a morphologically-analyzed childes corpus of hebrew

Author's personal copy

Ashes to ashes, charcoal to dust: micromorphological evidence for ash-induceddisintegration of charcoal in Early Neolithic (LBK) soil features in Elsloo(The Netherlands)

D.J. Huisman a,b,*, F. Braadbaart c, I.M. van Wijk d, B.J.H. van Os a

aCultural Heritage Agency, P.O. Box 1600, 3800 BP Amersfoort, The Netherlandsb Leiden University, Faculty of Archaeology, P.O. Box, 9515, 2300 RA Leiden, The NetherlandscUtrecht University, Department of Earth ScienceseGeochemistry, Faculty of Geosciences, Utrecht University, P.O. Box 80021, 3058 TA Utrecht, The NetherlandsdARCHOL, Leiden, P.O. Box, 9515, 2300 RA Leiden, The Netherlands

a r t i c l e i n f o

Article history:Received 14 June 2011Received in revised form23 November 2011Accepted 25 November 2011

Keywords:CharcoalDegradationAshClay illuviationpHLoess

a b s t r a c t

Charcoal and other forms of charred organic material e an important part of the archaeological record e

consist of benzenoids. Such components are unstable in basic or alkaline conditions. Since ashes arealkaline, this means that archaeological charcoal may have been disintegrated and lost if they wereburied together with ashes, e.g. as in fireplaces. Ash may also cause clay translocation in decalcified loessbecause of the disaggregating effect of Kþ ions in the soil solutions. We investigated the interplay of thesetwo processes, using micromorphological samples from the Early Neolithic site at the Joannes Rivius-straat in Elsloo. Evidence for charcoal disintegration was found in the form of cavities in charcoal frag-ments, most commonly filled in with thick reddish limpid clay coatings. The combination of cavities andclay coatings are evidence for the disintegration of charcoal under the influence of ash. Ash may also havebeen instrumental in preserving small bone fragments in these decalcified well-drained loess soils. Theevidence of ash-induced charcoal disintegration implies that charcoal preservation in the archaeologicalrecord is dependent on (1) whether or not is was buried alongside with ashes, and (2) on various soilcharacteristics that determine that determine how quickly the ash-derived alkalinity and potassium ionsare leached.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Fire produces several different products. Total combustion oforganic matter produces ash. Incomplete combustion results in theproduction of charred organic matter. And the heat of the fireresults in transformation processes in various types of materials,including soil and rocks.

Charcoal and other forms of charred organic material form animportant part of the archaeological record. They form the end-product of various types of human fire use, like crop processing,food preparation, land clearance, metal production and heating ofdwellings. Not only does charred organic material indicate thatsuch processes have taken place, the charred remains also providean opportunity to derive which fuels were used, and a means to

dating the material by 14C-dating. Additionally, charred remainsoften are preserved in environments inwhich non-charred remainsdecay.

Charred remains of organic materials are formed when planttissue is heated to temperatures between ca. 400 and 1200 centi-grade in the absence of oxygen. If oxygen is available, the planttissue is completely combusted. The remaining ash containsminerals that had been present in the plant tissue or have beenformed or transformed during combustion. The composition ofashes differs between different types of plant tissue; majorminerals may be Ca and K-(hydr)oxides that usually are quicklytransformed into carbonates. Opal (SiO2) phytoliths also occurregularly in ashes, although strictly speaking they are not ash butplant tissue residue (Canti, 2003; Braadbaart et al., in press).However, in most domestic fires the combustion is not complete,and fragments of charred material remain.

Despite the importance of charred materials for the archaeolog-ical record, basic research into the composition and formation ofcharred remains has only recently become a popular research topic.Up till now, it was generally assumed that charcoal (and other

* Corresponding author. Cultural Heritage Agency, P.O. Box 1600, 3800 BPAmersfoort, Netherlands. Tel.: þ31 33 4217 606.

E-mail addresses: [email protected] (D.J. Huisman), [email protected] (F. Braadbaart), [email protected] (I.M. van Wijk), [email protected] (B.J.H. van Os).

