The Groupe des Méthodes Pluridisciplinaires Contribuant à l'Archéologie (GMPCA) hosted their biennal conference at the University of Montreal between the 9th and 12th May 2019. The SAS sponsored three student prizes. The winners were Mélissa Morel, Asmodée Galy, and Alexia Nguyen Trung. Here are the abstracts of their award-winning research!
Iron Metallurgy along the Northeast Coast of Madagascar (7th to 17th centuries): A study of the variability of technologies
Mélissa Morel, Chantal Radimilahy, and Vincent Serneels
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| Mélissa Morel is a Ph.D. student at Université de Fribourg (melissa.morel@unifr.ch) |
During medieval times (7th - 17th century) the so-called “Rasikajy” lived on the northeast coast of Madagascar and were in contact with the Indian Ocean trade network. This is supported by excavations of rich graveyards (600 graves) in which imported artefacts from China, India and the Middle East were found (Gaudebout & Vernier, 1941; Vernier & Millot, 1971; Vérin, 1975). Because of the lack of archaeological research in Madagascar, the material culture of the Rasikajy remains however largely to be understood (Verin, 1986; Schreurs et al., 2011).
The presence of iron slag heaps on the eastern coast of Madagascar is reported in the existing archaeological literature (Vérin, 1986; Dewar & Wright, 1993). The focus of our project is to describe, date and understand these remains of iron production. During the first two field campaigns (2017 and 2018), more than 80 heaps of slag were located thanks to pedestrian surveys. These slag heaps are located along the coast between the estuary of the Manahara River and the modern city of Antalaha (Serneels et al., 2018; Serneels et al., 2019). Further exploration work is still needed to better define the geographical boundaries of this metallurgical district. Even though they are numerous these heaps are small and rarely exceed 5 tons of metallurgical waste. Excavations and surveys were carried out to better understand these different metallurgical sites and especially the technologies employed.
The Northeastern coast of Madagascar is fringed by quaternary sand deposits reworked by sea level fluctuations. Between Antalaha and Vohémar, concentrations of Magnetite and Ilmenite in these sands are reported in the geological literature. These black sands are available immediately on the beach; they are also easy to mine and to wash. It is indeed easy to separate by panning quartz and other light silicates from heavy minerals (Ilmenite, Magnetite, Garnet, Zircon, Monazite, etc.). XRF Bulk analyses were carried out on 120 slags found on smelting sites and on black sands collected along the coast (6 sampling locations, 18 samples analysed). These analyses show us that black sands are moderately rich in Iron (<60% wt.) but they have a high Ti content (>10% wt.) as well as high Zr, Th, P and REE contents. The Aluminium contents of black sands are low (5% wt.) in contrast to slags with high Al contents (10% wt.). The slags also have moderate concentrations of Ti, Zr, Th and REEs. The chemical signatures are completely different between the slags and black sands. Contrary to what was proposed by previous authors (Vérin, 1975) we can now demonstrate that ancient metallurgists did not use black sands as ores for making iron.
The inland hills rising above the coastal sandy sediment are made of old Precambrian basement rocks (granite, gneiss, etc.) intruded by more recent cretaceous basalts. They are covered by a thick layer of lateritic soil. Locally, this laterite contains iron oxide concretions forming a crust or as dispersed pisoliths. During our excavation, typical lateritic concretions were found at several smelting sites. Moreover, partially smelted concretions were observed entrapped in furnace bottom slags. At the excavated site of Amboronala 140, a large block of stone was used for crushing the ore, as shown by wear traces on its surfaces. The 16 laterite samples analyzed show chemical compositions with high Al and moderate Ti contents. They fit very well with the slag compositions. Chemical variability from one smelting site to another indicates the probable exploitation of several different locations. More field work is planned to identify precisely the mining areas.
The slag pieces can be divided between two main morphological categories: tapped slag and furnace bottom slag (for more details on the morphological description of these slags see Serneels et al. 2018 and 2019) From one slag heap to the other, the shapes and sizes of slags are very similar, but the proportions of the two categories are highly variable. No chemical difference between the two groups of slags can be seen. The mineralogical assemblage is also similar, containing fayalite, wüstite and spinels, including titanium-rich ulvöspinels. Petrological textural study by optical and electronic microscopy is ongoing to get a better understanding of these materials. For now, all slags are interpreted as the waste products of smelting. There is still no argument to support the interpretation of the bottom furnace slags as smithing slags.
