Charred Plant Research Articles

To pretreat, or not to pretreat, that is the question. The value of pretreatment protocols in the stable carbon and nitrogen isotope analysis of archaeobotanical cereal grains from Croatia and Serbia

ABSTRACT Isotopic analysis of archaeological charred plant remains is a useful tool to infer past agricultural practices. However, debate continues over whether charred seeds should be untreated or pretreated before analysis, to counteract any residual contamination and retrieve the “true” isotopic signature of the seed. This paper presents a case study examining whether archaeobotanical remains from Croatia and northern Serbia should be pretreated before isotopic analysis with the aim to provide a pragmatic technique for wider application. A small subset was first examined with an ATR-FTIR and then four different protocols were examined: water rinse only, two different acid-only methods and ABA (acid–base-acid). The results were inconsistent, displaying variability in the effect each protocol had on the isotopic values. Overall, it was concluded that the slight differences between untreated and pretreated sub-samples should not impact the archaeological interpretation, removing the need for pretreatment of the remaining archaeobotanical material.

The influence of plant residues on soil aggregation and carbon content: A meta‐analysis

AbstractBackgroundSoil aggregation and organic carbon (OC) content are important indicators of soil quality that can be improved with plant residue amendments. The extent of the effects of plant residue amendments on soil aggregation and OC content across different plant residue and soil types is not fully understood.AimIn this meta‐analysis, we evaluated the effects of plant residue amendments on soil aggregation and OC content for different plant residues (fresh, charred) and soil types varying in clay content, initial OC content, and pH.MethodsOur meta‐analysis included 50 published studies (total of 299 paired observations). We estimated the response ratios of mean weight diameter (MWD) and separate aggregate size classes, total soil OC (TSC), and aggregate‐associated OC. We also considered the effect of experimental factors (study duration, residue type, residue amount, initial soil OC, clay content, and pH).ResultsThe benefit of plant residue amendment on soil aggregation was larger in soils with initially low OC content and neutral pH. Initial soil OC content and pH were more important than soil clay content for OC storage in soil aggregates. Both fresh and charred plant residue amendments were effective in forming aggregates, whereas charred residues were more effective in increasing TSC. We found only a weak positive relationship between the response ratio of TSC and MWD indicating that other factors besides soil aggregation contributed to the increase in soil C storage.ConclusionsWhile plant residue amendments can enhance soil aggregation and TSC, these effects are likely governed by the type of plant residue and soil properties such as the initial soil pH and OC content.

Untangling the Taphonomy of Charred Plant Remains in Ritual Contexts: Late Antique and Medieval Churches and Graves from Croatia

ABSTRACT Food has played a central role in death rituals throughout human history, yet finding evidence of these practices in the archaeological record can be problematic. In particular, linking charred plant remains to inhumation burials requires careful consideration of the taphonomic processes involved. Here we focus on the recovery of charred plant macro-remains from four Late Antique and medieval cemeteries and one late medieval church in Croatia. The results showed low densities of both charcoal and other charred plant macro-remains, suggesting that the remains are general settlement debris that was accidentally deposited within the cemeteries and church context. At Bribirska Glavica, the sampling of stratigraphic layers at the multi-level cemetery allowed a greater understanding of taphonomic processes and corroborated the identification of a rubbish dump linked to an adjacent Roman villa. The results provide important insights for future sampling strategies, including the importance of taking control samples outside the graves and radiocarbon dating to determine whether botanical remains are related to the burials.

Crops and food choices at the Late Bronze Age city of Hala Sultan Tekke

The Late Bronze Age city of Hala Sultan Tekke (HST) is located on the south-eastern coast of Cyprus, c. 7 km south of modern-day Larnaca. The most recent excavations revealed four new city quarters (CQ1–4), where domestic and industrial activities took place. While the earliest occupational remains are from c. 1650/1600 BCE, the so far best attested period lasted from the 13th century to its final destruction in the mid-12th century BCE, after which the city was abandoned, never to be occupied again. The find material demonstrates intense industrial and trade activities resulting in an increased wealth. Agricultural products from the city’s hinterland certainly added to its rank as a leading trade hub in the eastern Mediterranean. The most recent archaeobotanical research revealed charred plant remains including that of barley, einkorn and emmer wheat, fig, olive, grape and lentil. These contribute to understanding the function and use of areas, spaces and specific installations at HST, and shed further light on Late Bronze Age agriculture on Cyprus.

