Experimental Archaeology As a Resource for Approaching Formation Processes of Seed As- Semblages

Experimental archaeology as a resource for approaching formation processes of seed assemblages. First results and future perspectives

Ferran Antolín Tutusaus CSIC-IMF. Laboratori d’Arqueobotànica, Departament de Prehistòria,Universitat Autò- noma de Barcelona. [email protected] RESUM El propòsit d’aquest article és obtenir una primera aproximació a certs processos de formació del registre arqueobotànic.

Per a aquest experiment s’ha treballat amb dues species: Triticum aestivum s.l. (5130 restes) i Lens culi- naris (1478 restes). El primer objectiu és avaluar com la combustió afecta les diverses propietats de les granes quan conjunts de restes són exposats a les mateixes condicions controlades. El segon és comparar dos contextos deposicionals: un en el qual les restes quedin exposades a les condicions atmosfèriques i un altre en el qual s’enterri les restes en fosses. Finalment, es pretenen analitzar els efectes produïts en les granes per l’ús de diferents tècniques de recuperació: excavant amb un paletí o amb un tornavís; i tractant el sòl per flotació o mitjançant el rentat per columna de garbells.

S’ha utilitzat un sistema de caracterització resta-per-resta per tal de descriure tots els canvis en les propietats de les granes després de cada fase de l’experiment. La carbonització de conjunts de diferent quantitat mostra algunes diferències que haurien de ser tingudes en compte quan s’interpreta el registre arqueolò- gic.

Paraules Clau: arqueologia experimental; processos de formació; carbonització; tècniques de recuperació de les mos- tres ABSTRACT The aim of this paper is to have a first approach to certain formation processes of the archaeobotanical record.

For the first experiment I worked with two species: Triticum aestivum s.l. (5130 items) and Lens culina- ris (1478 items). The first objective is to evaluate how charring affects the several properties of the grains when big assemblages are exposed to the same controlled conditions. The second one is to compare two different depositional contexts: leaving the grains exposed to open air conditions and burying the assemblage inside pits. Finally, I aimed to analyze the effects produced on the grains by using different recovery techniques: excavating with a trowel or with a screwdriver; and treating the soil by flotation or by water-sieving.

A seed-by-seed characterization system was used in order to describe all the changes in the properties of the grains after each stage of the experiment. Charring of assemblages of different quantity of grains shows some differences that should be considered when interpreting the archaeobotanical record.

Keywords: experimental archaeology; formation processes; charring; sample recovery techniques

Rebut: 12 febrer 2011; Acceptat: 21 octubre 2011

35 Estrat Crític 6. (2012): 35-48 Experimental archaeology as a resource for approaching formation processes of seed assemblages.

1. Introduction (such as the quantity of oxygen present Experimental works with grains have a in the environment, moisture content, long tradition in archaeobotany. Most etc.). And, as Wilson said, the process of them have concentrated on the ef- of carbonization is rarely uniform when fects of charring on seeds and fruits in dealing with big concentrations of order to register their morphological grain. and chemical modifications or their chances of preservation (see, for ins- Recent works have quite successfully tance, Wilson, 1984; Boardman and intended to find correlations between Jones, 1990; Gustafsson, 2000; Jaco- some properties of grains (size, shape met 2003; Wright, 2005; Märkle and and reflectance) and the heating tem- Rosch, 2008; Sievers and Wadley, perature to which the items were expo- 2008, among others). Moreover, seve- sed (e.g. Braadbaart, 2008; Braadbaart ral experiments have been undertaken et al., 2004). Such approximations are in order to compare different systems an excellent starting point for a new of sample recovery and processing (for methodology that allows establishing example, Wagner, 1982; Moulins, the thermal history of carpological as- 1996; Wright, 2005). Nevertheless, semblages. On the other hand, one va- other taphonomic agents, such as ero- riable has not been deeply considered: sion, transportation, soil pH, trampling the quantity of grain that is being cha- or bioturbation, have rarely been eva- rred. We cannot assume that the results luated. observed in single-grain experiments can be used for the interpretation of If carbonization has been the target of large assemblages like the ones found so many studies, why should we keep in archaeological sites. on experimenting? As Wilson (1984) wrote, “(…) Any single heating episode The experiment that is being presented in antiquity is thus likely to have left in this paper deals with three different some seeds uncarbonized, whilst car- taphonomic agents: first of all, carbo- bonizing others, while others again will nization, in order to understand not have been burned to destruction”. only single-grains’ reactions to heating Such statement summarizes the com- conditions but mainly grain assembla- plexity of the carbonization process. As ges’ reactions; secondly, the depositio- the above mentioned experiments have nal context, comparing the effects on already demonstrated, seeds and fruits the properties of grains after being bu- get carbonized at different temperatu- ried for one month as opposed to being res and after different periods of time, exposed to open air conditions; and fi- depending on several other variables nally, the system of recovery of the re-

