Group Of Benthic Foraminifera Research Articles

Can oxygen and carbon isotope ratios of Jurassic foraminifera be used in palaeoenvironmental reconstructions?

Oxygen and carbon isotope ratios of calcareous tests of foraminifera can serve as a tool for reconstructing seawater temperatures and bioproductivity. The foraminiferal isotope studies are, however, largely limited to Neogene, Paleogene and Cretaceous strata. In the current study are presented δ18O and δ13C values of well-preserved Jurassic representatives of different groups of benthic foraminifera: low-Mg calcite Lenticulina (Lagenata), high-Mg calcite Paleomiliolina (Miliolida, Tubothalamea) and aragonite Epistomina (Robertinida, Globothalamea) derived from clay deposits of Poland. Moreover, it provides the detailed comparison of isotopic data of Jurassic foraminifera with those of various co-occurring macrofossils (belemnite rostra, ammonite and bivalve shells). Our study and comparative data substantiate the existence of the offset of Lenticulina's δ18O values from isotope equilibrium of ca. 1‰, which seems to be relatively constant over geological time. This value may be used for calculation of ancient water temperatures from oxygen isotope ratios of well-preserved specimens of this very common and widespread Jurassic foraminiferal taxon. δ18O values of Epistomina and δ13C values of all studied foraminifera are significantly biased from isotope equilibrium.

Improved oxygen isotope temperature calibrations for cosmopolitan benthic foraminifera

Despite decades of use as a paleoceanographic proxy, considerable uncertainty still surrounds the temperature dependence of benthic foraminiferal δ18O. Widely applied paleotemperature equations may mix non-equilibrium foraminifera with equilibrium synthetic calcite, resulting in temperature sensitivities that are too large. Warm-water foraminiferal calibrations may give temperature sensitivities that are too small for very cold waters. Here we combine new core top measurements from the Florida Straits and the Arctic Ocean with published data to derive new δ18O:temperature relationships for three groups of benthic foraminifera. We derive a quadratic equation for Cibicidoides and Planulina that agrees well with equilibrium synthetic calcite, and that should be applicable over all oceanographic temperatures. We find that Uvigerina is not at equilibrium and is isotopically heavier than Cibicidoides and Planulina by 0.47‰, in contrast to the historically used 0.64‰. Hoeglundina elegans is further enriched and appears to be slightly heavier than equilibrium aragonite. Finally we discuss the implications of the Florida Straits observations for the hypothesis that benthic foraminifera precipitate their shells from a pH-dependent mixture of bicarbonate and carbonate ions.

Environmental metal pollution considered as noise: Effects on the spatial distribution of benthic foraminifera in two coastal marine areas of Sicily (Southern Italy)

We analyze the spatial distributions of two groups of benthic foraminifera ( A d e l o s i n a spp. + Q u i n q u e l o c u l i n a spp. and E l p h i d i u m spp. ), along Sicilian coast, and their correlation with six different heavy metals, responsible for the pollution. Samples were collected inside the Gulf of Palermo, which has a high level of pollution due to heavy metals, and along the coast of Lampedusa island (Sicily Channel, Southern Mediterranean), which is characterized by unpolluted sea waters. Because of the environmental pollution we find: (i) an anticorrelated spatial behaviour between the two groups of benthic foraminifera analyzed; (ii) an anticorrelated (correlated) spatial behaviour between the first (second) group of benthic foraminifera with metal concentrations; (iii) an almost uncorrelated spatial behaviour between low concentrations of metals and the first group of foraminifera in clean sea water sites. We introduce a two-species model based on the generalized Lotka–Volterra equations in the presence of a multiplicative noise, which models the interaction between species and environmental pollution due to the presence in top-soft sediments of heavy metals. The interaction coefficients between the two species are kept constant with values in the coexistence regime. Using proper values for the initial conditions and the model parameters, we find for the two species a theoretical spatial distribution behaviour in a good agreement with the data obtained from the 63 sites analyzed in our study.

Benthic foraminiferal zonation in deep-water carbonate platform margin environments, northern Little Bahama Bank

The utility of benthic foraminifera in bathymetric interpretation of clastic depositional environments is well established. In contrast, bathymetric distribution of benthic foraminifera in deep-water carbonate environments has been largely neglected. Approximately 260 species and morphotypes of benthic foraminifera were identified from 12 piston core tops and grab samples collected along two traverses 25 km apart across the northern windward margin of Little Bahama Bank at depths of 275-1,135 m. Certain species and operational taxonomic groups of benthic foraminifera correspond to major near-surface sedimentary facies of the windward margin of Little Bahama Bank and serve as reliable depth indicators.Globocassidulina subglobosa, Cibicides rugosus, andCibicides wuellerstorfiare all reliable depth indicators, being most abundant at depths >1,000 m, and are found in lower slope periplatform aprons, which are primarily comprised of sediment gravity flows. Reef-dwelling peneroplids and soritids (suborder Miliolina) and rotaliines (suborder Rotaliina) are most abundant at depths <300 m, reflecting downslope bottom transport in proximity to bank-margin reefs. Small miliolines, rosalinids, and discorbids are abundant in periplatform ooze at depths <300 m and are winnowed from the carbonate platform. Increased variation in assemblage diversity below 900 m reflects mixing of shallow- and deep-water species by sediment gravity flows.