Formation de Thorncliffe : un modèle théorique de système aquifère chenal cône pour la région du Grand Toronto Résumé Une séquence de sédiments glacio lacustres de la Formation de Thorncliffe d’une épaisseur de 50 à 100 m, stratigraphiquement située sous le till régional de Newmarket, présente un potentiel aquifère considérable. La formation occupe une grande superficie s’étendant de la baie Georgienne au lac Ontario, vers le sud, et au delà du lac Rice, vers l’est (~ 25 000 km2). Les séquences de sable, de gravier, de boue, de rythmites et de diamicton de la Formation de Thorncliffe semblent être des séquences de transition entre les lits glacio lacustres sous jacents plus anciens, liés à la hausse du niveau des lacs qui a eu lieu lorsque l’eau a été retenue contre l’escarpement du Niagara par l’avancée des glaciers, et les couches supérieures. Nous avons intégré et résumé une grande quantité de données de subsurface de haute qualité afin de mieux déterminer la répartition et le potentiel aquifère plus large des sédiments de la Formation de Thorncliffe. Nous avons compilé un modèle prédictif amélioré d’aquifère en testant les origines possibles de la Formation de Thorncliffe : delta, cônes subaquatiques ou dépôts sous glaciaires. Le modèle de sédimentation chenal esker cône résultant fournit un cadre théorique bien défini pour l’identification d’aquifères au sein de la Formation de Thorncliffe. Cette recherche porte à croire que des aquifères chenal cône composés de sédiments d’architecture, d’orientation, de géométrie et de composition similaires (comme l’aquifère de Yonge Street) pourraient être présents ailleurs dans le bassin de la Formation de Thorncliffe.

Afin d'améliorer les connaissances géoscientifiques sur les eaux souterraines dans le sud de l'Ontario, un modèle régional tridimensionnel de la géologie des formations superficielles du sud de l'Ontario a été élaboré dans le cadre d'une collaboration entre la Commission Géologique de l'Ontario et la Commission Géologique du Canada. Couvrant une superficie d'environ 66 870 kilomètres carrés, le modèle est une synthèse des modèles géologiques existants, de la cartographie de la géologie de surface et des données de subsurface. Le modèle est une reclassification simplifiée en 9 couches de nombreuses formations sédimentaires superficielles locales cartographiées, dont l'épaisseur dépasse par endroits 200 m et dont le volume total est d'environ 2 455 kilomètres cubes. Le modèle intègre la cartographie de la géologie de surface à l'échelle 1:50 000 avec un modèle numérique d'élévation (MNE) topographique corrigé bathymétriquement de 90 m et 8 modèles 3D locaux existants. Les données archivées sur le sous-sol comprennent 10 237 forages géotechniques et stratigraphiques, 3 312 pics de levés géophysiques, 15 902 sites et sections de cartographie de terrain, 537 puits de surveillance et d'approvisionnement en eau et 282 995 enregistrements de puits d'eau. Correspondant approximativement aux couches aquifères et aquitards régionaux, les couches primaires du modèle sont (de la plus ancienne à la plus jeune) : Le substratum rocheux, l'aquifère de base, les sédiments inférieurs, le till régional, le remplissage de chenaux après le till régional, les sédiments fluvioglaciaires, les boues après le till régional, les sables glaciolacustres et les sédiments récents/organiques. La modélisation a été réalisée à l'aide d'une application de modélisation implicite (LeapFrog®) complétée par une approche de la classification des données basée sur les connaissances d'experts et une procédure de système expert basée sur des règles pour l'interprétation et la validation des données. Un cycle itératif de codage automatisé des données, de construction de modèles intermédiaires et de corrections manuelles des données, d'évaluations d'experts et de révisions a conduit au modèle 3D final. Ce modèle de géologie de surface complète le développement d'une série de modèles géologiques et hydrogéologiques régionaux en 3D pour le sud de l'Ontario.

