Non-Invasive Geoarchaeology of Middens

Middens contain rich records of resources and clues to culture. Detailed excavations can extract features and 3D trends in a site as well as datable materials. In coastal settings shellfish remains supply important environmental information. In areas with acidic soils, such as northern New England, calcium carbonate buffering preserves bone and organic artifacts. High-resolution geophysical techniques allow non-destructive imaging of middens and associated environments that serve as preliminary indicators of site morphology, stratigraphy, and development trends. In Maine, we used high-resolution seismic profiling and vibracoring to assess environments offshore of known middens, as well as submerged potential targets. No intact submerged middens have been found, but ancient oyster bioherms in the Damariscotta River were used to develop a predictive site-location model (Leach and Belknap, 2007). We also used GPR to profile the legally protected Glidden midden (ca. 2200-800 BP) for comparison to submerged targets. GPR reveals sequential dumping and growth episodes, hiatuses, and activity sites that correspond well to early excavation records. In northwestern coastal Peru we used GPR to image beach ridges with capping middens that range in age from 5000 to 500 BP. These middens contain nearshore mollusks and barnacles, numerous hearths of fire-cracked rocks, and other artifacts. On this hyper-arid tropical coast, the middens form a continuous lag cover that prevents deflation by continuous onshore wind. Several themes of interest in these studies converge on middens and sea level (not exact indicators of sea level, but useful in some cases), geomorphic process-response models (middens as positive forms on coasts, or even a major determinant of morphology), and preservation potential (how much of the original coastal midden do we see today, and can a midden survive long-term sea-level rise and coastal transgression?). Non-destructive geophysical studies can be important guides, adjuncts, or even replacements for traditional excavation approaches.