Contents lists available at SciVerse ScienceDirect

Journal of Archaeological Science

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0305-4403/$ e see front matter � 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.jas.2011.11.019

Journal of Archaeological Science 39 (2012) 994e1004


charred remains) consist of pure carbon (e.g. Jones and Colledge,2001; p. 396 and Price, 2007; p. 362). Often, graphite-like micro-structures (e.g. Weiner, 2010; p. 180) are interpreted as representinggraphite proper. Braadbaart and Poole (2008) have shown, however,that the main component of organic remains e woody and non-woody e that have been heated to temperatures between 400 and1200 centigrade is not carbon, but polycyclic aromatic hydrocarbons(benzenoids). Apparently, during the carbonization process, allmajor components cellulose, hemicellulose ande inwoody plantselignin are all transformed into aromatic compounds.

Finding that charcoal does not consist of inert graphite-likecarbon, but of benzenoids, has unexpected consequences. Themost important follows from the fact that benzenes are unstable inbasic or alkaline conditions: According to Braadbaart et al. (2009),plant material heated at temperatures of 310 �C and above andsubsequently exposed to alkaline soil conditions can fragment, andtherefore be lost from the archaeological record. This is a far cryfrom the previous assumption that charred organic materials arecompletely inert. This implies that the absence of charredmaterialsin alkaline soils may be due to fragmentation of previously presentcharcoal. It may even be more severe than that. Plant and wood ashis alkaline because of its contents of Ca- and K-(hydr)oxides. Whenburied in the soil, it will locally cause alkaline conditions. Usually inopen-air sites, this alkalinity is lost relatively quickly because ofleaching of the soluble Ca- and K-(hydr)oxides. Only in very dryconditions, especially cave sites, these components may survive forlonger periods of time, e.g. resulting in the formation of the typicalcalcium carbonate mineral spheroids published by Canti (2003).Because of the instability of charred remains in alkaline conditions,it may well be possible that they degrade or even disintegrate oncontact with alkaline compounds from plant ash. If this is the case,this would mean that charred remains have the greatest chance ofsurvival if they are buried without ash. A potential pH-dependencyof charcoal stability was also postulated by Weiner (2010; p. 183),who found that in Kebara cave, charcoal was most abundant inareas with lower pH. The mechanism he postulates (oxidation byiron and manganese ions) however differs from what we propose.

In this study, we set out to find archaeological evidence that theintroduction of ash into the soil cause the decay of charred remains(like charcoal) buried along with it. Problem is e as stated above e

that the alkalinity-inducing components in ashes (i.e. the Ca- andK-(hydr)oxides) are very soluble and therefore are leached from thesoil readily. In our study we therefore focused on site conditionswhere there is other evidence for ash introduction into the soil, i.e.an Early Neolithic (Linear Pottery Culture/LBK, Modderman phase1c) settlement on decalcified loess deposits. Slager and van deWetering (1977) found that LBK soil features in decalcified loesscontained remarkably thick clay coatings in pores. Such coatingsare formedwhen clay disaggregates, and is transported downwardsin the soil profile by infiltrating water (eluviation). At deeper levelsit precipitates again, and forms coatings (illuviation). The disag-gregation of clays can have several causes including changes insalinity or acidification. In the case of the LBK soil features, Slagerand van de Wetering (1977) attributed the strong abundance ofvery thick coatings to destabilization of clay aggregates due to ash-derived Kþ ions in the soil. If clay disaggregation and charcoalfragmentation both have the same causee i.e. the addition of ash tothe soilewe expect to find charcoal dissolution features associatedwith clay illuviation. If a different process would be responsible forthe clay disaggregation e e.g. acidification e we would expect tofind no correlation provided charcoal disintegration can beobserved. Other processes that may result in coatings of finematerial e e.g. down-profile sorting, post-depositional tillage etc.,would be recognizable because they would not produce clear,limpid but rather dusty clay coatings. Other processes that may

result in fragmentation of charcoal, like backfilling, erosion andredeposition and trampling and down-profile should be recogniz-able by studying the matrix structure in micromorphological thinsections.

