What is carbonaceous shale?

What is carbonaceous shale?

CARBONACEOUS SHALE | Shale is formed from the cementation and lithification of very small grains of rock, commonly mud or clay. The black color of the rock indicates an organic-rich composition. GREAT FOR GEOLOGY CLASSROOMS | Black shale can contain trace amounts of oil, and is studied heavily for this reason.

How is carbonaceous shale formed?

Carbonaceous shales form important petroleum source rock globally. These are black to grey laminated shales, rich in organic content and pyrite. Generally, the shales are formed under reducing and anoxic conditions. When buried deeper at high temperatures, kerogen cracks to bitumen, which degrades to form oil and gas.

Does shale dissolve in water?

A typical shale is composed of about 58% clay minerals, 28% quartz, 6% feldspar, 5% carbonate minerals, and 2% iron oxides. There is evidence that shale acts as a semipermeable medium, allowing water to pass through while retaining dissolved salts.

Where can I find shale rock?

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.

Does shale contain oil?

Oil-bearing shales are underground rock formations that contain trapped petroleum. The petroleum trapped within the rocks is known as “tight oil” and is difficult to extract. Companies extracting tight oil often use hydraulic fracturing (fracking), while companies extracting shale oil most often use heat.

Does shale contain silica?

The common cementing materials are silica, iron oxide and calcite or lime. Accordingly, shales may be classified as siliceous, ferruginous or calcareous (sometimes also called limy), respectively.

What causes Fissility in shale?

Fissility is the result of sedimentary or metamorphic processes. Planes of weakness are developed in sedimentary rocks such as shale or mudstone by clay particles aligning during compaction. Planes of weakness are developed in metamorphic rocks by the recrystallization and growth of micaceous minerals.

How can you tell if a rock is 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.

Where does carbonaceous shale come from in the UK?

In some parts of the UK the natural sand and gravel aggregates contain variable proportions of coal and related materials, including carbonaceous shale. Coals are ranked according to the degree of carbon concentration and the lower ranks, such as bituminous coal and lignite, form weak and porous particles in concrete aggregate.

What kind of rock is carbonaceous shale made of?

Grey and black carbonaceous shale, shale, and grey shaly sandstone are in the lower part, grey and black mudstone is found in the middle part, grey lime mudstone, and shale and shaly sandstone are present in the upper part.

What is the density of pyrite and carbonaceous shale?

Carbonaceous shale density ranges from 2.0 to 2.6, and pure shale, clay, and sandstone have a density of about 2.6. The density of pyrite is about 5.0. The difference in density between pure coal and these impurities, in a liberated state, is sufficient to enable an almost complete separation to be achieved fairly easily.

Why are carbonaceous shales common in the McArthur Basin?

In their paper on the carbonaceous shales of the McArthur Basin, Shen et al. (2002) comment that euxinic conditions were common in marine-connected basins during the Mesoproterozoic, and they suggest that low concentrations of seawater sulfate and reduced levels of atmospheric oxygen at this time are compatible with euxinic deep ocean waters.