Dolomitization of carbonate rocks is a subject of considerable interest due to association with oil and gas reservoirs and Mississippi Valley Type ore deposits. Conceptual two-dimensional models of dolomitization are common in the literature, however numeric models supported by high quality data are rare to nonexistent. This paper presents three-dimensional (3-D) dolomitization patterns in the Salina Group A-1 Carbonate Unit and A-2 Carbonate Unit located in Sombra Township, Lambton County. The source data consists of percent dolomite measurements collected from 9727 drill cutting samples, stained with alizarin red, from 409 petroleum wells. Numerical interpolants of the percentage of dolomite versus limestone in the two formations are developed within the boundaries of lithostratigraphic formation layers derived from a 3-D geologic model of southern Ontario, published as GSC Open File 8795 (Carter et al. 2021b). The model was developed using Leapfrog© Works software with a 400 m grid resolution. Results show that increased proportions of dolomite vs limestone in both formations are spatially associated with the flanks and crests of pinnacles in the underlying Lockport Group carbonates, over which the B Salt has been dissolved, and the downthrown side of the Dawn Fault and Becher faults. In the A-1 Carbonate there is an increase in dolomite content over a minority of incipient reefs in the Lockport, and in the A-2 Carbonate Unit there is a gradational increase in dolomite content upwards from a basal limestone to 100% dolomite. The cross-cutting relationships of dolomite occurrence in the A-1 Carbonate on the flanks and crests of some pinnacles support a post-depositional burial diagenesis mechanism, consistent with previous interpretations. The pathway for the dolomitizing fluid was laterally through porous and permeable regional paleokarst in the underlying Lockport Group, uppermost Goat Island and Guelph formations, and upwards through the porous reefal carbonates of the pinnacles. Association of dolomitization haloes with dissolution features in halite of the overlying B Salt Unit further suggest that the dolomitizing fluids were also responsible for salt dissolution. The preferential association of dolomite with the Dawn and Becher faults suggest that movement of the dolomitizing fluid was also fault controlled. This project demonstrates the feasibility and merit of assignment and interpolation of attribute values constrained by lithostratigraphic layers in the regional 3-D geologic model of southern Ontario. Spatial associations of dolomite with other geological features are more clearly resolved than in a 2-D study.

The southern Ontario bedrock model is a valuable resource for researchers and practitioners, but its application is subject to uncertainty. To address this issue a semi-quantitative approach to visualize the relative effects of data sparsity for each layer, identify regions where a lack of data support reduces model confidence, and quantify potential errors in data collection and model construction is presented. This analysis summarizes several sources of error, including cartesian position error, error in the vertical position of the formation contact, error between the modelled topographic surface and recorded collar elevations, and error between the modelled formation top surface and formation top picks. Where data is present, these errors are added to provide an approximation of total uncertainty. Where data are not present, uncertainty is approximated as 50% of the range in formation top variation, with an average value of 27.5 m across all layers. The results show that data availability strongly influences the average total error for each layer, with deeper layers exhibiting higher total error due to lower data density. However, this analysis also suggests that the modelled surfaces likely carry errors of less than 5 to 10 m in most regions.

A hydrostratigraphic framework has been developed for southern Ontario consisting of 15 hydrostratigraphic units and 3 regional hydrochemical regimes. Using this framework, the 54 layer 3-D lithostratigraphic model has been converted into a 15 layer 3-D hydrostratigraphic model. Layers are expressed as either aquifer or aquitard based principally on hydrogeologic characteristics, in particular the permeability and the occurrence/absence of groundwater when intersected by a water well or petroleum well. Hydrostratigraphic aquifer units are sub-divided into up to three distinct hydrochemical regimes: brines (deep), brackish-saline sulphur water (intermediate), and fresh (shallow). The hydrostratigraphic unit assignment provides a standard nomenclature and definition for regional flow modelling of potable water and deeper fluids. Included in the model are: 1) 3-D hydrostratigraphic units, 2) 3-D hydrochemical fluid zones within aquifers, 3) 3-D representations of oil and natural gas reservoirs which form an integral part of the intermediate to deep groundwater regimes, 4) 3-D fluid level surfaces for deep Cambrian brines, for brines and fresh to sulphurous groundwater in the Guelph Aquifer, and the fresh to sulphurous groundwater of the Bass Islands Aquifer and Lucas-Dundee Aquifer, 5) inferred shallow karst, 6) base of fresh water, 7) Lockport Group TDS, and 8) the 3-D lithostratigraphy. The 3-D hydrostratigraphic model is derived from the lithostratigraphic layers of the published 3-D geological model. It is constructed using Leapfrog Works at 400 m grid scale and is distributed in a proprietary format with free viewer software as well as industry standard formats.

