Bone preservation in human remains from the Terme del Sarno at Pompeii using light microscopy and scanning electron microscopy

Archaeological bone can show marked and complex alterations depending on the environment in which it was buried. In this study, the state of preservation of 27 femurs recovered from the archaeological site of Pompeii was evaluated by light microscopy and scanning electron microscopy. Most of the bone samples, prepared by the grinding method, showed good histological preservation, although they were characterized by microfissures (microcracking). Nine bone samples showed different states of histological preservation, including worst preservation (two femurs), due to diagenetic processes. Cryostat bone sections stained with thionin or 4′,6′-diamidino-phenylindole (DAPI) revealed the persistence of DNA within some osteocyte lacunae. Scanning electron microscopy analysis showed that ultrastructural characters, such as lamellae and collagen fibres, are recognizable only in unaltered bone. Our results reveal that most Pompeian samples are well preserved since they have a bone microstructure virtually indistinguishable from that of fresh bone. In methodological terms, although each of the various morphological methods used contributes information, histological and histochemical analyses are the most informative for studying the preservation state of bone and allow for rapid essential screening of archaeological bone.     

Mineral weathering in forest soils and its relevance to the preservation of the buried archaeological resource

There is more woodland in Britain now than for many centuries and considering many international climate change mitigation policies, woodland cover, both in Britain and internationally, is being promoted. However, neither the management of existing woodlands nor their expansion should be at the expense of important archaeological evidence. Due to the large number of known archaeological sites, the large areas of land with uninvestigated archaeological potential and the expanding woodland cover, suitable mitigation strategies need to be developed to allow preservation in situ of important sites. An understanding of how woodland soils and the buried archaeological resource interact is, therefore, essential. This paper utilises ongoing environmental research into the mineral weathering rates in forest soils and considers its application to artefact preservation. The study concludes that soil water pH, its movement, and the saturation of dissolved ions in the soil solution are major factors determining both mineral and artefact longevity. A simple guide to artefact longevity based on these properties is proposed and a geochemical model for predicting loss is tested. These tools could be applied to any soil or individual horizon irrespective of land-use.     

Identifying the geochemical taphonomy of the osteological material from Katsambas rockshelter

We report analytical work undertaken in order to identify the geochemical taphonomy of the osteological collection (human and animal bones) recovered from a 1950s excavation at Katsambas, a small cavity in the marly limestone on the west bank of Kairatos River, Crete. The site had funerary use and yielded material of Neolithic and Minoan age with poor stratigraphical association. Disintegration of provenance labels from bags has introduced further uncertainty about the contexts of recovery. Samples of human and animal bones that macroscopically appear to belong to three taphonomic categories were studied by means of FT-IR spectroscopy, TEM microscopy and REE analysis to explore the taphonomical processes the bones have undergone. Although not novel in palaeontological research the use of REE opens a new path to investigating poorly provenanced osteological collections from old excavations. Such geochemical work offers a proxy to their relative dating through the evaluation of the time span bones have remained in the sediments and their respective taphonomic histories.     

Distinguishing between calcites formed by different mechanisms using infrared spectrometry: archaeological applications

Infrared spectrometry is a well-established method for the identification of minerals. Due to its simplicity and the short time required to obtain a result, it can be practiced on-site during excavation using portable infrared spectrometers. However, the identification of a mineral may not be sufficient. For example, a lime plaster floor and a crushed chalk surface have a similar appearance and are composed of the same mineral – calcite. Here we exploit differences in the infrared spectra of geogenic, biogenic and pyrogenic calcites for the identification of each calcite type. The infrared calcite spectrum has three characteristic peaks in the region of 400–4000 cm⁻¹, designated ν₂, ν₃, and ν₄. When a calcite sample is ground, as part of the measurement preparation procedure, some grinding dependent changes will be revealed in the infrared spectrum. With additional grinding, the ν₃ peak narrows and the heights of the ν₂ and ν₄ peaks decrease, when both are normalized to the ν₃ height. By plotting the normalized heights of the ν₂versus the ν₄ of several grindings of the same sample, a characteristic trend line is formed for each calcite type. The trend lines of geogenic calcites have the shallowest slopes and highest ν₄ values when compared to pyrogenic calcites, which can be further divided to ash and plaster/mortar samples. This method can assist in distinguishing between the various calcites, and provide insights into homogeneity and preservation state of the calcitic materials in question.     

