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Monday, June 4, 2007

The Emergence of Geoarchaeology in Research and Cultural Resource Management: Part I

Joseph Schuldenrein-Principal Archeologist and President of Geoarcheology Research Associates.

Since the early 1970s, the trajectories of geoarchaeology and cultural resource management (CRM)have followed contemporaneous if somewhat independent courses. As a widely applied strategy, geoarchaeology emerged in the wake of the “New Archaeology.” It was a logical vehicle for incorporating scientific methods to a theoretical orientation that emphasized human ecology. Perhaps the signature work that placed the discipline on the academic “archaeological map” was Karl Butzer’s second edition of Environment and Archaeology: An Ecological Approach to Prehistory (1971). At about the same time, the expansive reach of the National Historic Preservation Act (1966) mandated archaeological investigations across landscapes, environments, and contexts heretofore unanticipated across the U.S.

In hindsight, geoarchaeology’s landscape perspective and the preservation ethic would appear to be natural allies for implementing compliance projects, but the convergence of the two was slow to develop. The catalyst for integration was the growth of large-scale planning projects—reservoir expansions for major drainages of the Southeast and Forest Service inventories in the West, for example—that formally
designated natural landscapes as planning units. By the mid-1980s, it became apparent that an understanding of the systematics of landscape evolution would account for site/settlement distributions and the processes of site burial and preservation, items of paramount concern to cultural resource planners. The results of CRM research began to be reported in the professional literature (Waters 1992), and
geoarchaeology was eventually integrated into planning strategies.

While it is safe to say that geoarchaeology has demonstrated its worth in CRM, the science behind it remains mysterious to planners and general archaeologists alike. As in other archaeological specialties, the methods, techniques, and interpretive potential of the field have evolved over decades. Ideally, practitioners are extensively trained in both the natural and social sciences and have gained considerable experience by studying archaeological sites in their natural contexts. The purpose of these articles is to acquaint the archaeological public with the key concepts and applications of geoarchaeology, and specifically that aspect of geoarchaeology bearing on ancient landscapes. More importantly, the mission is to
enable planners, principal investigators, technicians, and students to identify those settings in which geoarchaeology is beneficial and to pose the right questions for professionals working at their sites. In Part I, the general concepts and principles of geoarchaeology are discussed, and field work and sampling are introduced. In Part II, which will appear in the next issue of The SAA Archaeological Record, a detailed assessment of geoarchaeology’s utility for compliance work in CRM will be provided.

Concepts and Principles

As the term implies, geoarchaeology addresses the interface between the earth sciences and archaeology. Archaeological problems form the basis of the inquiry. The term archaeological geology is also used, but it more accurately refers to a thematic bias in which geology is the primary focus and archaeology is simply an investigative technique.

A fundamental postulate is that cultural finds are always tied to a landscape—either on an exposed surface or buried underneath it. Irrespective of the aims of an archaeological project, the association between cultural materials and the ground is critical to assessing significance from the compliance perspective. Systematic associations between cultural features (e.g., artifacts, storage pits, processing stations, settlements, structures), their periods of occupation, and patterned distributions with particular terrain elements enables CRM professionals to structure observations in a way that is meaningful for clients and regulators.

A second postulate is that over the course of the 15,000 years of human occupation across North America, the landscape has been dynamic. Thus the history of landscape dynamics provides an independent context for explaining the variability in archaeological distributions across time and space. Landscape histories are initially reconstructed by examining the individual landforms that define an environmental
setting. An alluvial landscape, probably the most prominent setting for stratified sites, includes such landforms as terraces, flood basins, marshes, and meander scrolls. However, because of landscape dynamism, the configuration of landforms comprising the contemporary alluvial terrain may not correspond to that of the past. Surface artifacts of recent origin can be separated from prehistoric settings by
depths of deposit within the same landform or by distance from former landforms that are no longer exposed. Systematic study of landscape change is key to understanding patterned contexts of cultural features through time and determines if, for example, remains of a given prehistoric period will survive on the surface, erode away, or be buried. The study of landscape change—effectively, the change in landform configurations—is geomorphology.

Assembling landscape histories and assessing site integrity are the most critical objectives for the geoarchaeologist. Landform histories are grounded in absolute dating techniques, which, in North America, still center on the radiocarbon technique for carbonized cultural remains, but are now increasingly dependent on AMS and bulk sediment dating of organic deposits that may house archaeological materials.
Archaeomagnetism and thermoluminescense have gained increasing prominence for archaeological dating, while dendrochronology and obsidian hydration are routine across the western U.S. The most exciting recent development in absolute dating is optically stimulated luminescence (OSL), which expands the dating scale to 100 KYA and facilitates determinations in Aeolian environments.

To develop assessments of site integrity, geoarchaeologists draw on techniques from a variety of disciplines, including geology, sedimentology, pedology, hydrology, geomorphology, stratigraphy, chemistry, geophysics, photogrammetry, and engineering, as well as archaeology. Parenthetically, geoarchaeological approaches are colored by the training of the practitioner vis-à-vis these disciplines; the approach of a
pedologist, for example, differs considerably from that of a geomorphologist, since the former emphasizes soil sequences and stable environments, while the latter is keyed to dynamic landscapes and processes of change. Geoarchaeological approaches are widely applied to prehistoric settings but are increasingly drawn upon to reconstruct site formation processes at historic sites.

The initial strategy for modeling landform histories is an understanding of the subsurface materials that account for their formation. Subsurface materials can be divided into three basic categories: geological deposits, soils, and anthropogenic sediments. Geological deposits or sediments are laid down by gravity, water, or wind and represent the accretionary forces of the natural environment. The ideal
preservation context for ancient occupations in formerly active landscapes—coastal plains, stream margins, dune fields, rock shelters, and caves—is burial by low-energy deposition. More commonly, however, artifacts are mobilized after site abandonment. It is the geoarchaeologist’s job to determine how, why, and when such displacements occurred.

Soils are weathered (mechanically or chemically “broken down”) sediments that represent stable periods of a landscape’s history when prehistoric evidence is likely to be preserved in situ (thus retaining integrity and factoring into significance determinations). A broad rule of thumb is that buried soils are proxies for ancient surfaces. Many archaeologists are familiar with the “A-B-C” horizonation of soils,
although these designations are widely misused, and the terms “soils” and “sediments” are bandied about with abandon in field settings. While soil taxonomies are intricate and complicated, another simple rule for field archaeologists is that the “A” horizon is organic and typically black, “B” horizons are zones of mineral enrichment, often red or brown, and “C” horizons are the unmodified parent material or the sediment above which active soil formation occurs.

Finally, anthropogenic sediments are of unequivocal cultural origin and represent the human imprint on the earth; features such as roasting pits, storage facilities, house floors, and planting fields are examples. Typically, anthropogenic deposits and soils are found together and represent the most sensitive archaeological contexts.

To read the remainder of this article visit the SAA Archaeological Record