Middle Neolithic farming of open-air sites in SE France: new insights from archaeobotanical investigations of three wells found at Les Bagnoles (L\u2019Isle-sur-la-Sorgue, D\xe9pt. Vaucluse, France)

Previous reviews of Middle Neolithic agricultural practice (4400–3500 cal bc) in southern France have highlighted a change in crop assemblages after 4000 cal bc, with a reduction of naked wheat and an increase of emmer and partly of einkorn. The recent investigation of three wells from the site of Les Bagnoles (4250–3800 cal bc) in the periphery of the southern Rhône valley yielded an unprecedented amount of waterlogged uncharred and charred plant macro remains that offer new insights into crop diversity and its changes over time. The results from the wells at Les Bagnoles were compared with other dated sunken features from open-air sites (in contrast to caves and rock shelters), with the aim of identifying patterns suggesting changes in the crop spectra between the early (MN1) and late (MN2) Middle Neolithic phases from taphonomically comparable contexts. The results from Les Bagnoles demonstrate that oil crops and pulses are underrepresented in dry sites and that they were a significant part of Middle Neolithic agriculture. They also indicate an increase in the representation of einkorn (instead of emmer) during MN2 that is also visible in other open-air sites. The comparison of the archaeobotanical results with silo storage capacity values as a proxy for average production capacity per household leads us to propose a possible drop in naked wheat productivity and opens new questions in factors affecting crop choice at the beginning of the 4th millennium cal bc.

Effectiveness of different pre-treatments in recovering pre-burial isotopic ratios of charred plants.

Isotopic analysis of archaeological charred plant remains offers useful archaeological information. However, adequate sample pre-treatment protocols may be necessary to provide a contamination-free isotopic signal while limiting sample loss and achieving a high throughput. Under these constraints, research was undertaken to compare the performance of different pre-treatment protocols. Charred archaeological plant material was selected for isotopic analysis (δ13 C and δ15 N values) by isotope ratio mass spectrometry from a variety of plant species, time periods and soil conditions. Preservation conditions and the effectiveness of cleaning protocols were assessed through Fourier transform infrared spectroscopy and X-ray fluorescence (XRF) spectrometry. An acid-base-acid protocol, successfully employed in radiocarbon dating, was used to define a contamination-free isotopic reference. Acid-base-acid isotopic measurements were compared with those obtained from untreated material and an acid-only protocol. The isotopic signals of untreated material and the acid-only protocol typically did not differ more than 1‰ from those of the acid-base-acid reference. There were no significant isotopic offsets between acid-base-acid and acid-only or untreated samples. Sample losses in the acid-base-acid protocol were on average 50 ± 17% (maximum = 98.4%). Elemental XRF measurements showed promising results in the detection of more contaminated samples albeit with a high rate of false positives. For the large range of preservation conditions described in the study, untreated charred plant samples, water cleaned of sediments, provide reliable stable isotope ratios of carbon and nitrogen. The use of pre-treatments may be necessary under different preservation conditions or more conservative measurement uncertainties should be reported.

Reconsidering the MSA to LSA transition at Taforalt Cave (Morocco) in the light of new multi-proxy dating evidence

Amongst the least well-defined periods in North African prehistoric archaeology is the interval between ∼40 and 20 ka BP. This encompasses a phase (or phases) of major technological change which archaeologists describe as the MSA (Middle Stone Age) to LSA (Later Stone Age) transition. The nature of this transition is complicated by the fact that few sites spanning this period have been the object of modern scientific study. Two exceptions are the caves of Taforalt (Morocco) and the Haua Fteah (Libya) which have each been systematically excavated in the last decade and have yielded datable sequences that provide fresh light on the nature of the transition. In this paper we describe the results of new work at Taforalt and suggest that considerable variation exists across the region, in comparison with sites like the Haua Fteah. Initial results are also given on the rich charred plant remains (likely food residues) and wood charcoal evidence from the younger MSA layers dating to ∼27 ka BP.