To study the interplay of these two processes, we used micro-morphological samples from the LBK site at the Joannes Rivius-straat in Elsloo (The Netherlands, van Wijk et al., 2010; see Figs. 1and 2A). These samples were taken in 2009 as part of a largereffort to investigate the potential for micromorphological researchon soil features. The general idea was to reconstruct properties ofthe site and the surrounding landscape by studying the fill ofvarious types of features (postholes, foundation trenches, pits andditches), and to study the effects that soil processes and humanactivities have on these features.

The 2009 samples were takenwith the goal of studying the fill ofa specific type of pit fill. The pits that lay along the side of buildingson a typical LBK settlement were probably made for the extractionof loam. However, after that they probably had other uses. Such pitsare sometimes filled with reddish layers of heated loam and blacklayers that are very rich in charcoal. It is unclear how these layerswere formed. Theymay e.g. be refuse layers, the remains of an openfire, or the remnants of a pit-oven. The general richness in charcoalmade the pits also useful for studying charcoal fragmentation andits potential association with clay disaggregation. Both issues couldbe studied using micromorphology.

We sampled two large pits next to a house plan (Fig. 2A,B).These pits contained several layers rich in charcoal, and some layerswith reddish colouring because they were rich in of baked soilmaterial or clay (Fig. 2C). We took in total 13 samples for micro-morphological analysis. Additionally, samples were taken forpaleomagnetic research, pH measurement, reflectance measure-ments and handheld XRF measurements. The results of these lattermeasurements will be reported elsewhere, together with a moreextensive description of the thin sections. In this paper, we willfocus only on evidence for charcoal fragmentation and its potentialassociation with clay disaggregation.

2. Materials and methods

The 80 � 80 mm samples were sent to the thin section labora-tory of Stirling University (UK). There, the samples were firstimpregnated with resin. From the impregnated blocks, subse-quently thin sections were sawn, ground, polished and coveredwith a cover slip. The thin sections were studied at the CulturalHeritage Agency in Amersfoort using a Wild 420 macroscope anda Zeiss Axioskop 40 polarising microscope.

3. Results

A general description of the thin sections can be found in Table 1.The general composition of the soil material is a mixture of silt andclay (loam) that is typical for loess. Several of the thin sections (5, 9,10, 13) are very rich in charred plant remains (mostly charcoal), andthe others in general contain at least some fragments. In addition,fragments of pottery and fragments of heated loam occur in somesamples. In samples 7, 9, 10, 13, fragments of bone were found(Fig. 3A,B). Some of these bone fragments show evidence fordegradation, but not all. One piece has been fragmented bya tunneling earthworm. The presence of bone is very surprising,since unburned bone is usually not found in LBK settlements in thisregion due to degradation processes in the oxygenated, neutral toacidic burial environment. There are a few (3) instances of molarsthat were unaffected by heat e possibly from cattle e being foundwithin a settlement context but these are probably only the tooth

D.J. Huisman et al. / Journal of Archaeological Science 39 (2012) 994e1004 995


Fig. 1. Location of research site and other Linear Pottery Culture sites in the Limburg area.

D.J. Huisman et al. / Journal of Archaeological Science 39 (2012) 994e1004996


enamel. Charred bone is found more often but usually in smallconcentrations and heavily fragmented.

The silty groundmass of several of the thin sections showsmany clay coatings in pores, and sometimes in the groundmass. Thecoatings are in general limpid, but may include dusty parts orembedded silt coatings. They are well-oriented with high inter-ference colours. In some of the thin sections, remarkably thickcoatings were observed (Fig. 3C,D,E,F).

In some samples (e.g. 6 and especially 12), domains occur thatconsist only of the silty material that can be found in the loess,whereas the clay fraction is missing. Their groundmass hasa remarkably pale colour (in plain polarized light), which differsconsiderably from the surrounding material, and gives the domainsa leached-out appearance. The morphology of these domains are inaccordance with such leaching having occurred in situ. The siltfraction in the pale areas does not seem to differ from the siltfraction in the surrounding sediment (Fig. 4A,B,C).