Significant quantities of non-digital geoscience data exists on maps. In many cases this information has been scanned and is available in a raster format, but remains irretrievable for digital operations. This information may be in both a text and symbol format and it is also necessary to capture the georeferenced location. In many cases this data may also consist of handwritten characters, which have much greater variability than typed characters. An example of such a dataset is handwritten depth soundings that are a common aspect of Canadian Hydrographic Service (CHS) field sheets. CHS maintains a collection of scanned and georeferenced digital image files with handwritten depth soundings recorded directly on lake maps. To make use of this data for digital 3-D modelling, it needed to be converted to geo-referenced vector data. To avoid the time-consuming process of entering thousands of data points, a machine-learning algorithm was applied to automate the digitization process using open-source software. Robust machine-learning libraries available in Python were integrated within a custom work environment for this application. This is an example of how analogue geoscience datasets can be captured in a cost effective, timely and reliable manner.

A 3-D model consisting of 7 surficial geology layers overlying bedrock for 66,870 km2 of southern Ontario has been constructed. Model development involved the assembly of a comprehensive subsurface database that includes archival water well and geotechnical material logs, cored boreholes, and stratigraphically interpreted geophysical data. Other geospatial constraints are derived from topographic Digital Elevation Models (DEM), bathymetric DEMs and depth soundings, a bedrock surface DEM, and seamless surficial geology mapping. Existing sub-regional (<10,000 km2) higher resolution 3-D models were used to support the model development. The surficial geological legend provided the basis for a simplified stratigraphic layer structure (from oldest to youngest): 1-Bedrock, 2-Lower Sediment, 3-Regional Till, 4-Glaciofluvial Sediment, 5-Upper Till, 6-Glaciolacustrine Mud, 7-Glaciolacustrine Sand, and 8-Recent/Organic Sediment. A preliminary model based on high-quality interpreted data was used along with surficial geological mapping and expert knowledge in a rules-based algorithm to help assign stratigraphic coding to the widespread, archival material log data. An iterative cycle of automated coding, manual coding, periodic interim model inspection and revision has led to this 3-D surficial geological model. This model supports regional-scale groundwater flow modelling and, along with a companion model of bedrock geology, will comprise the first complete 3-D model coverage of southern Ontario from the Precambrian basement to post-glacial sediment.

The regional 3-D geological model of the Paleozoic bedrock of southern Ontario will be published in 2019. The model encompasses all 110,000 km2 of the western St. Lawrence Lowlands region of south-western and south-central Ontario, except for Manitoulin Island. The model is constructed in Leapfrog© Works (Aranz Geo Limited) - an implicit modelling application, with 56 layers representing 70 Paleozoic bedrock formations, the Precambrian basement, and overlying unconsolidated sediments. Layers were constructed using formation depth data from 26,900 petroleum borehole records in the Ontario Petroleum Data System (OPDS), supplemented by hundreds of deep bedrock boreholes compiled by OGS. Formation depth data in the borehole records comprise the primary data input for the 3-D model. Model layers are based on a new lithostratigraphic chart prepared for this project. A new digital bedrock topography surface has also been constructed and is combined with a new digital subcrop geology map to assemble a grid of 3-D points that approximate and constrain the subcrop surface of each modelled formation and better align the layers with expert knowledge and mapped geology. Model development was an iterative cycle of interim model construction, expert geological appraisal to identify errors/inconsistencies in both the model construction and borehole database, followed by QA/QC editing of formation depth data using well records, geophysical logs, drill cuttings and drill core. QA/QC issues included; incorrect borehole location coordinates, data entry errors, missing / inconsistent / incorrect formation contact picks, sparse data, extrapolation issues beneath Lake Huron, mismatch of digital bedrock topography and bedrock geology, and need for improved data filtering algorithms for calculation of formation bottom depths in individual wells. This project has generated a robust lithostratigraphic model which is a logical next step in the evolution of regional geological mapping. It illustrates the geological connections and continuity between the surface and subsurface; a necessary precursor for understanding hydrogeological links between surface water systems and groundwater, and provides a physical basis for future development of a full hydrostratigraphic model for the area. Other practical applications of the model include; natural resource extraction (e.g., water, gypsum, salt, gas, oil, aggregate), site selection for nuclear waste disposal, exploitation of geothermal energy, public outreach and education, identification of gaps in data and knowledge, and shortcomings in modeling algorithms. Users must recognize that the model is a data-driven algorithmic representation of the actual bedrock geology and is not a substitute for detailed geological mapping. The model is considered a work-in-progress subject to future improvements as new and improved data, modeling software, data processing tools, and geological interpretations become available. The availability of OPDS well database was a critical component in the development of the 3-D model. Model development QA/QC has, in turn, improved the quality of the borehole and related databases.

