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

Seismic facies and regional architecture of theOak Ridges Moraine area, southern Ontario1

A. Pugin, S.E. Pullan, and D.R. Sharpe

Abstract: Analysis of over 50 line-kilometres of land-based, shallow, seismic reflection profiles has provided a meansof investigating the subsurface architecture and stratigraphic relationships of the glacial deposits in and beneath theOak Ridges Moraine (ORM). The focus of this paper is the role of seismic reflection surveys, and the derived seismicfacies and facies geometry, in the development of a well-constrained, regional, conceptual model of the subsurfacestratigraphy in the area and the improved inferences these data allow regarding glacial event sequence and processinterpretations. The data define four major seismic facies that characterize the complex glacial sequence of the ORMarea. 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 laterallyextensive, glaciolacustrine sequences of sand, silt, and clay, respectively. A chaotic facies (IV) is common withinburied channels, and attributed to instability and (or) rapid channel-fill deposition. Seismic geometry (with boreholeverification) shows that a broad surface network of channels extends below thick ORM sediments. The channel systemis 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 withthe scenario of sheet flow and channel cutting by high-energy subglacial meltwater and filling with gravel, sand, andsilt in succession (facies II and III) as the flows waned.

Résumé: L’analyse de 50 km de profils de sismique réflexion terrestre à haute résolution ont permis une observationde l’architecture sédimentaire de subsurface et la relation entre les unités stratigraphiques glaciaires en-dessous de lamoraine de l’Oak Ridges (ORM). L’intension de cet article est de démontrer le rôle que joue la sismique réflexion,avec l’analyse des faciès sismiques et de leur géométrie, dans le développement d’un modèle conceptuel régional de lastratigraphie dont les limites sont bien reconnues. Ceci a pour conséquence que ces données améliorent l’interprétationde séquences et de processus glaciaires. Quatre faciès sismiques caratérisent la séquence de dépôt glaciaire complexede la région de l’ORM. Un faciès très réflectif (I) peut être suivi régionalement et mis en relation avec une surfaced’érosion du Till de Newmarket. Des faciès de moyenne (II) et de faible (III) réflectivité sont associés respectivement,avec des dépôts fluvioglaciaires de granulométrie grossière et des séquences glaciolacustres formées de sable, de limonet d’argile déposés régionalement sur de grandes surfaces. Un faciès chaotique (IV) se trouve fréquemment dans deschenaux enterrés et sont attribués à des instabilités et (ou) des dépôts rapides dans le chenal. Sur la base decalibrations avec des forages, la géométrie sismique montre l’existence d’un réseau de chenaux au-dessous de l’épaissecouche sédimentaire de l’ORM. Ce sytème de chenaux fait partie d’une disconformité régionale sur le Till deNewmarket (faciès I). Les bords des chenaux enterrés peuvent comporter de très fortes pentes et le remplissage montredes drappages horizontaux, des eskers ou des larges stratifications entrecroisées. Ces observations sont en accord avecdes inondations laminaires en nappes et des incisions de chenaux par de l’eau de fonte sous-glaciaire avec des dépôtsuccessifs de graviers, sables et limons lorsque le flux diminue (facies II et III).

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Introduction

The Oak Ridges Moraine (ORM) and underlying sedi-ments form a thick, extensive Quaternary aquifer complexthat supplies groundwater to more than 200 000 peoplewithin the Greater Toronto Area (GTA) (Fig. 1). However,there are questions relating to the long-term integrity of this

groundwater resource under the continuing pressures ofrapid urbanization (e.g., Gore and Storrie Ltd. and MacViroConsultants Inc. 1993). Much of this concern arises from apoor understanding of groundwater recharge, regionalgroundwater flow, and the extent, thickness, and connectiv-ity of surface and subsurface aquifers, and their geologicalsetting. A better understanding of the regional geology andarchitecture of the complex glacial sedimentary deposits inthe area is required to evaluate regional groundwater flowand to allow for cost-efficient searches for additionalgroundwater supplies.

An investigation of the architecture of the ORMhydrostratigraphy requires the assessment of several relatedaspects of the regional geological history, including (i) thepossible presence of significant bedrock channels (Sado etal. 1984); (ii ) a deeply buried sequence of older deposits,

Can. J. Earth Sci.36: 409–432 (1999) © 1999 NRC Canada

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Received June 15, 1998. Accepted November 16, 1998.

A. Pugin. Institut F.-A. Forel, Rte. de Suisse 10, 1290Versoix, Switzerland.S.E. Pullan2 and D.R. Sharpe.Geological Survey ofCanada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada.

1Geological Survey of Canada Contribution 1998081.2Corresponding author (e-mail: [email protected]).

perhaps traceable from the well-known Scarborough Bluffs(Fligg and Rodrigues 1983; Eyles et al. 1985); (iii ) defini-tion of the subsurface expression of a large channel network(Barnett 1990); and (iv) the need to decipher the structure ofthe ORM aquifer complex (Turner 1977).

During the last 5 years, considerable effort by universitygroups and federal, provincial, and municipal agencies hasbeen directed towards improving our understanding of thegeological and hydrogeological framework of the OakRidges Moraine area. Work has included the analysis of alarge quantity of archival surface and subsurface data(Hunter and Associates and Raven-Beck Environmental Ltd.1996; Brennand et al. 1994; Russell et al. 1996; Brennand1999), geological mapping (e.g., Sharpe et al. 1997), strati-graphic drilling (Barnett 1993), hydrogeological studies(Gerber and Howard 1996; Howard et al. 1997), detailedcharacterizations of potential landfill sites (e.g., Fenco-MacLaren 1994; Golder and Associates 1994), analysis ofremote sensing data (Kenny et al. 1996; Kenny 1997; Skin-ner and Moore 1997), and geophysical surveys (Todd et al.1993; Pilon et al. 1994; Pullan et al. 1994; Boyce et al.1995).

Because of the large area and the thickness of overburdenmaterials in the ORM area, surface and borehole geophysi-cal surveys play a critical role in subsurface investigations.This paper looks at the contribution that shallow seismic re-flection profiling can make to improving our knowledge ofthe stratigraphy of unconsolidated sediments in the ORMarea. It presents a seismic facies analysis and a summary ofthe subsurface architecture of the ORM area, based on a dataset consisting of over 50 line-kilometres of land-based, com-mon-midpoint (CMP), seismic reflection profiles acquired

by the Geological Survey of Canada between 1993 and1997.

The seismic program was designed to investigate the ar-chitecture of the ORM and adjacent strata to improve ourunderstanding of the character and origin of the ORM and toevaluate which geological or structural components might becritical influences on groundwater flow. An evaluation ofprevious geological investigations in the region led to theidentification of four specific issues to be addressed by seis-mic reflection techniques: (1) Is there evidence of extensivebedrock valleys which may be important factors in regionalgroundwater flow? (2) What is the regional geometry ofdeeper sedimentary packages beneath the ORM? (3) Dochannels that lose their surface expression at the northernflank of the ORM continue beneath it? (4) What is the formand type of sediment fills in these channels, and do the chan-nel fills relate to the formation of the ORM?

The addition of a well-constrained, high-resolution seis-mic reflection data set to an extensive three-dimensional(3D) database of verified water-well records supplementedwith high-quality boreholes and surface mapping and anemerging regional geological framework in the ORM areaalso provides the opportunity to comment briefly on glacialevent sequence and process hypotheses. For example, havethick regional till sheets been subjected to regionalsubglacial deformation (Boyce and Eyles 1991) or someother process? How does the subsurface configuration ofchannel features and their fills contribute to understandingthe role of meltwater processes in late-glacial sequences?This paper summarizes the contribution that seismic reflec-tion data have made to (i) identifying the nature of strati-graphic units, (ii ) delineating the large-scale subsurface

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Fig. 1. Map showing the location of the Geological Survey of Canada seismic reflection survey lines on the Oak Ridges Moraine(ORM) north of Toronto. Most lines are located on, or adjacent to, the Uxbridge wedge of the ORM; one line is located on thePontypool wedge to the east. The north–south (N–S) transect (broken line) is the cross section in Fig. 2. The grid in the ORM studyarea outlines 1 : 50 000scale map sheets.

architecture, and (iii ) addressing some critical geologicaland hydrogeological issues regarding event sequence andprocesses in the Oak Ridges Moraine area.

Geological setting

The Oak Ridges Moraine is a sandy, glaciofluvial–glaciolacustrine landform complex, deposited near the mar-gin of the Laurentide Ice Sheet towards the end of the lastmajor glacial advance (Late Wisconsinan: 25 000 to 12 000years BP) (Karrow 1989; Barnett et al. 1998). It forms araised ridge of ice-marginal sediment, but its predominantsandy character puts it into a class of moraines that are dom-inated by meltwater processes rather than active ice pro-cesses (e.g., Sharpe and Cowan 1990; Barnett et al. 1998). Itextends approximately 160 km from the Niagara Escarpmentin the west to east of Rice Lake, and is up to 20 km wide(Fig. 1); its crest is approximately 250 m above Lake On-tario (Fig. 2). The last major ice advance deposited a thickwidespread till sheet (Newmarket Till), which appears to becontinuous under the ORM (Gwyn and Cowan 1978). Wherethis till sheet is exposed north of the ORM, it forms north-east–southwest-trending drumlins that are dissected by a net-work of channels (Barnett 1995). The ORM rests on thiseroded terrain and underlying older sediments that are re-lated to the thick, tabular sediments exposed at ScarboroughBluffs (e.g., Karrow 1967) (Fig. 2). The total package ofPleistocene sediments can reach thicknesses of up to 200 m,and is underlain by Palaeozoic shales and carbonates.

