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EthnoarchaeologyJournal of Archaeological, Ethnographic and Experimental Studies

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Geo-ethnoarchaeology of Fire: GeoarchaeologicalInvestigation of Fire Residues in ContemporaryContext and its Archaeological Implications

David E. Friesem

To cite this article: David E. Friesem (2018): Geo-ethnoarchaeology of Fire: GeoarchaeologicalInvestigation of Fire Residues in Contemporary Context and its Archaeological Implications,Ethnoarchaeology, DOI: 10.1080/19442890.2018.1510616

To link to this article: https://doi.org/10.1080/19442890.2018.1510616

Published online: 24 Aug 2018.

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Geo-ethnoarchaeology of Fire: GeoarchaeologicalInvestigation of Fire Residues in Contemporary Context and itsArchaeological ImplicationsDavid E. Friesema,b

aMcDonald Institute for Archaeological Research, University of Cambridge, Cambridge, UK; bZinman Instituteof Archaeology, University of Haifa, Haifa, Israel

ABSTRACTGeoarchaeology focusing on microscopic and chemical remains hascontributed greatly to the study of archaeological fire. One of themethodological approaches geoarchaeologists have adopted inthe last two decades is the use of ethnoarchaeology to collectreference materials and construct models for how fire residues areformed and preserve or deteriorate in the archaeological record.Geo-ethnoarchaeology uses contemporary contexts to investigateboth living and recently abandoned sites in order to directly linkhuman behavior with the formation of microscopic and chemicalmarkers and to follow the post-depositional processes, whichaffect the formation of the archaeological record. This articlereviews the contribution of geo-ethnoarchaeology to the study ofarchaeological formation processes associated with fire residuesthrough the examination of several key case studies and theirarchaeological implications.

KEYWORDSGeoarchaeology;ethnoarchaeology; fire;micromorphology; FTIR;elemental analysis; phytoliths

Introduction

Human use of fire is considered one of the hallmarks of human technology. Pyrotechnol-ogy have attracted a lot of archaeological interest as the use of fire evinces developed skillsand knowledge as well as a wide range of behaviors from technological to social ones.However, the archaeological identification of fire is not always simple (Mentzer 2014;Goldberg, Miller, and Mentzer 2017). When burnt, organic matter transforms mostly toashes and charred materials, which do not always preserve well in the archaeologicalrecord. At the same time, burning also alters more durable materials such as mineralsthat are found in sediments and plants, bones and rocks (Weiner 2010). Archaeologicalresearch of fire residues is carried out mainly on charred remains by anthracologistsand on inorganic materials (e.g. minerals and chemicals) by geoarchaeologists (Goldbergand Macphail 2006; Goldberg, Miller, and Mentzer 2017). In recent decades a major focusof geoarchaeological research has been devoted to the study of archaeological site for-mation processes (Goldberg and Macphail 2006). In the case of archaeological fire,geoarchaeology aims at understanding how human activities resulted in the deposition

© 2018 Informa UK Limited, trading as Taylor & Francis Group

CONTACT David E. Friesem df360@cam.ac.uk McDonald Institute for Archaeological Research, University ofCambridge, Downing Street, CB2 3ER Cambridge, UK

ETHNOARCHAEOLOGYhttps://doi.org/10.1080/19442890.2018.1510616

of burnt materials as well as how taphonomic post-depositional processes alter, deteriorateor preserve certain residues.

The contribution of ethnoarchaeology to the archaeological research is based on thewealth of information provided by the living contexts about the intangible social andmaterial aspects that produce archaeological remains. In other words, by observing theformation of material remains related to human activity as it happens, ethnoarchaeologyallows to directly link specific types of human behavior and their cultural meaning toarchaeological formation processes (David and Kramer 2001; Friesem 2016). In thatsense, the ethnoarchaeology of fire provides an important source of data for understandingpyrotechnology in its broadest sense and meanings. It provides important referencematerial for the archaeological investigation and interpretation of fire use (Mallol andHenry 2017). In this article, I review how geoarchaeological studies conducted in contem-porary contexts provide valuable data in order to construct a reference framework for thestudy of archaeological microscopic fire residues.