Estrat Crític 6. (2012): 35-48 36 F. Antolín Tutusaus mains on the one hand, the excavation ving process was registered. The items tool used (trowel or screwdriver) and, come from one of the samples that on the other hand, the soil processing were collected after the last stage of method (flotation or water sieving). processing (fine sieving). For what This experiment is intended to be the concerns this paper, it should be speci- first one of a long series that aim to co- fied that a threshing sledge and a thres- rrelate the state of the properties of the hing stone were used, both being pulled grains that we recover in the archaeo- by a horse (see figure 1). logical record with the formation processes that originated them. The experiment consisted on several phases: charring under controlled con- 2. Materials and methods ditions, deposition of the grains for one A total number of 6,618 items were month and recovery of the grains. At chosen for this experiment. The assem- every stage of the experiment a com- blage contained hexaploid naked wheat plete seed-by-seed description was ca- grain (main component) and chaff, rried out in an Excel spreadsheet. The some barley spikelets and lentil seeds. variables that have been considered are Lentils were simply bought at the su- the following (for a complete definition permarket. More interestingly, the ce- see Antolín, 2010; Antolín and Buxó, real remains were collected in 2008 2011a): taxon, part represented, num- during the “Festa del segar i del batre” ber of remains, type of preservation, (Harvesting and Threshing fair) from number of parts (for instance, the num- La Fuliola (Lleida, Catalonia), where a ber of grains in an aggregate), frag- demonstration of traditional threshing mented part, state of preservation of the techniques takes place every year. The pericarp, type of fragmentation, pre- whole threshing, winnowing and sie- sence/absence of shiny surface, adhe-

Figura 1.- Threshing activities in La Festa del Segar i del Batre in La Fuliola (Lleida, Catalonia) (Pictures: Maria Bo- fill).

37 Estrat Crític 6. (2012): 35-48 Experimental archaeology as a resource for approaching formation processes of seed assemblages. rence of the embryo, presence/absence cm). They were heated at 150ºC for 20 of germinated embryo, presence/ab- minutes, then at 180ºC for 60 minutes, sence of morphological changes due to at 200ºC for 40 minutes and finally at the effects of charring, evidence of me- 250ºC for 45 minutes. chanical activities (for example, crac- 3. Weathering: the possible ef- ked grains due to processing activities). fects of exposing the grains to open air This time-consuming method aims to conditions were analyzed by leaving get quantitative data to provide patterns the grains exposed to weathering for on the state of the properties of the seed one month (from mid-December 2009 and fruit record after a long series of to mid-January 2010). experiments that the author is currently 4. Depositional context: the undertaking. vertical and horizontal distribution of the grains was limited by digging five A number of variables have been con- different pits, each one treated as a dif- sidered of major importance for the ex- ferent unit of analysis (see the point periment: below). Four of them were re-filled with soil after depositing the grains and 1.Composition of the assem- one was left open. Soil pH was measu- blage: it is essential for our purpose to red. have a complete description of the 5. Recovery and processing composition of the assemblage at every techniques: two systems have been stage of the experiment in order to state compared, excavation with a trowel the consequences of every taphonomic and with a screwdriver. Likewise, the agent on it. Thus, three descriptions effects of flotation and water sieving have been undertaken: one at the be- were analyzed. In order to be able to ginning of the experiment, another after compare the different possibilities of the heat treatment and one more after combination of the soil recovery and the deposition and recovery of the the soil processing techniques, 4 diffe- grains. rent pits were dug, making all combi- 2. Charring: for this study, a nations possible (excavating with the SELECT-HORN J.P.SELECTA muffle trowel and flotation, excavating with from the Inorganic Chemistry and the screwdriver and flotation, etc.). Flo- Analytic Chemistry Laboratory of the tation and water-sieving were carried University of Lleida was used in order out using a sieve of a 1 mm mesh size. to control the heating temperature. The The soil samples were measured and grains were put between two layers of soaked in water before processing, as sand (to create an anoxic environment) we usually treat our archaeobotanical in two aluminium trays (16x11x3.5 samples.

