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1. Expanding radiogenic strontium isotope baseline data for central Mexican paleomobility studies

   https://doi.org/10.1371/journal.pone.0229687  

   Pacheco-Forés, Sofía I.; Gordon, Gwyneth W.; Knudson, Kelly J. (February 2020, PloS one)

   null (Ed.)

   Radiogenic strontium isotopes (87Sr/86Sr) have long been used in analyses of paleomobility within Mesoamerica. While considerable effort has been expended developing 87Sr/86Sr baseline values across the Maya region, work in central Mexico is primarily focused on the Classic period urban center of Teotihuacan. This study adds to this important dataset by presenting bioavailable 87Sr/86Sr values across central Mexico focusing on the Basin of Mexico. This study therefore serves to expand the utility of strontium isotopes across a wider geographic region. A total of 63 plant and water samples were collected from 13 central Mexican sites and analyzed for 87Sr/86Sr on a Thermo-Finnigan Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). These data were analyzed alongside 16 published 87Sr/86Sr values from two additional sites within the region of interest. A five-cluster k-means model was then generated to determine which regions of the Basin of Mexico and greater central Mexico can and cannot be distinguished isotopically using 87Sr/86Sr values. Although the two clusters falling within the Basin of Mexico overlap in their local 87Sr/86Sr ranges, many locations within the Basin are distinguishable using 87Sr/86Sr values at the site-level. This study contributes to paleomobility studies within central Mexico by expanding knowledge of strontium isotope variability within the region, ultimately allowing researchers to detect intra-regional residential mobility and gain a greater understanding of the sociopolitical interactions between the Basin of Mexico and supporting outlying regions of central Mexico. 

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2. Trace element concentrations as proxies for diagenetic alteration in the African archaeofaunal record: Implications for isotope analysis

   https://doi.org/10.1016/j.jasrep.2024.104403  

   Bertacchi, Alex; Zipkin, Andrew M.; Giblin, Julia; Gordon, Gwyneth; Goepfert, Tyler; Asael, Dan; Knudson, Kelly J. (February 2024, Journal of Archaeological Science: Reports)

   Isotope ratio analyses of trace elements are applied to tooth enamel, ostrich eggshell, and other archaeological hard tissues to infer mobility and other aspects of hominin and animal paleoecology. It has been assumed that these highly mineralized tissues are resistant to diagenetic alteration, but this is seldom tested and some studies document diagenetic alteration over brief time spans. Here, we build on existing research on Maximum Threshold Concentrations (MTCs) to develop screening tools for diagenesis that can inform heavy isotopic analyses. The premise of the MTC approach is that archaeological tissues are likely contaminated and unsuitable for isotope ratio analysis when they exceed characteristic modern concentration ranges of trace elements. Furthermore, we propose a new metric called the Maximum Threshold Ratio (MTR) of 85Rb/88Sr or whole element Rb/Sr, which can be measured simultaneously with 87Sr/86Sr during laser ablation (LA) MC-ICP-MS or applied during post hoc screening of specimens. We analyzed 56 enamel samples from modern Kenyan mammals and 34 modern ostrich eggshells from South Africa, Namibia, and the United States by solution ICP-MS, as well as a subset of shells using LA-MC-ICP-MS. Our results indicate that thresholds are consistent across taxa at a single location, but likely vary across locations. Therefore, MTCs and MTRs need to be tissue and locality specific, but not necessarily taxon-specific. Other important differences are observed between the inner and outer surfaces of the eggshells and between LA and solution ICP-MS. This exploratory study provides guidelines for building reference thresholds to screen enamel and eggshell for diagenesis potentially impacting biogenic isotope ratios. 

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3. Biologically available Pb: A method for ancient human sourcing using Pb isotopes from prehistoric animal tooth enamel

   https://doi.org/10.1016/j.jas.2020.105079  

   Samuelsen, John R.; Potra, Adriana (March 2020, Journal of archaeological science)

   This study analyzes Pb isotopes combining biological (ancient human and prehistoric animal teeth) and geological (soil leachate, whole rock, and rock leachate) samples to determine the origins of prehistoric skeletal elements. It exemplifies how the biologically available Pb method assesses the early lifetime locations of ancient human populations using prehistoric animal teeth and the multivariate/linear nature of Pb isotope data. Lead isotopes provide a valuable technique, in part due to the correlation between their six stable isotope ratios. Other studies have used Pb isotopes for similar purposes, but no clear method for determining a local range has yet been formally defined and tested. The biologically available Pb method uses many prehistoric animal tooth enamel samples to establish a baseline for local ratios in the region, then compares their ratios’ linear patterning to human remains to test if they are non-local. The case study compares Pb isotopes from prehistoric animal teeth, human teeth, and whole rocks from southwest Arkansas. These results are compared to animal samples from Louisiana and Mississippi and human data from Illinois and New Mexico. Soil leachates, Pb concentrations of tooth enamel, and trace element analysis are used to assess contamination. Comparisons to southwest Arkansas whole rock Pb isotope ratios suggest they are too variable to be used for direct comparison to ancient human remains, illustrating that prehistoric animal teeth are more appropriate for direct comparison to prehistoric human teeth. The biologically available Pb method provides a key analysis tool needed for studies of ancient human sourcing. 

