Buried Bedrock Valleys and Glacial and Subglacial Meltwater Erosion in Southern Ontario, Canada

Home , Oak Ridges Moraine

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/232806604

Buried bedrock valleys and glacial and subglacial meltwater erosion in Southern Ontario, Canada

Article in Canadian Journal of Earth Sciences · May 2011 DOI: 10.1139/E10-104

CITATIONS READS 3 100

1 author:

Cunhai Gao Ontario Geological Survey

22 PUBLICATIONS 149 CITATIONS

SEE PROFILE

Available from: Cunhai Gao Retrieved on: 02 August 2016 801 Buried bedrock valleys and glacial and subglacial meltwater erosion in southern Ontario, Canada

Cunhai Gao

Abstract: Morphometric features from a recently compiled bedrock topography map by the Ontario Geological Survey suggest a glacial erosion origin for the buried large bedrock valleys and troughs in southern Ontario. The bedrock valleys at Milverton, Wingham and Mount Forest are tunnel valleys, resulting from subglacial meltwater erosion beneath the Huron ice lobe, probably during or shortly after the Late-Wisconsinan glacial maximum. Diagnostic features for this interpretation include abrupt valley beginning and termination, uneven longitudinal valley profiles and up-slope gradients. The Dundas bedrock valley is the western extension of the Lake Ontario Basin. No comparable bedrock valleys were found to connect it to the Milverton valley for a joint drainage system as previously suggested. The Laurentian bedrock trough is the southeastward extension of the Georgian Bay Basin, both developed along shale bedrock between the Precambrian shield highlands and the Niagara Escarpment, resulting from long-term mechanical weathering associated with Pleistocene glacial erosion. This bedrock low has a floor that exceeds 50 km in width and is 26 m and more below the current water level of Georgian Bay. It could drain Georgian Bay should the drift cover be removed. There is no evidence to suggest that a preglacial river channel, if it existed, is still preserved in the floor of the Laurentian trough as previously suggested. The framework for an intensely glacially sculpted bedrock surface differs from the previous view for simple modification of a preglacial landscape and is, therefore, important in regional subsurface geological mapping and groundwater studies. Résumé : Les caractéristiques morphométriques illustrées sur une carte topographique du socle rocheux faite par la Com- mission géologique de l’Ontario suggèrent que les grandes vallées et fosses enfouies du sud de l’Ontario aient une origine d’érosion glaciaire. Les vallées rocheuses à Milverton, Wingham et Mount Forest sont des vallées de tunnels et proviennent de l’érosion par l’eau de fonte sous les glaciers, sous le lobe glaciaire Huron, probablement durant ou peu de temps après le maximum glaciaire du Wisconsin tardif. Les caractéristiques de diagnostique pour cette interprétation comprennent des dé- buts et des fins de vallée abruptes, des profils longitudinaux et des gradients de pente amont irréguliers. La vallée rocheuse Dundas constitue l’extension vers l’ouest du bassin du lac Ontario. Aucune autre vallée rocheuse n’a été découverte la re- liant à la vallée Milverton pour constituer un système de drainage conjoint, tel que suggéré antérieurement. La fosse laurentienne dans le socle est le prolongement vers le sud-est du bassin de la baie Georgienne, les deux s’étant développés le long

For personal use only. du socle de shale entre les hautes terres du bouclier précambrien et l’escarpement du Niagara par la météorisation méca- nique à long terme associée à l’érosion glaciaire au Pléistocène. Ce creux du socle rocheux a un plancher qui a une largeur de plus de 50 km et il est à 26 m ou plus sous le niveau d’eau actuel de la baie Georgienne. Si le couvert glacio-sédimen- taire devait être retiré, ce creux pourrait drainer la baie Georgienne. Il n’existe aucune preuve suggérant qu’un chenal de ri- vière préglaciaire, s’il avait existé, soit encore préservé sur le plancher de la fosse laurentienne, tel que déjà suggéré. Le cadre pour une surface de socle intensément sculpté par les glaciers diffère de l’ancienne vue d’une simple modification d’un paysage préglaciaire et il est donc important dans la cartographie géologique régionale subsurface et les études de l’eau souterraine. [Traduit par la Rédaction]

Introduction the reason for the various interpretations proposed for their origins, including relict preglacial channels, glacial scours,

Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 Buried bedrock valleys have been reported in southern On- tectonically controlled Tertiary river valleys or subglacial tario since the late 19th century (Spencer 1881, 1890; Kar- meltwater valleys or channels (Spencer 1907; Straw 1968; row 1973; Flint and Lolcama 1986; Eyles et al. 1993, 1997). Karrow 1973; Brennand and Shaw 1994; Eyles et al. 1997; Early studies are based on hand-contoured maps, and details Kor and Cowell 1998). on the bedrock valleys are generally lacking as to the geome- Previous compilations for bedrock topography are lacking try, longitudinal profile, and their spatial relationships with quality controls on water-well records, the major source for other bedrock valleys in the vicinity. This is probably part of the depth-to-bedrock information. The current water-well da- Received 30 June 2010. Accepted 2 December 2010. Published tabase archived at the Ontario Ministry of Environment in at www.nrcresearchpress.com/cjes on 4 May 2011. Toronto has more than half a million records for southern Ontario. These records are notoriously inconsistent in quality, Paper handled by Associate Editor Timothy Fisher. containing georeferencing errors and incorrect geological de- C. Gao. Sedimentary Geoscience Section, Ontario Geological scriptions largely owing to the reporting procedure, inaccu- Survey, 933 Ramsey Lake Road, Sudbury, ON P3E 6B5, Canada. rate locations sketched and the lack of detailed material information because of the commonly used wash-bored drill- E-mail for correspondence: [email protected].

Can. J. Earth Sci. 48: 801–818 (2011) doi:10.1139/E10-104 Published by NRC Research Press 802 Can. J. Earth Sci., Vol. 48, 2011