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Figura2.- Description of the initial assemblage: taxa, part represented and number of items per group.

3. Results Initial description of the assemblage

A total number of 6,618 items were identified and described (see figure 2). Of those, 5,130 remains belonged to naked wheat, mostly grain (fig. 3a) but also 58 rachis fragments (fig. 3b). 1,478 were lentil seeds and 11 were hulled barley spikelets (fig. 3c). The latter can be considered as contamina- Figura 3.Photos of the assemblage before charring: a tions of the wheat harvest that survi- naked wheat grains; b naked wheat rachis fragments; c barley grains; d fragments of naked wheat grains; e ved until the last stage of processing. cracked grains of naked wheat; f naked wheat grains 100% of the remains had an intact sur- with peeled or abraded surface; g lentil cotyledon and fragment of cotyledon; h lentil seeds with different sta- face and grains still had the embryo tes of preservation of the testa. and apical hairs. 4 grain fragments The whole assemblage was split in two were found (fig. 3d), 9 grains had been parts (see figure 2): one with 5111 re- cracked during threshing (fig. 3e) and mains which were destined to be bu- 2 had been slightly peeled/abraded ried in 4 pits (Group 1), while the other (fig. 3f). As for the lentils, 4 cotyledon one contained 1507 remains that were fragments and 7 loose cotyledons were to be exposed to open-air conditions counted (fig. 3g). Most of the lentil (Group 2). These two groups would seeds had an intact testa (93,7%), but a allow a first comparison of the effects small percentage (4,9%) presented a of charring on grain assemblages of slight fragmentation of the testa, while different size. less than 2% of the items showed gre- ater affectation (fig. 3h).

39 Estrat Crític 6. (2012): 35-48 Experimental archaeology as a resource for approaching formation processes of seed assemblages.

Description of the assemblage after charring

Charring had different effects on both assemblages. At a general level, the vo- lume of the assemblage doubled, from 190 ml before charring to 380 ml after charring. Swelling of the grains was observed in all taxa. The grains from the smaller assem-