Changes in human bones boiled in seawater

The differences between boiled or unboiled bones are not often studied. However, they are crucial to understand postmortem rituals and to establish defleshing procedures and mortuary practices. In this work, human bones boiled in sea or fresh water are characterized. The bone composition, as well as the compounds present in the resulting materials, shows that salt alters the boiling process mechanism. Hence, from structural and morphological criteria, it is possible to distinguish if a bone has been boiled in salt or fresh water. In both sets of samples, the smoothness of the bone surface depends on boiling time, but only in bones boiled in seawater, filaments are observed apparently pouring out of the pores.Those differences which are mainly morphological (smoothness of the surface) are explained in terms of a collagen diffusional mechanism favored by sodium and chloride ions. For a boiling time of 6 h, the surface is covered by a thick layer or crusts of degraded collagen. Experiments with seawater may be used as model experiments to simulate taphonomical alterations in bones exposed to salt water.     

Macroscopic and microbiological alterations of bird and small mammal bones buried in a Cerrado biome (south western Brazil)

In this paper, we present the results of an experimental approach developed to study the macroscopic and microbiological alteration of bird and small mammal bones buried under a Cerrado biome. The first experiment evaluated the macroscopic alteration of cooked and fresh carcasses buried through the dry and rainy seasons. The second experiment analyzed the mycobiota associated to the decomposition of a complete bird that remained buried for almost a year. Results show that in tropical forest environments: 1) bone structure and pre-taphonomic factors determine its differential alteration by biochemical processes; 2) fungal populations associated to the decomposition of animal remains depend on soil chemistry and ecological dynamics; 3) even in a corrosive environment, bird bones are more capable of surviving to several mycological decomposition steps.     

Strontium isotope ratios in fossil teeth from South Africa: assessing laser ablation MC-ICP-MS analysis and the extent of diagenesis

This study tests the precision and accuracy of laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for measuring strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in fossil teeth from Swartkrans and Sterkfontein in South Africa, and explores the extent of diagenesis in these specimens. Compared to solution MC-ICP-MS or thermal ionization mass spectrometry (TIMS) methods, LA-MC-ICP-MS can be faster and less expensive, but has lower precision and accuracy. We found that ⁸⁷Sr/⁸⁶Sr ratios in fossil rodent teeth measured by LA-MC-ICP-MS were offset from solution values by a mean of 0.0005 ± 0.0010 (2σ). Because of the very wide spread of biologically available ⁸⁷Sr/⁸⁶Sr ratios (∼0.710 to ∼0.790) in the region, LA-MC-ICP-MS is more than sufficient for assessing the geographic origins of the fossil rodents. The concentration of strontium in modern and fossil enamel from the area is statistically indistinguishable, as is the range of ⁸⁷Sr/⁸⁶Sr ratios in modern rodents and fossil rodents from Swartkrans. Thus, there is little evidence of diagenetic Sr in the fossil enamel. In contrast, the fossil dentine may contain up to ∼50% diagenetic strontium, although many dentine ⁸⁷Sr/⁸⁶Sr ratios are still far removed from the background cave value of 0.729. We propose that LA-MC-ICP-MS will also be of use for investigating the geographic origins of other, non-rodent fossil teeth from the Sterkfontein and Swartkrans collections, and may prove of similar utility at other suitable sites.     