ing method, and, lastly, the fact that most water-well drillers Methods are not trained professional geologists (Russell et al. 1998). Depth-to-bedrock information was extracted from water- The database has been systematically filtered for georeferenc- well, petroleum, and geotechnical drill records, as well as ing errors in recent subsurface mapping (Kenny et al. 1997; from published geological maps. Detailed descriptions of the Logan et al. 2005); however, the geological content of the re- methods have already been released, and the following is a cords has rarely been critiqued. summary of the quality control procedures adopted in this Recently, the Ontario Geological Survey developed proto- compilation. Readers can refer to Gao et al. (2006, 2007) for cols and a methodology to generate digital regional bedrock details. surface maps (Gao et al. 2006, 2007). Using this methodol- The water-well database that contains over half a million ogy, rigid quality control measures were employed to track records is the largest source for depth-to-bedrock information. and eliminate problematic data during the compilation. The The water-well records were systematically filtered to remove resultant map has enabled better delineation of the bedrock georeferencing errors, including unreliable locations, ground topography, in particular, the regional extent of significant surface elevations inconsistent with digital elevation model buried bedrock valleys or depressions. This paper introduces (DEM) values, and wells located within lake boundaries. Ap- briefly the methodology, describes in detail major bedrock plying these restrictions provided an initial database with valleys in southern Ontario, and discusses the possible causal more than 350 000 water-well records for southern Ontario. mechanisms. In the discussion that follows, some large bed- The drift–bedrock contact was then assigned through an auto- rock depressions with a size of 20 km and greater in width mation process (Gao et al. 2006, 2007). However, water-well are referred to as troughs. records containing ambiguous or questionable entries for bedrock, such as basalt, conglomerate, greywacke, slate, sand- stone, and soapstone that do not occur or have limited Geological setting occurrence in southern Ontario, were inspected and the – Southern Ontario is underlain by a Precambrian basement drift bedrock contact was manually assigned. – containing Proterozoic gneissic rocks and an overlying Paleo- The borehole records with assigned drift bedrock contact zoic cover rock (Fig. 1A; Ontario Geological Survey 1991; were further filtered and those with inverted stratigraphy, e. Johnson et al. 1992). In the basement across southwestern g., a granite (Precambrian) overlying a limestone (Paleozoic) Ontario lie northeast-trending tectonic highs, referred to as or with duplicate locations, but having different depths to bedrock, were removed. Lastly, water-well records with ex- the Findlay and Algonquin Archs, which separate the Michi- cess depth to bedrock (>8 m) in the known thin-drift areas gan intracratonic basin to the northwest from the Appala- (<1 m) mapped by Ontario Geological Survey (2003) were chian foreland basin to the southeast (Fig. 1B). The inspected and many were removed because of the incorrectly Paleozoic bedrock thickens toward the basin centers, and, in assigned drift–bedrock contact resulting from misused termi- southern Ontario, it comprises Cambrian to Devonian-Missis- nology and misinterpreted geologic material. After these fil- For personal use only. sippian carbonate and clastic sedimentary rocks, reaching a tering processes, a database with about 250 000 drill records maximum thickness of 1.5 km (Johnson et al. 1992). In this was obtained to determine the bedrock elevation surface us- region, the widespread dolostone of the Middle Silurian ing the ESRI® ArcGIS® ordinary kriging routine (Gao et al. Amabel and Guelph Formations is erosion-resistant, whereas 2007). Over 16 000 water-well records not reaching bedrock rocks containing shale and evaporites, such as the Upper Or- but deeper than the interpolated bedrock surface were subse- dovician Queenston and Upper Silurian Salina formations, quently used to “push down” or adjust the surface. are susceptible to erosion. The Niagara Escarpment, a prom- The initially interpolated bedrock surface contains many inent regional landmark, is a result of erosion of soft shale excessively high peaks and deep holes. More than 1200 drill bedrock below a resistant cap rock of dolostone. The Onon- records causing such anomalous areas were carefully in- daga Escarpment is another bedrock high on the Niagara spected and compared with the boreholes within a radius of Peninsula. However, in contrast to its prominent relief in the 1 km. Many had erroneously assigned drift–bedrock contact New York State, it has a subtle surface expression as discon- resulting primarily from incorrect use of the geologic termi- tinuous low ridges along the northern shore of Lake Erie. nology and misinterpretation of boulders as bedrock in the Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 “ ” The study area was overridden by Pleistocene ice sheets borehole records. For instance, stones, although normally from the north. During the retreat of the ice sheet in the used to indicate a drift deposit, has been used by drillers to Late Wisconsinan, discrete ice lobes developed in the Great indicate bedrock, thereby causing unrealistic holes or highs Lakes Basins, which expanded and retreated independently in the generated bedrock surface. After removal of the prob- or semi-independently (Barnett 1992). The Nissouri ice ad- lematic data, the database was updated and kriged to refine vance deposited a variably textured clay to stony till named the bedrock surface; the drift thickness map was generated subsequently by subtracting the bedrock surface elevations the Catfish Creek till during the glacial maximum at about from the ground surface elevations (Gao et al. 2006, 2007). 20 000 years before present (BP); ice re-advance occurred during the Port Bruce and Port Huron stadials at about 15 000 and 13 000 BP, respectively. The ice advances and subse- Bedrock valleys and troughs quent retreats in this region have generated widespread till Many bedrock valleys and depressions exist beneath thick plains and a series of moraines, including the interlobate surficial deposits in southern Ontario, including a large bed- Waterloo and Oak Ridges moraines rich in sand and gravel rock low referred to here as the Long Point trench beneath deposits (Ontario Geological Survey 2003). Lake Erie (Figs. 2, 3, 4, 5). Although some of the bedrock

Published by NRC Research Press Gao 803

Fig. 1. (A) Bedrock geology of southern Ontario (modified from Ontario Geological Survey 1991). (B) Generalized basement contours (metres above sea level) and location of structural basins (modified from Johnson et al. 1992). Inset map shows location of southern Ontario. Fm., Formation; Gp., Group.

valleys have been reported before (e.g., Karrow 1973; Eyles (Fig. 3A). The bedrock valleys are lacking branching fea- et al. 1997), the current work provides much needed details tures, contradicting Eyles et al.’s (1997) work that outlines on their planform, floor topography, and longitudinal pro- well-developed dendritic or arborescent bedrock valleys. This

For personal use only. files, as well as their spatial relationships with the adjacent difference cannot be attributed to map scales because the cur- bedrock lows. rent geographical information system (GIS) map can be Apart from the Laurentian and Ipperwash bedrock troughs, viewed at substantially larger scales than the earlier maps named following Spencer (1890) and Karrow (1973), broad used by Eyles et al. (1997). It remains unclear why their bedrock lows also include the Walkerton and Brantford– compilation differs so strikingly from the current work. It is Welland troughs, both occurring along the Salina Formation speculated here that those small tributaries on their maps are and walled by the Onondaga Escarpment, with a tilted floor probably not the data-based delineations contoured by com- in transverse profile corresponding to the dip of the regional puters but derived largely from the authors’ interpretations. Paleozoic bedrock (Figs. 3A, 4, 5). In the Walkerton trough, On the Niagara Escarpment, many re-entrant valleys exist. a thalweg exists along the buried Onondaga Escarpment Among them, the Dundas valley is one of the largest. Other (Fig. 4), which corresponds more or less to Karrow’s (1973) large ones include the Owen Sound, Beaver, Meaford, and Walkerton valley. Small re-entrants are developed on the Colpoy Bay bedrock valleys (Figs. 3A, 4). Straw (1968) has scarp (Figs. 3A, 4). The Brantford–Welland trough occurs provided details on the geometry and dimension of these re-

Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 east of Woodstock and has an elongate, rectangular plan entrants. Although some of them terminate at the foot of the view (Figs. 3A, 4, 5). Although the current data does not al- escarpment, others incise into the floor of the Laurentian low mapping into the New York State, this bedrock low trough (Figs. 3A, 4). On the Bruce Peninsula, the large re- likely extends farther east because of the continuity of a sim- entrants continue beneath the lake, connecting to the linear ilar bedrock setting. depressions in the floor of Georgian Bay (Figs. 3, 4). Narrow but deep bedrock lows or gorges include the Mil- On the Niagara Peninsula, the Erigan bedrock valley con- verton, Wingham, and Mount Forest valleys to the west and sists of broad bedrock lows in the middle and re-entrants at northwest of Kitchener (Figs. 3A, 4, 5). Smaller such bed- St. Johns and Lowbanks, namely the 12 Mile Creek and rock valleys are also present, including the Elora and Rock- Lowbanks re-entrants on the Niagara and Onondaga escarp- wood valleys at Elora and Guelph (Figs. 3A, 4), named ments, respectively (Fig. 6). North of the Niagara Escarpment following Greenhouse and Karrow (1994). Previously, the to Lake Ontario, no prominent bedrock valleys are found, Milverton and Wingham valleys are referred to together as which differs from Flint and Lolcama’s (1986) compilation the “Wingham Valley” (Karrow 1973). In this study, this that outlines several well-defined, deep bedrock valleys (see name only refers to the valley between Wingham and Ethel Fig. 2B). Irregular, linear bedrock lows occur between because of a bedrock high at Ethel bisecting the valleys Wainfleet and Fraser (Fig. 6), probably corresponding to the

Published by NRC Research Press 804 Can. J. Earth Sci., Vol. 48, 2011

Fig. 2. Bedrock valleys proposed by (A) Spencer (1907), (B) Flint and Lolcama (1986), (C) Karrow (1973), and (D) by Eyles et al. (1997). For personal use only.