A regional three-dimensional (3-D) lithostratigraphic model of the Paleozoic bedrock of southern Ontario has been completed. The model encompasses the entire Phanerozoic succession of southern Ontario (110 000 km2), consisting of over 1500 m of sedimentary strata straddling regional arch, or forebulge, zones separating the Appalachian foreland basin from the Michigan structural basin. This initiative provides an unprecedented regional 3-D perspective and digital framework based on an updated regional lithostratigraphic chart. Constructed using Leapfrog Works, an implicit modelling software application, the model format can readily support numeric groundwater-flow modelling. Fifty-four Paleozoic bedrock layers representing 70 formations, as well as the Precambrian basement and overlying unconsolidated sediment, were modelled at a spatial resolution of 400 m. Borehole records in Ontario's public petroleum well database (Ontario Petroleum Data System (OPDS)) were the principal data source, supplemented by Ontario Geological Survey (OGS) deep boreholes, measured sections, control points and Michigan boreholes. A newly revised digital bedrock topography surface combined with revised subcrop geology and digitized 3-D surface polyline and point constraints were used to better align the modelled layers and their extrapolation to the subcrop surface. Model development was an iterative cycle of interim modelling, expert geological appraisal, and quality assurance and control (QA/QC) editing of geological data using geophysical logs, drill cuttings and core, supplemented by manual editing of model layers. The 3-D model provides a robust representation of regional bedrock geology. A properly constructed borehole database and its supporting information is an essential requirement for construction of a 3-D model, but data errors, inconsistencies, data gaps, location errors, etc. can compromise the reliability of the model. From 2015 to 2018, project geologists and geological contract staff of the Oil, Gas and Salt Resources Library completed edits to 30 320 formation tops in a total of 7812 wells, resulting in a revised data set and permanent improvements to the petroleum well database. This report highlights the importance of QA/QC of well data, specifically formation top identification, and summarizes the data improvements made in support of the present 3-D model. No seismic data was available.

