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Oak Ridges Moraine
The Oak Ridges Moraine is an ecologically important geological landform in the Mixedwood Plains of south-central Ontario, Canada. The moraine covers a geographic area of 1,900 square kilometres (730 sq mi) between Caledon and Rice Lake, near Peterborough. One of the most significant landforms in southern Ontario, the moraine gets its name from the rolling hills and river valleys extending 160 km (99 mi) east from the Niagara Escarpment to Rice Lake, formed 12,000 years ago by advancing and retreating glaciers (see geological origins, below) during the last glaciation period. Below the approximately 200 metre thick glacial derived sediments of the moraine lies thick bedrock successions of Precambrian rocks and up to 200 metres of Ordovician aged rock (see geology below), capped by a regional unconformity of erosion and non-deposition to the Quaternary period. Rivers and lakes scatter the landscape and are important for creating habitat for the rich diversity of species of animals, trees and shrubbery (see ecology). These are also the supply of fresh water to aquifers in the moraine through complex subterranean connections (see hydrology). Construction development nearby, and with expansion of communities around the moraine in need of potable water, it is a contested site in Ontario, since it stands in the path of major urban development (see political action). Conservation of the moraine is thus an important step for keeping aquifers in a safe drinkable condition while also protecting the natural ecosystems surrounding and within the moraine (see conservation). This region has been subject to multiple decades of scientific research to study the origins of formation, and how early communities used the land. A larger focus currently is how to source potable water without removing the aquifer entirely (see research section).
The Oak Ridges Moraine is a pair of large ridges composed of four elevated wedges. It is bounded to the west by the Niagara Escarpment, a cuesta which was critical to the formation of the moraine, and to the east by the Trent River and Rice Lake. The four wedges (Albion, Uxbridge, Pontypool and Rice Lake from west to east) formed in stages, though some synchronous formation also occurred at an early period of formation. The moraine peaks at the Uxbridge wedge, generally rising from east to west, a result of the moraine's west-to-east formation. That is, the western portion of the moraine received earlier and more frequent sedimentary deposition than the eastern portion, as the ice lobes which controlled the moraine's eastern formation slowly retreated. The Rice Lake wedge is separated from the other wedges where the Oak Ridges Moraine intersects Rice Lake. As the moraine is a local topographic high, streams originating in the lower Oak Ridges Moraine sediment packages, by groundwater movement, either flow south into Lake Ontario or north toward Lake Simcoe or Georgian Bay through large river valleys carved during melting of glaciers.
To the north are drumlinized uplands, referred to as the Peterborough drumlin field, which may continue south of Rice Lake and the Rice Lake wedge. Near the Rice Lake wedge and Peterborough drumlin field are a couple of low-lying terrain plains and small hills on bedrock basement.
The Oak Ridges Moraine probably formed in the Late Wisconsin glacial period. Ice melt from the Niagara Escarpment flowed into the western boundaries of the moraine, wherein conduits beneath the ice expanded to form a west-to-east passage between the main Laurentide Ice Sheet and a mass of ice in the Lake Ontario basin.
Stratified sediment was deposited rapidly on the high-relief erosional surface. Up to 150 metres (490 ft) in some areas, the deposits occurred on surfaces defined by highly eroded channels and drumlin uplands. The channel tunnels were primarily created by the erosion from glacial rivers, a typical process before moraine formation.
Characteristic of this moraine is the transition of deposition layers from glaciofluvial to glaciolacustrine. Sedimentary glaciofluvial areas form the core of the Oak Ridges Moraine, though restricted to subglacial cavity fills of confined subaqueous fans. Overlaying this core is a glaciolacustrine sedimentary layer that is younger and topographically lower, principally in the delta and basin areas of the moraine.
