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Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis
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Social spaces of daily life a reflexive approach to the analysis of chemical residues by multivariate spatial analysis

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  • 1. Social Spaces of Daily Life: A Reflexive Approachto the Analysis of Chemical Residues by MultivariateSpatial AnalysisSandra L. López Varela & Christopher D. DorePublished online: 22 June 2010# Springer Science+Business Media, LLC 2010Abstract Studying human activities requires an examination of the inherentepistemological problems in building arguments about the past based on chemicalresidues and modern observations. A reflexive approach to the analysis of chemicalresidues at the San Lucas archaeological site, a Classic Hohokam settlement locatedin Marana, Arizona, represents a unique opportunity to evaluate current techniquesand paradigms for the interpretation of daily life activities. By incorporating aninnovative program rooted in satellite remote sensing image analysis and spatialstatistics, including new techniques, such as bulk density, loss on ignition, electricalconductivity, and salinity, results suggest that soil chemical analysis will benefitmore from learning about structure and agency than from one single activity.Keywords Chemical analysis of residues . Agency. Multivariate spatial analysis .Hohokam archaeologyIntroductionThe number of publications discussing problems with the interpretation of chemicalsignatures to define human activities has increased over the last decade (e.g.,Hjulström and Isakssona 2009; King 2008; Wilson et al. 2008). This literature statesa certain degree of dissatisfaction related to the inability to link chemical elements tohuman activities in archaeological and modern contexts. The difficulty in establish-ing this one-to-one correlation, in some cases, is associated with the potential ofJ Archaeol Method Theory (2010) 17:249–278DOI 10.1007/s10816-010-9090-zS. L. López Varela (*)Departamento de Antropología, Universidad Autónoma del Estado de Morelos,Av. Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos 62209, Méxicoe-mail: slvarela@uaem.mxC. D. DoreSchool of Anthropology, The University of Arizona, Tucson, AZ, USA
  • 2. instrumental techniques to document chemical residues recovered on human habita-tion surfaces (Cook et al. 2006) to refine the relationship between past activities andpresent soil chemical signatures (Terry et al. 2004). Other studies examine the effectsof site lithology on the geochemical signatures for human occupation (Oonka et al.2009) or investigate the formation of anthropogenic chemical residues (Middleton2004) to better define activities. Recently, Wilson et al. (2008) questioned therationale behind the interpretation of soil element signatures for identifying spaceuse and function, emphasizing that the problem originates in our uses of ethno-graphic data to approach the past.Essentially, the analysis of chemical residues to define human activities has neverbeen investigated as a philosophical problem. From an epistemological perspective,how knowledge is created from geochemical data has never been examined interms of its foundations, pre-assumptions, and limits to validate the interpretationof human activities. As already noted by Wilson et al. (2008), studying humanactivities requires an examination of the inherent epistemological problems inbuilding arguments about the past based on chemical residues and modernobservations.Here, we discuss the advantages of adopting an epistemological approach to theanalysis of chemical residues for the identification of human activities at the SanLucas archaeological site, a Classic period (AD 1150–1350) Hohokam settlement,located northwest of Tucson, Arizona. A reflexive approach to the analysis ofchemical residues represents a unique opportunity to evaluate what can and cannotbe achieved with our current uses of techniques and paradigms for the interpretationof daily life activities in the past. In this study, we test the potential of soilphosphorus, organic matter, carbonates, pH, and fatty acids in the identification ofhuman activities. Innovative in our analysis is our inclusion of bulk density (Db),loss on ignition (LOI), electrical conductivity (EC), and salinity (TDS) tests to definehabitation surfaces. With such data, we explore the realms of interpretation byincorporating a program rooted in satellite remote sensing image analysis and spatialstatistics to the study of human activity areas.Equating Chemical Residues with Human ActivitiesArchaeologists began considering the potential of chemical residues to define humanactivities after the influential investigations by Olaf Arrhenius (1929) on the soils ofKagghamra in Sweden that demonstrated a correlation between high levels ofphosphate and fertile areas containing the remains of Viking farms and settlements.Arrhenius’ rationale that high level of phosphorus are an indication of humanactivities was applied in a later study in Norrland to identify a historic place wherethree women accused of using witchcraft had been burnt. Concerned with theubiquitous presence of phosphorus in the soil, Arrhenius successfully correlatedphosphoric acid in the soil with bone fragments, identifying those locations. Later,Arrhenius (1963) applied the same principle to define the distribution ofarchaeological sites in the southwestern United States. Cross-cultural resultsestablished phosphorus as indicative of human settlements, proving the value ofsoil studies to archaeology.250 López Varela and Dore
  • 3. The potential of phosphorus as a significant indicator of human activity continuesunder investigation by several scientists (see Holliday and Gartner 2007; Hutson etal. 2009). In comparison to southwestern archaeologists, Mesoamerican scientistsenthusiastically adopted the use of phosphorus to define human activities (Barba andBello 1978). Specifically, Luis Barba incorporated semiquantitative tests, commonlyused in agronomy, to his field studies expanding the associations of a larger numberof chemical residues with human activity (Barba et al. 1991). The successfulapplication of his research program in the Maya region (Barba and Manzanilla 1987)is the groundbreaking research supporting the current growth of chemical analysis todetermine human activities in Mesoamerica.At a theoretical level, the definition of an activity area as one activity performedin a specific area (Flannery 1976; Kent 1984, 1987) has structured the analysis ofgeochemical data. The definition has encouraged scholars to correlate a specificchemical element or compound to a particular activity. To illustrate the relationship,results are represented as a composite map of anomalies by plotting the distributionof each chemical residue under study as isopleths, becoming a standardrepresentation technique for most studies. To test the efficacy of chemical analysis,Barba and his colleagues (Barba and Ortiz 1992; Manzanilla and Barba 1990)considered ethnographic observations as a powerful tool for interpretation. Thus,ethnoarchaeology became the specific field of study to test the significance of thepatterning observed in the archaeological record.The reconstruction of human behavior in the past, based on modern observations,is one tactic used by scholars to study the formation processes of the archaeologicalrecord (Schiffer 1987). Several of these studies propounding the use of the present asan effective strategy for the interpretation of soil chemical data from archaeologicalsites are experiencing difficulties in defining the relationship between humanactivities and chemical signatures (see Fernández et al. 2002). Ethnoarchaeologicalinvestigations at Xaaga in Oaxaca, for example, isolated a low number (n=2) ofactivities (Middleton and Price 1996, 680–681).The use of ethnographic observations to support the interpretation of chemicalresidues has certainly advanced our understanding of the past by developing newmethodologies and theoretical approaches. As discussed in the pages that follow,there are boundaries to the construction of knowledge from the present andlimitations to the linking of a chemical element to a human activity.Why the Failure for Interpretation?The encountered limitations have different theoretical sources. Mostly, these werederived from a generalized static view of the past, embedded in an earlyunderstanding of the archaeological record as containing rich assemblages of insitu objects in their loci of use. Although many behavioral archaeologists havealready abandoned the in situ idealistic view of the past (see, for example, argumentspresented by Binford 1981), this theoretical orientation has been of great influence tothe study of chemical residues to interpret human activities.Linked to this early approach to the study of human activities, we argue, too, thatthe definition of an activity area is also part of the problem. Mainly, archaeologistsMultivariate Spatial Analysis of Chemical Residues at a Hohokam Site 251