Et monumentalt midtsulehus ved Nørre Holsted i Sydjylland

Et monumentalt midtsulehus ved Nørre Holsted i Sydjylland

Useful plants from the site Lutomiersk–Koziówki near Łódź (central Poland) with special reference to the earliest find of Xanthium strumarium L. seeds in Europe

Archaeological features at the multi-culture site of Lutomiersk–Koziówki 3a-c in central Poland contained preserved charred plant macro-remains. The site is located within the “Central European sand belt” characterised by sandy terraces and dunes, nowadays covered mainly by podzols and anthropogenically changed soils. The samples come from pits dated to the Middle Bronze Age (MBA, ca. 18th–14th centuries BC), the Late Bronze Age (LBA, ca. 10th–8th centuries BC), and the Roman Iron Age (RIA). The most intensive occupation was connected with the development of the LBA settlement of Lusatian culture. During that time mostly peas (Pisum sativum) and millet (Panicum miliaceum) were cultivated while remains of large-grained crops like einkorn (Triticum monococcum), emmer (Triticum dicoccum), spelt (Triticum spelta), and barley (Hordeum vulgare) were not common. In that time goosefoot (Chenopodium album) and wild buckwheat (Fallopia convolvulus) were probably used as a source of food. In the Roman Iron Age, the presence of those plants decreased and rye (Secale cereale) appeared, becoming the most common cultivated plant besides barley. The unique find of cocklebur (Xanthium strumarium) seeds in the LBA samples was possibly connected with their useful properties, primarily as medicinal plants and secondarily as a source of oil. The cocklebur remains were probably processed, but no by-products and no whole fruits were noted. The context of these finds is exceptional compared with the other samples from the site, possibly reflecting medicinal activities of the people. Taking into account the history and migration of the cocklebur in Europe during the Holocene, it must be emphasized that the charred seeds from Lutomiersk–Koziówki are currently the oldest radiocarbon-dated finds in Europe (2745±30 BP, ca. 975–818cal. BC) and can reflect distant contacts of the settlers mostly with south-eastern Europe although eastern routes cannot be excluded as well.

Impact of contamination and pre-treatment on stable carbon and nitrogen isotopic composition of charred plant remains.

RationaleStable isotope analysis of archaeological charred plants has become a useful tool for interpreting past agricultural practices and refining ancient dietary reconstruction. Charred material that lay buried in soil for millennia, however, is susceptible to various kinds of contamination, whose impact on the grain/seed isotopic composition is poorly understood. Pre-treatment protocols have been adapted in distinct forms from radiocarbon dating, but insufficient research has been carried out on evaluating their effectiveness and necessity for stable carbon and nitrogen isotope analysis.MethodsThe effects of previously used pre-treatment protocols on the isotopic composition of archaeological and modern sets of samples were investigated. An archaeological sample was also artificially contaminated with carbonates, nitrates and humic acid and subjected to treatment aimed at removing the introduced contamination. The presence and removal of the contamination were investigated using Fourier transform infrared spectroscopy (FTIR) and δ13C and δ15N values.ResultsThe results show a ca 1‰ decrease in the δ15N values of archaeological charred plant material caused by harsh acid treatments and ultra-sonication. This change is interpreted as being caused by mechanical distortion of the grains/seeds rather than by the removal of contamination. Furthermore, specific infrared peaks have been identified that can be used to detect the three types of contaminants studied. We argue that it is not necessary to try to remove humic acid contamination for stable isotope analysis. The advantages and disadvantages of crushing the grains/seeds before pre-treatment are discussed.ConclusionsWe recommend the use of an acid-only procedure (0.5 M HCl for 30 min at 80°C followed by three rinses in distilled water) for cleaning charred plant remains. This study fills an important gap in plant stable isotope research that will enable future researchers to evaluate potential sources of isotopic change and pre-treat their samples with methods that have been demonstrated to be effective. © 2014 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.

