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: mark.al...@l-3com.com
[mailto:mark.al...@l-3com.com]
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:a...@oztotl.com]
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.
