ABSTRACT. The Pre-Pottery Neolithic Β (PPNB) site of Yiftahel, Israel, contains abundant plaster floors. We surveyed the states of preservation of the plasters using an infrared spectroscopic assay that characterizes the extent of disorder of the atoms in the calcite crystal lattice. We identified the 3 best-preserved plaster samples that had disorder signatures most similar to modern plaster. We then studied the surface layers, fine-grained matrices, and large aggregates of these samples using micromorphology, Fourier transform infrared (FTIR) microscopy, stable carbon and radiocarbon concentrations. Even though some of the plaster components have a geogenic appearance in micromorphology slides and in FTIR spectra, the 14 C analyses show that all components were exposed to high temperatures and as a result were equilibrated with the 14 C content of the atmosphere ~ 10,000 yr ago. This implies that the plasters at Yiftahel were produced entirely from heat-altered calcite. We also show that these plasters have undergone significant diagenesis. The plaster component with the most disordered atomic signature, and hence the most similar in this respect to modern plaster, did indeed produce a 14 C date close to the expected age.
Obtaining accurate age determinations from minerals in archaeological ash is a major unsolved issue in radiocarbon (14C) dating. This is because the original 14C content of calcite, the main component of ash, is altered by isotopic exchange. Pyrogenic aragonite, another mineral phase recently discovered in ash, might preserve its 14C signature through time. Using a new method based on density separation and step combustion, we were able to isolate and date aragonitic ash from an archaeological destruction horizon of known age. Here we show that the 14C age of aragonite matches the age of the destruction horizon. Our results demonstrate that pyrogenic aragonite is a short-lived material suitable for 14C dating and directly related to human activities involving the use of fire, thus bearing major implications for the establishment of absolute chronologies for the past 50,000 yr.
ABSTRACT. Ash is formed when plant calcium oxalate crystals (CaC 2 O 4 ) decompose to form calcite (CaCO 3 ). We found that ash does retain the original calcium oxalate radiocarbon concentration, but in addition, there is another minor 14 C source. This is shown by the presence of a consistent small shift in the pMC and 13 C levels when comparing cellulose and ash from modern and archaeological woods. Possible mechanisms for 14 C exchange during combustion or due to diagenesis are considered in order to define parameters for identifying better-preserved wood ash samples.
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