Figura 5. 5 Photos of the most relevant consequences of charring observed on the grains: a incompletely charred naked wheat grains; b swelled lentil seeds with broken testa; c incompletely charred lentil seeds with intact testa; d incompletely charred barley grains; e popped naked wheat grain; f naked wheat grains Figura 4. Degree of carbonization of the grains be- with protrusions; g distorted barley grains; h lentils longing to Group 1. Values 1 to 4 with an ordinal with cracked surface and split cotyledons; i naked value, being 1 “completely charred” while 4 refers to wheat grain aggregates; j naked wheat grain fragment only “slightly charred” . after charring; k cracked naked wheat grains after charring; l single lentil cotyledon and fragments of cotyle- blage got completely charred but the don. ones from the larger one presented dif- 14,65% of the cereal grains of the big- ferent degrees of carbonization. The ger assemblage are popped or show results of the latter are presented in fi- protrusions (see fig. 5e and 5f), while gure 4. Around 12% of the remains 17,73% show these features in the showed signs of not being completely smaller assemblage. All the barley carbonized (fig. 5a). Chaff fragments grains from the smaller assemblage were completely carbonized in Group showed severe distortions (see fig. 5g). 2 but 12% of these remains in Group 1 The percentage of popped seeds of were also only partially carbonized. free-threshing wheat is very similar 100% of the lentil seeds from Group 1, among both groups (see Figure 6). but less than 70% in the bigger assemblage, appear with a broken testa (see Lentils also show some affectation due fig. 5b). The remaining percentage of to the exposition to high temperatures: lentil seeds from Group 2 appears with cracking of the surface and cotyledon an intact testa (see fig. 5c). Most of the splitting (see fig. 5h). The first one is barley grains were totally charred but characterized by clear cracks on the two of them presented only slight signs seed surface, whereas the second one of carbonization. Glumes were preser- consists in the opening or splitting of ved in intact conditions (see fig. 5d). the edges of the cotyledons without se-

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Figura 6. Number and percentage of popped grains and grains with protrusions of Group 1 and Group 2 after the heat treatment . parating completely. Both phenomena gregate is also higher in Group 1 (see are often found in the same seed: 6 fig. 8). These aggregates are generated seeds (one from Group 1 and 5 from due to the explosion of the endosperm Group 2) show evidences of cracking; of the grains. of these, only one from Group 2 does not present split cotyledons. There are no cases of seeds with split cotyledons that do not show cracks on the surface.

Aggregates of grains are present in both assemblages (fig. 5i). The percentage is a bit higher in Group 1 (see Figura 7. Absolute number and percentage of aggre- fig. 7) and the number of items per ag- gated grains per taxon and per group.

Figura 8. Number of aggregates according to the number of grains of each aggregate in each group.

41 Estrat Crític 6. (2012): 35-48 Experimental archaeology as a resource for approaching formation processes of seed assemblages.

Figura 9. Photos of the most relevant consequences of the deposition and recovery of the grains: a decomposing naked wheat grain; b reticulate pattern of the inner side of a charred lentil cotyledon; c plain surface of the inner side of a lentil cotyledon separated after charring; d concretions produced on naked wheat grains from Group 2 Grains that had suffered fragmentation Final description or cracking during threshing were cle- arly detected after charring (fig. 5j). No seed-by-seed description was un- Characteristic bulging sections, such as dertaken for the final description of the the ones described by other authors assemblage since the general affecta- (e.g. Valamoti 2002), have appeared on tion of the remains was very low. Ge- the caryopsis fragments produced du- neral qualitative appreciations are ring threshing. Cracked grains are not given. always easily identified, since they can be mistaken for grains with protrusions. No erosion or degradation was obser- Usually, the grain splits at the hilum ved on the surface of the grains. Hairs part and popping of the endosperm is and embryos remained attached to the visible (see fig. 5k). Peeled/abraded grains. One grain from Group 1 already grains can be detected by the straight started to decompose (fig. 9a). cut that can be observed on the grain and the subsequent popping of the en- An extremely low number of fragments dosperm due to charring, leaving a occurred as a result of the process of re- smooth and shiny surface. covery of the grains. These were only produced in the samples that were tre- Fragmentation prior to charring is more ated by water-sieving: 3 items in total difficult to detect on carbonized re- (see figure 10). In all cases, the section mains of lentil, at least when fragments of the fragments is of irregular type are exposed to the heat treatment that (uneven). we have applied. Post-charring fragmentation usually shows a more porous Some lentils were fragmented into two surface, while fragmentation produced cotyledons. As can be observed in fig. prior to charring presents a compact, 9b and 9c, cotyledons that were already shiny surface (fig. 5l). separated when exposed to high tem-

