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.
Highlights
Foraminifera are among the most important microorganisms in the earth sciences because they constitute a valuable tool for paleoenvironmental reconstructions and stratigraphic analyses
There has been no presentation to date of micro- or nanoscale structural observations coupled with geochemical characteristics of Paleozoic foraminifera
Fe was recorded in foraminiferal tests by electron microprobe, its concentration is very low (0.02–0.03 wt%), below detection limit (>0.05 wt%) (Supplemental Table 1)
Summary
Foraminifera are among the most important microorganisms in the earth sciences because they constitute a valuable tool for paleoenvironmental reconstructions and stratigraphic analyses. The class Fusulinata (taxonomic rank after Vachard[5] and Vachard et al.6), defined as a group possessing a “homogeneously microgranular” test composition[2,3,4,7,8] consisting of closely packed subangular grains several micrometers in size[7,9,10], is the most abundant group of Paleozoic foraminifera It comprises several hundred genera[11,12], including all Paleozoic calcareous taxa except representatives of Miliolida and Lagenida (Nodosariata)[6]. Most studies of Paleozoic foraminifera have been based on recrystallized specimens characterized by obscure original test compositions (see Mikhalevich[14]) Such specimens typically display micrometer-sized neomorphic calcite/overgrowths on test surfaces and within their interiors[8,9,10,15]. Our findings provide new insights into the biomineralization style and affinities of Paleozoic “fusulinid” foraminifera, and invalidate the “microgranular fusulinids” paradigm
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