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

Abstract

Analysis of over 50 line-kilometres of land-based, shallow, seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glacial deposits in and beneath the Oak Ridges Moraine (ORM). The focus of this paper is the role of seismic reflection surveys, and the derived seismic facies and facies geometry, in 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 data define four major seismic facies that characterize the complex glacial sequence of the ORM area. High-reflectivity facies (I) can be traced regionally and related to an eroded Newmarket Till surface. Medium (II) and low (III) reflectivity facies are generally associated with coarse-grained glaciofluvial deposits and laterally extensive, glaciolacustrine sequences of sand, silt, and clay, respectively. A chaotic facies (IV) is common within buried channels, and attributed to instability and (or) rapid channel-fill deposition. Seismic geometry (with borehole verification) shows that a broad surface network of channels extends below thick ORM sediments. The channel system is part of a regional unconformity formed on the Newmarket Till (facies 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 succession (facies II and III) as the flows waned.