Lithostratigraphic compilation of Phanerozoic bedrock units and 3D geological model of southern Ontario
Authors: Brunton F R , Carter T , Logan C , Clark J , Yeung K , Fortner L , Freckelton C , Sutherland L , Russell H A J 
Published: March 2017

A 3D geological model of the Paleozoic bedrock geology of Southern Ontario is being developed through a collaborative project involving the Ontario Geological Survey (OGS), Geological Survey of Canada (GSC), Ministry of Natural Resources &amp; Forestry
(MNRF), and Oil, Gas, Salt, Resources Library (OGSRL). This multi-year initiative involves a number of parallel objectives, including: 1) update of rock unit nomenclature at formation and group levels; 2) characterize criteria for delineating formational contacts; 3) better constrain the bedrock
topography surface by integrating data from regional MOECC (water) and OGSRL (oil and gas) wells; 4) develop a revised bedrock topography for Lake Ontario from legacy shallow reflection data; 5) revise formation boundaries to update the Paleozoic bedrock geology maps; and 6) delineate groundwater
types (potable vs non-potable) with a focus on potable groundwater within the shallow, karst-influenced, carbonate-dominated and cuesta-forming bedrock successions. The latter two initiatives will extend beyond the scope of the 3D Paleozoic bedrock model project. This project builds upon the OGS
mandate to map the potable groundwater resources of Ontario and the GSC mandate to delineate key aquifers across the country.
Preliminary 3D geologic models have been developed using LeapfrogTM Hydro implicit modelling software based on more than 26,700 deep petroleum boreholes and published OGS bedrock geology maps. The model area covers approximately 110,000 km2, extending across south-central and southwestern Ontario
and beneath the Great Lakes to the US border, but not Manitoulin Island. The model currently comprises 61 layers and attempts to render the bedrock topography, the Precambrian- Paleozoic contact, and the regional variability of 58 Paleozoic bedrock formations plus sediment cover. It is a product of
an ongoing, iterative process of interim modelling, model review, and QA/QC editing of formation picks. LeapfrogTM modelling software is used to produce 3D models based upon Radial Basis Functions primarily using the formation depth picks. LeapfrogTM lends itself well to iterative data QA/QC because
data inputs can be readily reloaded without the need to re-construct the formation contact structure and model chronostratigraphy. The formation model will eventually be reclassified to a hydrostratigraphic model. In 2015 and 2016 project geologists reviewed over 50,000 formation picks by
examination of geophysical logs, core and drill cuttings, and more than 100,000 digital water well records. Issues resolved include: well location errors, formation assignment, anomalous data points, and wells with missing or incorrect formation picks and bedrock characterization. The study
integrates traditional outcrop/field- and lab-based protocols and petroleum industry subsurface mapping techniques, with GIS, database mining and queries, and 2D and 3D mapping and modelling techniques.
Over the past 12 months, efforts have focused on refining formational contacts and regional distributions of Paleozoic formations, including: 1) stacked Ordovician-, Silurian- and Devonian-age carbonates that form regional karstic escarpments that are variably blanketed by Quaternary sediments; 2)
select Devonian and Cambrian siliciclastics; and 3) key regional clay-rich sedimentary rocks and mixed carbonates-siliciclastics that appear to form regional to sub-regional aquitards.