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MARGINAL NOTES Ministry of Hon. Alan W. Pope Minister Natural Essex County is an area of extremely low relief, its topography being the W T Foster result of the levelling action of Lake Whittlesey. the remnants of which REFERENCES Resources Deputy Minister surround Ihe area on three sides. Drainage is through small streams of man-made channels into Lake St, Clair and Lake Erie and through the Ontario Briggs, L.T. Sanford B.V. and Brady, W.B. Canard River system into the Detroit River to the west. The Detroit interlo Oliver Project 1959: PMysiua© Stratigraphy of lower Midd©e rocks h the Ba 1955: Paleozoic Geology of the Windsor-Sarnia Area, Ontario; Geological Survey bate moraine which runs from Leamington to Windsor is a small positive sin; Guidebook o* Michigan Basin, Geol. Soc., p.39-58 of Canada Memoir 278, ONTARIO GEOLOGICAL SURVEY feature, which survived the erosion of Lake Whittiesey, and against Chapman, L J. and Putnam, D.F. Summerson, C.H. and Swann, D.H, which beach deposits of sand and gravel were deposited near Leaming 1966: The Physiography of southern Ontario. Ontario Research Foundation, To 1970; Patterns of Devonian sand on the North American craton and their interpre PRELIMINARY MAP P.2396 ton. Chapman ana Putnam (1966), regard the bedrock high near Am ronto, tation; Geological Society of America Bulletin, 81, p 469-490. herstburg as a manifestation of the Findlay Arch which runs northeast- GEOLOGICAL SERIES southwest through Essex County. Typically, there is over 30 m ot glacial Kobluk, D,R,, Pemberton, S,G., Karolyi. M. and Risk, VI.J Telford, P.G. and Hamblin A.P. 1977: The -Devonian disconformity in southern Ontario; Bulletin of Cana clay deposits overlying the bedrock (Vagners et al 1973a,b): natural 1980: Paleo7oic Geology of the Simcoe Area, Southern Ontario; Ontario Geologi dian Petroleum Geology, p.1157-1186 cal Survey Preliminary Map P.2234, Geological Series, scale 1:50 000. Geol PALEOZOIC GEOLOGY outcrop is totally absent on the mainland Glacial cover is much less per ogy 1975,1976, vasive on Pelee Island where outcrop is quite extensive. Reavely, C.H and Winder. C.G. OF THE 1961. The in southwestern Ontario; Canadian Mining and Me Vagners, U.J., Sado, E.V. and Yundt, S,E, Because of the lack of natural outcrop, information concerning the be tallurgy Bulletin, 64, p 109-112. 1973a: Drift Thickness of the Windsor-Essex Area (Western Part), Southern Ontar drock can only be obtained by inspection of records of oil and gas wells, Sandord, B.V. io; Ontario Division of Mines Preliminary Map P.814, Drift Thickness Series, WINDSOR-ESSEX AND and observations of quarry sections, Sanford (1969), presents a map of 1967: Devonian of Ontario anc Michigan, in International Symposium on thaJDe- scale 1:50000. Geology 1970 1971, 1972. the bedrock of the area based on subsurface records. This is the main voman Systenr Alta. Soc. Petroleum Geol, Calgary v.©, p.973-999. 1 973b. Drift Thickness of the Windsor-Essex Area (Eastern Part). Southern Ontar source of the 1:250 000 map of this report, However,,the criteria for dis 1969- Geology of the Toronto-Windsor area; Map 1263A, Geological Survey of io: Ontario Division ot Mines Preliminary Map P.S15. Drift Thickness Series, PELEE ISLAND AREA tinguishing between various units in the subsurface cannot be consist Canada. scale 1:50000. Geology 1970 1971, 1972. ently extended to surface outcrops. Thus, the sections exposed in quar SOUTHERN ONTARIO ries near Amherstburg and on Pelee Island cannot be used lo assist in placing contacts. NTS Reference: 40 G/10.15:40 J/1,2,3.7,8 STRATIGRAPHY1 420 30©00" ODM-GSC Aeromagnetic Maps: 4579G-4583G Bass Island Formation (Upper Silurian) Berkle The presence of this unit is detected only by subsurface records; it sub- i-r i -i R&YfeLQAK ST CLAIR SHORES OMNR-OGS1981 crops in the area to the west of Colchester on the north shore of Lake Erie. The Bass Island Formation consists of grey and brown microsucro- Parts of this publication may be quoted if credit is given and the material sic dolostone with some oolitic zones. It is the lateral equivalent of the is property referenced, Bertie Formation of the Niagara Peninsula area (Telford and Hamblin AST DETROf 1980). The top of the Bertie Formation is marked by features distinctive This map is published with the permission of E.G. Pye, Director, Ontario of a period of shallowing and subaerial erosion (Kobluk et al. 1977). No Geological Survey. evidence for this type of feature has been reported from Essex County, Grbsse Poicrte Wdods fer but the generally irregular and eroded nature of the disconformity in north-central North America (Summerson and Swann 1970), suggests LAKE that a similar relationship exists in the area. SYMBOLS Grosse ointe Farms (Middle Devonian) Grosse/rointe v^V\ ST CLAIR ( x*^ .