Effects of Sediment Consolidation and Frost-Heaving on the Vertical Movement of Lithic and Ceramic Artifacts

Publication Date

5-1-2013

Type of Culminating Activity

Thesis

Degree Title

Master of Arts in Anthropology

Department

Anthropology

Supervisory Committee Chair

Mark G. Plew

Abstract

The goal of this research is to contribute to an understanding of how natural site- formation processes impact the spatial position of prehistoric artifacts over time. A clear understanding of site formation processes is critical to interpreting the meaning of the archaeological record. This research was designed to provide quantifiable and replicable models of artifact movement for site formation studies and artifact taphonomy. It addresses the impacts of sediment consolidation and frost-heaving upon lithic and ceramic artifacts through a series of laboratory and field experiments. Sediment consolidation refers to a decrease in sediment volume that is linked with natural overburden loading. Previous studies have demonstrated that a decrease in sediment volume associated with consolidation causes reductions in the inclination angles of artifacts. Sediment consolidation also causes the downward vertical movement of artifacts over time. In contrast, frost-heaving is known to cause an increase in the inclination angles of artifacts. Earlier studies have also shown that frost-heaving may cause the upward vertical movement of artifacts. This process occurs when water freezes beneath the soil surface and forms ice layers parallel to the ground surface. As the ice layers grow, they force overlying sediments upwards, causing a movement of both sediments and artifacts. The effects of sediment consolidation and frost-heaving were evaluated using experimental lithic and ceramic artifacts and an aeolian silt (or loess) found on the Western Snake River Plain, Idaho. The findings of this study may also assist field studies in distinguishing in situ artifacts from those moved out of their initial context by sediment consolidation and/or frost-heaving.

The results of this study demonstrate saturated sediment causes an increase in consolidation when compared to unsaturated sediment. The increase in consolidation leads to an increase in the downward vertical movement of artifacts. The results of the frost-heaving experiment suggest the upward movement of artifacts may be inhibited by sediment composition and that frost and thaw events may cause the breakage of ceramic artifacts. The results of these experiments also indicate that lithic and ceramic artifacts behave similarly as sediment becomes consolidated. Overall, the results suggest that sediment consolidation may occur rapidly, is influenced by moisture content, and that frost-heaving may not be a significant factor in the upward vertical movement of artifacts buried in the sediment type used for testing. Understanding the site formation processes connected with consolidation, artifact movement, and the spatial distribution of artifacts is crucial to interpreting the archaeological record.

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