SCLEROCHRONOLOGICAL OXYGEN ISOTOPE ANALYSIS IN PERUVIAN SEMELE CORRUGATA VALVES TO ASSESS ARCHAEOLOGICAL SEASON OF CAPTURE

Semele corrugata is a shallow marine bivalve mollusk commonly excavated from Terminal Pleistocene and Holocene shell middens along much of the Pacific Coast of South America. This clam may potentially be a source of archaeological and climate proxy data, however little fundamental research has been conducted into its biomineralogy or sclerochronology. Shell structure, growth patterns, and oxygen isotope (δ¹⁸O) distributions were measured in modern S. corrugata samples from the north coast of Peru in order to assess if such data can be used to determine archaeological season of capture and/or serve as a climate proxy. X-ray diffraction data confirm the valves are entirely aragonite, but they contain distinct layers that may complicate oxygen isotope sampling. Electron and light microscopy indicate geochemical sampling should be restricted to a single shell layer. Modern shell specimens were micromilled at high resolution parallel to growth increments through ontogeny for oxygen isotope analysis. Resulting data are compared to regional sea surface temperature (SST) records to evaluate their utility as season of capture and/or paleoclimate proxies. Interpretation of these profiles is improved by understanding shell growth rates and lifespan as determined by comparing apparent seasonal oscillations in δ¹⁸O to the local SST records. The comparatively narrow seasonal SST range in coastal Peru complicates season of capture estimates, however by identifying the timing of shell growth and mapping detailed growth patterns, season of capture, or higher-resolution time of death, may be estimated and contribute to a better understanding of site occupation and human activities.