Mona Seddighi - Academia.edu (original) (raw)
Papers by Mona Seddighi
Bollettino della societa paleontologica italiana. Societa paleontologica italiana, 2015
Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determine... more Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determined using a settling tube. The tests were collected from the nummulite banks of Pederiva di Grancona (A forms of N. lyelli and N. striatus, Middle Eocene) and San Germano dei Berici (A and B forms of N. fabianii, Late Eocene), both in the Berici Mts. (Veneto, northern Italy). The data were compared with estimated settling velocities that the same specimens might have had in life conditions. This was done by reconstructing their densities simulating water-filled condition and, to simulate post-diagenetic effects, under calcite-filled condition. These simulations show that A and B forms, even if they greatly diverge in shape, volume and size, still possess comparable settling velocities, and that each nummulite bank is characterized by specific hydrodynamic parameters. The use of settling velocity as a parameter to quantify the hydrodynamic behaviour of particles in seawater enables estimati...
A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benth... more A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benthic foraminifera (LBF) is available. The taxonomic and stratigraphic revision of the most diverse groups of LBFs (nummulitids, alveolinids, orthophragmines) in the 1970-1980 produced the Tethyan SBZ (Shallow Benthics Zonation) zonation. Recent developments in systematics, isotopic geochemistry, structural analysis of the complex tests, biostratigraphic interpretation of shallow marine sediments, Cenozoic paleogeography and paleoclimate in particular, need to be presented in a way that everyone may easily get up to date information about the species of this particular group of microfossils. In order to obtain full appreciation of recent progress, a group of micropaleontologists (the Working group on Larger Foraminifera, WOLF) working on Paleogene larger foraminifera decided that an useful means for integrating diverse data is to produce atlases. Traditionally, atlases are considered as the most useful tool for the field geologists, regional stratigraphers and paleontologists. Through several meetings (Ankara 2009, Miskolc 2010, Croatia 2011, Austria and Slovenia 2012), guidelines for the atlases, including a time-line, have been defined. The updated taxonomy, paleoecology and biostratigraphy of the diverse Paleogene larger foraminifera (including over 1150 recorded species) will be thus presented through atlases. It is planned to overcome discrepancies in quantity and quality of data between the Central Tethys area (for which monographs exist since the late 19th century, and more recently from Turkey and the Northern Peritethys) and the Middle-, Far East Tethyan and Caribbean bioprovinces, by a) a revision of museum collections; b) inviting micropaleontologists from these regions to join in this collaborative effort. The first stage is an Atlas of Paleocene larger benthic foraminifera, where each species-rank taxon (at least 153 known) will be described with original or emended species descriptions, synonymy, biostratigraphic range information (the S B Z biozonation), paleoenvironmental interpretation, illustrated with original and new images, including the holotype, and whenever possible, with SEM and CT-Scan3D images
PALAIOS, 2017
The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to s... more The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to shed light on it by observing the hydrodynamic behavior of selected larger foraminifera collected from both bank and nonbank deposits. Entrainment and settling velocity of both recent and fossil larger foraminifera were measured using a flume channel and settling tube. Both velocities give information about the reaction of foraminiferal shells to different hydrodynamic conditions affecting their capability to build bank-like sedimentary structures. To assess entrainment, experiments were performed on different substrates to simulate bed load transport on smooth surfaces, fine sand, coarse sand, and bioclastic substrates. Thirty-four recent and 49 fossil shells of foraminifera were used; recent taxa used are Operculina ammonoides, Heterostegina depressa, and Palaeonummulites venosus and fossil taxa used are Nummulites perforatus, N. fabianii, and N. tavertetensis (only A forms were used in this study). Our results seem to differentiate the hydrodynamic behavior of shells collected from banks from those collected from non-bank deposits. The latter possess settling velocities significantly lower than their entrainment velocities, while for taxa collected from nummulite banks, settling velocities are always close to entrainment velocities. Therefore, the relation between hydrodynamics and shape and size may explain why modern larger foraminifera, consistently of smaller size than fossil forms, cannot produce banks and that transport as bed load in moving water was possibly the main trigger for the production of nummulite banks.
