What depositional environment does black shale form in?
anoxic marine environment
The black shales in the Qusseir area (Duwi Formation, Campanian–Maastrichtian) were deposited in an anoxic marine environment, and are remarkably high in their enrichment of redox-sensitive and sulfide-forming trace metals.
How is black shale formed?
They were deposited under anaerobic conditions, but the exact mode of origin is debated. Some geologists hold that the conditions were produced at depth by a stable stratification of lighter, fresher water overlying and sealing off from the atmosphere a more saline, stagnant layer.
What does black shale indicate?
Black Shales are fine grained, generally organic carbon-rich sedimentary rocks that primarily consist of a mixture of clay minerals, quartz silt, organic particles (mostly planktonic algae and plant debris), and kerogen.
What type of sedimentary rock is black shale?
Shale is a laminated or fissile clastic sedimentary rock that composed of predominance of silt and clay other minerals , especially quartz and calcite.
Which factor was important for the formation of black shales?
Some researchers believe that the high organic matter content in black shales can be ascribed primarily to the elevated preservation efficiency of organic matter in the ocean, which was directly caused by oxygen deficiency resulting from seawater stagnation.
What is the composition of shale?
The data derived from these analyses indicate that the average mineralogical composition of shale is: 30.8 percent quartz, 4.5 percent feldspar, 3.6 percent carbonate, <0.5 percent iron oxides, 60.9 percent clay minerals, 1 percent organic material, and 2 per- cent other materials.
How shale rock is formed?
Shale is a fine-grained sedimentary rock that is formed when silt and clay are compressed. It is composed of many thin layers, and it readily splits into thin pieces where these layers meet—making it a relatively brittle stone.
What is shale geology?
Shale is a fine-grained, sedimentary rock formed as a result of the compaction of clay, silt, mud and organic matter over time and is usually considered equivalent to mudstone.
Is black shale clastic?
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.
What are the different types of shale?
They are formed from silts and clays that have been deposited and compacted or hardened into rocks. On the basis of texture therefore, the most common types of shales are silty shale (silt dominant) and clay shale (clay dominant). These two types of shales are also called argillaceous shales.
What is the characteristic of shale?
Shale is a fine-grained rock made from compacted mud and clay. The defining characteristic of shale is its ability to break into layers or fissility. Black and gray shale are common, but the rock can occur in any color. Shale is commercially important.
What is shale made from?
Shale is composed mainly of clay-size mineral grains, which are usually clay minerals such as illite, kaolinite, and smectite. Shale usually contains other clay-size mineral particles such as quartz, chert, and feldspar.
Is black shale coal?
Fresh coal is a jet-black rock that is noticably less dense than most other rocks. In the field, however, weathering often gives the coal a greyish, yellowish, or rust-colored coloring. If you see a dark gray or black sedimentary layer in an outcrop, it is probably either coal or black shale.
Is black shale a terrigenous sedimentary rock?
Likewise, shales are terrigenous rocks composed of clay- and silt-size particles.
Where is a shale formed?
Shale is a geological rock formation rich in clay, typically derived from fine sediments, deposited in fairly quiet environments at the bottom of seas or lakes, having then been buried over the course of millions of years.
What is shale composed of?
How is shale rock formed?
Shales are often found with layers of sandstone or limestone. They typically form in environments where muds, silts, and other sediments were deposited by gentle transporting currents and became compacted, as, for example, the deep-ocean floor, basins of shallow seas, river floodplains, and playas.
What is Terrigenous deposit?
Terrigenous deposits are deposits of mud, sand, gravel, and volcanic materials, derived from the denudation of continental rocks. The main sources of Terrigenous deposits are terrestrial sediments. They are mainly found on the Continental shelf.
How is shale formed in the rock cycle?
Shale is a fine-grained sedimentary rock that is formed by the compression of muds. This type of rock is composed primarily of quartz and minerals that are found in clay. Shales can be broken easily into thin, parallel layers. Shale is ground up for use in making bricks and cement.
What are black shales?
Shales that are rich in organic matter (>5%) are known as black shales. Black color is given to these rocks by organic matter. Organic matter should be decomposed in normal conditions by bacteria, but high productivity, rapid deposition and burial or lack of oxygen may preserve it. Pyrite is a common sulfide mineral in black shales.
Where was the black shale deposited?
The black shale was deposited at a variety of paleodepths (e.g., Maniki Plateau, Shatsky Rise, Resolution Guyot, deeper parts of the Mid-Pacific Mountains, Calera Limestones of California) which extend down to >4.5 km. The depth independence of the early Aptian event resolves an older discussion regarding the paleodepths of black shale deposition.
What is the difference between siliceous and black shale?
The shale with rich SiO 2 (sometimes more than 85%) is classified as siliceous shale. Shale with rich carbonaceous organic matter is classified as carbonaceous shale. Shale with a lot of scattered organic matter and iron sulfide is defined as black shale or organic-rich shale ( Zhang et al., 1987 ).
What is the depositional environment of a shale?
When the dominant organic matter content is from plant fragments such as pollen grains, stems and leaves, the shale is classified as carbonaceous, and the depositional environment is usually continental (lacustrine) or transitional (deltaic or lagoon).