A conceptual geological model has been developed for theglacial deposits of the ORM area (Sharpe et al. 1996; Sharpeand Barnett 1997). The model emphasizes the extensive na-ture of the Newmarket Till, and the importance of channelseroded into or through the Newmarket Till beneath the ORM(Fig. 2). Seismic reflection profiling, in conjunction withnew mapping and drilling, was used to test the buried-channel hypothesis. Since these channels appeared to have apredominantly north–south orientation, most seismic surveylines are east–west (Fig. 1). Gravel sequences within thechannels are potentially productive aquifers, and groundwa-ter flow through channels to aquifers within the lower de-posits may enhance recharge of aquifers in these lower strata(Sharpe et al. 1996). Such channels are obviously critical togroundwater flow within and beneath the moraine.

Five major sedimentary lithofacies within the ORM areaare derived from detailed surface mapping, section logging,and drill-core analysis (e.g., Duckworth 1979; Barnett 1995;Gilbert 1997; Russell et al. 1998). These facies occupy sev-eral stratigraphic positions within the unconsolidated sedi-ment sequence.

(1) Lithofacies D(diamicton): massive to crudely bedded,pebbly, sand, silt, and clay with gradational to sharp bases.Diamicton beds are 0.1–5 m thick, separated by sand or siltinterbeds, or stone horizons. Amalgamated, tabular se-quences of this facies are up to 40 m thick and regional(hundreds of square kilometres) in extent.

(2) Lithofacies G(gravel): sharp-based, massive or cross-bedded pebble and cobble sets, 0.5–5 m thick. Sequences20–50 m thick and 0.1–1 or 2 km in linear extent includebodies with channel, sheet, or arched ridge geometry.

(3) Lithofacies S(sand): ripple, cross-laminated fine sand,planar-laminated fine to medium sand, diffusely bedded me-dium sand, and coarser, cross-bedded pebbly sand. Sets are0.1 to 1–2 m thick and form stacked, fining-upward, planarsequences-5–25 m thick and in some cases are regional(km2) in extent.

(4) Lithofacies F(fines): graded fine sand, silt, and claybeds 0.1–100 cm thick. These facies are usually rhythmi-cally laminated in stacked sequences up to 25 m thick. Asso-ciations of facies F and S reach 100 m in thickness and fillbasins several square kilometres in area.

(5) Lithofacies R (bedrock): decimetre- to metre-scale,horizontal beds of limestone or shale (occasionallyinterbedded) extending everywhere beneath the ORM atdepths of up to 200 m. The gently sloping bedrock surface iscut by channels at the scales of kilometres wide and tens ofmetres deep.

Seismic reflection method

Seismic reflection methods have been the mainstay of hy-drocarbon exploration for decades, providing critical infor-mation on the deep structure and seismic facies ofsedimentary basins. Shallow seismic reflection methods arenow used increasingly to investigate subsurface structure andfacies of unconsolidated sediments within 200 m of the sur-face.

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Fig. 2. North–south schematic cross section from south of Lake Simcoe to Lake Ontario, showing major elements of the geologicalmodel of the Oak Ridges Moraine area (Sharpe et al. 1994; Sharpe and Barnett 1997).

Until recently, the application of seismic methods to themapping of unconsolidated sediment sequences has beenpredominantly through the use of marine, single-channel,subbottom profiling systems. These high-resolution, reflec-tion seismic (HRRS) surveys by water craft provide detailedimages of the shallow subsurface (resolution <1 m), and ac-quire data relatively quickly and inexpensively. Large quan-tities of regional, shallow, structural-mapping and seismicfacies data for Quaternary sediments collected by HRRShave been used to advance understanding of the architectureand environments of deposition in glaciated terrains (e.g.,Syvitski et al. 1997; Davies et al. 1997). Closely spaced pro-files and a combination of seismic profiling methods (single-and multi-channel acquisition and different sources) withvarying penetration and resolution provide better images inglacial sediments with complex stratigraphies (e.g., Toddand Lewis 1993; Davies and Austin 1997).

Seismic facies analysis is the interpretation ofdepositional environments and associated sedimentary pro-cesses from seismic reflection data and involves the descrip-tion and characterization of seismic reflection parameterssuch as configuration, continuity, and amplitude (Mitchum etal. 1977a, 1977b). Seismic facies analysis has also been ap-plied as an interpretational tool in complex glacial terrains(see Syvitski et al. 1997). The large-volume, high-resolution,marine seismic reflection data sets provide a wealth of data,which reveal a detailed record of event sequences and permitconfident inferences of glaciogenic processes to be made(e.g., Lyså and Vorren 1997; Mullins et al. 1996).

Land-based, shallow seismic reflection profiling has be-come technologically viable and, thus, more widely appliedduring the last 20 years (e.g., Steeples et al. 1995). An over-view of the practical application of the common-midpoint(CMP) method to shallow investigations can be found inSteeples and Miller (1990). In glaciated terrain, land-based,shallow seismic reflection surveys are an effective means ofdelineating the architectures of sequences of unconsolidatedsediments and also of mapping the underlying bedrock sur-face (e.g., Hunter et al. 1989; Slaine et al. 1990; Roberts etal. 1992; Sharpe et al. 1992; Boyce et al. 1995; Mullins et al.1996; Petruccione et al. 1996; Barnes and Mereu 1996; Lanzet al. 1996). Early attempts to use simple, single-channel,shallow seismic reflection methods in the ORM area (e.g.,Gartner Lee Limited 1987) met with limited success. Morerecent surveys, using advances in engineering seismographand computing technology, demonstrate that the seismic re-flection method is an effective means of mapping the com-plex glacial stratigraphy in the region (Pullan et al. 1994;Boyce et al. 1995; Pugin et al. 1996; Siahkoohi and West1998). Tests show variable-quality reflection data from theORM area, depending primarily on the surface conditions,but good results have been obtained at many sites.

A significant advantage of land-based surveys, as opposedto marine surveys, is the improved accessibility to geologicalground truth, especially borehole control supplemented withdownhole geophysical testing (e.g., Hunter et al. 1998). Be-cause of the difficulty in drilling holes offshore, most marineor lake-based seismic reflection surveys have extremely lim-ited borehole control (0.1–0.01 m of core per line-kilometre). In contrast, the ORM seismic data have goodgeological control, with-750 m of continuous core directly

associated with seismic profiles, and several kilometres ofnearby, high-quality core within the ORM area. Core datacoverage exceeds 20 m per line-kilometre of seismic profiledata in the ORM, and this is supplemented with detailedseismic velocity logging within available boreholes.

Oak Ridges data acquisition and processingThis paper is based on an analysis of 50 line-kilometres of

12- or 24-fold seismic reflection profiles. These data wererecorded using state-of-the-art, instantaneous-floating-point,24- or 48-channel engineering seismographs (EG&GGeometrics ES-2401, Strataview R-24, and OYO DAS-1),with single 50 Hz geophones as receivers and a 12 gauge,in-hole shotgun source (Pullan and MacAulay 1987). Theprofiles described in this paper were recorded with sourceand geophone spacings of 5 m, with the source positioned5 m off the end of the spread, resulting in offsets of 5–120 m.

The basic data processing steps applied are listed in Ta-ble 1, though the order of the processing sequence and thepresence of some steps vary slightly between profiles, de-pending on the quality of intermediate stacks. The carefulapplication of static corrections to shallow seismic reflectiondata is of critical importance to the quality of the final pro-file (Pugin and Pullan 1998). Most of the profiles presentedin this paper have been migrated, a process that collapsesdiffraction patterns or “bow-tie” structures related to deeplyincised channel features. All profiles have been convertedfrom two-way traveltime to depth profiles using the stackingvelocities determined from the reflection data. The profilespresented here vary in length from 1.2 to 3 km, but for easeof comparison all have been plotted at the same scale (with avertical exaggeration of-2). These “postage stamp” repre-sentations of the data are displayed as shaded plots of traceamplitude which allows a clear presentation of the main fea-tures of the seismic profiles; it is not possible to display in-dividual traces (2.5 m spacing) at this scale.

Seismic attribute analysisAs an aid to the interpretation of seismic reflection data,

particularly their lateral continuity and integrity, plots ofseismic attributes can be produced from the stacked profiles.The so-called “instantaneous attributes” associated with theseismic signal are calculated from the expression of the traceas a complex function (in the mathematical sense), in whichthe real component is the recorded signal itself and theimaginary component is the Hilbert transform of the realpart (Yilmaz 1987). The instantaneous amplitude measuresthe reflectivity strength, which is proportional to the squareroot of the total energy of the seismic signal at an instant intime; instantaneous phase is a measure of the continuity ofreflection events on a seismic profile; and the temporal rateof change of the instantaneous phase is the instantaneousfrequency. Spectral balancing of the ORM data (Table 1)prohibits the use of the instantaneous frequency attribute. Asall types of random noise limit the reliability of the results,this method of analysis is most effective on data where thesignal-to-noise ratio is high and care has been taken to pre-serve the amplitude and phase content of the signal duringprocessing.

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Downhole seismic loggingData obtained from downhole seismic logging provide ac-

curate velocity–depth functions and directly relate seismicreflections to depth (Hunter et al. 1998). Downhole seismiclogs have been obtained in fluid-filled boreholes using a 12gauge shotgun source on surface, and 12- or 24-channelhydrophone arrays with 0.5 m receiver spacing (Hunter andBurns 1991). Overlapping positioning of the array down thehole results in a redundancy of first arrival time data. Thefirst arrival data are processed to provide accurate intervalvelocities, which can be used as a lithological tool. Thetime–depth data allow for direct time–depth calibration ofreflection events, and can be processed to produce a “corri-dor stack” which is the equivalent section in two-way travelat the borehole location (Hunter et al. 1998).

