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.
Why are speleothems important to geologists?
Speleothems: Cave rocks. Because speleothem growth is influenced by geography, ground water chemistry, and other factors, the record from one cave cannot serve as a record of climate change. Scientists must look for similar patterns of growth in speleothems in caves over a broad area to infer that the climate changed.
What is A speleogen?
Speleogens (technically distinct from speleothems) are formations within caves that are created by the removal of bedrock, rather than as secondary deposits. These include: Lava tubes contain speleothems composed of sulfates, mirabilite or opal. When the lava cools, precipitation occurs.
How is uranium formed in the speleothem?
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. Uranium decays into thorium, which sticks to the clay in the bedrock instead of seeping into ground water and from there into the speleothem.
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 are speleothems formed?
Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depending on their depositional history and environment.
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 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.
