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MARGINAL NOTES REFERENCES Geological mapping of the Grand Bend area was carried out in the summer of 1974 with the assistance of B.E. Broster and T. Humphrey. Hewitt, D.F., and Liberty, B.A. 1972: Paleozoic Geology of Southern Ontario; Ontario Dept. Mines, Ontario Field techniques included the use of hand augers and soil sampling tubes Map 2254, scale 1 inch to 16 miles. Division of Mines combined with the examination of natural or man-made exposures available at the time of mapping. Supplementary information was obtained from the water well, Karrow, P.F., and Apon, J.F. and gas and oil well records for the area. Air photographs at a scale of four 1974: Quaternary Geology of the St. Marys Area, (East Half), Southern HONOURABLE LEO BERNIER, Minister of Natural Resources inches to one mile were used. Ontario; Ontario Div. Mines, Prelim. Map P.918, Geol. Ser., scale 1:50,000. Geology 1973. DR. J. K. REYNOLDS, Deputy Minister of Natural Resources PALEOZOIC GEOLOGY Karrow, P.F., Apon, J.F., Hutnik, F., Pucovsky, G.M. and Ferguson, A.J. G. A. Jewett, Executive Director, Division of Mines E. G. Pye, Director, Geological Branch Paleozoic bedrock does not outcrop in the map-area. The most recent 1974: Quaternary Geology of the St. Marys Area (West Half) Southern Paleozoic Geology map of the area (Hewitt and Liberty 1972) shows the middle Ontario; Ontario Div. Mines, Prelim. Map P.956, Geol, Ser., Devonian limestones of the Dundee Formation underlying the entire field-area. scale 1:50,000. Geology 1973, 1974. The limestones and dolostones of the Detroit River Group are believed to sub- Karrow, P.F., Ben-Tahir, I., Steele, D.B. and Morrison, W.D. crop slightly to the north and east of the map-area, and the shales and lime 1965: Grand Bend Sheet, Bedrock Topographic Series; Ontario Dept. Mines, PRELIMINARY MAP P. 974 stones of the Hamilton Group are known to outcrop just south of the field-area, Prelim. P.265, scale 1:50,000. Data compiled 1964. GEOLOGICAL SERIES at Thedford and on the Lake Huron shore southwest of Port Franks. Taylor, F.B. The bedrock topography, as determined from well records, has been pub 1913: The Moraine Systems of Southwestern Ontario; Royal Canadian lished by Karrow (1965). The addition of new data has necessitated revisions Inst. Trans., V.10, p.1-23. QUATERNARY GEOLOGY in the bedrock topography and a new bedrock topography map is in preparation. In general, the bedrock surface rises gently from a low of just under 500 feet Terasmae, J., Karrow, P.F., and Dreimanis, A. (150 m) a.s.l. along the Lake Huron shore to a high of 750 to 800 feet (220 1972: Quaternary Stratigraphy and Geomorphology of the Eastern Great to 240 m) along the eastern edge of the map-area. The bedrock surface tends Lakes Region of Southern Ontario; Field Excursion A 42, Guidebook GRAND BEND AREA • to rise slightly in the northeastern corner of the area with a resulting de Twenty-Fourth Session International Geological Congress, Montreal, crease in drift thickness. This decrease is reflected by the presence of Quebec, 75p. • several depressions with internal drainage which are believed to represent SOUTHERN ONTARIO ||j sink holes. In the southwestern corner of the map, south of the town of Grand ,| Bend, the bedrock surface is known to rise. With the exception of the north Scale: 1:50,000 eastern corner of the area, where the drift thickness may be less than 50 feet 1.25 inches to 1 mile approximately " (15 m), the entire area is covered with approximately 100 feet (30 m) of Miles 1 0 1 i,J Quaternary sediments. This figure increases locally to as high as 200 feet f=* T-——rf^-i i-=ii —-- (60 m) on the Wyoming Moraine. Metres 1000 0 1000
QUATERNARY GEOLOGY
The geomorphology in the Grand Bend area closely reflects the Quaternary NTS Reference: 40 P/5 Geology. The area is dominated by the compound ridge named the Wyoming Moraine ©ODM 1974 (Taylor 1913), which parallels the Lake Huron shore. The moraine is composed of three fairly distinct ridges in the north, but the easternmost ridge Parts of this publication may be quoted if credit is given to diminishes leaving only two ridges in the south. In the depressions between the Ontario Division of Mines and the material is properly the ridges and on the eastern margin of the moraine are plains of outwash sand referenced.
