Infrared and Isotopic Evidence for Diagenesis of Bone Apatite at Dos Pilas, Guatemala: Palaeodietary Implications

The use of stable carbon isotopic analysis of bone apatite to reconstruct prehistoric diets is hindered by the possibility of diagenetic alteration of carbonate during burial. We examine apatite preservation in Classic Period Maya skeletal remains from Dos Pilas, Guatemala, using Fourier transform infrared spectroscopy (FTIR). We use weight % CO₂evolved from apatite, FTIR carbonate/phosphate absorbance ratios, phosphate peak splitting crystallinity indices, fluoride peaks, and stable oxygen isotopic ratios to identify diagenetic change in apatite chemistry. Isotopically light carbon taken up from burial soil is adequately removed from most Dos Pilas bone by treatment with dilute acetic acid, but more severe alteration cannot be reversed by standard preparation methods. Infrared criteria identify recrystallized apatite in a subset of Dos Pilas burials, that is accompanied by isotopic exchange, and that no longer preserves biogenic δ¹³C. These results illustrate that comparatively recent bone may be diagenetically altered and demonstrate a need for systematic evaluation of mineral integrity in all archaeological bone prior to interpreting paleodiets with apatite δ¹³C.     

Micro-sampling of human bones for mobility studies: diagenetic impacts and potentials for elemental and isotopic research

The nature of long bone formation and the pathways of interaction between bone samples and the burial environment suggest that portions of the bones disconnected from the arterial system are resistant to diagenetic alteration. Preliminary work on femurs from Early Bronze Age hunter-gatherers in Cis-Baikal, Siberia shows that the nature and progression of chemical changes in the bone matrix due to microbial attack can be analyzed using laser ablation inductively coupled plasma mass spectrometry. Intra-osteon variability in elemental concentrations and strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) indicate the presence of unaltered portions of bone within diagenetically modified bone and suggest that useful data remain accessible. These biogenic signals can potentially be useful for mobility research in broad terms and the smaller timescales within an individual's lifetime (months, years), accessible therein. Laser ablation micro-sampling of femur specimens showed that intra-osteon elemental composition of Ba, Re, and Cs varied within and was correlated between multiple osteons of a single bone. Portions of chemically unaffected bone were identified within, and effectively discriminated from diagenetically altered bone tissue. Areas showing visual alterations and erratic or uncorrelated Ca and Sr elemental results also had anomalous Sr isotope ratios, suggesting diagenetic alteration in those places. Compositional and isotopic analysis of intact portions of bone supports the hypothesis that hunter-gatherer groups in Cis-Baikal made numerous major movements during their lives. Microscopic analysis of long bones clarifies aspects of biodeterioration and correlations between trace elemental results and diagenetic alteration. Micro-sampling of intact portions of bone expands the scope of available materials for research on mobility and other aspects of human past behavior.     

Diagenesis in bone and enamel apatite carbonate; the potential of density separation to assess the original composition

This paper presents a new approach to the isotopic measurement of diagenetically altered archaeological bone apatite carbonate. We describe how the existing differential dissolution method may be combined with a new approach to remove diagenetically reformed material on the basis of its greater specific gravity. We show that heavier, more diagenetically altered fraction has a higher (altered) δ¹³C and also increased crystallinity within one individual. In addition, we proposed one potential tool to check the validity of bone carbonate by comparing bone collagen, enamel carbonate and bone carbonate values of δ¹³C and radiocarbon content from the same individual. In the case of Danebury cattle, we estimated the biogenic δ¹³C_apa value for DC83 and DC89, although it is still difficult to overcome diagenesis in order to meet the expected value, which is shown to be 1.9‰ (DC83) and 3.5‰ (DC89).     

BONE POROSITY AND THE USE OF MERCURY INTRUSION POROSIMETRY IN BONE DIAGENESIS STUDIES*

Porosity measurements made on archaeological bones have revealed very-close relationships between changes in the porosity, remaining protein content and mineral alterations. The results have important implications for models that attempt to quantify the rates and extent of chemical reaction between bone and its geochemical environment. We report here on a novel application of an established technique, mercury intrusion porosimetiy, to investigate in more detail the pore size distribution of archaeological bones. Mercury intrusion porosimetry measures an ‘intermediate’range of bone porosity, ‘mesoporosity’, and produces data which permit the observation of significant structure characteristics in the porosity of modern laboratory altered and diagenetically altered bones.     

