Several processes control the distribution of organic compounds in recent sediments, including biologic production and consumption, geochemical and biologic transport processes, and chemically and biochemically controlled transformation reactions. In transformation reactions of specific biogenic organic compounds, steroids illustrate the reactivity and organic compounds which contain "biologic markers."

Steroid alcohols (sterols) can degrade through several possible chemical or microbiologic pathways in sediments to produce steroid ketones (stanones), reduced alcohols (stanols), and hydrocarbons (sterenes and steranes). Two marine sedimentary environments describe some of the potential mechanisms of the transformation pathways involved: (1) the highly productive upwelling areas of Walvis Bay, South Africa, and (2) the strongly reducing conditions of the Black Sea.

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