Crystal Beach channel, as previously mapped by Flint and USA side, and the eastward extension of this trench remains Lolcama (1986) (see Fig. 2B). However, this valley is shal- unknown. However, seismic surveys in this area indicate its low and lacking well-defined shoulders. probable extension further to the east-northeast (Morgan The St. Davids valley is confirmed, but its northern part 1964). The trench aligns with the deep, east–west-trending near the Whirlpool is not well defined, probably owning to trough in the floor of the eastern Lake Erie Basin. the sparse boreholes available there (Fig. 6). Organic material Till and postglacial lacustrine sediments probably fill the recovered from the valley fill has been radiocarbon-dated at trench. Off Long Point, under the lake, a large moraine ridge, 22 800 to 24 800 BP, indicating a Late-Wisconsinan affinity the Norfolk Moraine (Coakley et al. 1973), occurs as an arc- for the fill (Hobson and Terasmae 1969). It is believed that uate, transverse ridge aligning nearly perpendicular to the Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 this valley was created during the last interglacial Sangamo- trench (Fig. 7). The trench has an irregular longitudinal pro- nian Stage and filled during the Late to Middle Wisconsinan file (Fig. 8A). It probably connects to a large bedrock valley (Feenstra 1981). Later, it was truncated by the present Niag- in the onshore area at Bothwell (Figs. 3A, 4). However, in ara River at the Whirlpool. the offshore area west of the Median across Port Stanley, only a limited number of petroleum-well records are avail- Long Point trench able, rendering delineation of bedrock features there difficult. Defined by numerous offshore petroleum-well records, this As such, the relationship between these two bedrock depres- bedrock low extends for over 150 km beneath Lake Erie and sions remains to be confirmed. pinches out to the west in a direction at 10° to 25° oblique to the basin long axis (Figs. 3A, 4). Its deepest part is located Laurentian trough off Long Point, where the trench stands at 20 m above sea The depth-to-bedrock information is relatively sparse in the level (asl) and is 12 km wide. The trench appears to crosscut Laurentian bedrock trough largely owing to the presence of the Ipperwash trough (Figs. 3A, 4). No petroleum-well re- thick drift of the Oak Ridges Moraine (Fig. 3B). There is a cords are available across the international border on the need in the future to refine the floor topography. Nonetheless,

Published by NRC Research Press Gao 805

Fig. 3. (A) Bedrock topography of southern Ontario and Lake Erie. Bathymetric data for the Great Lakes came from the National Oceanic and Atmospheric Administration (1999). asl, above sea level. (B) Drift thickness with hill-shade relief of the present ground surface. Boxed areas are enlarged in Figs. 6, 9A, and 9B, as well as in Figs. 10A and 10B. For personal use only. Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11

Published by NRC Research Press 806 Can. J. Earth Sci., Vol. 48, 2011

Fig. 4. Highlighted bedrock valleys and troughs in southern Ontario. Contour interval = 25 m. Coded bedrock depressions are mentioned or discussed in the text. Refer to Fig. 1 for bedrock geology. For personal use only.

the current compilation shows a bedrock trough 50 to 1907; White and Karrow 1971; Eyles et al. 1993; Holysh et Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 70 km wide with a floor mostly below the 150 m contour. al. 2004). The trough stretches from Georgian Bay to Lake Ontario in Among the re-entrants that extend into the Laurentian the Ordovician shale and limestone, bordered to the east by trough, the one at Caledon East (Figs. 3A, 4) contains about the gentle Precambrian highlands and to the west by the 30 m of glaciofluvial sand and gravels resting on the valley steep Niagara Escarpment (Figs. 3A, 4, 5A). floor at the base of the Niagara Escarpment, forming the re- Linear depressions exist in the floor of the Laurentian bed- gionally significant aquifers (Davies and Holysh 2005; Rus- rock trough. By connecting some of the deeper ones, a thal- sell et al. 2006). It extends to the southwest, trending weg was defined, which rises toward the mid-point along the similarly but not overlapping with the present-day Grand trough (Fig. 4). Although it is similar in alignment and loca- River, and it is probably linked to the buried, southwest- tion to those mapped previously (White and Karrow 1971; trending Rockwood bedrock valley (Figs. 3A, 4). Drilling Eyles et al. 1993), this thalweg remains to be confirmed be- along the base of the Niagara Escarpment in a poorly defined cause of the limited data available. It has been interpreted as branch of the bedrock valley at Georgetown (Figs. 3A, 4, 9B) a relict channel of the preglacial Laurentian River draining also indicates thick sand and gravels below Late-Wisconsinan the upper Great Lakes Basins (see Fig. 2A; Spencer 1890, till deposits (Meyer and Eyles 2007).

Published by NRC Research Press Gao 807

Fig. 5. Cross sections A–A', B–B’,C–C', D–D', and E–E'. Thick line indicates bedrock surface and thin dotted line the ground surface. Refer to Fig. 4 for locations. asl, above sea level. For personal use only.

Mount Forest, Wingham, and Milverton valleys may be artificial because of the lack of data in these areas These bedrock lows are rectilinear to slightly curved (Fig. 10A). After removal of these highs, the valleys exhibit gorges with a width ranging from 2 to 4 km and depth of 40 a much subdued floor topography (Figs. 8B, 8C). to 70 m, trending to the southeast across the Algonquin Arch The Milverton valley extends for 46 km with an overall (Fig. 9). Their longitudinal profiles are irregular with multi- gradient of 0.3 m/km to the southeast. At Milverton, a closed ple thresholds and enclosed depressions, and some valley depression or basin stands as the deepest part of the valley, segments begin and terminate rather sharply (Figs. 8B, 8C, reaching to 268 m asl or 70 m depth below the valley 9). The boreholes in the valleys are not all distributed along shoulder (Figs. 8B, 9). A bedrock high about 6 km northwest of Milverton divides the valley into the western and eastern

Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 the thalwegs, and some areas even do not have data (Fig. 10). Nonetheless, the overall geometry of these valleys is well- segments (Fig. 9A). However, the lack of data in this area defined owing to the large number of drill records available (Fig. 10A) means that this bedrock high needs to be con- in the vicinity that clearly define the valley shoulders firmed by drilling or ground geophysical survey in the future. (Fig. 10). The valley crosscuts several bedrock units including, from The Mount Forest valley extends from Mount Forest to west to east, the Detroit River Group and the Bois Blanc, Drayton for 35 km in the Salina Formation, and, despite an Bass Island, and Salina formations (Fig. 9). East of Welles- extremely undulating longitudinal profile, it has a gradient to ley, it diverges into a broad lowland underlain by the Salina the southeast (Fig. 8C). This valley not only differs from the and Guelph formations. broad Walkerton trough in planform but also cuts into the lat- In Eyles et al.’s (1997) compilation, both the eastern and ter (Figs. 3A, 9A). The Wingham valley stretches from western segments of the Milverton valley are shown on the Wingham to Ethel for about 30 km, with an uneven floor computer-contoured bedrock surface map. However, they in- dipping to the northwest; it is truncated at Wingham by the terpreted the western segment atop the Algonquin Arch as a northward-aligned Hutton Heights valley (Figs. 8B, 9A). series of solution holes in limestone bedrock. Although this Some of the bedrock highs in this and other bedrock valleys interpretation is consistent with their proposition that the

Published by NRC Research Press 808 Can. J. Earth Sci., Vol. 48, 2011

Fig. 6. Erigan valley on the Niagara Peninsula, contoured at 5 m interval. Lower case letters indicate bedrock units. Refer to Fig. 1 for bedrock geology. For personal use only.

buried valleys were tectonically controlled river channels, were created on both Niagara and Onondaga escarpments draining the flanks of the Arch, the current work shows that and connected by shallow valleys between the escarpments the western segment is an integral part of the Milverton val- in a way similar to the present Niagara River (A.F. Bajc, per- ley that cuts across this tectonic high (Figs. 4, 9A). sonal communication, 2010). This proposition invokes the The Milverton valley is thought to extend eastward to con- presence of a high-relief Onondaga Escarpment to form bed- nect the Dundas valley, forming a joint preglacial river (Kar- rock gorges with a size comparable to the Milverton valley. Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 row 1973; Eyles et al. 1997). However, no comparable However, as evidenced by the current work as well as pre- bedrock gorges were found between Copetown and Wellesley vious compilations, the Onondaga Escarpment is subtle even for such drainage connection (Fig. 9). The absence of large along its most prominent segments on the Niagara Peninsula, bedrock valleys in this area cannot be ascribed to the lack of and there is no prominent bedrock cliff at the outlet of the data. Although limited data is available between Kitchener Milverton valley at Wellesley (Figs. 3A, 9). As such, it is un- and Paris, sufficient data is seen elsewhere along the pro- likely that the Milverton valley resulted from river-headward posed river pathway. This is particularly true for the area be- erosion on bedrock scarps. Indirect evidence comes from the tween Wellesley and Kitchener and between Paris and Mount Forest bedrock valley, which is developed in a single Copetown, where dense data points are available but no bed- bedrock formation without any salient slope break or bedrock rock gorges are delineated (Fig. 10B). escarpment at its outlet at Drayton (Fig. 9A). It should also Alternatively, the shallow bedrock lows found in a recent be borne in mind that the present Niagara River has not gen- geophysical study are suggested to be the connection be- erated on the Onondaga Escarpment any bedrock valleys with tween the Milverton and Dundas valleys (Zwiers et al. 2008, a size comparable to the bedrock gorge below the Niagara 2009; Bajc et al. 2009). It is thought that bedrock gorges Falls.

