Sapropel

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Sapropel ([ zaproˑˈpeːl ]; from ancient Greek σαπρός sapros , German 'lazy, rotten' ) or digested sludge is created under natural conditions at the bottom of nutrient-rich, stagnant water through the biochemical conversion of organic material in the absence of oxygen . Together with clay particles brought into the water from outside , the converted organic substance forms sludge masses that are colored gray to deep black by metal sulfides . Digested sludge can solidify and thus form a rock , the sapropelite , which, due to the high proportion of mineral substance, belongs to the acaustobiolites , the non-combustible organogenic sedimentary rocks ( bioliths ).

In soil science, the sapropel is a soil type from the class of subhydric soils . In the international soil classification World Reference Base for Soil Resources (WRB), the sapropeles belong to the Gleysols with Subaquatic Qualifier.

In geology they are grouped together with other organic-rich sediments under the generic term Mudden . They are considered to be an early stage on the path to converting biomass into fossil fuels , especially crude oil and natural gas .

Emergence

If the soil water is poorly mixed with higher water layers, as can occur in deep or, for other reasons, very calm areas of still waters , an oxygen-free (anoxic) and reducing, sulfidic ( euxinic ) environment is created. Dead organisms that sink to the bottom from the water column, mostly single-celled algae , are no longer completely decomposed, so that organic material accumulates in the background sediment (usually clay or silt ). This sediment enriched with organic material is called digested sludge . After it has solidified into sedimentary rock, it is called sapropelite . Due to the dark color and their small grain size , however, fossil digested sludge is usually referred to as black clay stone or black pelite. Finely distributed carbon and iron sulfides, especially pyrite, ensure the dark color . In addition, black shale can be enriched with valuable metals such as copper , uranium and vanadium . The lack of oxygen at the bottom of the water and the low movement of the water ensure that even the bodies of larger animals are only incompletely decomposed after they sink to the bottom and become embedded in the mud. In addition, due to the hostile conditions, digested sludge is not inhabited by more complex creatures ( endobenthos , endofauna ) that could destroy or damage embedded carcasses through their digging or feeding activity . For these reasons, as well as the fine grain of the sediment, which preserves very filigree structures, digested sludge offers an excellent environment for the transmission of fossils . In fact, many black clay stones are famous for their spectacular fossil preservation.

Examples

Euxinian conditions with digested sludge have recently existed on the bottom of the Black Sea and in deeper areas of the Baltic Sea. Examples of significant black pelite occurrences, i.e. H. fossil digested sludge, in Germany the Devonian black slate of the German low mountain range (including the roof slate of the Eifel ), the locally ore-rich copper slate of the Upper Permian of Central Europe ( Zechstein ), and the Posidonia slate from the southern German Lower Jurassic, known for its unique fossils . Also, the oil shale from the Eocene of Messel Pit near Darmstadt is an example of a traditional fossil digested sludge.

Sapropel coal

If organic material remains largely free of inorganic rock material, it turns into coal under appropriate conditions . Sapropel or digested sludge coal arises in the edge area of ​​humus coal, where the formation conditions are no longer optimal and therefore the degree of coalification is low. For this reason, the original components are easy to recognize. There is Sapropelkohle from plant spores , it is as a cannel , even Kannel- or Kännelkohle (of English .: candle  called = candle), dominated the algae content, this is called Bogheadkohle . If it is very finely layered and can be split into thin leaves with a leathery consistency, it is also called leaf charcoal , paper charcoal or dysodil . Due to its volatile bituminous content, sapropel coal is easily inflammable and is therefore counted among the caustobiolites , the combustible organic sedimentary rocks (bioliths).

The soft sapropel charcoal is suitable for carving figures, with traditional carvings mostly showing mining motifs.

Web links

Individual evidence

  1. ↑ Duden online: Sapropel
  2. ↑ The word "Dysodil" is borrowed from the Greek and means something like "foul smelling". The rock smells unpleasantly bituminous when burning. Franz Kirchheimer: Basics of a botanical science of the German brown coal . Knapp, Halle (Saale) 1937, p. 6 ( digitized version )
  3. ↑ objects from Kennel coal

literature

  • Wulf Amelung, Hans-Peter Blume, Heiner Fleige, Rainer Horn, Ellen Kandeler, Ingrid Kögel-Knabner, Ruben Kretzschmar, Karl Stahr, Berndt-Michael Wilke: Scheffer / Schachtschabel textbook of soil science. 17th edition. Heidelberg 2018. ISBN 978-3-662-55870-6 , p. 437 ff.