  • 4. assume that only one activity takes place at a specific location (Flannery 1976, 5–6;Kent 1984, 1; Manzanilla 1986, 11). This definition introduces a static conceptu-alization of the use of space. This correlation tends to oversimplify human space use,disregarding that humans move in space and time to accommodate the needs ofeveryday life. The use of space is dynamic.Human activities are the result of conscious learned decisions concerning thelocations at which a diverse range of activities will be performed (Hodder andCessford 2004; Kent 1984). Every time an activity takes place, individuals reproducetheir social world. If we would consider that these daily activities do not always takeplace at the same exact location, rather within a certain range in space, we wouldconfront that different multiple activities overlap at a particular location (Dore andLópez Varela 2004; López Varela 2005). This realization compels a differentrationale to analyze and interpret a collected sample in the field, as it is carrying thechemical residues of many activities differentially taking place in time.Also, advances in the application of soil chemical analysis to define humanactivities are increasingly demonstrating that chemical residues found in anexcavated area are not always the result of human activity and not all humanactivities affect or deplete, for example, soil phosphorus levels (Holliday and Gartner2007; Sánchez and Cañabate 1998). By inquiring about how chemical residues aredeposited on surfaces, it becomes clear that natural processes are involved in adding,subtracting, and altering chemical concentrations on surfaces (Middleton 2004). Fur-thermore, the atmospheric particulate matter could play an important role in the chemi-cal enrichment of heavy metals. For example, pollutants are rich in heavy metals, andthese might be influencing the chemical characteristics of modern surfaces.Even if we consider that chemical residues are deposited by natural conditions,their absorption and concentration might be subjected to human-induced activitiessuch as sweeping. If sweeping takes place on a daily basis, the probability that achemical element originating from a natural process or a human activity accumulatesor decomposes in the surface may be raised or diminished. If sweeping is a moresporadic activity, chemical residues might tend to concentrate in certain areas andlater further removed or dispersed by further sweeping. If the episode of cleaninginvolves water or soap, these may induce a reaction, giving place to new chemicalcompounds. If accumulation of waste, objects, or dust is taking place in a surfacethat requires cleaning, it means that many other activities are shedding residues.Chemical residues trapped in this surface represent palimpsests—traces originat-ing from the human body, the materials involved in different type of activities, and/or natural processes. It is only logical to ask how we can correlate a chemicalelement to an activity (see Wilson et al. 2008), if the chemical element in a samplemight be the result of many activities or natural processes. To answer this question,archaeologists have either worked under the premises of middle-range theory orintroduced instrumental techniques to differentiate between the human and non-human factors as agents for chemical enrichment of surfaces.The Ethnoarchaeological ApproachEthnoarchaeology works under the premises of middle-range theory, suggesting thatsome processes at work in the ethnographic present are identical to the processes that252 López Varela and Dore
  • 5. took place in the past. Chemical signatures in the present establish the connection tothe dynamic processes in the past. However, chemical signatures need to be placedin a social context to acquire meaning. Chemical signatures cannot be turned intoconcepts until they are given meaning (Binford 1983, 413) through middle-rangetheory.For archaeological interpretation, middle-range theory as an intermediaryanalytical process to general theory building is unsuccessful because it acknowl-edges that the activities taking place in the present equate to those taking place in thepast (Johnsen and Bjornar 2000). The selective transfer of information from onecontext to another, contemporary to past communities, falsely assumes that the livesof those that are studied in the ethnographic context have remained unaffected forcenturies (Thomas 2004). Thus, the meaning for the targeted activity in the past haschanged through time.When middle-range theory is used to give meaning to a chemical signature, weintroduced an error in the interpretation of the past. The paradox here is that middle-range theory promised to be a procedure entirely separate from our ideas concerningwhat happened in the past (Thomas 2004, 72). However, this is hard to claim as weare providing meaning from the present to a chemical signature of the past (Thomas2004, 75). The ethnographic context is already preconceived, as it is understoodunder the analogy that past and present are the same (Thomas 2004, 240).A linear and uniform approach to the ethnographic context introduces a bias tothe interpretation of chemical signatures in an archaeological context. According toThomas (2004, 241) “...the most important role of ethnographic analogy lies not infilling in the gaps in our knowledge of prehistoric societies but in troubling anddisrupting what we think we already know”. Analogies withdrawn from theethnographic record aim at establishing a testable hypothesis about what the pastwas like, instead of taking them as measurements of presumed similarity. Lookingfor answers to, what if the past was like this (Thomas 2004, 241), sets up a kind ofanalysis aiming to understand how the similarity has been modified and recon-textualized by human agency. In other words, the approach reconsiders humans asactive individuals influencing the deposition of chemical residues while reproducingtheir daily life activities (see Dore and López Varela, in this volume).The Instrumental ApproachTo correlate a chemical element to an activity, archaeologists have introducedsemiquantitative and instrumental techniques to differentiate between the human andnon-human factors as agents for chemical enrichment of surfaces. These techniqueshave provided invaluable data for the interpretation of space use in and aroundarchaeological remains, to define the extent of human activity beyond the structuralremains, and to locate archaeological sites (Wilson et al. 2008). The challenge todetermine the correlation between the chemical elements left by human activities hasintroduced the need to cope with multi-element data through a complete statisticalapproach (Middleton 2004; Wells et al. 2004) and to distinguish them from thefraction that is available in the soil solution, the nutrient-laden free water in the soil.In fact, the challenges faced by these investigations have refined uses of instrumentaltechniques. The use of inductively coupled plasma-mass spectrometry (ICP-MS) hasMultivariate Spatial Analysis of Chemical Residues at a Hohokam Site 253
  • 6. raised questions about the chemical interference of aggressive acids for soil extrac-tion (Cook et al. 2006). This method uses nitric acid for soil extraction instead ofdilute hydrochloric acid (HCL) that generates silver chloride (AgCl), interferingstrongly with the technique (Cook et al. 2006). Mild acid-extraction agents usedwith inductively coupled plasma-atomic emission spectrometry (ICP-AES), such asHCL, are suggested as effective means of extracting chemical residues from asediment modified by human activity and powerful enough to extract complexed andadsorbed ions (Middleton 2004; Wells 2004) and neutralize high concentrations ofcalcium carbonate. Alternatively, diethylenetriaminepentaacetic acid chelate hasbeen introduced as an alternative method to extract trace metals in combination withICP-AES (Fernández et al. 2002).The increased application of these techniques is demonstrating both their potentialand their limits in distinguishing separate activity areas (Cook et al. 2006; Hjulströmand Isakssona 2009). Knowledge created from the application of these techniques islimited because it is also important to consider that individuals influence thedeposition of chemical residues while reproducing their daily life activities. Chemi-cal enrichment of surfaces occurs, to a certain extent, because human activities aresocially driven.The research in the application of instrumental techniques, in most cases, is con-cerned about finding the right number of chemical elements to be optimal in defininghuman activities. The Laboratory for Archaeological Chemistry at the University ofWisconsin—Madison, for example, defines with ICP-AES twelve