Silvia Spezzaferri

In situ measurements of Li isotopes in foraminifera

In situ measurement of Li isotope ratios in foraminifera has been developed using a Cameca ims 1270 ion microprobe. In situ δ7Li analyses have been performed in biogenic calcite of planktonic foraminifera from various locations. Results show that for west Pacific mixed Globigerinoides and Globorotalia (22°S161°E), the isotopic variability between tests and within a single test, respectively, is not significantly greater than estimated analytical uncertainty (∼1.5‰). Mean δ7Li for several planktonic foraminifera tests corresponds to the seawater value, strongly suggesting negligible Li isotope fractionation relative to seawater, as previously inferred by Hall et al. (2005) using thermo-ionization mass spectrometer and multicollector-inductively coupled plasma-mass spectrometry techniques. Combined with scanning electron microscopy and ion microprobe imaging, micron-sized grains, enriched in lithium, silica and aluminum have been found in the foraminifera calcite matrix. A simple mixing model shows that 0.3–2 wt % of marine clays incorporated within the analyzed calcite would lower the foraminifera δ7Li value, by 3‰ to 10‰ relative to the isotopic composition of the pure calcite. By comparison, no such grains have been detected in corals. The presence of micron-sized silicate grains embedded within the foraminifera calcite is consistent with the Erez (2003) biomineralization model, involving calcite precipitation from seawater vacuoles. By contrast, coral calcium carbonate is instead precipitated from ions, which have been pumped or diffused through several membranes, impermeable to micrometric grains. Ion microprobe in situ δ7Li measurements in biogenic calcite present new methods for investigating both biomineralization processes and the past record of the ocean composition by exploring geochemical variations at a scale that is smaller in space and in time.

Integrated planktonic foraminifera, Bolboforma and carbon isotope stratigraphy in a mid/early late Miocene carbonate ramp setting from the Acreide area (Sicily)

Taxa of Bolboforma, a marine calcareous microfossil group of uncertain origin with affinities to protophytic algae, are generally used for biostratigraphy of lower Eocene to lower Pleistocene marine sediments from high latitudes. Biostratigraphy based on Bolboforma has been applied only rarely to European outcrop sections and very rarely to Mediterranean sections. Three Bolboforma and two planktonic foraminifera events are identified and used to interpret the sedimentation rate of the 90 m of slope sediments from the Palazzolo Section, Palazzolo Acreide area (Sicily) and spanning the interval from 11.9 to approximately 10.5 Ma. Carbon isotope stratigraphy supports the age assigment based on Bolboforma and planktonic foraminifera. In particular, the sediments of the Palazzolo Section seem to record the latest pulse of the Monterey Event, a major perturbation in the global carbon cycle related to global intensification of upwelling. Expanded use of the Bolboforma may, thus, improve stratigraphy in outcropping Miocene sequences in temperate regions, particularly in shallower water facies with poorly resolved planktonic foraminifera and nannofossil stratigraphy.

The Helgoland Experiment – assessing the influence of methodologies on Recent benthic foraminiferal assemblage composition

The aim of the present study was to compare preservation, staining and preparation techniques to assess the influence of different sample treatments and analyses on the accuracy of benthic foraminiferal assemblage data from NE Atlantic shelf seas. Replicate surface samples from the SE North Sea were preserved with ethanol–rose Bengal or formalin, some were stained after processing, or foraminifera were concentrated by flotation. Coloration of living specimens was different between samples treated with an ethanol–rose Bengal solution and those stained after washing. In the latter case, only the last two or three chambers were stained. The aliquot sample preserved with formalin showed dissolution features in agglutinated and porcellaneous species. Population density varied between different preservation, picking modes and investigators. The accuracy of picking was in the range of ±2 % (1σ), while external reproducibility ranged from −34 to +16 %. There was no significant difference between wet and dry picking. Samples that were concentrated by flotation generally yielded a lower number of specimens. Agglutinated species were under-represented in samples that were stained after washing and in the flotation concentrate. Size fractions showed a reduction of population density and Fisher alpha diversity index with increasing mesh size. Only half of the specimens and less than two-thirds of the species are captured if the >125 µm rather than >63 µm fraction is analysed. In oxygen minimum zones, where small-sized species dominate the assemblage, the recovery in larger size fractions could be lower.

