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Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the ...
Chalk is a highly porous and permeable rock, and rain falling onto chalk topography percolates directly into the ground, where the chalk layer acts as an aquifer.The groundwater flows through the chalk bedrock, re-emerging lower down the slope in springs.
The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Upper Cretaceous limestone ...
The concept of permeability is of importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, [4] and of groundwater in aquifers. [5]For a rock to be considered as an exploitable hydrocarbon reservoir without stimulation, its permeability must be greater than approximately 100 md (depending on the nature of the hydrocarbon – gas reservoirs with lower ...
Chalk deposits are generally very permeable, so the height of the water table in chalk hills rises in winter and falls in summer. [4] This leads to characteristic chalk downland features such as dry valleys or coombes, and seasonally-flowing streams or winterbournes. The practice of extracting water from this aquifer, in order to satisfy the ...
Chalk – Soft carbonate rock; Chert – Hard, fine-grained sedimentary rock composed of cryptocrystalline silica; Claystone – Clastic sedimentary rock composed primarily of clay-sized particles; Coal – Combustible sedimentary rock composed primarily of carbon; Conglomerate – Sedimentary rock composed of smaller rock fragments
A dry valley may develop on many kinds of permeable rock, such as limestone, chalk, sand stone and sandy terrains that do not regularly sustain surface water flow. Such valleys do not hold surface water because it sinks into the permeable bedrock. There are many examples of chalk dry valleys along the North and South Downs in Southern England.
The Channel Tunnel was constructed in the West Melbury Marly Chalk, a geological formation containing marl beds. This formation was chosen because of its very low permeability, absence of chert, and lack of fissures found in overlying formations. The underlying Glauconitic Marl is easily recognizable in core samples and helped establish the ...