chemical elementsconsidered to be representative of human activities such as food preparation,cooking, consumption, disposal, ritual, and transit areas (Middleton 2004; Middletonand Price 1996; Terry et al. 2004; Wells et al. 2004). The selected set includesaluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), magnesium(Mg), titanium (Ti), and phosphorus (P). These studies, by considering this set ofelements, have certainly contributed to the definition of these activities in the past.In a recent study at Cancuen, Cook et al. (2006, 636) encountered additionalactivities by considering a larger number of chemical elements with ICP-MS. Theconsideration of a total of 60 chemical elements detected elevated concentrations ofgold in floor surfaces up to seven times that which exists naturally in calcareoussoils, but this signature could not be securely attributed to a particular activity (Cooket al. 2006). Since the manufacture of gold for this area and time is not plausible, itwas suggested that this metal could be related to “Galactic Gold”, a particular kindof black jade still not found at Cancuen (Cook et al. 2006, 638) that is characterizedby inclusions of precious metals including gold. Incorporating a larger number ofelements established the possibility of detecting activities related to the working ofjade. From the Cancuen study, archaeologists learned that there is a large numberof activities that remain undetected if only a set of twelve chemical elements isconsidered. Clearly, the set of twelve chemical elements will provide a standardizedview of the activities that humans performed in the past. On the other hand, eightchemical elements in this given set are regarded as the most abundant chemicalelements on earth. In fact, Cook et al. (2006, 632) disregarded five of these chemicalelements in their study to better distinguish the activities occurring in space.Considering a set of 60 chemical elements is not the answer to identifying a largernumber of activities, but in considering that humans are social individuals using254 López Varela and Dore
  • 7. space according to the world they are embedded in. This world is experiencedindividually, as each person negotiates uniquely with the social environment,structuring the whole complex of habituated activities of ordinary living (Farnell2000) in an individualistic way. If we consider that humans have individualmotivations and desires, every time we approach the archaeological and ethno-archaeological record, we will be confronted with unique activities that might needfewer or a larger number of chemical elements to be detected. This realizationcompels the analyst to adjust instrumental techniques to this new challenge in orderto investigate the social meaning of chemical residues.In deconstructing the rationale of our current uses of instrumental techniques, it isimportant to notice that archaeologists are projecting their social world views, theirWeltanschaung, to interpret the past. Chemical analysis of floors has created ascientific discourse that, even in the presence of archaeological materials, theinterpretation of human activities by the archaeologists is guided by the authority ofinstrumental techniques. In those ethnoarchaeolocgical cases that ICP-AES takesinto account additional trace metals such as copper (Cu), mercury (Hg), or lead (Pb),their presence is associated with modern industrial objects (see Fernández et al.2002). For example, when zinc (Zn) was identified at Las Pozas, Guatemala, itsorigin was attributed to metal coating on cans, rubber tires, or batteries (Fernández etal. 2002). If we were going to find elevated concentrations of metals in anarchaeological context, most likely, we would interpret their presence as the result ofproduction activities (see Terry et al. 2004).A metal like Zn is not only present in “inorganic” objects. Zinc is present inorganic products, such as, pork, sardines, pumpkin seeds, or shellfish. What if thepresence of Zn is the result of an organic product? Again, the invaluable con-tributions of Barba to the study of human activities already have attempted to definefatty acids, carbohydrates, and proteins with semiquantitative techniques. However,there are useful methods to identify organic residues such as high performance liquidchromatography (HPLC) used extensively in biochemistry. HPLC is not foreign toarchaeology, as this method has been used to identify lipids (Passi et al. 1981) ororganic coloring of textiles (Karapanagiotis et al. 2007). HPLC is a powerful methodto identify and separate a target chemical compound, by purifying it from a mixtureof chemical compounds and at the same time quantifying its unknown concentrationin a known solution. In soil science, HPLC is combined with inductively coupledplasma time-of-flight mass spectrometry or with X-ray fluorescence spectrometry(van Campenhout et al. 2008). With great certainty, quantitative organic chemicalanalysis to the study of human activities will very soon be part of the archaeologicalliterature as more scholars are beginning to notice the importance of consideringorganic residues to define human activities (e.g., King 2008; Hjulström andIsakssona 2009).Adopting a Social ParadigmThe influence of epistemology on archaeology has prompted an explicit consider-ation of the role of field and laboratory methodologies for data collection, analysis,and interpretation (e.g., Lucas 2001; Shanks and Hodder 1995), as the way in whichMultivariate Spatial Analysis of Chemical Residues at a Hohokam Site 255
  • 8. archaeologists engage with archaeological data has direct consequences for ourinterpretation of the past. As we have already discussed, the methodologicalapproach to the study of human activities has been supported by both instrumentaland semiquantitative techniques (see Middleton et al., in this volume). Researchhistory confirms that human activities leave residues on the surfaces of habitationand that chemical analysis is a viable method to study them. However, efforts toenhance the act of archaeological interpretation have been limited. Despite therecognition that many different activities take place in a single space, when it comesto the interpretation of residues left by activity, results are expressed as a one-to-onecorrelation. Some of our colleagues do not agree with us (see Middleton et al., inthis volume) that the interpretation of data is presented and visually reconstructed asa one-to-one association, for example, carbonates to food preparation. In thisvolume, Dore and López Varela discuss how this approach was unable to representthe dynamics of space use in an ethnoarchaeological case (see Pecci et al. 2010).Relying on other pieces of information such as artifacts is a plausible solution.However, this solution only transfers to other realms the inability of our currentmethodologies to account for the other activities taking place in a single space. Weraise this concern because we have powerful tools to address these issues. Webelieve that if we aim our uses of technology not only to determine the chemicalcomposition of the activity but also to address its social components, we will extendthe potential of our methodologies.The identification of human activities through chemical analysis requires anunderstanding of the social and spatial settings in which the practice of everyday lifetakes place. It is important to recognize that the use of space is dynamic andorganized by social practice (Dore 1996; López Varela 2005; Dore and LópezVarela, this volume). These characteristics will influence chemical enrichment andinterpretation. Every activity has a beginning and an end, and time is a condition foractions to emerge and to transition from one action to the next (de Certeau 1988).Despite suggestions that the diachronic variation in the use of space is notproblematic (Middleton 2004), time poses a real challenge for the interpretation ofhuman activities and for understanding the chemical enrichment of surfaces. Over along period of deposition, the original chemical signature of the activity will start aprocess of “decomposition”. In the archaeological record, we will recover a chemicalfraction of the activity.The passage of time is what makes an activity a daily or a seasonal event, givingmeaning to space. In a modern context, for example, we were able to observe thedifferential uses of space by a woman potter. In the morning, a specific area could beused to prepare food. Later in the day, this same area might be used for makingpottery and even later, it could be used to place a mat to sleep upon (López Varela2005). Movement and time are conditions for activities to take place and to berepeated in space, both influencing how residues will be deposited on the surfaces.When humans perform an activity in space, they move within variables of direction,velocity, and time. In between what we call activities, many other types of actionsare taking place as well, such as walking or resting.At the end of the day, a particular space has received successive depositions ofmany chemical residues, originating from diverse activities. Every year inNovember, the same space in which the potter sleeps and makes griddles is256 López Varela and Dore
