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Shale is characterized by its tendency to split into thin layers less than one centimeter in thickness. This property is called fissility. [1] Shale is the most common sedimentary rock. [2] The term shale is sometimes applied more broadly, as essentially a synonym for mudrock, rather than in the narrower sense of clay-rich fissile mudrock. [3]
Although black shale is the dominant lithology, it also contains lighter shales and interbedded limestone layers due to sea level variation during its deposition almost 72] The black shale was deposited in relatively deep water devoid of oxygen, and is only sparsely fossiliferous.
[1] [2] The most common types include coal, lignite, oil shale, or black shale. [2] The organic material may be disseminated throughout the rock giving it a uniform dark color, and/or it may be present as discrete occurrences of tar, bitumen, asphalt, petroleum, coal or carbonaceous material.
These concretions occur in the black shale in the lower part of the Kettle Point Formation. Because the concretions are so much harder than the enclosing weakly indurated shale, they readily weather out of the shale along the shoreline and are incorporated into the rubble mantling the lake bottom adjacent to the outcrop. [3] [5]
The oil shale yield varies laterally, and may be as little as 7% for the lower layer and 4% for the upper layer. The formation is a very fine grained and laminated deposit ranging in color from dark gray to brown to black. While 60–70% of the shale consists of clay minerals, the balance is made up of organic matter. [3]
Iron- and sulfur-based Anoxygenic photosynthesis life forms that lived from 3.80 to 3.85 billion years ago on Earth produced an abundance of black shale deposits. These shale deposits increase heat flow and crust buoyancy, especially on the sea floor, helping to increase plate tectonics. Talc is another organic mineral that helps drive plate ...
There are many varieties of shale, including calcareous and organic-rich; however, black shale, or organic-rich shale, deserves further evaluation. In order for a shale to be a black shale, it must contain more than one percent organic carbon. A good source rock for hydrocarbons can contain up to twenty percent organic carbon.
The Alum Shale Formation (also known as alum schist and alum slate) is a formation of black shale of Miaolingian (Middle Cambrian) to Tremadocian (Lower Ordovician) in age found predominantly in southern Scandinavia. [1] [2] It is shale or clay slate containing pyrite.