Historical Biology, 2012
In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom ... more In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom Formation were deposited on a carbonate platform which is dominated by rhodalgal associations occurring in tropical–subtropical environment. The biogenic rhodalgal association is dominated by bryozoa, coralline red algae, bivalves and echinoids together with smaller amounts of photo-dependent biota including large benthic foraminifera and corals.
A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benth... more A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benthic foraminifera (LBF) is available. The taxonomic and stratigraphic revision of the most diverse groups of LBFs (nummulitids, alveolinids, orthophragmines) in the 1970-1980 produced the Tethyan SBZ (Shallow Benthics Zonation) zonation. Recent developments in systematics, isotopic geochemistry, structural analysis of the complex tests, biostratigraphic interpretation of shallow marine sediments, Cenozoic paleogeography and paleoclimate in particular, need to be presented in a way that everyone may easily get up to date information about the species of this particular group of microfossils. In order to obtain full appreciation of recent progress, a group of micropaleontologists (the Working group on Larger Foraminifera, WOLF) working on Paleogene larger foraminifera decided that an useful means for integrating diverse data is to produce atlases. Traditionally, atlases are considered as the most useful tool for the field geologists, regional stratigraphers and paleontologists. Through several meetings (Ankara 2009, Miskolc 2010, Croatia 2011, Austria and Slovenia 2012), guidelines for the atlases, including a time-line, have been defined. The updated taxonomy, paleoecology and biostratigraphy of the diverse Paleogene larger foraminifera (including over 1150 recorded species) will be thus presented through atlases. It is planned to overcome discrepancies in quantity and quality of data between the Central Tethys area (for which monographs exist since the late 19th century, and more recently from Turkey and the Northern Peritethys) and the Middle-, Far East Tethyan and Caribbean bioprovinces, by a) a revision of museum collections; b) inviting micropaleontologists from these regions to join in this collaborative effort. The first stage is an Atlas of Paleocene larger benthic foraminifera, where each species-rank taxon (at least 153 known) will be described with original or emended species descriptions, synonymy, biostratigraphic range information (the S B Z biozonation), paleoenvironmental interpretation, illustrated with original and new images, including the holotype, and whenever possible, with SEM and CT-Scan3D images
Journal of Foraminiferal Research, 2018
Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significa... more Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significance of these peculiar sedimentary structures has been debated, especially whether they are of autochthonous or allochthonous origin. At first considered as substantially autochthonous, an alternative interpretation as allochthonous deposits was suggested in the mid-1980s to explain the observation of sedimentary features indicating displacement of the nummulite tests. In more recent literature, we found examples of non-uniform use of the nummulite bank concept; sometimes the ‘banks’ are vaguely described as nummulite-rich beds, and illustrations may not allow recognition of the features characteristic of the real banks. In an attempt to achieve a scientifically robust model explaining the genesis of the nummulite banks, our objective was to test the original definition, based upon the most fundamental and useful characteristics that can be observed in the field, even in non-optimal outcr...
