The Niagara Peninsula Goes 3-D

ABSTRACT: In 2013, the Ontario Geological Survey (OGS) initiated a 5,000 km2 3-D sediment mapping project encompassing the Niagara Peninsula. The bedrock surface is characterised by southward-dipping strata forming 2 prominent escarpments. 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 a thick older drift package of diamicton and glaciolacustrine deposits 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 3-D 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 a typically thin aquifer composed of post-glacial to modern shoreline, aeolian and river sediments. This high-resolution stratigraphy provides the geological framework to understand the hydrogeological regime and model ground conditions to inform land use decision making, providing an improved water resource decision making tool for municipalities, conservation authorities, consultants and the province.