Applied Geochemistry (v.21, #10)

Archaeological geochemistry by Andrew Parker; A. Mark Pollard (1625).

Mineral waters in Britain show a wide range of 87Sr/86Sr isotope compositions ranging between 87Sr/86Sr = 0.7059 from Carboniferous volcanic rock sources in Dunbartonshire, Scotland to 87Sr/86Sr = 0.7207 in the Dalradian aquifer of Aberdeenshire, Scotland. The 87Sr/86Sr composition of the waters shows a general correlation with the aquifer rocks, resulting in the waters from older rocks having a more radiogenic signature than those from younger rocks. This wide range of values means that the Sr isotope composition of mineral water has applications in a number of types of studies. In the modern commercial context, it provides a way of fingerprinting the various mineral waters and hence provides a method for recognising and reducing fraud. From an environmental perspective, it provides the first spatial distribution of bio-available 87Sr/86Sr in Britain that can be used in modern, historical and archaeological studies.

In order to interpret pre-historic cultural interactions, the provenance of amphibolitic raw material used for flat-axes and adzes in lower to middle Neolithic cultures throughout present day Germany were investigated by elemental and Sr, Pb isotopic methods. Within all settlements studied, a homogeneous actinolite-hornblende schist rock type (AHS) was found to be massively dominating, with a distinct petrography of needle-shaped actinolite interwoven with single larger grains of hornblende along with calcic plagioclase and large amounts of ilmenite. Geochemically, the AHS group is very homogeneous and has a signature of an enriched basaltic precursor with high concentrations of particularly the LIL-elements. The geochemical signature is relatively rare and can not be matched in nearby geological outcrops, wherefore the conclusion of “imported material” is quickly reached. Strontium and Pb isotopic analyses of the AHS were compared to the isotopic composition of amphibolitic rocks with similar petrography and trace elemental signatures within possible archaeological trade regions. The isotopic data of the archaeological material point roughly to a Proterozoic age of the stone used; an age which can be reasonable matched to a single outcrop situated at Jistebsko within the Czech Republic. This area further shows archaeological traces of prehistoric mining. Based on petrographic, geochemical and isotopic evidence, this area is here presented as the provenance area of the stone raw material, which later spread throughout prehistoric Europe – establishing contact and trade routes between Neolithic cultures.

Establishing the potential of Ca isotopes as proxy for consumption of dairy products by Nan-Chin Chu; Gideon M. Henderson; Nick S. Belshaw; Robert E.M. Hedges (1656-1667).
A procedure has been developed which allows precise determination of Ca isotope ratios in natural and organic samples such as bones, milk and other biological materials. In this study the procedure is used to determine Ca isotope ratios in modern dietary systems and to establish the potential of Ca isotopes as a paleodiet tracer by analysis of bones. Multi-sampling across a 5 cm portion of a red deer jawbone shows invariant Ca isotope ratios and suggests negligible isotopic effect during bone remodelling. The difference between Ca isotopes in red deer diet and bones from one location was 0.65‰, in agreement with a previous study of diet/bone offsets. Similar values for modern deer-bone δ44/42Ca from four geographically diverse populations demonstrate that geological/environmental conditions do not cause large variability and suggest that diet is the major cause for variations in bone δ44/42Ca. δ44/42Ca of herbivore milk is found to be ≈0.5 to 0.6 higher than the corresponding diet. Modern human milk has a δ44/42Ca of −1.15 (n  = 4) and is isotopically the lightest material reported in this study. This suggests that, for these samples, a significant portion of Ca intake was from dairy sources, and that human milk has Ca which is, again, ≈0.6‰ isotopically lighter than dietary Ca intake. Finally, Ca isotope ratios are presented from a variety of samples formed during fermentation processes (e.g., curds, whey, etc.) which indicate that these processes do not fractionate Ca isotopes significantly. Together, the data in this paper indicate that, because milk is an important dietary source of Ca with a distinctive signature, Ca isotope ratios should provide a tracer for past dairy consumption. A simplified model is outlined to demonstrate the ability to quantify dairy consumption by the analysis of Ca isotopes in bones.

