3-D sediment mapping on the Niagara Peninsula
Authors: Burt A K 
Published: March 2017

In 2013, the Ontario Geological Survey (OGS) initiated a 3D sediment mapping project encompassing the Niagara Peninsula. As with other sediment mapping projects, the goals are to reconstruct the Quaternary history of the area, build a 3D model of Quaternary
deposits that form regional-scale aquifers and aquitards, and to define the internal characteristics of each sediment package. This study represents a multi-agency collaborative effort: a regional ground gravity survey (6828 stations covering 3920 km2) and sediment logging of hand auger cores,
natural sediment exposures, and 95 continuously cored boreholes have been completed by the OGS; the Geological Survey of Canada has completed shallow seismic reflection surveys (48.1 km) and downhole geophysical logging (14 wells); and 28 monitoring wells have been installed and sampled by
conservation authority and municipal partners.
This presentation will focus on the results of the 2014-2016 OGS drilling program. The bedrock surface is characterised by southward-dipping strata forming 2 prominent escarpments. Ordovician shale lies below the Niagara Escarpment, Silurian dolostone, shale and gypsum between escarpments and
Devonian limestone and cherty limestone above the Onondaga Escarpment. The surface is incised by buried and partially buried bedrock valleys that range from broad and shallow to narrow and deep. Drift thickness is largely controlled by bedrock topography; the thickest sediments are found within the
bedrock valleys while the thinnest sediments are found at the escarpments. Drumlins, moraines, deltas and fans form locally thicker sediment accumulations.
In the western part of the area there is a thick older drift package of diamicton, glaciolacustrine silt and clay and sand to gravelly sand that can be correlated with the main Late Wisconsin Catfish Creek Till aquitard, late glacial Port Stanley Till aquitard, Grand River outwash aquifer and
Wentworth Till aquitard from adjacent 3D sediment mapping areas. The central and eastern portions of the study area are dominated by younger sediments. Coarse-textured ice-contact stratified drift, glaciofluvial sand and gravel and glaciolacustrine sand that forms the Whittlesey aquifer was
deposited during and after ice retreat. Thick glaciolacustrine silt and clay was then deposited in a series of proglacial lakes that ponded against the retreating ice front. In the northern and eastern portions of the area these fine-textured glaciolacustrine deposits are separated into lower and
upper Whittlesey aquitards by a 'sandwich' of sandy aquifers and muddy Halton Till, diamicton and glaciolacustrine sediments (Halton aquitard) deposited during the late glacial ice advance out of the Lake Ontario basin. The uppermost unit is typically a thin aquifer composed of post-glacial to
modern shoreline, aeolian and river sediments. This high-resolution stratigraphy forms the framework for interpreting monitoring well data collected by conservation authorities and municipalities.
The results of the extensive drilling program mean that the physical properties of aquifer and aquitard sediments can now be defined across the region. This information, as well as seismic velocities obtained by downhole geophysical logging, will allow verification of seismic time sections into
depth sections. It is anticipated that combining the results of drilling and geophysics will provide the best possible definition of buried valley geometry and fill; an important objective of the project. The long-term impact of this study will be to provide conservation authority and municipal
partners with an improved water resource decision making tool.