Hi everyone,
I do happen to work with paleoenvironmental records from karst regions and from speleothems. This is a great abstract and the work looks promising.
There are a good number of published research papers providing paleoseismic records from speleothems. I would say that this research focus is about 30 years in the going (although some very early work goes back ~100 years) and the field is largely dominated by European researchers focused on the Mediterranean basin and/or the alps. There is also some new work from the last 2-3 years now coming out of China. The focus so far (again from my memory) has been on tilted and even broken stalagmites and/or fallen stalactites. What the researchers here are doing that is new is looking at the very first deposition of the calcite and linking that to opening up of new fractures and therefore assumed to be new drip points. They do not appear to be looking at broken speleothems as most everyone else has done before.
Having read the published abstract from the GSA, this looks like interesting and good work. They do say that they are working with a sample set of 60 and they list 15 age determinations they have so far (which would have been in June when the abstract were due). They are only a quarter of the way through their data so this should mature into a very nice piece of work.
They do not actually say that they are assuming that the earthquake is causing new fracturing.
I would suggest there is a weakness in saying that the new stalagmites must start from drips from newly created cracks and fissures in the ceiling. Earthquakes are also really good at tilting and shifting blocks of the earth. Even a 1 degree tilt would be more than enough to change the drip point on the ceiling. Tilt a cave a slight bit and you could go from having a soda straw with a stalagmite beneath it, to having a strip of bacon with a new tiny stalagmite just started even several feet away from the original drip point. Does it absolutely have to be that the earthquake opened a new crack ? Not necessarily. Would the earthquake have change/altered the drip points including possibly opening up new fractures? Almost certainly.
John Lovaas wrote:It looks like they are correlating the young formations with weather records, and the older formations using U-T dating.
There is no mention of using climate/weather records at least in the abstract. Uranium/Thorium (U/Th) dating is really quite good. The +/- standard deviation data they are providing is also most likely to 2 (TWO) standard deviations as that is the common practice with U/Th dates. The reason they have to resort to counting laminations for the young ones is that there is often not enough uranium in the sample to get a good date for less than say 1000 years. Besides, counting to 200 is not that big a deal.
I would mention that the laminations in speleothems are very often much thinner than what you can see with your naked eye and often require special light to see. Some speleothems, even from areas with snow melt and other nice seasonal factors, simply are not laminated no matter how they are examined. The rock between the surface and the cave acts as a big reservoir and smooths out the seasonal fluctuations to the drip points. What you most often see with your eyes are lines in the speleothem are actually much bigger events, like periods of time when the whole stalagmite stops growing, or the cave was flooding leaving mud on the calcite, or the forest above the cave burnt down letting alot of sediment come down from the surface, etc. Bruce Railsback provides a great atlas on speleothem imagery at
http://www.gly.uga.edu/speleoatlas/SAindex1.html Some of the images do a great job at showing just how subtle the laminations are -
http://www.gly.uga.edu/speleoatlas/SAimage0227.htmlJohn Lovaas wrote:I can appreciate the correlation between the speleothem dates and the other seismic dating methods- but without the other dates(sand blows, etc.), I think it would be tricky to point at a speleothem's age and go, "there was a seismic event at date X".
Actually it is the reverse. The U/Th dates from the speleothems are most likely WAY more accurate and precise than any date generated for the sand blows, etc. The U/Th dates are the gold standard.
John Lovaas wrote:I suppose most all limestone caves have some kind of tectonic origin
You get nice fracturing from all sorts of non-tectonic processes, such as isostatic rebound and flexing of whole regions when glaciers melt which is happening throughout the great lakes basin right now, you get shrinkage when carbonate become more dense as they mature (think of mud cracks here), you can get pressure cracking when additional sediments are loaded on top of one part of a region and not another (think of the sediments of the Mississippi river delta causing regional stress patterns), etc etc. So yes, there is of course some reason why the fracturing happens, but no it does not need to be related to plate tectonics.
Sorry for the long discussion - this is a great topic!
Trish