by Kate Holland,

Figure 1. An artist’s impression of what the foraminifers might have looked like.

Foraminifers, my favourite microscopic zooplankton, make tiny shells out of calcium carbonate or organic cements. Agglutinated foraminifers make their shells with materials they find on the seafloor. Some can be particularly selective only building with particular minerals, like barite, or parts of other sea creatures, like sponge spicules, and glue these together with organic cements.  During a particularly eventful time in Earth’s history the agglutinated foraminifers made exceptionally good use of the materials available to them on the seafloor.

real foram
Figure 2: A more accurate representation of what the foraminifer might have looked like (Kaminski et al., 2008)

The geological record the Cretaceous – Paleogene (K-Pg) boundary is marked by a clay layer which is high in iridium (an element common in meteorites) and even in some formations impact derived shock diamonds. These are a product of the metamorphism that occurs upon impact with graphite at suitably high pressures.  Unfortunately these are rather small (largest impact microdiamonds ~30μm). Most agglutinated foraminifers survived the mass extinction associated with the Chicxulub meteorite impact and continue to agglutinate on the seafloor. Some species even began to use minerals associated with the meteorite ejecta! Kaminski and others used spectroscopic techniques to identify diamonds incorporated into the walls of the foraminifers shells found at the impact boundary layer.

The abilities of the benthic agglutinated foraminifera to concentrate the ejecta signal could be very beneficial to further studies of the K-Pg boundary formations (as well as a cool idea for making art on a microscopic scale). Kaminski says they would make fine engagement rings for ants!

To read the entire story In: Kaminski, M.A & Coccioni E., (eds), 2008. Proceedings of the Seventh International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 13, 57-61.