Approach

The analysis of each seismic profile began with a descrip-tion of the main features and character of each reflectionpackage. Such an approach follows the basic principles ofseismic stratigraphy (Mitchum et al. 1977a) where reflectionpackages separated by surfaces of discontinuity are inter-preted as genetically related strata or depositional sequences(seismic sequence analysis). A subsequent process, seismicfacies analysis, examines the configuration, continuity(phase), amplitude, and interval velocity of reflection pat-terns within the seismic sequences and interprets these interms of stratigraphic context, depositional setting, and esti-mates of lithology (Mitchum et al. 1977b).

The definition of these ORM seismic facies and facies as-sociations affords comparison with facies descriptions fromother glaciated terrain where large marine seismic reflectiondata sets are available (e.g., Syvitski and Praeg 1989; Mul-lins et al. 1996). This, however, must be done with the pro-viso that variations in input signal obviously affect a seismicfacies analysis, and care must be taken to assess whetherchanges in reflection continuity, amplitude, and frequencyare due to subsurface variations or to changes in surfaceconditions that affect the coupling of source energy into theground.

The results of the analyses and interpretation of the ORMseismic data, and their implications with respect to the geo-logical questions outlined above, are presented as follows:

(1) Major seismic facies are described and illustrated on atype seismic profile (Nobleton). These facies are summa-rized in Table 2 along with their interpreted lithologies.

(2) Seismo-stratigraphic units are defined, based on theirseismic facies, geometry, and stratigraphic relationships (Ta-ble 3). The borehole and geological data from the area allowthese units to be correlated with lithofacies and the overbur-den stratigraphy (Table 3). These interpretations and associa-tions are illustrated using the type seismic profile.

(3) Major subsurface architectural elements (sets of simi-lar sediments or seismic facies), as identified on the seismicsections, and their regional aspects (Table 4), are illustratedthrough the Nobleton profile and four other seismic profilesfrom across the ORM.

Description of seismic facies

Four major seismic facies and 10 subfacies have been rec-ognized in the ORM area (Table 2). The major facies are de-fined primarily on reflection amplitude, with the subfaciesdefining varying configurations or continuity of reflections.Seismic velocity and facies geometry further characterizethese elements (Table 3). These seismic facies are the pri-mary building blocks of the seismo-stratigraphic sequencesthat characterize the thick glaciogenic and underlying Paleo-zoic bedrock terrain. Note that, because of the nature of thedata set, some facies will be defined primarily on their con-trast with surrounding units (e.g., surface reflectivity), andseveral sedimentary lithologies can result in similar seismicfacies.

Facies I: highly reflectiveLarge-amplitude reflections can be observed regionally

and in several stratigraphic settings within seismic reflectionprofiles obtained in the ORM area (Table 2). They extendlaterally for kilometres and cap a facies unit tens of metresthick. The high surface reflectivity that characterizes this fa-cies is attributed to large velocity contrasts with the overly-ing sediments. The lithologies of these units are interpretedto be coarse-grained sediments, diamicton, or bedrock (i.e.,high seismic velocity facies). Differentiation between theselithologies is based on internal reflection characteristics andon the stratigraphic position of the facies. Subfacies with ahummocky or irregular nature (Ia), internal diffractions (Ib),or planar geometries (Ic) likely represent occasional gravellags, dense till sheets, or bedrock (or thin till over bedrock)surfaces, respectively.

These high-velocity facies are common within glacial sed-imentary terrains. For example, highly reflective andhummocky, acoustically transparent facies have been inter-preted as diamicton or till tongues (e.g., King and Fader1986; Sexton et al. 1992) in marine, ice-marginal, or

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Convert data format (SEG2 to SEGY(KGS integer))Edit geometryInteractive manual trace edit (kill bad traces, correct polarity as

required)First break picking – refraction analysis and staticsAutomatic gain control (large window)Band-pass (BP) filterGroundroll and air wave mute as requiredCMP sortVelocity analysisNormal move-out corrections with stretch muteResidual staticsStackSpectral balancing (zero phase deconvolution and BP filter)Statics on a datum plane (long wavelength – elevation

corrections)Migration (phase-shift method)Depth conversionPlot section

Table 1. Processing steps applied to Oak Ridges Moraineseismic reflection data.

subglacial settings. Arched, high-amplitude reflectors are in-terpreted as eskers in subglacial channels (e.g., Pugin et al.1996; Mullins et al. 1996), or channel bedforms, while iso-lated, high-amplitude internal reflections have been inter-preted as boulder lags within thick diamicton sequences(Boyce et al. 1995).

Facies II: medium to high reflectivityMedium to high reflectivity facies (Table 2) occur in two

settings in the ORM, in channels or in strata displaying con-tinuous planar, sheet geometries (Table 3). These strata aretens of metres thick and may extend laterally for kilometres.The moderate reflectivity is attributed to significant velocitycontrasts between units. These units are interpreted to repre-sent medium- to coarse-grained lithologies (sands and grav-els; subfacies IIa), distinct layering of contrasting lithologies

(sands, silts, diamictons; subfacies IIb), or cross-beds (sandand gravel; subfacies IIc). Where this facies fills channels inthe ORM, it is interpreted as coarse sediment deposited inhigh-energy environments and is a potential high-yield aqui-fer.

Medium to highly reflective strata displaying horizontal,continuous reflective geometries in planar packages arecommonly attributed to glaciofluvial, glaciolacustrine (e.g.,Mullins et al. 1996), or glaciomarine settings (e.g., Lyså andVorren 1997) where laminated, fine-grained sediments areintercalated with coarser beds.

Facies III: transparent, low reflectivityTransparent (blind) facies, or units characterized by very

low reflectivity (Table 2) indicate massive sediment pack-ages or poor signal strength, and are found in several ORM

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Table 2. Simplified seismic facies of the ORM area.

settings. The packages are 10–40 m thick and may be sev-eral kilometres across. They are tabular and have a planarupper boundary in older sediments (e.g., Table 3, units B2,B3, and A2) and a well-defined lower boundary when onhigh-reflectivity bedrock (Ic). Subfacies with low-amplitude,(semi-) continuous reflections that drape underlying ele-ments or fill depressions (IIIa) probably record parallel-bedded, low-energy silt and sand sets mainly deposited from

suspension (e.g., Mitchum et al. 1977b). Distinct reflectivitychanges within the facies (IIIb) are interpreted to relate tobetter-defined, bedded glaciolacustrine sequences, or to im-proved signal strength and frequency (e.g., moist, fine-grained sediments at ground surface). Subfacies exhibitingpoor signal strength and continuity at depth (IIIc) are inter-preted to record lithologies with relatively low impedancecontrasts (e.g., sands, silts, diamictons within lower sedi-

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Seismic observation and setting Geological interpretation

Seismo-strati-graphic unit

Seismicfacies (fromTable 2)

Seismicvelocity(m/s) Geometry and architecture

Lithology(lithofacies)

Depositionalenvironment

Stratigraphicunit (age)a

D2 IIIa 1500–1700 Drapes or fills underlyingstructure; 2 or 3 majorpackages; wide shallowchannels; dipping, andcollapse structures

Silt, sand,minor clay(F, S)

Lacustrine; distalsubaqueous fan

Oak RidgesMoraine(Late Wisc.)

D1 IV 1500–2000 Occurs in large channelfeatures with steepmargins

Sand, silt(S, F, D?,G?)

Slump, mass flow;suspensiondeposition fromhyperconcentratedflow?

(late glacial;younger thanchannel fills)

D1 Ia, IIa 1700–2500 Fills channels (0.5–2 km);reflectors terminate atchannel walls; lenticular;onlapping reflectors;cross-bedded in places

Sand, gravel(S, G)

High-energy scour andfill; rapidaggradation; north–south paleoflow par-allels channel axis

Channel fills(Late Wisc.)

Regional unconformity

C Ia, Ib 2200–3000 Irregular, undulating (-1 km)surface; extensive,relatively flat base; thick(10–40 m), truncatedtabular geometry

Coarse (sandy)diamicton;sand; gravel(D, S, G)

Proglacial–subglaciallacustrinesedimentation; someerosion; includesinterbeds and stonelines

Newmarket Till(Late Wisc.)

B3 IIb, IIIb 1600–2000 Flat-lying reflectors; poorlydefined in places belowtill; multiple tabularpackages; commonplanar upper surface

Silt, sand,clay; clayeydiamicton;sand,organics(S, F, D)

Distal subaqueous fansedimentation;passive depositionof diamictons(debris flow ormeltout)

Thorncliffe Fm.Sunnybrook TillScarborough Fm.

(Middle toEarly Wisc.)

B2 IIIb, IIIc 1600–2000? Tabular, flat-lying geometry Silt, sand,clay??(F, S)??

Low- to medium-energy sedimentationin standing water?

Don Fm.(SangamonInterglacial)

B1 Ic 2300–2700? Thin, discontinuous units;occurs on bedrock

Shaleydiamicton(D)

Subglacial deposition;high basal shearstress

York Till(IllinoianGlaciation?)

Regional unconformityA2 IIIc 2500–3500 Discontinuous, chaotic

angularBlack shale

(R)Eroded shale bedrock

surfaceWhitby Shale

(Paleozoic)

A1 Ic >4000 Flat to large-wavelengthundulations

Carbonate(R)

Carbonate bank(platform)

Simcoe Grouplimestones(Paleozoic)

aFm., Formation; Wisc., Wisconsinan.

