As written in Natural Areas Inventory – Volume 1
By: Bert Murphy, Hons. BSc., MEd.
Bedrock Geology North Ohnia:kara
The northern portion of the peninsula is underlain by sedimentary rocks laid down in shallow seas during the Ordovician and Silurian periods (505 to 409 million years ago). The lowest formation is known as the Queenston Shale and underlies the portion of the peninsula from the base of the Niagara Escarpment northward to Lake Ontario. It is a red shale with thin limestone interbeds which forms the uppermost Ordivician strata in the area. The width of the outcrop, now buried under post glacial deposits, varies from 3.2 to 19.3 kilometres. At the Niagara River the strata is approximately 260 metres thick, thinning to 180 metres thick at Hamilton.
The Niagara Escarpment is formed from Silurian strata which overly the Queenston Shale. The strata are composed of sandstone, shale, limestone and dolostone
formations. At the Niagara River these layers can best be observed and consist of, from bottom to top, the Whirlpool Sandstone, Power Glen Shales and Sandstones, Grimsby Shales and Sandstones, Thorold Sandstone, Neahga Shale, Reynales Dolostone, Irondequoit Limestone, Rochester Shale, Decew Dolostone and Lockport Dolostone.
It is the hardness of the Lockport and Decew strata overlying softer shales and the Irondequoit and Reynales strata overlying softer shales and sandstones that resulted in the erosional feature known as the Niagara Escarpment. Because the backslope dips at an angle less than the face of the escarpment this feature is sometimes identified as the Niagara Questa. The escarpment is a continuous feature running in Ontario from Queenston to the tip of the Bruce Peninsula at Tobermory. In some places there are deep indentations which represent the sites of former river valleys now mantled by post glacial deposits, particularly in the St. David’s and Short Hills areas. In most sections the upper layer of Lockport Dolostone forms a cliff face that gives way to a scree slope beginning at the top of the Rochester Shale.
South of the brow of the escarpment the Guelph Formation overlies the Lockport Formation. It appears in the wall of the Niagara Gorge about the site of the Rainbow Bridge and forms the upper rapids above the waterfall. The Guelph Formation is between 30 and 60 metres thick but does not outcrop anywhere else in the peninsula, being buried beneath post glacial deposits.
Surface Geology North Ohnia:kara
Except for the Niagara Escarpment, the bedrock geology of the area is hidden beneath post glacial deposits. A layer of basal till was deposited directly on the bedrock as the last phase of continental glaciation waned. The till was then buried beneath lacustrine deposits of a series of post-glacial lakes. The most pronounced and longest lasting of these was post glacial Lake Iroquois which existed from 12,400 to 11,900 years ago. This lake, at a height of 102 metres a.s.l., occupied what is now the Lake Ontario basin to a southern limit that varied between a few hundred metres and several kilometres from the escarpment. The beach thus formed exists now as a well-defined feature along which runs Regional Road 81 (formerly Hwy 8). Between the beach and present day Lake Ontario deposits of silt were laid down over the 500 – 600 year life of the lake. In some areas sand deposits were laid down.
Rivers entering into Lake Iroquois flowed from south to north and cut through the beach deposits. At present day Homer (South east St. Catharines), a large baymouth bar was developed.
When Lake Iroquois drained away with the opening of the St. Lawrence River the water level dropped, exposing the flat lying silts of the lake bed and is referred to by some as The Fruit Belt. The positioning of lacustrine silt over the basal till can best be seen in the bluffs that now form the southern shoreline of Lake Ontario. The existing rivers began to downcut again to reach the new lower level of the lake. Twelve Mile Creek is an example of this. Where the rivers enter into Lake Ontario baymouth bars have developed with lagoons such as Martindale Pond trapped behind them.
Above the escarpment is evidence of an older post glacial lake called Lake Warren which had a height of 204 metres a.s.l. It existed while the ice still topped the
escarpment and drained southward to the Mississippi River. Its bed is known today as the Haldimand Clay Plain. Running parallel to the escarpment and just to the south is a ridge of unconsolidated material known as the Vinemount Moraine. It is best seen as one travels northward on Regional Road 24.
One feature of note is the Fonthill Kame Delta which was developed in Lake Warren by a river running off the ice. The delta has its highest point at Lookout Point where the river exited the ice. It grades southwest to a point near Fenwick where the edge can be determined by the sandy nature of the soil.
The post glacial clays of the Haldimand Clay Plain deepen southward toward the Wainfleet Bog and Onondaga Escarpment. An appreciation of their depth can be felt as one descends into the tunnel that passes under the Welland Canal on Townline Road. Here the sharp contact between the bedrock of the Salina Formation and the overlying till can be seen.
Bedrock Geology of South Ohnia:kara
The southern portion of the study area is underlain by sedimentary rocks laid down in shallow seas during the Silurian and Devonian Periods (440 to 350 million years ago). These are in turn overlain by glacial and post-glacial deposits that will be described later. South of the Welland River the Upper Silurian Salina Formation forms a belt 9.5 to 26 kilometres in width. The Salina Formation consists of grey and red shale, grey-brown dolomite, minor limestone and, in places, evaporates of salt, anhydrite and gypsum.
