3-dimensional mapping of Quaternary deposits in the southern part of the County of Simcoe, Southern Ontario

Abstract

A 3-dimensional (3-D) mapping investigation of Quaternary deposits in the southern part of the County of Simcoe is one of several 3-D mapping projects currently being undertaken as part of the Ontario Geological Survey's groundwater initiative within the Greater Golden Horseshoe area of southern Ontario. Following completion of these projects, a significant proportion of the most densely populated and fastest growing region of the country will be modelled in 3-dimensions, laying the foundation for regional syntheses of subsurface geology. The objective of this project is to develop an interactive 3-D model of Quaternary geology that can: 1) aid in studies involving groundwater extraction, protection and remediation; 2) assist with the development of policies surrounding land use and nutrient management; and 3) help to further understand the interaction between surface and ground waters. A better understanding of the geometry and inherent properties of the Quaternary sediments that overlie bedrock will assist with the development of revised source water protection plans and with the development of a geoscience-based management plan for the groundwater resource. Geoscience data collection was initiated in 2010 and consisted of detailed Quaternary mapping and sedimentological studies of the shallow subsurface, continuous coring to bedrock at 25 locations and a variety of geophysical surveys including: ground gravity, airborne time-domain electromagnetics, downhole geophysical logging and seismic reflection. Supplementary grain size, carbonate, heavy mineral and geochemical analyses enabled an improved interpretation of the subsurface stratigraphy. The information gained from this work resulted in a refined understanding of drift thickness and bedrock topography for the Laurentian trough area as well as the identification of 6 regionally significant chronostratigraphic units further subdivided into 15 layers. The main elements of the model, from youngest to oldest, include: 1) postglacial valley-fill deposits; 2) Oak Ridges Moraine (ORM) and equivalent deposits; 3) Newmarket Till; 4) Scarborough-Thorncliffe Formation equivalents; 5) non-glacial (Sangamon- Middle Wisconsin) deposits and 6) Illinoian and possibly older glacial deposits. Advancements in the understanding of the regional-scale architecture, contact relationships and depositional settings of these elements has allowed for an improved knowledge of the Quaternary history of the region. Notable observations include the identification of a widespread, non-glacial unit in the deep subsurface that likely spans the Sangamon to Middle Wisconsin time interval and the recognition of significant topographic relief of the Newmarket Till, extending from drumlinized uplands into broad valleys previously interpreted as tunnel valleys produced by the catastrophic release of subglacial meltwater. A protracted evolution for these valleys is currently being proposed. The character of groundwater flow within valley settings is more complex than observed in valleys underlying the ORM to the south. In Southern Simcoe County, the valleys are largely infilled with fine-grained units and upward hydraulic gradients commonly inhibit interaction of shallow with deep groundwater flow systems.

The pre-Late Wisconsin stratigraphy of southern Simcoe County, Ontario: implications for ice sheet buildup, decay, and Great Lakes drainage evolution

“…Field work in southern Simcoe County was conducted during the summers of 2010-2012 and the fall of 2013, commencing with surficial mapping investigations (Bajc and Rainsford 2010;Mulligan 2011;Mulligan and Bajc 2012), followed by geophysical surveying and drilling of continuously cored boreholes Bajc et al 2012Bajc et al , 2014Bajc et al , 2015bFigs. 3, 4).…”

“…Recent three-dimensional mapping investigations in the southern part of Simcoe County (Figs. 1c,1d) have identified a complex, but consistent sediment succession underlying Late Wisconsin glacial deposits Bajc et al 2012Bajc et al , 2014Bajc and Mulligan 2013). This paper presents an overview of the pre-Late Wisconsin stratigraphic succession identified and discusses the significance of this record to interpretations of changing environmental conditions and regional extents of the Laurentide Ice Sheet (LIS).…”

Geophysical, geological, and hydrogeological characterization of a tributary buried bedrock valley in southern Ontario

“…In southern Ontario, these complex and variably distributed features comprise an extensive network of bedrock valleys that formed through, or were enhanced by, intense glacial and glaciofluvial erosion during the Pleistocene (Karrow et al 1979;Eyles et al 1997;Kor and Cowell 1998;Gao 2011), and were subsequently infilled with Quaternary-age glacial and interglacial sediment (Karrow 1968;Barnett 1992). Although province-wide mapping (Gao et al 2006) and regional mapping of some specific areas (e.g., Burt 2011;Marich et al 2011;Bajc et al 2012) have been carried out, the location and geometry of these BBVs and their tributaries is not well constrained in many parts of Ontario.…”

“…2006, c. 22 (Ministry of the Environment and Climate Change 2006). This has led to significant investments in three-dimensional (3D) sediment and bedrock surface mapping across Ontario both by the geological surveys (e.g., Gao et al 2006;Sharpe and Russell 2006;Bajc 2008;Davies et al 2008;Bajc and Rainsford 2010;Bajc et al 2012Bajc et al , 2014Burt 2012) and municipalities and conservation authorities that were tasked with creating source water protection plans (e.g., Gartner Lee Ltd. 2004;Golder Associates Ltd. 2006;AquaResource Inc. 2010). These activities have supported the conceptualization of aquifer and aquitard units and the delineation of regional-scale groundwater flow systems within and around BBVs.…”

“…Studies utilizing multiple geophysical methods combined with geologic and hydrogeologic data are particularly effective for 3D mapping of hydrostratigraphic units (e.g., Gabriel et al 2003;Jørgensen et al 2003aJørgensen et al , 2003bSteuer et al 2009; Stumpf and Ismail 2013;Cassidy et al 2014;Sapia et al 2014). In Ontario, shallow seismic reflection, gravity, and electromagnetic surveys have been used at mostly regional scales to delineate the nature of the infilled sediment and bedrock valley geometry (e.g., Greenhouse and Monier-Williams 1986;Greenhouse and Karrow 1994;Zweirs et al 2008;Burt 2011;Bajc et al 2012;Pugin et al 2013). Elsewhere, airborne transient electromagnetic methods are mostly used (e.g., Sandersen and Jørgensen 2003;Jørgensen et al 2003aJørgensen et al , 2003bSørensen and Auken 2004;Sapia et al 2015).…”