Foraminifera biomineralization

Because of its relatively long mean residence time, ocean water has a constant isotope composition. Corals are about l%c and foraminifera are about 4.5%o lighter than ocean water. Thus significant Mg isotope fractionations occur during biomineralization of carbonate secreting organisms which is larger than for Ca isotopes (see Section 2.11). 

Lowenstam and Weiner (1989, pp. 8-11, table 2.1) clearly show that carbonates dominate in biomineralization. They even occur in plants and fungi. The volume percent of limestone and marbles is well documented from the Precambrian to the present. Whether these rocks are inorganic precipitates or festooned with fossils, many of the living creatures had biomineralized with calcium carbonate, is usually clear. Indeed, some strata are composed entirely of calcium carbonate shells. We present examples of carbonate mineral deposition in cyanobacteria, corals, coccoliths, foraminifera, mollusks, echinoids, and the arthropods. 

Erez, J. 2003. The source of ions for biomineralization in foraminifera and their implications for paleo-ceanographic proxies. Review in Mineralogy and... 

Hemleben Olsson (2006) have described the test ultrastructures of Eocene planktonic foraminifera. Test texmres are broadly similar and sometimes virtually identical to living species, indicating that models of biomineralization based on observations of living forms are applicable to the fossil record. 

Hemleben, C., Anderson, O. R., Berthold, W. U. Spindeer, M. 1986. Calcification and chamber formation in foraminifera — a brief overview. In Leadbeater, B. S. C. Riding, R. (eds) Biomineralization in Lower Plants and Animals. The Systematics Association, Special Volume, 30, 237-249. 

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