The "nummulite bank" is an accumulation of nummulite tests, mainly monospecific, with b... more The "nummulite bank" is an accumulation of nummulite tests, mainly monospecific, with both microspheric and megalospheric generations of the same species. Moreover, it usually contains more tests of larger B forms as compared with the normal nummulite-bearing limestones.Previous works on nummulite banks have resulted in the proposition of two models. The first, by Arni, suggests that nummulite test accumulations form autochthonous or in-situ banks acting as an effective barrier, analogous to present-day coral reefs. On the other hand Aigner, based upon several evidences of physical transportation shown in sedimentary structure and biofabrics of Nummulites deposits, considered them as allochthonous.So far there is no quantitative data available about the taxonomic composition of nummulite banks. Here we present the preliminary results of a quantitative examination on a case-study from the Middle Eocene of Northern Italy. The samples were collected in Pederiva di Grancona (Vicenza Province, Veneto area). The Nummulites lyelli from this well-known site were described and figured by Schaub in his monograph.The present work is based upon the preliminary examination of 50 grams from a washed sample of the nummulite bank. In this fraction, 509 individuals (A forms) of Nummulites have been counted. The dominant species is N. lyelli accounting for approximately 77.1%, followed by N. striatus with 10.5%. The rest are the accessory species including N. biarritzensis (5.9%), N. discorbinus (4.9%), and N. beaumonti (1.6%). According to the dominance of N. lyelli and the stratigraphic distribution of the other Nummulites species the sample is assigned to the SBZ 17 (early Bartonian).N. lyelli A in this sample has a mean diameter of 5.75 mm, whereas that of N. striatus Ais 4.20 mm. The two most abundant species display a clear difference in size: N. lyelli mean diameter exceeds about +37% in comparison with N. striatus. Given that N. lyelli is also more inflated than N. striatus, they probably had a quite different hydrodynamic behaviour.The taxonomic composition of the bank in this case study shows that it is not strictly monospecific, as in the models from the literature: even if there is a strong dominance of N. lyelli, N. striatus cannot be discarded as negligible. Moreover, there are three more species of the same genus which are present in significant percentages, pointing to an unexpectedly rich nummulite assemblage. This in turn casts serious doubts on the allochthonous model for nummulite bank accumulations
European Geosciences Union General Assembly 2011 Vienna | Austria | 03 \u2013 08 April 201
La prima descrizione della peculiare facies oggi nota come banco a nummuliti si deve a Nemkov (19... more La prima descrizione della peculiare facies oggi nota come banco a nummuliti si deve a Nemkov (1962). Ciononostante, l'introduzione dell'espressione 'banco a nummuliti', accompagnata da una definizione chiara e dettagliata delle sue caratteristiche, \ue8 data soltanto da Arni (1965), che resta i l lavoro di riferimento per ogni successiva interpretazione. Nella sua definizione originale compaiono quali elementi distintivi del banco a nummuliti la monospecificit\ue0 (in rari casi la dominanza di due specie) e l'inusuale abbondanza delle grandi forme microsferiche (B). Questi elementi, presi insieme, consentono di individuare facilmente in affioramento un banco a nummuliti, grazie all'abbondanza ed alla monotonia dei fossili visibili ad occhio nudo. La diffusione del concetto e dell'espressione 'banco a nummuliti' a livello geologico non corrisponde per\uf2 ad una maggiore chiarezza nel distinguere ci\uf2 che \ue8 banco da ci\uf2 che non lo \ue8. Il concetto originale, pur essendo di fatto abbastanza chiaro, non \ue8 finora stato definito in modo pi\uf9 rigoroso e quantitativo, lasciando troppo spazio alla soggettivit\ue0 dell'osservatore. In particolare, mancano finora definizioni chiare di quali siano i limiti a) per considerare un'associazione fossile come 'monospecifica' e b) per poter individuare un'abbondanza inusuale di forme B del genere Nummulites. Una serie di osservazioni quantitative eseguite su diversi casi di presunti banchi a nummuliti, e su alcuni esempi di normali calcari a nummuliti, hanno permesso di individuare parametri numerici che permettono di decidere se ci si trova davanti un banco a nummuliti o no. Le osservazioni sono state svolte su rocce di diverse et\ue0 (Eocene inferiore, medio e superiore) e diverse aree geografiche (Spagna, Italia, Germania, Romania). I risultati permettono di proporre dei limiti numerici alla dominanza di una specie, che viene individuata in almeno il 75% degli esemplari dell'associazione fossile, ed al rapporto tra forme A e forme B . Per quanto riguarda quest'ultimo parametro, i l rapporto tradizionalmente riportato come 'normale' di 10:1 si dimostra del tutto irrealistico nei casi osservati. Infatti, per i casi di banchi a nummuliti presi in esame per il presente studio, il rapporto A/B risulta