Wild fruit use among early farmers in the Neolithic (5400–2300 cal bc) in the north-east of the Iberian Peninsula: an intensive practice?

The archaeobotanical record of 24 sites from the Neolithic period (5400–2300 cal bc) in the north-east of the Iberian Peninsula is evaluated. Remarkable amounts of data have recently been obtained for the early and middle Neolithic phases. Most of the studied sites were dry and they only yielded charred plant material. Among dry sites, several types of context were evaluated: dwelling areas, hearths, roasting pits and byres. Material was also analysed from a waterlogged cultural layer of one early Neolithic lakeshore site, La Draga. Quercus sp. (acorns), Corylus avellana L. (hazelnuts), Pistacia lentiscus L. (mastic fruits) and Vitis vinifera L. var. sylvestris (wild grapes) were among the most frequently encountered fruits and seeds. Their presence in the archaeobotanical record clearly maps their past ecological distribution in the region. There are differences observed between the charred dry-land material and the waterlogged uncharred material. Wild fruits were mostly present in an uncharred state in La Draga. Therefore, their consumption could go unnoticed in dry sites when fruits were eaten raw or without roasting. Larger amounts of charred remains of certain wild fruits like acorns and hazelnuts found in mountain areas are highlighted as potential evidence of the regular practice of roasting, potentially indicating regional traditions. All in all, our results support an intensive wild plant use at least during the first 1,300 years of the Neolithic period. Evidence of wild plant food consumption becomes scanty towards the second phase of the middle and the late Neolithic (4th and 3rd millennium cal bc). This, however, might also be due to taphonomic reasons.

An integrated perspective on farming in the early Neolithic lakeshore site of La Draga (Banyoles, Spain)

A combined analysis of the faunal and charred plant macroremains from the early Neolithic lakeshore site of La Draga (Banyoles, Spain) is presented. The aim was to characterise the farming strategies practiced by the first Neolithic communities in the north-east of the Iberian Peninsula in terms of their degree of intensity. The joint discussion of the data allowed the observation that permanent plots could have been kept, that a high harvest would have been practiced and that a low-scale processing of the crop could have taken place within the domestic space, where the grain would be stored. This type of crop husbandry would permit the livestock to access the fields and graze the stubble, which would result in the manuring of the plots. Herds were kept close to the dwellings and different management and consumption practices were observed between the larger and the smaller animals. Smaller animals were probably produced and consumed at a household scale while larger animals would require a cooperative management and consumption. It is concluded that the available evidence points towards an intensive mixed farming model.

How useful is chemical oxidation with dichromate for the determination of “Black Carbon” in fire-affected soils?