Bone Diagenesis and Taphonomic History of the Paso Otero 1 Bone Bed, Pampas of Argentina

Samples of guanaco bone from an archaeological site in the Pampas of Argentina have been analysed to understand the diagenetic profile of the bone assemblages that characterized the taphonomic history of the site. Two archaeological occupations of Paso Otero 1 were investigated, encompassing similar landscape settings, climates, and depositional environments. The time span is a c. 2000 year period from c. 4800 to 2800 years . A total of 30 bone samples taken from both occupations were used to provide a preliminary characterization of the diagenetic pathways at the site. The parameters investigated provide a comprehensive account of how both mineral (hydroxyapatite) and bone protein (collagen) have been altered. In order to compare the two bone assemblages in terms of their diagenetic parameters, multivariate analyses were conducted. Results indicate two different diagenetic profiles in the site, % N being one of the variables that accounts for most of the variation in Paso Otero 1. The diagenetic analyses indicate that protein is less preserved in the bone assemblage from the middle stable landscape. Alternative interpretations of the diagenetic profiles are discussed in light of the taphonomic history of the site, and palaeoenvironmental information of the region. One hypothesis stresses the importance of the role of climate in defining the different diagenetic pathways, and the other the continued action of the combined diagenetic factors along time as the main explanation for the variability in the state of preservation of the bones in Paso Otero 1.     

Sub‐micron spongiform porosity is the major ultra‐structural alteration occurring in archaeological bone

Total pore volume and pore size distribution are indicators of the degree of post‐mortem modification of bone. Direct measurements of pore size distribution in archaeological bones using mercury intrusion porosimetry (HgIP) and back scattered scanning electron microscopy (BSE‐SEM) reveal a common pattern in the changes seen in degraded bone as compared to modern samples. The estimates of pore size distribution from HgIP and direct measurement from the BSE‐SEM images show remarkable correspondence. The coupling of these two independent approaches has allowed the diagenetic porosity changes in human archaeological bone in the >0.01 µm range to be directly imaged, and their relationship to pre‐existing physiological pores to be explored. The increase in porosity in the archaeological bones is restricted to two discrete pore ranges. The smaller of these two ranges (0.007–0.1 µm) lies in the range of the collagen fibril (0.1 µm diameter) and is presumably formed by the loss of collagen, whereas the larger pore size distribution is evidence of direct microbial alteration of the bone. HgIP has great potential for the characterization of microbial and chemical alteration of bone. Copyright © 2002 John Wiley & Sons, Ltd.     

Diagenesis and survival of osteocalcin in archaeological bone

It has been demonstrated that the protein osteocalcin can survive in bone in the archaeological record, and postulated that it has the potential to survive over geological time periods. The precise mechanism for this longevity of survival is not yet fully understood, and has not been extensively studied in comparison to other diagenetic aspects of archaeological bone. We report a comparison between osteocalcin survival and the state of preservation of more than 60 bones from 14 archaeological sites. The amount of osteocalcin, assayed immunologically, was compared with diagenetic parameters that measure: the amount of ‘collagen’ in the bone, the mineral changes, the porosity, and the histological preservation of the material. The findings indicate that microbial taphonomy and mineral alteration of bone have a profoundly damaging effect on the preservation of osteocalcin.     

Patterns of Diagenesis in Bone II: Effects of Acetic Acid Treatment and the Removal of Diagenetic CO3

Archaeological bones of varying preservation have been treated with 0·1 M acetic acid in order to investigate the effect on structural and chemical alterations caused by diagenesis. Acetic acid is commonly used as a “cleaning agent” for removing diagenetic carbonate from bone and enamel, in an attempt to recover original, biogenic signals for use in dietary and¹⁴C dating studies.Diagenetic parameters were measured before and after treatment on a range of archaeological bones with good and bad preservation. Histological preservation defined the behaviour of the correlating parameters, where correlation coefficients between carbonate content and crystallinity, microporosity and macroporosity increased significantly after treatment. For histologically well preserved material, acetic acid is effective at returning carbonate content to around that of modern bone. Where bone is extensively damaged by micro-organisms, “loose” diagenetic material can be removed, but a fraction largely composed of hypermineralized bioapatite remains, which, we believe, cannot be reliably used to obtain accurate biological signals.     

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones.     

THE USE OF OXYGEN ISOTOPES IN SHEEP MOLARS TO INVESTIGATE PAST HERDING PRACTICES AT THE NEOLITHIC SETTLEMENT OF ÇATALHÖYÜK,CENTRAL ANATOLIA

This paper presents a pilot study designed to test the use of oxygen isotopes for investigating aspects of early herding practices in the Neolithic of western Asia, using the site of Çatalhöyük in central Anatolia as a case study. Time‐sequenced δ¹⁸O values in dental enamel of archaeological sheep are assessed for post‐depositional diagenetic effects and compared with seasonal δ¹⁸O meteoric water values in the region today. The evidence is used to indicate the environmental conditions in which individual sheep spent their first year, enabling management of breeding and birthing seasons, and movement to seasonal pastures, to be investigated.     