5, and lacustrine silt and clay. To the east of the Wyoming Moraine, flat to gently rolling ground moraine is present. To the south the ground moraine rises into a very poorly defined end moraine at Centralia. On its western flank, adjoining Lake Huron, the Wyoming Moraine has been modified by the erosive action of ancient Lake Warren. This is represented by a broad lake plain along the edge of present Lake Huron. In the Grand Bend LEGEND area, the presence of Lake Warren is also recorded by a well developed beach ridge at approximately 740 feet (225 m) a.s.l. which runs in a line from CENOZOIC Blake in the north, through Dashwood, to Mount Carmel in the south. QUATERNARY RECENT In the southwestern corner of the map-sheet, there is an extensive area which represents a former embayment at a time when the water level in the Huron 11 Alluvium; young stream deposits of gravel, basin was just over 600 feet (180 m). The presence of a water level is re sand and silt. corded by a series of bay mouth bars and an accompanying shore bluff at approx imately 605 feet (183 m) on the eastern side of the embayment, and two bar-like 10 Organic deposits; peat, muck and marl. structures, slightly below 600 feet (180 m) between the old Ausable River channel and the present Lake Huron shore. The elevation of these shoreline features woi^ld suggest formation during the time of Lakes Algonquin and/or Nipissing. PLEISTOCENE Extensive sand dune ridges have been developed on top of the bar closest to the WI SCONSINAN STAGE present lake. Late Wisconsinan Substage Map-unit 2 is a variable silt to clayey silt till with a moderate stone 9 Windblown deposits; sand and silt. content. This till is variable in both grain size and stone content and in some areas it is very difficult to distinguish from the Wyoming Moraine till 8 Older alluvium; «and and gravel, fossil- (map-unit 3). In the field, unit 2 is generally more gritty and tends to be iferous. coarser grained. The western boundary of this till is placed at the Ausable River, which follows the eastern flank of the Wyoming Moraine. Karrow 7 Glaciolacustrine clay, silt and sand. (Karrow and Apon 1974; and Karrow et al. 1974) has mapped this till as far east as the Thames River valley, and notes a similar variation in the character of 6 Glaciolacustrine beach deposits; sand and the unit. gravel. Map-unit 3, referred to above as the Wyoming Moraine till, forms the bulk a) Lake Whittlesey of the Wyoming Moraine and covers the majority of the map-area. It is a clayey b) Lake Warren silt till and is fairly homogeneous throughout the area with the exception of c) Lakes Algonquin and Nipissing. the eastern edge of the moraine. On the eastern edge of the moraine the till becomes less gritty and, in places, is almost grit free. The Wyoming Moraine 5 Glaciofluvial outwash; sand, minor gravel. till has a sparse to moderate grit and stone content. In the shorebluff sec tions in the area of Drysdale and St. Joseph, the till shows a gradation down 4 Glaciofluvial outwash; gravel, minor sand. wards into laminated lacustrine silt and very fine sand. Detailed examination of all available cuts did not demonstrate a temporal relationship between map- 3 St. Joseph Till; clayey silt till. units 2 and 3; however, several exposures along the Ausable River in the Park- hill area, to the south, are believed to represent Wyoming Moraine till (unit 2 Silt to clayey silt till; Seaforth Moraine 3) over unit 2. 