Geo-ethnoarchaeology

The aim of geo-ethnoarchaeology is to study both the anthropogenic and natural agentsthat affect the formation processes of archaeological materials (Friesem 2016). To do so,geoarchaeologists sample remains from contemporary traditional settlements wherethey can document human activity as it happens and directly link specific types of behav-ior with the formation of a microscopic signature. In addition, studies have also been con-ducted in recently abandoned settlements (Shahack-Gross, Marshall, and Weiner 2003;Goodman-Elgar 2008; Friesem et al. 2011, 2014a, 2014b, 2016), where detailed infor-mation regarding human activity is available from living informants or detailed historicalrecords. Recently abandoned sites mimic a near-archaeological context where taphonomicprocesses can be identified and the post-depositional mechanism can be studied. Thisunique combination of a geoarchaeological analysis augmented by ethnographic data isinvaluable for the construction of a reference library that can be used for the interpretationof the archaeological record.

In order to study how archaeological fire residues were deposited and the mechanismbehind their preservation, the entire process of formation needs to be tracked. Ethnoarch-aeological studies of fire used ethnographic observations and interviews to document howpeople utilized different fuel materials and fire installations as well as how combustion fea-tures are operated, maintained and cleaned (Mallol and Henry 2017). Geo-ethnoarchaeo-logical studies of fire further contributed a microscopic perspective showing how specificbehaviors associated with the use of fire result in the deposition of microscopic and chemi-cal residues. An important part of geo-ethnoarchaeological studies lays in the investigationof the taphonomic and post-depositional processes that affect the preservation of fire resi-dues in different environments.

Case studies

It is not within the scope of this article to describe all the works and analytical methodsused to study fire residues in ethnoarchaeological contexts. Below I choose to describeonly a few key studies that illustrate the breadth, limitations and advantages of geo-

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ethnoarchaeology to the study of fire residues from prehistoric and protohistoric contextsto domestic and urban ones.

Foragers and open fires

Hominins have been foraging for their subsistence for millions of years before the emer-gence of farming during the Late Pleistocene – Early Holocene transition. The investi-gation of forager use of fire is particularly challenging as these groups often useephemeral open-air fires. The challenges of recognizing Paleolithic combustion featuresassociated with hunter–gatherers (Goldberg, Miller, and Mentzer 2017) encouragedgeoarchaeologists to understand the formation processes of fire residues associated withforagers in an ethnoarchaeological context.

A geo-ethnoarchaeological study by Mallol et al. (2007) was pioneering in its focus onfire. Following ethnographic work among the Hadza, a hunting and gathering society inEast Africa, their aim was to assess the prospects for tracing the sedimentary componentsof ephemeral hearths and the ability to identify them in archaeological contexts. Duringfieldwork among the Hadza Mallol et al. (2007) documented the location of five openfires, the type of fuel, the fire function, and its duration as well as the time from abandon-ment to sampling. The hearths were sampled between ten days to a year after their aban-donment. Sediment block samples collected from the five hearths were analyzed using soilmicromorphology. The analysis showed that open-air fires sampled days after abandon-ment presented a good state of preservation to the extent that even a short duration ofuse (e.g. 15–20 minutes) left indicative fire residues in the form of calcitic ash, charcoalsand altered soil substrate. On the other hand, when sampled after a year from abandon-ment, regardless of the duration of use, only a few carbonized organics on a reddened sub-strate could be traced. Mallol et al. (2007) argued that the poor preservation of fire residuesis due to taphonomic processes namely wind and rain erosion alongside the disturbance ofthe sediments due to root activity. By comparing the preservation of fire residues indifferent localities, they concluded that when hearths were protected from the elements,for example when located inside huts or other shelters, they presented better preservationof indicative burnt features. This study highlighted the challenges to interpret forager useof open fire due to its ephemeral nature and the destructive post-depositional processes.