Published by NRC Research Press Gao 809

Fig. 7. Moraines and eskers in southern Ontario, formed during the Late Wisconsinan (Modified from Ontario Geological Survey 2003). For personal use only.

Dundas valley broadens in a way similar to the terminus of the Dundas val- This is a partly filled, deep bedrock gorge that crosscuts ley at Copetown (Fig. 9B). Irregularly shaped, poorly defined the Niagara Escarpment in Hamilton and extends into Lake shallow bedrock lows also occur around Brantford (Fig. 9B). Ontario (Figs. 3A, 4). Because of the thick overburden mate- However, the data in this area is relatively scanty, and the rial in the valley, water wells often terminate in the valley in- morphometry of these bedrock lows needs to be refined in fill, leading to the limited depth-to-bedrock information the future. available. This is probably the reason why the valley has an Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 extremely uneven floor shown in this compilation. Future Origin of bedrock valleys and troughs drilling may help better delineate the floor topography. The valley floor is at 50 m asl in Hamilton but plunges Long Point trench into a small but very deep basin with a base at 30 m asl at The broad plan view morphology and thick fill of glaci- Copetown (Fig. 9B). The valley widens and rises sharply by genic material suggest that this bedrock feature can best be more than 120 m prior to its closure about 3 km west of Co- explained in the context of glacial erosion (Figs. 3, 4). Fast petown (Fig. 9B). Further to the west, no comparable bed- moving ice was probably responsible for the formation of rock gorges exist. The recent drilling and subsurface this bedrock low. Instead of entering the Ipperwash trough, mapping in this area has reached the same conclusion (Bajc the proposed westward-moving ice stream appears to crosscut et al. 2009; Zwiers et al. 2009). Instead, a broad, shallow it (Figs. 3A, 4). The reason for this may be that the Huron bedrock low, referred to here as the Innerkip valley, occurs ice lobe moved in a direction against the Erie lobe, which in the direction of the Dundas valley. It cuts into the Onon- could potentially have jammed the trough. The other reason daga Escarpment forming a small but deep re-entrant at In- is probably related to the alignment of the Ipperwash trough nerkip (Fig. 9B). Prior to its termination, the Innerkip valley that orients at a high angle to the direction of the proposed

Published by NRC Research Press 810 Can. J. Earth Sci., Vol. 48, 2011

Fig. 8. Longitudinal valley floor profiles. Upper line is the actual measurement, and the lower one the profile after the removal of the bedrock highs where no borehole records exist. (A) Long Point trench. (B) Wingham and Milverton valleys. Note the former is cut by the Hutton Heights valley. (C) Mount Forest valley. (D) Erigan valley. a.s.l., above sea level. For personal use only.

ice stream. The Norfolk Moraine off Long Point marks the Georgian Bay Basin has a floor dissected with numerous lin- stillstand position of the retreating ice lobe after the Port ear depressions or valleys (Fig. 3A). These valleys were Bruce ice advance (Coakley et al. 1973; Barnett 1992). The probably scoured by subglacial meltwater during the Late Long Point trench has an alignment oblique to the basin Wisconsinan (Kor and Cowell 1998). The linear bedrock axis, suggesting no direct link between this bedrock low and lows in the floor of the Laurentian trough can probably be the proposed preglacial river that drained eastward along the ascribed to a similar origin. Presently, thick drift material of long axis of the Lake Erie Basin (see Fig. 2A; Spencer 1890, Late-Wisconsinan age occurs in the Laurentian trough 1907). (Fig. 3B; Barnett 1992). Conceivably, drift material of pre- Wisconsinan ice advances could have existed there and acted Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 Laurentian trough as a surface armour, preventing the trough from excessive The morphology and alignment suggest that the Laurentian glacial excavation. The convergence in planform and rise in trough is the southeastward extension of the Georgian Bay floor elevation toward the centre of the trough suggests that, Basin (Figs. 3A, 4). The fact that both are located along soft apart from the Georgian Bay ice lobe, the northward-moving shale bedrock between the Precambrian Shield highlands and Ontario lobe also played a role in shaping this bedrock low, the Niagara Escarpment suggests bedrock control on their de- consistent with the occurrence in the trough of the interlobate velopment. It is likely that the Laurentian trough resulted Oak Ridges Moraine resulting from the coalescence of these from long-term mechanical weathering associated with Pleis- ice lobes during the Late Wisconsinan (Figs. 3B, 7; Barnett tocene glacial erosion. 1992). The Georgian Bay Basin, which stands at 80 m asl and Spencer (1890, 1907) first recognized the Laurentian lower in the centre, ascends to the southeast along a ramp to trough as part of the Georgian Bay Basin. However, the over- 120 m asl at Wasaga Beach to connect the Laurentian trough, all geometry and floor depth of the trough remained un- suggesting increased erosion toward basin centre (Fig. 3A). known at that time. Based on the drill records available, he Like the northeastern part of the Huron Lake Basin, the noted a bedrock surface deeper than the water level of Geor-

Published by NRC Research Press Gao 811

Fig. 9. Bedrock valleys and the surrounding bedrock topographic features contoured at 10 m intervals. (A) Milverton, Wingham, and Mount Forest valleys. (B) Dundas and Innerkip valleys. asl, above sea level. Boreholes OGS 03-5, OGS 04-04, DV-06, and DV-08 are from Bajc and Hunter (2006), Bajc et al. (2009), and Zwiers et al. (2009); UW34-78 and 83-81 from Greenhouse and Karrow (1994); and G2, SL3, and M2 from Meyer and Eyles (2007). Refer to Fig. 4 for the coded bedrock valleys. Lower case letters are bedrock formations (refer to Fig. 1 for bedrock geology). For personal use only. Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11

Published by NRC Research Press 812 Can. J. Earth Sci., Vol. 48, 2011

Fig. 10. Drift thickness and location of drill records. The bedrock topography is outlined by 10 m contours. The hill-shade relief represents the present ground surface. (A) Milverton, Wingham, and Mount Forest valleys and surrounding area. (B) Dundas and Innerkip valleys and surrounding area. For personal use only. Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11

