Project Title

Paleochannel or Palisade? Preliminary Geophysical Investigations of a Linear Feature at the Runion Archaeological Site, Washington County, Tennessee

Authors' Affiliations

Montana L. Kruske, Department of Geosciences, College of Arts and Sciences, East Tennessee State University, Johnson City, TN. Dr. Eileen G. Ernenwein, Department of Geosciences, College of Arts and Sciences, East Tennessee State University, Johnson City, TN.

Location

Ballroom

Start Date

4-12-2019 9:00 AM

End Date

4-12-2019 2:30 PM

Poster Number

12

Faculty Sponsor’s Department

Geosciences

Name of Project's Faculty Sponsor

Dr. Eileen Ernenwein

Type

Poster: Competitive

Classification of First Author

Graduate Student-Master’s

Project's Category

Floodplains, Geophysics, Magnetics

Abstract Text

Runion is a protohistoric Native American village located on the floodplain of the Nolichucky River in western Washington County. Previous archaeological excavations and radiocarbon dates suggest that the village was occupied during the mid-16th to mid-17th century. The Nolichucky River, in contrast, has been flowing through the area for millennia. Geophysical surveys are used to image the subsurface non-invasively, without disturbing protected land and/or organisms. Preliminary geophysical data collected at Runion include ground penetrating radar (GPR), electromagnetic induction (EMI), and magnetometry. These data show a linear feature surrounding the protohistoric village. Given its placement around the margins of the village, the feature could be interpreted as a fortification ditch, which is often paired with a palisade wall to defend a village from attack. The feature is also consistent with typical meandering floodplain stratigraphy, where sections of channel are often abandoned to form oxbow lakes. Over time these abandoned channels fill in and are called paleochannels.

Each geophysical method measures the properties and characteristics of the linear feature, a presumed paleochannel. GPR sends electromagnetic radar waves into the ground, which reflect off different subsurface layers and are recorded as radargrams. Magnetometry measures subtle changes in earth magnetism, including the magnetization of rocks, soils, and/or ferrous objects. EMI systems transmit low frequency electromagnetic waves to measure both electrical conductivity (EC) and magnetic susceptibility (MS). Each of these instruments are used to collect data in transects and then processed to produce profiles, maps and, in the case of GPR, three-dimensional datasets of the subsurface.

It is anticipated that GPR will reveal details about the stratigraphy of the linear feature. Magnetic, EC, and MS measurements will further help to interpret the GPR data by distinguishing between different types of sediments. These data may show if the feature is a paleochannel or a ditch excavated into older stratigraphic layers by village inhabitants for fortification. Ultimately, the feature will be tested with soil cores to study the sediments directly.

At this preliminary stage the feature is interpreted to be a paleochannel. The stratigraphic layers revealed by GPR show a broad depression with stratigraphic layers characteristic of a paleochannel. In addition, magnetic readings are anomalously low on the eastern margin (closer to the modern river channel) and high on the western margin. This could indicate paired point bar sands and paleochannel fill, respectively. This interpretation is still tentative, however, because we have not yet integrated the EMI data, extracted soil cores, or dated the feature. Radiocarbon dates might help determine the relative age of the feature if organic carbon is present. In conclusion, preliminary data currently suggests that the structure is geological rather than archaeological. In the coming months we will collect more GPR data with different frequency GPR antennas, integrate the EMI data, and test the findings by extracting soil cores and reconstructing the stratigraphy.

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Apr 12th, 9:00 AM Apr 12th, 2:30 PM

Paleochannel or Palisade? Preliminary Geophysical Investigations of a Linear Feature at the Runion Archaeological Site, Washington County, Tennessee

Ballroom

Runion is a protohistoric Native American village located on the floodplain of the Nolichucky River in western Washington County. Previous archaeological excavations and radiocarbon dates suggest that the village was occupied during the mid-16th to mid-17th century. The Nolichucky River, in contrast, has been flowing through the area for millennia. Geophysical surveys are used to image the subsurface non-invasively, without disturbing protected land and/or organisms. Preliminary geophysical data collected at Runion include ground penetrating radar (GPR), electromagnetic induction (EMI), and magnetometry. These data show a linear feature surrounding the protohistoric village. Given its placement around the margins of the village, the feature could be interpreted as a fortification ditch, which is often paired with a palisade wall to defend a village from attack. The feature is also consistent with typical meandering floodplain stratigraphy, where sections of channel are often abandoned to form oxbow lakes. Over time these abandoned channels fill in and are called paleochannels.

Each geophysical method measures the properties and characteristics of the linear feature, a presumed paleochannel. GPR sends electromagnetic radar waves into the ground, which reflect off different subsurface layers and are recorded as radargrams. Magnetometry measures subtle changes in earth magnetism, including the magnetization of rocks, soils, and/or ferrous objects. EMI systems transmit low frequency electromagnetic waves to measure both electrical conductivity (EC) and magnetic susceptibility (MS). Each of these instruments are used to collect data in transects and then processed to produce profiles, maps and, in the case of GPR, three-dimensional datasets of the subsurface.

It is anticipated that GPR will reveal details about the stratigraphy of the linear feature. Magnetic, EC, and MS measurements will further help to interpret the GPR data by distinguishing between different types of sediments. These data may show if the feature is a paleochannel or a ditch excavated into older stratigraphic layers by village inhabitants for fortification. Ultimately, the feature will be tested with soil cores to study the sediments directly.

At this preliminary stage the feature is interpreted to be a paleochannel. The stratigraphic layers revealed by GPR show a broad depression with stratigraphic layers characteristic of a paleochannel. In addition, magnetic readings are anomalously low on the eastern margin (closer to the modern river channel) and high on the western margin. This could indicate paired point bar sands and paleochannel fill, respectively. This interpretation is still tentative, however, because we have not yet integrated the EMI data, extracted soil cores, or dated the feature. Radiocarbon dates might help determine the relative age of the feature if organic carbon is present. In conclusion, preliminary data currently suggests that the structure is geological rather than archaeological. In the coming months we will collect more GPR data with different frequency GPR antennas, integrate the EMI data, and test the findings by extracting soil cores and reconstructing the stratigraphy.