Bulk stable light isotopic ratios in archaeological birch bark tars by B. Stern; S.J. Clelland; C.C. Nordby; D. Urem-Kotsou (1668-1673).
The authors report a preliminary study of the light stable isotopic (δD, δ 13C and δ 18O) values for bulk archaeological birch bark tars, over a geographical (e.g. Greece to Norway) and chronological (9500–3000 BP) range. For δ 13C an increase in fractionation with increase in latitude is observed in samples from Greece which are less depleted than those from northern Europe. There is no clear difference between the samples from northern Europe. There is no apparent trend in δ 13C value with the 14C age of the sample. Due to biosynthetic fractionation all the samples are significantly depleted in 2H and enriched in 18O relative to the global meteoric water line. This study indicates that archaeological birch bark tar from Greece can be distinguished from those of northern Europe; this separation is probably based on the extreme geographical range of the samples examined here. But this does provide evidence that the birch bark tars were probably made locally rather than traded.

The potential of the baobab (Adansonia digitata L.) as a proxy climate archive by I. Robertson; N.J. Loader; C.A. Froyd; N. Zambatis; I. Whyte; S. Woodborne (1674-1680).
The large girth and immense size of the baobab has caused many to speculate about its age. Unfortunately reliable age estimates cannot be determined from growth rates as the girth varies in response to different moisture regimes. In a similar way, ages cannot be determined from ring-width measurements or X-ray densitometry as the absorbent nature of the soft fibrous wood and distortion upon drying prevent the application of these techniques. The Southern Hemisphere bomb radiocarbon curve was used to demonstrate that the rings of a recently-fallen baobab (Adansonia digitata L.) from Kruger National Park appear to be annual. The detrended C isotope values of finely-ground wholewood from another baobab specimen were found to be highly associated with January precipitation (r  = 0.72; p  < 0.01). This study demonstrates that high resolution information about past climates may be obtained by analysing the C isotope values from baobab samples even if distortion of ring-widths has occurred during drying. However, this relationship must be replicated before the baobab can be demonstrated to be a reliable palaeoclimatic proxy.

A dendrochemical study of Pinus sylvestris from Siljansfors Experimental Forest, central Sweden by Charlotte L. Pearson; Sturt W. Manning; Max Coleman; Kym Jarvis (1681-1691).
Inductively coupled plasma mass spectrometry (ICP-MS) was used to investigate changes in trace element concentration in two high resolution sequences of tree rings from central Sweden. Individual annual growth increments from 1800–2002 to 1930–2002 were sampled from two Scots pine (Pinus sylvestris) trees from the Siljansfors Experimental Forest. The aims of the study were: to test the viability of conventional solution induction ICP-MS as a technique for investigating the multi-elemental chemistry of long tree ring sequences at annual resolution, and, to test this specifically with a view to detecting changes in elemental concentrations of Swedish tree rings contemporary with the major (and relatively proximal) Icelandic eruption of Askja (1875). It was found that despite a time consuming sample preparation process, it was possible to use conventional ICP-MS for multi-elemental analysis of a long sequence of tree rings at annual resolution. Although promising data were produced, no truly conclusive concentration anomaly could be detected in the sequence to indicate the impact of the Askja eruption on environmental chemistry. Overall findings underlined the complexity of the tree/environment interaction and the cautious approach to data interpretation essential for any dendrochemical study.

Some numerical considerations in the geochemical analysis of distal microtephra by A.M. Pollard; S.P.E. Blockley; C.S. Lane (1692-1714).
The use of Late Quaternary tephra horizons as isochronous markers for high resolution correlation between records is of growing importance in a number of scientific fields. Particular advancements have been made through the identification of microtephra deposits (very distal deposits of volcanic ash invisible to the naked eye). The successful correlation of ash layers and volcanic eruptions depends on the acquisition of the major element chemistries of a tephra layer, derived from microprobe analyses of individual glass shards. This is particularly important for microtephras where aeolian fractionation has removed much of the mineral phase of the ash deposit, which often aids tephra discrimination. There are, however, difficulties in distinguishing precisely between different eruptions of the same volcano using major element composition and this may not always be resolved by the use of trace elements. Given the potential of tephrochronology as a correlative tool in many disciplines it is important to resolve this difficulty. One way forward is to perform more robust statistical analyses on the geochemical data, as in general, analyses are confined to a series of bi-plots of major elements. Here the authors explore some of the problems associated with dealing with microprobe data generated for individual tephras and pay particular attention to the ‘unit sum problem’. Using a subset of data generated as part of a EURODELTA project on tephra distribution in the Adriatic, the authors demonstrate that this problem is detectable in major element data from tephras and have consequently applied the logratio method before further analyses of the data. It is demonstrated that the use of logratios combined with discriminant functions analysis provides a more robust assessment of likely chemical correlations between tephras, and are superior to the use of bi-plots alone; and obviate the need for any data normalization, a particular point of contention between tephrochronologists.