Diagenetic Arsenic Uptake in Archaeological Bone. Can we Really Identify Copper Smelters?

In a recent paper Oakberg, Levy & Smith (2000) reported measurements of arsenic concentrations in bone from the Chalcolithic site of Shiqmim, Israel. They inferred that since elevated levels of As had been found in the bone of modern copper smelter workers in Sweden, high concentrations in archaeological bone could be used to infer copper smelting activities in the past. However, their argument ignores the effects of post-depositional mobility of arsenic between soil, groundwater and bone. Here, we outline the processes influencing mobilization of As and post-depositional As incorporation in bone. We argue that the As concentrations reported by Oakberg, Levy & Smith (2000) can be accounted for by diagenetic uptake and are unlikely to reflect biogenic As concentrations. We therefore conclude that the data presented by Oakberg, Levy & Smith (2000) cannot be used to infer past copper smelting.     

Assessing mussel shell diagenesis in the modern vadose zone at Lyon's Bluff (22OK520), Northeast Mississippi

This study considers the chemical alteration of archaeological freshwater shell above the water table at the Lyon's Bluff site (22OK520), a single-mound and village complex located in east-central Mississippi, and the changes in trace element concentrations between unfired and fired shell. Thin-section petrography, X-ray diffraction, cathodoluminescence, and scanning electron microscopy analyses were conducted on archaeological shell from four natural layers from Unit 20N20W, over a depth of 80 cm and spanning 450 years. ICP–MS analysis also was conducted on a modern freshwater shell subjected to kiln firing. Microscopy results indicate a pristine aragonite crystal structure in the archaeological samples. ICP–MS data show that certain trace elements within the modern shell maintain their concentration after firing at 500 °C. The broader implications are: 1) that diagenetic alteration does not hinder chemical sourcing of shell at Lyon's Bluff, and 2) that certain trace elements are more reliable than others, namely Sr²⁺, Al²⁺, Ba²⁺, and Mn²⁺, when conducting trace element provenance studies on fired-shell temper.     

The taphonomy of cooked bone: characterizing boiling and its physico–chemical effects

Cooking is perhaps the most common pre–burial taphonomic transformation that occurs to bone, yet it is still one of the least understood. Little progress has been made in determining a method of identifying cooked bone in the archaeological record, despite its import for various branches of archaeology. This paper attempts to describe boiling in terms of its physico–chemical effects on bone, and uses a suite of diagenetic indicators to do this. It is shown that cooking for brief periods of time has little distinguishable effect on bone in the short term, but that increased boiling times can mirror diagenetic effects observed in archaeological bone. The relationship between the loss of collagen and alterations to the bone mineral is explored through heating experiments, and the results compared with archaeological data.The possibility of boiling being used as an analogue for bone diagenesis in future studies is raised, and the key relationship between protein and mineral is once again highlighted as vital to our understanding of bone diagenesis.     

Restrictions on fluorine depth profiling for exposure age dating in archaeological bones

Archaeological fragments of bone and teeth that are exposed to a humid environment take up fluorine from the surrounding soil. The fluorine ion replaces the hydroxyl group in the mineral phase of the bone, forming chemically more stable fluorapatite. In cortical parts of the long bone diaphysis a fluorine concentration profile can be observed, which decreases from the outer surface and the marrow cavity towards the inner parts of the bone matrix. Geological time spans are needed for this process to reach equilibrium and for the distribution to become uniform. As the shape of the profile, which can be described by a diffusion model, contains information on the exposure duration of the fossil object, several attempts to use fluorine profiling as a dating method have been undertaken. The distribution of fluorine in an archaeological sample however is strongly influenced by environmentally induced processes of bone diagenesis, i.e. alteration in the structure and composition of the mineral phase and degradation of organic components that may make the time information indistinct. The primary chemical composition of bones can thus be obscured by diagenesis within tens, hundreds or thousands of years. This depends more on the diagenetic environment than on the geological age. To observe the impact of environmental influence on the profile shape, samples from several burial sites featuring various soil conditions have been analyzed for their fluorine distribution and preservation state. This paper provides an overview on the restrictions that have to be considered when attempts are undertaken to relate a fluorine diffusion pattern to the archaeological age of a bone specimen.     

