Susan M Mentzer

Resin-impregnated sediment blocks are a by-product of micromorphological sample processing. These blocks can be further studied using a variety of destructive, nondestructive, and minimally destructive geochemical techniques. X-ray fluorescence microanalyses conducted on sediment blocks yield semiquantitative major and trace elemental abundances that can be used to generate compositional maps, and to illustrate compositional change within or between archaeological strata and features. Sediment blocks can also be drilled to obtain small sediment samples for stable oxygen and carbon isotopic analyses. Both elemental and isotopic analyses can be conducted in conjunction with micromorphological analyses to yield a holistic picture of archaeological sediment composition, source, and depositional processes. The integration of micromorphological, compositional, and isotopic analyses is used here to aid in the differentiation of calcareous ash and lime plasters from the Neolithic site of Asıklı Höyük, Turkey.

Combustion features inform archaeologists about the prehistoric use of space, subsistence behaviors, and tempo of site visitation. Their study in the field is difficult because burned sediments are susceptible to reworking and diagenesis. Microarchaeological analyses, including micromorphology, are essential for documenting the composition, preservation, and function of hearths and other burned residues. These investigations focus on the description of fuels, depositional fabrics and structures, and mineralogy. As evidenced by a literature review, microarchaeological analyses have much to offer Paleolithic archaeologists, while applications of the techniques to Late Pleistocene and Early Holocene sites and in ethnographic or experimental contexts are presently rare.

Site formation processes at the Late Pleistocene rockshelter deposit of Obi-Rakhmat were reconstructed through soil micromorphology and Fourier transform infrared spectroscopy (FTIR). The entire sequence has undergone limited diagenesis and is well preserved. The base of the stratified sequence represents a karstic setting with intermittent, low-energy deposition of autochthonous gravitational debris and anthropogenic material in a wet, muddy environment. These sediments were post-depositionally affected by episodic waterlogging. The bulk of the sequence overlying the karstic layers comprises a continuous series of primary freshwater spring deposits containing reworked anthropogenic material that was buried penecontemporaneously with calcium carbonate deposition. The top of the sequence is weakly cryoturbated, indicating a periodically cold, wet environment. No alluvial elements that could suggest sediment inputs from the nearby river terraces were documented. A single exogenous layer was identified, representing an episode of colluviation from directly above the rockshelter preceding a major roofspall event. The basal part of the sequence contains slightly reworked anthropogenic remnants of intense activities, including combustion. The anthropogenic elements present in the spring deposits show higher degrees of reworking, suggesting within-layer translocation. The development of spring activity at the site did not cause humans to abandon the rockshelter; they continued to carry out their activities throughout a changing local environment. © 2009 Wiley Periodicals, Inc.

As part of a broader geoarchaeological project at the Middle Stone Age site of Sibudu (KwaZulu-Natal, South Africa), we conducted a mineralogical study in order to reconstruct the impacts of sediment chemistry and rockshelter microenvironments on the preservation and distribution of archaeological materials and features. During the 2014 excavation season, we collected and analyzed more than 700 sediment samples in the field using a portable Fourier transform infrared spectrometer (FTIR). The on-site analyses yielded 1762 individual spectra, which were paired with three dimensional coordinates collected using a Total Station. We identified at least 10 distinctive primary and secondary mineral phases, and plotted their distributions on the archaeological profiles. Supplemental analyses conducted in a laboratory setting include micro-FTIR analyses on thin sections and resin-impregnated blocks, and x-ray diffraction.

The results for three main profiles and a limited sample of a fourth indicate that the distributions of primary and secondary mineral phases are vertically and horizontally variable. Primary minerals that we identified in the sequence include calcite, opal, quartz, feldspar, mica minerals, and kaolinite. As Sibudu is a sandstone shelter, the primary source for calcite to the archaeological deposits is wood ashes. Likewise, bedding layers provide one source of opal. These observations are supported by previous micromorphological analyses of both combustion features and bedding (Goldberg et al. 2009, Wadley et al. 2011). Our FTIR analyses indicate that calcite is consistently present in the uppermost 30 cm of the deposits, while opal is present throughout. Sulfate minerals, such as gypsum, are abundant within the upper portions site, where they variably appear in the form of large nodules and cements. In addition, the lateral distribution of sulfate minerals appears to correlate with proximity of the deposits to the bedrock wall. Secondary phosphate minerals in the form of crusts and nodules include members of the apatite and whitlockite groups, as well as brushite and taranakite.

Our results suggest a more complicated history of diagenesis at the site than the one presented in previous works by Schiegl and colleagues (Schiegl and Conard 2006, Schiegl et al. 2004). Furthermore, the distributions of calcite and phosphate minerals are indicative of dissolution and phosphatization of ash sourced from combustion features. Finally, opal in the form of primary phytoliths and secondary nodules, the latter in association with other end-stage diagenetic phases, are suggestive of variability in the preservation of bedding layers at the site.

References:

Goldberg, P., Miller, C. E., Schiegl, S., Ligouis, B., Berna, F., Conard, N. J., & Wadley, L. (2009). Bedding, hearths, and site maintenance in the Middle Stone age of Sibudu cave, KwaZulu-Natal, South Africa. Archaeological and Anthropological Sciences, 1(2), 95-122.

Schiegl, S., & Conard, N. J. (2006). The Middle Stone Age sediments at Sibudu: results from FTIR spectroscopy and microscopic analyses. Southern African Humanities, 18(1), 149-172.

Schiegl, S., Stockhammer, P., Scott, C., & Wadley, L. (2004). A mineralogical and phytolith study of the Middle Stone Age hearths in Sibudu Cave, KwaZulu-Natal, South Africa: Sibudu Cave. South African Journal of Science, 100(3 & 4), p-185.

Wadley, L., Sievers, C., Bamford, M., Goldberg, P., Berna, F., & Miller, C. (2011). Middle Stone Age bedding construction and settlement patterns at Sibudu, South Africa. Science, 334(6061), 1388-1391.