Rock magnetic characterization of archeological pottery and natural materials from the Kiya petroglyph site (Russia): an insight into post-burial alteration

While processes that lead to recording magnetic information in stone and ceramic artifacts have been extensively investigated, the preservation of archeomagnetic signal after the artifacts have been abandoned has received much less attention. Our rock magnetic study of basalt and pottery artifacts found in two distinct burial environments – topsoil and alluvial sand – within a single archeological site on the Kiya River in the Khabarovsk Region of Russia demonstrates that archeological burial alteration is a complex process highly sensitive to local microenvironments that control the availability and diffusion characteristics of ions involved in diagenetic chemical reactions. Burial of basalt fragments in alluvial sand results primarily in a minor decrease in the effective magnetic grain size. Decomposition of basalt in a topsoil environment is more advanced and is characterized by the production of new magnetic phases and by oxidation of particles with the formation of magnetite core-maghemite shell structures. Although basalt and freshly fired pottery have similar initial magnetic assemblages dominated by magnetite, their burial alteration patterns differ. Firing pottery produces new magnetite grains. However, the pyrogenic particles are unstable in topsoil conditions and dissolve during archeological burial, in contrast to the production of new diagenetic magnetic phases in basalt. Thus, stone and pottery artifacts from the same archeological context may have different burial alteration signatures. Such differences should be taken into consideration in archeomagnetism studies.