Expanding radiogenic strontium isotope baseline data for central Mexican paleomobility studies

Abstract

Radiogenic strontium isotopes (87 Sr/ 86 Sr) have long been used in analyses of paleomobility within Mesoamerica. While considerable effort has been expended developing 87 Sr/ 86 Sr 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 87 Sr/ 86 Sr 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 87 Sr/ 86 Sr on a Thermo-Finnigan Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). These data were analyzed alongside 16 published 87 Sr/ 86 Sr 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 87 Sr/ 86 Sr values. Although the two clusters falling within the Basin of Mexico overlap in their local 87 Sr/ 86 Sr ranges, many locations within the Basin are distinguishable using 87 Sr/ 86 Sr 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.

Drinking Locally: A Water 87Sr/86Sr Isoscape for Geolocation of Archeological Samples in the Peruvian Andes

“…Water type should also be considered carefully when devising baseline sampling campaigns. As other studies have argued, it is critical to sample the most likely drinking water sources for a given archeological site (Hodell et al, 2004;Montgomery et al, 2007;Pacheco-Forés et al, 2020;Snoeck et al, 2020). This study's examination of spatial outlier water 87 Sr/ 86 Sr generally agrees with this proposition.…”

“…Water samples were prepared for analysis in the Archaeological Chemistry Laboratory (Center for Bioarchaeological Research) at Arizona State University following established protocols (Pacheco-Forés et al, 2020). Water was strained into metal-free vials through a 2.5 µm pore size filter paper and acidified with 5% HCl to prevent microbial growth.…”

“…The potential of using water 87 Sr/ 86 Sr for archeological skeleton provenience has varied according to study location and approach. Many baseline studies including water do not directly compare water and archeological human 87 Sr/ 86 Sr (Hodell et al, 2004;Bentley and Knipper, 2005;Frei, 2011, 2013;Lengfelder et al, 2019;Ladegaard-Pedersen et al, 2020;Pacheco-Forés et al, 2020), although some incorporate water into a mixed or predictive model and evaluate archeological data points against that model (e.g., Montgomery et al, 2007;Snoeck et al, 2020). Among studies in mountainous regions comparing skeletal 87 Sr/ 86 Sr directly to local water measurements, a relationship is reported between water elevation, sample variability, and fit of archeological samples to local water.…”

“…Methods for defining the expected local 87 Sr/ 86 Sr range have shifted over the last few decades from statistically parsing human skeletal 87 Sr/ 86 Sr around the sample mean (e.g., Wright, 2005;Slovak et al, 2009;Price et al, 2015) to testing archeological and modern fauna with small home ranges (Price et al, 2002(Price et al, , 2007Evans and Tatham, 2004;Hedman et al, 2009Hedman et al, , 2018Knudson and Tung, 2011). More recently, many scholars have argued that the only reliable way to determine the local 87 Sr/ 86 Sr range is by analyzing the bioavailable strontium in local environmental reference or baseline materials like soils, plants, and local fauna, and then aggregating those reference 87 Sr/ 86 Sr to geological units, soil units, or statistical groupings of baseline and/or skeletal materials (Valentine et al, 2008;Evans et al, 2010;Maurer et al, 2012;Knudson et al, 2014;Kootker et al, 2016;Grimstead et al, 2017;Willmes et al, 2018;Barberena et al, 2019;Pacheco-Forés et al, 2020;Snoeck et al, 2020). Unfortunately, because underlying bedrock geology is highly variable even at a short distance, and because rock weathers unevenly throughout catchments, these methods do not enable the sourcing of a sample to any location beyond the immediate vicinity of the sampling location.…”

Investigating Mexican paleoclimate with precisely dated speleothems

“…These chapters use stable isotope ratios of oxygen and carbon, commonly expressed as δ 18 O and δ 13 C, and ratios of Mg and Sr to Ca. There are other proxies, such as Sr isotopes, Ca isotopes, δ 234 U, U concentration, and U/Ca, that are also useful in analyses of carbonates, but those will not be used here Pacheco-Forés et al, 2020).…”