Mudrock

A few important hurdles to their classification include the following: Mudrocks make up 50% of the sedimentary rocks in the geologic record and are easily the most widespread deposits on Earth.

[1] With increased pressure over time, the platey clay minerals may become aligned, with the appearance of parallel layering (fissility).

This finely bedded material that splits readily into thin layers is called shale, as distinct from mudstone.

They can also contain the following particles at less than 63 micrometres: calcite, dolomite, siderite, pyrite, marcasite, heavy minerals, and even organic carbon.

In order for a rock to be considered a claystone, it must consist of at least fifty percent clay (phyllosilicates), whose particle measures less than 1/256 of a millimeter in size.

However, quartz, feldspar, iron oxides, and carbonates can also weather to the sizes of typical clay mineral grains.

This means a clay particle will travel 1000 times further at constant water velocity, thus requiring quieter conditions for settlement.

Silt is believed to be the product of physical weathering, which can involve freezing and thawing, thermal expansion, and release of pressure.

One of the highest proportions of silt found on Earth is in the Himalayas, where phyllites are exposed to rainfall of up to five to ten meters (16 to 33 feet) a year.

Shale is a fine grained, hard, laminated mudrock, consisting of clay minerals, and quartz and feldspar silt.

Generally, black shale receives its influx of carbon from algae, which decays and forms an ooze known as sapropel.

Southeast Asia, including Bangladesh and India, receives high amounts of rain from monsoons, which then washes sediment from the Himalayas and surrounding areas to the Indian Ocean.

The Amazon system, for example, has the third largest sediment load on Earth, with rainfall providing clay, silt, and mud from the Andes in Peru, Ecuador, and Bolivia.

[6] Rivers, waves, and longshore currents segregate mud, silt, and clay from sand and gravel due to fall velocity.

The Ganges in India, the Yellow in China, and the Lower Mississippi in the United States are good examples of alluvial valleys.

Delta environments are found at the mouth of a river, where its waters slow as they enter the ocean, and silt and clay are deposited.

The Amazon River supplies 500 million tons of sediment, which is mostly clay, to the coastal region of northeastern South America.

[4] 70-percent of the Earth's surface is covered by ocean, and marine environments are where we find the world's highest proportion of mudrocks.

There are various environments in the oceans, including deep-sea trenches, abyssal plains, volcanic seamounts, convergent, divergent, and transform plate margins.

The world's rivers transport the largest volume of suspended and dissolved loads of clay and silt to the sea, where they are deposited on ocean shelves.

[8] We can imagine the beginning of a mudrock's life as sediment at the top of a mountain, which may have been uplifted by plate tectonics or propelled into the air from a volcano.

The products of weathering, including particles ranging from clay to silt, to pebbles and boulders, are transported to the basin below, where it can solidify into one if its many sedimentary mudstone types.

Eventually, the mudrock will move its way kilometers below the subsurface, where pressure and temperature cook the mudstone into a metamorphosed gneiss.

[4] Mudrocks form in various colors, including: red, purple, brown, yellow, green and grey, and even black.

Inevitably, mudrock preserved countless specimens from the late Jurassic, roughly 150 million years ago.

Metamorphosed shale can hold emerald and gold,[6] and mudrocks can host ore metals such as lead and zinc.

Mudrocks are important in the preservation of petroleum and natural gas, due to their low porosity, and are commonly used by engineers to inhibit harmful fluid leakage from landfills.

Interbedded between the high-energy events are mudrock formations that have recorded quieter, normal conditions in our Earth's history.

Sandstones provide the big tectonic picture and some indications of water depth; mudrocks record oxygen content, a generally richer fossil abundance and diversity, and a much more informative geochemistry.