63-2 Characterizing anthropogenic impacts and modification of soils to aid in interpreting shallow geophysics in archeology

Session: Geoarchaeology of Sites to Landscapes: Current Research on Long-Term Water and Soil Management and Maladaptation (Posters)

Poster Booth No.: 117

Presenting Author:

Hendrick England

Authors:

Feinberg, Joshua M.¹, Brown, Andy², Schirmer, Ronald³, Larson, Phillip Herman⁴, Fisher, Beth⁵, England, Hendrick⁶

(1) Institute for Rock Magnetism, Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA, (2) EARTH Systems Laboratory, Minnesota State University, Mankato, Mankato, MN, USA, (3) Department of Anthropology and Geography, Minnesota State University, Mankato, Mankato, MN, USA; EARTH Systems Laboratory, Minnesota State University, Mankato, Mankato, MN, USA, (4) EARTH Systems Laboratory, Minnesota State University, Mankato, Mankato, MN, USA; Department of Anthropology and Geography, Minnesota State University, Mankato, Mankato, MN, USA, (5) Department of Biochemistry, Chemistry, and Geology, Minnesota State University, Mankato, Mankato, MN, USA, (6) Department of Anthropology and Geography, Minnesota State University, Mankato, Mankato, MN, USA; EARTH Systems Laboratory, Minnesota State University, Mankato, Mankato, MN, USA,

Abstract:

Non-invasive geophysical methods like ground penetrating radar (GPR), electrical resistivity (ER), and magnetometry provide non-destructive, high-resolution data that allow geoarcheologists to identify and interpret geologic and anthropogenic features in the subsurface. As technology and application of these techniques grows, little work has attempted to characterize and understand the sediment and soil properties in and around geophysical “anomalies” observed at archeological sites. These anomalies are often hypothesized as anthropogenic in origin, but the causes of the anomalies are not well understood and could lead to erroneous interpretations. This necessitates further study of the geochemistry, sedimentology, and geomorphology of these anomalies and the sites in which they are found. 

We present a case study from an archeological site located on a stream terrace of the Cannon River valley, MN, USA (21GD0072). Nearly a decade of ER, magnetometry, and GPR surveys, along with archeological and geologic field observations, have been compiled at and near this site. Geophysical data indicates anomalies of variable magnetic field strength, electrical resistivity, and shallow irregular/disrupted GPR reflections that are often consistent with known archeological features. The geophysical anomalies range in size from <1m to >10m but are consistently <2m in depth. We hypothesize these anomalies result from anthropogenic activity changing soil geochemistry and microbial ecology. We investigate the soil properties at two archeological features: one with increased magnetic field strength and another with decreased electrical resistivity - both show irregular/disrupted GPR reflections. We also sampled two control locations to allow for comparison with the surficial geology and soils present at the site. Samples were analyzed via a vibrating-sample magnetometer, magnetic properties measurement system, scanning electron microscope and microprobe, elemental analyzer, Malvern mastersizer 3000, and pH sensor to understand soil chemical and physical properties and magnetic grain formation and alteration. We present our preliminary results and contextualize these profiles by interpreting the geomorphic, sedimentologic, and archaeological setting in which they are found. These data reveal the complexity and variability of geophysical data at archeological sites, but provide a more robust understanding of how indigenous land use altered soil and sedimentary properties likely generating geophysical anomalies. This work provides a more comprehensive step towards a blueprint for interpreting geophysical data in archeological sites in similar geomorphic and sedimentologic settings.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8829

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