The excavations led to the discovery of smelting structures on three different sites. Unfortunately, they are poorly preserved and fragile. These are simple elliptical bowls dug directly into the sand about 20 cm deep and of similar diameter (80 x 100 cm). No trace of clay lining inside the bowl was seen. Moreover, no trace of a built superstructure was observed in situbut we found a few fragments of partially fused and sintered quartz sand wall around a clay tuyere. The largest fragment allows us to reconstruct a 30 centimeter high wall. In one case at Matavy the bowl was surrounded by a few blocks of stone, probably used as reinforcement for the sand wall. Many tuyere fragments were found and these show significant variability. Some are pierced blocks of stone, others are shaped in clay. The study of these objects allowed us to reconstruct the smelting structure despite poorly preserved vestiges (Figure 1). It would be a small fireplace with a single tuyere connected to a bellows. The metallurgist dug a channel in the sand to allow the slag to be evacuated if needed.
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| Figure 1. Reconstruction of the smelting structure. |
Along the coast, each site has its own particularities but they show the same main features. First, slag heaps are small (5-25 tons). A Iron-rich lateritic ore was smelted inside a bowl furnace with a low superstructure made of sand and without clay lining. The air was injected into the furnace by a single tuyere and bellows. Moreover the radiocarbon dates show that these furnaces were active between the 11thand the 15thcentury. These sites are probably part of the same technology with variations linked to different community practices or the availability of raw materials. Within the Indian Ocean trade network, the Rasikajy were able to benefit from trade exchanges, but also from exchanges of knowledge and technology. As a continuation of this work on Rasikajy iron technology, we now hope to reconstruct the origins of this technology.
References:
Dewar, R., E., Wright, H., T., 1993. The Culture History of Madagascar. Journal of World Prehistory7(4), 417-466.
Gaudebout, P., Vernier, E., 1941a. Notes à la suite d’une enquête sur les objets en pierre de la région de Vohémar. Bulletin de l’Académie Malgache24, 91-94.
Gaudebout, P., Vernier, E., 1941b. Notes sur une campagne de fouille à Vohémar „Mission Rasikajy 1941“.Bulletin de l’Académie Malgache24, 100-114.
Serneels, V., Morel, M., Nitsche, C., Radimilahy, C., Rakotoarisoa, J.-A., Rasoraifetra, B., Schreurs, G., 2018. Pierre et Fer à Madagascar (1) – Vestiges sidérurgiques de Benavony et de la rivière Matavy, SLSA Jahresberich 2017, pp.109-156.
Serneels, V., Morel, M., Nitsche, C., Radimilahy, C., Rakotoarisoa, J.-A., Rasoraifetra, B., Schreurs, G., Velomora, S., accepté. Pierre et Fer à Madagascar (2) – Les scories d’Amboronala et les carrières de Milanoa, SLSA Jahresberich.
Schreurs, G., Rakotoarisoa, J.-A., 2011. The archaeological site at Vohémar in a regional geographical and geological context. Etudes Océan Indien(INALCO-Paris) 46-47, 27-49.
Verin, P., 1975. Les échelles du commerce sur les côtes nord de Madagascar, thèse d’Etat, Université de Lille.
Verin, P., 1986. The History of Civilization in North Madagascar, Rotterdam/Boston, A.A. Balkema.
Vernier, E., Millot, L., 1971. Archéologie Malgache – Comptoirs musulmans, Museum d’Histoire Naturelle, Paris.
Developing New Methods of U-series dating: Micro-sampling using femtosecond laser ablation coupled with ICP-MS spectrometry
Asmodée Galy, Loïc Martin, Gaëlle Barbotin,Fanny Claverie, Edwige Pons-Branchu, Chantal Tribolo, Norbert Mercier, and Christophe Pécheyran
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| Asmodée Galy is a Ph.D. student at Université Bordeaux Montaigne (asmodee.galy@u-bordeaux-montaigne.fr) |
Uranium/Thorium (U/Th) is a radiometric dating method, based on disequilibrium in the 238U series-chain induced during the formation of calcitic materials in particular. Although this method has been theorized since the 1950’s, and is, in principle, applicable to a wide variety of archaeological remains, its current application in this domain is limited because of three main causes. Firstly, the usual chemical protocol requires a significant amount of material, which is dissolved in acids, and then homogenized in the resulting liquid, with a high risk of contamination for small samples. Secondly, because of this dissolution, the potential incorporation and/or leaching of exogenous radioelements are difficult to correct for, and may necessitate several sub-samples, increasing the quantity of material required. Thirdly, detection limits of instruments render difficult the study of materials containing only traces or even ultra-traces of uranium.