variabile da 7 a 50, mentre per i normali calcari a nummuliti esso varia da 60 a circa 350. In alcuni casi, quando i parametri siano vicini ai valori limite, si sono considerati i campioni come non-banco senza per questo ritenere che si tratti di facies 'normali'; appare chiaro infatti che devono esistere una serie di facies di transizione tra il banco propriamente detto ed i normali calcari a nummuliti. In almeno un caso \ue8 stata identificata una facies di banco nella quale la specie dominante non appartiene al genere Nummulites, ma ad Assilina. Tale facies pu\uf2 essere quindi indicata come banco ad assilina (assilina bank). Arai P. (1965). L'\ue9volution des nummulitinae en tant que facteur de modification des d\ue9p\uf2ts littoraux. M\ue9moirs du Bureau de Recherches g\ue9ologiques et Mini\ue8res, 32: 7-20. Nemkov G. (1962). Remarques sur la pal\ue9o\ue9cologic des Nummulites. Voprosy Micropaleontologii SSSR, 6: 64-72
Sedimentology, 2021
Biostromes and low‐relief bioherms, some of which are characterized by exceptionally large, flat ... more Biostromes and low‐relief bioherms, some of which are characterized by exceptionally large, flat specimens of larger benthic foraminifera, are common in Palaeogene and Miocene carbonates, most notably those deposited along the Neotethys Seaway and tropical Pacific islands. By incorporating insights from palaeoceanographic research and the biology of living larger benthic foraminifera, a scenario is proposed that can account for palaeontological and sedimentological features while augmenting previous interpretations. Sexual reproduction by gamete broadcasting is common in foraminiferal taxa, including extant Nummulitidae and Amphisteginidae. Resultant zygotes can develop into tiny, resistant, easily dispersed propagules that recruit in suitable benthic‐environmental conditions. The role of algal symbiosis in the biology of larger benthic foraminifera is well‐documented. Palaeoceanographically, such taxa proliferated during times of reduced thermal stratification of the oceans. In regions with exceptionally clear, nutrient‐depleted waters, ‘twilight‐zone’ light penetration was sufficient, at least intermittently, to support some photosynthesis. On outer‐shelf or promontory sites at depths of ca 100 to 200 m, the tiny propagules of larger benthic foraminiferal species, incorporating algal symbionts with the lowest light requirements, could have settled and recruited, growing very slowly, nourished by feeding on bacteria and the limited photosynthate produced by their algal symbionts. Under such conditions, thin microspheric individuals of one or two larger benthic foraminiferal taxa could have survived and grown slowly over several years to very large shell diameters, seldom reproducing asexually. Resulting carbonate accumulation rates would have been very slow, such that even rare disturbances by currents, major storms or internal waves could have produced evidence of winnowing and sedimentary structures. The fossil evidence of such habitats should include biostromes or possibly low‐relief bioherms of low diversity assemblages characterized by abundant, exceptionally large, flat, microspheric larger benthic foraminifera.
Journal of Foraminiferal Research, 2018
Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significa... more Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significance of these peculiar sedimentary structures has been debated, especially whether they are of autochthonous or allochthonous origin. At first considered as substantially autochthonous, an alternative interpretation as allochthonous deposits was suggested in the mid-1980s to explain the observation of sedimentary features indicating displacement of the nummulite tests. In more recent literature, we found examples of non-uniform use of the nummulite bank concept; sometimes the ‘banks’ are vaguely described as nummulite-rich beds, and illustrations may not allow recognition of the features characteristic of the real banks. In an attempt to achieve a scientifically robust model explaining the genesis of the nummulite banks, our objective was to test the original definition, based upon the most fundamental and useful characteristics that can be observed in the field, even in non-optimal outcrop conditions: the A/B ratio and the percentage composition (dominance) of the fossil assemblage. Both can be quantified using simple techniques on samples collected for this purpose.
In an extensive survey of nummulite banks and non-banks from Italy, Spain, Romania, and Germany, we determined A/B ratios and taxonomic composition of the nummulite assemblages. Recognized nummulite banks are characterized by A/B ratios <60 and dominance of one species accounting for at least 75% of the specimens of Nummulites. Non-bank samples show A/B ratios between 60–350 and dominance usually <50%. An unexpected result was the discovery of an ‘Assilina bank’, characterizing both conditions for recognition of a nummulite bank, but with Assilina cuvillieri as the dominant species representing >75% of the larger foraminiferal assemblage.