GEOGRAPHICAL PATTERNS IN BIOLOGICALLY AVAILABLE STRONTIUM,CARBON AND OXYGEN ISOTOPE SIGNATURES IN PREHISTORIC SW GERMANY*

In order to interpret strontium and oxygen isotope values in Neolithic human skeletons analysed previously, we begin to map the biologically available strontium, carbon and oxygen isotopic signatures of prehistoric southern Germany by analysing tooth enamel of pigs from archaeological sites distributed around the region. The mapping shows a marked upland–lowland difference in biologically available ⁸⁷ Sr/ ⁸⁶ Sr values, ranging between 0.7086 and 0.7103 in the sedimentary lowlands, and from 0.710 to as high as 0.722 in the crystalline uplands of the Odenwald, the Black Forest and the Bavarian Forest. In addition, carbon isotopes in the carbonate fraction of pig enamel were generally about 1–2 more enriched in ¹³ C in the uplands. Despite the expected depletion of ¹⁸ O with altitude, oxygen isotopes in pig enamel showed little correlation with site altitude, although for pig samples not older than the Iron Age there was some geographical correlation withδ¹⁸O patterns in modern precipitation.     

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.     

Stable isotopes and human diet in central western Argentina

Central western Argentina is the southern boundary of prehispanic maize in the archaeological record. This paper explores the stable isotope information from human bone (δ¹³C, from collagen and δ¹³C from apatite) and tooth (δ¹³C from enamel) samples in order to characterize the temporal and spatial trends of these isotopes and to understand them in terms of human diet. We analyzed 104 human individuals from the last 6000 years. Using the Kellner and Schoeninger (2007) model the results shows a high variation in human diet with few human individuals with a notably high significance of C₄ plants (probably maize) as an energy source and these samples have a chronology around ca. 1000 years BP. On the other hand a high variation in an individual’s dietary life history is shown by differences between δ¹³C collagen, apatite and enamel.     

Alkali extraction of archaeological and geological charcoal: evidence for diagenetic degradation and formation of humic acids

Charcoal forms a crucial source of archaeological and palaeoenvironmental data, providing a record of cultural activities, past climatic conditions and a means of chronological control via radiocarbon (¹⁴C) dating. Key to this is the perceived resistance of charcoal to post-depositional alteration, however recent research has highlighted the possibility for alteration and degradation of charcoal in the environment. An important aspect of such diagenesis is the potential for addition of exogenous “humic acids’ (HAs), to affect the accuracy of archaeological and palaeoenvironmental reconstructions based upon chemical analyses of HA-containing charcoal. However the release of significant quantities of HA from apparently pristine charcoals raises the question whether some HA could be derived via diagenetic alteration of charcoal itself. Here we address this question through comparison of freshly produced charcoal with samples from archaeological and geological sites exposed to environmental conditions for millennia using elemental (C/H/O) and isotopic (δ¹³C) measurements, Fourier Transform Infrared Spectroscopy (FTIR) and proton Liquid-State Nuclear Magnetic Resonance (¹H NMR). The results of analyses show that the presence of highly carboxylated and aromatic alkali-extractable HA in charcoal from depositional environments can often be attributable to the effects of post-depositional processes, and that these substances can represent the products of post-depositional diagenetic alteration in charcoal.     

Bone diagenesis: an overview of processes

This overview is a summary of the state of understanding of processes and states in bone diagenesis, as seen from a chemical perspective. It deals with the significance and usefulness of the measurements of ‘diagenetic parameters’—that is, of measures of diagenetic alteration—and of the theories of physico–chemical processes which are considered to underlie the measured changes. In many ways these two aspects are seen to come together quite well, and some progress has been made in relating different burial environments to the observations of alteration. Such a framework also allows us to ask more penetrating questions, such as how characteristic differences in diagenetic alteration might arise, and how the pre–burial environment might influence the eventual course of diagenesis.     

Polarizing Microscopy Identification of Chemical Diagenesis in Archaeological Cementum

Cementum increment analysis can potentially retrieve relatively complete, high-precision seasonality and mortality profiles from archaeological mammalian tooth assemblages. However, cementum exhibits many similarities to bone in composition, histology, ultrastructure, and even microstructure. Consequently, the mineralized dental tissue may be prone to the same processes of post-depositional chemical alteration that affect bone. This article reviews the issues surrounding chemical diagenesis in cementum and presents a new application to archaeological ungulate cementum of a polarizing microscopy technique that has previously been utilized to identify the effects of chemical diagenesis in archaeological bone and human cementum (Geusa et al., 1999; Gilbert, 1989; Watson, 1975; Zeder, 1978). It is argued that the post mortem leaching of collagen and the diagenetic growth of apatite crystallites can develop into banded features that mimic seasonal cementum increments. This pattern of diagenesis is demonstrated in multiple locations on a macroscopically well-preserved Upper Pleistocene-age archaeological tooth, which was previously interpreted by the author to exhibit biogenic seasonal cementum increments (Stutz, 1993; Stutz et al., 1995). It is suggested that if researchers seek to retrieve seasonality and mortality data from archaeological cementum, the microscopy analysis protocol must include screening of a pilot sample for the frequency and extent of chemical diagenesis.