A 9000-year Record of Vertical and Lateral AccretionOn the Floodplain of the Lower Thames River,

Southwestern Ontario, Canada

Andrew M. Stewart and Joseph R. Desloges

Department of Geography, University of Toronto

Paper presented in session 186, “Alluvial Geoarchaeology of Large River Valleys,” Geological Society of America annual meeting, Philadelphia, 22-25 October, 2006. Copyright Andrew M. Stewart and Joseph R. Desloges

Figure 1: Locations of some main rivers in the Northeast and lower Great Lakes regions in relation to maximum ice sheet extent (after Dyke and Prest 1987).

Figure 2: Main drainage systems in Southern Ontario, showing location of the Thames and Grand River drainages.

Figure 3: Southwestern Ontario showing origin of some of the main surface geological deposits (after Ontario Geological Survey 2003).

Figure 4: The lower Thames River, showing origin of surface geological deposits (after Ontario Geological Survey 2003).

Figure 5: Part of the lower Thames River at Big Bend / Wardsville showing origin of surface geological deposits (after Ontario Geological Survey 2003).

Figure 6: Archaeological site distribution in relation to surface geology and terrace scarps.

Figure 7: Location of radar transects and cores on main study point bar.

Figure 8: Corn field on main study point bar, showing coring locations.

Figure 9: Ground-penetrating radar with 50 MHz antennae (foreground) employed at one of the study sites on the Thames River floodplain.

Figure 10: Topographic profile (top), plan view (middle) and ground-penetrating radar profiles (bottom) from the main study point bar.

Figure 11: Stratigraphy and radiocarbon dates from cores (for explanation, see Stewart 2006).

Figure 12: An interpretation of floodplain formation, with sequential units of deposition (numbered).

Figure 13: Paraglacial / Early Holocene deposition (see Figure 12).

Figure 14: Main period of point bar development (see Figure 12).

Figure 15: Overbank and chute channel activity during and following lateral accretion (see Figure 12).

Figure 16: Possible cut and fill episode (see Figure 12).

Figure 17: Possible post-settlement alluvium vertical accretion (see Figure 12).

Figure 18: Sites on middle and lower reaches of the Thames and Grand Rivers, within their respective basins.