In a more recent study, Friesem et al. (2017) studied the use of fire among the Nayakapeople, a contemporary hunting and gathering society living in the tropical forests of theWestern Ghats hills in South India. Following ethnographic work among the Nayaka, twoopen-air sites and one rock-shelter, which were abandoned for 20–30 years by the samegroup of people, were excavated and sampled for geoarchaeological analysis (Figure 1).The aim of the study was to investigate how forager use of space can be detected archae-ologically through microscopic analysis. In addition, a major part of this research wasdevoted to study the mechanism of site formation processes in the humid tropical environ-ment (Friesem et al. 2017; Friesem and Lavi 2017). Focusing on fire residues, Friesem et al.(2017) presented ethnographic data demonstrating the association of social notions suchas sharing, immediacy and mobility with Nayaka use of fire. Hearths were reported to belocated only outdoor in full visibility of the other members of the hamlet. The Nayakapeople’s wish to share things, actions and space with as many members of the group aspossible, makes them to frequently change their locations and their activity areas within

GEO-ETHNOARCHAEOLOGY OF FIRE: GEOARCHAEOLOGICAL INVESTIGATION OF FIRE RESIDUES 3

the site (Bird-David 2009; Lavi and Bird-David 2014). As a result, hearths were erectedand abandoned frequently, ever-changing their location reflecting the social dynamicsat the settlement (Friesem et al. 2017; Friesem and Lavi 2017). Small branches, twigsand few logs were collected daily from the forest and used as fuel (Figure 1(a)). Thehearths were not reported to be specifically constructed and, although usually burningthroughout the night, they were constantly kept at low fire intensity. Friesem et al.(2017) pointed out that only a low signal of partly charred wood, charcoal and ashcould be traced after the fire died (Figure 1(b)). Excavating recently abandoned sites,Friesem et al. (2017) reported that fire residues were only found in situ in the rock-shelter where they probably represent the last episode of fire before abandonment(Figure 1(c,d)). Their post-depositional preservation is argued to be associated with theprotection from wind and rain erosion offered by the shelter. An important observationmade during the ethnographic work was related to the daily routine of raking-out andsweeping the hearths, which cleared the primary location from most fire residues

Figure 1. Geo-ethnoarchaeology of hunter–gatherer open fires. Ethnographic work among contempor-ary hunter–gatherers in South India by Friesem et al. (2016, 2017), Friesem and Lavi (2017). (a) Hearthsare used as open fire at low temperatures without a structure to accommodate the fire. (b) Smallbranches and twigs are mostly used as fuel depositing partly burnt wood, charcoal and wood ash.(c) In cases when hearths preserve they appear as a thin black horizon visible to the naked eye(arrow). Note the bulk sediments sampling (tags) and the sediment block for micromorphology(with scale bar) from this abandoned rock-shelter. Scale bar = 20 cm; (d) The scan of a thin sectionmade from the sediment block shows that the black horizon is composed of charcoals presentingthe location of an in situ hearth left at the site at the time of abandonment; (e) In most cases, thedaily practice of sweeping and rake-out removes the majority of fire residues from their primary depo-sition locus. (f) Cleaning and site maintenance practices result in redeposition of ash and charcoal inwaste areas. (g) The waste area excavated in an abandoned open-air site showing small black particles(arrow) only found at the slope of the site; (h) scan of a thin section made from a sediment block fromthe slope showing charcoal remains (arrow) to be in secondary deposition context typical for wasteareas. Note that no other fire residues were found elsewhere in the site besides in waste areas.

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(Figure 1(e)) and re-deposited them in waste areas (Friesem et al. 2017; Friesem and Lavi2017) (Figure 1(f)). The excavation of two open-air sites did not yield evidence for fire resi-dues in the main activity area. However, microscopic residues were found in secondarycontext in the waste areas, where activity remains were re-deposited by the sweepingand rapid rate of accumulation promoted higher preservation (Figure 1(g,h)). Taphono-mically, the geoarchaeological analysis showed rapid dissolution (within a few weeks ofabandonment) of calcitic ash remains and bones. Friesem et al. (2017) argued that theacidic conditions (pH < 7) in a humid tropical forest environment cause carbonates(e.g. ash and bones) to dissolve rapidly and completely, while under such conditions char-coal, phytoliths and certain elements indicative of fire residues (mostly P and Mg, and tosome extent Sr) are preserved. Intensive biological activity within the forest sediments wasreported to disturb the sedimentary sequence and to challenge the preservation of fire resi-dues as well as the identification of primary activity contexts. Overall, by using infraredspectroscopy, soil micromorphology, phytolith and elemental analysis Friesem et al.(2017) demonstrated that although the natural conditions in humid tropical environmenthamper the good preservation of fire residues it was still possible to detect microscopicmarkers, and to associate them with specific deposition patterns related to forager useof fire.