Published by NRC Research Press Gao 813

gian Bay (176 m asl) and suggested the presence in this bed- is consistent with such an interpretation. Although the water- rock low of a preglacial Laurentian River channel that well records provide limited details on the subsurface mate- drained the upper Great Lake Basins into the Lake Ontario rial, those in the Milverton valley indicate frequent occur- Basin (see Fig. 2A). In the subsequent studies, thalwegs, sim- rence of sand and gravels resting on the valley floor. Recent ilar to that in Fig. 4, have been mapped in the Laurentian boring at Wellesley confirms the occurrence of glaciofluvial trough and are believed to be the relict channel of this pregla- sand and gravels below Late-Wisconsinan till in the Milver- cial drainage often referred to as Laurentian Channel (White ton valley (Fig. 11; Bajc and Hunter 2006; Bajc et al. 2009; and Karrow 1971; Eyles et al. 1993; Holysh et al. 2004). Zwiers et al. 2009). Such a valley infill is consistent with a However, as the current compilation shows, the trough has a tunnel-valley origin. It is worth noting that the term “tunnel floor that exceeds 50 km in width and is 26 m and more be- channel” is used to imply that water completely filled the val- low the current water level of Georgian Bay. The thalweg of leys when they were formed (e.g., Clayton et al. 1999; Fisher the trough is not the only area that could drain Georgian Bay et al. 2005). To avoid this genetic connotation, the term “tun- should the drift cover be removed. While it is possible that a nel valley” was used in the discussion that follows. preglacial river, as Spencer (1890, 1907) speculated, flowed The Milverton, Wingham, and Mount Forest bedrock val- in a pathway along this trough, any such valleys would have leys do not show prominent branching (Figs. 3A, 4, 9), been altered or removed during the subsequent Pleistocene which is in contrast to an anabranching channel network glaciations that shaped Georgian Bay and other Great Lake commonly proposed for tunnel valleys (Brennand and Shaw Basins. 1994; Praeg 2003). However, recent studies indicate that The “Laurentian Channel” is thought to have remained anabranching is not ubiquitous, and the network may have re- open and drained Georgian Bay during the last interglacial sulted from onlapping or crosscutting of tunnel valleys because of the occurrence of the Sangamonian deposits in formed at various stages (Jørgensen and Sandersen 2006; the Laurentian trough (Eyles and Williams 1992; Karrow et Kristensen et al. 2007). Valley crosscutting is seen at Wing- al. 2001). But these sediments alone may not be used as evi- ham, where the Hutton Heights valley cuts through the dence for the presence of such a drainage system. This is be- Wingham valley (Figs. 4, 8B, 9A). cause they could simply be the deposits in local lakes or Subglacial meltwater drained along the tunnel valleys, car- rivers draining into Lake Ontario just like the present-day rying subglacial debris to lakes or to outwash fans at ice Don River. Based on geophysical data, Eyles et al. (1985) sheet margins. As such, the terminus of tunnel valleys com- proposed the subsequent development of a large delta stretch- monly marks the marginal zone of the ice lobes (Mullins ing from Barrie to Toronto in the channel during the early and Hinchey 1989; Hooke and Jennings 2006). The Milver- Wisconsinan, implying that the channel was still open by ton valley ends at Wellesley, suggesting that the convergence this time. However, except for the deltaic sediments in the and breakup of the Laurentide ice sheet during the associated Scarborough Formation seen in the shore bluffs of Lake On- ice advances was centered in this area, corresponding well to tario at Scarborough and the Rouge River valley in Toronto the location of the interlobate Waterloo Moraine (see

For personal use only. to the north, there is no convincing sedimentological evi- Figs. 3B, 10). Between Drayton and Elora, a thick drift de- dence to confirm this suggestion. posit occurs at the outlet of the Mount Forest bedrock valley The Ipperwash trough can be regarded as a smaller version (Figs. 3B, 10), suggesting that its emplacement was probably of the Laurentian trough, resulting from glacial erosion of related to this tunnel valley. Future detailed boring in this Devonian shale. The ice lobes from the Lake Huron and area may provide insight into this deposit and its relationship Erie basins moved in opposite directions and probably coa- with this bedrock valley. lesced in this bedrock low. Consequently, the bedrock low shows a convex-up longitudinal profile with a sill located Dundas valley and other re-entrants near the mid-point along the trough (Figs. 3A, 4). The Wal- The Dundas bedrock valley protrudes as the western exten- kerton and Brantford–Welland bedrock troughs differ from sion of the Lake Ontario Basin (Figs. 3A, 4), likely resulting the Laurentian and Ipperwash troughs in morphology in that from repeated cycles of glacial erosion during the Pleisto- they do not terminate in lake basins on both ends (Figs. 3A, cene. A series of arcuate-shaped moraine ridges occur around 4). But both troughs are closely related to the bedrock and the head of this bedrock gorge (Fig. 7). The valley infill con- align with the regional ice flows. It is likely that they resulted Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 tains primarily Late-Wisconsinan glacigenic deposits, as re- from long-term weathering, in particular, the erosion by vealed by recent drilling in the valley (MacCormack et al. Pleistocene glaciers. 2005; Zwiers et al. 2008, 2009; Bajc et al. 2009). Such a landform and sedimentary setting indicates the latest glacial Milverton, Wingham, and Mount Forest valleys overriding and erosion of this bedrock depression. A glacial Assuming that, as Karrow (1973) suggested, the Milverton origin of the Dundas valley is consistent with the interpreta- and Wingham bedrock valleys had an eastward flow directions of other re-entrants on the Niagara Escarpment (Straw tion, then prominent upslope gradients occur (Fig. 8B). They 1968; Kor and Cowell 1998). have irregular longitudinal profiles and contain segments that Based on the morphometric features and glacial deposits, start and terminate abruptly. Such features exclude the possi- Straw (1968) proposed a glacial origin for the re-entrants on bility for a normal fluvial origin. Instead, the valleys resem- the Niagara Escarpment, including the Dundas valley. Be- ble tunnel valleys or channels carved by subglacial meltwater, cause of the slight variation in valley strike, he suggested as described elsewhere (e.g., Sjogren et al. 2002; Jørgensen that these valleys were a result of multiple glacial scouring and Sandersen 2006; Kristensen et al. 2007). Their alignment and expansions during the Late Wisconsinan. Kor and Cow- with the pathway of Huron ice lobe of the Late Wisconsinan ell (1998) noticed that the deepest parts of Georgian Bay