1 1 till. 11 It is here proposed that the Wyoming Moraine till (unit 3) be formally 1 Ice-contact stratified drift; sand, gravel, ;j named the St. Joseph Till. Due to the temporary nature of exposures along the 1 1 silt. Lake Huron shore, a type-area rather than one specific type section is proposed. ,,, The till is well exposed on the lake shore in the map-area north of Grand i Bend, and especially between the towns of St. Joseph and Drysdale, where 30 feet (9 m) of St. Joseph Till is exposed over 10 feet (3 m) of lacustrine silt and clay which is believed to be of Lake Arkona age. The St. Joseph )'| Till has previously been referred to as the Goderich till (Terasmae et al. 1972). A fairly extensive area of outwash sand with minor gravel was deposited on the eastern edge of the Wyoming Moraine. This deposit is the result of drainage SYMBOLS of glacial meltwater southwards after the Port Huron ice advance, which deposited the Wyoming Moraine. ^x>^ Shoreline of former glacial lake marked by scarp. There are three main subdivisions of the deposits termed beach deposits (unit 6). These subdivisions are based on elevations and historical age. The Geological boundary (approximate). oldest unit (unit 6a) represents the shoreline of Lake Whittlesey (Terasmae et al. 1972) and is found in the southeastern corner of the map-sheet at an Sand and (or) gravel pit. elevation of just over 800 feet (240 m). As mentioned previously, the Lake Warren shoreline (unit 6b) runs along the western flank of the Wyoming Moraine @ Sink hole. at an elevation of approximately 740 feet (225 m). The lowermost beach units (6c) occur at approximately 600 feet (180 m) elevation and are believed to represent the presence of Lakes Algonquin and Nipissing. Lacustrine silt and clay deposits (unit 7) are scattered throughout the map-area and are derived from several sources. Patches of lacustrine sediments on and to the east of the Wyoming Moraine are the product of local pondings. Lacustrine deposits below the Lake Algonquin-Nipissing level are derived from those lakes, and the lacustrine deposits between the Algonquin-Nipissing level and the Lake Warren level are Warren in age. Older alluvium (unit 8) denotes SOURCES OF INFORMATION two localities where alluvial terrace deposits are graded to the Algonquin- Ni pissing level rather than the modern Lake Huron level. Geology by A.J. Cooper, Jack Clue and assistants, 1974. Eolian deposits of silt and sand (unit 9) are of very local extent except Topography from Map '40 P/5 of the National Topographic Series. in the Thedford embayment area, south of Grand Bend. Here the wind blown de Aerial Photography: Ontario Ministry Natural Resources, posits are up to 60 feet (20 m) thick in places. These deposits are derived Toronto and National Air Photo Library, Ottawa. from and, therefore, must postdate the Algonquin-Nipissing shore and bar deposits. Additional information from water well records, Ministry of " Most of the larger creeks and rivers in the area show mappable alluvial the Environment, and gas and oil well records, Petroleum Re floodplain deposits (unit 11). There are several occurrences of bog deposits sources Branch, Ministry of Natural Resources. (unit 10), noteably the Thedford bog in the Algonquin-Ni pis sing embayment. I! i 'l| ECONOMIC GEOLOGY Issued 1974. I 11 Two problems limit the use of local gravel deposits in the Grand Bend area: j most of the deposits are extremely sandy and would require grain size improve ment, and the chert content of the gravels is often quite high (0-20 percent, average 6.5 percent). Deposits of the Whittlesey and Warren shorelines are dominantly sand with minor gravel. The large outwash sand deposit east of the Wyoming Moraine has very little gravel in it. The gravel exposed in the Algonquin-Nipissing bars in the Thedford embayment is more suitably graded but Parts of this publication may be quoted if credit is given to also has a high chert content. the Ontario Division of Mines. It is recommended that reference In several localities, peat has been extracted on a small scale, and one to this map be made in the following form: area of lacustrine clay has been mined for the manufacture of brick and tile in the past. Cooper, A.J. and Clue, Jack 1974: Quaternary Geology of the Grand Bend Area, Southern 15' Ontario; Ontario Div. Mines, Prelim. Map P.974, 82 W 55' Geol. Ser., scale 1:50,000. Geology 1974.