Navarella is an upper Cretaceous large lituolid, attaining a maximum length of 5 mm, with a first streptospirally enrolled test, later uncoiled and with an aperture varying during the ontogenesis from slit-like to cribrate. The genus was originally described by Ciry & Rat (1951) from the Maastrichtian flysch of the Spanish Pyrenees, then reported from Campanian-Maastrichtian rocks of Suisse Alps, Bavaria, Austria, northeastern Italy, France and Serbia (e.g., Maync, 1954; Sampò, 1972; Radoičić et al., 2010). Recently, several large Navarella-like lituolids were discovered in Thanetian hemipelagites of the Belluno Basin (Giusberti et al., 2016; Plate 4, figs. 14, 20). They are common in the >500 µm fraction of the residues up to the uppermost Thanetian and abruptly disappear at the Paleocene-Eocene boundary, in coincidence with the exit of Paleocene cosmopolitan extinction taxa (Benthic Foraminiferal Extinction Event; Giusberti et al., 2016). In order to document the internal chamber arrangement and the agglutinated wall microstructure of the Paleocene lituolids and to compare them with Navarella’s individuals recovered in Maastrichtian strata of the study area, the specimens were sectioned and analysed through a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX). Our results confirm the attribution of the Paleocene specimens to Navarella, thus permitting to expand the stratigraphic distribution of this poorly known deep-water lituolid. Despite intensive researches, we did not find any trace of Navarella in Danian-Selandian strata, implying a >7 Myr gap in the stratigraphic range of this peculiar agglutinated foraminifer. Based on available data, we infer that Navarella reappeared as “Lazarus” genus in the Thanetian having survived the Cretaceous-Paleocene mass extinction, but it was eventually driven to extinction during the environmental perturbations associated to the Paleocene-Eocene Thermal Maximum (Giusberti et al., 2016).
The large lituolid Navarella Ciry & Rat 1951: an upper Paleocene Lazarus occurrence?
MANCIN, NICOLETTA
2016-01-01
Abstract
Navarella is an upper Cretaceous large lituolid, attaining a maximum length of 5 mm, with a first streptospirally enrolled test, later uncoiled and with an aperture varying during the ontogenesis from slit-like to cribrate. The genus was originally described by Ciry & Rat (1951) from the Maastrichtian flysch of the Spanish Pyrenees, then reported from Campanian-Maastrichtian rocks of Suisse Alps, Bavaria, Austria, northeastern Italy, France and Serbia (e.g., Maync, 1954; Sampò, 1972; Radoičić et al., 2010). Recently, several large Navarella-like lituolids were discovered in Thanetian hemipelagites of the Belluno Basin (Giusberti et al., 2016; Plate 4, figs. 14, 20). They are common in the >500 µm fraction of the residues up to the uppermost Thanetian and abruptly disappear at the Paleocene-Eocene boundary, in coincidence with the exit of Paleocene cosmopolitan extinction taxa (Benthic Foraminiferal Extinction Event; Giusberti et al., 2016). In order to document the internal chamber arrangement and the agglutinated wall microstructure of the Paleocene lituolids and to compare them with Navarella’s individuals recovered in Maastrichtian strata of the study area, the specimens were sectioned and analysed through a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX). Our results confirm the attribution of the Paleocene specimens to Navarella, thus permitting to expand the stratigraphic distribution of this poorly known deep-water lituolid. Despite intensive researches, we did not find any trace of Navarella in Danian-Selandian strata, implying a >7 Myr gap in the stratigraphic range of this peculiar agglutinated foraminifer. Based on available data, we infer that Navarella reappeared as “Lazarus” genus in the Thanetian having survived the Cretaceous-Paleocene mass extinction, but it was eventually driven to extinction during the environmental perturbations associated to the Paleocene-Eocene Thermal Maximum (Giusberti et al., 2016).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