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Figura 10. Recovery techniques applied to the different pits in which grains were covered with soil during the experiment. Soil pH of and the number of caryopsis fragments are presented peratures show a clear reticulate pat- as consequences of the processing tech- tern on their surface. Such pattern is niques. It was observed how a thres- not observed in the ones that separated hing board and a threshing stone were after the heat treatment. used in La Fuliola. Thus, it is highly possible that the types of features we Group 2, which was not covered with have observed on the grains are asso- sediment, had some new soil naturally ciated with such aggressive techniques. deposited, which resulted in the for- Still, it should be a matter for future re- mation of concretions that affected the search, since we should not rule out the grains (fig. 9d). Also some grains were possibility that other threshing techni- involuntarily displaced by snails. ques, such as animal trampling, could cause the same effects on the grains. 4. Discussion We must consider, then, that some frag- Some interesting elements for further mentation and cracking of the grains discussion can be drawn from this ex- can be expected in large grain assem- periment. blages and it does not need to be the result of any type of culinary process On the initial assemblage (such as the making of bulgur). It is also interesting to know that such ag- There are elements in the composition gressive threshing techniques did not of the initial assemblage, especially cause damage on the surface of the concerning the cereal remains, that can grains and that the embryos (often lac- be related to the threshing techniques king in archaeobotanical assemblages) applied during the wheat harvest. also remained attached to the grains after all the threshing, winnowing and The presence of cracked and pee- sieving process. led/abraded grains along with fragments of grains should be interpreted The presence of hulled barley shows

43 Estrat Crític 6. (2012): 35-48 Experimental archaeology as a resource for approaching formation processes of seed assemblages. how its spikelets can survive as conta- ours. The formation of aggregates is minants until the very last stage of the probably linked to the present number cereal threshing process. In an ar- of grains. The possibilities of aggregate chaeological case, such low percenta- formation increase when assemblages ges of barley could respond to different are bigger. Since aggregates are formed practices. Maslins, for example, are fre- due to the explosion of the endosperm quently separated during sieving (see out of the grains, sticking to nearby Jones and Halstead, 1995), which is un- items, they are fragile and we should likely to produce two perfectly separa- consider the possibility that they don’t ted different products. In this case, if survive as such in the archaeobotanical one had harvested naked wheat and record. This variable is, then, less relia- barley the final product would be one ble than others. Around 5% or less of assemblage of barley with some wheat the items form aggregates in the hea- grain contaminations and one wheat ting conditions that we have created. grain assemblage with barley intru- sions. Uncharred grains can appear together with grains with protrusions. Thus, the About the heating treatment process sole presence of grains with protrusions in an archaeological assemblage does- The quantity of grains exposed to the n’t ensure that it was completely cha- heating treatment is an important va- rred and preserved. One should assume riable in the charring process. Different that our assemblages are hardly ever results are to be expected, being the the same deposit that once was expo- smaller assemblages more likely to be- sed to heat. The bigger the assemblage come completely charred, while bigger the higher are the possibilities of ha- assemblages would need a much lon- ving incompletely charred wheat grains ger exposition to heat in order to show and chaff. In our case, around 12% of a homogeneous degree of carboniza- the wheat remains of the original depo- tion. sit of Group 1 would have not survived in a dry site for a long time, at least in Popping of the grains and the appea- a recognisable way. The percentage rance of protrusions seems to be more rises up to the 30% when considering frequent in the smaller assemblage, lentil seeds. These results confirm that while most aggregates appear in the charring of lentil seeds is possible at bigger one. In any case, percentages low temperatures, but also that lentil under 20% are to be expected when as- seeds can be more seriously underre- semblages are charred at low tempera- presented in the archaeological record tures and at low heating rates such as than cereals.