Published by NRC Research Press 814 Can. J. Earth Sci., Vol. 48, 2011

often coincide with the thalweg of the re-entrants at the and Jennings 2006; Jørgensen and Sandersen 2006). It may shoreline on the Bruce Peninsula. This relationship is inter- be speculated that meltwater ponding at ice base occurred in preted as a result of raised subglacial stream velocity and in- parts of the Huron Lake Basin, and the catastrophic release creased erosion from flow convergence in the re-entrants in of the stored subglacial water created the Milverton, Wing- front of the escarpment. Based on these observations, they ham, and Mount Forest bedrock valleys. It is suggested that interpreted the re-entrants as tunnel valleys scoured by cata- deep permafrost at ice margins impedes the substrate drain- strophic release of stored subglacial meltwater. The Caledon age and freezes the glaciers to the ground, helping raise the East re-entrant contains thick glaciofluvial sand and gravels hydraulic head for catastrophic release of stored subglacial along the valley base, consistent with a subglacial flood ero- water (Piotrowski 1997; Clayton et al. 1999; Cutler et al. sion origin (Davies and Holysh 2005; Russell et al. 2006). A 2002; Hooke and Jennings 2006). As indicated by ice-wedge more gradual sedimentary process is suggested for a similar casts and polygons, permafrost did occur in southern Ontario fill in the bedrock valley at Georgetown (Fig. 9B; Meyer and during the Late Wisconsinan (Morgan 1982; Gao 2005). The Eyles 2007). In that study, however, the bedrock valley and presence of permafrost would, thus, have created favorable those in the vicinity are poorly defined, and their relationship conditions for tunnel valleys to form in this region. It is note- with and possible controls on the sedimentation remain un- worthy that subglacial sediments can be squeezed by defor- known. mation into small tunnels at ice base owing to increased The small basin in the front of the 12 Mile Creek re-en- pore pressure, and the regular basal meltwater then removes trant at the base of the Niagara Escarpment (Figs. 6, 8D) is the debris under steady state. Such a process can gradually thought to be a plunge pool of the Erigan preglacial valley generate deep tunnel valleys (e.g., Boulton and Hindmarsh draining the Lake Erie Basin into the Lake Ontario Basin 1987). However, the fact that the tunnel valleys in the study (Feenstra 1981; Flint and Lolcama 1986). As mentioned ear- area are in the Paleozoic bedrock, which does not deform ap- lier, similar pool-like basins also occur elsewhere at the base preciably under glacial stress, negates this model. of the escarpment, resulting from flow convergence in a sub- In explanation of the present landscape, Shaw and Gilbert glacial meltwater setting (Gilbert and Shaw 1994; Kor and (1990) and Sharpe et al. (2004) proposed the outburst of two Cowell 1998). Subglacial meltwater erosion is suggested to subglacial megafloods responsible for the development of have played a key role in shaping the 12 Mile Creek re-entrant tunnel valleys and drumlin fields across much of the Great and the surrounding landscape (Tinkler and Stenson 1992). Lakes region during the Late Wisconsinan. The Milverton, The re-entrant is bordered to the south by the Fonthill Wingham, and Mount Forest bedrock valleys have an align- Kame, a deltaic complex formed when the Ontario ice lobe ment oblique to, and a flow direction against, the proposed was fronted by proglacial Lake Warren to the south (Feenstra flow lines toward the south-southwest and west, indicating 1981). Various glacial lakes developed in the middle part of that they are not related to such flood events. Instead, these the Erigan valley, where broad bedrock basins developed in bedrock valleys were likely carved by different, both tempo- less resistant Salina Formation (Fig. 6; Feenstra 1981). Dur- rally and spatially, subglacial meltwater floods. Similarly, the For personal use only. ing the last deglaciation, for example, glacial Lake Wainfleet tunnel valleys in the floor of Georgian Bay show various drained into the Lake Ontario Basin through several outlets flow directions (see Fig. 3), and they may record multiple re- on the Niagara Escarpment (Pengelly et al. 1997). As such, leases of stored subglacial water, as suggested by Kor and the Erigan valley may have resulted from a combination of Cowell (1998). glacial, subglacial meltwater and lacustrine erosion. Even if Faults exist in the Paleozoic bedrock in southern Ontario a preglacial river draining the Lake Erie Basin did exist, as and the basement faulting, as reflected by the aeromagnetic suggested by Spencer (1907), the original valley may have lineaments, can displace or have the potential to fracture the been intensively, if not entirely, altered or modified. Paleozoic cover rock (Boyce and Morris 2002). Areas with fractured Paleozoic bedrock are susceptible to erosion. This Discussion is probably true for the Laurentian, Ipperwash, and Walker- ton troughs that are within aeromagnetic linear zones. As op- The present bedrock topography has some inheritance posed to this situation, the Long Point trench and the from a preglacial landscape (Horberg and Anderson 1956; Milverton, Wingham, and Mount Forest valleys have an Karrow 1973). However, as evidenced by the bedrock valleys Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 alignment oblique to the aeromagnetic lineaments. Although and troughs, intense glacial and subglacial meltwater erosion the Dundas valley may have been fractured along some large occurred during the Pleistocene, leading to deep carving and aeromagnetic linear zones (Boyce and Morris 2002), other alteration of the bedrock surface. In a glacial environment, large re-entrants, such as the Owen Sound, Meaford, and the resultant landscape tends to be uneven and complex, Beaver valleys, do not align with any aeromagnetic linea- marked by numerous highs and lows; the linear bedrock ments or faults. As such, faults may have provided favorable lows such as tunnel valleys commonly occur as discrete de- conditions for selective glacial erosion, but they are not the pressions without tributaries. Realization of this is important controlling factors on the development of the linear bedrock in regional subsurface geological mapping and groundwater depressions in southern Ontario. studies. The age of the bedrock valleys and troughs is difficult to Catastrophic outburst of trapped subglacial meltwater has determine owing to a poor understanding of the subsurface been suggested to be responsible for the formation of tunnel drift stratigraphy and the lack of detailed borings in these valleys under the Laurentide and Scandinavian ice sheets bedrock lows. The bedrock troughs likely have experienced a (Wright 1973; Piotrowski 1997; Clayton et al. 1999; Cutler long-term weathering process typified by multiple cycles of et al. 2002; Russell et al. 2003; Fisher et al. 2005; Hooke glacial erosion during the Pleistocene. In the Laurentian

Published by NRC Research Press Gao 815

Fig. 11. Borehole records in the lower part of the Milverton bedrock valley (Bajc and Hunter 2006; Bajc et al. 2009; Zwiers et al. 2009). Note the presence of sand and gravels and the Catfish Creek till in the bedrock valley. m asl, metres above sea level.

trough, the York till of the penultimate Illinoian glaciation during the Early Wisconsinan, but was re-used during the

For personal use only. has been recorded below the last interglacial deposits (Eyles Nissouri ice advance. To prove this, it requires a thorough et al. 1985; Eyles and Williams 1992; Karrow et al. 2001). understanding of the relationship between the valley infill The occurrence of this till suggests glacial overriding and as- and the drift in the immediately adjacent region. However, sociated erosion of this bedrock low at least during the Illi- the current data available does not allow any detailed evalua- noian Stage. tion of these sediments as to their sedimentary facies, age, The Milverton, Wingham, and Mount Forest bedrock val- and lateral extent. Boreholes in the re-entrants along the base leys are buried features without surface expression. This sug- of the Niagara Escarpment all indicate a valley fill with a gests an age older than the surficial sediments of till plains, Late-Wisconsinan affinity and hence a minimum age for moraines, and eskers emplaced by the retreating glaciers after these bedrock lows (Davies and Holysh 2005; MacCormack the Port Bruce ice advance at 15 000 BP. The eskers indicate et al. 2005; Russell et al. 2006; Meyer and Eyles 2007; Bajc a regional hydraulic gradient to the east and east-southeast et al. 2009; Zwiers et al. 2009). Glacial deposits predating beneath the Huron ice lobe. They crosscut the Mount Forest the Catfish Creek till have been reported to occur in the and Milverton valleys (Fig. 7), suggesting the development of Elora and Rockwood bedrock valleys, suggesting an age a later hydraulic gradient that differed from the previous one Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 older than the Nissouri ice advance (Greenhouse and Karrow responsible for those bedrock valleys. The eskers, on the 1994). This means that the buried bedrock valleys in south- other hand, align well with the Wingham and Hutton Heights ern Ontario likely developed during various stages. Only can valleys (Fig. 7), suggesting a similar hydraulic gradient under future detailed boring in this region provide the needed in- that part of the ice lobe or, alternatively, the re-use of these sights that would help better understand the subsurface till valleys by subglacial meltwater or both. stratigraphy and provide age control on the buried bedrock The drilling in the lower part of the Milverton valley at valleys. Wellesley shows glaciofluvial gravelly deposits and till corre- lated to the Catfish Creek till (Fig. 11; Bajc and Hunter Conclusions 2006; Bajc et al. 2009; Zwiers et al. 2009). This till was deposited during the Nissouri ice advance (Bajc and Shirota The recent compilation of the bedrock topography by the 2007), and its presence suggests that this valley probably de- Ontario Geological Survey has enabled better delineation of veloped during or shortly after the Late-Wisconsinan glacial the regional extent of significant buried bedrock valleys in maximum around 20 000 BP. There is also a possibility that southern Ontario. This is largely attributable to the rigid qual- this valley predated the Late Wisconsinan, e.g., developed ity control measures adopted in this compilation to track and