Traces of burrowing soil fauna are present in most samples, butsome of the samples (5,7,9,10,13) are very heavily affected. Espe-cially crescent-shaped infillings of earthworm burrows occurfrequently in these samples (Fig. 5A). A considerable proportion ofcharcoal present in these samples is fragmented and taken up inthe crescent-shaped infillings, indicating that they have beeningested and excreted by earthworms. Since earthworm activityseems to have been much more intensive in the samples with highcontents of charcoal, it seems that earthworms were activelyseeking out the charcoal. Such observations have recently also beendone by soil biologists (Dr M. Pulleman, Wageningen University,Pers. Comm.). One of the bone fragments has also been subject toearthworm ingestion and excretion.

Numerous fragments of charcoal that have not been affected byearthworms, are well preserved. E.g. the fragment of charred woodin Fig. 6A,B still retains its wood structure with recognizable vesselsand cell walls. In the vessels of this fragment, some illuviated clay

Fig. 2. A,B Origin of the samples within the Elsloo-Joannes Riviusstraat site. A: Central part of the settlement site, showing the combined results of all published excavations. Thesample area is identified with a red oval. B: Location of the sampled extensive pits, with the associated house plan. The sampled pits are marked with red, and the profiles areindicated. C: Profiles of the pits; sample positions are indicated with an M.


Author's personal copyTa

ble

1Gen

eral

micromorpholog

ical

description

ofthesamples.

Sample

Groundmass

Agg

rega

tes

Structure

Clayilluviation

Iron

precipitation

Biopores

Charco

alBon

e

1Red

dishwithalarge

cavity

(>1cm

across)

fille

din

withlig

ht-

colouredloam

Suba

ngu

larbloc

ky;

wea

klyseparated

Com

mon

illuviated

clay

indom

ains

(upto

15mm

across),possibly

bioturbated

.

eCom

mon

ee

2Brownloam

;alarge

cavity

(1e3cm

across)

isstill

partlyop

en,a

nd

partlyfille

din

with

laye

red,light-co

loured

loam

.

Suba

ngu

larbloc

ky;

wea

klyseparated

Com

mon

illuviated

clay

indom

ains

(upto

15mm

across),possibly

bioturbated

.Som

ein

pores

Inclay

illuviation

dom

ains

Com

mon

Rare

e

3Brownloam

Large(>

2cm

)su

brou

nded

torounded

aggreg

ates

ofmassive

reddishloam

Porous

Thin

tomod

erate

coatings

inpores

eMan

ybiop

ores.

Somemod

erate

(<5mm)ch

arco

alfrag

men

ts

e

4Ligh

tbrow

nloam

withdarkbrow

nan

dreddishbrow

nmottles

Suba

ngu

larbloc

kywithco

mmon

horizon

talplanar

voids.

Com

mon

thin

clay

coatings.

eMan

ycrescent-sh

apes

infille

dbiop

pores,

somerounded

open

biop

ores.

Few

frag

men

tsof

disintegrated

charco

al

e

5Brownloam

with

darkmottles

Verylarge(>

5cm

)su

brou

nded

frag

men

tof

reddishloam

.

Suba

ngluar

bloc

kyCom

mon

illuviated

clay

indom

ains

(upto

15mm

across),

possiblybioturbated

.So

mein

pores

eMan

ycrescent-sh

aped

infillings

ofbiop

ores.

Onezo

newithintense

bioturbation,running

across

thesample

isproba

blyan

oldroot

chan

nel

Largeam

ounts

ofch

arco

alfrag

men

tse

6Ligh

tbrow

nloam

;some

dom

ainsve

rypale

Somesu

bangu

lar

bloc

kyag

greg

ates

ofreddishloam

Porous

Com

mon

clay

coatings

inpores

andin

grou

ndmass

eMan

ycrescent-sh

apes

infille

dbiop

pores,som

erounded

open

biop

ores.

Com

mon

charco

alfrag

men

ts

e

7Brownloam

Man

yrounded

agrega

tesof

reddishloam

Porousto

wea

kly

separated

suba

nkg

ularbloc

ky

Man

yclay

coatings

inpores

andin

grou

ndmass

eMan

ybiop

ores.

Com

mon

charco

alfrag

men

ts

Seve

ralbo

ne

frag

men

ts.

