Sedimentary Petrology Chapter 5: Diagenesis, Porosity, and Dolomites.

What is dissolution?

Dissolution (the opposite of cementaton) is a common diagenetic process in the meteoric environment. Favored by unstable minerology, low temperatures, and low pH an

What is dolomite?

Dolomite is a mineral composed of CaMg(Co3)2. Dolomite crystalizes in the trigonal system, is stable at Earth's surface. Many ancient carbonate rocks consist in whole or in part of the mineral dolomite.

What are the three major settings diagenesis happens in?

Diagenesis happens in three major settings 1. shallow and deep marine 2. meteoric 3. deep burial

What is Diagenesis?

Diagenesis is all post-depositional processes occurring over a long period of time that cause sediments to become lithified into a sedimentary rock.

What is cementation?

Cementation is the chemical precipitation of a new mineral from dissolved solids of porewater to fill inter-granular space between sediments. Cementation effectively binds loose sediment together, often having distinct textual forms. Cement's mineralogy depends on water chemistry, calcium carbonate being the most common cement.

What is marine cementation?

Marine cementation is cementation that produces beachrocks. In a marine environment the cement is sourced from the direct precipitation during evaporation on tidal flats, and biochemical (microbial precipitation).

What is micritization?

Micritization is a diagenetic process where carbonate grains are converted to micrite when barteria bore holes in carbonate minerals in which micrite precipitates.

What is neomorphism?

Neomorphism is a term used to cover two processes that go together which are inversion and recrystalization. Inversion refers to the change of one mineral to it's polymorph. When this change happens in the precence of water, first aragonite dissolves and nearly simultaneously, the more stable calcite is precipitated. Recrystalization indicates a change in the size or shape of a crystal with little or no change in chemical composition or mineralogy.

What is porosity?

Porosity is the measure of space in a material. Porosity of carbonate sediments after deposition is very high (40-80%). Compaction, cementation, and pressure dissolution reduce porosity. Dissolution and tectonic fracturing create new porosity. Porosity of limestone is of two types Primary- (depositional) Secondary (diagenetic-tectonic)

What is replacement?

Replacement is the diagenetic process that involves the dissolution of one mineral and the subsequent precipitation of another mineral with a pseudomorph composition in it's place. Replacement of calcium carbonate minerals by other minerals is a common diagenetic process. -dolomitization

What are some diagenetic processes?

Some diagenetic processes are: 1. Cementation 2. Dissolution 3. Compaction 4. Micritization 5. Neomorphsim 6. Replacement

What are the chemical reactions that produce dolomite?

The chemical reactions that produce dolomite are 1. direct precipitation from sea water 2. dolomitization: the process in which a calcium carbonate rock alters to dolomite as Ca is replaced with Mg at a 1:1 ratio. Mg is added and Ca is removed. 3. by dolomizing fluids that provide Mg and carbonate ions. Dedolomitization is dolomite being replaced by calcite to produce limestone.