Washburnetal_2021_Plosone

Abstract

• Strontium isotope (87Sr/86Sr) analysis helps examine past human mobility in archaeology.

• 87Sr/86Sr signatures are influenced by bedrock.

• This study conducted a survey of 100 modern flora and fauna from 14 sites in the Conchucos region of Peru.

• Found significant variation in 87Sr/86Sr values (0.7078–0.7214) affecting local vs. non-local differentiation.

• Created a bioavailable 87Sr/86Sr map (3,840 km²) as a resource for future studies.

Introduction

• Mobility and migration in archaeological studies have risen significantly, utilizing isotopic analyses.

• Strontium isotopes provide insights into movement across landscapes due to their substitution for calcium in bones.

• Study aims to present a regional map of bioavailable 87Sr/86Sr values in the Conchucos region, highlighting geological complexity.

Background: Strontium Geochemistry

• Strontium is found in low concentrations in various environments.

• 87Sr isotope results from the decay of rubidium and is influenced by bedrock age.

• Biologically available 87Sr varies due to geologic and environmental factors affecting isotope signatures.

Isotope Analysis in Archaeology

• 87Sr/86Sr helps distinguish local from non-local populations in archaeological remains.

• Existing local ranges were primarily established through site-based measurements, which may underestimate non-locals.

• Improved methods include using modern proxy materials (flora and fauna) to establish local baselines.

Geology of the Peruvian Andes

• Central Andes divided into Cordillera Occidental (west) and Cordillera Oriental (east) with varying 87Sr/86Sr values.

• Geological diversity in the Andes complicates the determination of isotopic signatures in archaeological analysis.

Study Region and Materials

• Study focuses on the Conchucos region (2,640 km²), characterized by archaeological sites from 1100 BCE to the 16th century.

• Area consists mainly of folded Mesozoic sedimentary rocks.

• Collected snail shells and grasses from 14 geological units for 87Sr/86Sr analysis.

Methods

• 100 samples were prepared and analyzed in a clean lab environment to verify strontium concentrations using MC-ICP-MS.

Results

• 87Sr/86Sr values measured from 100 environmental samples showed a range (0.7078–0.7215).

• Significant differences in isotopic values suggest varying biological sources of strontium in close proximity.

Discussion

• Interpreting 87Sr/86Sr values is complex, with implications for understanding ancient mobility.

• The use of isotopes is crucial for examining residential patterns and mobility across distinct geological landscapes.

• Established isoscapes can improve local mobility studies comparing human remains.

Conclusion

• This study enhances understanding of strontium variability in the Conchucos region, offering a foundation for archaeological mobility studies.