Mark,
Maybe one of the specialists in this area will respond with more detailed information but yes, speleothems can be dated by analyzing the ratios of radioactive elements. They do have growth rings but the ones you see with the naked eye do not equate to dates like tree rings - it is a lot more complicated than that. In the past, ice cores have been used to determine atmospheric gas composition and estimates about climate back to approximately 100,000 years. I understand that the speleothem dating techniques can take the dating back almost 400,000 years with surprisingly good resolution (20+ years?) and are now becoming the gold standard for age dating and climate studies with microcrystalline growth rings being used to estimate regional rainfall. It is also much complicated than I've described. Speleothems have the added advantage in that they occur almost anywhere there are caves so therefore, you can create a local data base of dates rather then depending upon ice cores which can only be obtained from high mountains or the Polar Regions. Dating of speleothems used to be a pretty arcane practice done by very few geologists/speleologists who were looking to answer specific questions such as whether speleothems continued to grow during ice ages which would imply that the area above the cave was ice free or to try and determine a relative minimum age for a cave passage. The techniques have become more refined and speleothems have now a hot field of study and have become a critical piece of data to understand global climate change. Generally, the speleothem is cut in half and rock specimens are removed along the axis of the speleothem and analyzed for their uranium thorium content through a process which involves a lot of complex chemistry using some fairly strong acids (needless to say, you can't do this at home with your rock tumbler). Regarding your comment about whether speleothems should be removed for use in scientific interest. Well that depends - most scientists are very responsible about the removal of speleothems and would not recommend that prominent formations be removed and if a specimen needed to be collected, that it be done so to minimize the impacts to a cave. Removal should also only occur with permission of the owner. Cave formations are very nice to look at and the indiscriminate destruction of formations should certainly be discouraged. However, the removal of a few formations for scientific use is considered by many scientists to be acceptable. Note that cave sediments can also be used for relative age dating and should not needlessly be disturbed, not only does an undisturbed floor look nice but the sediments may provide some important scientific data. Formations have been removed from a number of caves in Texas including Devils Sinkhole. The UT Geosciences Department has one of the better labs in the country and has published their results in a number of scientific publications. Geary -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Wednesday, January 23, 2008 12:27 PM To: Allan Cobb; Texascavers Mailing List Subject: RE: [Texascavers] Caving Show on Discovery Channel Did anyone happen to watch this show the other night? Were you as horrified as I was when the overly dramatic host and another scientist took a chisel to an ~ 3 foot by 4 inch stalagmite in order to break it free in order to count the rings? Apparently, they were wanting to calculate the rate of annual water flow in order to match it up to the apparent demise of the below mentioned headless skeleton. Their theory was that the hapless victim was sacrificed at about the same time as a drought was occurring and, by doing so, the gods would be pleased with the sacrifice and send rain. How you could correlate the age of the stalag with the victim's death is beyond me. Is this appropriate behavior? I'm surprise no one else hear saw this or thought to comment on it. Y'all's thoughts? Mark A. ________________________________ From: Allan Cobb [mailto:[email protected]] Sent: Sunday, January 20, 2008 10:58 PM To: Texascavers Mailing List Subject: [Texascavers] Caving Show on Discovery Channel Monday night (January 21) at 8 PM is a new series called Bone Detectives. This episode is about a headless skeleton in a cave in Belize. The cave that the show centers around is called Midnight Terror and it was only discovered about a year ago. The show also did filming in several other caves in Belize.
