Authigenesis

Authigenesis is a term in sedimentology and geology that describes the formation of minerals in their present place within a sediment or sedimentary rock, during diagenesis, rather than as inherited detrital grains. Authigenic minerals crystallize from pore waters or by reaction of the existing sediment under conditions of burial, temperature, and pressure that differ from those at the time of deposition.

Most authigenic mineral formation occurs during shallow to moderate burial, when pore-water chemistry and microbial processes drive precipitation. Common environments include marine shelf settings with reducing conditions, where pyrite and other sulfide minerals form, and carbonate-rich settings where calcite or dolomite cements bind grains. Diagenetic clays such as illite can form through the alteration of smectite during burial, while glauconite can form authigenically in slow-deposited marine sands.

Representative authigenic minerals include pyrite, siderite, calcite and dolomite cements, glauconite, illite and other diagenetic clays, authigenic quartz overgrowths, and certain zeolites. The textures often show paragenetic sequences, zoning, and rounded, well-cemented grains that differ from the original framework.

Authigenesis is important for interpreting diagenetic history, reservoir quality, and paleoenvironments, as the presence and morphology of authigenic minerals record pore-water chemistry, redox states, and burial temperature. Analytical methods include petrography, scanning and transmission electron microscopy, X-ray diffraction, cathodoluminescence, and isotopic analyses.

See also: diagenesis, cementation, sedimentary rock.