Foraminifera

Foraminifera are unicellular, predominantly marine, benthic and planktic animals with calcareous and agglutinated (aranaceous) shells, averaging 0.1 - 1 mm in size, but may be larger than 5 mm. Because of their diversity, rapid evolution, abundance (they account for half of the known protozoa), and wide geographic distribution in neritic to abyssal sediments, they have traditionally been the most important microfossil group in stratigraphic palaeontology, especially in the petroleum industry. The benthonic species which live on the seafloor and evolved in the early Paleozoic, have been used since the early 1900's for age determinants and palaeoenvironmental information. Two benthic groups are recognised - the small benthics and the larger benthics - the latter by their size and complex interiors. The larger benthics which are routinely studied in thin-sections, have important Paleogene stratigraphic applications, and are used with agglutinated species for late Paleozoic biostratigraphic zonation. On continental slopes benthonic species have restricted distributions associated with each species tolerance to water depth, salinity, nutrient flux, dissolved oxygen and sediment pH. Bathyal species also exhibit considerable morphological variations as a consequence of evolutionary adaptation to the physical environment.