Home > Diagenesis

After deposition, sediments are compacted as they are buried beneath successive layers of sediment and cemented by minerals that precipitate from solution. Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis. Porosity usually decreases during diagenesis, except in rare cases such as dissolution of minerals and dolomitization.

The study of diagenesis in rocks is used to understand the tectonic history they have undergone, the nature and type of fluids that have circulated through them and, from an economic standpoint, allows the assessment of the likelihood of finding various economic minerals and hydrocarbons.

The role of diagenesis in hydrocarbon generation

When animal or plant matter is buried during sedimentation, the constituent organic molecules ( lipids, proteins, carbohydrates and lignin- humic compounds) break down due to the increase in temperatureTemperature is the physical property of a system which underlies the common notions of "hot" and "cold"; the material with the higher temperature is said to be hotter. General description The formal properties of temperature are studied in thermodynamics. and pressurePressure (symbol: p is a measure of force per unit area. where p is the pressure F is the force A is the area Often F is taken to be the of the magnitude of the mean vector force normal to the surface of area A upon which it exerts; the "surface" not nece. This transformation occurs in the first few hundred meters of burial and results in the creation of two primary products: kerogenKerogens are chemical compounds formed by the low-grade metamorphism (i. diagenesis) of organic molecules derived from decaying plant and animal matter. Kerogens are the precursors to hydrocarbons ( fossil fuels). Labile kerogen breaks down to form heavys and bitumenBitumen is a category of organic liquids which are highly viscous, black, sticky and wholly soluble in carbon disulfide. Asphalt and tar are the most common forms of bitumen. In British English, 'bitumen' is often used interchangeably with both 'asphalt's.

It is generally accepted that hydrocarbons are formed by the thermal alteration of these kerogens (the biogenic theory). In this way, given certain conditions (which are largely temperature-dependent) kerogens will break down to form hydrocarbons though a chemical process known as crackingIn petroleum geology and chemistry, cracking is the process whereby complex organic molecules (e. kerogens) are converted to simpler molecules(e. hydrocarbons) by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end prod, or catagenesisCatagenesis is a term used in petroleum geology to describe the cracking process which results in the conversion of organic kerogens into hydrocarbons. This chemical reaction is believed to be a time, temperature and pressure dependent process which creat.