Reworked microfossils as a paleogeographic tool

The abundant occurrence of reworked microfossils within the paleogeographically restricted Upper Rhine Graben of central Europe represents a unique opportunity to investigate their inherent information, allowing new insights into the paleogeographic framework and past sedimentary pathways. In the late Rupelian and early Chattian a transgression-regression cycle linked to the global Ru2–Ru3 sequences affected the entire Upper Rhine Graben basin, leading to the deposition of a thick marine to lacustrine series. The occurrences of abundant reworked planktonic foraminifera are grouped into several events that are linked to intervals of increased clastic input during regressive phases. The biostratigraphic ranges of the reworked taxa indicate Late Cretaceous, Ypresian, Lutetian, and Bartonian–Priabonian ages for the sediment sources. The reworking originated from related west alpine source deposits via a northward-draining fluviatile system. A fast uplift of Priabonian and older deposits within the alpine realm during the late Rupelian is accordingly inferred, confirming the increased rate of the mesoalpine orogeny at that time. The careful analysis of reworked microfossil assemblages thus provides a valid tool for future paleogeographic, tectonic, and provenance studies.

Correlation between pollution and decline of Scleractinian Cladocora caespitosa (Linnaeus, 1758) in the Gulf of Gabes

During an expedition in 2014 in the Gulf of Gabes that aimed to evaluate the impact of the pollution of the phosphate industry on the marine environment, numerous dead coral fragments were retrieved from several stations along a 18 km long transect in front of the industry complex of Gabes. Detailed taxonomy of these coral fragments shows clearly that all fragments belong to the species Cladocora caespitosa (Linnaeus, 1758). Quantitative analysis of the coral fragments indicates a positive correlation with stations characterized by positive bathymetric anomalies. We suggest the presence of probable small-scaled (up to 4 m high) biogenic (palaeo-) build-ups composed mainly of coral colonies and bryozoans. Radiocarbon dating of three coral fragments show ages as old as 1897, 1985 and 1986 AD and suggests the presence of living C. caespitosa as close as 6 km to the phosphate treatment industry of Gabes at least until 1986 AD. This latter age coincides with the construction of the ammonium phosphate production plant, in 1979, in the Gulf of Gabes with an increase of the natural phosphate production. The higher impact of pollution on the marine environment in the inner part of the Gulf of Gabes likely induced the decline of C. caespitosa. This is well in agreement with enhanced siltation processes suggested by the sedimentary facies and grain-size analyses presently characterizing the Gulf of Gabes nowadays.