A common approach for the quantification of Black Carbon (BC) in soils and sediments represents the chemical oxidation with acid potassium dichromate. Because this method is still associated with some uncertainties, its applicability for the detection of BC produced during vegetation fires was examined by analyzing fire-affected and unaffected soil organic matter, including fresh and charred plant residues and a charcoal briquette. Comparably to the organic matter in a fire-unaffected soil sampled under pasture, grass and beech sawdust remains were completely oxidized after 4 to 6 h, whereas approximately 12% of the organic carbon (C org) in pine needles resisted the chemical oxidation. Based on solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, this C org was assigned to plant waxes. In the fire-unaffected control soils located under pine and oak forests such acid-resistant paraffinic structures accounted for 6 to 22% of C org of the untreated samples. Approximately half of them were removable by a subsequent Soxhlet extraction, clearly demonstrating that their survival is rather explainable by their hydrophobic nature than caused to their chemical recalcitrance. Chemical oxidation of charcoal briquette for 6 h resulted in a survival of 82% of its C org. Beech sawdust BC and grass BC showed lower recalcitrance and only 66% and 40% were recovered. Dipolar dephasing NMR techniques used to elucidate the average protonation degree of the aromatic C of BC demonstrated that the variable reaction to chemical treatment cannot be explained by differences in the condensation degree. Further, after oxidation, the residual aromatic C of the reference chars shows no major decrease of the protonation degree, which contradicts a possible preferential preservation of polycondensed aromatic structures from the oxidative attack. Increasing the treatment time to 24 h, considerably lowered the amount of chemical oxidation resistant elemental carbon (COREC) to 18% for the grass BC and 60% for the charcoal briquette. This confirms that the amount of determined BC varies not only with source material but also relies strongly on the applied oxidation time. Considering further a contribution of non-BC derived paraffinic structures of up to 19 mg g − 1 soil in the fire-unaffected soils, the reliability of BC data of soil organic matter obtained solely by chemical oxidation methods is questionable. Therefore, additional characterization of extraction residue is obligatory. Using solid-state 13C NMR spectroscopy, on the other hand, allowed the identification of BC by signal intensity assignable to aromatic C. However, using this signal as a means for BC-quantification, one has to encounter that chemical oxidation even attacks charcoal BC, which is most tentatively a major reason for BC underestimations in soils investigated by this method.

Revised black carbon assessment using benzene polycarboxylic acids

Black carbon (BC), the ubiquitous stable product of incomplete combustion, is believed to be a potential sink for atmospheric CO 2 and therefore a contributor to the Earth’s radiative heat balance. Nevertheless, analytical procedures to measure BC are inconsistent, giving a non-systematic variation by factors of 14–571 for estimates of its content in soil. We hypothesized that the HCl used to isolate benzene polycarboxylic acids (BPCAs) as markers for BC helps form these compounds, which could then cause an overestimation of the BC content of the soil. We found that indeed up to 90% of BPCA yields may be attributed to this HCl pre-treatment. To correct this error we developed a revised method that uses BPCAs as BC markers but which allows us to eliminate any confusion in the results. This aim was achieved by digestion with 4 M trifluoroacetic acid (TFA). After oxidation with HNO 3, the BPCAs were purified using a cation exchange resin and derivatized to form the trimethylsilyl derivatives. Analyses were performed using a gas chromatograph (GC) equipped with a flame ionization detector (FID); constant linearity was obtained at ⩾7 ng BPCA injection amount and peak purity was determined using mass spectrometry (MS). The recovery of the BPCAs averaged 93.5 ± 5.1% for pure standards and 95.0 ± 3.6% for spiked charred plant material. The contribution of BPCAs from aspergillin to soil organic carbon was estimated to be negligible. No close correlation between the results obtained with the original method and our revised procedure was observed.

Accelerator mass spectrometry dating at Çatalhöyük

Summary Several charred plant and charcoal samples from various stratigraphic levels of the Neolithic Site, Çatalhöyük – Turkey, were dated in the AMS facility of Purdue University (PRIME Lab). Radiocarbon dates reveal a complicated chronology, as was foreseen from archeological investigations. Our measurements suggest that this unique Neolithic town may have been initiated at the East mound around 8390 BP.

Observation of the Charred Plant Particles and Opal Phytoliths Separated from Kurobokudo (Ando Soils) Using Scanning Electron Microscope

Observation of the Charred Plant Particles and Opal Phytoliths Separated from Kurobokudo (Ando Soils) Using Scanning Electron Microscope

Dalginross and Dun: excavations at two Roman camps

Limited excavations at Dalginross, Comrie, Perthshire, uncovered an entrance of the Stracathro type and showed that the camp was of two phases of construction; at Dun, Angus, only the enclosure ditches were identified. There are specialist contributions by Stephen Carter `Micromorphological analysis' (283--5) and Sheila Boardman `Charred plant material' (285, 288--9 & microfiche).