authigenically

Authigenically, or in an authigenic manner, refers to processes or materials that form in place within a sediment after its deposition, during diagenesis, rather than being transported from elsewhere. Authigenic minerals precipitate from pore waters or react with existing sediment components, leading to cementation, mineral replacement, or new mineral growth within the sediment matrix.

The term derives from authigenesis, describing in-situ formation during diagenesis. In sedimentology and petrography, authigenic minerals are distinguished from detrital minerals, which are eroded or transported from distant sources, and from syngenetic minerals, which form contemporaneously with sediment deposition. Authigenic formation is influenced by burial depth, temperature, pressure, redox state, and pore-water chemistry, and it commonly records diagenetic history.

Common examples of authigenic minerals include calcite cement precipitated in pore waters, quartz overgrowths that cement sand grains, pyrite formed during burial under reducing conditions, and certain clay minerals such as illite or glauconite that crystallize authigenically in marine settings. Authigenic processes can modify rock porosity and permeability, influence porphyry and reservoir quality in hydrocarbon systems, and provide clues about past environmental conditions.

In practice, identifying authigenic minerals involves petrographic examination, textural analysis, and, when relevant, isotopic or geochemical data to distinguish in-place precipitation from detrital provenance. The concept is central to interpreting diagenetic alteration and the evolution of sedimentary rocks.