon dioxide) dissolves the underground limestone deposits, thereby forming a cavern. As the water drips from the ceiling of the cave, the carbon dioxide if ->st... 

White, E.L. and White, W.B., 1968, Dynamics of sediment transport in limestone caves, Natl. Speleol. Soc. Bull 30 115-129. 

Bretz, J. H., 1942, Vadose and phreatic features of limestone caves, J. Geology, L 675-811. 

Limestone cave levels within the Dukes system in the Buchan district of East Gippsland in Victoria, southeastern Australia (Fig. 1) can be correlated with a series of three river terraces in the valley of the Buchan River (Webb et al., 1992). Both caves and terraces are thought to have developed in the Pleistocene, because uranium series dating of speleothems in this system gives ages of more than 350,000 years, and perhaps greater... 

Caves are present through much of the limestone. The topographically highest caves have formed in the Murrindal Limestone in the centre of the synclinorium. These caves vary from simple shafts to complex joint-controlled mazes of narrow passages, but all display predominantly vertical development. The Murrindal Limestone caves are believed to have formed beneath an Eocene river system, and were probably drained by incision of the rivers in the Late Eocene - Early Oligocene (Webb et al., 1991). 

The topographically lower caves in the Buchan area are predominantly horizontal systems, usually developed sub-parallel to the strike of bedding, and are present only within the Buchan Caves Limestone. The main passages in these caves are less than 30 m above the nearest surface stream or river bed, and many contain active streams in their lowest levels. Thus these caves are of more recent origin than the Murrindal Limestone caves. 

PALEOCLIMATE RECORDS FROM SPELEOTHEMS IN LIMESTONE CAVES... 

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