"Foraminifera shells" are the outer coverings of tiny organisms called foraminifera. They are made of calcium carbonate and are commonly found in oceans or seafloors. Full definition
(11) + The rise looked even more abrupt when David Ericson and collaborators inspected the way fossil foraminifera shells varied from layer to layer in the Lamont cores. (history.aip.org)
Much to their surprise carbon isotope measurements of foraminifera shells (tiny plankton skeletons) showed the ventilation age had actually decreased and there had been no extra CO2 storage in the deep Pacific during the latest ice age, and no big release towards the end. (bitsofscience.org)
By separating the different atomic masses («isotopes») of the element boron in the foraminifera shells, they tracked how the pH of seawater changed during the PETM. (sciencedaily.com)