Micro-XRF geochemical and micropaleontological evidence for prehistoric land disturbance: construction of the Middle Woodland (ca. 300 BCE – 700 CE) Serpent Mounds Complex, Rice Lake (Ontario, Canada)
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abstract
Serpent Mounds is a prehistoric (Middle Woodland, ca. 2000-1000 BP) burial mound complex located on the north shore of Rice Lake (Ontario, CA). The complex includes a 60m long and 10m wide sinuous earthwork ridge and eight oval mound structures. The timing of mound construction is poorly constrained limited radiocarbon dates on human burials, and sparse paleoenvironmental data. Serpent Mounds is of high cultural importance as the only known effigy mound structure in Canada; no further excavations are permitted onsite and all future work must employ non-invasive techniques. XRF Core Scanning and micropaleontologic analysis (testate amoebae) of 12 lake sediment cores was employed to investigate the timing of mound construction and assess prehistoric land
disturbance. Land disturbance is indicated by increasing minerogenic elements (K, Ti, Zr, Si, Fe) within a distinctive silt-rich gyttja unit. Heightened terrigenous sediment influx coincides with abundant D. oblonga, C. tricuspis, and D. proteiformis, indicating a more eutrophic, turbid lake environment. Principal component analysis and cluster analysis of µ-XRF data identifies the event as a distinctive chemofacies across several cores. AMS 14C dates for the land disturbance event correspond with the Point Peninsula occupation of sites around Serpent
Mounds, indicating a protracted occupation over from 2050–1300 cal BP with two major peaks in soil erosion at ca. 2200 and 1350 cal BP. The sediment accumulation rate (> 1.5mm/yr) during the phase of enhanced erosion was comparable to that during the 1838 CE dam construction.
The reconstructed Middle Woodland paleoshoreline and water levels indicate shallow lake and
wetland and environments, which provided suitable habitats for the growth of wild rice stands and shellfish resources. The results demonstrate that XRF Core Scanning and micropaleontological methods are important tools for the investigation of culturally-sensitive archaeological sites.
