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Chapter 3
Analysis of Sediments Associated with Human Remains Found at Columbia Park, Kennewick, WA
Gary Huckleberry and Julie K. Stein

Figure 6

Figure 6 includes 4 Loss-on-ignition charts that compare five sediment samples from the Kennewick skeletal remains and nine control samples taken at increasing depths from the discovery site along the Columbia River. The first chart presents the percentage of organic matter between 0-3% for 5 element samples for the skeleton sediments. The second chart presents the percentage of organic matter between 0-3% for 9 control samples from the bank and core of the site. The third chart presents the percentage of organic matter between 0-50% for the same 5 elements as in chart #1 of the skeleton sediments. The fourth chart presents the percentage of organic matter between 0-50% for the same control sample of site sediments as in chart #2. These thermogravimetric analyses were undertaken to establish similarities between the skeletal and site samples that may suggest the approximate depth and soil unit in which the skeleton lay prior to washing into the Columbia River.

Weight reductions between 70°C and 550°C reflect a loss of organic matter; overall percentage losses of weight due to oxidation of organic matter were very low, rarely exceeding 2 percent. As Huckleberry and Stein note, weight loss due to oxidation of carbonates between 550°C and 1000°C is more varied and dramatic. They further state "In sum, the thermogravimetric curves indicate that although the amount of organic matter and carbonate varies between samples, the kind of organic matter and mineralogy present is similar in samples above 135 cm depth which includes all of Lithostratigraphic Unit I and the upper part of Lithostratigraphic Unit II...but different for samples below 135 cm depth (middle and lower portion of Lithostratigraphic Unit II...." The strong similarity between organic and carbonate contents in the sample from skeletal bone 97.I.25c and a control sample from the upper portion of Lithostratigraphic Unit II supported this stratigraphic association; percentage weight loss due to oxidation of carbonates exceeded 45 percent in both the skeletal and site samples.

A linear regression curve illustrated in Figure 5 suggested a direct correlation (R2 = .64) between maximum weight-loss and increasing depth, or that 64 percent of the loss in weight is "explained" by increasing depth. Consistent temperatures of peak weight-loss in four skeletal sediment samples (700°C-780°C) suggested a depth association with the lowest 8 cm of Lithostratigraphic Unit I and the upper 40 cm of Lithostratigraphic Unit II. Such an association is consistent with the data presented in Figure 6, but Huckleberry and Stein urge caution in evaluating the specific depth since the cause of the direct correlation between maximum weight-loss temperatures and increasing depth is not known.

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