Numerous reports and reviews of groundwater management in Canada, and more specifically in Ontario, have identified the need for the capture and consolidation of data within more structured and accessible database formats with online availability. There remains an enormous amount of valuable legacy geoscience data available in hardcopy and scanned PDF format and more recent work that is primarily available in PDF files. In the past year the GSC has collaborated with the Ontario Geological Survey (OGS), Ministry of Environment and Climate Change (MOECC), Ministry of Natural Resources and Forestry (MNRF), and conservation authorities toward this end. Activities have focused on the data capture, consolidation and classification of data sets collected under the Drinking Water Source Protection Program, legacy municipal and conservation authority information on municipal wells, non-digital legacy data of the OGS and GSC, consolidation of OGS and GSC published work and OGS-GSC geophysical data sets. Work was also completed on enhancing the geological content of the Provincial Groundwater Monitoring Network. Much of this information has been entered into a relational database; however, much of it remains in flat files and requires additional iterative QA/QC before it is suitable for dissemination online. The most extensive effort was expended on the capture and consolidation of aquifer parameter information tied to municipal wells. Initial efforts focused on Source Protection (SP) reporting available online and expanded to include 19 report types of which 8 were associated with SP and 11 are reports types that may predate SP but support municipal water supplies. To-date approximately 500 reports have been reviewed with 946 municipal wells identified in 32 SP areas, with cross indexing of 84% of the wells with the WWIS and 97% with the PTTW database. Information was assembled on over 30 attributes in 5 general groupings that capture well information. Based on the reports reviewed, 399 aquifer entries, preliminary grouped into 213 aquifers units have been tabulated. Both the GSC and OGS have legacy hardcopy data holdings that are beig scanned, commonly to a PDF format. This nevertheless leaves the laborious task of capturing pertinent information for consolidation in a database structure. Two distinct activities have been undertaken, i) the capture of legacy section descriptions and analytical data from reports, and ii) consolidation of digital information from standalone publications into a single database. The focus of this activity has been on data that will support the stratigraphic classification necessary for 3-D geological modelling. Additionally two GSC datasets have been consolidated the downhole geophysical data and reflection seismic data. As part of an ongoing national data compilation new borehole geophysics data collected with the OGS has been integrated into the national dataset. Additionally for the first time reflection seismic data has been consolidated into a database structure bringing together 10 years and hundreds of km of seismic data, of which approximately 20 percent is in southern Ontario. An ongoing challenge is to complete the necessary QA/QC on the datasets and making them available online. It is anticipated that with the retooling of the Groundwater Information Network (GIN) to the GWML 2.0 standard much of this information will be able to be displayed in the coming 18 months.

In glaciated terrain, buried valleys often host aquifers that are significant groundwater resources. However, given the range of scales, spatial complexity and depth of burial, buried valleys often remain undetected or insufficiently mapped. Accurate and thorough mapping of bedrock topography is a crucial step in detecting and delineating buried valleys and understanding formative valley processes. We develop a bedrock mapping procedure supported by the combination of seismic reflection data and helicopter time-domain electromagnetic data with water well records for the Spiritwood buried valley aquifer system in Manitoba, Canada. The limited spatial density of water well bedrock observations precludes complete depiction of the buried valley bedrock topography and renders the water well records alone inadequate for accurate hydrogeological model building. Instead, we leverage the complementary strengths of seismic reflection and airborne electromagnetic data for accurate local detection of the sediment-bedrock interface and for spatially extensive coverage, respectively. Seismic reflection data are used to define buried valley morphology in cross-section beneath survey lines distributed over a regional area. A 3D model of electrical conductivity is derived from inversion of the airborne electromagnetic data and used to extrapolate buried valley morphology over the entire survey area. A spatially variable assignment of the electrical conductivity at the bedrock surface is applied to different features of the buried valley morphology identified in the seismic cross-sections. Electrical conductivity is then used to guide construction of buried valley shapes between seismic sections. The 3D locus of points defining each morphological valley feature is constructed using a path optimization routine that utilizes deviation from the assigned electrical conductivities as the cost function. Our resulting map represents a bedrock surface of unprecedented detail with more complexity than has been suggested by previous investigations. Our procedure is largely data-driven with an adaptable degree of expert user input that provides a clear protocol for incorporating different types of geophysical data into the bedrock mapping procedure.