Domestic cooking installations

The study of cooking practices had attracted a lot of interest among ethnoarchaeologistsbecause of the exceptional window that ethnography opens to the entire chaîne opératoireof one of the most fundamental human activities (David and Kramer 2001). Geo-eth-noarchaeological works used multiple analyses, including soil micromorphology, infraredspectroscopy, stable isotopes, elemental analysis and microscopic analysis of micro-remains (e.g. wood ash pseudomorphs, phytoliths and dung spherulites) in order toassociate the domestic use of fire for cooking with microscopic and chemical proxies.

One of the first ethnoarchaeological studies of chemical signatures related to humanactivity was conducted by Middleton and Price (1996). They analyzed the chemical com-position of earth floor sediments from a living house in Mexico in order to build a refer-ence framework for future elemental analysis at archaeological sites. Although their studydid not focus on fire residues specifically, they argued that elevated concentrations of P, Kand Mg in floors result from deposition of wood ash due to food processing and burning.Middleton and Price (1996) concluded that people’s cleaning practices remove ash andorganic matter from the house floor which reduce the concentrations of P, K and Mgwithin the activity floors but increase their concentrations in waste areas where fire resi-dues are redeposited. The results of Middleton and Price (1996) were repeated by a laterstudy conducted by Rondelli et al. (2014) who studied a domestic unit in rural India. Ron-delli et al. (2014) analyzed the chemical composition of earth floors in different activityareas inside a living house including areas used for storage, sleeping, cooking andeating, as well as a cooking fireplace located outdoor in the veranda. They show thatareas used for cooking, indoors and outdoors, exhibit elevated concentrations of P, Kand Mg due to the deposition of ash. An expansion of this study focused specifically onfireplaces integrating phytolith and elemental analysis with the ethnographic data inorder to test the usefulness of these analytical methods to detect combustion features,

GEO-ETHNOARCHAEOLOGY OF FIRE: GEOARCHAEOLOGICAL INVESTIGATION OF FIRE RESIDUES 5

fire residues and type of fuel used (Lancelotti, Ruiz-Pérez, and García-Granero 2017). Lan-celotti, Ruiz-Pérez, and García-Granero (2017) were able to identify different fuel practicesincluding the use of dung and wood. They demonstrated how the center of the fireplacemay present only the last episode of use and concluded that in order to grasp the fullextent of fuel use it is essential to consider also samples from the fireplace’s immediatesurroundings.

Lancelotti and Madella (2012) worked in rural India focusing on the archaeologicalmarkers for the use of animal dung as a fuel material. Animal dung was first mixedwith water, shaped into “cakes”, dried and then used as fuel. Working in a living villagethey were able to follow the production process of the dung cakes and correlate it tothe microscopic remains they later analyzed in the laboratory. They carried out a chemicalanalysis and studied the distribution of phytolith and dung spherulite concentrations ofthe dung cakes. Lancelotti and Madella (2012) showed that the phytolith content ofdung cakes is mostly associated with grass leaf/stem phytoliths (ca. 95%) and very fewinflorescences and woody phytoliths. Very few dung spherulites were reported fromtheir dung cake samples. Hence, they argued that that the absence of spherulites couldnot be taken as an evidence for the absence of dung input. Their elemental analysis ofthe dung cakes demonstrated that the main factor influencing the chemical compositionof their samples was whether the dung was fresh or burnt. As opposed to their fresh mode,burnt dung cakes presented elevated concentrations of Al, Ba, Ca, Co, Cr, Fe, Mn, Mo, Ni,Pb, Sc, Sr, Ti and V. Concentrations of P did not show a significant difference between thefresh and burnt samples.