Table 3. Seismic facies, character, geometry and stratigraphic-environmental associations in the ORM area sediments.

ments, or low-velocity bedrock beneath till), which are notwell-defined on the seismic profile because of low signalstrength.

Transparent to near-transparent facies characterized byweak signal return are common in marine and lacustrine re-flection seismic surveys (Syvitski and Praeg 1989; Mullinsand Hinchey 1989) or on land (Pugin and Rossetti 1992;Pullan et al. 1994; Boyce et al. 1995), and have been inter-preted to record massive, fine-grained sediment or occasion-ally as diamicton (Stewart and Stoker 1990).

Facies IV: incoherent, chaoticIncoherent, chaotic facies (Table 2) with disorganized,

discontinuous reflections reach tens of metres in thicknessand kilometres in width. Commonly, this facies has a well-defined lower boundary and poorly defined upper boundary.Lack of associated core data makes it difficult to interpret. Itis attributed to (i) high-energy fill sequences (possible dif-fusely graded sands with dewatering structures and soft-sediment “rafts”?), (ii ) slumping of sediment along channelmargins resulting in a loss of original structural characteris-tics, or (iii ) poor seismic signal due to surface conditions.

Incoherent and disorganized facies are similarly inter-preted as slump deposits from the walls of Norwegian fiords,deep lake margins, and ice-marginal environments wheresteep slopes and sediment reworking are common (e.g.,

Syvitski and Praeg 1989; Mullins and Hinchey 1989). Thesefacies may also indicate rapid deposition from suspension indistal parts of subaqueous fans where multiple scour and fillevents are indicated by steeply cut banks in earlier depositsand metre-scale clasts of these earlier deposits floating inmassive or diffusely graded sand (e.g., Rust 1977).

Seismic stratigraphy

A series of seismo-stratigraphic units are identified (Ta-ble 3), based on an interpretation of the seismic facies de-scribed above in conjunction with their subsurfacearchitecture and stratigraphic relationships as observed onthe seismic reflection profiles. This seismic stratigraphy out-lines the regional architectural elements of the ORM area.This architecture, together with borehole data and observa-tions in exposed profiles, allows matching of the seismo-stratigraphies and lithofacies (Table 3). Downhole seismiclogs from 10 deep boreholes have provided the seismic ve-locity ranges for each unit. The seismic stratigraphy, archi-tectural associations, and geological interpretations areillustrated using a type seismic profile (Nobleton).

Type seismic profile: NobletonThe Nobleton profile (Fig. 4) was chosen as a type seis-

mic profile because it overlies a suspected deep bedrock val-

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Architectural element(seismo-stratigraphic unit) Characteristics (based on seismic profiles) Structural and depositional significance

Channels Evidence of many subsurface channel features cutinto or through the Newmarket Till, including

Extension of surface channel networks north ofORM

CSteep-sided, deep channels (Figs. 4, 8)CSteep sidewalls maintained (Figs. 4, 8)

Compatible with subglacial meltwater erosionscenario

CBroader, shallower features (Fig. 9)CPossible undulating profile (Fig. 10)

Channels allow direct connection between ORMsediments and lower deposits

Channel fills (D1) Usually very reflective facies (Figs. 4, 8–10)Can be up to 100 m thick (Fig. 8)

Coarse-grained fills imply high-energydepositional environment

Interpreted to be alternating coarse- and fine-grained deposits (gravels and sands) (Fig. 6)

Possible esker deposits suggest subglacialconditions

Large-scale cross-beds observed (Fig. 10) Offer potential groundwater target

Newmarket Till (C) Variable thickness (to >50 m) (Figs. 7, 10)Very reflective surface (Figs. 4, 7–10)Undulating upper surface (Figs. 4, 7–10)Flat-lying, low-amplitude base (Figs. 4, 7, 10)

Originally thick (-50 m) regional depositEroded subglacially by high-energy meltwater

Lower deposits (B) Always present (Figs. 4, 7–10)Thick, well-stratified, laterally extensive, flat-lying

deposits (Figs. 4, 8)

Correlatable to Scarborough and Bowmanvillebluffs

In some cases appears massive (Figs. 7, 10)

Bedrock (A1, A2) Two distinctive facies, shales and limestonesCShales, with poor reflection contrasts(Figs. 4, 7–9)CLimestones, with good reflections (Figs. 4, 10)

No evidence of bedrock high beneath ORM Poten-tial bedrock mapping tool

Bedrock observed at-150 m asl (Figs. 7–10)(except in Laurentian channel;Fig. 4)

Table 4. Architectural elements (based on seismo-stratigraphic units) in the ORM area, their regional characteristics (including a listingof their occurrence in the figures of this paper), and their structural and depositional significance.

ley (e.g., Brennand et al. 1997a) that may record the mostcomplete terrestrial Quaternary sequence in the Greater To-ronto Area and possibly eastern North America. The profiletraverses the probable southern extension of a large surfacevalley and suspected drift channel, the Holland Marsh(Fig. 3), and crosses ORM sediments buried beneath a fine-textured till. A continuously cored 192 m deep borehole tobedrock in the centre of this seismic line allows direct com-parison of the lithological facies and the interpreted seismicprofile (Fig. 4). The corridor stack obtained from thedownhole seismic survey is superimposed on the seismicprofile in the upper portion of Fig. 4. Since migration pro-duced no observable effect on these data, this profile has notbeen migrated.

ObservationsThe Nobleton profile shows two distinct reflection styles,

coherent and incoherent. Between 500 and 750 m there is adeterioration from the coherent, continuous reflection char-acter observed in the eastern part of the profile to the inco-herent, disorganized character (facies IV) to the west. In theeast, particularly from 2000 to 2500 m where the data ex-hibit a very high signal-to-noise ratio, a shallow blind facies(IIIa; characterized by very low amplitude internal reflec-tions) overlies a strong reflection (Ib). This large-amplitudereflection continues across the profile (to <750 m), and is ir-regular or undulating in elevation (between 200 and 250 masl). Beneath this reflection there is a sequence of widelyspaced, continuous, relatively flat lying reflections (IIb; toelevations of-125 m asl). The lowest, coherent seismic re-flection in the centre of the profile (700–2000 m) is a large-amplitude, flat-lying reflection (Ic) at-90 m asl. To eitherside, this reflection is less well defined (IIIc). In contrast tothe coherent reflections described above, the reflection char-acter observed on the westernmost 500 m of this profile is

chaotic, discontinuous, and angular, with low to medium re-flection amplitudes (IV).

Seismo-stratigraphic interpretationThe interpretation of the east and central (east of 750 m)

portion of the Nobleton profile has been aided by thelithological information provided by the borehole (Fig. 5).The high-quality borehole sedimentology (e.g., Russell et al.1998) and downhole seismic logs have been used to corre-late seismic facies with geological units.

Bedrock (A1, A2):Though the bedrock in this area is pre-dominantly Whitby Shale (A2), the shale in the central re-gion of this profile (700–2000 m) has been eroded, and thebedrock surface, at an elevation of less than 100 m asl, is theunderlying Trenton Limestone (A1), characterized by a highreflectivity. Where erosion has not completely removed theshale, the bedrock surface offers a much smaller acousticimpedance contrast with the overlying glacial sediments, andas a result is less well defined on the seismic profile. Theeroded bedrock surface in this area is believed to be the bedof the Laurentian channel system (e.g., Spencer 1881;Brennand et al. 1997a).

Lower deposits (B1–B3):A thick sequence of lower strata(B) above the bedrock surface was recovered from the bore-hole. This sequence is represented on the seismic profile bythick units, with continuous, relatively flat lying reflections,extending from 700 to 2500 m. The lowest drift observed onthe seismic profile, the Don Formation (B2), exists only inthe central bedrock low (below 125 m asl), and pinches outagainst the Whitby Shale (A2) to both the east and west. Atshallower depths (elevations >220 m asl), lithologicalchanges noted in the borehole correlate well with the ob-served reflections (e.g., clay to sand at-190 m asl; sand todiamicton at-150 m asl), and also produce visible reflection

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Fig. 3. Map of the Uxbridge wedge of the ORM, showing the seismic reflection profiles acquired by the Geological Survey of Canada(grey lines) and the locations of the seismic profiles shown in Figs. 4 and 6–10 (black lines).

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Fig. 4. Type seismic reflection profile acquired near the town of Nobleton in the western region of the Oak Ridges Moraine study area(Figs. 1, 3). The upper panel shows the processed seismic data (plotted as a depth section; no migration applied) with a corridor stackcomputed from downhole seismic data superimposed at the borehole location. The seismic facies observed on this profile are indicated inbold characters (see Table 2). The lower panel is an interpretation of the profile in terms of the architecture of seismo-stratigraphic units(see Table 3); heavy lines indicate regional unconformities. A schematic lithological borehole log has been superimposed on theinterpreted profile; the log is shown in more detail in Fig. 5. The depth scale on the left-hand side indicates depths below an above-surface datum; elevations on the right-hand side are in metres above sea level.

energy on the corridor stack. The lower drift stratigraphy(B3) appears to be extensive in nature; this facies (II, III)can be traced over 3 km to the east on this seismic profile(Fig. 3).

Newmarket Till (C):While no Newmarket Till (C) was en-countered in the borehole core, our interpretation of the seis-mic profile is that this unit is present, at least intermittently,across the eastern half of the profile. Its surface represents aregional erosional unconformity, and, in places the erosiveevent completely removed the Newmarket Till (e.g., 700–1200 and 1700–2200 m). Remnants of the till (e.g., 1200–1700 m) are characterized by a highly reflective surface (fa-cies I) and a relatively flat base.