8Ligh

tye

llowish-

brow

nloam

Porous

Clayco

atings

arerare

Someiron

and

man

ganese

precipitation

Man

ybiop

ores.

ee

9Grey-brow

nloam

Com

mon

clay

illuviation,

locally

very

thick

coatings

(upto

4mm).

eMan

ycrescent-sh

aped

infille

dan

dop

enbiop

ores;somelarger

(upto

10mm

across).

Largeam

ounts

ofch

arco

alfrag

men

tsdistributed

heterog

eneo

usly

through

outthe

grou

ndmass

Seve

ralbo

ne

frag

men

ts

10Grey-brow

nloam

withex

trem

ely

largeam

ounts

ofch

arco

alfrag

men

ts

Oneex

trem

ely

largefrag

men

t(>

5cm

)of

reddishloam

Porousto

very

wea

kly

separated

amgu

larbloc

ky

Com

mon

clay

coatings

inpores

andcracks.

Com

mon

dom

ains

(upto

15mm

across);

possiblybioturbated

.Lo

cally

very

thick

coatings

(upto

5mm).

eMan

ycrescent-sh

aped

infille

dan

dop

enbiop

ores;somelarger

(upto

10mm

across).

Onelargepartly-fille

dbu

rrow

(15mm

across).

Verylargeam

ounts

ofch

arco

alfrag

men

tsan

dparticles,

heterog

eneo

usly

distributed,p

ossibly

laye

red.

Seve

ralbo

ne

frag

men

ts

11Red

dishmottled

loam

Wea

klyseparated

aggreg

ate

Clayco

atings

arerare

eSo

mebiop

ores.

Afew,p

artly

disintegrated

large(upto

20mm)

charco

alfrag

men

ts

e



can be recognized. Sporadically, charcoal fragments showan overallpreserved wood structure, which at larger magnification appears tobe in the process of fragmenting (Fig. 6C,D). Frequently, charcoalfragments show cavities that seem to have formedwithin the woodstructures. All these cavities without exception are filled in by claycoatings. These cavities may sometimes be associated with cracksor channels that run through charcoal (Fig. 6E,F). More often theyare unconnected and spherical to mammilate in form (Fig. 6G,H). Insome cases, parts of the charcoal fragments seem to have beenreplaced completely by clay, whereby the original wood structureof the charcoal has been retained (Fig. 6I,J). The charcoal-richsamples do not only contain charcoal in the form of recognizablefragments, in various stages of fragmentation: In their groundmass,ample fine fragments of charred material are present. This materialdoes not contain any recognizable organic structures, but consistsrather of sand to silt-sized, irregular to rounded particles (Fig. 6K).

4. Discussion

Two very different processes seem to have been active in the soiland the soil features of the Elsloo site. One is the formation of claycoatings in pores and other cavities, the other is the formation ofcavities in charcoal, that are subsequently filled in with claycoatings.

Clay coatings may be formed by various processes. The relativelyclear coatings without silt or dust, as we see in our samples, aretypical for soils where the clay disaggregates, and is transporteddownwards with percolating water. The disaggregation of clay infreshwater soil environments can occur when polyvalent ions likeCa2þ or Mg2þ on the clay minerals’ cation exchange complex (CEC)are replaced by monovalent ions like Hþ, or Kþ. Such clay transportis a fairly common process when soils acidify (van Breemen andBuurman, 2002). Alternatively, clay coatings may form when claydestabilizes due to Kþ from when that is added to the soil (Slagerand van de Wetering, 1977; Courty et al., 1989).

In the region, the presence of clay coatings is therefore wellknown from fine-grained soils without human influence. Accordingto Miedema (1987), the formation of clay coatings was mainlyactive during the late pleniglacial, and has stopped in the earlyHolocene. The pits and soil features on the Elsloo-Riviusstraat sitewere dug through a Bt-horizon, i.e. a soil horizon that was formedby clay illuviation. When compared to these “natural” coatings, theclay coatings in the archaeological features are thicker and morereddish in colour. Following Slager and van deWetering (1977) andCourty et al. (1989), we assume that the addition of ash to the soil,and the release of Kþ from the ash has been an important factorhere also. The red colour of the coatings may tentatively be linkedto dissolution of iron (hydr)oxides due to the high alkalinity of ashfollowed by crystallization and precipitationwith the clayminerals.This would also explain the grey domains that seem leached: Inthese domains, along with the clay eluviations, iron may havedissolved under alkaline conditions, and precipitated lower in theprofile at the clay coatings.