^" © ©^ Bed rock outcrop LEGEND The which lies stratigraphically between the Bass Gfosse Pointe Park Island Formation and the Detroit River Group does not subcrop in the Quarry PALEOZOIC area, having been overlapped by the Detroit River Group. The Detroit DEVONIAN River Group has been divided into several formations in the subsurface Geological boundary but they could not be distinguished in the two extensive quarry sections. The total thickness of the Detroit River Group is about 180 m (Sanford Geological boundary, approx ©Hamilton Group 1 grey shale and argillaceous lime- 1969). imate slone

Sylvania Sandstone (Middle Devonian) Geological boundary, inter Dundee Furmalion: bruwn cherty crinoidal limestone preted in subsurface; massive brown bituminous bioclastic Resting disconformably on an erosional surface of the Bois Blanc Forma limestone on Pelee Island. tion and Bass Island Formation, the Sylvania Sandstone is one of the Eastern edge of Sylvania For several Lower to Middle Devonian sandy units characteristic of north- mation in subsurface DETROIT RIVER GROUP central North America. It varies in thickness from zero at the eastern dep ositional edge to over 30 m in the western part of the county. It consists 1 grey brown calcilutite; massive cor Approximate eastern edge of of a pure white fine-grained quartz arenite of well rounded grains, af alline bioclastic limestone; light brown stromatotitic Sylvania Formation in subsur fected by pressure solution or quartz overgrowths, grading into a grey calcarenite; anhydrite in subsurface. face dolomitic quartz arenite. A cherty grey blue dolostone interval appears in : brown laminated, massive the lower part of the unit near the Detroit River The sandstone is envi and vuggy dolostone; oolitic and bioclastic dolostone; saged as a beach or shallow marine deposit of reworked wind-trans coralgal limestone: cherty locally. ported grains derived from the Cambro- St. Peters Sandstone ot Wisconsin (Briggs 19b9). It represents the basal unit of the southward ©Sylvania Formation: white and grey pure and dolomi transgressing Detroit River sea and is therefore of the same age in the tic quartz arenite, with cherty dolostone interbedded in Essex area as the Amherstburg Formation to the north. Its upper contact western part. is sharp but conformable near Windsor, but becomes gradational in the south and west (Reavely and Winder 1961). 41 D 51© DISCQNFQRMITY Amherstburg Formation (Middle Devonian) 2Bois Blanc Formation This unit forms the bedrock of She southern part of Essex County and is exposed in the Amherst quarry, Amherstburg (LS275623). In the subsur 20riskany Formation face, the Amherstburg Formation consists of dark coloured finely crystal line limestones and dolostones, characterised by zones with bituminous DISCQNFORMiTY and cherty natures. The section at Amherstburg itself apparently spans the Amherstburg/Lucas Formation boundary, but the exact location can not be identified. The base of the section exposes medium bedded lami ©Bass Island Formation-fan and cream oolitic micro- nated bituminous dolostones, definitely of the Amherstburg Formation. sucrosic dolostone. The rest of the section consists of oolitic, bioclastic and coralgal lime stones and brown bituminous calcisiltites. Further work is required to re late the subsurface subdivisions of the Detroit River Group to surface 2Salina Formation outcrops. Sanford (1969), shows a thickness of about 49 m lor the unit. In the subsurface, the top of the Amherstburg Formation is defined as the 2Guelph Formation base of the lowermost anhydrite bed in the Detroit River Group. 2Lockport-Amabel Formation Lucas Formation (Middle Devonian) CLINTON GROUP Overlying the Amherstburg Formation conformably, the Lucas Formation is characterized by a lighter colour and the presence of anhydrite in the 2Rochester Formation subsurface. It is exposed in the McGregor quarry (LS340695), but anhy 2Reynales Formation drite is not observed; the rock types here include bituminous dolostones, coralline bioclastic limestone, calcarenites and calcilutites which are CATARACT GROUP brecciated locally. These calcilutites may represent the Anderdon Mem ber of the Lucas Formation identified in the subsurface as sublitho 2Cabot Head Formation graphic high purity limestone, which is a subfacies of the Lucas Forma ^Manitoulin Formation tion in the extreme southeast of the Michigan