User:RockySurfaces/Oak Ridges Moraine

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Oak Ridges Moraine

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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 km2 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 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 meter thick glacial derived sediments of the moraine lies thick bedrock successions of Precambrian rocks and up to 200 meters of Ordovician aged rock (see bedrock 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). 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 below).

At present many large rivers have eroded the landscape to its current form during outwash of glacial melting, or by deposition of sediment into lower lying areas of paleo river valleys.

The many rivers and lakes of this region are key to the supply of water to aquifers for recharge or human consumption. Presence of lakes, rivers, wetlands, springs and aquifers support the vast and complex network of ways in which water is stored of transferred in the area. 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).

Urban expansion may also put stresses on local ecosystems and limit the extent and diversity of wildlife, especially those considered to be at risk. Being a mainly forested ecosystem, this moraine system is habitat to various species of butterfly, salamander and birds; trees including Elm, Red or Silver Maple, Hemlock, White Cedar or Black Ash; and a varying diversity of shrubbery and grasses.

Bedrock geology of the moraine consists of a crystalline Precambrian basement sitting below up to 200 meters of Ordovician aged shales and limestones. Above these are a 150 to 200 meter thick stratigraphic record from glacial advance, meltwater outwash flooding, and river valley erosion, all depositing sediment over the existing terrain.

For the past 50 years this area has been host to research projects about the origins of this landscape. In the 1990's there came some important origin theories as to the formation of different sections of the moraine. Research in the 2020's shifts the focus to resource management and conservation methods to reduce the impact of the human development pressures from large cities.

Physiography
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.

Geology
Glacial Sediments

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 meters thick in some places. Extensive research in the moraine area indicate there may be 6 different period 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 meters 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 meters thick. This unit is thought to extend 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 meters of gravels or 10 to 75 meter sands that decrease in grain size during later deposition 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 stratigraphic package start as coarse sands and gravels whereas upper sediments are interbedded fine sands and silts. There may also be sequences of sediments decreasing in size from medium sands to silts and clays up to 10's of meters thick. Above these sediments lie clayey-silt to silt till of the Halton Till, at thicknesses reaching 20 meters.

Glacial lake sediments cap the entire sequence of stratigraphy in the Oak Ridges Moraine, glacial Lakes Algonquin and Iroquois. The main depositional ingredient form these lakes is silt with some clay content, as layers of 2 to 20 meters thick. Glacial sediments are subject to modern erosional forces and valley cutting processes, removing previously laid sediments and placing them further along the river path, at the mouth during lowering of lake levels.

Unconformity

At the Oak Ridges Moraine system, rocks from the Ordovician Period underlie the sediment and are a large part of the bedrock geology, aside from the presence of some older basement rock beneath. From the basement rocks to the overlying stratigraphic successions is an unconformity (a gap in the geologic record) where many millions of years of depositional or crystalline record are erased. A large time gap is important in this context to correlate where and when this event occurred with respect to both local and surrounding geology of the lithostratigraphic record. Cause of this sedimentary gap may originate from a couple large scale meltwater events, the Algonquin and Ontarian erosional floods from melting glaciers of the Late Wisconsinan glaciation.

Paleozoic bedrock

Basement layers are composed of Early Ordovician aged dolostone as a first sequence only to be stripped away by erosion in the Middle Ordovician. Sea transgression in the Middle Ordovician brought in a second sequence of deposition as clastic and carbonate sediments above this new unconformity due to sea regression between the Early and Middle Ordovician. A third depositional sequence is found in the Late Ordovician, separated from the Middle Ordovician by local erosion and clastic sediments, consists of a shale base topped with more shale interbedded with limestone and calcareous siltstones. Above this sits an unconformity due to sea regression in the Late Ordovician to Early Silurian time. Large gaps in deposition from the Early Silurian through Mesozoic time allowed large scale erosion to occur in this geographic region to the onset of Quaternary glaciation and subsequent sediment deposition. A 1997 report from the Geological Survey of Canada estimates the bedrock thickness to range between 50 and 500 meters thick, below approximately 200 meters of Pleistocene aged sediments.

Precambrian bedrock

Rocks from the Grenville Province of Precambrian age lie below Ordovician aged limestones and shales in the Oak Ridges Moraine area. These come from a period of continental scale orogeny in eastern North America about 1.2 to 1.3 billion years ago. This area of the Grenville Province is mainly composed of metamorphosed gneiss and mylonite, while also including intrusions of granitic composition as well. Both the metamorphic and igneous rocks are able to better withstand erosional forces from the advancing ice sheets compared to some softer rock types. Softer metamorphic rocks of the Precambrian basement include marbles or metaturbidites, both from sedimentary origin.

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-expand upon geological concepts such as unconformity and add importance in relation to where is sequence and causes

-expand upon entire draft about geology and find newer content to aide in accurate and up to date descriptions of ORM

-possibly create subsections with relevant information to expand details of periods and geological processes or sedimentary accumulations in each

-possible reworking of other major sections (Physiography, Ecology, Development Pressures) to aide in expanding amount of material in each section

-potential equity gap of being home to 100's of 000's people and could use more information about supply/ demand of water and material resources