Fragmentation of carbonized material that resulted fromtrampling or biological activity common in thin sections fromarchaeological sites. However, the disintegration and post-burialfragmentation features that we found in charcoal from Elsoo e

Riviusstraat have not been previously been identified in thinsections. Fig. 6A,B gives the appearance of charcoal that iscommonly observed. We assume that the cavities that we haveobserved in charcoal fragments were formed under the influenceof ash-related alkalinity, resulting in dissolution processes. Thefoci of dissolution are local, which is explained by an inhomoge-neous e pore distribution-dependent e transport of Kþ throughthe soil profile. The infilling of the cavities with clay coatings may

12Ligh

tbrow

nloam

;disco

ntinuou

slaye

r(ca.

2cm

thick)

show

sve

rypaleco

lour

Stronglyseparated

towea

klysaparated

aggreg

ate

Clayco

atings

common

inpores

andgrou

ndmass

eFe

wbiop

ores.S

ome

faecal

pellets

ininteragg

rega

tevu

gh.

Few

charco

alfrag

men

tse

13Darkb

rownloam

Porousto

wea

kly

separated

aggreg

ate

Clayco

atings

common

inpores

andgrou

ndmass.

Veryfew

dom

ains(upto

10mm

across)possibly

biotuba

ted.

eMan

ycrescent-sh

aped

infille

dan

dop

enbiop

ores.

Verylargeam

ounts

ofch

arco

alfrag

men

tsan

dparticles,

heterog

eneo

usly.

Seve

ralbo

ne

frag

men

ts

14Red

dishmottled

loam

Wea

klyseparated

aggreg

ateto

wea

klyporou

sClayco

atings

arerare

eSo

mebiop

ores.

Afew

charco

alfrag

men

tse



reflect the common origin of both processes: Ashes introducedinto the soil cause alkalinity which promotes the dissolution ofcharcoal and the formation of cavities, whereas the ash-derivedKþ causes clay to disperse and to form limpid clay coatings. Thesporadic fragmentation of charcoal where no clay illuviation ispresent (e.g. Fig. 6C,D) may have been caused by other processes(e.g. trampling) or it may demonstrate Kþ availability did notcause with clay disaggregation.

The presence of (small) bone fragments in some samples issurprising: The LBK settlement sites on decalcified loess in the

Netherlands have up till now never yielded preserved bonematerial,with the exception of a few bovine teeth (may be only tooth enamel).In the burial ground associated with the Elsloo LBK settlement at theJoannes Riviusstraat, the inhumation burials contained only anoutline or a silhouette of the body (Modderman,1970). The relativelylarge amount of observed bone fragments that we found, and theirposition in the deeper layers of the pitewhereas no bone fragmentswere observed occur in the shallower layers e makes it highlyunlikely that they are more recent bones that were transported todepth by bioturbation. Bone readily degrades in burial environments

Fig. 3. A,B Bone fragments. A: Well-preserved bone that has been fragmented, ingested and excreted as crescent-shape infilled burrow by soil fauna, probably worm (cf. Fig. 5).B: Degraded bone fragment. Part of the bone mass has disappeared due to degradation processes. CeF: Examples of clay coatings in Elsloo (plane polarized light, unless specifiedotherwise; XPL ¼ crossed polarized light). C, D (XPL): Typical thick multilayered reddish clay coating e indicated by “c” - in pit (Sample 3). E, F (XPL): Compound clay coatings nextto a pore, showing multiple layers of silt - one indicated by arrows in E � in between thick pure clay coating. This coating is not reddish (Sample 10).