Basin. The thickness of the Lucas Formation is given as about 76 m for the DISCONFORMITY Windsor-Sarnia area by Sanford (1969), the 25 m section at McGregor presumably composing the upper third of this. The unit can be traced as ORDOVICIAN far east as the Simcoe area (Telford and Hamblin 1980), where it is over 2Queenston Formation lapped by the Dundee Formation, which disconformably overlies the De troit River Group. ^Georgian Bay Formation Dundee Formation (Middle Devonian) ^Whitby Formation Although this unit subcrops beneath the glacial cover over most of the northern part of the area, no exposures exist. Extensive exposures are 2 Lindsay Formation available on Pelee island. The lower contact with the Detroit River Group, probably reoresents sf major disconformity (Sandford 1967). The Dun Pel K Passage Lighl A if* ^X. ft Middle Sister Mond 2Verulam Formation dee Formation generally consists of brown and tan microcrystalline cri noidal limestone with occasional sand grains, brown chert, and amber spore cases (Tasmanites). On Pelee Island, the section exposed in the NOTES one active quarry (LSB32306) shows 6 m of massive brown medium- to 1 Subcrop only in Windsor-Essex area; lithology from subsurface records. coarse-grained bituminous bioclastic limestone, with corals, brachiop- 2Does not occur as subcrop in Windsor-Essex area. ods, bryozoa, and tribolites. The massive brown limestone extends at least 30 m below the exposed section, This gives a minimum thickness (36 m), of the Dundee Formation for Pelee Island which is oimilar to that quoted for the mainland {33 m, Sanford 1969). Hamilton Group (Middle Devonian) SOURCES OF INFORMATION The Hamilton Group is the youngest Paleozoic unit to subcrop in Essex County It underlies areas to the east of Windsor and at the extreme east Subsurface contacts from Sanford (1969). ern edge of Essex County. The small number of well records show that Additional subsurface data compilation by D. Russell (1981). from oil the Hamilton Group is composed of grey shales and argillaceous lime and gas well records of Petroleum Resources Section. Ministry of Natural stones. These are divided into several formations where more detailed Resources, London. subsurface and surface data are available, The contact with the underly ing Dundee Formation is not exposed, but Sanford (1967), states that the Bell Formation, close to the base of the Group, rests disconformably on underlying strata, Subsurface records in the Windsor area suggest a thickness of about 15 m. CREDITS

ECONOMIC GEOLOGY Geology by P.G. Telford and assistant. 1977. Additional work by D.J. Several small oil and gas fields underly the area. The Malden gas pool, in Russell, 1980. reen blond"3 / \-i C the extreme southwest of the County, produces gas from a dome struc Every possible effort has been made to ensure the accuracy of the infor ture in the Guelph Formation (Sanford and Brady 1955), over which suc mation presented on this map; however, the Ontario Ministry of Natural ceeding strata are thinned. The Guelph Formation is also the producing Resources does not assume any liability for errors that may occur. Users horizon for the Staples pool in the Tilbury Township and the pool near may wish to verify critical information; sources include both the refer Kingsville. ences listed here, and information on file at Ihe Resident or Regional Ge Large volumes of salt (sodium chloride), are extracted from the Upper ologist©s office and the Mining Recorder©s office nearest the map-area Silurian Salina Formation at two sites near Windsor. The Canadian Salt Company produces salt from brine wells in the B-salt at Sandwich. The Canadian Rock Salt Company extracts salt for road de-icing from a mine A \ K E Issued 1981 in the F-salt at Ojibway. Scale 1:50000 Quarrying of the Detroit River Group carbonates is active near Amherst Information from this publication may be quoted if credit is given. It is burg, due to the small amount of overburden in that area. Crushed stone O l Mile recommended that reference be made in the following form: for road base and other uses is extracted at Amherstburg by Amherst l Kilometre Quarries Limited. Raw material for the chemical plant of Allied Chemicals Telford, P.G and Russell, D J Limited at Amherstburg is quarried at McGregor, 1981: Paleozoic Geology ot the Windsor-Essex and Pelee Island Area, Southern Ontario: Onfario Geological Survey Preliminary Map P.2396, Geological Series, Scales 1-250 000, 1:50 000. Geology ©Only those units which outcrop or subcrop beneath glacial cover are described. 1977, 1980. 420 00© 41 030©00 41 0 30©00© 41"43© 41"43©