T88 Three-Dimensional Geological Mapping to Support Societal Development I

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

DEVELOPMENT OF A 3-D HYDROSTRATIGRAPHIC MODEL FOR THE BEDROCK OF SOUTHERN ONTARIO

Paper number: T88-9
Program: Technical Sessions
Time: 3:10 PM – 3:25 PM

Authors

Abstract

Groundwater movement in the subsurface is best understood when viewed in three dimensions. A regional lithostratigraphic 3-D model consisting of 56 layers has been developed for southern Ontario covering 110,000 km2 with a modelled volume of over 75,000 km3. The principal source of data is the nearly 250,000 formation top and bottom depths in 27,000 wells from the Ontario Petroleum Data System, supplemented by measured sections, control points, selected Michigan borehole records and Ontario Geological Survey test boreholes. To support optimal use of the 3-D geological model the lithostratigraphy has been classified as 14 hydrostratigraphic layers within three distinct hydrochemical regimes: brines (deep), brackish-saline sulphur water (intermediate) and fresh (shallow). The uppermost three hydrostratigraphic units consist of a surficial sediment unit, a contact aquifer, and shallow karst. The remaining 11 hydrostratigraphic units consolidate the lithostratigraphy to the Precambrian basement. Hydrostratigraphic assignment is based on shared lithological, sedimentary and diagenetic features, hydrochemistry, and hydrogeological expression as either aquifers or aquitards. Fluid flow in the subsurface is controlled by karst development at regional unconformities, both ancient and recent (<10,000 yr), as well as sedimentary facies, diagenesis and dolomitization. Some lithostratigraphic units occur as aquifers within the shallow karst and as aquitards within the intermediate/deep regime. The distribution and extent of the shallow karst commonly correlates with bedrock subcrop. Mapping suggests the fresh water regime is limited to depths of <250 m. The hydrostratigraphic unit assignment provides a standard nomenclature and definition for regional flow modelling of potable water and deeper fluids. The classification of the lithostratigraphic layers provides model layers suitable for import and discretization in groundwater modelling software.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-356180

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