Establishing an Ecuadorian Isoscape: The Importance of Baseline Strontium Data in a Volcanic Landscape

Strontium isotopes (⁸⁷Sr/⁸⁶Sr) have been used worldwide to track migrations and identify nonlocal individuals in the past. In South America, these studies often use comparative baseline maps, or isoscapes, established by samples from archaeological fauna and geologic formations. However, baseline research has focused on coastal Peru and the Central and South Andean Highlands. Currently, no comparable isoscape exists for Ecuador. Thus, scholars approximate baselines from predictive models and geologic studies, which may not accurately reflect the biologically available strontium in archaeological samples. This study tested the accuracy of predictive archaeological and geologic models for Ecuadorian strontium.

We collected 11 faunal samples from eight archaeological sites across three coastal regions and the northern highlands to test for ⁸⁷Sr/⁸⁶Sr. All samples were collected from animals with narrow home ranges. Samples were processed at the University of North Carolina at Chapel Hill.

Strontium values ranged from 0.704226 to 0.709764, with significant regional distribution. The lowest values came from highland samples (mean = 0.704296) and clustered by coastal region from north to south (central coast mean = 0.707561; south coast mean = 0.7064118; far south coast mean = 0.709764).

This pilot study reveals two trends: First, strontium values cluster regionally despite stratigraphic volcanic influences, and second, values do not correspond to predictive models, particularly along the coast. We suggest that the unique geology of Ecuador means that predictive models based on Peruvian baselines are inappropriate for Ecuadorian strontium studies. There is a need for a large-scale baseline study of biologically available strontium in Ecuadorian archaeological samples.