Artifact preservation and post-depositional site-formation processes in an urban setting: a geoarchaeological study of a 19th century neighborhood in Detroit, Michigan, USA

摘要

A geoarchaeological study was carried out to assess levels of artifact deterioration occurring in a historicperiod urban soil during the 20th century. The study site is a former house-lot in a park created in 1919 by demolition of a residential community in Detroit Michigan, USA. The results show that despite nearly a century of burial in an urban soil impacted heavily by pollution and other anthropogenic activity, many 19th century artifacts are remarkably well preserved. The observed weathering stability sequence of glass > bone > mortar > plaster > paint is consistent with decreasing solubility product values of the corresponding principal mineral constituent (glass < apatite < portlandite < gypsum < cerrusite). Even severely weathered 19th century nails and mortar can often be distinguished using optical petrographic and SEM-EDAX methods. The excellent state of artifact preservation is attributed to a calcareous soil microenvironment, and artificial compaction which limited the weathering effects of water and oxygen. Artifact preservation was further enhanced by burial beneath a thick biomantle created by the casting activity of an invasive species of earthworm. However, Lumbricus terrestris may now pose the greatest threat to artifact preservation because casting and burrowing activities are decreasing bulk density, and promoting the diffusion of air and water into the soil. Early excavation is recommended to recover artifacts in soils impacted by the combined effects of urban pollution and earthworm burrowing. Anthropogenic microparticles smaller than those normally classified as microartifacts were found to be useful indicators of human occupation. (C) 2014 Elsevier Ltd. All rights reserved.