A study by Gur-Arieh et al. (2013) used a geo-ethnoarchaeological approach for study-ing the archaeological formation processes of microscopic residues found within cookinginstallations (see also Portillo et al. 2017). They investigated contemporary cooking prac-tices in rural Uzbekistan where the use of earth-made hearths and ovens was recorded andsampled (Figure 2). They investigated two types of cooking installations, tandir – a cylind-rical oven, made of two layers of rammed earth with a large opening at the top and a ven-tilation hole at the bottom which was either placed vertically on the ground or horizontallyon an earth-made platform (Figure 2(a)); and ochock – a partially enclosed hearth (keyhole or horseshoe-shaped) built from soil mixed with chaff with two large openings,one at the top on which cooking utensils are balanced and one at the front where fuelis added (Figure 2(b,c)). Gur-Arieh et al. (2013) measured the temperatures within thedifferent types of cooking installations when using different types of fuel, namely dungor wood (Figure 2(a,b)). The pattern recorded showed that in all the installations, regard-less of the type of fuel, at first the temperature climbed up as high as 800̊C, while after ca.20 minutes temperatures usually dropped rapidly with the actual cooking temperaturesstable at around 350–250̊C. Later, they sampled the mud walls of the installations aswell as the fuel remains left at the bottom of the installations for further laboratory analysis(Figure 2(c)). Infrared spectroscopy of the earthy wall material revealed that the clay in theinner part of the installations showed alteration associated with exposure to the highesttemperature (800°C), much higher than the actual cooking/baking temperature. Theexterior walls, on the other hand, showed no signs of clay alteration due to burning.Gur-Arieh et al. (2013) devoted a large part of their research to study the micro-remains of fuel materials, namely wood ash particles, phytoliths (Figure 2(d)) and dungspherulites (Figure 2(e)). They develop methods to distinguish between wood and dung

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fuel remains. They sampled each fuel material separately before it was used in the installa-tions as well as the originated ashes after use. They showed that phytolith analysis was notsufficient by itself, as both dung and wood ashes present similar phytolith assemblages dueto the local animal diet and mixing of fuels in the installation base. Using pure and mixedsamples, they were able to build a model for the identification of fuel type based on phy-tolith concentration together with the ratio between two indicative markers: (1) theamount of calcitic wood ash pseudomorphs for wood fuel; and (2) calcitic dung spherulitesfor dung cake fuel. This method significantly improved the ability of geoarchaeologists toidentify the type of fuel used in archaeological combustion features, and to assess the rela-tive intensity of fuel used in mixed ashes (e.g. Gur-Arieh et al. 2014; Portillo et al. 2017).

Burnt houses

Archaeological fire is mostly associated with human use of fire for cooking, heating andtool making (e.g. ceramic, metallurgy and lime plaster). Nevertheless, many archaeologicalsites present fire residues due to conflagrations. Friesem et al. (2014a, 2014b) carried out ageo-ethnoarchaeological research of mud-brick houses in rural Greece. Part of this studyfocused on two adjacent mud structures that were burnt down due to conflagration(Figure 3(a,b)). Informants who owned the structures provided information regardingtheir use as a stable and a barn. They were also able to supply detailed informationabout how earth floors were constructed and maintained, the production of mud bricksfor the walls and the composition of roofs made of beams covered with branches and

Figure 2. Geo-ethnoarchaeology of cooking installations. Work in rural Uzbekistan by Gur-Arieh et al.(2013) investigated two cooking installations: (a) tandir, a traditional oven. Note the high intensity offire during ignition as shown on the thermometer (502°C); and (b) ochock, a partially enclosed hearth.Note the presence of dung cakes used as fuel. (c) Sampling bulk sediment sediments (tags) from twoochocks. Note that here the fuel is composed of wood. Laboratory analysis showing microscopic fireresidues namely (d) wood ash pseudomorphs particles (upper arrow), siliceous phytoliths (lowerarrow) and (e) dung spherulites (arrow). This microphotograph was taken under the crossed polarizedlight. The photographs were taken by R. Shahack-Gross (a, b) and S. Gur-Arieh (c–e).

GEO-ETHNOARCHAEOLOGY OF FIRE: GEOARCHAEOLOGICAL INVESTIGATION OF FIRE RESIDUES 7

topped by industrial clay tiles. The ethnographic data also included the description of howthe fire started in the nearby field and was caught by the roof causing it to collapse on thefloor. The structure was then abandoned (about 30 years before the sampling took place)and left to slowly decay as the structure was exposed to the elements. Their field obser-vations noted a darkly burnt horizon measuring a few centimeters in thickness above asterile substrate and below industrial roof tiles (Figure 3(c)). The lower parts of theinner wall surface showed reddening probably due to burning. Friesem et al. (2014a,2014b) trenched the structures and sampled sediments from the sterile substrate, thefloor and black layer as well as wall material. The sediment samples were analyzed inthe laboratory using soil micromorphology, phosphate concentrations, phytolith analysisand infrared spectroscopy. The authors showed that the walls were exposed to higher