Bolboforma — an overview

A summary of the present knowledge ofBolboforma is presented in this paper. The genusBolboforma contains a diverse group of marine, mostly single-chambered enigmatic microfossils (phytoplankton, possibly Chrysophyta) which produced calcitic monocrystalline spheroidal tests with or without inner cysts and with various types of ornamentation. The genusBolboforma occurs in the time interval between late Early Eocene to Late Pliocene, at middle and higher latitudes, and thus, has not been recorded in Quaternary to Recent Sediments. The genus is represented globally, but the first and the last occurrence of the genus appear to be spatially diachronous in both hemispheres.Bolboforma started in the southern hemisphere at the Campbell Plateau (SW Pazific) during the Early Eocene approximately 53 Ma ago, and the genus lived there until latest Miocene times (5.3 Ma at the Kerguelen Plateau, Southern Indian Ocean). The first occurrence ofBolboforma in the northern hemisphere is observed in Upper Eocene Sediments (ca. 36.5 Ma) in the Labrador Sea (North Atlantic), and its youngest occurrence is observed in the Hatton-Rockall Basin (North Atlantic) in the Late Pliocene at 2.84 Ma. Well established and common species permit the definition of nineteenBolboforma zones/subzones. Not all of these are observed in both hemispheres. In the southern hemisphere all four Paleogene zones, but only eight Neogene zones are present, in the northern hemisphere only one Paleogene zone, but fourteen Neogene zones have been determined.Bolboforma distribution, which appears to be broadly bipolar in temperate to cool regions at middle to higher latitudes, aso seems to be linked to the evolution of surface watermasses and their boundaries.KurzfassungDer Wissensstand zuBolboforma wird dargestellt. Zur GattungBolboforma werden Mikrofossilien (Phytoplankton, Chrysophyta ?) gestellt, die zwiebeiförmige, einkammerige, selten länglich-zweikammerige, unterschiedlich ornamentierte, monokristallin-kalzitische Gehäuse, mit und ohne innere Zysten, ausbilden. Bolboformen werden weltweit in marinen Sedimenten des unteren Eozän bis oberen Pliozän, hauptsächlich in mittleren bis hohen Breiten, beobachtet. Das erste und letzte Auftreten von Bolboformen ist in beiden Hemisphären zeitlich unterschiedlich zu datieren: ihre Entwicklung startete im frühen Eozän vor ca. 53 Ma in der südlichen Hemisphäre (Campbell Plateau, SW Pazifik), und ihr letztes Auftreten wurde dort im späten Miozän vor 5.3 Ma (Kerguelen Plateau, S Indik) beobachtet. In der nördlichen Hemisphäre wurden sie erst im späten Eozän vor ca. 36.5 Ma (Labrador Sea, N Atlantik) beobachtet, und das jüngste Auftreten ist im späten Pliozän vor 2.84 Ma (Hatton-Rockall Basin, N Atlantik) zu vermerken. Gut zu unterscheidende und häufige Arten definieren neunzehnBolboforma Zonen/Subzonen. Nicht alle Zonen werden in beiden Hemisphären beobachtet. So sind in der südlichen Hemisphäre zwar alle vierBolboforma Zonen des Paläogens präsent, aber nur acht der neogenenBolboforma Zonen. Für die nördliche Hemisphäre sind nur eine paläogene, aber 14 neogeneBolboforma Zonen belegt. Die biogeographische Verteilung der Bolboformen ist an die Entwicklung der Oberflächen-Wassermassen und ihrer Begrenzungen gekoppelt.

Microfossils, a Key to Unravel Cold-Water Carbonate Mound Evolution through Time: Evidence from the Eastern Alboran Sea

Cold-water coral (CWC) ecosystems occur worldwide and play a major role in the oceans carbonate budget and atmospheric CO2 balance since the Danian (~65 m.y. ago). However their temporal and spatial evolution against climatic and oceanographic variability is still unclear. For the first time, we combine the main macrofaunal components of a sediment core from a CWC mound of the Melilla Mounds Field in the Eastern Alboran Sea with the associated microfauna and we highlight the importance of foraminifera and ostracods as indicators of CWC mound evolution in the paleorecord. Abundances of macrofauna along the core reveal alternating periods dominated by distinct CWC taxa (mostly Lophelia pertusa, Madrepora oculata) that correspond to major shifts in foraminiferal and ostracod assemblages. The period dominated by M. oculata coincides with a period characterized by increased export of refractory organic matter to the seafloor and rather unstable oceanographic conditions at the benthic boundary layer with periodically decreased water energy and oxygenation, variable bottom water temperature/density and increased sediment flow. The microfaunal and geochemical data strongly suggest that M. oculata and in particular Dendrophylliidae show a higher tolerance to environmental changes than L. pertusa. Finally, we show evidence for sustained CWC growth during the Alleröd-Younger-Dryas in the Eastern Alboran Sea and that this period corresponds to stable benthic conditions with cold/dense and well oxygenated bottom waters, high fluxes of labile organic matter and relatively strong bottom currents

Fossil planktic foraminifera (an overview)

