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.

Origin and evolution of lago Yehuin (Tierra del Fuego, Argentina): Results from a geophysical survey

“…9F). As an example, similar facies has been recognized in Lake Malawi in East Africa (Scholz et al, 1998;Lyons et al, 2011), Lake Baikal and Lake Tanganyika (Scholz et al, 1998) and southern Ontario (Pugin et al, 1999). This type of seismic facies generally corresponds to channel valleys with their sedimentary infill and laterally-located terraces.…”

“…These are composed by a mainly chaotic configuration of the reflectors and sometimes with an incipient layering, which can be ascribed to a complex till landform (Pinson et al, 2013). These deposits can be interpreted as moraine deposits based on the similarity (mainly the ridge-shape) with features described by other authors (i.e., Pugin et al, 1999;Fernández et al, 2017). The distribution of the seismic lines across the lake allows to recognize this seismic unit and their morphology in different parts of the LY (Fig.…”

“…Three seismic units have been individuated in the seismic record acquired within LY (Table 1; see Pugin et al, 1999;Fernández et al, 2017). These units were defined as parts of the seismic sections based on their geometric patterns, architecture and stratigraphic relationships.…”

Comment on “Converging ice streams: a new paradigm for reconstructions of the Laurentide Ice Sheet in southern Ontario and deposition of the Oak Ridges Moraine”

“…Sookhan et al (2018) suggest that geomorphologic data provide unambiguous evidence that the ORM was formed between converging paleo ice streams. This approach and the subsequent interpretation is at odds with the extensive work completed over the past 30 plus years by academic (e.g., Duckworth 1979;Boyce et al 1995;Paterson and Cheel 1997;Russell and Arnott 2003) and government survey organizations (e.g., Barnett et al 1998;Pugin et al 1999;Pullan et al 2002;Sharpe et al 2004). These studies have commonly been accomplished by analyzing large integrated data sets of both legacy data (geotechnical, water well records, hydrogeological data) and newly collected geomorphological, surficial geological mapping, sedimentological, continuous cored boreholes, and geophysical data (e.g., Logan et al 2006;Sharpe et al 2002).…”

“…As a surface expression of the landscape, valleys stop at the moraine because the ORM sediment overlies and infills the southward subsurface extension of the valleys (e.g., Barnett et al 1998). Data from seismic and drillcore are extensive and unambiguous in the documentation of valley extension beneath the ORM, in papers cited by Sookhan et al (2018) (e.g., Russell et al 2004;Brennand et al 2006;Sharpe et al 2007;Sharpe et al 2013) and in additional publications (e.g., Pugin et al 1996Pugin et al , 1999Barnett et al 1998;Sharpe et al 2002Sharpe et al , 2004Russell et al 2003aRussell et al , 2003b. Drawing upon technical groundwater reports, Sookhan et al (2018) reference Kassenaar and Wexler (2006) as supporting the absence of a regional network of tunnel valleys.…”