Speciation and weathering of copper in “copper red ruby” medieval flashed glasses from the Tours cathedral (XIII century) by François Farges; Marie-Pierre Etcheverry; André Scheidegger; Daniel Grolimund (1715-1731).
Three “copper ruby red” (or “flashed”) glasses from the St Gatien cathedral in Tours (windows from the XIII century) were investigated at the Cu K-edge by synchrotron X-ray fluorescence microscopy and μ-XANES/EXAFS spectroscopies. The spectra are compared to XANES/EXAFS spectra collected for modern glasses synthesized at various O2 fugacities. Two main types of red glasses are present in Tours, which show a distinct Cu speciation. In the first type (“plaqués”), Cu is present as sub-micron metallic nucleates, which coexist with monovalent Cu linear moieties (30:70 at.%). In contrast, the glasses of the other type (“feuilletés”) show mostly monovalent Cu (together with some evidence for metallic Cu in the edge region of the XANES).The plaqués glasses appear to have been synthesized at lower O2 fugacity and higher temperatures to promote homogeneous nucleation of metallic Cu. A relative enrichment in Al (provided by the addition of orthoclase in the melt) greatly enhances the glass durability by decreasing the melt peralkalinity by a factor of ∼4. In contrast, the feuilletés were equilibrated at much higher O2 fugacities. Hence, metallic Cu, despite being scarce in that glass, is not at equilibrium and could have well been added on purpose during the melt cooling. It is proposed that a technique called ‘tourage’ could have been used to help create the micron scale greenish and red layers. The feuilleté glasses are also weathered at their surface, promoting the formation of amorphous Cu(II) species related to a Cu sulphate.

Evaluation of the dissolved contaminant load transported by the Tinto and Odiel rivers (South West Spain) by M. Olías; C.R. Cánovas; J.M. Nieto; A.M. Sarmiento (1733-1749).
The Tinto and Odiel rivers are heavily affected by acid mine drainage (AMD). However, the exact quantities of contaminants transported into the Huelva estuary and the Gulf of Cadiz are unknown. The existing previous investigations are, in general, based on studies with few data or incorrect methodology, and are therefore unreliable. This study aims to present a reliable estimation of the dissolved contaminant load transported by both rivers for the periods 1995/96 to 2002/03. The methodology used is based principally on the correlation between contaminant concentration and flow rate. The results show that both rivers transport enormous quantities of dissolved contaminants: 7900 t a−1 of Fe, 5800 t a−1 Al, 3500 t a−1 Zn, 1700 t a−1 Cu, 1600 t yr−1 Mn and minor quantities of other metals. These values represent 60% of the global gross flux of dissolved Zn transported by rivers in to the ocean, and 17% of the global gross flux of dissolved Cu.

Low-molecular-weight (LMW) organic acids occur widely in soils. Results in pure mineral systems and podzols suggest that LMW organic acids can promote the dissolution of Al from kaolinite, Al oxides and soils, but limited information is available concerning the role of these organic acids on Al mobilization in variable charge soils as yet. This paper deals with the effect of LMW organic acids on Al mobilization and mobilized Al distributed between the solution phase and exchangeable sites in two acidic variable charge soils. The results indicated that LMW organic acids accelerated Al mobilization through proton- and ligand- promoted reactions. The ability of different organic acids to mobilize Al followed the order: citric acid > oxalic acid > malonic acid > malic acid > tartaric acid > salicylic acid > lactic acid > maleic acid. This order was in general agreement with the magnitude of the stability constants of Al–organic acid complexes. The ratio of soluble Al to exchangeable Al also increased as the stability constants increased. These results showed that the organic acids with strong Al-complexation capacity were most effective in Al mobilization, whereas the weak organic acids promoted the retention of mobilized Al by the soil exchangeable sites. Increase in both organic acid concentration and solution pH promoted Al mobilization and also increased the ratio of soluble Al to exchangeable Al due to the increase in the concentration of the effective organic ligands, especially in the strong organic acid systems. These findings may have their practical significance for establishing more effective amelioration procedures for variable charge soils with increased acidity and higher mobility of Al.