  • 9. transformed into a ritual space. The repetition of activities in a given time willinfluence how chemical residues are absorbed, decomposed, preserved, or dispersedon a surface. For the interpretation of the activity, it is necessary to recognize that therepetition of activities is the materialization of people’s actions.There are other variables influencing the chemical enrichment of surfaces,developing within the realm of the social, that are important to consider if the goal isto assign space functionality or to determine human activities with chemicalelements, such as space.Space itself imposes boundaries to the human body, allowing or restricting theperformance of activities. For an activity to take place, humans need to rememberthe locations at which a diverse range of activities will be performed (Hodder andCessford 2004). The repetition of activities takes place because humans are guidedby the knowledge of how to do things. The ways individuals do things aredetermined by rules provided by the world they live (Giddens 1981, pp. 54). Theprocess of learning and memorizing these rules is individually experienced. It isexpected then that the repetition of activities might be similar, but not identical, eachtime they are performed. Apparently, these activities do not leave residues but theymaterialize with the repetition of activities.All of these social variables are important to consider for the interpretation ofspace use, as the variability expressed by the chemical data could be the result of anindividualized expression of a particular activity. Humans perform activities becausethese are socially embedded and individually experienced. These social character-istics of activities are important to consider, particularly, when the analyst willextrapolate the result to another site or feature.The spatiality of daily life gives meaning to space, creating a practiced place (deCerteau 1988). The intensity and diversity of human activities are measures ofimportance in understanding the structuring of agency. These measurements suggestthe dynamism of everyday life. In this regard, chemical residues are telling us aboutthe structuring and organization of socialized actions, not only about a specificactivity.Here, we would like to suggest that soil chemical analysis would benefit more onlearning about structure and agency. If we were to understand the structuring ofsocial practices, then, we will be in a position to direct technology to address thepractice of everyday life.A Heuristic Approach to Soil Chemistry Analysis at the San LucasArchaeological Site in Marana, AZIn the Hohokam region, archaeologists support their interpretation of humanactivities and space use based on historic documents and ethnographic observationsof the Pima, Papago, and Maricopa populations (Seymour and Schiffer 1987,pp. 588). This is related to the scarcity of artifacts on archaeological floors and tothe burning of structures during site abandonment (Eric Klucas, personal com-munication 2004). Hohokam archaeology has focused on the house as an analyticalunit to understand social organization. As in many other archaeological cases, thecharacteristics and the location of architectural features and objects are studied asMultivariate Spatial Analysis of Chemical Residues at a Hohokam Site 257
  • 10. evidence of social complexity (Crown and Fish 1996). Based on investigations atSnaketown, several activities have already been recognized from features andartifact distribution in these structures (Seymour and Schiffer 1987). Variability insize, form, and distribution of pits suggests that some of these features weresuitable for cooking and others were used at night for heating (Seymour andSchiffer 1987, pp. 588). Based on ethnographic observations, posthole alignmentsin association with large pits are similar to those used as outdoor kitchen areas bythe Pima, Papago, and Maricopa (Seymour and Schiffer 1987, pp. 588). Somehouses appear to have served a wide range of functions in that they containevidence not only of domestic and craft-related activities, but also, of storage(Seymour and Schiffer 1987, pp. 586). In the case of production activities, such aspottery making, these areas are assumed to have been located in the middle of acluster of houses (Seymour and Schiffer 1987, pp. 589–590). Ethnohistoric sourcesrefer to the Pima and Maricopa sleeping on mats of woven reeds or plant fiber(petates) on each side of the hearth (Seymour and Schiffer 1987, pp. 585).Similar spatial arrangement of structures, open spaces, and pits are normallyinterpreted as a household courtyard group, sharing a diverse set of activities, not allof them domestic in nature (Abbot 2000; Seymour and Schiffer 1987; Wells et al.2004; Wilcox and Sternberg 1983). In general, these Classic Hohokam settlementsare characterized by wattle and daub structures built around shallow pits, with sets of2–4 dwellings clustered around a main plaza (Plog 2003, pp. 73). The Classic dietarysystem of the Hohokam included meat that was acquired by hunting of rabbit, deer,bighorn sheep, fox, or raccoon (Bayman 2001). Agave cultivation was one of themain economic characteristics of the northern Tucson Basin (Fish et al. 1992).Archaeologists suggest that craft production of pottery and marine shell objects wereundertaken by non-elite household dwellers and that these were traded for other kindof resources (Bayman 1999). These developments may be evidence of socialdifferentiation and the existence of elite groups.The San Lucas ProjectIn 2004, Statistical Research, Inc. (SRI) initiated excavations at the San Lucasarchaeological site, in Marana, Arizona. The San Lucas village was probablyintegrated to the nearby Marana Mound community (Fish et al. 1992). Excavationsat the San Lucas site are part of an applied archaeological project. While nottypically undertaken at Hohokam sites, chemical analysis as a method for definingactivity areas at the site was implemented as an innovative idea with research merit.The application of chemical analysis to the study of human activities lost its impetusin southwestern archaeology around 1965 (see as an exception Whittlesey et al.1982). The analysis designed for the San Lucas project is unique in the region, inthat (1) it is a comprehensive study that expands techniques previously used todetermine human activities; (2) it incorporates a program of statistics and spatialanalyses for the study of human activity areas; and (3) it critically evaluates fieldexcavation techniques.Given the constraints on this project, work required the use of methods that couldrapidly assess and define activity areas within a budget that prohibited theincorporation of instrumental techniques. The use of quantitative tests commonly258 López Varela and Dore
  • 11. used in agronomy to determine soil properties and their suitability for agriculturalpurposes were proposed. These tests are inexpensive and easy to perform in thelaboratory, yet robust enough to identify potential markers of human activities, suchas soil phosphorus, organic matter, and carbonates (see Middleton et al., in thisvolume). To measure fatty acids, a semiquantitative technique was used.For the San Lucas site, distinguishing archaeological floors from the natural soilis not clear in certain areas, mostly due to erosional–depositional processes, but alsodue to the burning of structures, making it necessary to investigate the properties ofthe surfaces and to determine if human activities took place on archaeological floorsor on a modified soil terrain. To answer this question, we incorporated bulk density(Db), loss on ignition (LOI), electrical conductivity (EC), and salinity (TDS) tests todistinguish between these two types of surfaces.Given the complexities in the identification of specific activities in the archae-ological record, instead of identifying a precise activity, it was decided to learn fromthe structuration of these chemical residues and to recognize the dynamic uses ofspace. Structuration is visible to archaeologists because of our capability ofexamining temporal spans (Joyce and Lopiparo 2005). To investigate the basicassumption that empirically recoverable chemical data may provide evidence of thepractice of everyday life, we have developed a suite of premises that are tested bymeans of rule-based approaches combined with map algebra. For Mesoamericanstudies, the identification of floors is not a major issue. If a simple decision rule isused, such as the research questions we are addressing in this analysis, then theoutcome of each implementation of the rule will produce a yes or no answer(Wheatley