DECONSTRUCTING THE SUBSURFACE: ARCHITECTURAL ELEMENT ANALYSIS OF QUATERNARY GLACIOFLUVIAL DEPOSITS, LIMEHOUSE, ONTARIO, CANADA

Thick successions of glacial deposits host significant aquifers in northern North America. However, glacial depositional environments are dynamic and result in complex sedimentary successions that make characterization of the aquifers they host, difficult. This paper utilizes architectural element analysis (AEA) to characterize heterogeneity within a Quaternary age coarse-grained glaciofluvial deposit exposed in the Limehouse Pit, Ontario and provides an analogue for the analysis of more deeply buried aquifers in the region.

AEA is a methodology that involves identification of the scale and form of sedimentary units and their bounding surfaces and allows documentation of three-dimensional textural variability (heterogeneity) in sedimentary successions. Exposures of glaciofluvial sediment were logged in an active aggregate pit in Limehouse, recording grain size, sedimentary structure, clast lithology, shape, size, and orientation, thickness, unit contacts, and facies types. Nine facies were identified, including gravel facies (Gm, Gp, Gt), sand facies (Sr, Sp, St, Ss) and fine-grained facies (Fl and Fd). Variations in facies associations and the geometry of unit contacts (4^th-order bounding surfaces) allowed demarcation of five architectural elements (AEs), including gravel sheet (GS), sand complex (SC), concave fill (CF), fine-grained sheet (FS), and gravel foreset body (GFB) elements. The spatial arrangement of AEs and higher order bounding surfaces also allowed the discrimination of six larger scale element associations (EAs), including those representing sandy braided river (EA1), delta front (EA2), gravelly braided river/ delta top (EA3), delta front/ lacustrine (EA4), braided river/ deltaic (EA5), and sand-dominated fluvial (EA6) environments.

AEA is utilized here to both enhance paleoenvironmental reconstructions of the study area and to also capture three levels of heterogeneity in the exposed glaciofluvial deposits that can be applied to detailed aquifer characterization and computer-based modeling. Outcrop analogue studies such as this provide insight to the architecture of more deeply buried coarse-grained deposits that form important aquifers, and can be utilized to enhance paleoenvironmental reconstruction of subsurface alluvial deposits elsewhere.