Sapropel (a contraction of ancient Greek words sapros and pelos, meaning putrefaction and mud, respectively) is a term used in marine geology to describe dark-coloured sediments that are rich in organic matter. Organic carbon concentrations in sapropels commonly exceed 2% in weight.
Sapropels are thought to develop during episodes of reduced oxygen availability in bottom waters, such as an Oceanic Anoxic event (OAE). Most studies of sapropel formation mechanisms infer some degree of reduced deep-water circulation. Oxygen can only reach the deep-sea by new deep-water formation and consequent "ventilation" of deep basins. There are two main causes of OAE: A reduction in deep-water circulation or a raised upper level oxygen demand.
A reduction in deep-water circulation will eventually lead to a serious decrease in deep-water oxygen concentrations due to biochemical oxygen demand associated with the decay of organic matter that sinks into the deep-sea as a result of export production from surface waters. Oxygen depletion in bottom waters then favours the enhanced preservation of the sinking organic matter during burial in the sediments. Organic-rich sediments may also form in well-ventilated settings that have highly productive surface waters; here the high surface demand simply extracts the oxygen before it can enter the deep circulation currents so depriving the bottom waters of oxygen.
Sapropelic deposits from global Ocean Anoxic Events form important oil source rocks. Detailed process studies of sapropel formation have concentrated on the fairly recent eastern Mediterranean sapropels, the last of which was deposited between 9.5 and 5.5 thousand years ago.
The Mediterranean sapropels of the Pleistocene reflect increased density stratification in the isolated Mediterranean basin. They record a higher organic carbon concentration than non-sapropel times; an increase in the δ15N and corresponding decrease in δ13C tells of rising productivity as a result of nitrogen fixation. This effect is more pronounced further east in the basin, suggesting that increased precipitation was most pronounced at that end of the sea.
According to Romanian tycoon Dinu Patriciu, the sapropel has a huge potential of being developed into a wide array of products, including a new form of alternative energy. Currently Dinu Patriciu has a marine exploration project in the Black Sea, that examines the sapropel sediments in that region, with sediment cores collected and investigated by several universities and research institutes across the world.
The monograph "Geology and Non-traditional resources of the Black Sea" examines the origin, properties and application of deep sea organogenic mineral sediments (DSOMS) formed during the newest ages of the geological history of the Black Sea. It examines also the natural conditions influencing the formation of the sediment complex and the mineral resources. The Black Sea is seen as a unique natural geobiotechnological reactor capable of generating specific geological resources. The object of this study is the Black Sea bottom and more specifically the Bulgarian economic zone and the western region of the Black Sea and the subject of the study is the origin, the properties and the distribution of deep sea organogenic mineral sediments (DSOMS) and the evaluation of the possibilities to use them as a complex raw material. This paper lays the foundations of the application of a new type of complex raw material from the bottom of the Black Sea and examines the composition, the properties, the distribution and the origin of DSOMS as well as the possible spheres of their economic application and extraction.
- Philip A. Meyers and Michela Arnaboldia (2008). "Paleoceanographic implications of nitrogen and organic carbon isotopic excursions in mid-Pleistocene sapropels from the Tyrrhenian and Levantine Basins, Mediterranean Sea". Palaeogeography Palaeoclimatology Palaeoecology 266: 112. doi:10.1016/j.palaeo.2008.03.018.
- Patriciu: Examination of sapropelic mud in Black Sea could last 2-3 years, 19 June 2009, wall-street.ro, retrieved at 30 July 2010