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

摘要

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