is a term used in marine geology
Marine geology or geological oceanography involves geophysical, geochemical, sedimentological and paleontological investigations of the ocean floor and coastal margins...
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
Oceanic anoxic events or anoxic events occur when the Earth's oceans become completely depleted of oxygen below the surface levels. Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events may have caused...
(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
Biochemical oxygen demand or B.O.D. is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. The term also refers to a chemical procedure for...
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 rock
In petroleum geology, source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. They form one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including...
s. 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 δ15
N and corresponding decrease in δ13
C 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
Dan Costache "Dinu" Patriciu , is a billionaire businessman and entrepreneur with a long standing involvement in real estate. In 1998 he led an investor buyout of the previously state-owned Romanian oil company, Rompetrol...
, 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
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
, that examines the sapropel sediments in that region, with sediment cores collected and investigated by several universities and research institutes across the world.