The significance of buried valleys to groundwater systems in the Oak Ridges Moraine region, Ontario: extent, architecture, sedimentary facies and origin of valley settings in the ORM region

Abstract

The fieldtrip traverses the glaciated landscape of southeastern Ontario from the Niagara Escarpment to the Ottawa Valley. The focus of the trip is on the glacial geology of a continental basin and tunnel valleys hosted within the glacial stratigraphy of the Oak Ridges Moraine region. Using digital elevation models, and detailed geological mapping, a system of anabraching valleys has been classified on the basis of length, width and depth. The valleys have been traced beneath the Oak Ridges Moraine using high-quality shallow reflection seismic and continuous borehole data. The trip presents a suite of subsurface data with outcrop sedimentology in support of meltwater process models and depositional environments. Process models are considered to relate to regional subglacial landscapes and are used to explain the origin of regional unconformities and the formation of tunnel valleys. Depositional process models, such as the jet-efflux model, will be discussed to interpret key sedimentary facies and evidence for hydraulic jumps where rapid flow meets standing bodies of water. The trip starts at the famous Scaborough Bluffs on Lake Ontario, with a discussion of the regional glacial stratigraphy and units beneath the late glacial Newmarket Till, truncated by regional unconformities. Subsequent stops on day one highlight inter-valley sediments beneath the Oak Ridges Moraine and outcrop sediments of the ORM interpreted within a subaqueous fan setting. Day two reviews the surface expression of tunnel valleys, seismic mapping of buried valleys and regional meltwater concepts for tunnel valley formation. It will also visit an outstanding outcrop site that reveals depositional elements (jet- model and hydraulic jump processes) beyond the inferred tunnel channel depression. On day three, the trip traverses the length of the Oak Ridges Moraine and beyond, to view tunnel valleys, sediments of the ORM, drumlin fields and eskers. The final day of the trip offers a hands-on inspection of continuous cores, highlighting the sedimentary facies, downhole geophysics and geochemistry of key basin stratigraphic units that frame channel complexes. The principal objective of the fieldtrip is to assess a 200 m thick glacial basin with tunnel valleys and fills with respect to its reservoir analogue potential for similar Paleozoic glaciogenic deposits. Such deposits represent important hydrocarbon reservoirs in North Africa and the Middle East. The secondary trip objective is to demonstrate the field support for a range of methods and process-based sedimentary models for tunnel valley formation and deposition of related channel-fill facies.