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4. Data report: 87Sr/86Sr in pore fluids from IODP Expedition 355 Arabian Sea Monsoon

   https://doi.org/10.14379/iodp.proc.355.201.2017  

   Carter, S.C.; Griffith, E.M.; Scher, H.D. (October 2017, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   Here we report the strontium isotope ratios (87Sr/86Sr) from pore fluids collected during International Ocean Discovery Program (IODP) Expedition 355. Ratios from Sites U1456 (N = 21) and U1457 (N = 20) are reported. Pore fluid 87Sr/86Sr is a useful tool to establish fluid-rock reactions, sources of Sr, and fluid mixing. The measured 87Sr/86Sr of the pore fluid has significant variations at both sites, and three distinct zones are identified. At Site U1456, 87Sr/86Sr starts at values similar to that of modern seawater (~0.7092) from near the seafloor down to ~100 meters below seafloor (mbsf). Over this interval, Sr concentration increases, whereas Ca decreases (Zone 1). Below 100 mbsf, 87Sr/86Sr values increase to a max of ~0.7100 at ~224 mbsf, and Sr concentrations decrease (Zone 2). Isotopic values then gradually decrease to ~0.7085, with an increase in Sr concentrations (Zone 3). Site U1457 displays the same general trends in pore fluid 87Sr/86Sr composition; however, there are distinct differences. First, Zone 1 occurs over a shorter interval (~0–54 mbsf) due to a lower sedimentation rate, and it also has lower Sr concentrations compared to Site U1456. Additionally, 87Sr/86Sr reaches a higher peak value in Zone 2 than at Site U1456. Finally, in Zone 3 the maximum Sr concentration reached is significantly lower than that at Site U1456. 

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5. Migratory behavior in the enigmatic Late Pleistocene bovid Rusingoryx atopocranion

   https://doi.org/10.3389/fearc.2023.1237714  

   O'Brien, Kaedan; Podkovyroff, Katya; Fernandez, Diego P.; Tryon, Christian A.; Ashioya, Lilian; Faith, J. Tyler (August 2023, Frontiers in Environmental Archaeology)

   Reynolds, Sally (Ed.)

   For many animals, migration is an important strategy for navigating seasonal bottlenecks in resource availability. In the savannas of eastern Africa, herds of grazing animals, including blue wildebeest (Connochaetes taurinus), Thomson's gazelle (Eudorcas thomsonii), and plains zebra (Equus quagga), travel hundreds of kilometers annually tracking suitable forage and water. However, we know nearly nothing about migration among the extinct species that often dominated Late Pleistocene communities. Using serially sampled 87Sr/86Sr and δ13C, we characterize the prehistoric movement and diet of the enigmatic wildebeest Rusingoryx atopocranion from two localities (Karungu and Rusinga Island) in the Lake Victoria Basin of western Kenya. We find clear evidence for migration in all four individuals studied, with three 87Sr/86Sr series demonstrating high-amplitude fluctuations and all falling outside the modeled isoscape 87Sr/86Sr ranges of the fossil localities from which they were recovered. This suggests that R. atopocranion exhibited migratory behavior comparable to that of its closest living relatives in the genus Connochaetes. Additionally, individuals show seasonally-variable δ13C, with a higher browse intake than modern and fossil eastern African alcelaphins indicating behavioral differences among extinct taxa otherwise unrecognized by comparison with extant related species. That this species was highly migratory aligns with its morphology matching that of an open grassland migrant: it had open-adapted postcranial morphology along with a unique cranial structure convergent with lambeosaurine dinosaurs for calling long distances. We further hypothesize that its migratory behavior may be linked to its extinction, as R. atopocranion disappears from the Lake Victoria Basin fossil sequence coincident with the refilling of Lake Victoria sometime after 36 ka, potentially impeding its past migratory routes. This study characterizes migration in an extinct eastern African species for the first time and shapes our ecological understanding of this unique bovid and the ecosystems in which Middle Stone Age humans lived. 

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