Channel fill (D1): Above the lower deposits, a thick (15 m)gravel (D1) rests directly on the lower deposits at the bore-hole site, where Newmarket Till has been eroded away. Inour interpretation of the seismic profile this gravel unit istraced-500 m west of the borehole, while immediately tothe east, the gravel onsteps a surface eroded into NewmarketTill (C). Thus, these coarse-grained deposits, and those far-ther to the east on this profile (D1; 1600–2200 m), were de-posited on a regional unconformity which, in places,involved complete removal of the Newmarket Till (seeabove).

ORM sediments (D2):The shallowest unit that can be seenon the seismic profiles is the blind facies interpreted to befine-grained sands and silts of the ORM deposits (D2). Thesurficial sediments in the area are mapped as Halton Till(and interbedded sand and silt), but the unit is too thin to beresolved on these seismic profiles (probably <10 m). How-ever, these fine-grained sediments at the ground surfacelikely contributed to the good quality of seismic data ob-tained here.

Disorganized facies:The nature of the chaotic facies (IV)observed on the western end of the Nobleton profile (Fig. 4)remains in question. It is interpreted as the fill of a majorchannel that is on the order of kilometres wide, and probablyrepresents the extension of the Holland Marsh valley (Fig. 3)beneath the ORM. The chaotic seismic facies may be relatedto a rapid infilling of the channel with diffusely bedded sandthat may show large dewatering structures, or to disturbanceof existing sediments by large-scale slumping. However, it ispossible that some unrecognized, near-surface conditionscaused a severe deterioration of signal quality in this area.Further investigation of this facies is required to refine theseinterpretations.

Downhole seismic loggingThe downhole seismic log of the Nobleton borehole

(Fig. 5) supplements the lithological log, confirms the loca-tions of the facies boundaries, and supports the seismic fa-cies analysis. It especially affords direct correlation betweenthe seismic reflection profile (Fig. 4) and the geological log.The velocity log (Fig. 5) shows the interval velocities calcu-lated from the picked first arrival times (five-point (2 m) fit).The prominent feature in this log is the high velocity of thegravel unit at 45–60 m depth below ground surface. Thisunit has seismic velocities of about 2200 m/s. Although this

velocity is high for unconsolidated sediments, otherdownhole seismic logs from the ORM area record evenhigher velocities (>2500 m/s) for the Newmarket Till. Infact, velocities in excess of 2500 m/s appear to be diagnosticof this dense till (Pullan et al. 1994; Hunter et al. 1998).

A synthetic (modelled) VSP (vertical seismic profile)stack, which is compared to the corridor stack derived fromthe downhole data, was calculated from a smoothed (15layer) version of the interval-velocity log (Fig. 5). The corri-dor stack is also superimposed on the reflection profile(Fig. 4). Such VSP stacks represent the equivalent seismicreflection profile at the borehole location. They clearly showthat the reflection events and relative amplitudes correlatewell with velocity contrasts observed in the borehole; that is,the reflection events at 40, 85, 120, 155, and 190 m depthare all associated with marked changes in velocity in the ve-locity log, with the largest amplitude reflections correlatingwith the largest velocity changes at the top of the gravel unitand at the bedrock surface.

The combination of borehole geology,P-wave velocitylogging, and “corridor” stacking of the downhole records inthis example maximizes our confidence in interpretations ofthe complex high-resolution seismo-stratigraphy.

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Fig. 5. Downhole seismic logging results for the Nobletonborehole, with a simplified lithological log shown at left. Therightmost log shows interval velocities; a smoothed version ofthis log has been used to calculate a synthetic (modelled) VSPstack (centre), and this is compared to the corridor stack to theleft derived from the downhole seismic data.

Seismic attribute analysisSeismic attribute displays of a portion of the Nobleton

type seismic profile with a high signal-to-noise ratio furtherillustrate the potential of the seismic reflection method fordetailed stratigraphic interpretation (Fig. 6). The instanta-neous phase plot (Fig. 6c) brings out the internal structure ofunits, and contrasts the low continuity of reflections in theupper half of the profile (facies IIIa; 25–75 ms; and IIIb;100–130 ms) with more continuous ones in the lower se-quences (IIb; 130–200 ms). The instantaneous amplitudeplot (Fig. 6d) provides a qualitative picture of the relative re-

flection coefficients in this profile. The application of an au-tomatic gain control (AGC) in the processing sequence hasaffected relative amplitudes to some extent, but a large AGCwindow (250 ms) has been used to preserve as much infor-mation as possible. The plot shows the large reflection coef-ficients associated with an erosional surface (cutting intoNewmarket Till) and the coarse-grained fills of channelsformed during this erosional process (Ia and Ib; 75–100 ms).The high reflectivities are associated with large contrasts invelocity (see Fig. 5). Figure 6d also shows that significantreflectivities are associated with lithological changes at

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Fig. 6. Instantaneous attributes calculated for a short section of the Nobleton seismic line (Fig. 4) showing major reflection boundariesand seismic facies. (a) Data plotted (as a function of time) in a variable area display (wiggle trace with positive amplitudes filled in).(b) The wiggle-trace display with a colour amplitude scale. (c, d) Colour plots of the instantaneous phase (c) and amplitude (d) over awiggle-trace display of the data. (e) Stratigraphic interpretation of the profile.

greater depth (IIb; 130 and 200 ms) and that the bedrock(Whitby Shale) surface (IIIc; >200 ms) is characterized by arelatively low reflection coefficient.

While seismic attribute analysis must be applied withcare, this example illustrates how such representations of thedata, supplemented with borehole information, strengthenthe interpretations of facies and stratigraphy based on seis-mic data (Fig. 6e), particularly for regional correlations.

Regional architectural elements

Five significant subsurface architectural elements (bed-rock, lower deposits, Newmarket Till, channel forms, andchannel fills) have been identified on the seismic profiles ona regional basis throughout the ORM study area. These indi-vidual elements provide insight into the fundamental geolog-ical and hydrogeological issues raised in the introduction tothis paper. These elements are summarized in Table 4 and il-lustrated below by the Nobleton profile and four seismicprofiles from elsewhere in the ORM (Fig. 3). The elementsare listed in stratigraphic order in Table 4, but are discussedhere in an order more in keeping with their prominence asobserved on the seismic profiles and their regional geologi-cal significance.

Newmarket Till (C)The seismo-stratigraphic unit (C) interpreted to represent

the Newmarket Till (Table 3) appears on all seismic profilesacquired to date. It is highly variable in thickness and is notalways continuous across profiles. The regional characteris-tics of this seismic unit are (i) a highly reflective surface(i.e., high-amplitude reflections from the top of the unit; fa-cies I), typically with major variations in elevation; (ii ) littlesuggestion of internal structure such as major layeringwithin the unit; and (iii ) a characteristically flat lying, low-amplitude base. This seismo-stratigraphic unit underlies theORM and is typically several tens of metres thick, with amaximum observed thickness of-50 m. Downhole seismiclogging indicates that the velocity of the Newmarket Till isusually 2500–3000 m/s, notably high for unconsolidatedoverburden materials (Table 3). All these characteristics re-late to the geological history and bear on the regionalhydrogeological significance of the Newmarket Till.

15th Sideroad seismic profileThis profile (Fig. 7) provides an excellent illustration of

the regional form of the Newmarket Till, particularly itsvariable thickness and flat base. The 3 km east–west profileis from the side of a suspected buried channel (Aurora) andlies between two diverging ridges of ORM sediment, ap-proximately 6 km to the east of the Nobleton type seismicprofile (Fig. 3). Interpretation of this profile is in the contextof regional geological mapping rather than on-site boreholeinformation.

The main feature across the entire profile is a large-amplitude reflection defining an undulating surface (1–1.5 km wavelength) at 50–100 m depth (facies I; Table 2).On a smaller scale, this reflection is characterized by diffrac-tions (e.g., at 250 m asl), though these have mostly been col-lapsed by migration. The large-amplitude reflection marksthe top of a package of low internal reflectivity determined

by normal moveout velocity analysis to be a high seismicvelocity unit. The base of the package is a low-amplitude,but relatively continuous, horizontal reflection at 80–90 mdepth (-210 m asl).

The undulating, high-amplitude reflection is interpreted torepresent a high-relief, erosional surface, which we correlatewith the channelized and drumlinized surface of theNewmarket Till (C; Table 3) that forms the landscape northand south of the ORM (Sharpe et al. 1994; Barnett andGwyn 1997; Sharpe and Barnett 1997). This unit shows littleinternal structure, and was deposited on an essentially planarsurface (elevation 205–215 m asl). In the eastern half of theprofile (east of 1500 m), the high-amplitude reflector is atrelatively low elevation with relatively low relief (Fig. 7).Assuming the till was originally of uniform thickness, thislow part of the profile represents enhanced erosion. Thethinner, high-velocity layer may explain the better signal-to-noise ratio observed in the lower part of the seismic profile(B3, below 200 m asl), compared with the west where theNewmarket Till is thicker (up to 40 m).

