Unlocking the biomineralization style and affinity of Paleozoic fusulinid foraminifera

Abstract

Fusulinids are the most diverse, abundant and geographically widespread Paleozoic foraminifera which are widely considered to possess a “homogeneously microgranular” test microstructure composed of subangular grains of several micrometers in size. However, this texture appears to be a diagenetic artifact. Here we describe well-preserved Devonian calcareous fusulinids (Nanicella) from the Holy Cross Mountains (HCM) in central Poland. Foraminifera from Poland in which the primary nature of tests have not been masked by diagenesis are composed of low magnesium calcite spherical grains up to about 100 nanometers in diameter, identical to those observed in Recent and fossil hyaline foraminifera (Rotaliida, Globothalamea). These data call the paradigm of microgranular test microstructure of Foraminifera into question, and suggest a possible phylogenetic relationship between globothalamids and some fusulinids.

Rapid grain boundary diffusion in foraminifera tests biases paleotemperature records

“…Depending on the assumed grain boundary thickness (δ), this suggests that the average diameter of a spherical Ammonia sp. nanocrystallite lies between 65 and 115 nm (δ = 0.5–1 nm 54 , 57 ), which is consistent with SEM observations 30 , 31 . After the equilibration of these grain boundaries with oxygen in the pore fluids, grain boundary diffusion ceases to change the O-isotope value of the foraminifera tests.…”

“…Rotaliida foraminifera consist of benthic and planktonic calcitic tests that are multi-chambered, spiraled and perforated by pores. At the nanoscale, the fundamental building blocks of their tests are subspherical nanocrystallites 10–150 nm in diameter, similar to those in most other known biocarbonates 19 , 30 , 31 , 38 . Prior to incubation (for details cf.…”

“…In addition, they are compositionally heterogeneous 25 , 26 with concentration bands rich in magnesium, strontium, sodium, and other trace elements creating regions of relatively higher calcite solubility 27 , 28 that are hence also more susceptible to recrystallization. This complexity is further complicated by phylogeny, which separates foraminifera into several groups with distinct ultrastructures, crystalline morphologies, crystallite sizes, chemical compositions, and oxygen isotope disequilibrium “vital effects” 2 , 26 , 29 , 30 . In particular, different orders of foraminifera have different fundamental ultrastructural nanocrystallite shapes and sizes.…”

“…In particular, different orders of foraminifera have different fundamental ultrastructural nanocrystallite shapes and sizes. The nanocrystallites that compose the tests of hyaline foraminifera (order Rotaliida), which is the order most used in recent paleoclimate reconstructions, are subspherical and 50 nm in diameter, whereas Lageniida tests are composed of large >1-μm hollowed single-crystal fibers, and Millioida tests are composed of thin ~400-nm long needle-shaped nanocrystallites 30 , 31 . Altogether, the properties of foraminifera calcitic tests (and of most other biogenic carbonates) are radically different from the classical crystal properties of abiotic carbonates.…”

Element/Ca ratios in Nodosariida (Foraminifera) and their potential application for paleoenvironmental reconstructions

“…This order or class specific signature of the shell's composition supports a fundamental differences in their calcification mechanisms (Dubicka, Owocki, and Gloc 2018;Dubicka and Gorzelak 2017). Such a difference is also suggested with a fundamentally distinct morphology (i.e.…”