Gifford-Gonzalez Etal 1985

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Society for American Archaeology

The Third Dimension in Site Structure: An Experiment in Trampling and Vertical Dispersal Author(s): Diane P. Gifford-Gonzalez, David B. Damrosch, Debra R. Damrosch, John Pryor, Robert L. Thunen Source: American Antiquity, Vol. 50, No. 4 (Oct., 1985), pp. 803-818 Published by: Society for American Archaeology Stable URL: . Accessed: 20/09/2011 11:21Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact

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THE THIRD DIMENSION IN SITE STRUCTURE: AN EXPERIMENT IN TRAMPLING AND VERTICAL DISPERSALDiane P. Gifford-Gonzalez, David B. Damrosch, Debra R. Damrosch, John Pryor, and Robert L. ThunenTwo measuredand weighedassemblagesof lithic debitage weresubjectedto human treadage,one set on a sand. Theassemblageswereexcavated, the otheron unconsolidated compactsandysilt ("loam")substrate, plotted in threedimensions,and documentedfordamage. Downwardmigrationof pieces at the loam site was minimal: fracture of small pieces was the dominant damage pattern. Most sand site pieces migratedto 3-8 cm depth; a normalcurve,and edge-damageto largerpieces was the dominant verticaldistribution of pieces approximated a patternobserved in two other damagepattern. Verticaldistribution of artifactsat the sand site approximated Factors influencingthese distributions are tramplingexperimentsand a numberof archaeologicaloccurrences. discussed.

Most archaeologists now recognizethat assessingthe influenceof varioussite-formationprocesses is a prerequisiteto inferencesabout human behavior from spatial or statistical patterningin archaeologicalmaterials.Butzer (1982) has recentlydiscussed culturaland sedimentologicalaspects of archaeologicalsite formation in detail, and Schiffer(1983) has recently reviewed the growing body of literatureon site formationprocessesin this journal. Some site-formationresearchhas focused on vertical artifactdistributionswithin sites. Interest in closer specificationof the processesthat structuresites' verticalaspect arose more or less simultaneously in analyses of archaeologicalsites (e.g., Barton and Bergman 1982; Cahen et al. 1979; Cahenand Moeyersons 1977; Moeyersons 1978; Stockton 1973; Van Noten 1978; Villa 1982), and in ethnoarchaeological studies (e.g., Gifford 1980; Giffordand Behrensmeyer1977; Yellen 1977). This article reports on the findings of an experiment assessing the potential of on-site human traffic(treadage and trampling)to cause subsurface, verticaldispersalof artifactsin a site's substrate. Our findings augment those of Courtin and Villa (1982; Villa and Courtin 1983) and Stockton (1973), and they are relevantto recentdiscussionsof verticaldispersalof artifactsin archaeological sites (e.g., Barton and Bergman 1982; Cahen et al. 1979; Rowlett and Robbins 1982; Siirianen 1977). Paola Villa's recent article (1982) in this journal summarizedthe literatureon vertical dispersal; we will thereforediscuss only those aspects of others'findingsthat provide a context for the results of our own experimentalwork. Conjoinablepieces of stone, bone, or pottery have been retrieved from two or more sedimentologicallydistinct strata, separatedby up to 1 m vertically, with no tracesof disturbanceto the deposits perceptibleto the excavatingarchaeologists(Courtinand Villa 1982;M. J. Mehlman,personalcommunication1981;Villa 1982).In sites withoutstratabut likewise lacking clear evidence for disturbanceof sediments, artifactsfrom vastly differentarchaeological phases have been encounteredin the same level, as was the case with Middle Stone Age and Iron Age materialsat Gombe Point site in Zaire(Cahen 1976;Cahenand Moeyersons1977). Conversely, conjoinablepieces have been recoveredas much as 40 cm apartverticallyin sites thoughtto result from relativelyshort single episodes of occupation,as in the case of Meer (Van Noten et al. 1978) and FxJj50,Koobi Fora, Kenya (e.g., Bunn et al. 1980). Materialsin such sites have been recovered through 10 or more vertical cm of sediment. These findingsclearlyillustratethat verticaldispersal of materialsin sites occursin a varietyof circumstances, and they raisequestionsaboutthe processes that cause such movements of archaeologicalmaterialsin their sedimentarymatrices.Diane P. Gifford-Gonzalez, David B. Damrosch,Debra R. Damrosch,John Pryor, and RobertL. Thunen, Board of Studies in Anthropology, University of California,Santa Cruz,CA 95064. AmericanAntiquity,50(4), 1985, pp. 803-818. Copyright?) 1985 by the Society for AmericanArchaeology