Environmental assessment of abandoned mine tailings in Adak, Västerbotten district (northern Sweden) by Aparajita Bhattacharya; Joyanto Routh; Gunnar Jacks; Prosun Bhattacharya; Magnus Mörth (1760-1780).
Sulfide-rich mine tailings in Adak that are exposed to weathering cause acid mine drainage characterized by low pH (2–4) and high SO4 (up to 800 mg L−1). Surface water, sediment and soil samples collected in this study contain higher concentrations of As, Cu, Fe and Zn, compared to the target and/or intervention limits set by international regulatory agencies. In particular, high As concentrations in water (up to 2900 μg L−1) and sediment (up to 900 mg kg−1) are of concern. There is large variability in trace element concentrations, implying that both physical (grain size) and chemical factors (pH, secondary phases as sulfides, Al-oxides or clay minerals) play an important role in their distribution. The low pH keeps the trace elements dissolved, and they are transported farther downstream. Trace element partition coefficients are low (log  K d  = 0.3–4.3), and saturation indices calculated with PHREEQC are <0 for common oxide and sulfidic minerals. The sediment and soil samples indicate an enhanced pollution index (up to 17), and high enrichment factors for trace elements (As up to 38,300; Zn up to 800). Finally, leaves collected from different plant types indicate bioaccumulation of several elements (As, Al, Cu, Fe and Zn). However, some of the plants growing in this area (e.g., Salix, Equisétum) are generally resistant to metal toxicity, and hence, liming and phytoremediation could be considered as potential on-site remediation methods.

Origin and mobility of heavy metals in contaminated sediments from retention and infiltration ponds by Blandine Clozel; Véronique Ruban; Cédric Durand; Pierre Conil (1781-1798).
The metal content of sediments from 4 ponds representative of contrasting environments and design was determined through speciation studies using both sequential chemical extraction and mineralogical observation. Surprisingly, the speciation for a given pond appears to be very homogenous, with the homogeneity being independent of total metal content, particle size or location within the pond. In contrast to what is commonly expected, no increase in metal content was found with decrease in size class. The proportion of metals in the different phases is distinct from one pond to another, reflecting distinct catchment areas. Contributions of alloys and atmospheric particles from industrial processes can be ascertained by SEM. Cadmium showed the highest availability in all 4 ponds with 40–60% extracted during the first step of the Community Bureau of Reference extraction scheme. Zinc, Pb and Cu, mostly sorbed on organic matter or oxides, may also become more mobile depending on physico-chemical changes. In France, an estimated volume of 5 million tons of sediment is extracted annually, and it is obvious that the risk, both environmental and human, associated with its heavy metal content and speciation cannot be totally ignored for the future use of this sediment.

Spatial variations in water composition at a northern Canadian lake impacted by mine drainage by M.C. Moncur; C.J. Ptacek; D.W. Blowes; J.L. Jambor (1799-1817).
Release of acid drainage from mine-waste disposal areas is a problem of international scale. Contaminated surface water, derived from mine wastes, orginates both as direct surface runoff and, indirectly, as subsurface groundwater flow. At Camp Lake, a small Canadian Shield lake that is in northern Manitoba and is ice-covered 6 months of the year, direct and indirect release of drainage from an adjacent sulfide-rich tailings impoundment has severely affected the quality of the lake water. Concentrations of the products from sulfide oxidation are extremely high in the pore waters of the tailings impoundment. Groundwater and surface water derived from the impoundment discharge into a semi-isolated shallow bay in Camp Lake. The incorporation of this aqueous effluent has altered the composition of the lake water, which in turn has modified the physical limnology of the lake. Geochemical profiles of the water column indicate that, despite its shallow depth (6 m), the bay is stratified throughout the year. The greatest accumulation of dissolved metals and SO4 is in the lower portion of the water column, with concentrations up to 8500 mg L−1 Fe, 20,000 mg L−1 SO4, 30 mg L−1 Zn, 100 mg L−1 Al, and elevated concentrations of Cu, Cd, Pb and Ni. Meromictic conditions and very high solute concentrations are limited to the bay. Outside the bay, solute concentrations are lower and some stratification of the water column exists. Identification of locations and composition of groundwater discharge relative to lake bathymetry is a fundamental aspect of understanding chemical evolution and physical stability of mine-impacted lakes.