Planktic foraminifera are unicellular marine organisms able to produce calcareous tests, which can be fossilized and, therefore, can give important information about the geologic record. In this overview a summary of the present knowledge of fossil planktic foraminifera together with the gradual steps from the earliest and pioneering to the more recent studies on this microfossil group, is given. In particular, the criteria at the base of the classification of these organisms from the earlier studies until the present, are described and summarized. An overview of the biostratigraphic schemes based on species first and last occurrences and assemblages from different latitudes and different regions is also given. The evolution and the response of planktic foraminifera to changing environmental condition are summarized from the more primitiveGlobigerina-like Jurassic forms, to the specialized and diversified Cretaceous species, until their dramatic crisis across the Cretaceous/Tertiary boundary, their successive recovery in the Paleocene and their evolution toward modern organisms. Finally, an overview is given of the use of planktic foraminifera to reconstruct paleoenvironments from the more simple methods to those implying more sophisticated and recent techniques.KurzfassungPlanktische Foraminiferen sind marine Einzeller, die kalkige Gehause ausbilden. Diese können fossilisiert werden und sind dann wertvolle Datenträger zur Lösung geologischer Fragestellungen. Ein Überblick, beginnend mit den frühesten Studien an planktischen Foraminiferen bis hin zu den jüngsten Erkenntnissen über diese Organismengruppe wird hier gegeben. Diskutiert und bewertet werden die Merkmale und Kriterien die zur systematischen Klassifikation der planktischen Foraminiferen führten. Biostratigrafische Schemata, die aufgrund des Ein- und Aussetzens diverser Taxa erarbeitet wurden, gültig für unterschiedliche geografische Breiten und Regionen, werden erläutert. Die Evolution der planktischen Foraminiferen wird als Antwort dieser Organismen auf die wechselnde geologische Geschichte interpretiert: beginnend mit einfach gebautenGlobigerina-ähnlichzn jurassischen Formen, der großen Artenfülle und Spezifikation während der Kreide, bis zu ihrem dramatischen Rückgang an der Kreide/Tertiär-Grenze, ihrer erneuten schrittweisen Entfaltung im Paläozän und ihrer Entwicklung im Paleogen und Neogen, bis hin zu den rezenten Formen. Diskutiert werden die Möglichkeiten mit Hilfe planktischer Foraminiferen palökologische Analysen und Rekonstruktionen durchzuführen. Zusammenfassend darf gesagt werden, dass planktische Foraminiferen zur Beantwortung unterschiedlichster geowissenschaftlicher Fragen herangezogen werden können.

Internal pore measurements on macroperforate planktonic Foraminifera as an alternative morphometric approach

Because of the lack of genetic control on extinct species, the morphologic approach remains the only way of identifying fossil Foraminifera. In addition to comparative description of gross shell morphology, morphometry became more important in recent years and was extended to encompass the ultrastructure of the shells. In particular, some studies focused on porosity, as determined by the pore diameters plotted against the number of pores per given surface. However, taking into account the poor preservation and recrystallization, which often affects and characterizes fossil specimens, and/or the deficiencies connected to the interpretation of scanning electron microscope images, pore measurements are often distorted, limited in number and lacking precision, and thus unreliable. We demonstrate that, by measuring the pores from inside the shell and individually, it is possible to obtain numerous and precise data either on an individual basis or for statistical purposes. This study also suggests that in the Early Miocene Globigerinoides, which is generally strongly susceptible for dissolution, the dissolution proceeds from the external towards the internal side of the shell.

Growth and demise of a Paleogene isolated carbonate platform of the Offshore Indus Basin, Pakistan: effects of regional and local controlling factors

Based on high-resolution seismic and well datasets, this paper examines the evolution and drowning history of a Paleocene–Eocene carbonate platform in the Offshore Indus Basin of Pakistan. This study uses the internal seismic architecture, well log data as well as the microfauna to reconstruct factors that governed the carbonate platform growth and demise. Carbonates dominated by larger benthic foraminifera assemblages permit constraining the ages of the major evolutionary steps and show that the depositional environment was tropical within oligotrophic conditions. With the aid of seismic stratigraphy, the carbonate platform edifice is resolved into seven seismic units which in turn are grouped into three packages that reflect its evolution from platform initiation, aggradation with escarpment formation and platform drowning. The carbonate factory initiated as mounds and patches on a Cretaceous–Paleocene volcanic complex. Further, the growth history of the platform includes distinct phases of intraplatform progradation, aggradation, backstepping and partial drownings. The youngest succession as late-stage buildup records a shift from benthic to pelagic deposition and marks the final drowning in the Early Eocene. The depositional trend of the platform, controlled by the continuing thermal subsidence associated with the cooling of volcanic margin lithosphere, was the major contributor of the accommodation space which supported the vertical accumulation of shallow water carbonate succession. Other factors such as eustatic changes and changes in the carbonate producers as a response to the Paleogene climatic perturbations played secondary roles in the development and drowning of these buildups.