DiscussionThe flat base of this unit observed on the seismic profiles

usually lies at an elevation of 210–230 m asl over the west-ern and central areas (e.g., Figs. 4, 7), but at a slightly lowerelevation (190–200 m asl) farther east. This flat-lying base,conformable with underlying beds, indicated that theNewmarket Till was probably deposited over a nonerosivesurface as part of a continuum with the lower deposits; thisconclusion is supported by interbedded, stratified sand anddiamicton observed at the base of the Newmarket Till(Karrow 1967; Sharpe et al. 1994, 1997; Brennand 1997;Walsh 1995). Till deposition was heralded by debris flows,perhaps formed when advancing ice dammed a regional lakeor lakes. Near flotation of the ice sheet would explain thelimited deformation at this contact (e.g., Sharpe et al. 1994;Boyce et al. 1995; Brennand 1997). The Newmarket Till isdense, indicating loading by thick ice, though the underlyingsediments were not deformed by this high pressure (Sharpeand Barnett 1997; Brennand 1999). The planar base andundeformed stratified sediment beneath the Newmarket Tillcontradict its origin by wholesale subglacial deformation asproposed by Boyce and Eyles (1991).

The high velocities of the Newmarket Till, and the result-ing high reflection coefficients at its surface (e.g., Fig. 7),further support the inference of overcompaction (and per-haps some cementation) by ice loading during, or after, itsdeposition. As well, internal diffractions likely result fromboulders; possibly bullet-shaped boulders formed duringlodgement (Barnett 1993), and (or) boulder lags representingintervals of meltwater erosion interrupting till deposition(Shaw 1985; Boyce et al. 1995).

The variable thickness of the Newmarket Till (e.g., Fig. 7)and it’s absence in places (e.g., Fig. 4) suggest that majorerosion sculpted channels and drumlins into the till and un-derlying beds. Thus, after this erosional event, the surfacetopography of the Newmarket Till displayed drumlin fieldsand a network of channels. Remnants of this surface domi-nate the present landscape north of the ORM (Skinner andMoore 1997). Regional erosion has been attributed tosubglacial outburst floods (Shaw and Sharpe 1986). By con-

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Fig. 7. A 3 km east–west seismic reflection profile (migrated) obtained along 15th Sideroad,-6 km to the east of Fig. 4 (Fig. 3). Thebreak in the profile at-1900 mmarks the crossing of a major north–south road (Dufferin Street) where no data were collected. See Table 3 for description of the seismo-stratigraphic units. Heavylines on the interpreted profile indicate regional unconformities; m, areas where interference from multiple reflections is suspected.

trast, Boyce and Eyles (1991) attribute the drumlins to ero-sion and deposition by subglacial deformation. Thedeformation origin of drumlins as proposed by Boyce andEyles (1991) predicts thick deformation till in the swales be-tween drumlins and drumlin formation after deposition ofthe ORM. Neither of these expectations is observed. Rather,the erosional surface is overlain by stratified and sorted sedi-ment and it predates the deposition of the ORM (Figs. 2, 4)(Barnett et al. 1998).

ChannelsThe seismic profiles show many erosional features be-

neath the ORM deposits that cut into or through theNewmarket Till. By extension, the erosional features are pre-sumed to be channels similar to those in the present land-scape to the north of the ORM (Sharpe et al. 1997; Barnettet al. 1998). Two types of channels are observed on seismicsections: (i) deep, steep-sided channels (e.g., Fig. 8); and(ii ) shallow, broad channels cut into a hard substrate, inplaces into Newmarket Till; elsewhere the channel beds arewithin lower deposits (e.g., Fig. 9).

Vandorf Sideroad seismic profileThis profile (Fig. 8) is 1.2 km long and aligned east–west

just east of the small community of Vandorf (Fig. 3). It ex-plores the internal structure of the ORM and was designed toinvestigate suspected buried channels (e.g., Barnett 1993).Though the survey is on sandy ORM sediments, it follows asmall river valley, where slightly lower elevations anddamper soil conditions created favourable conditions for

seismic surveying. A 132 m deep borehole adjacent to thisseismic line extends close to bedrock. The interpretation ofthis seismic profile is based on the control provided by thelithological and geophysical information obtained from thisborehole.

The eastern part of the profile (>500 m) is dominated by a100 m deep trough. The trough contains three sets ofmoderate-amplitude, coherent, semicontinuous reflections(at elevations of 260, 210, and 175 m asl), interspersed withtwo, thick (40–50 m), low-amplitude zones (facies II andIII). These sequences onlap against the trough sides. Thetrough crosscuts the high-amplitude reflection package (fa-cies I; at-250 m asl) observed in the western part of theprofile (0–400 m).

The borehole intersects the trough side and samples someof its fill and the immediately underlying strata. The troughis interpreted as a deep channel, 500–750 m wide and 100 mdeep, cut through the Newmarket Till and underlying olderdeposits (B) to bedrock. Newmarket Till (C), represented bythe high-amplitude reflection package (facies I) at-240 masl, is preserved on either side of the channel (0–400 and1000–1200 m). The channel appears to be an extension of anetwork seen at the surface to the north in the area west ofMount Albert (Fig. 3).

Diamictons and sands encountered in the borehole be-tween 230 and 190 m asl may be interbedded fill andslumped sediments derived from the channel. Larger faultblocks at the eastern edge of the channel mark slope failureduring channel infill. This fill is likely to be massive sands(D1), with large-amplitude reflections representing coarse

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Fig. 8. Portion of an east–west seismic reflection profile (migrated) acquired near the community of Vandorf (Fig.3). The upper panelshows the processed seismic data (migrated) with a corridor stack computed from downhole seismic data superimposed at the locationof the Geological Survey of Canada borehole. The lower panel is an interpretation of the profile with a schematic lithological log fromthe borehole. See Table 3 for description of the seismo-stratigraphic units. Heavy lines on the interpreted profile indicate regionalunconformities.

sand or gravel deposited by periodic increase in flow power.Gravel at the base of the channel may reach 15–20 m inthickness. Finer grained Oak Ridges sediments (D2) cap thechannel deposits and extend over the entire area. This upper,low-reflectivity facies (D2) is comprised of silts and finesands that are typical of the ORM deposits (e.g., Gilbert1997).

Ballantrae seismic profileThe Ballantrae seismic profile (Fig. 9) is 1.5 km long and

is aligned east–west to the west of the town of Ballantrae(Fig. 3). It was also positioned to investigate suspected bur-ied channels (e.g., Barnett 1993), possibly part of the chan-nel system near Vandorf (Fig. 8). Though the profile liesonly a few kilometres northeast of the one near Vandorf, thesurface materials, ORM sands, and the low water table (5–10 m below surface) combine to cause poorer data thanthose from other profiles. There are lower dominant frequen-cies (100–150 Hz) and signal-to-noise ratios in this profile.

A 159 m deep borehole on this seismic line extends infor-mation obtained at the site from a 90 m deep borehole(Barnett 1993). The deeper borehole still did not reach bed-rock, but terminated in a shale-rich till believed to be withina few metres of the shale bedrock surface. Although regionalgeological observations aided profile selection and evalua-tion at this site, the borehole information was crucial to sedi-

mentary interpretations. The borehole record adds confi-dence to interpretations of the complex subsurface sedimentsbased on relatively poor quality seismic data.

The seismic profile (Fig. 9) shows a strong, low-frequencyreflection (facies I) dipping to the east from-260 m asl at0–500 m. To the east, there is a series of high-amplitude re-flections (facies II) between 170 and 260 m asl. This se-quence is complex, with limited coherency and a somewhathummocky internal structure. Migration better defines thestructure by collapsing diffractions. In general, reflectionsbelow 200 m asl are poorly defined.

The high-amplitude, dipping reflection at the westernedge of the profile is interpreted as the surface ofNewmarket Till (C), which thins over a distance of 500 mand is eroded completely over most of the profile. Thus, theseismic profile is taken to delineate the western margin of asubsurface channel, wider and shallower than the one ob-served at Vandorf (Fig. 8). Although the erosion of thischannel removed Newmarket Till over an east–west distanceof >1 km, it did not cut deeply into the lower deposits. A15 m thick sequence of coarse (bouldery) gravel at a depthof 90 m at the borehole site is interpreted to be the basal fillof this wide (>1 km) channel. The precise orientation of theBallantrae channel is not known, though, based on a perpendic-ular seismic line (Fig. 3), itprobably trends north–south ornortheast–southwest. Further support for a north–south align-

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Fig. 9. Portion of an east–west seismic reflection profile (migrated) acquired near the town of Ballantrae (Fig.3). A lithological log issuperimposed on the interpreted profile at the bottom, and the corridor stack obtained from the downhole seismic data is superimposedon the seismic profile in the upper portion of the figure. The break in the profile at-1100 m marks the crossing of a north–south road(McCowan Road), and a north–south offset of 150 m of the seismic line. At this site, the dry, sandy surface conditions of the morainelowered the data quality. The interpretation of the data depended critically on the borehole. See Table 3 for description of the seismo-stratigraphic units. Heavy lines on the interpreted profile indicate regional unconformities.

ment is given by well data 1.5 km due north of the boreholewhich indicates a similar gravel sequence at-240 m asl(Sharpe et al. 1996).

DiscussionAt least two channel types are observed on the seismic

profiles in the ORM area. The Vandorf profile (Fig. 8) delin-eates a narrow (500 m), deep (100 m) buried channel be-neath the ORM. It provides clear evidence of channelsbeneath the ORM and of the interconnection these channelsprovide between ORM sediments and older sediments andbedrock (Fig. 2). The Ballantrae profile (Fig. 9) intersectsthe western margin of a broader (>1 km), shallower (50 m)channel. Although the seismic data are of relatively lowquality, combined with the borehole observations, they alsoprovide evidence of a channel buried by deposits of theORM. These seismic profiles are taken to record a south-ward subsurface extension of the surface channel system inthe modern landscape near Mount Albert (Fig. 3). We con-sider that the Ballantrae and Vandorf channels may be di-rectly linked, even though they show very different geometryand fill. This type of variability over distances of only a fewkilometres is to be expected if these channels were formedby subglacial outburst floods.

