Silica coating developed in cave art walls had an impact in the preservation of the paintings themselves. Despite it still exists a controversy about whether or not the effects contribute to the preservation of the artworks; it is evident that identifying these silica coatings would have an impact to assess the taphonomy of the walls and the paintings preserved on them. Unfortunately, current techniques -especially non-invasive ones- can hardly address amorphous silica characterisation. Thus, its presence is often detected on laboratory observations such as SEM or XRD analyses. In the paper “Light in the Cave: Opal coating detection by UV-light illumination and fluorescence in a rock art context - Methodological development and application in Points Cave (Gard, France)”, Quiers and collaborators propose a new method for the in situ detection and characterisation of amorphous silica in a rock art context based on UV laser-induced fluorescence (LIF) and UV illumination [1].

The results from both methods presented by the authors are convincing for the detection of U-silica mineralisation (U-opal in the specific case of study presented). This would allow access to a fast and cheap method to identify this kind of formations in situ in decorated caves. Beyond the relationship between opal coating and the preservation of the rock art, the detection of silica mineralisation can have further implications. First, it can help to define spot for sampling for pigment compositions, as well as reconstruct the chronology of the natural history of the caves and its relation with the human frequentation and activities. In conclusion, I am glad to recommend this original research, which offers a new approach to the identification of geological processes that affect -and can be linked with- the Palaeolithic cave art.

[1] Quiers, M., Chanteraud, C., Maris-Froelich, A., Chalmin-Aljanabi, E., Jaillet, S., Noûs, C., Pairis, S., Perrette, Y., Salomon, H., Monney, J. (2022) Light in the Cave: Opal coating detection by UV-light illumination and fluorescence in a rock art context. Methodological development and application in Points Cave (Gard, France). HAL, hal-03383193, ver. 5 peer-reviewed and recommended by Peer community in Archaeology. https://hal.archives-ouvertes.fr/hal-03383193v5

Tektites, a naturally occurring glass produced by major cosmic impacts and ejected at long distances, are known from five impacts worldwide [1]. The presence of this impact-generated glass, which can be dated in the same way as a volcanic rock, has been used to date archaeological sites in several regions of the world. This paper by Marwick and colleagues [2] reviews and adds new data on the use and misuse of this specific material as a chronological marker in Australia, East and Southeast Asia, where an impact dated to 0.78 Ma created and widely distributed tektites. This material, found in archaeological excavations in China, Laos, Thaïland, Australia, Borneo, and Vietnam, has been used to date layers containing lithic artifacts, sometimes creating a strong debate about the antiquity of the occupation and lithic production in certain regions.

The review of existing data shows that geomorphological data and stratigraphic integrity can be questioned at many sites that have yielded tektites. The new data provided by this paper for five archaeological sites located in Vietnam confirm that many deposits containing tektites are indeed lag deposits and that these artifacts, thus in secondary position, cannot be considered to date the layer. This study also emphasizes the general lack of other dating methods that would allow comparison with the tektite age. In the Vietnamese archaeological sites presented here, discrepancies between methods, and the presence of historical artifacts, confirm that the layers do not share similar age with the cosmic impact that created the tektites.

Based on this review and these new results, and following previous propositions [3], Marwick and colleagues conclude that, if tektites can be used as chronological markers, one has to prove that they are in situ. They propose that geomorphological assessment of the archaeological layer as primary deposit must first be attained, in addition to several parameters of the tektites themselves (shape, size distribution, chemical composition). Large error can be made by using only tektites to date an archaeological layer, and this material should not be used solely due to risks of high overestimation of the age of the archaeological production. 

[1] Rochette, P., Beck, P., Bizzarro, M., Braucher, R., Cornec, J., Debaille, V., Devouard, B., Gattacceca, J., Jourdan, F., Moustard, F., Moynier, F., Nomade, S., Reynard, B. (2021). Impact glasses from Belize represent tektites from the Pleistocene Pantasma impact crater in Nicaragua. Communications Earth & Environment, 2(1), 1–8, https://doi.org/10.1038/s43247-021-00155-1

[2] Marwick, B., Son, P. T., Brewer, R., Wang, L.-Y. (2022). Tektite geoarchaeology in mainland Southeast Asia. SocArXiv, 93fpa, ver. 6 peer-reviewed and recommended by PCI Archaeology, https://doi.org/10.31235/osf.io/93fpa.