and Gillings 2002). To reconstruct the dynamic uses of space, we useremote sensing image analysis techniques to identify structure in the data, departingfrom plotting single chemical residues in space as isopleths promoting that only oneactivity took place in space.The Chemical Survey of the San Lucas Archaeological SiteArchaeological investigations at the San Lucas site defined five adobe structures,open spaces, and a variety of pits (Fig. 1), covering 650 m2. In this area, consideringour sample (n), we initiated a systematic chemical survey of a 650-m2excavated areausing a 1-m grid to learn about the social uses of space. To obtain the samples, anelectric drill was used to perforate the surface up to 5–8 cm in depth. In surfacesmade hard from burning (including interior floors and walls), a 2.5-cm diameter bitin an electric drill was used to perforate the surface up to 5–8 cm in depth. A trowelwas used to penetrate the surface instead of the drill when softer sediments permitted.To avoid introducing our predetermined conceptions of the uses of space,sampling was not guided by the presence of architectural features, since we alsoconsider these elements as a palimpsest of discrete events. The chemical surveyyielded a total of 650 samples. However, to save time and to reduce laboratoryexpenses, we selected a subset of 172 samples, obtaining an off-set systematicspatial sample with point spacing approximately every 2 m (1 point per 3.33 m). Thechemical analysis of 172 samples provided us with a representative approximation ofthe uses of space, allowing us the flexibility to process additional samples for moreintensive research at a later stage.Multivariate Spatial Analysis of Chemical Residues at a Hohokam Site 259
  • 12. Rapid Assessment Techniques for Chemical ResiduesCharacterizing the type of surface where human habitation developed is of relevanceto the chemical enrichment of surfaces, as it may influence preservation, absorption,and decomposition. We decided to test several premises to determine (a) if thesampled surfaces were natural soils compacted by human activity, (b) if thesesurfaces were artificially created, and (c) if chemical residues remained despiteabandonment practices and excavation procedures that tend to remove thick layers ofsoil.To achieve these goals, López Varela and Palacios-Fest determined the watercontents, the presence of organic matter, and the identification of calcium carbonatefor all samples with a loss-on-ignition (LOI) test. Additionally, the 172 samples weretested for pH levels, electrical conductivity, and salinity contents, as well as forcontents of phosphates. For every sample, we measured the physical characteristicsof the soil, such as color and weight, with and without gravel.Fig. 1 The excavated area with the location of structures and features that were sampled for chemicalanalyses (Illustration by Christopher D. Dore)260 López Varela and Dore
  • 13. Phosphates To measure phosphate contents for each sample, we used a Mehlich-IIdilute acid extraction. Concentrations were measured with a spectrophotomer. So,2 g of sample were placed in a 60-ml plastic bottle and were mixed with 25 ml of 1:6dilute Mehlich-II solution. The plastic bottles were mounted in a hollowed tray thatwas later placed in a shaker for 10 min. Sets of containers were prepared with funneland filter paper to filter the solution and to recover liquid. Standards at 0.1, 0.5, and1.0 mg/L of PO4 and blank (distilled water) were prepared. The colorimeter was setup for Program 79 and calibrated to read PO4. Colorimeter vials were labelled withappropriate sample number. Then, 1 ml of filtered solution was placed in vial andfilled with 10 ml of distilled water. One pillow of PhosVer3 reagent was added andshaken vigorously. The vial was placed in the colorimeter chamber and the valuewas read. The reading was repeated after running the first batch.Bulk Density (Db) Bulk density is defined as the mass of soil per unit volume in itsnatural field state, including air space and mineral plus organic materials. It is a testcommonly used to learn about the potential of a soil for crop productivity, erosion,and leaching of nutrients. The purpose of this test, namely, the clod method, is todistinguish natural soils from archaeological surfaces based on density and porosity.Bulk density can only be measured in a soil with well-developed structure, forexample, in a soil that is cemented. Soils with high Db values impede rootpenetration and adequate aeration so potential for agricultural purposes isdiminished. The “clod method” that estimates total water storage capacity whenthe soil moisture content is known (Evanylo and McGuinn 2000). For each sample,the volume was determined by weighing 1–3 clods in air and by coating the clodwith wax for its immersion in water, making use of Archimedes’ principle. However,López Varela, Palacios-Fest decided not to follow the customary procedure ofrepeating the sample until an ideal number is found below 5% in density. Here, wedepart from this procedure to understand higher density values, as there are rocksthat exhibit much higher values in density such as feldspars, dolomite, sandstone,quartz, or limestone.Loss-On-Ignition Test This is a fast and inexpensive means of determining not onlyorganic matter, but also water and carbonates with precision and accuracycomparable to other sophisticated analysis. The procedure involves weighing thesample in a crucible that was exposed to three different temperatures in a ParagonTouch and Fire DTC 800 furnace. The samples were processed to estimate watercontents, the presence of organic matter, and calcium carbonate in the samples. Theprocedure includes weighing of the crucible before it is exposed to heat.Approximately, 1 g of the sample is added to the crucible. The exact weight ofadded sample is calculated by determining the mass of air-dry soil. Then, eachcrucible with 1 g of sample is heated to 105°C in the furnace for 12 h to eliminatethe water in the sample. Then, each crucible with the reheated sample is weighed todetermine the loss of water. The percentage of water is then calculated.The second step includes reheating the sample to 550°C for 4 h to determine theloss of organic matter that is oxidized and leaving possible ash residues. After thesample cooled down for 15 h, the crucible is removed from the furnace and placed inthe desiccator for 20/30 min. Then, the sample is weighed once more to calculate theMultivariate Spatial Analysis of Chemical Residues at a Hohokam Site 261
  • 14. new mass. The difference between the mass of the crucible and the new mass isequivalent to the amount of organic matter in the sample.The third step includes reheating the remaining sample to 900°C for 2 h and acooling period of 20 h at 105°C. The reaction releases carbon dioxide (TIC) in thepresence of calcium carbonate (CaCO3) at 950°C, leaving oxide residues. The sam-ple is weighed again. The difference between the mass of the crucible and the newmass is equivalent to the amount of carbonates in the sample.pH, EC, and TDS Tests The alkalinity and acidity of the soil were measured with apH meter, as were electric conductivity (EC) and salinity (TDS). EC is the ability ofthe soil to conduct an electrical current and is measured by introducing an electricalcurrent through a soil sample solution. Salinity represents the total dissolved solids(TDS in milligrams per liter). It is a soil property referring to the amount of solublesalt in the soil. Plants are severely affected, both physically and chemically, byexcess salts. Excess salinity is generally a problem in arid and semiarid regionsbecause a large number of soluble salts can be found in these soils, along with calciteand carbonates that can buffer soil pH. To measure pH, 10 g of every sample wereweighed, placed in a container, and diluted in 10 ml distilled water. The sample wasvigorously mixed and allowed to rest for 15 min. A pH meter electrode wasintroduced to read the value in the meter and the measurement was taken again aftera couple of minutes. The meter was then changed to measure EC and TDS modes toread electrical conductivity and salinity, respectively. Measurement was repeatedafter a couple of minutes.To explore the potential of finding fatty acids, we measured their presence in thesamples following a simple technique developed by Barba et al. (1991). Thetechnique assesses the presence or absence of fatty acids by weighing 0.05 g ofsample and making it react with chloroform, ammonium hydroxide, and hydrogenperoxide. This test quantifies the presence of fatty acids on a qualitative scale,ranging from absent to very abundant.A detailed description of test procedures for these techniques are included as partof an appendix.Defining the Surfaces of Chemical EnrichmentA soil is understood here as a complex natural body formed through time inpreviously unweathered sediment under the influence of plants, microorganisms, andsoil sediments (van Breemen and Buurman 2002).Premise 1. If the surfaces associated with human habitation at the San Lucas sitesexhibit the chemical, physical, and biological characteristics thatenable soils to perform a wide range of functions, then these surfacesare natural soils that were compacted by human activity.Following soil science conventions, we differentiate between anthrosols andarchaeological floors. According to the European Soil Bureau Network, anthrosolsare characterized by at least one or more of the following diagnostic horizons: hortic,irragric, plaggic, terric, or ananthraquic with underlying hydragric horizon, resultingfrom deep or wet cultivation, long-term irrigation, or the addition of compost or262 López Varela and Dore
