Lithostratigraphic Characterization of a Buried Bedrock Valley Using Airborne and Surface Geophysics by Oliver Conway-White A Thesis presented to The University of Guelph In partial fulfilment of the requirements for the degree of Master of Applied Science in Engineering Guelph, Ontario, Canada © Oliver R. Conway-White, May, 2020 ABSTRACT LITHOSTRATIGRAPHIC CHARACTERIZATION OF A BURIED BEDROCK VALLEY USING AIRBORNE AND SURFACE GEOPHYSICS Oliver Conway-White Advisor: University of Guelph, 2020 Dr. Beth Parker A helicopter-borne frequency-domain electromagnetic instrument was used to investigate the lithostratigraphic architecture of a buried bedrock valley near Elora, Ontario. The resulting airborne electrical resistivity model was evaluated against co-located high-resolution ground- based electrical resistivity, seismic refraction, and gravity surveys across two sections of the valley. Results were interpreted using published geological datasets including continuous core, geophysical logs, and an existing regional Quaternary geologic model. A comparison between the local geophysically-based model and the regional Quaternary model shows that an airborne electromagnetic survey can markedly improve characterization of bedrock valley morphology and Quaternary architecture. These results provide confidence in regional-scale interpretations of airborne electromagnetic data for the purpose of delineating lithostratigraphic boundaries. Such data would provide valuable insight into the placement of boreholes for additional and complementary characterization at the borehole scale, leading to delineation of hydrostratigraphic boundaries. In combination, these data will inform 3-D groundwater flow models. iii ACKNOWLEDGEMENTS First, I would like to thank Dr. Colby Steelman who was the lead on assisting me with this thesis. While paperwork may have prevented him from being officially on my committee, we all know he went above and beyond as my ‘scientific’ advisor. From initial data collection and fieldwork, to data processing and analysis, to helping me with the writing and editing of this thesis, his guidance throughout the process has been essential. Colby’s generosity with his time and knowledge went a long way to helping me bring this thesis to its present form. His excellent handle on life must also be duly noted. I would like to thank my supervisor Dr. Beth Parker for taking me into the G360 group and giving me the opportunity to participate in this research. I would also like to thank her for ‘encouraging’ me to look at the bedrock geology in more detail than I had originally planned. This proved an exciting addition to my thesis that I did not expect but (mainly) enjoyed writing. Her detailed comments on my thesis drafts helped sharpen the message of my thesis considerably. I would like to thank my advisory committee Dr. Emmanuelle Arnaud for her help in ensuring Quaternary sediments were accurately considered in my thesis. The clarity she brought to the complexity of glacial geology and her patience in teaching me about it was very much appreciated. Her comments on my thesis draft both on the scientific side as well as teaching me the difference between the use of ‘which’ and ‘that’ must also be noted. I would like to thank Dr. Pete Pehme for providing feedback on my thesis and acting as the external examiner for my defense. I would like to thank Dr. Hernan Ugalde at Brock University for lending us his gravity meter, helping with collection of the gravity surveys, and answering all my questions about gravity and gravity processing. I would like to recognize and thank Adam Smiarowski of CGG Multiphysics Ltd. for collecting, processing, and inverting the airborne survey results presented in this thesis. I would like to thank Dr. Jonathan Munn for his assistance in deciphering the bedrock geology at the last minute. Looking back, it would be easy to assume the fieldwork schedule for the geophysical surveys in this thesis was selected specifically to coincide with the hottest summer days on record. A big thank you to Nathan, Brent, and James for sloughing it out so cheerfully – without these guys the data collection could not have been completed. Way to swing the ol’ sledgehammer! A list of acknowledgements would not be complete without a thank you to Dr. Tony Endres at the University of Waterloo who first introduced me to geophysics, and hydrogeophysics in particular, during my undergrad. I would not have pursued this area of research without him. Finally, I would like to thank the entire community at G360 for helping as I stumbled my way through grad school. And to those in the student pool, our impromptu ‘scientific’ discussions always made my day that little bit more fun. Thank you. iv TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................................... iii TABLE OF CONTENTS ............................................................................................................... iv LIST OF TABLES ......................................................................................................................... vi LIST OF FIGURES ...................................................................................................................... vii 1 Introduction ............................................................................................................................. 1 1.1 Overview .......................................................................................................................... 1 1.2 Motivation ........................................................................................................................ 3 1.3 Objectives ......................................................................................................................... 4 2 Background .............................................................................................................................. 5 2.1 Study Area ........................................................................................................................ 5 Regional Setting ........................................................................................................ 5 Historical Water Well Records ................................................................................. 7 Three-Dimensional Quaternary Sediment Model ..................................................... 7 Groundwater Resource Assessments ........................................................................ 8 2.2 Geological and Hydrogeological Setting ......................................................................... 9 Silurian Geology and Hydrogeology ........................................................................ 9 Quaternary Geology and Hydrogeology ................................................................. 11 Buried Bedrock Valleys .......................................................................................... 13 3 Methods ................................................................................................................................. 15 3.1 Study approach ............................................................................................................... 15 3.2 Airborne Electromagnetic (AEM) and Residual Magnetic Survey ............................... 18 3.3 Surface Geophysical Survey Acquisition and Processing.............................................. 19 Gravity Survey ........................................................................................................ 19 Seismic Refraction Profiles..................................................................................... 22 Electrical Resistivity Profiles .................................................................................. 24 3.4 Geophysical Interpretative Framework .......................................................................... 26 Regional Quaternary Facies Model ........................................................................ 26 Local Quaternary and Bedrock Facies .................................................................... 28 Local Borehole Geophysical Logs .......................................................................... 30 4 Results ................................................................................................................................... 35 v 4.1 Airborne Electromagnetic and Magnetic Survey ........................................................... 35 4.2 Gravity ............................................................................................................................ 39 4.3 Seismic Refraction ......................................................................................................... 40 4.4 Electrical Resistivity Tomography (ERT)...................................................................... 41 5 Discussion .............................................................................................................................. 44 5.1 Comparison of Surface Geophysics and Airborne Electromagnetic Measurements over a Buried Bedrock Valley ........................................................................................................... 44 Comparison of Surface Data Acquisitions .............................................................