A three dimensional (3D) digital geological model of the Spiritwood buried-valley aquifer complex in southwestern Manitoba is developed to support quantitative hydrogeological modelling. The model maps the bedrock surface and delineates the various hydrostratigraphic units in three-dimensions. The model is based on borehole logs, surficial geological maps, a helicopter time-domain electromagnetic (HTEM) survey covering 1062 km2 as well as 63.5 line-km of high-resolution seismic reflection (HRSR) profiles. A 3360 km2 model area was selected within a larger data capture area of ~12000 km2. The methodologies used for preparing and interpreting various subsurface datasets to construct the geological model are presented. The 3D geological surfaces were modelled using Leapfrog Hydro software. Multiple episodes of glacial erosion and sedimentation superimposed on a broad pre-glacial bedrock valley have resulted in a complex configuration of buried channels and valleys. The bedrock surface shows major erosional features: i) the broad Spiritwood buried valley, ii) deep valleys incised into shale bedrock within the broad Spiritwood buried valley, iii) narrow, steep-sided valleys both within and outside the broad buried valley, and iv) the modern Souris and Pembina river valleys. This bedrock surface detail is only possible because of the spatial continuity of the geophysical data sets and could not have been practically obtained from borehole records alone. The geological model includes 13 hydrostratigraphic units including sandstone, unfractured and fractured shale bedrock, 3 coarse sediment aquifers, 4 till units and 3 thin, near-surface units. Coarse sediment aquifers include the deep buried-valley aquifer, deep sands and gravels both within and outside the broad buried valley and inter-till aquifers at variable depths throughout the model. The model indicates potential hydraulic connections from surface recharge to the deep buried-valley aquifer and for discharge from the deep buried-valley aquifer to streams. Two digital versions of the model are provided - a 'view-only' format accessible with the freely available Leapfrog Viewer and a Drawing Exchange Format (DXF) that can be imported to many 3D modelling applications.

Summary We develop a 3D geological modelling procedure supported by the combination of helicopter time-domain electromagnetic data, seismic reflection data, and water well records for the Spiritwood buried valley aquifer system in Manitoba, Canada. Our procedure is an innovative hybrid of knowledge-driven and data-driven schemes that provides a clear protocol for incorporating different types of geophysical data into a 3D stratigraphic model framework. The limited spatial density of water well bedrock observations precludes detection of the buried valley bedrock topography and renders the water well records alone inadequate for accurate hydrogeological model building. The expert interpretation of the geophysical data allows for leveraging of a spatially extensive dataset with rich information content that would be otherwise difficult to utilize for lithostratigraphic classification.

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 fill 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 mud-are identified 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 flowed through a subglacial conduit (R-channel), within which the narrow gravelly central ridge was deposited. Most mud and finer sand bypassed the conduit and was deposited proglacially on the floor of the Champlain Sea, first as sandy outwash and, farther basinward, as muddy carbonate-rich rhythmites. Gradual ice-front retreat superposed distal facies over proximal facies, generating the upward-fining succession that starts with the esker gravel and ends with muddy rhythmites. Most esker sediment appears to have been deposited during rapid, jokulhlaup-like floods that punctuated gradual 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 flood events that deposited the esker must have been seasonally mediated, and the basin water must have attenuated the flood 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 infilling of glaciated basins.

The Nobleton continuously-cored borehole (Golden Spike) is situated on the southern flank of the Oak Ridges Moraine (ORM) 4.25 km north of Nobleton, Ontario. It was drilled in 1996 as part of the Oak Ridges Moraine Hydrogeology Study of the Geological Survey of Canada. The Nobleton borehole, with a core length of 193 m, is one of the deepest hydro-stratigraphic reference sites in the region. The location was selected to provide subsurface ground truthing for a 7 km long seismic profile completed across a broad bedrock depression known as the Laurentian valley. Detailed sedimentological core logging is complemented by downhole geophysics, grain size analysis, total organic carbon analysis, and nested piezometer installation. The base of the borehole intercepts limestone of the Paleozoic Lindsay Formation. Overlying Quaternary deposits interpreted to be Don, Scarborough, Sunnybrook and Thorncliffe formations, referred to as Lower sediment, are overlain by Oak Ridges Moraine sediment and Halton Till. Of particular note is the large number of rhythmites documented in the Scarborough (500) and Thorncliffe (1000) formations and the distinct geophysical signatures associated with these rhythmites. In contrast to the relatively fine grained rhythmic character of these deeper formations is a basal 20 m thick gravel unit and overlying sandier ORM deposits. The Nobleton golden spike borehole provides new hydrogeological insight on Lower sediment (Alliston Aquifer), tunnel channel fills that may host significant aquifer potential, and Oak Ridges Moraine sediment that is an important aquifer for domestic water supply.