Contained in this paper is detailed information on the analysis of accumulation and humification of organic material in marine and lagoonal sediments in various areas of the north-western Mediterranean Sea. Typical geographic and hydrodynamical conditions such as the absence of tides, sudden climatic variations, and discharge by low-water rivers and strong floods govern the geological situation. In contrast to the coastal and lagoonal sediments, the sediments of the open sea are only slowly accumulating without a major contribution by deposition and humification of organic substances. Abundant biological activity directly influencing the geochemical situation in the sediment takes place only in lagoons (such as the Etang de St. Nazaire and the Bages-Sigean complex), and certain parts of the coastal zone (including the Bay of Port Vendres, the Gulf of Marseille, and the Banyuls region). Geochemical analysis on carbon content, sulfur compounds present, nitrogen content, and humus characterization, as well as biomass estimation and bacterial counts from the investigated areas, are reported. Major biopedological factors involved were found to be temperature, presence or absence of oxygen, activity of benthic organisms, and concentration of organic matter. With increasing depths of burial, the biogeochemical alterations were found to slow down.