[3] Tada, T., Tada, R., Chansom, P., Songtham, W., Carling, P. A., Tajika, E. (2020). In Situ Occurrence of Muong Nong-Type Australasian Tektite Fragments from the Quaternary Deposits near Huai Om, Northeastern Thailand. Progress in Earth and Planetary Science 7(1), 1–15, https://doi.org/10.1186/s40645-020-00378-4

The paper by Plutniak [1] presents a new method that uses refitting to help interpret stratigraphy using the topological distribution of conjoinable material culture. This new method opens up new avenues to the archaeological use of network analysis but also to assess the integrity of interpreted excavation layers. Beyond its evident applicability to standard excavation practice, the paper presents a series of characteristics that exemplify archaeological publication best practices and, as someone more versed in computational than in refitting studies I would like to comment upon.

It was no easy task to find adequate reviewers for this paper as it combines techniques and expertise that are not commonly found together in individual researchers. However, Plutniak, with help from three reviewers, particularly M. Peeples, a leading figure in archaeological applications of network science, makes a considerable effort to be accessible to non-specialist archaeologists. The core Topological Study of Archaeological Refitting (TSAR) method is freely accessible as the R package archeofrag, which is available at the Comprehensive R Archive Network (https://CRAN.R-project.org/package=archeofrag) that can be applied without the need to understand all its mathematical, graph theory and coding aspects. Beside these, an online interface including test data has been provided (https://analytics.huma-num.fr/Sebastien.Plutniak/archeofrag/), which aims to ease access to the method to those archaeologists inexperienced with R. Finally, supplementary material showing how to use the package and evaluating its potential through excellent examples is provided as both pdf and Rmw (Sweave) files. This is an important companion for the paper as it allows a better understanding of the methods presented in the paper and its practical application.

The author shows particular care in testing the potential and capabilities of the method. For example, a function is provided “frag.observer.failure” to test the robustness of the edge count method against the TSAR method, which is able to prove that TSAR can deal well with incomplete information. As a further step in this direction both simulated and real field-acquired data are used to test the method which further proves that archeofrag is not only able to quantitatively assess the mixture of excavated layers but to propose meaningful alternatives, which no doubt will add an increased methodological consistency and thoroughness to previous quantitative approaches to material refitting work, even when dealing with very complex stratigraphies.

All in all, this paper makes an important contribution to core archaeological practice through the use of innovative, reproducible and accessible computational methods. I fully endorse it for the conscious and solid methods it presents but also for its adherence to open publication practices. I hope that it can become of standard use in the reconstruction of excavated stratigraphical layers through conjoinable material culture.

[1] Plutniak, S. 2021. The Strength of Parthood Ties. Modelling Spatial Units and Fragmented Objects with the TSAR Method – Topological Study of Archaeological Refitting. OSF Preprints, q2e69, ver. 3 Peer-reviewed and recommended by PCI Archaeology. https://doi.org/10.31219/osf.io/q2e69.

This article by L. Doyon et al. [1] represents an important step to the recognition of bone expedient tools within archaeological faunal assemblages, and therefore deserves publication.

In this work, the authors compare bone flakes and splinters experimentally obtained by percussion (hammerstone and anvil technique) with fossil ones coming from the Palaeolithic site of Lingjing in China. Their aim is to find some particularities to help distinguish the fossil bone fragments which were intentionally shaped, from others that result notably from marrow extraction. The presence of numerous (>6) contiguous flake scars and of a continuous size gradient between the lithics and the bone blanks used, appear to be two valuable criteria for identifying 56 bone elements of Lingjing as expedient bone tools. The latter are present alongside other bone tools used as retouchers [2].

