Geochronology and archaeological dating

SUMMARY: Chapter 4, in Renfrew & Bahn's textbook (Archaeology: Theories, Methods, and Practice), covers archaeological dating methods and their applicability and limitations, including stratigraphy (relative dating), typologies (e.g., seriation), linguistic dating, climatic clues (e.g., ice & deep=sea cores), absolute dating (e.g., pollen; ancient calendars; tree-ring/dendrochronology; radiocarbon dating; potassium-argon dating; uranium-series dating; thermoluminescence dating; optical dating; electron spin-resonance dating; global events; etc.).  In my view, this is one of the best college textbooks available, and is invaluable for students, archaeologists, and the public in general, to obtain a top notch overview of approaching and interpreting the archaeological record; also including a case study on the instructor's work at a late Old Kingdom fort at Ras Budran, in South Sinai (Egypt).  REVISED: Feb. 2023.

The vast majority of known archaeological sites in arid Northeast Asia are surface assemblages containing few or no organic remains. The lack of stratified sites and a relative absence of organic remains in surface assemblages hinders our ability to date sites, create local chronologies, and contextualize technological and socio-economic change. Such problems are common in arid regions around the world. New radiocarbon and luminescence dates on collections from the Gobi Desert of Mongolia and China are used here to assess the potential for direct dating of commonly occurring artefacts like ostrich eggshell and pottery. Direct dating also allows for the identification and sorting of mixed-age assemblages. Here, we compare dates derived from Accelerator Mass Spectrometry (AMS) on ostrich eggshell, AMS on pottery, and luminescence on pottery. Our findings show that Accelerator Mass Spectrometry and luminescence are highly complementary methods and produce results consistent with expected archaeological ages, while ostrich eggshell dates were older than the associated site assemblages.

Abstract Here we report a detailed archaeomagnetic and rock-magnetic study of a pottery kiln from Burgos (Spain) to reconstruct its burning conditions and date its last use and abandonment age. During the course of a rescue archaeological excavation carried out in 2015 in the center of Burgos city, a medieval pottery workshop was discovered. Two well-preserved kilns appeared and archaeomagnetic analyses were performed on one of them. In addition to a large amount of pottery remains, some numismatic and documental evidences provided a general chronological estimation, but the abandonment age of the workshop remains unknown. On the basis of the existing archaeological information we carried out an archaeomagnetic study in order to date its last use. 69 archaeomagnetic samples were collected from the combustion chamber and the kiln's fire tunnel. Stepwise alternating field and thermal demagnetization of the natural remanent magnetization (NRM) were carried out to retrieve the mean direction. Additional experiments consisted in the acquisition of isothermal remanence (IRM), low-field magnetic susceptibility and its anisotropy as well as thermomagnetic curves. Despite the high temperatures expected in the combustion chamber, it appeared that the bricks´ samples from the fire tunnel exhibit the most successful directional results. Magnetite and variable contributions of hematite are the main ferromagnetic minerals observed in the thermomagnetic curves. The type of lithology studied, its previous magnetic history and their location in the kiln strongly condition the observed directional and rock-magnetic results. Additionally, AMS data revealed the manufacturing fabric of the fire tunnel's bricks, showing moderately high anisotropy degrees, but not enough to casts doubts on the directional NRM record. In order to test the reproducibility of the dating results, archaeomagnetic dating was carried out using different geomagnetic field models and the Iberian secular variation curve. The small differences observed in the dating results are mainly due to the density and type of input data of these records. The combination of the archaeomagnetic analyses with the archaeological and documental suggests that last kiln's usage took place during the first half of the XVIth century CE. Overall, this paper illustrates how the combination of archaeological data and archaeomagnetic analyses may improve our understanding about the manufacturing processes, use and age of abandonment of archaeological combustion structures.

We describe the finding of five male bodies from the salt mine of Chehr Abad, Zanjan province, Iran. Radiocarbon determinations suggests that two of the bodies date to the late Sassanian period, while the other three died sometime between 410 B.C. and 350 B.C. We speculate that these deaths may have been the result of an earthquake between 405-380 B.C. We have also obtained new isotopic data on skin and hair, and conclude that they may not have come from the Zanjan area. A preliminary study of stomach contents and parasite load for one of the bodies has also been carried out.

Rehydroxylation (RHX) dating was recently suggested as a simple, cheap, and accurate method for dating ceramics. It depends on the constant rate of rehydroxylation (the slow reintroduction of OH) of clays after they are fired and dehydroxylated (purged of OH) during the production of pots, bricks, or other ceramics. The original firing of the ceramic artifact should set the dating clock to zero by driving all hydroxyls out of the clay chemical structure. To examine whether this assumption holds, especially for pot firings of short duration and low intensity, as those in small-scale traditional settings, we performed thermogravimetric analysis of clay samples of known mineralogy at temperatures and for durations reported from traditional sub-Saharan, American, and South Asian pottery firings. If a sample was not completely dehydroxylated during its production, then current RHX methods would systematically overestimate its age. Results demonstrate that in the majority of samples, complete dehydroxylation (DHX) did not occur within, or even beyond, the conditions common in traditional firings. Consequently, between .01 and 1.5% of a sample’s mass in residual OH may remain after firings analogous to those observed in the ethnographic record. Lack of complete DHX at the scales we have observed can result in the over-estimation of ceramic ages by decades to tens of thousands of years, depending largely on the age of the sample, and the amount of residual OH present.

We present here evidence of pre-Portuguese presence in the Azores Islands, Portugal, found near the site of Grota do Medo (Posto Santo), discovered by Rodrigues (2013) in Terceira Island, Azores. This evidence was dated by Accelerator Mass Spectrometry, and indicates the presence of human activity in Terceira Island before or during the XIth century. The evidence consisted in a man-made rock basin, which was found in a site that contains also striking similarities with many other as-pects from ancient cultures, including other man-made rock basins, arrangements of large stones which resemble megalithic constructions, and inscriptions in stones which resemble ancient pe-troglyphs. Although the dating of this evidence is highly suggestive of the presence of human ac-tivity in the Azores Islands long before the arrival of the Portuguese navigators of the XVth century, there is no clear evidence which enables us to identify which specific culture may have existed in

Measurements of hydration depths of prehistoric obsidian artefacts by thin-section techniques have yielded dates of mixed accuracy in different parts of the world, but have been notably unsuccessful in New Zealand. Resonant nuclear reactions, widely employed to study surface diffusion in solids, were attempted on Mayor Island obsidian from New Zealand. It was found that artefacts of varying ages have hydration rinds of very similar overall thickness and that the relationship between the theoretical and actual character of the diffusion front is more complex than is widely assumed.