These are in turn overlain by a narrow band of the Bertie Formation that extends from a point approximately 8 kilometres north of Lake Erie southward to outcrops of the Onondaga Escarpment. This escarpment, approximately 4 kilometres north of Lake Erie, forms a discontinuous feature running from Fort Erie to beyond Dunnville. The Bertie Formation consists of massive bedded brown dolostone with minor thin-bedded shaley dolomite.
The Middle Devonian Bois Blanc Formation rests unconformably on the Bertie Formation and forms a band 5 to 16 kilometres wide ultimately dipping southward beneath the waters of Lake Erie. It consists of medium brownish grey, medium crystalline, medium to thin-bedded cherty limestone. The Bois Blanc Formation forms the cap-rock of the Onondaga Escarpment. It is highly fossiliferous and is exposed as rock beaches along many stretches of Lake Erie.
The exposed portions of the Onondaga Escarpment form local features of note. These include the exposures just north of Port Colborne on the West Side Road that marks the boundary of the Wainfleet Bog, and Highway 140 at Chippawa Road. Further east it provides the route of the scenic Ridge Road north of Ridgeway and the Battle of Ridgeway exposure on Highway 3. Where the escarpment is exposed the overburden is thin to absent but thickens southward in the direction the rocks dip.
The Bois Blanc Formation is quarried for crushed stone in operations on both the east and west sides of Port Colborne. Along with the active operations there are many abandoned quarries along the escarpment.
The bedrock formations have a general northeast to southwest dip of 3.75 to 9 metres per kilometer towards a low point known as the Michigan Basin.
Surface Geology of South Ohnia:kara
The surface geology consists of glacial and post-glacial deposits. During the retreat of the last continental ice sheet the study area was inundated by a series of post glacial lakes beginning 12,900 years ago with the formation of post-glacial Lake Warren. It had a height of 204 metres a.s.l. (above sea level). It was followed by two lower phases known as Lakes Grassmere and Lundy at 195 and 189 metres a.s.l.
With the retreat of the ice into the Lake Ontario Basin about 12,500 years ago Lake Warren and its lower levels drained northward over the Niagara Escarpment via a short lived lake known as Lake Tonawanda. Below and north of the Niagara Escarpment the basin was filled by Lake Iroquois that reached a height of 102 metres a.s.l.
When Lake Warren drained away to become early Lake Erie some remnants of its waters were trapped between the land rising to the Niagara Escarpment in the north and the face of the Onondaga Escarpment to the south. These entrapments became the present day Wainfleet Bog, Humberstone Marsh, Willoughby Marsh and numerous other small wetlands. Prior to the construction of the Welland Canals drainage from these wetlands was eastward toward the Niagara River.
Once the Welland Canals and the Feeder Canal were constructed drainage out of the Wainfleet Bog was accelerated and rerouted into the canals. Drainage projects to facilitate agriculture further reduced the extent of the wetlands. Today, only areas east of the canal now drain to the Niagara River. Those west of the canal drain either into it or down the power canal in Niagara Falls via the Welland River. South of the Onondaga Escarpment a few short streams drain into Lake Erie.
Today, those areas of the former bed of Lake Warren that completely drained away several thousand years ago are covered with deep clay deposits characteristic of a lake bottom. They are referred to as the Haldimand Clay plain.
In the north portions of the Haldimand Clay Plain the soils are described as Pedalfer (formerly Grey Brown Podzols).
Those areas that were the remnant wetlands of Lake Warren are covered by organic soils derived from deposits of peat and other vegetation characteristic of bogs and marshes. The post-glacial clay deposits are buried beneath them. The depths of the deposits vary in thickness but in general are deepest just north of the Onondaga Escarpment, thinning as they extend northward.
The soils that developed on the poorly drained areas in the southeast portion of the study area are Humic Gleysols.
West of the Wainfleet Bog is an extensive sand plain extending all the way to the Grand River.
Along stretches of the Lake Erie shore are sand dunes, notably in the areas east and west of the entrance to the Welland Canal and at Point Abino. The sand dunes are a result of materials blowing out of the exposed bed of a smaller early phase of Lake Erie. These dunes have migrated inland ahead of the expanding lake. They have been stabilized by vegetation and their highest point today is known as Sugarloaf Hill.
Beaches along the Lake Erie shoreline consist of sand in some areas and exposed bedrock in others. Generally the sand beaches are located in the bays while the
intervening headlands are bedrock. This is the result of wave action by the lake waters. Numerous large boulders can often be found sitting on the surface of the bedrock beaches. These are glacial erratics left behind by the retreating glacier. The surface of the exposed bedrock shows long linear scratches extending from northeast to southwest. These are the result of gouging by rocks frozen into the ice as the glacier advanced.
In all areas the present day soils sit unconformably on the bedrock surface. They are derived from transported materials and do not exhibit the C horizon gradation from bedrock to regolith characteristic of soils which have developed “in situ”. Instead the C horizon is derived from glacial till.