Speleothem dating

How are speleothems dated?

Speleothems, despite their uniform mineralogy (calcite, less commonly aragonite), occur in a great variety of forms, dimensions, and colors, and any of these can be dated by U-series methods provided their age is within the dating limit of the particular method.

How old are speleothems in caves?

Entering a cave decorated with various sorts of speleothems commonly prompts questions about the age of these formations. It is intuitive to suggest that tall stalagmites or thick flowstone took a long time to form, but until the middle of the 20th century no method existed which allowed the quantitative determination of how old speleothems are.

What is the uranium-thorium dating method?

The dating method of choice for speleothems, known as the uranium-thorium (U-Th), or 230 Th method, belongs to the family of uranium-series methods and was first applied to speleothems in the early 1970s, although its physical principles were known since the beginning of the 20th century.

How is the age of a stalagmite determined?

Using state-of-the-art instrumentation this method allows dating speleothems between essentially zero and ca. 600,000 years before present. Multiple age determinations are typically performed along the extension axis of a stalagmite in order to decipher its detailed growth history.

What are the prerequisites for the dating of speleothems?

As with any dating method a fundamental prerequisite is the lack of post-depositional alteration, that is, no gain or loss of isotopes within the decay chain of interest. Using state-of-the-art instrumentation this method allows dating speleothems between essentially zero and ca. 600,000 years before present.

How do scientists date the layers of a speleothem?

Scientists can date the layers in the speleothem by measuring how much uranium, a radioactive element, has decayed. Uranium from the surrounding bedrock seeps into the water and forms a carbonate that becomes part of each layer of the speleothem as it forms.

What do 14 C dates of speleothems mean?

In short, 14 C dates of speleothems provide only a rough estimate of their formation age and samples older than ca. 50,000 years cannot be dated using this method.

How old are speleothems in caves?

How long does it take for stalactites to form?

Limestone stalactites form extremely slowly – usually less than 10cm every thousand years – and radiometric dating has shown that some are over 190,000 years old. Stalactites can also form by a different chemical process when water drips through concrete, and this is much faster.

What are stalactites and stalagmites?

Stalactites and stalagmites are the most common speleothems. Stalactites are centimeter to meter in scale, hang from the ceiling and grow toward the cave floor. Stalagmites grow from the cave floor upward and are commonly fed by water dripping from an overhead stalactite.

How are stalagmites decorated in caves?

Stalagmites often grow directly beneath stalactites, mopping up any minerals from water droplets that splash down onto the cave floor. However, the two types of cave decoration dont always come in pairs: either one can appear on its own. Limestone caves can also contain other kinds of cave decoration.

What is the difference between limestone and stalactites?

They spread outwards more, so they have a wider, flatter shape than stalactites, but they gain mass at roughly the same rate. Limestone stalactites form extremely slowly – usually less than 10cm every thousand years – and radiometric dating has shown that some are over 190,000 years old.