  • 15. sods. None of these horizons typify the habitation surfaces analyzed. When soils arecomprised of anthropogenic material such as urban waste or mine spoil, these areconsidered by soil science as technosols—soils whose properties and pedogenesisare dominated by their material origin, measuring between 50–100 cm in depth.Archaeological floors are closer to technosols in their definition. These are formedby the layering of lime or mortar, covered by plaster and then coated with a wash(Littman 1962, pp. 100). The top layer seals the influence of natural soils undernormal conditions making them suitable to preserve chemical residues left by humanactivity or natural process.In contrast, soils play a dominant role in the biogeochemical cycling of water,carbon, nitrogen, and other elements, influencing the chemical composition and ratesof substances in the atmosphere and the hydrosphere. The main physical processesinfluencing soil formation are movement of water, dissolved substances (solutes) andsuspended particles, temperature gradients and fluctuations, and shrinkage andswelling (van Breemen and Buurman 2002, pp. 15). Water content in the soil isimportant because it demonstrates the feasibility of sustaining plant life. In coarse-textured soils, water movement is particularly slow in non-saturated conditions.Thus, water movement is dependent upon soil porosity. Results obtained by the LOItest in 170 samples indicate a water content ranging from 0.05–5.62%, a mean of0.83%, and a standard deviation of 0.80%. These values indicate very low moisturecontents in the samples to sustain plant life.Premise 2. If the occupation surfaces are floors, samples will yield high Db values.Ideally, the bulk density of a soil ranges between 1.10–1.60 g/cm3.Statistical values for Db of 142 analyzed samples range from 1.26 to2.58, with a mean of 1.63. Porosity ranged from 2.8–52.5%. Based onthese values, it is possible to suggest that the structure and density ofthe surface is not related to a natural soil.Premise 3. If the habitation surfaces are floors, the samples are expected to havelow contents of organic matter and, if detected in large concentrations,phosphorus was added by a different process. Organic matter is anothervital component of soil for plant growth since it contains essentialnutrients such as phosphorus (van Breemen and Buurman 2002). It alsoinfluences soil structure, water holding capacity, nutrient contributions,biological activity, water, and air infiltration rate. Results from the loss-on-ignition (LOI) test indicate statistical values for organic mattercontent ranged from 1.54% to 7.93% with a mean of 2.24% and astandard deviation of 0.53% in the 169 samples (Table 1).Carbonate (CaCO3) plays an important role in soil management, as its distributionand quantity affects soil fertility, erosion, and available water capacity. The statisticalvalues obtained for CaCO3 in 170 samples ranged from 0.11–3.71% with a mean of1.29%, and a standard deviation of 0.41% (Table 1).Premise 4. If occupation surfaces are floors, pH and phosphorus concentrationsare expected to have high values. The statistical values of pH for the172 analyzed samples range between 7.97 and 9.65 with a mean of8.86 and a standard deviation of 0.26 (see Table 1). These values fitMultivariate Spatial Analysis of Chemical Residues at a Hohokam Site 263
  • 16. well with slightly to moderately calcareous soils. Values beyond 9.2 areunexpected for this area.Premise 5. If pH is low and organic matter and phosphates are high, then these(organic matter and phosphates) have been added artificially.The high concentration of phosphates in the sample was unreadable to thespectrophotomer, so the solution had to be diluted tenfold (see Table 1 forrecalculated values). In the end, concentrations of phosphates range between 25.71and 113.69 ppm (or milligram per kilogram) with a mean of 46.56 ppm.Premise 6. If the surfaces of occupation are floors, then water content, salinity,electrical conductivity, and organic matter should exhibit very lowvalues.The statistical values of electrical conductivity detected in the 172 analyzedsamples indicate a minimum value of 0.02 S/cm and a maximum of 0.57 S/cm(Table 1). Most values concentrate in the low range as indicated by the mean 0.11 S/cm;however, values greater than 0.30 S/cm are rather unusual, suggesting an analyticaldiscrepancy with the rest of the data.Results from chemical analyses indicate poor conditions to sustain naturalvegetation, indicating that other processes influenced the chemical enrichment ofsurfaces. The high values of bulk density are above the ideal levels for any soil,leading us to suggest that the sampled area is an artificially created surface. LOIvalues reveal a very low percentage of water in each sample, making plant growthdifficult. Consequently, the pH values are high in most samples due to a restrictedmovement of water that would impede plant growth.Table 1 Statistical Summary of VariablesDb Porosity EC TDS WaterN of cases 142 142 172 172 170Minimum 1.260 2.800 0.020 0.010 0.050Maximum 2.580 52.500 0.570 0.280 5.620Mean 1.625 38.672 0.105 0.050 0.827Standard deviation 0.210 7.916 0.078 0.038 0.797Organic matter Carbonate pH PhosphatesN of cases 169 170 172 172Minimum 1.540 0.110 7.970 25.710Maximum 7.930 3.710 9.650 113.690Mean 2.236 1.294 8.864 46.556Standard deviation 0.530 0.412 0.256 15.868Fatty acidsN of cases 172Minimum 0.0Maximum 3.000Mean 0.465Standard deviation 0.634264 López Varela and Dore
  • 17. Some samples, however, show considerable amounts of organic matter and lowvalues of water contents. At the same time, the highest values for phosphatesdistribute around pits and structures.Based on these results, we can rule out our Premise 1 and suggest that thesurfaces under study could be regarded as archaeological floors. The determinationof carbonates in the samples and the high values of bulk density yield preliminaryevidence of a floor construction mixture based on sand. Knowing that the habitationsurfaces are floors, is an advantage for interpreting chemical residue results. At theSan Lucas site, the presence of fatty acids is low, but some features exhibit particularconcentrations that could be analyzed later by mass spectrometry. Despite thelimitations of this semiquantitative technique, it is providing a preliminaryassessment of its presence, and in the future, specific samples could be analyzedwith instrumental techniques.We can assume that the identified chemical residues have a higher probability ofhaving been created by human activities, as the chemical enrichment developed on afloor. In the absence of assigning a particular activity to a particular chemicalresidue, one can still learn much about the structuring of human activities in space.Even if different human activities simultaneously deposited trace amounts ofdifferent chemical residues on the surface, their location can be discerned from thespatial structuring of chemical data.The Structuring of Chemical Data at San LucasIn recent years, we have been exploring techniques that are rooted in satellite remotesensing image analysis to better reflect the socialized use of space. These techniquesallow individual residue data sets to be combined and processed simultaneously, toidentify and tease out complex combinations of residues that may equate with sets ofactions (see Dore and López Varela, this volume). Although this might involve themeasurement and description of built and open spaces as they are revealed to us inthe present, the objective of their application is to understand the structure ofchemical data and the intensity of the use of space. To arrive to such anunderstanding, we formulated a series of premises, following the ruled-basedapproach.Premise 7. If activity areas are differentiated on the basis of one chemical elementto identify discrete spatial areas, we could not rule out the enrichmentof natural soils from those of floors. Using multiple chemical elementssimultaneously to identify discrete spatial areas raises our analyticability to identify unique combinations or suites of chemical elementsin space. This may provide clues to the way space is socially used andstructured.Thus, we created a raster surface for each variable (carbonates, phosphates,organic matter, water, etc.) and rescaled values to 8-bit data space (0 to 255). Toreduce redundancy in the data, without sacrificing variability, we undertook a spatialprincipal component analysis. With these techniques, we obtained three rasters thatretained 96.0% of the variability and allowed us to display the data setMultivariate Spatial Analysis of Chemical Residues at a Hohokam Site 265