Charcoal reflectance measurements: implications for structural characterization and assessment of diagenetic alteration

Charcoal is a valuable source of archaeological and palaeoenvironmental proxy data. However growing evidence suggests that production conditions can strongly influence post-depositional alteration of charcoal. Consequently, both reconstruction of production temperature and understanding of the potential for diagenetic alteration are of great interest. Here, we use mean random reflectance (Ro_mean) in conjunction with other chemical characterization methods to address these questions. Ro_mean was obtained for a suite of modern analogue charcoal, produced under controlled conditions, and for a series of natural charcoal samples, obtained from archaeological and palaeoenvironmental deposits. Ro_mean proves to be a robust measure to assess formation temperature for samples produced at 400 °C and above, even after exposure to highly oxidizing conditions. Ro_mean is also useful for samples formed between 300 °C and 400 °C. However, if an assemblage of charcoals has been exposed to oxidizing conditions, lower temperature charcoals may be preferentially lost. It is apparent that charcoal produced at lower temperatures is more highly susceptible to chemical oxidation, and that there is a continuum in charcoal degradation potential, dependant upon fuel material and production conditions.     

Holocene sulphur-rich palaeochannel sediments: diagenetic conditions,magnetic properties and archaeological implications

Extensive aggregate extraction in the middle Trent valley, England, has revealed a sequence of Holocene palaeochannels associated with nationally important, and predominantly organic, archaeological remains. This paper reports observations of hyper-acidity (below pH 2), high natural magnetism and metallic sphaerules (framboids) in Holocene palaeochannel sediments at two sites in the middle Trent valley. These properties are associated with high natural remanent magnetism which has allowed the successful palaeomagnetic dating of palaeochannel fills at one of these sites (Hemington). These sediment properties are the result of the formation of ferromagnetic iron sulphides, including griegite, under conditions of high sulphur availability (from groundwater) in the presence of metallic ions and organic matter under low redox conditions, with later oxidation producing the extreme natural acidity through oxidation of disulphide (pyrite). These findings explain why, under certain groundwater conditions, alluvial palaeochannel sediments can carry post-depositional remanent magnetisation and be suitable for palaeomagnetic dating. The low pH may also be beneficial in the initial stage of wood preservation and if the sediments remain waterlogged, but probably not retard decomposition after drainage and acidification, a process that is increasingly being recognised as a threat to archaeological sites in wetland environments.     

Preservation assessment of Miocene–Pliocene tooth enamel from Tugen Hills (Kenyan Rift Valley) through FTIR,chemical and stable-isotope analyses

We investigated fossil tooth enamel of mammals and crocodiles from two Mio-Pliocene East-African formations (Lukeino and Mabaget Fms) using infrared spectroscopy and chemical and stable-isotope analyses. Infrared spectra indicate that the fossil enamel contains biological apatite (bioapatite), without significant secondary carbonate contaminations. Several empirical infrared indexes were used to analyze the crystal–chemical characteristics of enamel. Fossil enamel has less organic matter, water and structural carbonate of apatite than modern enamel with which it was compared. Fossil apatite has a better crystallinity than bioapatite. The calcium/phosphorus mass ratio and the fluorine content of fossil apatite show intermediate values between bioapatite and geological fluorapatite. The samples also display significant crystal-chemical variations, depending on the vertebrate group (mammals vs. reptiles) and the taphonomic context (Lukeino Fm vs. Mabaget Fm). In spite of these changes, no relationship was observed between the chemical contents (carbonate and fluorine) and the stable-isotope ratios of carbonate (δ¹³C and δ¹⁸O) in fossil enamel. Preservation of the palaeoenvironmental signals is strongly supported by the fact that the stable-isotope composition of the three investigated fossil mammalian taxa (deinotheres, equids and hippos) is consistent with their ecological features. For instance, typical C₃- and C₄-plant isotope compositions are reflected in the deinotheres and equids, respectively, and amphibious hippos display lower δ¹⁸O values than terrestrial herbivores, as expected.