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Analysis of 56 outcrop exposures in cut banks along the Nottawasaga River in southern Simcoe County, Ontario, Canada, has led to the identification of eight stratigraphic units (SU1-SU8) that represent a record of changing environmental conditions during deglaciation and exhibit strong controls on shallow groundwater flow in the region. The stratigraphic succession is floored by the Late Wisconsin Newmarket Till (SU1), which is locally overlain by ice-proximal debris flow deposits (SU2). These glacial sediments are overlain by glaciolacustrine silt rhythmites (SU3) that pass upwards into deltaic sand (SU4) and channelized fluviodeltaic sand and gravel (SU5). Lying above the fluvial deposits are widespread interbedded glaciolacustrine sands and silt (SU6), which coarsen up-section toward the ground surface. The succession is locally capped by fluviodeltaic (SU7) and younger fluvial (SU8) deposits. These SUs record sedimentary environments that existed during deglaciation of the region and provide insight into the evolution of glacial lakes Schomberg and Algonquin and the Nipissing phase of the upper Great Lakes. The environmental changes described from sediments along the Nottawasaga River provide insights into basin-scale events that occurred throughout the upper Great Lakes during deglaciation. Qualitative observations of groundwater discharge from sediments at outcrop faces are used to characterize the hydraulic function of the stratigraphic units as well as possible preferential groundwater flow pathways in the shallow subsurface. L'analyse de 56 affleurements dans des berges érodées le long de la rivière Nottawasaga dans le sud du comté de Simcoe (Ontario, Canada) amené à la reconnaissance de huit unités stratigraphiques (SU1-SU8) qui constituent un registre de l'évolution des conditions ambiantes durant la déglaciation et présentent de forts contrôles sur l'écoulement souterrain peu profond dans la région. La séquence stratigraphique comprend à sa base le till de Newmarket (SUI), du Wisconsinien tardif, sur lequel reposent localement des dépôts de coulées de débris juxtaglaciaires (SU2). Sur ces sédiments glaciaires reposent des rhytmites de silt glaciolacustre (SU3) passant vers le haut à du sable deltaïque (SU4) et du sable et du gravier fluviodeltaïques chenalisés (SU5). Des sables et silts glaciolacustres interlités (SU6) répandus, de plus en plus grossiers vers le haut de la coupe et la surface du sol, reposent sur les dépôts fluviaux. La séquence est localement surmontée de dépôts fluviodeltaïques (SU7J et de dépôts fluviaux plus jeunes (SU8). Ces unités stratigraphiques témoignent de milieux sédimentaires qui existaient durant la déglaciation de la région et fournissent de l'information sur l'évolution des lacs glaciaires Schomberg et Algonquin et sur la phase Nipissing du secteur supérieur des Grands Lacs. Les variations des conditions ambiantes décrites à la lumière des sédiments le long de la rivière Nottawasaga fournissent des renseignements sur les évènements qui se sont produits à l'échelle du bassin durant la déglaciation du secteur supérieur des Grands Lacs. Des observations qualitatives sur les débits d'eau souterraine sortant de sédiments affleurants dans des coupes sont utilisées pour caractériser la fonction hydraulique des unités stratigraphiques ainsi que les possibles voies préférentielles d'écoulement souterrain à faible profondeur dans le sol. [Traduit par la Rédaction], 1. Introduction Large areas of Canada and the northern United States were covered by glacial lakes at the end of the Late Wisconsin glaciation, as meltwaters draining from retreating ice [...]