Other seismic profiles illustrate channels with a wide vari-ation in widths and depths, including (i) small-scale chan-nels cut into, but not through, the Newmarket Till (e.g.,Fig. 7 at 750 m, (channel width)/(depth) = 200/20 m);(ii ) broad, shallow channels, cut through the Newmarket Till(e.g., Fig. 4 east of 1700 m, (channel width)/(depth) =500/20 m, east of Nobleton, possibly linked to the Auroraburied channel network to the northeast); (iii ) very largescale, deep channels, in places cut through the lower depos-its and extending to bedrock (e.g., Fig. 4 west of 700 m; thisfigure shows the eastern margin of a feature that is-3 kmwide and-150 m deep, possibly the downflow extension ofthe Holland Marsh); and (iv) channels with undulating longprofiles, and in part, slopes opposite to the former flow di-rection (e.g., Fig. 10); (v) channels with surface expressionnorth of the ORM, and the architecture of their partial fills(e.g., Pugin et al. 1996; Sharpe and Barnett 1997).

The steep sides of the deeper channels cut into surficialdeposits (e.g., Figs. 4, 8) are expected to have been rela-tively unstable immediately after channel erosion. This in-stability is likely to have been aggravated by overloading asthe ice sheet settled onto interchannel beds during waningmeltwater flow, causing groundwater flow towardssubglacial channels and collapse of the valley walls (e.g.,Barnett 1997). In the case of the Vandorf profile (Fig. 8), itis suggested that the original steep sides of the channel havebeen preserved because of the support of rapidly depositedinfilling sediments (though the eastern side of the channelmay have partially collapsed). The large-scale channel at thewest side of the Nobleton profile (Fig. 4) appears to havestarted out broad and shallow (cutting through theNewmarket Till and underlying fine-grained sequence), andbecame steep-sided with deep incision into the erodiblelower deposits (Fig. 2). This explanation for the variablestyle of channels depends on material response; hydrauliccontrols such as discharge, flow velocity, and flow powerwould also have been important to channel form.

The characteristics of the channels inferred from seismicprofiles (e.g., variation in scale, stabilization of banks by arapid infilling, probable coarse fills, undulating long pro-files) are as expected for anabranching tunnel channels (e.g.,Brennand 1994; Brennand and Shaw 1994). Such channelsmay well have operated beneath ice sheets of different ages(e.g., Pugin et al. 1996).

Channel fills (D1)Seismic reflection profiles show stratified fills (D1), in

places >100 m thick, in both channels with surface expres-sion north of the ORM (Pugin et al. 1996) and those buriedbeneath ORM sediments (Fig. 8). The sole profile obtainedon the ORM with a north–south orientation (Fig. 3) revealssome particularly interesting channel-fill structures whichare discussed below.

Grasshopper Park Road seismic profileThe Grasshopper Park Road profile (Fig. 10) is 3 km long

and aligned north–south just southeast of Lake Scugog(Fig. 3). It is situated on the Pontypool wedge of the ORM,within a small creek valley down the south slope of the mo-raine from close to its crest. This valley lies south of an ex-tensive channel network leading into the moraine from thenorth (Fig. 3) (Barnett and Dodge 1996). Unfortunately,high-quality borehole control is not available to complementthe regional geological information for this area.

A very complex, high-amplitude, reflection facies domi-nates the entire profile between 190 and 240 m asl (Fig. 10).This facies has hummocky or dipping internal structureswith moderate reflection amplitudes (facies IIb and IIc), andrests on a modulating, high-amplitude lower bounding sur-face (facies I). In general, reflections within this unit tend todip towards the south (e.g., at depths of 25–50 m on thenorthern portion of the line). In the central part of the profile(around the road crossing), the hummocky facies infills atrough (labelled T) at a relatively shallow depth. Farther tothe south (2100–2700 m), the same facies infills a deepertrough (160–200 m asl), and displays reflection amplitudesthat decrease upwards.

The regional marker on this profile (Fig. 10) is the undu-lating, high-amplitude erosional surface cut into theNewmarket Till (C; facies I). The Newmarket Till displays acharacteristic flat base (at-190 m asl) (Table 4). The topsurface of the till is best defined at the north end of the pro-file, where overlying, highly reflective channel (coarse-grained) sediments are thinner. The Newmarket Till is about40–50 m thick at the north end of the profile, and almostcompletely eroded 1 km to the south. Zones of thicker till al-ternate with scallop-like erosional depressions in the centraland southern portions of this profile (Fig. 10). It is suggestedthat the scallops are periodic erosional marks with wave-lengths >500 m. The scalloped erosional surface was mostlikely cut by powerful meltwater currents (e.g., Kor et al.1991).

The hummocky facies overlying the Newmarket Till (C) isinterpreted to be the basal part of a coarse-grained channelfill (D1), which may grade upwards into the ORM sedi-ments. Alternating gravel and sand beds appear in stackedsets 5–15 m high (e.g., 1000–1500 and 2200–2500 m); suchlithofacies would produce the highly reflective nature of this

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Fig. 10. A 3 km north–south seismic reflection profile (migrated) acquired on the south flank of the moraine east of Port Perry (Fig. 3). The upper panel shows theprocessed seismic data (migrated); the lower panel is an interpretation of the profile. The break in the profile at-1700 m marks the crossing of an east–west road(RR 20). See Table 3 for description of the seismo-stratigraphic units. Heavy lines on the interpreted profile indicate regional unconformities.

seismic facies. Large-scale cross-bedding within scallops at1000–1300 m (Fig. 10) dips to the south, indicating a strongsoutherly paleoflow. In each scallop, large-scale cross-bedding indicates climbing dunes migrating down the proxi-mal slopes of the scallop and up the distal slopes. At thesouth end of the profile (>2200 m), one of the channels ap-pears to have cut into the lower deposits (B3). The probablesouthward migration indicates paleocurrents during the earlychannel-filling stage, which precede the east–westpaleoflows of the ORM. A dome-shaped feature at the northend of the profile (centred at 250 m) may represent an esker.It could also be interpreted as an in-phase wave deposit(Brennand 1994) or as a bedform. The paleocurrent directionand the large scale of the cross-bedding, together with theanabranching channel system containing these deposits, sug-gest a subglacial depositional environment similar to that in-ferred from bedforms and deposits at Trout Creek to thenortheast (Fig. 1) (Shaw and Gorrell (1991). The inferencesas to esker or large-scale forms are compatible with asubglacial fluvial origin.

DiscussionThe uppermost deposits on the seismic profiles are subdi-

vided into two stratigraphic units: (i) a coarse-grainedchannel-infill facies (D1); and (ii ) an overlying, less reflec-tive facies corresponding to the Oak Ridges silts and sands(D2). Occurrences of D1 vary in thickness throughout theORM area from 10 or several tens of metres (Figs. 4, 7, 9,10) to-100 m (Fig. 8). The channel fills identified on east–west seismic lines (Figs. 4, 7–9) are inferred to appear incross section. By contrast, the Grasshopper Park north–southprofile (Fig. 10) gives a longitudinal view of the fill facies(D1). As such, it shows details of both the geometry of theerosional surface and the internal structure of the channelfill. The channel-fill facies (D1) is inferred to have been de-posited rapidly by high-energy, subglacial meltwater flowfrom evidence of steep sidewalls and large-scale cross-bedding climbing up the upflow slopes of the distal parts ofscallops. The seismic data clearly support two distinctivelate-stage sedimentary environments: (i) a high-energy envi-ronment during channel scour and fill (D1); followed by(ii ) waning flow that resulted in deposition of silts and sandsof the ORM (D2). The paleocurrent shift between these twostages indicates a major change in drainage conditions.

Lower deposits (B)Lower deposits (B) are significant seismo-stratigraphic

units, well defined on seismic profiles, and correlated to thewell-exposed, thick sequence along the Scarborough andBowmanville bluffs (e.g., Karrow 1967; Brookfield et al.1982; Eyles and Eyles 1983; Brennand 1997). They are re-gional in extent (Fligg and Rodrigues 1983; Barnett in Sadoet al. 1984; Eyles et al. 1985; Siahkoohi and West 1998),and contain significant aquifer potential (Sharpe et al. 1996).

Facies B appears on all seismic profiles (except where ithas been eroded locally, e.g., Fig. 8). It forms thick se-quences usually about 50 m thick, though in places itreaches thicknesses of >100 m (Fig. 4). The lower depositsconsist of well-stratified, laterally extensive, generally flatlying beds (e.g., Fig. 4), though in some locations seismicprofiles show more massive structure (Figs. 7, 10).

The lower deposits consist of several stratigraphic unitsthat cannot always be easily recognized from seismic data. Itis only in areas where reflection quality is particularly goodthat distinct subdivisions, based on reflection character, canbe reliably differentiated (e.g., Figs. 4, 6). The high reflec-tivity of the oldest deposits (B1) suggests coarse-grained(gravel) or diamictic beds (York Till (Illinoisian); Fig. 8). Ablind facies (B2), noted at the base of the lower deposits inthe bedrock channel (Fig. 4), was identified as the intergla-cial Don Formation from borehole samples (e.g., Russell andArnott 1997). The most common seismic facies of the lowerdeposits exhibits poor to medium reflectivity and, in places,shows very continuous reflections (B3; Figs. 4, 8). In the ab-sence of later erosion, its surface is at a consistent elevationof -180–200 m asl.