Figure 3. Geo-ethnoarchaeology of burnt houses. Work by Friesem et al. (2014a, 2014b) in NorthernGreece investigated two adjacent mud brick structures which were abandoned following conflagration:(a) a stable and (b) a barn. (c) The stratigraphic sequence in both structures shows a lower sterile sub-strate at the bottom, a black layer overlain by roof tile covered with lighter sediment resulting from walldegradation. Scale bar = 20 cm. (d) Microphotograph of the black layer in the barn showing at thebottom a dark B horizon sediment with increased compaction at its top indicating a beaten earthfloor with vegetal remains trampled into it (arrow). The black layer presents charred vegetalremains resulting from the burning of the fodder stored on the barn’s floor. The upper gray materialis composed of ashy vegetal material burnt at high temperatures representing the burnt thatch roofthat collapsed on the floor.

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temperatures at their lower part when the roof collapsed while still burning, in accordancewith the ethnographic information. The most interesting evidence provided by this studywas the identification and distinction between two micro-layers that formed the darklyburnt horizon. The upper layer exhibited elevated concentrations of phosphate, phytolithsand wood ash, while the lower part showed more charred remains indicative of lowerburning temperatures (Figure 3(d)). Although the two layers presented a similar micro-stratigraphy, the lower part of the burnt layer in the stable contained dung remains andfragments of quicklime spread deposited just on top of a beaten earth floor. Indeed,when the informants were asked about the quicklime spread they detailed the use oflime for periodically cleaning the stable floor. At the adjacent barn, the equivalent lowerpart of the burnt layer showed charred vegetal remains trampled into the beaten earthfloor. The taxonomy of the phytoliths from the upper layer indicated the deposition ofplants that were used for roofing while the lower layer showed phytoliths assemblagesindicative of fodder. Friesem et al. (2014b) argued that the lower part of the burnt layerrepresented the activity remains (e.g. dung and lime spread in the stable and fodder inthe barn) while the upper part represented the remains of the thatch roof that collapsedon the floor while burning and experienced higher temperatures. Based on the geo-eth-noarchaeological data, Friesem et al. (2014b) introduced the term “floor-roof complex”– referring to a layer of millimeters to a few centimeters thick composed of collapsedroof remains mixed with activity remains from the floor. The authors concluded thatonly microscopic analysis allows distinguishing roof remains from floor deposits. Thisobservation has significant implications for archaeological studies that often attributedfire residues on floors only to activity remains, while they probably represented bothfloor and roof remains rather than only primary floor residues. Following this study,geoarchaeological studies were able to successfully identify roof remains in burnthouses from domestic archaeological contexts (e.g. Regev et al. 2015).

Archaeological implications

Human behavior

Human behavior is reflected by a wide range of practices, but these activities are often sub-jected to specific constraints that make them identifiable. For example, as demonstrated bythis article, there is great variability in the types of fuel (at least in prehistory) and theability to build a reference framework of the material evidence for such practices iswhat makes geo-ethnoarchaeology fundamental to inform archaeological interpretation.Geo-ethnoarchaeological studies dealing with chemical and physical signatures wereable to contribute general guidelines that have proven invaluable for understanding thearchaeological formation of fire residues.

The ethnoarchaeological setting helped geoarchaeologists to associate specific micro-scopic and chemical markers as indicative to different types of fuel, mainly plants anddung, and to develop new methods to distinguish between them (Lancelotti andMadella 2012; Gur-Arieh et al. 2013; Lancelotti, Ruiz-Pérez, and García-Granero 2017).In addition, the amount of fuel, for example in cooking installations (Gur-Arieh et al.2013) as opposed to open fires (Mallol et al. 2007; Friesem et al. 2017), was studied inorder to understand the correlation between the intensity of use and the deposition of

GEO-ETHNOARCHAEOLOGY OF FIRE: GEOARCHAEOLOGICAL INVESTIGATION OF FIRE RESIDUES 9

fire residues. To date, the main focus in the study of fuels concentrated mainly on woodand dung. Archaeological studies suggested the possibility of other organic materials usedas fuel, for example, bones (e.g. Schiegl et al. 2003; Mentzer 2009; Yravedra and Uzquiano2013; Reidsma et al. 2016) or peat (e.g. Branigan, Edwards, and Merrony 2002; Simpsonet al. 2003; Braadbaart, Marinova, and Sarpaki 2016). Geo-ethnoarchaeological studiesshould be encouraged to broaden the study of other sources of fuel that will increasethe ability to trace them in the archaeological record.

