In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Oceanography (from the greek words Ωκεανός meaning Ocean and γράφω meaning to write also called oceanology or Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of Lithification (from the Greek word lithos meaning 'rock' and the Latin -derived suffix -ific) is the process in which Sediments compact Weathering is the decomposition of earth rocks, Soils and their Minerals through direct contact with the planet's Atmosphere. Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i These changes happen at relatively low temperatures and pressures and result in changes to the rock's original mineralogy and texture. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific The boundary between diagenesis and metamorphism, which occurs under conditions of higher temperature and pressure, is gradational. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface

After deposition, sediments are compacted as they are buried beneath successive layers of sediment and cemented by minerals that precipitate from solution. In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Porosity usually decreases during diagenesis, except in rare cases such as dissolution of minerals and dolomitization. Porosity is a measure of the void spaces in a material and is measured as a fraction between 0–1 or as a Percentage between 0–100% Solvation, commonly called dissolution, is the process of attraction and association of Molecules of a Solvent with molecules or Ions of a

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. From a commercial standpoint, such studies aid in assessing the likelihood of finding various economically viable mineral and hydrocarbon deposits. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon.

Contents 1 The role of diagenesis in anthropology 2 The role of diagenesis in hydrocarbon generation 3 See also 4 References

The role of diagenesis in anthropology

The term diagenesis is extensively used in geology. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit However, this term has filtered into the field of anthropology to describe the changes and alterations that take place on skeletal (biological) material in a burial context. Anthropology (/ˌænθɹəˈpɒlədʒi/ from Greek grc ἄνθρωπος anthrōpos, "human" -λογία -logia) is the study of Specifically, diagenesis “is the cumulative physical, chemical and biological environment; these processes will modify an organic object’s original chemical and/or structural properties and will govern its ultimate fate, in terms of preservation or destruction”. ^[1][2] In order to assess the potential impact of diagenesis on archaeological bones, many factors need to be assessed, beginning with elemental and mineralogical composition of bone and enveloping soil, as well as the local burial environment (geology, climatology, groundwater). Archaeology, archeology, or archæology (from Greek grc ἀρχαιολογία archaiologia – grc ἀρχαῖος archaīos Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce Climatology (from Greek grc κλίμα klima, "region zone" and grc -λογία -logia) is the study of Climate, scientifically Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations ^[2]

The composite nature of bone, comprising one third organic (mainly protein collagen) and two thirds mineral (calcium phosphate mostly in the form of hydroxyapatite) renders its diagenesis more complex. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein Calcium phosphate is the name given to a family of Minerals containing Calcium Ions (Ca2+ together with orthophosphates (PO43- Hydroxylapatite, also called hydroxyapatite, is a Mineral. It is a naturally occurring form of calcium Apatite with the formula Ca5(PO43(OH ^[3] Alteration occurs at all scales from molecular loss and substitution, through crystallite reorganization, porosity and microstructural changes, and in many cases, to disintegration of the complete unit. ^[4] Three general pathways of the diagenesis of bone have been identified:

1. chemical deterioration of the organic phase.
2. chemical deterioration of the mineral phase.
3. (micro) biological attack of the composite. ^[5]

They are as follows:

1. The dissolution of collagen depends on time, temperature and environmental pH. ^[5] At high temperatures, the rate of collagen loss will be accelerated and extreme pH can cause collagen swelling and accelerated hydrolysis. pH is the measure of the acidity or alkalinity of a Solution. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions ^[5] Due to the increase in porosity of bones through collagen loss, the bone becomes susceptible to hydrolytic infiltration where the hydroxyapatite, with its affinity for amino acids, permits charged species of endogenous and exogenous origin to take up residence. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this ^[6]
2. The hydrolytic activity plays a key role in the mineral phase transformations that exposes the collagen to accelerated chemical- and bio-degradation. ^[5] Chemical changes affect crystallinity. ^[6] Mechanisms of chemical change, such as the uptake of F- or CO3- may cause recrystallization where hydroxyapatite is dissolved and re-precipitated allowing for the incorporation of substitution of exogenous material. ^[6]
3. Once an individual has been interred, microbial attack, the most common mechanism of bone deterioration, occurs rapidly. ^[5] During this phase, most bone collagen is lost and porosity is increased. ^[6] The dissolution of the mineral phase caused by low pH permits access to the collagen by extracellular microbial enzymes thus microbial attack. ^[5]

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 temperature and pressure. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most Lignin or lignen is a complex Chemical compound most commonly derived from Wood and an integral part of the secondary Cell walls of Plants Humus (Origin 1790–1800 Latin: earth ground) is the organic material in Soil lending it a dark brown or black colouration Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface This transformation occurs in the first few hundred meters of burial and results in the creation of two primary products: kerogens and bitumens. Kerogen is a mixture of organic Chemical compounds that make up a portion of the organic matter in Sedimentary rocks It is insoluble in normal organic Bitumen is a mixture of organic Liquids that are highly Viscous, black sticky entirely soluble in Carbon disulfide, and composed primarily

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 through a chemical process known as cracking, or catagenesis. In Petroleum geology and Chemistry, cracking is the process whereby complex organic Molecules such as Kerogens or heavy Hydrocarbons See Catagenesis (biology for usage in the field of biology where it refers to retrogressive evolution

See also

• Chalcedony
• Chert
• Flint
• Concretion
• Fossil

References

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