We present a new record of deep-water agglutinated foraminifera (DWAF) across the Eocene-Oligocene Transition (EOT) in the southern Labrador Sea (ODP Site 647). We studied 82 samples from Cores 647A-37R to -27R, and recovered over 100 species and generic groups. The EOT represents an interval of rapid climatic change connected with global cooling, Antarctic glaciation, a substantial decrease in atmospheric CO2, and concurrent changes in the composition of deep waters in the world ocean. Our high-resolution quantitative study of the DWAF faunal succession in abyssal Hole 647A confirms earlier findings that the EOT was an interval of significant faunal turnover. The faunal succession in Hole 647A is subdivided into two assemblages based on the stratigraphic ranges of characteristic benthic foraminiferal species: late Eocene Spiroplectammina trinitatensis-Reticulophragmium amplectens Zone and early Oligocene Ammodiscus latus-Turrilina alsatica Zone. The boundary between these zones, i.e., the Eocene/Oligocene (E/O) boundary, is characterized by the disappearance of 11 DWAF taxa, most of them organically-cemented taxa. The boundary interval was also characterized by a striking sharp decrease in DWAF abundance and diversity. Organically-cemented DWAF taxa increased in abundance in the early Oligocene, but their diversity and abundance never recovered to Eocene values. These data suggest a deepening of the calcite compensation depth and associated changes, such as more vigorous ocean circulation in coincidence with the E/O boundary interval. The analysis of DWAF morphogroups reveals an acme in robust suspension-feeding tubular forms previous to the extinction, suggesting increased bottom water activity. The E/O boundary interval is characterized by an increase in DWAF infaunal taxa and Spiroplectammina species, probably related to increased productivity, as already suggested by the analysis of benthic elongate-cylindrical foraminifera at the same locality. The faunal turnover across the EOT at Hole 647A suggests more vigorous deep-ocean circulation in the latest Eocene and across the E/O boundary interval in the Labrador Sea. It seems reasonable to link the disappearance of DWAF at the E/O boundary at Site 647 to more than one mechanism, including inferred higher productivity, possible competition from calcareous benthic foraminifera, changes in the CO2 content of the atmosphere and ocean, the deepening of the calcite compensation depth, and concurrent changes in taphonomic conditions caused by changes in the water masses in the North Atlantic.
Analysis of a 630m section of an exploration well penetrating the distal part of the Congo Fan (~2000m water depth) yielded high abundance and diversity assemblages of agglutinated and calcareous benthic foraminifera. Planktonic foraminifera constrain the age to Early – Middle Miocene, and 18O records reveal the Mi1 (~16.3 Ma) isotopic shift. Relatively few taxonomic studies of deep-water calcareous and agglutinated benthic foraminifera exist from this time period in this locality. All species encountered are therefore taxonomically described and documented using SEM photography (over 170 species), along with 27 species of planktonic foraminifera. Faunas show close affinities to those of the eastern Venezuela Basin, Gulf of Mexico and Central Paratethys. Seven assemblages are defined and analysed using morphogroup analysis and Correspondence Analysis, documenting the response of benthic foraminifera to three primary environmental-forcing factors; energy levels in the benthic boundary layer, oxygen levels relating to changing surface water productivity, and fluctuations in the level of the CCD. Near the top and bottom of the studied section both foraminiferal abundance and diversity decrease, corresponding with increased sand content implying greater energy levels and environmental disturbance. The majority of the section consists of shales with very low percentage sand, high foraminiferal abundance and diversity, and high sedimentation rates of ~10cm/kyr. Morphogroup analysis reveals a major switch in the fauna at around oxygen isotope event Mi1, with the transition from an epifaunal-dominated Cibicidoides assemblage to shallow infaunal-dominated Bulimina assemblage. We regard this as likely due to expansion of the oxygen minimum zone (paleobathymetric estimates are ~1000m) related to increased surface-water productivity and global cooling. Shifts in calcareous foraminiferal percentage over the studied interval overprint these signals and are believed to be related to a shoaling CCD, linked to reduced oceanic acidity and global atmospheric CO2 levels during the early Middle Miocene Monterey Carbon Isotope Excursion.
We propose a methodology as a possible standard approach for micropaleontological studies addressed to detect test microstructure and the chemical/mineralogical composition of grains used by agglutinated foraminifera. Themethodology was tested on over 200 specimens of fossil agglutinated foraminifera, mostly belonging to the textulariid group, collected from Cenozoic successions of theMediterranean region. The approach assesses the internal morphological and compositional features of agglutinated foraminifera by Scanning ElectronMicroscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses, performed on representative specimens that were embedded in epoxy resin and subsequently sectioned and polished.With respect to similar techniques that perform SEM and EDS analyses mostly on the agglutinated wall surface of free specimens or broken tests, this methodology provides the preparation of cross sections of isolated individuals. The use of cross sections has the advantages of: (i) documenting the internal chamber arrangement and other morphological elements (such as alcoves or canaliculi), even considering if the recognized features remain constant or change during ontogeny; (ii) measuring the testwall thickness and the grain distributionwithin the testwalls; (iii) detecting the chemical composition of the agglutinated grains and the cement in order to highlight mineralogical grain selectivity and arrangement; (iv) studying the agglutinated grains in their original position within the test wall and during test growth; and (v) the elemental compositional data collected from polished sections are more accurate than those collected on the rough surface of specimens.
Agglutinated benthic foraminifera were investigated in the central Northern Aegean Sea. Eighteen samples were collected along a neritic to mid-bathyal transect in Saros Bay at water depths ranging from 15 to 500m in March 2003. This study documents for the first time in detail, agglutinated foraminiferal species and their bathymetric distribution in this area.Atotal of 96 species belonging to 51 genera were recognised. Statistical analyses (CA and PCA) allowed us to identify different assemblages that can be related to bathymetric depth and trophic level and, in turn, to different hydrological zones. The shallowest assemblage (15m) is characterised by the lowest species richness that might result from the influence of the Black Sea outflow into Saros Bay. The shallow assemblages stations (21–70m) are characterized by relatively low diversity and higher dominance values. On the other hand, assemblages from intermediate water (80–200m) are characterised by high diversity values and the dominance of elongate keeled forms associated with elongated tapered forms, providing evidence of mesotrophic conditions. The deepest assemblages, including stations ranging from water depths of 200 to 500m, are very well-diversified and mainly represented by epifaunal taxa. The dominance of tubular morphogroup might be due to the low food supply, which acts as a limiting factor for more eutrophic dependent taxa and meso-oligotrophic conditions might be inferred.
We herein describe a new family, the Ammolagenidae, and emend the description of the genus Ammolagena Eimer and Fickert, 1899 based on a study of paralectotypes of the type species Ammolagena clavata (Jones and Parker 1860) in the Natural History Museum, London. The genus Ammolagena possesses a second aperture that opens out of the proloculus opposite the tubular chamber. Because no other genus belonging to the Suborder Ammodiscina possesses a second opening, and in the absence of any regular mode of coiling, we remove the genus Ammolagena from the Ammodiscina, and place it in the new family Ammolagenidae within the Suborder Hormosinina, Superfamily Hormosinellacea.
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