  • 18. simultaneously in red, green, and blue (RGB) color space (Fig. 2). These methodsare identical to those described in more detail in the article by Dore and LópezVarela in this volume.While this colored raster composite is valuable to visualize spatial areas havingunique combinations of residues, it is limited in its ability to be quantified and to producesecondary vector data sets of utility. It can, however, be used as a reference for anunsupervised classification to ensure that a meaningful number of classes are obtained.Classification is a discriminate technique used to partition space into areas havingsimilar characteristics of inputs, in this case, chemical residues. We used a neuralnetwork-base classifier and through experiments with a number of classes, settled on 16to approximate the principal component RGB (Red/Green/Blue) visualization (Fig. 3).Proxy measures of activity intensity (frequency of repetition) and diversity (number ofactions) can be computed from the classification raster. Intensity can be calculated asthe frequency of polygon centroids in a given area (Fig. 4). Diversity can be calculatedas the number of different activities in a given area (Fig. 5).Fig. 2 Display of the data set in RGB color space, after spatial principal component analysis (photographcourtesy of Statistical Research, Inc. and modified by Christopher D. Dore)266 López Varela and Dore
  • 19. The resulting model is an estimate of the number of areas that could have beenrepresented in space, as we artificially created groups of unique residues that mayequate with unique sets of activities (Fig. 6). However, we can observe that (1) thefrequency of activities can be discussed relatively despite the fact that we don’tknow what these were in the past; (2) the relative amount of spatial area attributed tothese actions may be computed, and (3) the similarity, at least in terms of residueoutput, may be examined with the dendrogram from the classification. With thisdendrogram, three major groups of related activities may be distinguished and that afew pairs of activities are very closely related (Fig. 7). The main advantage of doingthis classification is its heuristic capacity to demonstrate that the structure ofchemical elements to architectural features is not a one-to-one correlation as moststudies suggest (Manzanilla 1996; Terry et al. 2004).The spatial arrangement of the five excavated structures, open spaces, and pits atthe San Lucas site may be visible to us in the present as bounded (Fig. 8). The SanLucas excavated data continues to be studied, including the analysis of artifacts.Chronometric dating of archaeological data included archaeomagnetic studies.Fig. 3 Neural network-base classifier based on 16 classes (illustration by Christopher D. Dore)Multivariate Spatial Analysis of Chemical Residues at a Hohokam Site 267
  • 20. Preliminary dating results that still need to be tied to other avenues of investigationare suggesting that none of the structures were occupied at the same time (Deaver,personal communication to Dore 2005). This is not the first time archaeomagneticdates suggest that two houses with associated work areas and trash deposits were notoccupied at the same time (Roth 2000). Adding structures to an existing settlementmay not always be behind population growth. These structures could have beensimply abandoned as the consequence of residential movement, resulting from asocially negotiated process induced by the environment, ideology, conflict, and evenby health issues (Nelson and Schachner 2002).This residential shifting is challenging to chemical analysis for interpretation ofspace use. The sets of activities that we isolated with the classification may or maynot signal differential uses for these structures (Fig. 6). The perceived groupings ofunique residues could be related to similar activities involving different objects,foods, or peoples. Differences in the structuring of the data could be related to theFig. 4 Proxy measures of activity intensity calculated as the frequency of polygon centroids in a givenarea—blue (low) to red (high) (photograph courtesy of Statistical Research, Inc. and modified byChristopher D. Dore)268 López Varela and Dore
  • 21. time when the activities took place. Although one could explore the function of astructure based on the artifacts found on floors, the paucity of material data makesthis difficult (Eric Klucas, personal communication 2004). Artifacts left on floors,particularly during abandonment, represent a fragment of time in the lives of pastpeople (Fig. 9). Despite the challenging issues residential shifting imposes tointerpretation, it is evident that spaces are constantly restructured to accommodatethe practice of everyday life.ConclusionsThe reflexive approach adopted for the analysis of chemical residues at the SanLucas site, contrary to all expectations (Berggren and Hodder 2003), originates inthe world of applied archaeology. Chemical analysis is a potential tool to understandFig. 5 Proxy measures of activity diversity can be calculated as the number of different activities in agiven area—blue (low) to red (high) (photograph courtesy of Statistical Research, Inc. and modified byChristopher D. Dore)Multivariate Spatial Analysis of Chemical Residues at a Hohokam Site 269
  • 22. the uses of space in applied or research contexts. Excavation strategies in the appliedsector might contradict research expectations. However, the study we have discussedhere demonstrates that chemical residues can be recovered as part of an appliedsector project, proving the impact of Luis Barba’s studies to this field of inquiry andexplaining why we decided to honor him with this publication.Additionally, this particular setting has provided us with a unique opportunity toassess the advantages and limitations of our current methodologies and theoreticalparadigms in soil analysis and interpretation. The approach has exposed the prob-lematic issues for the interpretation of human activities and space use in the past.Particularly, it has raised questions about the possibilities of recognizing theindividuality of space use and the ways we document time at multiple scales.Archaeologists can no longer assume that the chemical residues recovered fromareas in which occupation is evident always correlate with human activities. Naturalfactors also influence the deposition of chemical residues. This understanding ismeans for the selection of analytical techniques both in the field and the laboratoryto recover and interpret chemical residues. But if we are to distinguish if a chemicalFig. 6 Chemical-based “activity areas” within architectural structures. Colors correspond to uniquemultivariate signatures across the suite of chemical elements analyzed (Illustration by Christopher D. Dore)270 López Varela and Dore
  • 23. Fig. 8 The spatial arrangement of the five excavated structures, open spaces, and pits, and chemicalsample area at San Lucas (illustration by Christopher D. Dore)Fig. 7 The classification dendrogram shows that three major groups of related activities may bedistinguished ([8, 6, 4] [5, 9, 7, 11, 16, 3, 2, 10, 14, 15, 13] [12]). One also can see that a few pairs ofactivities are very closely related ([7, 9] [11, 16] [13, 15]) [illustration by Christopher D. Dore]Multivariate Spatial Analysis of Chemical Residues at a Hohokam Site 271