The materials presented here are potentially concerned by these last two issues. They come from South African Middle Stone Age sites and are contemporary with the first modern behaviors associated to anatomically modern humans. These materials, namely ostrich eggshells, terrestrial snail shells, and herbivore teeth, contained very low 238U initial contents at the time of their burial. Thus, detecting within these small samples the few ppq of230Th produced by the disintegration of the 234U during the time of burial is an analytical challenge. To overcome it, the protocol implemented in our study draws on the advantages of coupling a femtosecond laser ablation station (Lambda III, Nexeya SA/Amplitude System, Bordeaux, France) with a high-resolution ICP-MS spectrometer (Element XR, Thermo Scientific, Bremen, Germany). The objective is to obtain the best possible spatial resolution while lowering the current detection limits. Its main advantage relies on the possibility to detect small volumes of material preserved from past geochemical changes or degradations.
To test our approach, isotopic mappings of the surface of speleothems were carried out using our system and the deduced ages were compared with those obtained with the usual approach (chemical protocol). We observed that, without any prior sample preparation, consistent ages can be calculated from the mapping, which were obtained with only 0.03 mg of material (a thousand times less than the mass usually required for the usual approach). Moreover the total analysis time was only two hours. The uncertainties on the ages are dependent on the counting statistics, but are lower than 5% in the case of a calcite containing 44 ppb of 238U and a hundred attograms of 230Th.
The same approach has been applied to the above-mentioned biocarbonates, by carrying out isotopic images of their prepared slices. First, these images are a powerful tool because they allow us to visualize the distribution of radioelements. It is then possible to identify different areas according to their characteristics, and divide the sample according to the uranium and thorium distributions, while identifying and eliminating contaminated or leached areas. The spatial resolution is only a few micrometers. Appropriate image processing using the ImageJ software allowed us to identify different areas according to these criteria, and therefore, from the measurement of the uncorrected activity ratios in each area, to apply the isochron technique for correcting these ratios (detritic thorium correction). In order to increase the accuracy of this correction, and because the measurements are fast, we were able to measure a series of images per sample.
This approach was applied to an ostrich eggshell fragment coming from the Late Howiesons Poort level of the site of Diepkloof Rock Shelter (Figure 2), and containing between 1 and 15 ppb of uranium. Thus, with 1 mg of sampled material, and three days of analyses, an age of 51±10 ky (two sigma) was calculated, consistent with the luminescence ages performed by two different laboratories (Jacobs et al., 2008; Tribolo et al., 2013). The accuracy on this age is of the same order of magnitude than the accuracies traditionally obtained by luminescence techniques. It is due to the counting statistics since only 2 attograms of 230Th were detected, i.e. a total of 115 ions of mass 230 detected during the analysis. The analysis of a giant terrestrial snail shell from the site of Bushman Rock Shelter (South Africa), also gave interesting results, but the uranium and thorium incorporation scheme is different from the previous material.
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| Figure 2. Isotopic mappings made on the slice of an ostrich eggshell fragment (DRS 10) from Diepkloof Rock Shelter (South Africa) |
Finally, the last material tested during our study was a herbivore tooth from the Sibudu site. Our protocol allowed the measurement of all the radioelements necessary to calculate ages in porous tissues such as dentine and in dental enamel, known to be a tissue much more resistant to contamination or leaching. A direct dating of the enamel was therefore possible thanks to the LA-Fs-HR-ICP-MS protocol. An age of 73± 3 ky was obtained on the dentine and the enamel for this tooth, using only 0.02 mg of material, for a total of 232 ions detected at the mass 230.
The U/Th dating by LA-Fs-HR-ICP-MS is therefore a powerful tool for studying calcitic materials of various types and origins. Isotopic mappings can be carried out thanks to micro-destructive analyses. This protocol contrasts with the chemical protocol (bulk analysis) since the heterogeneity of the sample can be taken into account at a scale of only a few microns. Thus, a selection of the regions of interest within the sample is possible, opening the possibility for isochron correction of detrital thorium. The considerable time saved using this approach as well as the consequent miniaturization of the sampling zone allows us now to consider dating using this method at another scale, and opens new perspectives for dating a wide range of materials neglected until now.
