Sculpted Bedrock Forms along the Niagara Escarpment, Niagara Peninsula, Ontario

Abstract

Assemblages of subglacial sculpted bedrock forms (p-forms; Dahl, 1965) are identified on resistant units of the Niagara Escarpment in the Niagara Peninsula, and on the Onondaga Escarpment. The scale of the features is much larger than previously recorded for bedrock glacial features in the Peninsula (Feenstra, 1981) and we suggest that there is a continuous spectrum of forms from small obstacle marks with dimensions of a few centimetres, through ridges and furrows measured in tens of metres, to promontories on the order of kilometres. Such assemblages comprise fluted surfaces with a consistent orientation between N40E and N45E, and which show very little variation within a site. Mapping the features has increased our awareness of their extent, and of the problems they pose for mechanisms proposed to explain them. The morphometry of the forms is similar to that described elsewhere, and the irregular edge of the Niagara Escarpment to oncoming flows is thought to be responsible for the prominent features described. The apparent removal of substantial bedrock blocks implies flow velocity well in excess of 3 m/s. Therefore the sculpting of the forms is attributed to fast flowing subglacial meltwater which may have had a discharge of the magnitude of 2.1 x 106 cumecs.On a identifié des ensembles de formes sous-glaciaires sculptées dans la roche en place (p-forms) dans des unités de roches résistantes de l'escarpement du Niagara et de l'escarpement d'Onondaga. L'échelle de ces formes est beaucoup plus grande que ce qu'on a déjà rapporté sur les formes glaciaires dans la roche en place de l'escarpement (Feenstra, 1981); nous croyons que ces formes existent dans toutes les tailles, à partir des simples marques de quelques centimètres en passant par des crêtes et des entailles décamétriques, jusqu'aux promontoires de l'ordre du kilomètre. De tels ensembles comprennent des surfaces cannelées dont l'orientation préférentielle se situe entre N40E et N45E et qui montre très peu de variation à l'intérieur d'un même site. La cartographie de ces formes a permis de se rendre compte de leur grande étendue et des difficultés de comprendre les mécanismes qui en sont à l'origine. La morphométrie des formes est semblable à ce que l'on a déjà décrit; on croit que la forme irrégulière du rebord qu'oppose l'escarpement du Niagara aux écoulements est responsable pour les formes remarquables décrites. L'enlèvement apparent de gros blocs de roche en place suppose des vitesses d'écoulement de plus de 3 m/s. Conséquemment, la sculpture des formes est attribuée à une eau de fusion sousglaciaire très rapide qui a pu avoir un débit de l'ordre de 2,1 x 10em3/s

Subglacial erosion forms in northwest Ireland

“…The s‐forms that are developed across the bedrock surface are morphologically identical to those reported in many other studies, mainly from the bed of the former Laurentide Ice Sheet (e.g. Sharpe & Shaw 1989; Kor et al . 1991; Tinkler & Stenson 1992; Shaw 1994; Pair 1997; Munro‐Stasiuk et al .…”

“…Sheetflood models of subglacial drainage (e.g. Tinkler & Stenson 1992; Sjogren & Rains 1995; Munro‐Stasiuk et al . 2005) indicate that hydraulic jacking and uniform meltwater flow take place across the substrate, followed by progressive channelization during waning flows.…”

“…Although s‐forms have been linked genetically to subglacial meltwater erosion, it is more useful to consider s‐forms as one part of a landform continuum (Tinkler & Stenson 1992) in which the landforms are shaped by a number of erosional processes, including direct subglacial abrasion. As such, therefore, this continuum also includes whalebacks, roches moutonnées (Glasser & Warren 1990; Sugden et al .…”

Subglacial deforming bed conditions recorded by late Quaternary sediments exposed in Vineland Quarry, Ontario, Canada

“…The southern margin of the Ontario basin was completely overridden by the Laurentide Ice Sheet (LIS) during the Nissouri Stadial (between 22 and 16 Ka; Dreimanis and Karrow, 1972). Ice withdrew from the region during the Mackinaw Interstadial (Karrow, 1984;Meyer and Eyles, 2007) and the final re-advance of the Ontario Lobe of the LIS during the Port Huron Stadial (around 13 Ka) allowed the ice to breach the crest of the Niagara Escarpment (Tinkler and Stenson, 1992). Advance of ice toward the northward-facing portion of the Niagara Escarpment from the north and east allowed the development of extensive proglacial lakes between the ice margin and the escarpment and encouraged rapid movement of the ice over freshly deposited fine-grained, water saturated glaciolacustrine sediments (Menzies, 2001).…”

Geophysical, geological, and hydrogeological characterization of a tributary buried bedrock valley in southern Ontario

“…As elsewhere in Europe and North America, catastrophic meltwater erosion has been proposed for some bedrock erosional forms associated with escarpments northwest of the study area (Tinkler and Stenson 1992;Kor and Cowell 1998). Recent review papers have highlighted the controversial aspects of these interpretations (Jørgensen and Sandersen 2006;Kehew et al 2012), which are difficult to resolve for BBVs in Ontario with current data sets.…”