With regards to C14 dating. I liked the 50’s A-bomb testing avenue and know that it would increase the available neutrons which in turn increases C14 concentrations. I’m still digging on that subject. Thanks for pointing it out.
Here is where I am also going. What effect, and how would C14 dating be adjusted for sealed underground water reservoirs seepage? Correct me if I’m wrong, but the sealed water chamber would be free of C14 because it has been shielded from cosmic radiation. If it were to leech out at, some point, it would upset C14 ratio’s?
This is a new avenue of thought for me, but there are/were a lot of underground water that move and seep due to tectonic movement throughout the ages?
As usual, you are the field expert and I’d love to hear your thoughts.
K4
A sealed water source would receive no C14 from the atmosphere, and the existing levels would eventually drop below the detectable level. (However, tiny amounts of C14 can be created by radioactivity in rocks, which is why coal, dinosaur bones, and other ancient materials often produce measurable amounts of C14.) This could result in dates on that water being too old.
You can get the same problem with water exposed to limestone. It absorbs carbon with no appreciable C14 content, hence dating too old. Freshwater shellfish who live in such water also date too old. These problems have been studied. These effects generally result in dates a few hundred to, perhaps in extreme cases, a thousand or more years too old.
The solution is to know what you are dating and to date multiple materials and compare the dates one against another. My last major excavation produced 31 radiocarbon dates.
A better example is deep water in oceans. Through the upwelling effect, deep water with lower amounts of C14 can enter the food chain and be absorbed by shellfish and sea mammals, as well as the humans who consume those items as food. When these materials, or the humans, are subsequently dated, the dates can be too old.
There are two ways to correct for this. First, for humans, establish the C13/C12 and N15/N14 ratios (these are stable isotopes). This can let you estimate the percent of marine organisms in the diet and hence the amount of carbon from upwelling.
For shellfish and sea mammals you assume 100% marine carbon, and apply a reservoir correction. There have been a lot of studies comparing charcoal and shellfish, for example, as well as dates done on shellfish collected at known dates prior to the atomic bomb tests. These have led to a correction factor applied to dates on marine shell. (See Marine Reservoir Correction Database.) In our area the average correction is on the order of 650 years.
The test of these corrections is how closely marine shell and charcoal date when two samples from the exact same provenience are dated (for example a trash or fire pit). All of the paired samples I have had dated have been statistically the same, showing the calibration is accurate.
Hope this helps.