References:
Jacobs, Z., Roberts, R.G., Galbraith, R.F., Deacon, H.J., Grun, R., Mackay, R., Mitchell, P., Vogesland, R., Wadley, L., 2008. Ages for the Middle Stone Age of Southern Africa: Implications for Human Behavior and Dispersal. Science 322, 733-735. https://doi.org/10.1126/science.1162219
Tribolo, C., Mercier, N., Douville, E., Joron, J.-L., Reyss, J.-L., Rufer, D., Cantin, N., Lefrais, Y., Miller, C.E., Porraz, G., Parkington, J., Rigaud, J.-P., Texier, P.-J., 2013. OSL and TL dating of the Middle Stone Age sequence at Diepkloof Rock Shelter (South Africa): A Clarification. Journal of Archaeological Scienve 40, 3401-3411. https://doi.org/10.1016/j.jas.2012.12.001
Tracing Human Ancestral Migrations Using Symbiotic Bacteria
Alexia Nguyen Trung, Bastien Boussau and Vincent Daubin
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| Alexia Nguyen Trung is a PhD student at Université Claude Bernard Lyon 1 (alexia.nguyen-trung@univ-lyon1.fr) |
The genetic heritage of Homo sapiensis much more substantial and complex than presented by 20th century genetics. We now know that each human is the place and ultimately the product of the interaction of a multitude of symbiotic organisms, each carrying its own genome. Some of these associations are stable over the life course, and in some cases even over generations. This is the case of Helicobacter pylori, a bacterium generally considered to be pathogenic to humans, which is present in the stomach of 50% of the current world population (Breurec, 2011). Its transmission occurs particularly during childhood within the family (Weyermann and al., 2006), limiting the spread of infection. As a result, each strain is confined to a distinct human group and H. pylorityping can allow identification of different ethnic groups within the same population, even when it comes to very recent migrations (Wirth and al., 2004). For that reason, the study of strains collected from different locations allows us to spatially trace human ancestral movements and its presence in humans can be traced to the origin of Homo sapiensin Africa before the great/major migrations. H pylori has accompanied its host during its peregrinations on the different continents, to the point that the phylogeny of the current strains traces in broad lines the history of human migrations since the Out of Africamigration (Falush and al., 2003; Linz and al., 2007).
Like many bacterial species, H. pylorihas the ability to acquire genetic material from other bacteria which are not parents, by a process called horizontal gene transfers (HGT). We have previously developed a method which allows the identification of ancient events of HGT in bacterial genomes. As a result, it is possible to identify donor and recipient lineages in a phylogeny. A corollary is that we can determine which lineages are contemporary in the phylogeny of species, because HGT supposes a community of time and space. More specifically, on a phylogenetic tree, an HGT event attests that the ancestors of a donor species are older than the descendants of the recipient species. We have developed MAXTIC, a new method to use this information to date a phylogenetic tree based on HGT (Chauve et al., 2017), and showed its power to infer the timing of diversification in the tree of life (Arellano Davin, 2017).
The objective of this work was to make a proof of principle that HGT in Helicobacter pylori, a symbiont of humans, could be used to refine dates in the historyof human populations. To do this, we retrieved a dataset of 35 strains for which a complete genome sequence was available and geographic information was confirmed (Yahara et al., 2013). We analyzed the complete genome of each of the 35 strains to optimize the chances of observing ancestral horizontal gene transfers. The goal is to compare the complete genomes of H. pylori strains to 1) infer as general phylogeny of the strains and 2) compare each gene history to this reference tree in order to identify all HGTs that occurred throughout this history.
More specifically:
- We clustered homologous genes together to study all gene families using MMseqs (Steinegger and Söding, 2017). We kept all families present in at least 3 genomes for further analysis. This left 1622 families for study.
- We built the tree ofH. pyloristrains based on the concatenate of those families present in all strains (502 ubiquitous genes).
- Using ALE, a probabilistic phylogenetic reconciliation method reconstructing HGT scenarios, we inferred the history of all 1622 gene families within the species tree.From this dataset, we detected 900 transfer events, which corresponded to 40 time constraints.
- Finally, based on this set of constraints, we were able to reconstruct a dated species tree for H. pyloriusing MAXTIC (Chauve and al., 2017), and assess the statistical support for the resulting chronogram. The results show that HGTs provide a strong signal which is in accordance with the current knowledge on the timing of human migrations.