Published by NRC Research Press 816 Can. J. Earth Sci., Vol. 48, 2011

eliminate the problematic borehole records, in particular, Ontario Geological Survey, Open File Report 6240. pp. 24-1–24- those in the water-well database that contains over half a mil- 6. lion records. The morphometric features suggest that these Barnett, P.J. 1992. Quaternary geology of Ontario. In Geology of large linear bedrock depressions were carved through glacial Ontario. Ontario Geological Survey, Special Vol. 4, Part 2. and subglacial meltwater erosion. The bedrock topography is pp. 1011–1090. uneven and complex, containing numerous highs and lows. Boulton, G.S., and Hindmarsh, R.C.A. 1987. Sediment deformation This view differs from the previous views for simple modifi- beneath glaciers: rheology and geological consequences. Journal of Geophysical Research, 92(B9): 9059–9082. doi:10.1029/ cation of a preglacial landscape and features such as river JB092iB09p09059. valleys. Boyce, J.I., and Morris, W.A. 2002. Basement-controlled faulting of The Laurentian bedrock trough is the southeastward exten- Paleozoic strata in southern Ontario, Canada: new evidence from sion of the Georgian Bay Basin, resulting from long-term geophysical lineament mapping. Tectonophysics, 353(1–4): 151– mechanical weathering associated with Pleistocene glacial 171. doi:10.1016/S0040-1951(02)00280-9. erosion. It has a valley floor that exceeds 50 km in width Brennand, T.A., and Shaw, J. 1994. Tunnel channels and associated and is 26 m and more below the current water level of Geor- landforms, south-central Ontario: their implications for ice-sheet gian Bay. This bedrock low could drain Georgian Bay should hydrology. Canadian Journal of Earth Sciences, 31: 505–522. the drift cover be removed. There is no evidence to suggest Clayton, L., Attig, J.W., and Mickelson, D.M. 1999. Tunnel channels that a preglacial river channel, if it existed, is still preserved formed in Wisconsin during the last glaciation. In Glacial in the floor of this bedrock depression. The Milverton, Wing- processes past and present. Edited by D.M. Mickelson and J.W. ham, and Mount Forest bedrock valleys are discrete, rectilin- Attig. Geological Society of America, Boulder, Colo. pp. 69–82. Coakley, J.P., Haras, W., and Freeman, N. 1973. The effect of storm ear to slightly curved bedrock gorges without prominent In branching features. Their undulating longitudinal profiles surge on beach erosion, Point Pelee. Proceedings of the 16th Conference on Great Lakes Research. International Association of and upslope gradients exclude the possibility for a normal Great Lakes Research. pp. 377–389. fluvial origin. Instead, such features indicate a tunnel valley Cutler, P.M., Colgan, P.M., and Mickelson, D.M. 2002. Sedimento- origin related to subglacial meltwater erosion under the logic evidence for outburst floods from the Laurentide ice sheet Huron ice lobe. The till stratigraphy of the valley infill sug- margin in Wisconsin, U.S.A: implications for tunnel-channel gests the development of these bedrock valleys probably dur- formation. Quaternary International, 90(1): 23–40. doi:10.1016/ ing or shortly after the Late-Wisconsinan glacial maximum. S1040-6182(01)00090-8. Lastly, the Dundas and Milverton bedrock valleys are two Davies, S.D., and Holysh, S. 2005. An investigation of buried valley different systems and there are no comparable bedrock val- aquifer systems in the area north of Lake Ontario. In Summary of leys existing between them for a joint drainage system as pre- field work and other activities 2004. Ontario Geological Survey, viously suggested. The Dundas valley is the westward Open File Report 6172. pp. 30–1to30–7. extension of the Lake Ontario Basin, resulting from glacial Eyles, N., and Williams, N.G. 1992. The sedimentary and biological record of the last interglacial–glacial transition at Toronto, Canada.

For personal use only. to subglacial meltwater erosion. This is evidenced by the val- – ley infill consisting of glacial and related deposits of the Wis- Geological Society of America, Special Paper 270. pp. 119 137. Eyles, N., Clark, B.M., Kaye, B.G., Howard, K.W.F., and Eyles, C.H. consinan. 1985. The application of basin analysis techniques to glaciated Acknowledgments terrains: an example from the Lake Ontario Basin, Canada. Geoscience Canada, 12:22–32. The author wishes to thank Jiro Shirota, Steve van Haaf- Eyles, N., Boyce, J., and Mohajer, A.A. 1993. The bedrock surface of ten, and Frank Brunton for technical support in compilation the western Lake Ontario: evidence of reactivated basement of the bedrock topography map for this study, and Peter Bar- structures? Géographie physique et Quaternaire, 47: 269–283. nett for useful discussions. Andy Bajc, Ross Kelly, and Cam Eyles, N., Arnaud, E., Scheidegger, A.E., and Eyles, C.H. 1997. Baker reviewed an early version of the manuscript and pro- Bedrock jointing and geomorphology in southwestern Ontario, vided critical but helpful comments and suggestions. Thanks Canada: an example to tectonic predesign. Geomorphology, 19(1– – are also extended to John Shaw, Phil Kor, and the Associate 2): 17 34. doi:10.1016/S0169-555X(96)00050-5. Editor Timothy Fisher for their detailed reviews and com- Feenstra, B.H. 1981. Quaternary geology and industrial minerals of the Niagara-Welland area, southern Ontario. Ontario Geological

Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 ments that greatly improved the quality of this manuscript. Survey, US. Geological Survey, Open-file Report 5361. References Fisher, T.G., Jol, H.M., and Boudreau, A.M. 2005. Saginaw Lobe tunnel channels (Laurentide Ice Sheet) and their significance in Bajc, A.F., and Hunter, J.A. 2006. Results of 2003–2004 overburden south-central Michigan, USA. Quaternary Science Reviews, 24(22): drilling programs in the Region of Waterloo, southwestern 2375–2391. doi:10.1016/j.quascirev.2004.11.019. Ontario. Ontario Geological Survey, Miscellaneous Release— Flint, J.J., and Lolcama, J. 1986. Buried ancestral drainage between Lake Data 205. Erie and Ontario. Geological Society of America Bulletin, 97(1): 75– Bajc, A.F., and Shirota, J. 2007. Three-dimensional mapping of 84. doi:10.1130/0016-7606(1986)97<75:BADBLE>2.0.CO;2. surficial deposits in the Regional Municipality of Waterloo, Gao, C. 2005. Ice-wedge casts in Late Wisconsinan glaciofluvial southwestern Ontario. Ontario Geological Survey, Groundwater deposits, southern Ontario, Canada. Canadian Journal of Earth Resources Study 3. Sciences, 42(12): 2117–2126. doi:10.1139/e05-072. Bajc, A.F., Brunton, F.R., Priebe, E.H., MacCormack, K.E., and Gao, C., Shirota, J., Kelly, R.I., Brunton, F.R., and van Haaften, J.S. Bingham, M. 2009. An evaluation of deeply buried aquifers along 2006. Bedrock topography and overburden thickness mapping, the Dundas buried valley at Lynden and Copetown, southern southern Ontario. Ontario Geological Survey, Miscellaneous Ontario. In Summary of field work and other activities 2009. Release—Data 207 [1 CD-ROM.]

