Authigenesis

Authigenesis process

The authigenesis process is driven by particles of sediment that are not in thermodynamic equilibrium with the conditions surrounding it. This often occurs in the ocean where changing conditions due to biological processes is common. In water, changing oxygen content or changing saturation causes precipitation of minerals into the sediments, changing the state of the sediments. Precipitation is the main process of authigenesis on the surface of the ocean floor, with carbonates being the primary precipitates. For any mineral to be precipitated, the water must be supersaturated with respect to that mineral. For example, the area of deposition must be above the carbonate compensation depth or the pore waters must be sufficiently saturated due to dissolution of other grains for calcite to precipitate. The high porosity of deposited sediments allow for precipitation of minerals in the porous features, as the pore water can often have different saturation than the surrounding waters, thus diminishing the porosity and creating authigenic minerals.

Over time, sediments become more buried by deposition and precipitation. This causes compaction and cementation to occur and decreases porosity farther, changing the control on the authigenesis process from fluid composition to temperature. Increased temperatures around sediments leads to increased reactions in order for the sediment to reach thermodynamic equilibrium with the surroundings. This often is done through dehydration reactions because these reactions have a high entropy release.