Cheltemham-Badlands
The Badlands are an exposed section of the Queenston Formation, which was formed between 420 and 415 million years ago during the Middle and Late Ordovician periods.[8] During this period, the collision of Gondwana into Laurentia resulted in the formation of the Taconic Mountains.[9][10] The creation of these mountains also resulted in several basins, such as the Appalachian Basin and the Michigan Basin, in the interior of Laurentia.[8] Over time, the erosion of these mountains resulted in the formation of the Queenston Delta,[11] which drained into the Michigan Basin.[8] The deposition of mud eroded from the mountains during the Middle and Late Ordovician period formed the Queenston Shale.[9] The continuous deposition of the mud and sand from the mountains extended the Queenston Delta further into the Michigan Basin; however, as the mountains continued to erode, less and less mud and sand reached the delta, resulting in the formation of inter-layered beds of sandstone, shale and limestone throughout the Silurian period.[8] These inter-layered beds that overlay the Queenston Shale include Lower Silurian sandstones, such as the Whirlpool Formation, and dolostones, such as the Manitoulin Formation, which can be seen along the Niagara Escarpment.[12] The Queenston Shale overlies the shales and the inter-bedded limestones of the Georgian Bay Formation.[12] At the badlands site, glacial erosion of the overlaying sandstones and dolostones has caused the Queenston Formation to be the first layer of rock to underlie the soil.[8]
Queenston Formation[edit]
The Queenston Formation is characterized by its brick-red to maroon shales which are interlaced with smaller amounts of green shale, sandstone, and limestone.[9][12] The darker red shale is the result of introduction of the terrestrial muddy deposits into the Queenston Delta.[9][1] The shale beds are thin and fractured, with a structural dip westward towards the centre of the Michigan Basin.[9] Shales in the Queenston Formation are considered to have high density, low cation exchange capacities, and low water content.[13][1] The lighter red shale, which sits on top of the darker shale, is highly bioturbated and is composed of a combination of bioclasts and the reworked pieces of the darker shale below.[1] The distinct red, due to iron-oxide, colouring of these rocks is broken up with green-grey bands. The green-grey bands are thought to be caused by a change in the oxidation rate due to circulating groundwater[1] or bleaching by acidic groundwater.[11]
The lithology of the lighter and darker red shales at the Cheltenham Badlands site is categorized as smectite-poor, due to the clay content, ranging from 58% to 68% clay, and the dominant clay minerals, illite and chlorite.[1][11] The non-swelling illite in the shales can cause high pressures with repeated wetting and drying, resulting in failure of the shale structures.[1] The difference in the water absorption between illite and chlorite clay minerals can cause differences in swelling which results in larger shards of the shales breaking into smaller shards.[1] Once the shards are reduced to tiny and flaky shards, they become compacted and smooth; however, surface cracks during drying periods can lead to further erosion.[1]
Cheltemham-Badlands
The Badlands are an exposed section of the Queenston Formation, which was formed between 420 and 415 million years ago during the Middle and Late Ordovician periods.[8] During this period, the collision of Gondwana into Laurentia resulted in the formation of the Taconic Mountains.[9][10] The creation of these mountains also resulted in several basins, such as the Appalachian Basin and the Michigan Basin, in the interior of Laurentia.[8] Over time, the erosion of these mountains resulted in the formation of the Queenston Delta,[11] which drained into the Michigan Basin.[8] The deposition of mud eroded from the mountains during the Middle and Late Ordovician period formed the Queenston Shale.[9] The continuous deposition of the mud and sand from the mountains extended the Queenston Delta further into the Michigan Basin; however, as the mountains continued to erode, less and less mud and sand reached the delta, resulting in the formation of inter-layered beds of sandstone, shale and limestone throughout the Silurian period.[8] These inter-layered beds that overlay the Queenston Shale include Lower Silurian sandstones, such as the Whirlpool Formation, and dolostones, such as the Manitoulin Formation, which can be seen along the Niagara Escarpment.[12] The Queenston Shale overlies the shales and the inter-bedded limestones of the Georgian Bay Formation.[12] At the badlands site, glacial erosion of the overlaying sandstones and dolostones has caused the Queenston Formation to be the first layer of rock to underlie the soil.[8]
Queenston Formation[edit]
The Queenston Formation is characterized by its brick-red to maroon shales which are interlaced with smaller amounts of green shale, sandstone, and limestone.[9][12] The darker red shale is the result of introduction of the terrestrial muddy deposits into the Queenston Delta.[9][1] The shale beds are thin and fractured, with a structural dip westward towards the centre of the Michigan Basin.[9] Shales in the Queenston Formation are considered to have high density, low cation exchange capacities, and low water content.[13][1] The lighter red shale, which sits on top of the darker shale, is highly bioturbated and is composed of a combination of bioclasts and the reworked pieces of the darker shale below.[1] The distinct red, due to iron-oxide, colouring of these rocks is broken up with green-grey bands. The green-grey bands are thought to be caused by a change in the oxidation rate due to circulating groundwater[1] or bleaching by acidic groundwater.[11]
The lithology of the lighter and darker red shales at the Cheltenham Badlands site is categorized as smectite-poor, due to the clay content, ranging from 58% to 68% clay, and the dominant clay minerals, illite and chlorite.[1][11] The non-swelling illite in the shales can cause high pressures with repeated wetting and drying, resulting in failure of the shale structures.[1] The difference in the water absorption between illite and chlorite clay minerals can cause differences in swelling which results in larger shards of the shales breaking into smaller shards.[1] Once the shards are reduced to tiny and flaky shards, they become compacted and smooth; however, surface cracks during drying periods can lead to further erosion.[1]