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GSA Connects 2022 meeting in Denver, Colorado

Paper No. 36-9
Presentation Time: 3:40 PM

UTILIZING CARBONATE FACIES ANALYSIS TO CONCEPTUALIZE EVOLVING FLOW PATHWAYS THROUGH A BURIED BEDROCK VALLEY


BROWN, Jesse1, ARNAUD, Emmanuelle2, DIX, George R.3, GORRIE, Connor4, CONWAY-WHITE, Oliver4, STEELMAN, Colby5 and PARKER, Beth L.6, (1)School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada, (2)School of Environmental Sciences, University of Guelph, Alexander Hall, 50 Stone Rd East, Guelph, N1G 2W1, Canada, (3)Department of Earth Sciences, Carleton University, 2115 HERZBERG LABORATORIES, 1125 COLONEL BY DRIVE, Ottawa, ON K1S 5B6, Canada, (4)Morwick G360 Groundwater Research Institute, University of Guelph, 50 Stone Road East, Guelph, ON N1G2W1, Canada, (5)Dept of Earth and Environmental Sciences, University of Waterloo, Centre for Environmental and Information Technology (EIT), 200 University Ave. W, Waterloo, ON N2L 3G1, Canada, (6)Morwick G360 Groundwater Research Institute, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada

A critical step in conceptualizing the evolution of flow paths through bedrock valleys is predicting the subsurface structure of permeable and impermeable geologic features. In the Silurian carbonate bedrock of Elora, Ontario, Canada, the hydrogeology is impacted by porous bioconstructions, thick (~ 60 m) low porosity dolomudstone, and a 50-60 m deep Quaternary sediment-filled buried bedrock valley (BBV). The Elora BBV, mapped by an airborne electromagnetic survey, offers an opportunity to study the relationship between bedrock facies, diagenesis, glacial drainage, valley morphology, and groundwater flow pathway evolution.

Analysis of bedrock facies and diagenesis is underway using core and downhole geophysical data from four boreholes continuously cored to ~150 mbgs on the flank and thalweg of the BBV. Key features include bioconstructions, comprising <5 m tall coral and stromatoporoid framestone reefs, 1-2 m crinoid accumulations, and a single 60 m composite structure comprising smaller stacked bioconstructions (5-10 m each) that grade from crinoid to coral to stromatoporoid reefs. These structures have high porosity within and high fracture intensity at their boundaries. Low-porosity dolomudstone, found between bioconstructions, is thought to form an aquitard, though cavernous porosity (~0.5 m) in the thickest of these units warrants hydraulic testing. Future transmissivity data and head profiling will reveal to what degree flow pathways are controlled by these structures.

The Elora BBV incises into this geology. Core analysis reveals diagenetic alteration and dissolution-enhancement beneath the thalweg of a steep-walled reach of the valley as well as in deeper intervals. Previous studies of BBVs have hypothesized that during incision a hydraulic gradient towards the open channel developed, causing dissolution enhancement in adjacent bedrock. While the data are consistent with this mechanism, the timing of dissolution enhancement and relative importance of pre-glacial vs glacial drainage remains to be determined through the integration of bedrock and Quaternary datasets. Process-based analysis of the entire geologic history of a BBV and its associated and evolving hydrogeologic properties will aid in understanding BBV flow systems and their modern groundwater resource potential.

Session No. 36

T9. Over the Hills and through the River: The Mechanisms of Change in Bedrock River Influenced/Controlled Landscapes
Sunday, 9 October 2022: 1:30 PM-5:30 PM
406 (Colorado Convention Center)
Geological Society of America Abstracts with Programs. Vol 54, No. 5
doi: 10.1130/abs/2022AM-382383
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