Another important contribution of the geo-ethnoarchaeological research is found inthe examination of use patterns in association with the deposition of fire residues.Mallol et al. (2007) and Friesem et al. (2017) demonstrated how ephemeral open fires,common among foragers, are expected to leave very scarce remains, but also how micro-scopic analysis is able to detect “fire proxies” even when macroscopically there is a lack ofevidence. Works in domestic households showed that repeated use of cooking installationsis more likely to produce a set of fire residues including a chemical signature (Middletonand Price 1996; Rondelli et al. 2014) and higher volumes of fuel remain (Gur-Arieh et al.2013). In such contexts, it was demonstrated that although the cooking temperatures canbe relatively low, microscopic fire residues record the highest temperature, usually associ-ated with the short but repetitive duration of ignition (Gur-Arieh et al. 2013).

Ethnoarchaeological studies highlighted the abundance of routine cleaning practices. Inparticular, sweeping plays a significant role in the removal of residues from their primarylocation and their re-deposition in waste areas (e.g. O’Connell 1987; Fisher and Strickland1989; Milek 2012; Friesem and Lavi 2017). The re-deposition of fire residues due to clean-ing practices is crucial because, in the case of open-air sites, the rapid rate of accumulationin waste areas is a key factor for the preservation of activity residues, being in such casesthe only marker documenting fire use (Friesem, Zaidner, and Shahack-Gross 2014;Friesem et al. 2017). Unfortunately, the practice of sweeping is still neglected in manyarchaeological studies probably due to the difficulty to provide direct evidence for itsoccurrence.

Finally, in abandoned houses, the main factor that seems to control the preservation ofoccupation residues is the type of abandonment (Cameron and Tomka 1993). Several geo-ethnoarchaeological studies showed that when planned abandonment of houses occurs thepreservation of primary microscopic activity remains is poorer, including fire residues, asopposed to sudden abandonment due to destructive events, where often a burnt layer isfound in close proximity of the floor (e.g. Goodman-Elgar 2008; Friesem et al. 2011;Milek 2012; Friesem et al. 2014b). However, a geo-ethnoarchaeological study byFriesem et al. (2014b) argued that in many cases this burnt layer might represent theremains of a collapsed burnt roof rather than primary activity residues.

Taphonomic processes

In addition to anthropogenic processes, natural processes play a crucial role in the for-mation and taphonomy of the archaeological record. Geo-ethnoarchaeology has broad-ened the use of ethnographic contexts also to inform on taphonomic processes bystudying recently abandoned settlements. This methodological approach proved highlyuseful to follow environmental processes occurring post-abandonment and to evaluatetheir effect on our ability to detect human activities. This near-archaeological setting

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can only rarely be constructed experimentally and manifests the importance of ethnoarch-aeology for the study of archaeological site formation processes. Geo-ethnoarchaeologicalstudies that examined recently abandoned sites provided models for how differentenvironments and contexts affect the formation and the preservation of archaeologicalmaterials (e.g. McIntosh 1974; Shahack-Gross, Marshall, and Weiner 2003; Mallol et al.2007; Goodman-Elgar 2008; Friesem et al. 2011; Milek 2012; Friesem et al. 2014a,2014b, 2016).

