Fossil Benthic Foraminifer Fossil Benthic Foraminifer Benthic Foraminifer Fossil Benthic Foraminifer

What are Benthic Foraminifers?

Kingdom Protista includes the order Foraminiferida. Similar to amoeboid organisms in cell structure, the foraminifera differ in having granular rhizopodia and elongate filopodia that emerge from the cell body. Foraminifers are covered with an organic test that varies from a simple single chamber with an aperture, to a complex, multichambered, perforate, calcitic wall, to an agglomeration of mineral grains embedded in the organic test. The foraminifera are divided into two primary groups based on their mode of life, planktonic (marine floaters), and benthic (sea floor dwellers).

Benthic foraminiferal morphologies are very diverse, from simple single-chambered to multi-chambered, complex forms composed of calcite or mineral grains. The benthic foraminifera utilize rhizopodia extended through single or multiple apertures and test perforations for gathering prey and locomotion. Benthic foraminifera display a variety of life cycles that include sexual and asexual phases and produce megalospheric and microspheric generations. The length of an individual's life can range from a few weeks to up to 5 years. Since an individual's mortality is dependent on when it reproduces, there are many factors controlling its life span. Benthic foraminifera occupy a wide range of marine environments, from brackish estuaries to the deep ocean basins, and occur at all latitudes.

Application to Earth Science Research

Environmental Studies - Because benthic foraminifera occupy a wide range of marine environments they are very useful as environmental indicators. Particular species and assemblages can be used to identify paleoenvironments ranging from brackish estuaries to the deep sea. Application of modern benthic foraminifera distribution data to deep sea core data has been utilized to identify paleoceanographic changes in intermediate and deep water circulation. Using water depth ranges of benthic foraminifera as paleobathymetric indicators help determine past sea level changes in coastal regions. Changes in benthic foraminiferal assemblages and test morphologies are becoming increasingly useful for assessing environmental quality (changes in water salinity, temperature, dissolved oxygen, nutrient input, heavy metals and other toxic materials) in coastal regions, and reconstructing historical changes in near shore ecosystems. Geochemical analyses of benthic foraminiferal tests provide information on water salinity and temperature.

Biostratigraphy - Benthic foraminifera can be used as biostratigraphic indicators. Although not as useful as planktonic foraminifera due to their usual long ranges, benthic foraminifera provide regional utility for biostratigraphic zonation (e.g., Gulf of Mexico, New Zealand). Larger benthic foraminifera are very useful biostratigraphically in Late Paleozoic and Early Mesozoic stratigraphy.

Meet the Expert

Scott E. Ishman, Reston, VA, Cenozoic benthic foraminfers, paleoclimatology, and paleoceanography.

Current USGS Projects using Benthic Foraminifers

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