Figure 3 shows an example of the type of information provided by HGT on the relative timing of diversification of H. pyloristrains. In this example, ALE detects HGTs from the East-Asian clade (in blue) to the American clade (in fuchsia). According to these events, the ancestor of Asian donors is older than the descendants of the recipient lineage. This is in accordance with the history of the populations, because Homo sapiensfirst migrated to Asia before reaching the Americas.
Figure 3. (left)ALE has detected gene transfers from East-Asian clade (in blue) to the American clade (in fuchsia). These transfers attest that the donor's ancestors (represented by a triangle) are older than the recipient's sons (represented by a circle); (right) From the constraints of fig a, our phylogenetic tree should then be represented in this way: the East-Asian ancestors are older than the American.
This study demonstrates that there is a strong potential in using Homo sapienssymbionts for dating human migrations. We show that HGT is abundant in H. pylorigenomes, and that it provides strong statistical support for a phylogeographic sequence which corresponds to current knowledge on human migrations. There is little to be learned on such a small instance (only 35 strains of H. pylori), but it opens the door to a larger study using the >1000 genomes of H. pyloriavailable in public databases. Interestingly, ancient H. pyloriDNA has been recently extracted and sequenced from mummies. The inclusion of this data into our dataset will be of great interest as they provide direct absolute dates to calibrate our phylogenies. With this in mind, we have recently developed and implemented in RevBayes (Höhna et al., 2016) a new method to combine dating information from HGT with molecular clock methods to further improve dating.
References:
Breurec S., 2011. Helicobacter pylori: migrations humaines et cancer gastrique. Sciences agricoles. Université Paris Sud - Paris XI.
Weyermann, M., Adler, G., Brenner, H., Rothenbacher, D., 2006. The mother as source of Helicobacter pylori infection. Epidemiol. Camb. Mass 17, 332–334.
Wirth, T., Wang, X., Linz, B., Novick, R.P., Lum, J.K., Blaser, M., Morelli, G., Falush, D., Achtman, M., 2004. Distinguishing human ethnic groups by means of sequences from Helicobacter pylori: Lessons from Ladakh. Proc. Natl. Acad. Sci. U. S. A. 101, 4746– 4751.
Falush, D., Wirth, T., Linz, B., K Pritchard, J., Stephens, M., Kidd, M., J Blaser, M., Y Graham, D., Vacher, S., Perez Perez, G., Yamaoka, Y., Megraud, F., Otto, K., Reichard, U., Katzowitsch, E., Wang, X., Achtman, M., Suerbaum, S., 2003. Traces of Human Migrations in Helicobacter pylori Populations. Science 299.
Linz, B., Balloux, F., Moodley, Y., Manica, A., Liu, H., Roumagnac, P., Falush, D., Stamer, C., Prugnolle, F., van der Merwe, S.W., Yamaoka, Y., Graham, D.Y., Perez-Trallero, E., Wadstrom, T., Suerbaum, S., Achtman, M., 2007. An African origin for the intimate association between humans and Helicobacter pylori. Nature 445, 915–918.
Arellano Davin, A., 2017. Utilisation des transferts horizontaux de gènes pour dater des phylogénies. Lyon.
Cédric Chauve, Akbar Rafiey, Adrian Davin, Celine Scornavacca, Philippe Veber, et al. MaxTiC:Fast ranking of a phylogenetic tree by Maximum Time Consistency with lateral gene Transfers. 2017.hal-01532738v1
Yahara, K., Furuta, Y., Oshima, K., Yoshida, M., Azuma, T., Hattori, M., Uchiyama, I., Kobayashi, I., 2013. Chromosome Painting. In: Silico in a Bacterial Species Reveals Fine Population Structure. MEB, Molecular Biology and Evolution 30, 1454–1464.
Höhna, S., Landis, M.J., Heath, T.A., Boussau, B., Lartillot, N., Moore, B.R., Huelsenbeck, J.P., Ronquist, F., 2016. RevBayes: Bayesian Phylogenetic Inference Using Graphical Models and an Interactive Model-Specification Language. Syst. Biol. 65, 726–736.
Szöllősi Gergely J., Davín Adrián Arellano, Tannier Eric, Daubin Vincent and Boussau Bastien, 2015. Genome-scale phylogenetic analysis finds extensive gene transfer among fungi370Phil. Trans. R. Soc. B
Steinegger, M., Söding, J., 2017. MMseqs2 enables sensitive protein sequence searching for the analysis of massive data sets. Nat. Biotechnol.
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