This approach is especially important when examining the archaeological evidence (orthe lack of evidence) accounting for the use of fire. The growing number of geo-ethnoarch-aeological studies in different parts of the world help to better evaluate the influence of theenvironment on the integrity of the archaeological record. Working in a tropical forest,Friesem et al. (2017) showed that in humid tropical environments, high precipitationwith intensive biological activity within the soil provides acidic conditions that result inthe complete dissolution of carbonates which include wood ash and bone. This study high-lighted the importance of studying charcoal, phytolith and certain elements as reliablemarkers for the use of fire in tropical forests, simply because in acidic conditions theyare better preserved than ash and bones. According to the authors, this explains whythe majority of archaeological fire residues found in humid tropical environments arereported as charcoal, whereas the few cases where ashes and burnt bones were found cor-respond exclusively to sites located in a carbonate-rich environment preventing acidicconditions such as karstic systems (see Friesem et al. 2017 for review on fire residues inhumid tropical environment). Working in a semi-arid environment, Mallol et al. (2007)showed how ashes are easily transported by the wind and that even with low precipitationash can dissolve. These two studies (Mallol et al. 2007; Friesem et al. 2017) showed how inopen-air sites wind and rain are the major agents in the weathering of fire residues, along-side root and biological activity within the soil. But beyond the environmental conditions,geo-ethnoarchaeological studies focusing on roofed areas or enclosed spaces (Middletonand Price 1996; Mallol et al. 2007; Rondelli et al. 2014; Friesem et al. 2014b), rock-sheltersor caves (Friesem et al. 2016; Friesem et al. 2017) and closed installations (Gur-Arieh et al.2013, 2014) reported much better fire residue preservation states. Thus, the conclusion ofthese studies is that the preservation of archaeological residues is dependent upon theirprotection from the elements through rapid burial and/or anthropogenic covers.

The insights provided by the geo-ethnoarchaeological studies allow us to understandwhy the majority of prehistoric fire residues are found in caves and rock-shelters (Gold-berg, Miller, and Mentzer 2017) with only very few rare cases providing evidence for theuse of fire in open-air sites (Goren-Inbar et al. 2004; Friesem, Zaidner, and Shahack-Gross2014). In other words, the geo-ethnoarchaeological works on fire residues clearly indicatethat the lack of widespread evidence for the use of fire in open-air sites is due to tapho-nomic processes rather than to human preferences.

Conclusions

Understanding the use of fire is very important to archaeologists as they try to reconstructpast human life. However, understanding how fire residues are formed, preserve or disap-pear from the archaeological record is often difficult. Geo-ethnoarchaeology uses contem-porary contexts to investigate both living and recently abandoned settlements in order to

GEO-ETHNOARCHAEOLOGY OF FIRE: GEOARCHAEOLOGICAL INVESTIGATION OF FIRE RESIDUES 11

directly link human behavior with the formation of microscopic and chemical markersand to unravel the post-depositional processes that affect the formation of archaeologicalevidence. Geo-ethnoarchaeological studies provided several markers associated with fireresidues such as altered sediments, wood ash pseudomorphs, phytoliths, charcoal, burntbones, chemical elements (e.g. P, Mg, K) and deposition patterns. They also highlightedthe main agents in the preservation and deterioration of fire residues that are wind,water, bioturbation, soil acidity and human practices such as sweeping and rake-out.Geo-ethnoarchaeology is an emerging approach that has proven to be very useful tounderstand archaeological site formation processes. Future geo-ethnoarchaeologicalresearch, in particular regarding the use of fire, is needed to broaden our understandingof how specific human behaviors result in different formation processes of fire residues,alongside the study of how distinctive environments affect the preservation and archaeo-logical visibility of fire.

Acknowledgements

This paper was formed following fruitful discussion during the symposium on the ethnoarchaeol-ogy of fire held at the University of La Laguna, Spain. I am especially thankful to Carolina Malloland Auréade Henry, the organizers of this symposium, who encouraged me to focus in my eth-noarchaeological research on fire residues. I thank all the researchers who shared their researchwith me and together demonstrated the utility of geo-ethnoarchaeology. Last, I would like tothank Shira Gur-Arieh, Marco Madella, Carla Lancelotti and Georgia Tsartsidou for their invalu-able comments that helped to improve this article.

Disclosure statement

No potential conflict of interest was reported by the author.

Notes on contributor

David E. Friesem is a researcher at the McDonald Institute for Archaeological Research, Universityof Cambridge and the Zinman Institute of Archaeology, University of Haifa. He is an anthropolo-gical archaeologist who studies the human past through ethnography and geoarchaeology. His workfocuses on how materials, particularly microscopic ones, are formed due to the interplay betweenhumans and the environment. In his research, he integrates a multi-proxy microscopic analysiswith ethnography and anthropological theory to unravel human social and ecological behaviorand reconstruct past environments. He has been working on mud structure, pyrotechnology, useof space, foraging societies and archaeological formation processes in sites ranging from theMiddle Palaeolithic to the Iron Age.

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