Significance Methods Results Discussion

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The outlet of Lake Huron is the only unregulated outlet in the Great Lakes. It contains ... at the outlet. After georectification of historic aerial photos and an 1880's map onto ... acquired from the University of Waterloo Geospatial Centre. Natural ...
Wesley Campbell ([email protected])

A Stratigraphic Examination of Holocene Beach Deposits at the Outlet of Lake Huron

John Johnston

Department of Earth and Environmental Sciences and Water Institute University of Waterloo, Canada

Results

Abstract The outlet of Lake Huron is the only unregulated outlet in the Great Lakes. It contains unconsolidated sediments, making it susceptible to changes in sedimentation and/or erosion that could affect conveyance in the St. Clair river, and lake levels in the upper Great Lakes. A spit landform has been identified at the outlet via air photo interpretation. This feature holds geologic clues regarding the natural history of sedimentation patterns at the outlet. After georectification of historic aerial photos and an 1880's map onto current satellite imagery, locations possibly containing paleo-remnants of the spit were identified. Due to restricted land access in the study area, water wells from the Ontario Well Record were used to examine the sub-surface stratigraphic record. To visualize well logs from this database, a Python script was written. The script reads and deciphers data from the entire database, generates 2D plots of user-specified well logs, and outputs files containing the corresponding log descriptions. The study is bounded by a prominent surface elevation contour (180 m) and the modern lake/river shoreline (176 m). 180 m is below the peak Nipissing lake level highstand elevation measured near the outlet, indicating the spit landform was deposited in the last four millennia. A collection of 132 water wells were selected within the study area, and organized into spatial clusters. Each cluster of wells was plotted using the Python script, and analyzed to establish a stratigraphic framework of the sediments at the outlet. Water wells confirm the expected general, vertical stratigraphic sequence in Point Edward. Modern lacustrine deposits are underlain by glacial sediments, which sit on top of the Upper Devonian Kettle Point Formation. Additional subsurface information is required to build a more detailed geologic model of this site.

1955

On the shores of Point Edward, an elongate geomorphic landform has been identified. It is approximately 578 m long (where both of its shorelines are exposed to water), 169 m wide, and trends approximately SSE. The outline of two similar, smaller geomorphic landforms can be seen immediately to the east of the main feature. Locations to best sample this landform are outlined in the figure to the right. The landform is vertically bounded by surface elevations of 176 m and 180 m, and has previously been modified by humans, likely for aggregate resources. The shallowest sediments in the study area are composed mainly of sand and gravel and fine with depth, increasing in silt content. Below are examples of two well clusters plotted.

1880

1978

Significance The Great Lakes are relied upon by approximately 35 million Canadians and Americans. Martin Associates (2011) estimates the total economic impact of the Great Lakes-St. Lawrence Seaway at approximately 56 million USD. The International Upper Great Lakes Study (2009) was commissioned by the International Joint Commission to study the only unregulated outlet in the Great Lakes, in Point Edward, Ontario. Hydraulic modeling G.I.A. Hydroclimate River bed morphology Focused on erosion at the outlet, but there were gaps in the IUGLS http://www.iugls.org/ Final_Reports

McGill University (2011)

Methods An 1880's map of Point Edward was obtained from McGill University's Canadian County Digital Atlas project. Aerial photographs from 1955 and 1978 were also acquired from the University of Waterloo Geospatial Centre. Natural and anthropogenically induced geomorphological changes were observed so that areas showing minimal human disturbance could be identified, guiding the design of direct and indirect subsurface surveys. All three of the above photos were georectified onto current (ESRI, 2015) satellite imagery in ArcGIS. The outline of the 1880's shoreline was digitized and overlain on the aerial photos and satellite imagery. With the 1880's shoreline overlain on a time series of images of the study area the past geomorphology could be compared to the present. Due to restricted land access, water wells were used to investigate the subsurface stratigraphy. Wells were selected between the modern shoreline and the 180 m elevation contour. Well logs were plotted in clusters for the sake of quality control. The major lithologies in each well cluster were catalogued. The catalogued lithologic units were classified genetically.

http://waterdata.usgs.gov/nwisweb/ local/state/ak/text/ijc_logo.jpg

Acknowledgements Linda Fan Wenxin Li Paul Karrow

Jenny Davis Jason Verstraeten Andre Morin

Dave Posliff Tom Morris

Sean Morrison

Jim Burns Joe Dodecker

Upper Mid

180 Cluster 3 References Ollerhead, J., & Davidson-Arnott, R. G. D. (1995). The evolution of Buctouche Spit, New Brunswick, Canada. Marine Geology, 124(1-4), 215– 236. http://doi.org/10.1016/0025-3227(95)00042-W Allard, J., Bertin, X., Chaumillon, E., & Pouget, F. (2008). Sand spit rhythmic development: A potential record of wave climate variations? Arçay Spit, western coast of France. Marine Geology, 253(3-4), 107–131. http://doi.org/10.1016/j.margeo.2008.05.009 Martin Associates (2011). The Economic Impacts of the Great Lake – St. Lawrence Seaway System. The St. Lawrence Seaway Management Corporation. http://www.greatlakes-seaway.com/en/seaway/facts/eco_impact.html#Impacts Tribe, H. M., & Kennedy, D. M. (2010). The geomorphology and evolution of a large barrier spit: Farewell Spit, New Zealand. Earth Surface Processes and Landforms, 35(15), 1751–1762. http://doi.org/10.1002/esp.2009 Thompson, T. A., Johnston, J. W., & Lepper, K. (2014). The contemporary elevation of the peak Nipissing phase at outlets of the upper Great Lakes. Geological Society of America Special Papers, 508, 15–29. http://doi.org/10.1130/2014.2508(02)

(Shale)

Discussion & Recommendations Based on previous research (Allard et al. 2008; Ollerhead & Davidson-Arnott, 1995; Tribe & Kennedy, 2010) combined with the results of this study, the landform identified in Point Edward is a sand spit. Associated with this spit are two smaller paleo-geomorphic landforms, which if confirmed as spits as well, could contain geologic evidence of the lake level and sedimentation at the time of deposition of each remnant “paleo-finger.” The elevation (180 m), used to constrain water well selection is below the presently buried elevation in a shoreline identified by Thompson, Johnston, and Lepper, (2014) which corresponds to the lake level of the peak Nipissing phase in the Great Lakes, 4,500 years ago. The spit has therefore been deposited in the last 4,500 years. From analysis of the water wells, there were three main stratigraphic units identified within a generalized stratigraphic framework of the Point Edward area. The bedrock in this area is the Upper Devonian shale of the Kettle Point Formation. Overlying the shale bedrock are glacial sediments consisting primarily of clay and silt, but also containing minor sand and gravel, and having thicknesses of approximately 22-44 m. On top of the fine glacial sediments are lacustrine deposits consisting primarily of sand, but also containing silt and gravel. This package has a thickness of 4-17 m, and exhibits a coarsening upward sequence in the water wells; a characteristic of spits. To better characterize the Point Edward spit and the associated “paleo-fingers,” it is recommended that the subsurface be sampled using ground-penetrating radar (GPR), vibracore and/or geoprobe, and optically stimulated luminescence (OSL) techniques, allowing the determination of sediment volumes and absolute ages. This information would help to model sedimentation at the outlet, thus identifying the natural context in which the only unregulated outlet in the Great Lakes lies.