  • 24. element is the result of human activity, we need first to move beyond the staticorientation introduced by those studies attempting to define the functionality of builtspaces based on the identification of a single activity. To a certain extent, thisorientation is further enhanced with the use of isopleths. For this study, modellingthe spatial structure of chemical data with satellite image analysis and spatialstatistics was useful to illustrate the dynamic use of space.Second, archaeologists need to be cautious in their use of the ethnographiccontext for the interpretation of human activities. The lives of those that are studiedin a modern context have changed through time, and the present is not a staticrepresentation of the past. Ethnoarchaeological studies are helpful to investigatewhat motivates the structuring of activities in space. In this regard, the structuring ofactivities in space may be studied similar to the chaîne opératoire (Leroi-Gourhan1943–1945) analytical concept of describing the sequences of steps by which naturalresources were transformed into meaningful and functional objects. Several scholars(LaMotta and Schiffer 2001; Joyce and Lopiparo 2005) already have suggestedstudying the chains of activities responsible for the formation of the archaeologicaldeposits. We are aware that this might be more difficult to recognize inarchaeological cases and that the approach we have introduced might not solve allproblems. However, we may be able to move from the experienced limitations forthe interpretation of chemical residues if we consider that the social logic of space isleading to the chemical enrichment of surfaces.Acknowledgements We would like to thank Dr. Eric Klucas, who managed the San Lucas project, forhis consideration of chemical analysis as a potential tool to define human activities at the site and for hiskindness in submitting our request to disseminate our research. Our special gratitude goes to projectFig. 9 Artifacts left on floors particularly during abandonment represent a fragment of time in the live ofpast peoples and these may not be representative of everything that happened in that space (photographcourtesy of Statistical Research Inc.)272 López Varela and Dore
  • 25. sponsor Mr. Robert Zammit of BCIF for his openness and disposition to grant us permission to present andpublish the San Lucas chemical data at various scientific forums. We are grateful to Robert Heckman andDrs. Jeffrey Homburg and Manuel Palacios-Fest for their support in collecting the samples in the field and forsharing their inquisitive thoughts and observations that have extended the potential of this research beyondour original expectations. With support of Mitch Eichsenseer and Jim Lofaro, we were able to process theresults of this investigation. We would like to thank all of the SRI staff for their support and enthusiasm,particularly Dottie Ohman and Michelle Wienhold, in helping all of those who have worked in this project toachieve our goals. López Varela would like to express special gratitude to Donn Grenda, Terry Majewski,and Jeff and Debbie Altschul for supporting this investigation as part of my sabbatical year (2004–2005) atStatistical Research Inc. Thanks to our anonymous reviewers for their insightful comments.Appendix: Detailed Description of Test Procedures for Chemical Analysesof Floor SamplesManuel R. Palacios-Fest and Sandra L. López VarelaI. Bulk Density Determination by the Clod Method1) Select 2–3 clods of soil of equal size and weight, whenever possible.2) Tie a piece of thread, about 20 cm long, to each clod.3) Weigh the bulk clod on an electronic balance, capable of reading 1/10,000 of agram and weighing suspended samples.4) Record the weight in a log form.5) Coat the clod with paraffin (density is 0.9) at approximately 60°C. Allow thecoating to dry. It is important that no holes are left uncoated. If bubbles appear,repeat the coating several times to ensure that the sample is sealed. Then, weighthe sample. One should be careful in not over coating the sample with paraffin,as the excess may interfere with its weight in water.6) Place a 1,000 ml beaker on a scale, with a specific volume of water that is toremain constant for all the samples.7) Suspend the coated sample and let it submerge into the beaker. Record theweight. Be cautious in letting the clod hang at the same distance, to maintain aconstant error. If this is not followed, one can obtain different weightmeasurements for the same clod, as this test is based on Archimedes’ principle.8) Then assume the value of the density of water (1.00 g/cm3) and estimateporosity. The bulk density must be reported in milligram per cubic meter.II. Loss on Ignition (LOI) to Estimate Contents of Water, Organic Matter,and Carbonates with a Paragon Touch and Fire DTC 800 FurnaceThis test requires the sieving of the sample to separate the gravel, through a 2-mmsieve, from the fine fraction <2 mm. The use of gloves is recommended to avoidadding grease, dust, or fat to the crucible. To obtain better results, the crucibles usedin this analysis after washing them, without soap, should be dried carefully to avoidany water contents.To determine the water content in the sample:1) Control that porcelain crucibles are cleaned and marked with lead pencil.2) Always use metal pliers when moving crucibles.Multivariate Spatial Analysis of Chemical Residues at a Hohokam Site 273
  • 26. 3) Weigh every crucible and record its weight.4) Add 1 g of sample to the crucible and record the new weight.5) Place each crucible with 1 g of sample in drying oven at 105°C for 12 h orovernight.6) Place hot crucibles in the desiccator for 30 min to cool the sample.7) Weigh the crucibles that are now at temperature taken from desiccator.8) Record the weight.To determine the organic matter in the sample:1) Control that porcelain crucibles continued to be marked with lead pencil aftertheir exposure to the dry oven.2) Place the crucibles in the furnace by using metal pliers and/or gloves.3) Turn the furnace ON.4) Press Enter to Idle the furnace.5) Press Ramp Hold and determine the user programming the kiln by setting anumber.6) Press Enter to set the time and temperature segments for heating and coolingdown the samples.7) Choose 2 for two segments. The first one to set the heating temperature at 550°C(RA 1) and the second one to set the cooling of the sample down to 105°C (RA2).8) Press Enter to set the time of operation for those two segments: 4 h (Hold 1) at550°C and 15 h (Hold 2) of cooling down at 105°C.9) Press Enter twice to GO. An idle and dashed line will appear and the furnacewill start its operation.10) After 15 h, the cooling process is complete and the samples can be removedfrom the furnace and transferred into the desiccator for 30 min.11) Weight the crucibles that are now at temperature taken from desiccator.12) Record the weight.To determine the total inorganic carbon (TIC) content in the sample:1) Turn the furnace ON.2) Press Enter to Idle the furnace.3) Press Ramp Hold and determine the user programming the kiln by setting anumber.4) Press Enter to set the time and temperature segments for heating and coolingdown the samples.5) Choose 2 for two segments. The first one to set the heating temperature at 900°C(RA 1) and the second one to set the cooling of the sample down to 105°C (RA2).6) Press Enter to set the time of operation for those two segments: 2 h (Hold 1) at950°C and 20 h (Hold 2) of cooling down at 105°C.7) Press Enter twice to GO. An idle and dashed line will appear and the furnacewill start its operation.8) After 20 h, the cooling process is complete and the samples can be removedfrom the furnace and placed into the desiccator.9) Then weigh the crucible and record the measurement.10) Discard the samples and wash crucibles with distilled water (no soap).274 López Varela and Dore
  • 27. III. Determination of pH, Electrical Conductivity, and SalinityMeasure pH, electrical conductivity (EC in mMhos/cm), and salinity (TDS [totaldissolved solids] in milligram per liter) using a pH meter with temperature control in1:1 slurry of 10 g of sample and 10 ml of distilled water. Maintain lab roomtemperature at (∼20°C).Record pH measurements.1) Calibrate pH meter using buffers (following manufacturers instructions).2) Place 10 g of sample in small container.3) Add 10 ml of distilled water.4) Stir vigorously and let sit for 15 min.5) Introduce pH meter electrode and read the value.Record Conductivity and Salinity1) Change the pH meter mode to EC and TDS to read conductivity and salinity,respectively.2) Repeat measurement after a couple of minutes.3) In between measurement, rinse the electrode with distilled water.4) Record value in log worksheet.Extractable Phosphate Procedure, using the Mehlich-II methodwith a Hach Spectrophotometer1) Weigh 2 g of <2-mm sample.2) Place sample in a 60-ml plastic bottle.3) Add 25 ml of 1:6 dilute Mehlich-II solution.4) Mount in hollowed wooden tray and place tray in shaker for 10 min.5) Prepare a set of containers with a funnel and filter paper to filter solution andrecover only the filtrate.6) Prepare standards at 0.1, 0.5, and 1.0 mg/L of PO4 and blank (distilled water).7) Enter Program 79 in the Hach spectrophotometer (follow manufacturer’sinstructions).8) Calibrate the Hach spectrophotometer to read PO4.9) Label colorimeter vials with appropriate sample number.10) Take 1 ml of filtered solution and place it in the vial.11) Fill with distilled water to the 10 ml mark.12) Add one pillow of PhosVer3 reagent and shake for 3–4 min.13) Place vial in the Hach spectrophotometer chamber and read the value.14) Repeat the reading after running the first batch.15) Record values in log worksheet.Fatty Acid Determination Test1) Weigh 0.05 g of sample.2) Place the sample in a beaker.3) Carefully add 1 ml of chloroform.Multivariate Spatial Analysis of Chemical Residues at a Hohokam Site 275
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