that are not lime-buffered and oxygenated. This explains the verycommon absence of well-preserved bone in the LBK sites in theNetherlands, and it explains why some of the bone fragmentsobserved in the Elsloo thin sections show evidence for degradation.It does not explain how most of these fragments could survive c.7000 years of burial in an aggressive soil environment without

evidence for microbial decay. One possible explanation is that thesoil pH has been affected by ash addition e causing alkalinity e andhas recovered only slowly. This is, however, difficult to corroborateespecially since the modern soil pH-values have probably beeninfluenced by later land-use and liming. Still, Courty et al. (1989)describe a comparable situation where the dumping of ash in

Fig. 4. A: Scan of thin section no. 12, showing a large domain with a bleached appearance e indicated by the arrows. B,C: Boundary between silt with bleached appearance (b)and non-affected soil mass (s) in sample 12. The size and amount of silt-sized grains does not change across the boundary, but the fines are missing in the light-coloureddomains.

Fig. 5. A,B Trace of soil faunal burrow with crescent e shaped infilling containing fragments of charcoal, clay coatings and clay aggregates that are dislocated remains of claycoatings. Probably made by an earthworm (Sample 5).



a Neolithic soil feature resulted in clay disaggregation and a pHincrease that in modern times was still measurable (pH 7 in the pits,whereas the surrounding soil had pH 4).

The combination of clay coatings and evidence for charcoaldissolution may be a feature that occurs only rarely. If ash andcharcoal get buried under more basic conditions or in less perme-able soils, the charcoal may get degraded without leaving much

trace. Maybe the “charcoal powder” that is sometimes reported inthin sections from archaeological sites (and macroscopically;Weiner, 2010; p. 183) is a product of such conditions. If ash andcharcoal become buried under more acidic conditions, or in morepermeable soils, the Ca2þ and Kþ may become leached and alka-linity buffered so quickly that the charcoal is notmuch affected, andfragmentation may be less likely. Especially under such conditions,

Fig. 6. A,B (XPL): Well-preserved charcoal fragment, with recognizable wood structure. Some clay coatings e indicated by arrows e are present in vessels (Sample 3). C,D (Detail):Charcoal fragment showing evidence for fragmentation. The overall shape of the fragment is still recognizable, as are the shapes of the original wood vessels (arrows in C and “V” inD). Also, some of the wood cells are recognizable (immediate surrounding of “c” in D). However, the interior structure is broken up into a multitude of small fragments (Sample 6).E,F (XPL): Detail of charcoal fragment showing longitidunal fissure with side-cavities, filled with illuviated layered clay. The clay contains layers with numerous very small charcoalfragments (e.g. the one indicated by an arrow) (Sample 3) G,H (XPL): Charcoal fragment with large cavities with layered clay infillings. The central, irregulary shaped cavity is onlypartly filled in (Sample 10). I,J (XPL): Charcoal fragment showing extensive loss of charred material, which is replaced by clay. In the right side of the fragment, the illuviated clayseems to form pseudomorphic shapes after the original wood structure. (Sample 10). K: Soil mass with fragments of charcoal of various sizes. No recognizable wood structure is left,and the material is for a significant part disintegrated into micron-scale fragments (Sample 3).



the common interpretation of trampling and wetting-drying cycliremains a likely cause of fragmentation.

5. Conclusions

The LBK soil features sampled in contain many fragments ofcharred organic material (mostly charcoal) with clay-filled cavities.These cavities were probably formed by fragmentation of thecharred material under ash e induced potassium-rich alkalineburial conditions. The presence of ash also caused extensivedispersion and redeposition of clay within the soil profile, fillingpores, cracks and cavities.

Fragmentation of charred material by ash introduction into thesoil is probably a common, but often overlooked phenomenon. It is,however, difficult to assess whether or not such processes havebeen active. In some cases, all charred material may have beendegraded whereas in other cases the active components in the ashleached before it could do much damage.

Acknowledgements

Wewould like to thank GeorgeMacLeod from Stirling Universityfor preparing the thin sections used in this study. We also wouldlike to thank Ricardo Fernandez (now at Kiel University) for

Fig. 6. (continued).



assistance during fieldwork. Three anonymous reviewers arethanked for their comments.

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a morphologically-analyzed childes corpus of hebrew

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