From correlations with boreholes (Nobleton, Fig. 4;Vandorf, Fig. 8) and outcrops (Woodbridge, North York,Scarborough Bluffs; Karrow 1967), this facies (B3) includes,from oldest to youngest, (i) the Scarborough Formation(silts–sands), (ii ) the Sunnybrook diamicton, and (iii ) theThorncliffe Formation sands and silt–clay rhythmites. Ingeneral, these represent subaqueous distal fan deposits anddeposition from lacustrine suspension (Table 3). Since theseformations lie 25–100 m above the present elevation of LakeOntario, ice in the St. Lawrence River valley must havedammed a lake which extended beyond the Toronto area.These thick Early to Middle Wisconsinan deposits cover alarge area and form regional aquifers within regional bed-rock lows (discussed below).

Bedrock (A1, A2)The configuration of the bedrock surface in the ORM area

has been of interest for-100 years (e.g., Spencer 1881), andpotentially affects regional groundwater flow (e.g., Haefeli1970). Existing boreholes (e.g., Brennand et al. 1997b)rarely reach bedrock in thick drift areas and geophysicalmethods such as seismic reflection profiling take on a addedimportance as a tool for mapping the bedrock surface.

There are two distinct reflective facies associated with thebedrock surface: (i) A2 is characteristic of shales (e.g.,Georgian Bay, Whitby formations), and (ii ) A1 indicates thepresence of limestones (Trenton Group). High-velocity lime-stones (4000–6000 m/s) provide a better reflection contrastwith the overburden, and produce strong reflections fromtheir upper surface (Figs. 4, 10). In contrast, shales (2500–3500 m/s) offer a relatively weak reflection coefficient, espe-cially where they are overlain by thick, high-velocity till orgravel. Seismic profiles in areas underlain by shale do notshow a well-defined bedrock surface, rather they usually dis-play moderate-amplitude reflection packages interpreted torepresent bedrock plus overlying till or gravel (Figs. 4, 7, 8).The bedrock contact is not visible where data quality is poor(e.g., Fig. 9).

With few exceptions, the seismic profiles obtained to date(Fig. 3) record bedrock at about 150 m asl (± 20 m). Theseprofiles cover the area from Nobleton to east of Port Perry,and are generally located close to the axis of the ORM(Fig. 1). The exceptions to this observation are seen on theNobleton profile (Fig. 4), where the bedrock elevation is<100 m asl in the bedrock valley, and on the two most north-erly profiles west of Uxbridge, where bedrock elevations are

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notably higher than 150 m asl. One of these northern lines iswell north of the ORM in an area where higher bedrock ele-vations are expected (Brennand et al. 1997a), but the other(north of Ballantrae) shows a local bedrock high (-190 masl) beneath the ORM. The Nobleton profile (Fig. 4) identi-fies a deep bedrock valley which is considered to be part ofthe Laurentian channel (Spencer 1881; White and Karrow1971). There is no evidence of the continuous bedrock ridgebeneath the ORM mapped by Eyles et al. (1993) fromunedited water-well records.

Conclusions

Shallow seismic reflection profiling provides a means ofinvestigating the subsurface architecture and stratigraphic re-lationships of sediments beneath the Oak Ridges Moraine(ORM). This paper presents a series of seismic reflectionprofiles acquired in the ORM area which are interpreted interms of their seismic facies (Table 2), their seismic stratig-raphy (Table 3), and the regional sedimentary architecture(Table 4). Figure 11 shows a schematic representation of theelements of the ORM seismo-stratigraphic model; it is aconceptual block diagram that illustrates the major architec-tural elements identified on the seismic profiles and their in-terrelationships in the subsurface. Detailed descriptions ofthe elements and their geological interpretation are given inTable 3. A summary of the major findings is listed below.

(1) The clear definition of four major (and six minor) seis-mic facies and the identification of the facies architecture inthe ORM complex allow regional stratigraphic correlationand improved understanding of event sequences and associ-ated erosional and depositional processes in this and othercomplex stratified moraines.

(2) The wealth of lithologic control from continuous drillcore (-20–50 m per line-kilometre) in the ORM area affords

a tightly constrained seismic facies analysis rarely achievedfor complex glaciogenic sequences.

(3) This borehole control for land-based multichannel sur-veys, together with downhole seismic logging, permits re-finement of the interpretations of acoustic reflectors andtheir properties (coherence, amplitude, and frequency). Thisability offers advantages over marine, largely single-channel,seismic reflection surveys, although marine surveys offerlonger survey lines and higher signal resolution.

(4) The ORM seismic reflection profiles identify a re-gional unconformity separating a regional, dense, high-velocity marker bed, the Newmarket Till, and the overlyingORM sediment package.

(5) The regional unconformity is marked by an irregularsurface (drumlins) on a highly reflective facies (I) and bywell-defined channels of an anabranching network.

(6) The buried-channel configuration can be defined andtraced beneath the ORM complex from surface channelsfound north of the ORM.

(7) The buried channels can have forms which vary ineast–west profile (cross section) from narrow (1 km), withsteep and partially failed side slopes, to broad (2–3 km),with low-angle sides and slopes. Eroded scallops are seenover a distance of several kilometres along the apparent axisof a channel.

(8) Channel fills consisting of high-reflectivity (facies II),coarse-grained beds with cross-bedded sets and hummockyforms are overlain by successions of planar, moderate tolower reflectivity (facies III) sand, silt, and clay packages.

(9) Chaotic facies (IV) define disturbed channel fills thatmay have resulted from side-slope instability during rapidchannel cutting and filling, or suspension deposition of dif-fusely bedded sands from hyperconcentrated flows.

(10) Channel scour and fill are best explained by the ac-tion of regional-scale, high-energy, subglacial outburstfloods.

(11) Channel erosion also extended into extensive lowersediment packages that are usually defined by continuous,moderate-amplitude reflectors (facies III). The higher ampli-tude facies of these lower deposits probably record interbedsof sand, silt, and clay.

(12) Channel erosion and fill allow groundwater connec-tions between the thick overlying ORM sediments and lowerdeposits.

(13) The channel fills have potential as high-yield aqui-fers. Seismic reflection methods have a place in an explora-tion strategy for such groundwater prospects.

(14) The contact of the lower sediment sequence with theoverlying Newmarket Till is commonly remarkably planar.

(15) This regional planar contact, combined with field ob-servations over several kilometres of exposed sedimentshowing little if any deformation of the underlyingglaciolacustrine sediments, suggests that initial deposition ofthe thick Newmarket Till was a passive glacial process anddid not involve wholesale bed deformation.

(16) Shallow seismic reflection profiling in the ORM areahas improved our ability to locate groundwater reservoirs incoarse-grained, channel-fill sequences and in extensive lowerdeposits beneath the regional unconformity and theNewmarket Till.

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Fig. 11. Schematic diagram showing the major elements of aseismo-stratigraphic model that has been developed as part of theOak Ridges Moraine project. The object of this block diagram isto illustrate the architectural relationships between these units(Table 3). X–Y and Y–Z are cutaway surfaces to illustrate thedrumlinized surface of the Newmarket Till (regionalunconformity) buried beneath the Oak Ridges Moraine.

(17) A second unconformity defines the boundary be-tween the eroded, and in places channelled, bedrock surface,and the overlying thick, widespread lower sediment pack-ages. Coarse-grained fills in bedrock channels, such as theLaurentian channel, may provide additional groundwaterprospects.

The multichannel seismic data collected for the ORM ofsouthern Ontario form a high-quality terrestrial data set thathas excellent borehole control. Seismic facies can be readilydefined and seismic facies analysis is well supported by de-tailed and regional knowledge of lithofacies and geologicalmapping (e.g., Russell et al. 1998; Sharpe et al. 1997). Thispaper contributes seismic facies descriptions and interpreta-tions based on well-calibrated seismic profiles. The seismicstratigraphy is refined by core descriptions and downholeseismic information at a type seismic profile. It has beenshown that high-quality, land-based, shallow seismic reflec-tion surveys have the resolution necessary to improve ourunderstanding of sedimentary processes and environments,and our ability to find large aquifers in and beneath theORM sedimentary complex.

Acknowledgments

This work forms one component of a regionalhydrogeology study of the ORM area, initiated in 1993 bythe Geological Survey of Canada (GSC) (D.R. Sharpe, pro-ject leader), and carried out with the support and assistanceof the Ontario Geological Survey (OGS). Many of the ideaspresented in this paper have evolved from long discussions,covering all aspects of the study, with other participants inthe project, including Peter Barnett (OGS), Tracy Brennand(Simon Fraser University), Larry Dyke, Marc Hinton, andHazen Russell (GSC). Our coworkers have also providedvery insightful reviews of various drafts of this paper whichgreatly contributed to the final product. The seismic datawere acquired with the assistance of Robert Burns, MartenDouma, and Ron Good (GSC), and Jill Belisle, Eric Gilson,Steve Grant, Jim Hazzard, Simone Mercier, Jamie Rosen,and Paul White who made up our student crews. Larry Dykemanaged the borehole drilling along the Vandorf andBallantrae profiles, and George Gorrell managed the drillingat Nobleton. The core logging was completed with the ableassistance of Hazen Russell, George Gorrell Lucy Maurice,and Don Cummings. We acknowledge the support providedto one of the authors (A.P.) in the form of a postdoctoralgrant from the Swiss National Fund for scientific research.We also wish to thank Dr. Alan Green for providing accessto main-frame computers at ETH Zürich for some of the ad-vanced processing applications. We thank Mike Roberts andJohn Shaw for their thorough and constructive reviews.

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Documents

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