In the late stages of its development, random unstratified accumulation (known as diamicton) occurred along the ice margins. Whereas the glacial river deposits were more substantial by volume, the diamicton deposits represent a greater portion of the moraine's exposed surface. Research suggests that sedimentation occurred in a west to east sequence along the four main sedimentary wedges: Albion, Uxbridge, Pontypool and Rice Lake. The wedges may have formed in a relatively short period of time, perhaps no more than a few hundred years, as indicated by the annual deposition cycles in glacial lakes (known as varves) within the moraine sediments. However, the lowest beds in the moraine may have experienced synchronous sedimentation.
In the area of the Oak Ridges Moraine, glacially derived sediments, mainly of Pleistocene age, may overlie a regional unconformity and lower Newmarket till, up to 200 metres thick in some places. Extensive research in the moraine area indicate there may be 6 different periods of sedimentation from the onset of glaciation. There are lower deposits of sand, silt and clay, which rest directly above the regional time unconformity up to 100 metres (330 ft) thick in some areas. These lower deposits are thought to be proglacial lake derived, and contain from bottom to top: York Till, Don Interglacial beds, Scarborough Formation, Sunnybrook Till and Thorncliffe Formation. Next comes the Newmarket Till of stony, silty sand and sandy-silt diamicton ranging from 5 to 50 metres (16 to 164 ft) thick and is thought to extend southward under Lake Ontario. Cutting into the Newmarket Till is another regional unconformity, which led to coarse grained channel fill sediments. Some channel fills are 10 to 25 metres of gravels or 10-to-75-metre (33 to 246 ft) sands that decrease in grain size during later deposition following a period of slowing meltwater runoff. Channel fill sediments comprise the base of Oak Ridges Moraine sediments, atop the unconformity. Lower deposits of the Oak Ridges Moraine sediments stratigraphic package start as coarse sands and gravels whereas upper sediments are interbedded fine sands and silts with channel fill. There may also be sequences of sediments decreasing in size from medium sands to silts and clays up to ten's of metres thick. Above these sediments lie clayey-silt to silt till of the Halton Till, at thicknesses reaching 20 metres (66 ft). The Halton Till is not present over the entire expanse of the moraine, cropping out locally and interspersed.
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Oak Ridges Moraine
The Oak Ridges Moraine is an ecologically important geological landform in the Mixedwood Plains of south-central Ontario, Canada. The moraine covers a geographic area of 1,900 square kilometres (730 sq mi) between Caledon and Rice Lake, near Peterborough. One of the most significant landforms in southern Ontario, the moraine gets its name from the rolling hills and river valleys extending 160 km (99 mi) east from the Niagara Escarpment to Rice Lake, formed 12,000 years ago by advancing and retreating glaciers (see geological origins, below) during the last glaciation period. Below the approximately 200 metre thick glacial derived sediments of the moraine lies thick bedrock successions of Precambrian rocks and up to 200 metres of Ordovician aged rock (see geology below), capped by a regional unconformity of erosion and non-deposition to the Quaternary period. Rivers and lakes scatter the landscape and are important for creating habitat for the rich diversity of species of animals, trees and shrubbery (see ecology). These are also the supply of fresh water to aquifers in the moraine through complex subterranean connections (see hydrology). Construction development nearby, and with expansion of communities around the moraine in need of potable water, it is a contested site in Ontario, since it stands in the path of major urban development (see political action). Conservation of the moraine is thus an important step for keeping aquifers in a safe drinkable condition while also protecting the natural ecosystems surrounding and within the moraine (see conservation). This region has been subject to multiple decades of scientific research to study the origins of formation, and how early communities used the land. A larger focus currently is how to source potable water without removing the aquifer entirely (see research section).
