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Geoarchaeology at Leetsdale: Reconstructing Prehistoric Landscapes of the Upper Ohio Valley

Geoarchaeology at Leetsdale: Reconstructing Prehistoric Landscapes of the Upper Ohio Valley. Joseph Schuldenrein, Geoarcheology Research Associates Frank Vento, Clarion University Suanna Selby-Crowley, Geoarcheology Research Associates.

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Geoarchaeology at Leetsdale: Reconstructing Prehistoric Landscapes of the Upper Ohio Valley

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  1. Geoarchaeology at Leetsdale: Reconstructing Prehistoric Landscapes of the Upper Ohio Valley Joseph Schuldenrein, Geoarcheology Research Associates Frank Vento, Clarion University Suanna Selby-Crowley, Geoarcheology Research Associates 2009 GSA Annual Meeting, October 18-21, 2009 Portland, Oregon

  2. Objectives • Developing linked archaeological and geological stratigraphies at a complex, multi-component site in a region that is relatively unknown. • Structuring geoarchaeological observations that interface with paleoenvironmental trends. • Modeling “geo” and “archeo” trends into a diachronic model of site formation. • Extending the model valley wide, regionally and extra-regionally.

  3. Project Setting Site area is 40km south of glacial margin. There is an expectation for outwash sedimentation on major valley floors.

  4. Industrialized Landscape on Right Bank, Ohio River

  5. Area 3 Area 1 Area 2 Primary Excavation Areas within Project Footprint Individual areas selected on the basis of potential impact and archaeological potential. The latter is previewed by subsurface stratigraphy.

  6. Project investigation parcels and terrace relations

  7. Historic Physiography and Land Use GIS layering generates area-specific images of former land cover.

  8. Archaeological Excavations At depths of ±1 m, excavation extends into terrace substrate which exposes Bw, Bt, or Btx horizons depending on terrace elevation and paleosol articulation. Prehistoric features are housed within soil horizons to variable depths.

  9. Baseline Chronology Initial testing disclosed carbonized residue to depths of 7m but definitive cultural features extended to 4 m, well into Middle Archaic time ranges.

  10. Leetsdale: Initial Sensitivity Map Isobar delimits extent of Bt horizon. Superposed perimeters offset zones of older and younger prehistoric distributions. Intersection forms zone of multi-component stratification.

  11. Sedimentation Rates and Soil Formation Terrace construction was most dynamic around 6-5 kya (Area 2N) and rates of alluviation declined after 3 kya. Evidence for deep soil formation is pervasive in the Late Archaic horizons.

  12. Site Formation in the Back-Channel & Area 1 Lamellae signify episodic flood events and limited pedogenesis in the back channel. This trend carries over into Area 1, where Late Archaic horizons were found both in lamellar and Bt horizons.

  13. Micromorphology Medium sands with silty infillings. This is typical of episodic flooding followed by translocation of clays. Finer textured parent material with clay coatings characteristic of alluvial paleosol (Bt horizon).

  14. Geoarchaeological Variability in Area 2

  15. Leetsdale Composite Section

  16. Back Channel: Changing Vegetation Through Time AU-2 to AU-3 marks peak of oak frequency and general displacement of tree cover by cheno-ams and herb communities. Is this related to forest clearance at the latter stages of the Late Archaic?

  17. Composite Block Diagram, Leetsdale Prehistoric Site

  18. Leetsdale: Detailed Radiometric Chronology

  19. Phosphates Register Anthropogenic Signatures Phosphate fractionation differentiates occupational signatures. Locus A depicts long term habitation while Locus B represents single use events (at Leetsdale).

  20. Diachronic Model I: Leetsdale Terrace Construction

  21. Diachronic Model II: Leetsdale Terrace Stabilization

  22. Geoarchaeological Landscapes Along the Ohio River Valley

  23. Ohio Valley Sites, Landscapes, and Topographies

  24. Landform-Sediment Assemblages, Ohio Valley Site Complexes Preservation contexts of prehistoric assemblages. They are vertically stacked upstream (one terrace), laterally and spatially zoned downstream (two terraces).

  25. Geoarchaeological Landscapes Across Pennsylvania

  26. Representative Geoarchaeological Columns for Pennsylvania’s Trunk Streams

  27. Implications of the Leetsdale Study • Allostratigraphic principles accommodate the latitude necessary for explaining complex site formation process. • Terrace construction at Leetsdale had effectively been completed by 5000 B.P. Subsequent additions to terrace landscapes were the product of dynamic (alluvial) events. The Bt horizon is a marker of landscape stability. • By 3000 B.P. there is some evidence of terrain change in the form of human interference (deforestation?). • Broader geoarchaeological correlations are suggested by comparing the Leetsdale sequence with valley-wide (Ohio River) and inter-valley (Pennsylvania) chrono-stratigraphies.

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