87Sr/86Sr variability in Puerto Rico: geological complexity and the study of paleomobility

The temptation to use biogeochemical techniques to resolve issues of paleomigration is evident and well intentioned. Knowledge of radiogenic strontium isotope baselines in a region of interest is a sine qua non of such archaeological studies of paleomobility. Here, we present the first detailed study of baseline 87Sr/86Sr values for the island of Puerto Rico. The high degree of 87Sr/86Sr variability present in this corpus of modern Puerto Rican bedrock and terrestrial malacological samples (0.70406–0.70909) is a testament to the complex geology of that island. This diversity of 87Sr/86Sr values makes parsing issues of origin a difficult and highly contingent task. Given these complexities, regional studies seeking to assess paleomigration by such isotopic means should proceed with a great deal of caution.

► 87Sr/86Sr signatures of Puerto Rican geological samples vary widely.
► Observed 87Sr/86Sr range subsumes variation reported for entire insular Caribbean.
► Complexity of Puerto Rican geology makes mapping of 87Sr/86Sr signatures difficult.
► Non-discrete geology of Puerto Rico makes tracking paleomobility highly problematic.