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. These changes happen at relatively low temperatures and pressures and result in changes to the rock's original mineralogy and texture. The boundary between diagenesis and metamorphism, which occurs under conditions of higher temperature and pressure, is gradational. This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Thermohaline circulation Oceanography (from Ocean + Greek γράφειν = write), also called oceanology or marine science, is the branch of Earth Sciences that studies the Earths oceans and seas. ... 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 water or other liquid. ... Lithification (from the Greek word lithos meaning rock and the Latin-derived suffix -ific) is the process whereby sediments compact under pressure, expel connate fluids, and gradually become solid rock. ... Metamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i. ... Minerals are natural compounds formed through geological processes. ...

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 rocky side of a mountain creek near Orosí, Costa Rica. ... Three small ammonite fossils, each approximately 1. ... Used in geology, building science and hydrogeology, the porosity of a porous medium (such as rock or sediment) is the proportion of the non-solid volume to the total volume of material, and is defined by the ratio: where Vp is the non-solid volume (pores and liquid) and Vm...

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 an economic standpoint, that study aids in assessing the likelihood of finding various economic minerals and hydrocarbons. Hydrocarbons are refined at oil refineries and processed at chemical plants A hydrocarbon is a chemical compound that consists only of the elements carbon (C) and hydrogen (H). ...

The role of diagenesis in anthropology

The term diagenesis is extensively used in geology. 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. 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).^[2] This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Anthropology is the study of the anatomical and mental composition of humanity through the examination of historical and present geographical distribution, cultural history, acculturation, cultural relationships, and racial classifications. ...

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.^[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.^[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.^[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. This transformation occurs in the first few hundred meters of burial and results in the creation of two primary products: kerogens and bitumens. In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure... Lipids are a class of hydrocarbon-containing organic compounds. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Lactose is a disaccharide found in milk. ... Lignin (sometimes lignen) is a chemical compound that is most commonly derived from wood and is an integral part of the cell walls of plants, especially in tracheids, xylem fibres and sclereids. ... Humus is a word actually used for two different things, which are both related to soil and thus get used interchangeably. ... Fig. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ... Kerogens are chemical compounds that make up a portion of the organic matter in sedimentary rocks. ... Bitumen is a mixture of organic liquids that are highly viscous, black, sticky, entirely soluble in carbon disulfide, and composed primarily of highly condensed polycyclic aromatic hydrocarbons. ...

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 (e. ... Catagenesis can refer to: The cracking process in which organic kerogens are broken down into hydrocarbons (see catagenesis (geology)) Retrogressive evolution, as contrasted with anagenesis (see catagenesis (biology)) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

See also

• Chalcedony
• Chert
• Flint
• Concretion
• Fossil

Chalcedony knife, AD 1000-1200 Bloodstone redirects here. ... Chert Chert (IPA: ) is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. ... A flint nodule from the Onondaga limestone layer, Buffalo, New York. ... 1. ... Three small ammonite fossils, each approximately 1. ...

References