[Vol. 50, No. 4, 1985]

Traditionally, archaeologists have conceived of the causes of vertical displacements to be postdepositional, "disturbance" phenomena, either biological or geological. A host of post-depositional disturbance processes have been documented, and their effects described (e.g., Wood and Johnson 1979). Cahen and Moeyersons (1977; Moeyersons 1978) demonstrated that cycles of wetting and drying in sandy deposits can effect substantial vertical movements of artifacts without creating any discernible traces of these movements. The same authors have proposed that reworking of loose sand matrices by termites and worms might, over long periods, cause substantial subsidence and creep of sediments, with resultant vertical displacement of archaeological materials, without leaving visible traces of such movements. These and other recent observations of the behavior of materials in uncemented sediments (e.g., Harris 1979; Limbrey 1975; Rolfsen 1980) all suggest that vertical movement of artifacts and other debris in their sedimentary matrices after deposition is more common than most archaeologists previously suspected. Particularly apt is Villa's (1982:287) statement that, without evidence to the contrary, "layers and soils should be considered as fluid, deformable bodies ... through which archaeological items float, sink, or glide." Treadage of debris into the substrate by the creators of a site during the time they live at that locale is another source of vertical dispersal that is neither post-depositional nor post-abandonment. The potential for on-site activity to cause downward migration of debris into loose substrates was recognized in the 1970s by a number of ethnoarchaeologists, including John Yellen (1977), James O'Connell and Peter White (personal communications 1977), and the senior author (Gifford 1980; Gifford and Behrensmeyer 1977). While excavating Shaw's Creek Shelter (1973), Eugene Stockton also recognized that treadage by humans could effect downward migration of debris. Stockton conducted the first experiment on treadage during his fieldwork; human traffic over glass fragments lying in a loose substrate caused subsurface migration of materials as much as 16 cm below their original locations. Stockton argued that treadage might also have been responsible for the sizedependent sorting of debris that he observed in the upper 20 cm of the Shaw's Creek archaeological site, where larger pieces were higher and smaller pieces lower in the section. More recently, Jean Courtin and Paola Villa (1982; Villa and Courtin 1983) conducted another such experiment in connection with their excavation of La Baume Fontbregoua in southeastern France, and we have carried out the experiment described in this report. The senior author became interested in treadage as a depositional process when excavating a small Dassanetch campsite at Lake Turkana, Kenya, in 1974. This site was created in 1973, over a period of three days, by eight men on a foraging trip. It was then abandoned, and buried in flood silts about six months later during the following rainy season of 1974 (Gifford and Behrensmeyer 1977). On the day it was abandoned, around 340 pieces of bone were observed and place-plotted on the surface of the site. It was, therefore, surprising when a smaller portion of the site, where only 200 bones had been noted on the surface, yielded an excavated sample of 1,955 pieces. Even allowing for the effects of equatorial sun on the efficiency of the first survey, this difference seemed excessive. Many of the bones recovered during excavation lay entirely within the site's original sandy substrate and were very small, less than 3 cm in maximum dimension. It seemed possible that treadage by the camp's occupants might have sent many of these small pieces into the sandy substrate during their three-day stay. While this in itself might be a banal bit of archaeological lore, the small debris recovered were of the same size ranges specified by Schiffer (1977) and various ethnoarchaeologists (D. Anderson, L. Binford, J. O'Connell, personal communications 1977) as highly likely to remain where generated as primary refuse. If microdebris were deposited well into a "permeable" substrate simply in the course of daily human activities, it would be even less liable to displacement away from the actual place of their production (see Schiffer 1983). THE EXPERIMENT We set up an experiment to assess how much subsurface migration of either microdebris or larger pieces can occur simply as a result of on-site human traffic. Since a number of post-depositional processes have been implicated in creating vertical dispersal of materials in sites, we also wanted



to assess whether trampled assemblages exhibit