Recent three-dimensional mapping investigations in southern Simcoe County, Ontario, allow refinement of the existing regional stratigraphic framework. Analysis of 25 continuously cored boreholes has revealed a complex but consistent sediment succession that provides a record of the last two glacial cycles (Marine Isotope Stages 1-6). Five stratigraphic units (SU1-SU5) comprise the pre-Late Wisconsin record. The stratigraphy is floored by a presumed Illinoian glacial complex consisting of a lower, coarse-grained till (SU1), locally overlain by stratified glaciolacustrine and glaciofluvial sediments (SU2), but more commonly capped by a stone-poor, fine-grained till (SU3) of the Georgian Bay lobe. A widespread subaerial unconformity developed on the upper surface of SU3 contains organic-bearing, nonglacial deposits (SU4) ranging between 54 800 [+ ou -] 3000 years BP (considered beyond the limits of radiocarbon dating) and 37 450 [+ ou -] 590 [.sup.14]C years BP. SU4 is abruptly overlain by a thick succession of rhythmically laminated lacustrine muds graded upwards into glaciolacustrine silts and clays interrupted by regionally continuous sand bodies (SU5). The succession is capped (and locally truncated) by Late Wisconsin Newmarket Till. The sedimentary record of southern Simcoe County is correlated with other well-studied reference sections in southern Ontario and contains information that informs reconstructions of former ice extents in the lower Great Lakes region following the Illinoian glaciation. Several sediment units host aquifers, but limited thickness and spatial extent, as well as issues with naturally occurring dissolved gases and solids, restrict their use for groundwater supply. Des études cartographiques tridimensionnelles récentes dans le sud du comté de Simcoe, en Ontario, permettent de peaufiner le cadre stratigraphique régional existant. L'analyse de 25 forages carottés en continu révèle une séquence sédimen-taire complexe mais cohérente qui offre un profil des deux derniers cycles glaciaires (étages 1-6 de la stratigraphie isotopique marine). Cinq unités stratigraphiques (SU1-SU5) renferment le profil pré-wisconsinien tardif. La base de la coupe stratigraphique est un complexe glaciaire d'âge illinoien présumé consistant en un till inférieur à grains grossiers (SU1) sur lequel reposent localement des sédiments glaciolacustres et fluvioglaciaires stratifiés (SU2), mais qui est plus couramment recouvert d'un till à grains fins pauvre en pierres (SU3) du lobe de la baie Georgienne. Une discordance subaérienne répandue formée sur la surface supérieure de SU3 contient des dépôts non glaciaires contenant de la matière organique (SU4) allant de 54 800 [+ ou -] 3000 années BP (considéré comme étant hors des limites de la datation au radiocarbone) à 37 450 [+ ou -]590[.sup.14]C années BP. SU4 est abruptement recouverte par une épaisse séquence de boues lacustres à laminations rythmiques passant vers le haut à des silts et des argiles glaciolacustres interrompus par des corps de sable d'ampleur régionale (SU5). La séquence est recouverte (et localement tronquée) par le till de Newmarket, du Wisconsinien tardif. Le profil sédimentaire du sud du comté de Simcoe est corrélé à d'autres coupes géologiques de référence bien étudiées dans le sud de l'Ontario et renferme de l'information qui éclaire la reconstitution des limites des glaces passées dans la région des Grands Lacs inférieurs suivant la glaciation illinoienne. Plusieurs unités sédimentaires contiennent des aquifères, mais leur épaisseur et leur étendue spatiale limitées, ainsi que des problèmes associés à des gaz dissous et des solides présents à l'état naturel, restreignent leur utilisation possible pour l'approvisionnement en eau souterraine. [Traduit par la Rédaction], Introduction Knowledge of changing paleoenvironments throughout the Quaternary Period in southern Ontario has been evolving since the latter parts of the nineteenth century. Early workers focussed on improving understanding of [...]

Analysis of 56 outcrop exposures in cut banks along the Nottawasaga River in southern Simcoe County, Ontario, Canada, has led to the identification of eight stratigraphic units (SU1-SU8) that represent a record of changing environmental conditions during deglaciation and exhibit strong controls on shallow groundwater flow in the region. The stratigraphic succession is floored by the Late Wisconsin Newmarket Till (SU1), which is locally overlain by ice-proximal debris flow deposits (SU2). These glacial sediments are overlain by glaciolacustrine silt rhythmites (SU3) that pass upwards into deltaic sand (SU4) and channelized fluviodeltaic sand and gravel (SU5). Lying above the fluvial deposits are widespread interbedded glaciolacustrine sands and silt (SU6), which coarsen up-section toward the ground surface. The succession is locally capped by fluviodeltaic (SU7) and younger fluvial (SU8) deposits. These SUs record sedimentary environments that existed during deglaciation of the region and provide insight into the evolution of glacial lakes Schomberg and Algonquin and the Nipissing phase of the upper Great Lakes. The environmental changes described from sediments along the Nottawasaga River provide insights into basin-scale events that occurred throughout the upper Great Lakes during deglaciation. Qualitative observations of groundwater discharge from sediments at outcrop faces are used to characterize the hydraulic function of the stratigraphic units as well as possible preferential groundwater flow pathways in the shallow subsurface. [ABSTRACT FROM AUTHOR]

Recent three-dimensional mapping investigations in southern Simcoe County, Ontario, allow refinement of the existing regional stratigraphic framework. Analysis of 25 continuously cored boreholes has revealed a complex but consistent sediment succession that provides a record of the last two glacial cycles (Marine Isotope Stages 1-6). Five stratigraphic units (SU1-SU5) comprise the pre-Late Wisconsin record. The stratigraphy is floored by a presumed Illinoian glacial complex consisting of a lower, coarse-grained till (SU1), locally overlain by stratified glaciolacustrine and glaciofluvial sediments (SU2), but more commonly capped by a stone-poor, fine-grained till (SU3) of the Georgian Bay lobe. A widespread subaerial unconformity developed on the upper surface of SU3 contains organic-bearing, nonglacial deposits (SU4) ranging between 54 800 ± 3000 years BP (considered beyond the limits of radiocarbon dating) and 37 450 ± 590 14C years BP. SU4 is abruptly overlain by a thick succession of rhythmically laminated lacustrine muds graded upwards into glaciolacustrine silts and clays interrupted by regionally continuous sand bodies (SU5). The succession is capped (and locally truncated) by Late Wisconsin Newmarket Till. The sedimentary record of southern Simcoe County is correlated with other well-studied reference sections in southern Ontario and contains information that informs reconstructions of former ice extents in the lower Great Lakes region following the Illinoian glaciation. Several sediment units host aquifers, but limited thickness and spatial extent, as well as issues with naturally occurring dissolved gases and solids, restrict their use for groundwater supply. [ABSTRACT FROM AUTHOR]