A Microstratigraphic Approach to Evaluating Site Formation Processes at Eagle Cave (41VV167)
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Dry rockshelters in the Lower Pecos Canyonlands (LPC) provide a unique setting for archaeological research, preserving otherwise perishable artifacts and organic materials within the site deposits. However, many of the excavations done in the LPC were conducted during the 1930s and 1960s when the focus was recovering unique prehistoric items and/or chronology. The excavation methods during these times were unrefined, data was not reported in great detail, and little effort was made to discuss or interpret site formation processes. My thesis research focused on the northern sector of Eagle Cave, which was first sampled during the 1963 excavations by the University of Texas at Austin. The goal of my thesis research was to use a “microstratigraphic” approach to evaluate the natural and cultural processes that led to the accumulation of the strata in this sector of Eagle Cave, focusing on the source of sediments in each stratigraphic layer, methods of transport of the sediments, and the specific natural and cultural processes responsible for forming and/or reorganizing the deposits. The microstratigraphic approach included recording stratigraphy in high resolution (i.e., “splitting” rather than “lumping” strata) and the collection and analysis of micromorph samples to examine in situ stratigraphy. Multiple lines of evidence, including data derived from the stratigraphic documentation, geoarchaeological sampling, macrobotanical and faunal identification, constituent size distribution, and radiocarbon dating, were used to evaluate the various formation processes. The 75 stratigraphic layers defined, recorded, and sampled in UT North were categorized into general strat types such as discrete ash lenses, thick ash deposits, refuse midden, earth oven heating element remnants, and limestone spall deposits. The results of the analyses revealed that some of our initial impressions of the deposits were incorrect, the most significant being that the “thick ash deposits” contained far less wood ash than what was initially though. The results of the analyses indicate that the deposits in UT North are comprised of natural sediments derived from both inside and outside the shelter (e.g., limestone spall, aeolian silt- and sand-sized grains), biogenic deposits derived from animals (e.g., feces), and anthropogenic materials brought in to the shelter by humans for plant processing and baking (e.g., rock, fuel, foodstuffs, alluvium to cap earth oven), animal butchering, consumption, and tool manufacture (i.e., faunal remains), and stone tool production (i.e., lithics debris and tools). The reorganization of deposits through time in this portion of the rockshelter is primarily a result of prehistoric cleanout activities and pit digging, although bioturbation from animal burrowing also contributed a substantial amount of reorganization. This thesis provides an initial evaluation of the formation processes that led to the accumulation of the strata in Eagle Cave. However, my research focused on one small area of the shelter and additional analyses need to be completed on the samples from the central portion of the shelter to get a better picture of the various formation processes at play. Subsequent 2015–2016 Eagle Cave investigations have done just this and have benefited from my hard-won lessons.