Abstract
Natural and anthropogenically induced soil erosion can cause serious loss of the archaeological record. Our work shows the value of multi-scalar geoarchaeological study when excavating and re-excavating rockshelters in a highly dynamic sedimentary environment where erosion is prominent. Here we present our work on Kisese II rockshelter, Tanzania, originally excavated in the 1950s and largely unpublished, that preserves an important Pleistocene-Holocene archaeological record integral to understanding the deep history of the Kondoa Rock-Art World Heritage Center. Unlike rockshelters in quiescent tectonic settings, like much of central Europe or South Africa, Kisese II exists in highly dynamic sedimentary environments associated with the active tectonics of the Great Rift Valley system exacerbated by human-induced environmental and climate change. We report on our 2017 and 2019 exploratory research that includes integrated regional-, landscape-, and site-scale geoarchaeological analyses of past and present sedimentary regimes and micromorphological analyses of the archaeological sediments. Historical records and aerial photographs document extensive changes in vegetation cover and erosional regimes since the 1920s, with drastic changes quantified between 1960 and 2019. Field survey points to an increased erosion rate between 2017 and 2019. To serve future archaeologists, heritage specialists, and local populations we combine our data in a geoarchaeological catena that includes soil, vegetation, fauna, and anthropogenic features on the landscape. At the site, micromorphological coupled with chronological analyses demonstrate the preservation of in situ Pleistocene deposits. Comparison of photographs from the 1956 and 2019 excavations show a maximum sediment loss of 68 cm in 63 years or >10% of >6-m-thick sedimentary deposit. In the studied area of the rockshelter we estimate ~1 cm/yr of erosion, suggesting the ongoing removal of much of the higher archaeological sediments which, based on the coarse stratigraphic controls and chronology of the original Inskeep excavations, would suggest the loss of much of the archaeological record of the last ~4000 years. These multi-scalar data are essential for the construction of appropriate mitigation strategies and further study of the remaining stratigraphy.
Highlights
Caves and rockshelters are important sedimentary archives for studying the deep human past because of their persistent and repeated use across the Pleistocene and Holocene for habitation, burial of the dead, as surfaces for painting or engraving, and other purposes
This paper extends from a simple observation: comparison of archival photographs and present-day field observations suggest the loss of up to 60 cm of sediment by erosion at Kisese II between 1956 and 2019, a loss that likely removed most of the “Iron Age” archaeological record at the shelter, and sediments sampling the period when much of the rock art for which the region is famous was made (Bwasiri and Smith, 2015)
Reconstructions by Eriksson and others (2000) that combine geology and OSL dating of colluvial and alluvial sediments trace the chronology of early Holocene erosion and show that the Kondoa district has been characterized by a K-cycle with periods of erosion and depositions punctuated by hillslope stability that allow for pedogenesis (Eriksson et al, 2000)
Summary
Caves and rockshelters are important sedimentary archives for studying the deep human past because of their persistent and repeated use across the Pleistocene and Holocene for habitation, burial of the dead, as surfaces for painting or engraving, and other purposes. Excavation of these sites require an archaeological methodology attuned to reconstructing the environmental processes that formed and shaped them over millennia. In arctic environments archaeologists have documented accelerated loss of heritage in association with melting ice (e.g., Hollesen et al, 2018) Despite these known processes, methods to study how landscape dynamics can potentially erase records of the past are still uncommon. The results of this study can both contribute to roadmaps for future climate change responses and provide a model for integrating multiple stakeholder community perspectives in the reconstruction and study of ancient social and environmental processes
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