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Lentils have high possibilities of losing On the applied recovery techniques their testa due to charring since the swelling of the cotyledons fragments it. No differences have been observed Some lentils showed cracks on the sur- when comparing excavation with face or split cotyledons. These effects screwdriver or with a trowel. The soil were more frequent in the smaller was too loose due to the short time of group. Nevertheless, the number of af- exposition. Thus, grains were not frag- fected seeds was very low. mented during excavation.

Barley spikelets can completely distort Concerning the washing method, at low temperatures and if it wasn’t for water-sieving is probably more aggres- the good preservation of the glumes sive to grains than flotation, but no de- they would be unidentifiable. finite conclusions can be drawn from our experiment. On the context of deposition 5. Conclusions and future perspecti- Formation processes have had very lit- ves tle effect during the period of deposi- The experiment that we have presented tion, recovery and processing of the in this paper is of great interest for remains. Covering the grains with soil everyday archaeobotanical analyses. actually protected them and the soil Taphonomy is an essential part in the was still very loose when excavation analysis of the seed and fruit record and took place, which resulted in a very low our discipline still has a long way to go fragmentation rate. compared to others such as archaeozo- ology. Short-term exposition of grains to open-air conditions can leave no traces It has been shown how the quantity of but the formation of soil concretions. grain must be considered as an impor- This is an interesting feature that will tant variable during charring. A seed- be targeted in future experimentations, by-seed description of the assemblage since recognizing exposition of the under study seems the best option in grains to open-air conditions and natu- order to get quantified data to work ral sedimentation is important to un- with. This description can help us to get derstand the taphonomy of an a rough approximation to the heating assemblage. temperature to which the assemblage was exposed (some first attemps on archaeobotanical materials can be seen in Antolín and Alonso, 2009; Antolín and

45 Estrat Crític 6. (2012): 35-48 Experimental archaeology as a resource for approaching formation processes of seed assemblages.

Buxó, 2011a; Antolín and Buxó, This researcher is funded by the Jae 2011b). Program of the CSIC, within the fra- mework of the consolidated group The possibility of detecting the effects AGREST (2009 SGR 734, AGAUR). of certain types of threshing techniques Thanks to Natàlia Alonso and Jordi on the state of the properties of the Voltas for helping with the charring of grains is also of interest and should be the grains. Also to Andrea Balbo for ge- targeted in future ethnographical and oarchaeological advice. Special thanks experimental works. also to Oriol López and Débora Igle- sias for the digging and picture taking. Our experiment doesn’t allow definite Finally, I would like to thank Núria for conclusions on the depositional context the comments on this paper. and the recovery techniques applied. References For the improvement of future experi- ANTOLÍN, F. (2010): Les propietats ments several observations must be del registre carpològic: el punt de par- highlighted. tida per a l’estudi de la seva represen- tativitat arqueològica, Cypsela, 18, • In order to obtain some patterns of af- 299-306. fectation of the assemblages, several other carbonization experiments should ANTOLÍN, F. & ALONSO, N. be carried out both repeating the heat (2009): A Mourela (As Pontes, A Co- treatment applied in this experiment ruña): evidencias carpológicas de las and also at other temperatures and he- prácticas de roza y del procesado y ating rates, always comparing at least consumo de cereales en el monte ga- two different volumes of grain. llego (siglos VII-XVII), in BONILLA, A. & FÁBREGAS, R. (eds.), Círculo • Covering of the grains with soil for a de engaños. Excavación del cromlech short period doesn’t generate a typical de A Mourela (As Pontes de García Ro- archaeological consolidated layer. dríguez, A Coruña), (pp, 57-68). San- Thus, possible fragmentation is mini- tiago: Andavira. mized and the whole experiment fails. This period should be increased and it ANTOLÍN, F. & BUXÓ, R. (2011a): would probably be more interesting to Proposal for the systematic description let the pits fill naturally with soil and and taphonomic study of carbonized eventually excavate them in order to re- cereal grain assemblages. A case study produce a more realistic situation. of an early Neolithic funerary context Acknowledgements in the Cave of Can Sadurní (Begues,

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