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TitleAn Early Lake Ontario paleo-barrier beach built at sea level about 12.8-12.5 cal ka BP
AuthorLewis, C F MORCID logo; Todd, B JORCID logo
SourceGSA Annual Meeting in Indianapolis, Indiana, USA - 2018; Geological Society of America, Abstracts With Programs vol. 50, no. 6, 140-3, 2018 p. 1,
Alt SeriesNatural Resources Canada, Contribution Series 20180207
PublisherGeological Society of America
MeetingGSA 2018 - Geological Society of America, Annual Meeting 2018; Indianapolis, IN; US; November 4-7, 2018
Mediapaper; on-line; digital
File formathtml; pdf
ProvinceOntario; Quebec
NTS30M; 30N; 31B; 31C; 31D; 31E; 31F; 31G; 40O; 41A; 41B; 41G; 41H
AreaLake Ontario; Lake Huron; St. Lawrence River; New York State; Lake Champlain; Canada; United States of America
Lat/Long WENS -84.0000 -74.0000 46.0000 43.0000
Subjectssurficial geology/geomorphology; Nature and Environment; Holocene; barrier beaches; paleo-sea levels; shoreline changes; lakes; water levels; glacial history; glaciation; deglaciation; isostatic rebound; crustal uplift; paleodrainage; paleohydrology; marine sediments; sands; gravels; muds; erosion; sediment dispersal; glacial lakes; bathymetry; flow regimes; hydraulic analyses; Early Lake Ontario; Champlain Sea; Laurentide Ice Sheet; Lake Ontario Basin; marine beach sediments; lacustrine sediments; Phanerozoic; Cenozoic; Quaternary
ProgramClimate Change Geoscience Coastal Infrastructure
Released2018 11 01
AbstractAn overstepped, concave-eastward, barrier beach beneath Holocene mud in western Lake Ontario has been delineated by acoustic and seismic reflection profiles and piston cores, and related to Early Lake Ontario (ELO). The average ELO barrier depth below present mean lake level is 77.4 m to 80.6 m, or about -6 to -2.8 m above present sea level (asl). Trend surface analysis of Champlain Sea (Atlantic Ocean) marine limits defined the contemporaneous marine water surface in valleys of the upper St. Lawrence, and Ottawa rivers, and Lake Champlain. Projections of this surface pass ~25 m above the outlet sill of the Lake Ontario basin and extend to the ELO paleo-barrier, a unique sand and gravel deposit beneath western Lake Ontario. ELO was connected to the Champlain Sea above the isostatically rising outlet sill for up to 3 centuries after about 12.8 cal ka BP, while the glacio-isostatically-depressed St. Lawrence River Valley was inundated by the Atlantic Ocean. During the period of this connection, ELO level was confluent with slowly rising sea level, and the lake constructed a transgressive beach deposit with washover surfaces. ELO remained fresh due to a high flux of meltwater inflow. The marine water level connection stabilized water level in ELO relative to its shore and facilitated shore erosion, sediment supply, and barrier construction. Glacio-isostatic uplift of the outlet sill, faster than sea-level rise, lifted ELO above the Champlain Sea about 12.5 cal ka. Shortly after, a hydrological deficit due mainly to a combination of diverted meltwater inflow and dry climate, well known from regional pollen studies, forced the lake into a lowstand. The lowstand stranded the barrier, which remains as evidence of sea level, the farthest inland in eastern North America north of the Gulf of Mexico at the time. The highest paleo-washover surface provides a sea level index point ~12.5 cal ka BP with elevation -3.1±3.9 m asl, referenced to modern transgressive beach washover surfaces in southwestern Gulf of St. Lawrence with elevations of 2.5±1.2 m asl. Climatic change and increasing meteoric water supply began raising Lake Ontario over the barrier about 3 millennia later, and subsequently buried it with offshore mud.
Summary(Plain Language Summary, not published)
A concave-eastward sand and gravel deposit up to 5 m thick was located with seismic and acoustic profiles and piston cores about 75 to 79 m below the surface of western Lake Ontario. The deposit underlies 4 to 5 m of deep-water silty clay mud, and is interpreted to be a paleo-barrier beach, similar in origin to the present Burlington Beach that separates Hamilton Harbour from Lake Ontario. Extended profiles from a trend surface map of the Champlain Sea shore known mainly in southeastern Ontario and northeastern New York connect with the paleo-beach. This connection and other data show that the deposit is an abandoned barrier beach of Early Lake Ontario, constructed while the lake was at the same level as the Champlain Sea about 12 800 to 12 500 years ago before glacial uplift raised the lake above the Champlain Sea. Although the barrier beach was constructed at sea level, abundant glacial meltwater flowed through the lake and kept it fresh.

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