SEDIMENTARY ARCHITECTURE AND HYDROSTRATIGRAPHY OF QUATERNARY GLACIAL SEDIMENTS IN GEORGETOWN, ONTARIO, CANADA

Architectural element analysis is a methodology used for the delineation of sedimentary geometry from outcrop exposures. Detailed reconstruction of facies geometries provides valuable information regarding sedimentary heterogeneity at various scales and allows more accurate construction of hydrostratigraphic models, which is fundamental to groundwater investigations in glaciated terrains with complex stratigraphy.

This poster presents a detailed architectural reconstruction of subsurface sediments recorded from 9 fully-cored boreholes, which penetrate unconsolidated Quaternary glacial sediments and Paleozoic bedrock, drilled in the east Sixteen Mile Creek and Cedarvale valley areas of Georgetown, Ontario. Twelve facies types (including gravel, sand, diamict and fine-grained facies) were identified in core and grouped into facies associations (FAs) based on similarities in depositional context and stratigraphic position. The relationship between FAs and their various bounding surfaces (4^th- to 7^th-order) allowed the demarcation of 9 different architectural elements (AEs). The arrangement of AEs and their bounding surfaces delineated 9 major stratigraphic units (U1-U9) that have been used to reconstruct past depositional environments. Glaciofluvial and deltaic sands and fine-grained units (U2, U4, U9) have a sheet-like external geometry and variable internal architecture. Colluvial and subglacial diamict units (U1, U3, U6) have a sheet-like external geometry, a complex internal architecture and are incised in places by chanelized coarse-grained glaciofluvial units (U4 & U7). This regional stratigraphy is locally truncated and incised by more recent fluvial deposits (U8).

Multiple incision events associated with fluvial and glaciofluvial processes facilitate the development of significant hydraulic connections through aquitards to underlying aquifers. Establishing the geometry and architecture of stratigraphic units can improve understanding of fluid flow pathways, facilitate prediction of facies types and geometries in areas with a paucity of outcrop/ borehole data, and enhance the accuracy of local and regional three-dimensional geologic/ hydrogeologic models in southern Ontario and similar glaciated terrains elsewhere.