Bathymetry of Lake Ontario 80 00'W 76 00'W 79 30'W 76 30'W 79 00'W 78 30'W 78 00'W 77 30'W 77 00'W 76 32'W 76 30'W 76 28'W 76 26.4' 44 4.2' 44 04'N 4 ATMOSP 44 04'N ND HE T OF C Small Rounded Basin at Charity Shoal A RI N O IC C E M N A M M A D T 0 E M R E C I N A R O I S P C 10 L T A E E R N A D A small equidimensional circular depression 1000 meters in O T I D I 5 T O 20 A N U N A diameter, with a continuous encircling rim, coincides with the N U I C e 20 T I . E S C E R 44 30'N . feature referred to as Charity Shoal on nautical charts. An D R D E 44 30'N E E 10 P M CIRES S M p A M RT O T A MENT OF C ATES O F elongated ridge extends southwest from the feature, resembling the tail of a crag-and-tail feature common to some drumlin fields. t 15 National Geophysical Data Center Nautical Charting Division Cooperative Institute for Research in Environmental Sciences U.S. Department of Commerce The basin is slightly deeper than 18 meters and the rim rises to h National Environmental Satellite, Data, and Information Service Canadian Hydrographic Service University of Colorado National Oceanic and Atmospheric Administration depths of 2-6 meters. The origin of the feature remains unknown. 20 2 10 Boulder, Colorado Department of Fisheries and Oceans Boulder, Colorado Although a sinkhole in the limestone terrane is a possibility, an i 18 Ottawa, Ontario, Canada origin related to a meteor crater, that was subsequently glaciated, 4 n 25 Great Lakes Environmental Research Laboratory seems more likely. Aeromagnetic mapping by the Geological 44 02'N 40 44 02'N Office of Oceanic and Atmospheric Research Survey of Canada revealed a negative magnetic anomaly over 30 6 Ann Arbor, Michigan Charity Shoal, which is a characteristic feature of simple impact M 20 craters (Pilkington and Grieve, 1992). e 35 W.T. Virden, CIRES, University of Colorado, Boulder, CO 80303 t km r e 40 J. S. Warren, Canadian Hydrographic Service, Ottawa, ONT., K1AOE6 Rive 0 5 t r 30 n 45 44 0.498' T.L. Holcombe, NOAA/National Geophysical Data Center, Boulder, CO 80303 re Scale 1:65,000 s World Data Center for Marine Geology and Geophysics, Boulder, CO, Report MGG-15 T 76 31.998' 1999 Transverse Mercator 50 D.F. Reid, 50 Published by the National Geophysical Data Center NOAA/Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 48105 Projection http://www.ngdc.noaa.gov/mgg/greatlakes/greatlakes.html 44 00'N 44 00'N T.L. Berggren, Geological Society of America, Boulder, CO 80303 76 32'W 76 30'W 76 28'W This map is intended to depict lake floor topography, and is not to be used for navigation. Lake floor feature names have been approved by the U.S. Board on Geographic Names. e k Kingston NGDC wishes to thank the following individuals for reviewing this poster: a er L iv Depth in Meters Bruce Sanford, Geological Survey of Canada (retired), Nepean, ONT. K2G5J4 R e Scotch Bonnet and Point Petre Ridges ce Mike Lewis, Geological Survey of Canada (Atlantic), Dartmouth, N.S. B2Y4A2 ic te en n 20 . r i I Seismic sections show that the Scotch Bonnet and Point Petre Ridges u e w 0 12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192 204 216 228 240 252 R Q co Wolfe a John Coakley, Canadian Centre for Inland Waters, Burlington, ONT. L7R4A6 f m are underlain by bedrock highs; at one location the Scotch Bonnet Ridge is d i L o n S Island . sla t bounded on the northwest by a 25 meters escarpment (Anderson and Lewis, ay t I S km B rs Recommended citation: 1975; Forsyth, et al., 1994). Valleys also interpreted as bedrock features extend he 0 30 m Scale 1:275,000 Virden, W.T., J.S. Warren, T.L. Holcombe, D.F. Reid, and T.L. Berggren, 1999, Bathymetry NE-SW, paralleling the two main ridges and lying between and adjacent to these A Transverse Mercator Projection of Lake Ontario, National Geophysical Data Center, World Data Center for Marine Geology ridges (Hutchinson, et al., 1993). These features are lineated in the same direction as Trenton 30 2 meter contour intervals and Geophysics, Boulder, CO, Report MGG-15, scale 1:275,000 poster. faults and bedrock lineations occurring to the northeast in Ontario in the distinct NE-SW fabric of the Grenville basement rocks (Forsyth, et al, 1994). The Scotch