REINTERPRETATION OF FACIES IN BORDEN, ONTARIO SEDIMENT CORES USING OUTCROP ANALOGUE OBSERVATIONS

Lithofacies mapped in sediment cores from the well-known Borden aquifer have relatively distinct cumulative distribution functions for both permeability (k) and chlorinated solvent sorption (K_d). Combining these functions with the known distribution of lithofacies provides a description of the spatial distribution of k and K_d, leading to improved predictions of groundwater contaminant transport.

In cores, the sediment facies were distinguished by grain size, sorting, lamination dip and frequency, and bedding distinctness (which is controlled by concentration of metallic minerals). The cores were spaced 0.25-1.0 m apart, providing information that is essentially continuous vertically, but discontinuous laterally. Because of the wide spacing of cores, large-scale, non-planar features in the sediment, such as scours and troughs, cannot be identified.

At a nearby outcrop, photographs were used to map approximately 200 m² of analogous sediment exposed by cuts at multiple orientations. Facies were distinguished by the same metrics used for sediment cores. These maps provide insight into the sedimentological structures and spatial facies distributions of the sediments which compose the Borden aquifer.

By interpreting the core data in the context of the outcrop analogue observations, lithofacies boundaries can be interpolated between cores. These maps show clear patterns matching large-scale structures observed in the outcrop. This method demonstrates the emendation of 1-D vertical core interpretation to 2-D, which allows us to relate the spatial distribution of k and K_d to sedimentological architecture. This approach will lead to spatial distributions of aquifer transport properties (k and K_d) that are continuous and geologically authentic - attributes that are critical to accurately predicting subsurface contaminant transport.