Seismic facies and regional architecture of the Oak Ridges Moraine area, southern Ontario

Analysis of over 50 line-kilometres of land-based, shallow, seismic reflect ion profiles has provided a means of investigating the subsurface architect ure and stratigraphic relationships of the glacial deposits in and beneath the Oak Ridges Moraine (ORM). The focus of this paper is the role of seismi c reflection surveys, and the derived seismic facies and facies geometry, i n the development of a well-constrained, regional, conceptual model of the subsurface stratigraphy in the area and the improved inferences these data allow regarding glacial event sequence and process interpretations. The dat a define four major seismic facies that characterize the complex glacial se quence of the ORM area. High-reflectivity facies (I) can be traced regional ly and related to an eroded Newmarket Till surface. Medium (II) and low (II I) reflectivity facies are generally associated with coarse-grained glaciof luvial deposits and laterally extensive, glaciolacustrine sequences of sand , silt, and clay, respectively. A chaotic facies (IV) is common within buri ed channels, and attributed to instability and (or) rapid channel-fill depo sition. Seismic geometry (with borehole verification) shows that a broad su rface network of channels extends below thick ORM sediments. The channel sy stem is part of a regional unconformity formed on the Newmarket Till (facie s I). The buried channels can have steep sides, and their fills frequently include tabular sheets, eskers, and (or) large cross-beds. The observations are consistent with the scenario of sheet flow and channel cutting by high -energy subglacial meltwater and filling with gravel, sand, and silt in suc cession (facies II and III) as the flows waned.