Foraminifers

Globigerinoides fistulosus (planktonic foraminifers) and Uvigerina peregrina (benthic foraminifers) from SW-Pacific Source: BGR

Foraminifers are unicellular organisms (protozoa) living in the sea, which are on average 0.5 mm and smaller (small foraminifers), but can also grow to 1-2 mm and several centimetres in size (large foraminifers). Their shells usually consist of calcium carbonate (CaCO3 = calcite or aragonite and trace elements) or of foreign particles in an organic-tectinous matrix. Traditionally, a distinction is made between agglutinating foraminifers or sand shells, porcelain-like chalk shells (without pores) and hyaline chalk shells (with pores).

Foraminifers are single or multi-chambered and extraordinarily rich in form. Approximately 80,000 species have been described in recent and fossil records. They have been known since the Cambrian, i.e. for 540 million years, and live on or in the seabed (sessile, epi-, endo-benthic), and since the Jurassic they have also been floating in the water column (planktonic). They colonize all sea depths from the shallowest tidelands to the deepest deep-sea trenches, from the tropics to the polar regions, with different species and characteristic associations.

Because they underwent an intensive phylogenetic evolution during the Earth's history, many of them, which existed for a relatively short period of time, are suitable as very good guide fossils for the relative age determination of sedimentary rocks (biostratigraphy). Furthermore, they provide important information for the reconstruction of the depositional conditions (palaeoenvironment, palaeogeography).

Since the mineralized shells are carriers of chemical information (oxygen, carbon isotopes, magnesium, cadmium, barium, zinc, boron, uranium, strontium, neodymium), if well preserved, conclusions can be drawn about past water masses (palaeooceanography) or climate conditions (palaeoclimate) in analogy to today's conditions.

Foraminifers are one of the most common groups in marine strata. They are significant in the search for marine raw materials, in climate analysis of the recent past or in chemostratigraphy.