The Oak Ridges Moraine is a pair of large ridges composed of four elevated wedges. It is bounded to the west by the Niagara Escarpment, a cuesta which was critical to the formation of the moraine, and to the east by the Trent River and Rice Lake. The four wedges (Albion, Uxbridge, Pontypool and Rice Lake from west to east) formed in stages, though some synchronous formation also occurred at an early period of formation. The moraine peaks at the Uxbridge wedge, generally rising from east to west, a result of the moraine's west-to-east formation. That is, the western portion of the moraine received earlier and more frequent sedimentary deposition than the eastern portion, as the ice lobes which controlled the moraine's eastern formation slowly retreated. The Rice Lake wedge is separated from the other wedges where the Oak Ridges Moraine intersects Rice Lake. As the moraine is a local topographic high, streams originating in the lower Oak Ridges Moraine sediment packages, by groundwater movement, either flow south into Lake Ontario or north toward Lake Simcoe or Georgian Bay through large river valleys carved during melting of glaciers.
To the north are drumlinized uplands, referred to as the Peterborough drumlin field, which may continue south of Rice Lake and the Rice Lake wedge. Near the Rice Lake wedge and Peterborough drumlin field are a couple of low-lying terrain plains and small hills on bedrock basement.
The Oak Ridges Moraine probably formed in the Late Wisconsin glacial period. Ice melt from the Niagara Escarpment flowed into the western boundaries of the moraine, wherein conduits beneath the ice expanded to form a west-to-east passage between the main Laurentide Ice Sheet and a mass of ice in the Lake Ontario basin.
Stratified sediment was deposited rapidly on the high-relief erosional surface. Up to 150 metres (490 ft) in some areas, the deposits occurred on surfaces defined by highly eroded channels and drumlin uplands. The channel tunnels were primarily created by the erosion from glacial rivers, a typical process before moraine formation.
Characteristic of this moraine is the transition of deposition layers from glaciofluvial to glaciolacustrine. Sedimentary glaciofluvial areas form the core of the Oak Ridges Moraine, though restricted to subglacial cavity fills of confined subaqueous fans. Overlaying this core is a glaciolacustrine sedimentary layer that is younger and topographically lower, principally in the delta and basin areas of the moraine.
In the late stages of its development, random unstratified accumulation (known as diamicton) occurred along the ice margins. Whereas the glacial river deposits were more substantial by volume, the diamicton deposits represent a greater portion of the moraine's exposed surface. Research suggests that sedimentation occurred in a west to east sequence along the four main sedimentary wedges: Albion, Uxbridge, Pontypool and Rice Lake. The wedges may have formed in a relatively short period of time, perhaps no more than a few hundred years, as indicated by the annual deposition cycles in glacial lakes (known as varves) within the moraine sediments. However, the lowest beds in the moraine may have experienced synchronous sedimentation.
In the area of the Oak Ridges Moraine, glacially derived sediments, mainly of Pleistocene age, may overlie a regional unconformity and lower Newmarket till, up to 200 metres thick in some places. Extensive research in the moraine area indicate there may be 6 different periods of sedimentation from the onset of glaciation. There are lower deposits of sand, silt and clay, which rest directly above the regional time unconformity up to 100 metres (330 ft) thick in some areas. These lower deposits are thought to be proglacial lake derived, and contain from bottom to top: York Till, Don Interglacial beds, Scarborough Formation, Sunnybrook Till and Thorncliffe Formation. Next comes the Newmarket Till of stony, silty sand and sandy-silt diamicton ranging from 5 to 50 metres (16 to 164 ft) thick and is thought to extend southward under Lake Ontario. Cutting into the Newmarket Till is another regional unconformity, which led to coarse grained channel fill sediments. Some channel fills are 10 to 25 metres of gravels or 10-to-75-metre (33 to 246 ft) sands that decrease in grain size during later deposition following a period of slowing meltwater runoff. Channel fill sediments comprise the base of Oak Ridges Moraine sediments, atop the unconformity. Lower deposits of the Oak Ridges Moraine sediments stratigraphic package start as coarse sands and gravels whereas upper sediments are interbedded fine sands and silts with channel fill. There may also be sequences of sediments decreasing in size from medium sands to silts and clays up to ten's of metres thick. Above these sediments lie clayey-silt to silt till of the Halton Till, at thicknesses reaching 20 metres (66 ft). The Halton Till is not present over the entire expanse of the moraine, cropping out locally and interspersed.