Speleothem dating method

speleothem dating method

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 do speleothems help us understand the past of climate?

Since caves exist all over the Earth, speleothems have the potential to become a pivotal land-based climate record. Other land features help fill in the picture of climate in the past. Water marks trace the shorelines of ancient lakes where none exist now.

How much speleothem is needed to determine the age of a sample?

It is possible to obtain a meaningful age from as little as 10–20 mg of speleothem material. Most laboratories, however, prefer larger samples (e. g., 50–200 mg) to improve precision and possibly run duplicates. As a rule of thumb, the younger the sample and the lower its U concentration, the more sample is required to obtain a good result.

Why sample broken speleothems from a cave?

Many dripstone caves contain abundant broken speleothems, locally reworked by a cave stream. Sampling such fragments is clearly easier to justify than removing in situ stalagmites and still provides valuable insights into the history of a cave or the regional paleoclimate.

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.

What are speleothems in a cave?

Geologists refer to the mineral formations in caves as “speleothems.” While the water flows, the speleothems grow in thin, shiny layers. The amount of growth is an indicator of how much ground water dripped into the cave. Little growth might indicate a drought, just as rapid growth could point to heavy precipitation.

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: Cave popcorn, or cave coral, are small, knobby clusters of calcite;

How is calcium carbonate formed in speleothems?

Groundwater saturated with carbonate dioxide dissolves calcium carbonate (CaCO 3 from the bedrock and reprecipitates it inside the cave when carbonate dioxide volatilizes. Most caves are developed in limestone or marble , so CaCO 3 forms most speleothems.

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