A large integrated data set of cores, outcrop data, and seismic transects from the mud-buried Vars-Winchester esker in the Champlain Sea basin, Canada, was studied to gain insight into how muddy glaciated basins fi ll with sediment, and how esker sedimentary systems contribute to this process.Three stratigraphic units-a till sheet over carbonate bedrock, the Vars-Winchester esker , and overlying Champlain Sea mudare identifi ed in the data set. The till is massive, mud rich, carbonate rich, and drumlinized. The esker is also carbonate rich, and rests erosively on till or bedrock. It consists of two elements, a narrow gravelly central ridge and a broad sandy carapace. Three units comprise the overlying mud package: gray carbonate-rich rhythmites, massive bioturbated mud, and carbonate-poor, red-andgray rhythmites. A sequence stratigraphic model is proposed to explain these observations. Emphasis is placed on gradual ice-front translation superimposed by rapid meltwater events. The esker is interpreted to have been derived from the underlying till by water that fl owed through a subglacial conduit (R-channel), within which the narrow gravelly central ridge was deposited. Most mud and fi ner sand bypassed the conduit and was deposited proglacially on the fl oor of the Champlain Sea, fi rst as sandy outwash and, farther basinward, as muddy carbonate-rich rhythmites. Gradual ice-front retreat superposed distal facies over proximal facies, generating the upward-fi ning succession that starts with the esker gravel and ends with muddy rhythmites. Most esker sediment appears to have been deposited during rapid, jökulhlaup-like fl oods that punctuated grad-ual retreat. Discharges are estimated to have been high, possibly on the order of several hundred to, perhaps more commonly, several thousand cubic meters per second. The chaotic and random-looking appearance of the resultant sedimentological signatures in the esker sensu stricto is sharply contrasted with the regularity of the muddy rhythmites. If the rhythmites are indeed correlative to the esker, which seems reasonable given their geochemistry and the fact that their volume scales to the volume of mud in the till, the fl ood events that deposited the esker must have been seasonally mediated, and the basin water must have attenuated the fl ood signal, resulting in a rhythmic "on-off" signature in more distal portions of the system. The regularity of the rhythmites does not betray the chaotic nature of the esker sensu stricto, and vice versa. Studying either one in isolation would lead to a very different "end-member" impression of how eskers form and how esker sedimentary systems operate during the infi lling of glaciated basins.
The Oak Ridges Moraine area, southern Ontario, includes most of the Greater Toronto Area, which is the most populated region of Canada. The ∼11,000 km 2 region is bounded to the south by Lake Ontario and to the north where Paleozoic bedrock abuts Precambrian Canadian Shield. The area extends 160 km eastward from the Niagara Escarpment, a prominent 100 m high regional bedrock scarp. The surficial sediment is up to 200 m thick, and reveals exposures of the oldest Quaternary sediment in southern Canada. Population growth has caused land use conflicts and increased pressure on groundwater resources. Construction of a regional 3-D geological model of the glacial stratigraphy was needed to support a better understanding of aquifer distribution, scale, and resource potential and protection.Mapping of the regional glacial geomorphology and sediment succession identified a number of distinct landforms: tunnel channels, drumlins, eskers, moraines, and till and lacustrine plains. Using sequence stratigraphic concepts, strata have been grouped into four principal units that unconformably overlie Paleozoic bedrock: Lower sediment, Newmarket Till, Oak Ridges Moraine, and Halton Till.These four Quaternary units plus bedrock have been mapped in the subsurface as a succession of interpolated surfaces using an innovative stratigraphic database-GIS approach. The model-building process involved stratigraphically coding high-quality data, then integrating an extensive and diverse array of subsurface geological and archival datasets using an expert system (geological rules). Stratigraphic data subsets were then extracted and merged with DEM-controlled surface mapping and interpolated in a GIS.
A basin analysis approach is used to help understand a complex aquifer system in the Oak Ridges Moraine and Greater Toronto areas, southern Ontario, Canada. The aquifer complex consists of a sequence of discontinuous strata that have a prominent regional unconformity. To help visualize this architecture, a stratigraphic database has been developed and used to construct a 3-D stratigraphic model, through selective integration of disparate data. To accurately interpret borehole logs, geological context was supplied by using expert knowledge constrained with a conceptual stratigraphic framework. Utilizing a digital stratigraphic training framework derived from manually coded, high-quality data, an expert system automatically interpreted and coded a large number of low-quality water well records. The expert system was designed to emulate the manual borehole interpretation process by applying knowledge-based geological rules, within the constraints of the digital training framework. Issues of poorly constrained interpolation due to sparse data are addressed by the integration of additional spatial rules defined by thematic map coverages within the expert system. As quantitative hydrogeological modelling moves to more regional scales, geological knowledge input becomes increasingly more valuable. The availability of seamless geological mapping improves 3-D modelling and helps to limit the effect of deficiencies in data coverage and data quality, often encountered in regional hydrogeological studies.
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