Another important point underlined by this study is the co-occurrence of impact and flake scars among the experimentally broken specimens (~90%), while this association is seldom observed on archaeological ones. Thus, according to the authors, a low percentage of that co-occurrence could be also considered as a good indicator of the presence of intentionally shaped bone blanks.

About the function of these expedient bone tools, the authors hypothesize that they were used for in situ butchering activities. However, future experimental investigations on this question of the function of these tools are expected, including an experimental use wear program.

Finally, highlighting the presence of such a bone industry is of importance for a better understanding of the adaptive capacities and cultural practices of the past hominins. This work therefore invites all taphonomists to pay more attention to flake removal scars on bone elements, keeping in mind the possible existence of that type of bone tools. In fact, being able to distinguish between bone fragments due to marrow recovery and bone tools is still a persistent and important issue for all of us, but one that deserves great caution.

[1] Doyon, L., Li, Z., Wang, H., Geis, L. and d'Errico, F. 2021. A 115,000-year-old expedient bone technology at Lingjing, Henan, China. Socarxiv, 68xpz, ver. 4 peer-reviewed and recommended by PCI Archaeology. https://doi.org/10.31235/osf.io/68xpz

[2] Doyon, L., Li, Z., Li, H., and d’Errico, F. 2018. Discovery of circa 115,000-year-old bone retouchers at Lingjing, Henan, China. Plos one, 13(3), https://doi.org/10.1371/journal.pone.0194318.

The article submitted by Guillaume Porraz et al. [1] shed light on the evolutionary changes recorded during the Pre-Still Bay Lynn stratigraphic unit (SU) from Diepkloof (Southern Africa). It promotes a multi-proxy and integrative approach based on a set of innovative behaviors, such as the engraving of geometric forms, silcrete heat- treatment, the use of adhesive, bladelet and bifacial tools production. This approach is not so common in Middle Stone Age (MSA) studies and makes a lot of sense for discussing the mechanisms that have fostered later innovations during the Still Bay and Howiesons Poort periods. The various innovations that emerge synchronously in this layer contrast with earlier innovations which appear as isolated phenomena in the MSA archaeological record. The strong inventiveness documented in Lynn SU is reported to a phase of experimentation for testing new ideas, new behaviors that would have played a crucial role for the emergence of the Still Bay in a context of socio-economic transformation.

The data presented in this article broadens the scope of two previous articles [2-3] based on a more representative record, collected on an area of 3,5 m² opposed to 2 m² previously, and on the first presentation and description of an engraved bone with a rhomboid pattern. Macro- and microscopic analyses together with the analysis of the distribution of the engraved lines argue convincingly for an intentional engraving. This article constitutes a key contribution to the question of HOW emerged modern cultures in Southern Africa, while calling for further research related to sites’ function, environment and local resources to address the ever-debated question of WHY the MSA groups from Southern Africa developed such unprecedented inventiveness. It makes no doubt that this article deserves recommendation by PCI Archaeology.

[1] Porraz, G., Schmidt, P., Bereiziat, G., Brugal, J.Ph., Dayet, L., Igreja, M., Miller, C.E., Viola, C., Tribolo, C., Val, A., Verna, C., Texier, P.J. 2020. Experimentation preceding innovation in a MIS5 Pre-Still Bay layer from Diepkloof Rock Shelter (South Africa): emerging technologies and symbols. 10.32942/osf.io/ch53r

[2] Porraz, G., Texier, P.J., Archer, W., Piboule, M., Rigaud, J.P, Tribolo, C. 2013. Technological successions in the Middle Stone Age sequence of Diepkloof Rock Shelter, Western Cape, South Africa. Journal of Archaeological Science 40, 3376–3400. 10.1016/j.jas.2013.02.012

[3] Porraz, G., Texier, J.P. Miller, C.E., 2014. Le complexe bifacial Still Bay et ses modalités d’émergence à l’abri Diepkloof (Middle Stone Age, Afrique du Sud). In: XXVIIème Congrès Préhistorique de France, Transitions, Ruptures et Continuité en Préhistoire. Mémoires de la Société Préhistorique Française, 155–175.