Bonnet Ridge lies on the northward extension of the Clarendon-Lynden Fault system in New York 40 l e (Hutchinson, et al., 1979). A channel (Scotch Bonnet Gap) which breaches the West and East Kingston, Galloo, and Stony Basins 10 n Charity n Scotch Bonnet Ridge connects the Mississauga and Genesee Basins near l Shoal ana a y C Lake Margin Topography rra h the deep axis of the lake. Deep connections also occur between the Mu Several small shallow basins with intervening ridges occur West C l Niagara and Mississauga Basins and the Genesee and in the northeastern extremity of Lake Ontario, all having e Black River Around the perimeter of the lakefloor, the high energy of water circulation has evidently prevented the deposition of postglacial Rochester Basins (Genesee Gap). 30 Kingston d n depths of generally less than 40 meters. The bathymetry n 44 00'N n 20 10 44 00'N Basin a 30 muds, except in sheltered areas (Thomas et al., 1972). Strongly linear bathymetric features displaying the imprint of exhibits a preferred orientation of NE-SW, and appears to be largely a l a s h glaciation, or of exhumation of bedrock topography and structure, occur at intervals along almost all of the water-covered extension of the topography occurring northeast of the lake. I C Galloo lakeshore. Study of bottom sediment types off the western lakeshore between Niagara and Oshawa The basins were probably produced by glaciation followed by some East e e o c Basin revealed that extensive areas of exposed bedrock, boulder pavement, sand deposits, and glacial Cobourg sedimentary infilling and topographic smoothing. Bedrock, consisting of Kingston c n 10 drift occur here (Rukavina, 1969; Rukavina, 1976). Apparently in most areas around the lake Port Hope Ordovician limestones and e Basin m n 20 t i r i l perimeter, Quaternary sediments are relatively thin or absent, and bedrock exposures are shales, lies at or near the oin s e 30 d P S M w a ar B n w ai common, possibly reflecting the effects of subglacial erosion and subsequent abrasion 30 surface beneath the ridges Ed n a n nce Duck I. L . y a Pri I n . h by lacustrine waves and currents. 40 and shoals separating the o o I t llo t y C 50 n a S n r 10 basins. (Sly and Prior, 1984). i G to e Scotch Bonnet Island a S v S i int R Po e Whitby Oshawa n tr Duc k Ledges and Channels in the Mississauga Basin 60 o e k-G c lm P a Stony Sa t llo a in o l Point o R B P id In the deep axis of the Mississauga Basin from 146-182 meters depth, there are several ledges of a few meters relief, ge ork separated by scarplets that trend north to south. These features step down from west to east toward the deepest 20 Y 20 point in the basin. Although the origin of the ledges is not known, they might have formed on the eroded edges 70 Ontariow of a succession of gently dipping strata which are characterized by bed-to-bed variation in resistance to erosion. 40 Ne 40 Rudimentary valleys and channels of only a few meters relief are superimposed on the ledges 80 and appear to represent a drainage pattern. Formation of the ledges could have been 60 90 e 30 20 40 10 the result of the erosional action of Wisconsin glaciation and/or subglacial meltwater floods, 100 g 60 acting against the differential resistance to erosion and layered aspect of the 110 d 50 80 i 60 sedimentary strata (probably Trenton Limestone; Sanford and Baer, 1981) 120 e 80 70 underlying the lake floor. R g 80 130 d t i 100 90 140 e R 100 110 Toronto n e 100 r t 130 120 150 n e 140 160 o 150 B 120 P 120 Ontario t 160 170 New York in h 180 170 c 140 o t P 180 o 190 140 c Mississauga S 160 200 160 Mississauga 190 Genesee Niagara Whitby-Olcott Basin e 180 Genese Gap Rochester Ridge Scotch Bonnet Basin 170 43 30'N Basin140 43 30'N 170 Gap Duck-Galloo Ridge, Simcoe Island Channel, 160 Basin Saint Lawrence Channel, and Black River Channel 150 210 140 At the southern rim of the East Kingston, Galloo, and Stony Basins Oswego 130 130 120 there occurs a series of broad low ridges which individually trend 100 110 90 NE-SW, but which coalesce to form a complex ridge extending 1 80 20 from the west near Prince Edward Point, Ontario to the east near 120 70 110 60 Stony Point, New York.