Dating method
Pedogenic carbonate
An attempt to date carbonate that formed in a soil. It is easy to contaminate, and at these sites it is not treated as a construction clock.
What is measured
Carbonate can precipitate in a soil after a surface has been buried. In principle, the carbon in that carbonate might be measured by radiocarbon. In practice, older limestone dust, later rainwater, and mixed layers can all enter the sample.
A carbonate date that disagrees with dates on plaster, charcoal, or bone is a reason to ask which material belongs to which event. It is not, by itself, a reason to declare a new founding year.