Geochemical impacts to prehistoric iron-rich siliceous artifacts in the nearshore coastal zone

Abstract

In the Middle Atlantic region of the United States, landscapes drowned by sea level rise contain scores of prehistoric archaeological sites. These sites provide archaeologists with a rare opportunity to investigate various geologic processes. During the transition from a terrestrial to an offshore setting, the materials associated with an archaeological site are exposed to a series of geochemical processes inherent to the formation of tidal marsh. The duration of the geochemical exposure to tidal marsh is largely dependent on the rate of marine transgression. Here we describe the stages associated with the sulfidization and sulfuricization scheme and the impact to iron-rich lithic artifacts from naturally drowned archaeological sites. Sulfidization and sulfuricization should also impact buried archaeological materials as a result of anthropogenic dredge spoil dumping and the creation of man-made tidal marshes along modern coastlines. Our results indicate that the surfaces of an iron-rich artifact, as well as its interior are visually and geochemically altered by prolonged exposure to the anaerobic conditions of a tidal marsh. Not only should researchers be cautious about making lithic material identification on artifacts found within coastal tidal marsh areas, but museum curators should be aware of the damaging impact of long-term aerobic storage. The geochemical tidal marsh scheme that has altered or corroded iron-rich lithic artifacts in the nearshore zone is an expression of a process that has impacted numerous earlier prehistoric sites currently located on the continental shelf or beneath the coastal estuaries around the world.