| MadSci Network: Earth Sciences |
Hi Tim, That fossil bat mentioned at: http://www.nps.gov/cave/tours/lower/bat.htm isn't really as "shocking" as it might at first seem. The first issue that needs to be put to rest is the rate at which speleothems grow. I think that for you to be "greatly shocked" you must have approached the problem with the assumption that all speleothems, being a geologic process, must naturally take very long time intervals over which to grow. This seems to be a common misconception people have of geology, that the prevailing assumption is that everything happens very slowly. In reality, the pure Uniformitarianism of times past has been replaced with the realization that occasionally some things can happen very quickly. Turbidite deposits, for example, are strata that can be deposited on a time scale of hours. Other "events" that can be preserved in the geological record are tidal deposits, some pyroclastic (volcanic debris) deposits, landslides (though rarely preserved for long), and tempestites (storm-deposited strata). Speleothems are not produced catastrophically like the above examples, but they can be "rapidly" formed in that they don't necessarily require geologically important time intervals. For example, consider that speleothem growth has been documented in historical times, in one instance Treble et. al. (2003) correlated annual growth ring trace element concentrations in a speleothem that had grown on a boardwalk laid down in 1911 to historical climate data. And that is one way in which the age of a speleothem can be estimated, by studying thickness of annual layers and comparing them to other climatic records. Carbon-14 can be used, as carbon of organic origin is leached from the soil horizon into the cave and trapped in the growing ornamentation. Other dating methods can be used as well, as various techniques are becoming more sensitive at quantifying trace element concentrations with progressively decreasing disturbance to samples. One common application is the fine-tuning of the paleoclimate record, for example Vacco et. al. (2005) did a study of the isotopic variation of oxygen and carbon in a speleothem from the Klamath Mountains of Oregon, sampling at about 50-year intervals. They were able to identify the Younger Dryas cooling event in the sample and were looking for changes in vegetation in response to the climate change. The second part of the problem is how long the bat would exist in the cave so that it could be preserved. This is another interesting feature of caves; they tend to preserve organic material fairly well. The statement mentioned in your NPS Internet link that says that freetailed bats don't live in the lower cave today, but the remark that "You will see their remains throughout the tour" tells me that we have plenty of time for the speleothem to encase the bat, since presumably the remains of many of his non-encased fellows are commonly seen today as well. Another page in their online tour mentions historical artifacts found in the lower cave, "including wooden flare handles, old matches, nails, rope, and even a pack of Chesterfield cigarettes". http://www.nps.gov/cave/tours/lower/hist.htm That isn't really remarkable in itself. In Mammoth Cave much of the wood from the ca. 1812 saltpetre works is still in good shape, although they've been scrounged and moved over the years. I've seen one cave recently where there was a newspaper from the 1950s that was fifty years old with the dates still legible. The biggest threat to such artifacts other than maybe some microscopic invertebrates are people that trample over them. While that bat is very much a curiousity, I don't think it does any violence to accepted time frames for speleothem formation. --Gene Marlin ---------------- Pauline Treble, J. M. G. Shelley and John Chappell. Comparison of high resolution sub-annual records of trace elements in a modern (1911–1992) speleothem with instrumental climate data from southwest Australia. Earth and Planetary Science Letters Volume 216, Issues 1-2 , 15 November 2003, Pages 141-153. Elsevier Science Direct search and abstract retrieval used, www.sciencedirect.com David A. Vacco, Peter U. Clark, Alan C. Mix, Hai Cheng, and R. Lawrence Edwards. A speleothem record of Younger Dryas cooling, Klamath Mountains, Oregon, USA. Quaternary Research Volume 64, Issue 2 , September 2005, Pages 249-256. Elsevier Science Online search and abstract retrieval used, www.sciencedirect.com Carlsbad Caverns National Park (website), National Park Service. http://www.nps.gov/cave/tours/lower/bat.htm and http://www.nps.gov/cave/tours/lower/hist.htm
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