catagenesis

Catagenesis is a term used in both geology and biology to describe transitional or regressive phases in a process of maturation or development. In geology, catagenesis refers to the thermal maturation of organic matter within sedimentary rocks, transforming kerogen into liquid and gaseous hydrocarbons as burial temperatures rise.

In petroleum geology, catagenesis occurs after diagenesis as rocks experience increasing temperature and pressure during burial. The type of kerogen present influences the hydrocarbon products: oil-prone kerogens (types I and II) tend to generate liquid hydrocarbons, while gas-prone kerogen (type III) yields natural gas. This stage encompasses the oil window and the gas window, where progressively higher temperatures drive hydrocarbon generation, alteration of organic matter, and hydrocarbon expulsion. Catagenesis is typically followed by higher-temperature metagenesis in the maturation continuum.

In biology, catagenesis (often referred to as the catagen phase) denotes the regression transition in the hair growth cycle between the active growth phase (anagen) and the resting phase (telogen). It lasts roughly two to three weeks in humans. During catagen, cell proliferation in the hair matrix ceases, the hair follicle involutes, and apoptosis reduces the epithelial cell population. The club hair forms as the follicle degenerates, after which the follicle enters telogen and may later re-enter anagen to begin a new cycle.

Etymology traceable to Greek katagenēsis, meaning descent or regression, catagenesis thus conveys a downward transition in both geological maturation and biological development. The two uses are distinct and context-specific, sharing only the broad idea of a transitional phase.