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Geology is the Way

Larger benthic foraminifera

Sketch showing the main morphological features of larger benthic foraminifera. Modified after Carpenter, 1850.

Foraminifera are single-celled organisms (amoeboid protists) with calcareous shells that produce a network of reticulating strands of cytoplasm to catch food and live predominantly in seawaters. Larger benthic foraminifera are a group of foraminifera with relatively large size (around 1-5 cm, rarely up to 20 cm). They are distinguished from the small benthic foraminifera not by their size, but due to their complicated internal structures. Indeed, many larger benthic foraminifera are actually smaller than small benthic foraminifera. Larger benthic foraminifera develop morphologically complex tests (i.e. shells) with small chambers that spiral around the center of the shell and are repeated meticulously one after the other. The taxonomic classification of larger benthic foraminifera relies on the observation of their internal structure, whereas small benthic foraminifera can be classified based on their external morphology only.

Larger benthic foraminifera live on the seafloor of shallow, tropical and subtropical seas in carbonate-rich environments, such as reefs and lagoons. Living members of the group tolerate minimum temperatures of 18 °C and a maximum depth of 35 meters. The presence of larger benthic foraminifera in the fossil record is, therefore, thought to indicate warm, shallow waters (careful: fossils may be transported in deeper environments). Many living species of larger benthic foraminifera are also sensitive to variations in depth, nutrient levels, and light intensity. Their external morphology, in particular, changes with respect to these parameters. Larger benthic foraminifera can be either sessile (living anchored to the seafloor) or vagile (they can move on the seafloor).

The first larger benthic foraminifera appeared in the Carboniferous, evolving from agglutinated foraminifera (i.e. organisms producing tests of sedimentary particles). Since then, foraminifera evolved several taxa with characteristic shapes and morphology, making them really useful in stratigraphy for relative dating of rocks and to understand the evolution of life.

Polished slab with fossils of nummulite (a type of larger benthic foraminifera) from Saint-André de Cubzac, Aquitaine, France. Photo by Géry Parent.

Fossils of Yabeina globosa (fusulinid – another larger benthic foraminifera) from Akasaka Limestone, Upper Permian; Kinshozan, Gifu, Honshu, Japan. Photo by James St. John. Width: 2.9 cm across.

Fusulinid limestone from the Pennsylvanian of Kansas, USA. Width: 3.9 centimeters across. Photo by James St. John.

Nummulitic limestone

Nummulite limestone from the stone walls of Girona, Catalunya, Spain. Photo: Samuele Papeschi/Geology is the Way.

Nummulitic limestone

External shape of a nummulite from the stone walls of Girona, Catalunya, Spain. Photo Samuele Papeschi/Geology is the Way.

Nummulite

Sectioned larger benthic foraminifera packed together in the limestone walls of Girona, Catalunya, Spain. Photo: Samuele Papeschi/Geology is the Way.

References
Beavington-Penney, S. J., & Racey, A. (2004). Ecology of extant nummulitids and other larger benthic foraminifera: applications in palaeoenvironmental analysis. Earth-Science Reviews67(3-4), 219-265.
BouDagher-Fadel, M. K., & Price, G. D. (2010). Evolution and paleogeographic distribution of the lepidocyclinids. The Journal of Foraminiferal Research40(1), 79-108.
Boudagher-Fadel, M. K., & Price, G. D. (2013). The phylogenetic and palaeogeographic evolution of the miogypsinid larger benthic foraminifera. Journal of the Geological Society170(1), 185-208.
Hallock, P. (1981). Production of carbonate sediments by selected large benthic foraminifera on two Pacific coral reefs. Journal of Sedimentary Research51(2), 467-474.
Haynes, J. R. (1981). Foraminifera. Springer.
Murray, J. W. (1973). Distribution and ecology of living benthic foraminiferids.

         

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Detrital and Authigenic Minerals
Textures
Sedimentary Structures
Fossils
Sedimentary Rocks

 

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