Published by NRC Research Press Gao 817

Gao, C., Shirota, J., Kelly, R.I., Brunton, F.R., and van Haaften, J.S. Meyer, P.A., and Eyles, C.H. 2007. Nature and origin of sediments 2007. Bedrock topography and overburden thickness mapping, infilling poorly defined buried bedrock valleys adjacent to the southern Ontario. In Proceedings of the 60th Canadian Geotech- Niagara Escarpment, southern Ontario, Canada. Canadian Journal nical Conference and the 8th joint Canadian Geotechnical Society – of Earth Sciences, 44(1): 89–105. doi:10.1139/E06-085. International Association of Hydrologists (CGS–IAH) Conference. Morgan, N.A. 1964. Geophysical studies in Lake Erie by shallow Canadian Geotechnical Society, Ottawa, Ont. pp. 378–385. marine seismic methods. Ph.D. thesis, University of Toronto, Gilbert, R., and Shaw, J. 1994. Inferred subglacial meltwater origin of Toronto, Ont. lakes on the southern border of the Canadian Shield. Canadian Morgan, A.V. 1982. Distribution and probable age of relict Journal of Earth Sciences, 31(11): 1630–1637. doi:10.1139/e94- permafrost features in southwestern Ontario. In Proceedings of 144. the 4th International Permafrost Conference (the R.J.E. Brown Greenhouse, J.P., and Karrow, P.F. 1994. Geological and geophysical memorial volume). National Research Council of Canada, Ottawa, studies of buried valleys and their fills near Elora and Rockwood, Ont. pp. 91–100. Ontario. Canadian Journal of Earth Sciences, 31: 1838–1848. Mullins, H.T., and Hinchey, E.J. 1989. Erosion and infill of New Hobson, G.D., and Terasmae, J. 1969. Pleistocene geology of the York Finger Lakes: implications for Laurentide ice sheet buried St. Davids Gorge, Niagara Falls, Ontario: geophysical and deglaciation. Geology, 17(7): 622–625. doi:10.1130/0091-7613 palynological studies. Geological Survey of Canada, Paper 68-87. (1989)017<0622:EAIONY>2.3.CO;2. Holysh, S., Davies, S.D., and Goodyear, D. 2004. An investigation National Oceanic and Atmospheric Administration. 1999. Bathyme- into buried valley aquifer systems in the Lake Simcoe area. In try of Lake Erie and Lake Saint Clair. National Oceanic and Summary of field work and other activities 2004. Ontario Atmospheric Administration, National Geophysical Data Center, Geological Survey, Open File Report 6145. pp. 28-1–28-6. World Data Center for Marine Geology and Geophysics, Report Hooke, R.L., and Jennings, C.E. 2006. On the formation of the tunnel MGG-13 [Online]. Available from http://www.ngdc.noaa.gov/ valleys of the southern Laurentide ice sheet. Quaternary Science mgg/greatlakes/erie.html [Cited on 10 October 2006]. – – Reviews, 25(11 12): 1364 1372. doi:10.1016/j.quascirev.2006. Ontario Geological Survey. 1991. Bedrock geology of Ontario, 01.018. southern sheet. Ontario Geological Survey, Map 2544, scale Horberg, L., and Anderson, R.C. 1956. Bedrock topography and 1 : 1 000 000. Pleistocene glacial lobes in central United States. The Journal of Ontario Geological Survey. 2003. Surficial geology of southern 64 – Geology, (2): 101 116. doi:10.1086/626328. Ontario. Ontario Geological Survey, Miscellaneous Release—Data Johnson, M.D., Armstrong, D.K., Sanford, B.V., Telford, P.G., and 128 [2 CD-ROMs.] Rutka, M.A. 1992. Paleozoic and Mesozoic geology of Ontario. In Pengelly, J.W., Tinkler, K.J., Parkins, W.G., and McCarthy, F.M. Geology of Ontario. Ontario Geological Survey, Special Vol. 4, 1997. 12 600 years of lake level changes, changing sills, Part 2. pp. 907–1010. ephemeral lakes and Niagara Gorge erosion in the Niagara Jørgensen, F., and Sandersen, P.B.E. 2006. Buried and open tunnel Peninsula and Eastern Lake Erie basin. Journal of Paleolimnology, valleys in Denmark-erosion beneath multiple ice sheets. Quatern- 17(4): 377–402. doi:10.1023/A:1007946401036. ary Science Reviews, 25(11–12): 139–1363. doi:10.1016/j. Piotrowski, J.A. 1997. Subglacial hydrology in north-western quascirev.2005.11.006. For personal use only. Germany during the last deglaciation; groundwater flow, tunnel Karrow, P.F. 1973. Bedrock topography in southwestern Ontario: a valleys and hydrological cycles. Quaternary Science Reviews, 16(2): progress report. The Geological Association of Canada, Proceed- – ings, Vol. 25. pp. 67–77. 169 185. doi:10.1016/S0277-3791(96)00046-7. Karrow, P.F., McAndrews, J.H., Miller, B.B., Morgan, A.V., Praeg, D. 2003. Seismic imaging of mid-Pleistocene tunnel-valleys in Seymour, K.L., and White, O.L. 2001. Illinoian to late the North Sea Basin-high resolution from low frequencies. Journal – Wisconsinan stratigraphy at Woodbridge, Ontario. Canadian of Applied Geophysics, 53(4): 273 298. doi:10.1016/j.jappgeo. Journal of Earth Sciences, 38(6): 921–942. doi:10.1139/cjes-38- 2003.08.001. 6-921. Russell, H.A.J., Brennand, T.A., Logan, C., and Sharpe, D.R. 1998. Kenny, F.M., Hunter, G., and Chan, P. 1997. Georeferencing quality Standardization and assessment of geological descriptions from control of Ontario’s water well database for the Greater Toronto water well records: Greater Toronto and Oak Ridges Moraine In and Oak Ridges Moraine areas of southern Ontario. Proceedings areas, southern Ontario. Current research. Geological Survey of – of 1997 Canadian Geomatics Conference (GER’ 97), Ottawa, Ont. Canada, Paper 1998-E. pp. 89 102. Abstract 219. Russell, H.A.J., Arnott, R.W.C., and Sharpe, D.R. 2003. Evidence for Kor, P.S.G., and Cowell, D.W. 1998. Evidence for catastrophic rapid sedimentation in a tunnel channel, Oak Ridges Moraine, Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11 subglacial meltwater sheetflood events on the Bruce Peninsula. southern Ontario, Canada. Sedimentary Geology, 160(1–3): 33– Canadian Journal of Earth Sciences, 35(10): 1180–1202. doi:10. 55. doi:10.1016/S0037-0738(02)00335-4. 1139/cjes-35-10-1180. Russell, H.A.J., Pullan, S.E., Hunter, J.A., Sharpe, D.R., and Holysh, Kristensen, T.B., Huuse, M., Piotrowski, J.A., and Clausen, O.R. S. 2006. Buried valley aquifers: new data collection for municipal 2007. A morphometric analysis of tunnel valleys in the eastern water supply and watershed management, Caledon East, Ontario. North Sea based on 3D seismic data. Journal of Quaternary Geological Survey of Canada, Open File 5275. Science, 22(8): 801–815. doi:10.1002/jqs.1123. Sharpe, D.R., Pugin, A., Pullan, S.E., and Shaw, J. 2004. Regional Logan, C., Russell, H.A.J., and Sharpe, D.R. 2005. Regional 3-D unconformities and the sedimentary architecture of the Oak Ridge structural model of the Oak Ridges Moraine and Greater Toronto Moraine area, southern Ontario. Canadian Journal of Earth Area, southern Ontario: version 2.1. Geological Survey of Canada, Sciences, 41(2): 183–198. doi:10.1139/e04-001. Open File 5062. [1 CD-ROM.] Shaw, J., and Gilbert, R. 1990. Evidence for large-scale subglacial MacCormack, K.E., Maclachlan, J.C., and Eyles, C.H. 2005. Viewing meltwater flood events in southern Ontario and northern New the subsurface in three dimensions: initial results of modeling the York State. Geology, 18(12): 1169–1172. doi:10.1130/0091-7613 Quaternary sedimentary infill of the Dundas Valley, Hamilton, (1990)018<1169:EFLSSM>2.3.CO;2. Ontario. Geosphere, 1(1): 23–31. doi:10.1130/GES00007.1. Sjogren, D., Fisher, T.G., Taylor, L.D., Jol, H.M., and Munro-Stasiuk,

Published by NRC Research Press 818 Can. J. Earth Sci., Vol. 48, 2011

M.J. 2002. Incipient tunnel channels. Quaternary International, 90(1): the Niagara Escarpment, Niagara Peninsula, Ontario. Géographie 41–56. doi:10.1016/S1040-6182(01)00091-X. physique et Quaternaire, 46: 195–207. Spencer, J.W. 1881. Discovery of the preglacial outlet of the basin of White, O.L., and Karrow, P.F. 1971. New evidence for Spencer’s Lake Erie into that of Lake Ontario; with notes on the origin of our Laurentian River. In Proceedings of the 14th Conference on Great lower Great Lakes. Proceedings of the American Philosophical Lakes Research. International Association of Great Lakes Society, 19: 300–337. Research. pp. 394–400. Spencer, J.W. 1890. Origin of the basins of the Great Lakes of Wright, H.E., Jr. 1973. Tunnel valleys, glacial surges, and subglacial America. Quarterly Journal of the Geological Society of London, hydrology of the Superior lobe, Minnesota. Geological Society of 46(1–4): 523–533. doi:10.1144/GSL.JGS.1890.046.01-04.33. America, Memoir 136. pp. 251–276. Spencer, J.W. 1907. The falls of Niagara: their evolution and varying Zwiers, W.G., Rainsford, D.R.B., and Bajc, A.F. 2008. Investigation relations to the Great Lakes; Characteristics of the power, and the of the Dundas buried bedrock valley. In Summary of field work effects of its diversion. Department of Mines, Geological Survey and other activities 2008. Ontario Geological Survey, Open File Branch, Ottawa, Ont. Report 6226. pp. 33-1–33-7. Straw, A. 1968. Late Pleistocene glacial erosion along the Niagara Zwiers, W.G., Bajc, A.F., Priebe, E.H., and Marich, A.S. 2009. Escarpment of southern Ontario. Geological Society of America Investigation of the Dundas buried bedrock valley, southern Bulletin, 79(7): 889–910. doi:10.1130/0016-7606(1968)79[889: Ontario. In Summary of field work and other activities 2009. LPGEAT]2.0.CO;2. Ontario Geological Survey, Open File Report 6240. pp. 23-1–23-7. Tinkler, K.J., and Stenson, R.E. 1992. Sculpted bedrock forms along For personal use only. Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 142.141.31.173 on 05/05/11

Published by NRC Research Press