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A typical shale is composed of about 58% clay minerals, 28% quartz, 6% feldspar, 5% carbonate minerals, and 2% iron oxides. [8] Most of the quartz is detrital (part of the original sediments that formed the shale) rather than authigenic (crystallized within the shale after deposition). [9]
The Marcellus Shale was formed from the very first deposits in a relatively deep, sediment- and oxygen-starved , trough that formed parallel to the mountain chain. [111] These clastic fragments of rock were carried in braided streams to the ancient Catskill Delta , a river delta probably similar to the present day Niger Delta of Africa.
For example, concretions in sandstones or shales are commonly formed of a carbonate mineral such as calcite; those in limestones are commonly an amorphous or microcrystalline form of silica such as chert, flint, or jasper; while those in black shale may be composed of pyrite. [18]
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.
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.
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 Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from Pembina Valley in Canada [2] to New Mexico. The Pierre Shale was described by Meek and Hayden in 1862 in the Proceedings of the Academy of Sciences (Philadelphia).
Organic-rich black shales formed, ultimately producing oil and gas which is now extracted. Black shales hold broadly similar fossil assemblages to Silurian and Ordovician deposits, but have particularly well preserved calcareous stromatoporoid sponge fossils, which are found at the Falls of the Ohio close to Louisville.