In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom ... more In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom Formation were deposited on a carbonate platform which is dominated by rhodalgal associations occurring in tropical– subtropical environment. The biogenic rhodalgal association is dominated by bryozoa, coralline red algae, bivalves and echinoids together with smaller amounts of photo-dependent biota including large benthic foraminifera and corals. The abundance of heterozoan association and the bloom of suspension-feeding organisms are the result of an increase in nutrient availability which has profound controlling effect on the biotic system. The low occurrence of symbiont-bearing benthic foraminifera and coral, typical of stable, oligotrophic condition, represents their low tolerance to unstable, nutrient-rich environment. In the investigated Oligocene – Miocene shallow marine carbonate succession, 10 different microfacies were distinguished through depositional texture and biotic components. The rock sequences investigated are referred to an open shelf carbonate platform in which the depositional environments range from outer shelf to inner shelf conditions.
The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to s... more The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to shed light on it by observing the hydrodynamic behavior of selected larger foraminifera collected from both bank and non-bank deposits. Entrainment and settling velocity of both recent and fossil larger foraminifera were measured using a flume channel and settling tube. Both velocities give information about the reaction of foraminiferal shells to different hydrodynamic conditions affecting their capability to build bank-like sedimentary structures. To assess entrainment, experiments were performed on different substrates to simulate bed load transport on smooth surfaces, fine sand, coarse sand, and bioclastic substrates. Thirty-four recent and 49 fossil shells of foraminifera were used; recent taxa used are Operculina ammonoides, Heterostegina depressa, and Palaeonummulites venosus and fossil taxa used are Nummulites perforatus, N. fabianii, and N. tavertetensis (only A forms were used in this study). Our results seem to differentiate the hydrodynamic behavior of shells collected from banks from those collected from non-bank deposits. The latter possess settling velocities significantly lower than their entrainment velocities, while for taxa collected from nummulite banks, settling velocities are always close to entrainment velocities. Therefore, the relation between hydrodynamics and shape and size may explain why modern larger foraminifera, consistently of smaller size than fossil forms, cannot produce banks and that transport as bed load in moving water was possibly the main trigger for the production of nummulite banks.
Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determine... more Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determined using a settling tube. The tests were collected from the nummulite banks of Pederiva di Grancona (A forms of N. lyelli and N. striatus, Middle Eocene) and San Germano dei Berici (A and B forms of N. fabianii, Late Eocene), both in the Berici Mts. (Veneto, northern Italy). The data were compared with estimated settling velocities that the same specimens might have had in life conditions. This was done by reconstructing their densities simulating water-filled condition and, to simulate post-diagenetic effects, under calcite-filled condition. These simulations show that A and B forms, even if they greatly diverge in shape, volume and size, still possess comparable settling velocities, and that each nummulite bank is characterized by specific hydrodynamic parameters. The use of settling velocity as a parameter to quantify the hydrodynamic behaviour of particles in seawater enables estimation of palaeoenvironmental conditions such as depth, substrate and the energy scenario. Such information is useful in obtaining further insights into the genesis of nummulite banks, the autochthony or allochthony of which is still being debated. Our results point to an autochthonous interpretation. RIASSUNTO-[Nuovi risultati sul comportamento idrodinamico dei gusci fossili di Nummulites da due banchi a nummuliti del Bartoniano e Priaboniano dell'Italia settentrionale]-La genesi delle strutture bio-sedimentarie note come banchi a nummuliti è tuttora dibattuta. Sono state proposte sostanzialmente due interpretazioni: genesi autoctona, dovuta a particolari condizioni paleoecologiche e genesi alloctona, determinata da trasporto passivo ed accumulo per rideposizione. Questo studio ha lo scopo di fornire dati sulle proprietà idrodinamiche dei gusci fossili di Nummulites. Su 58 esemplari fossili ben conservati di tre diverse specie di questo genere sono state determinate sperimentalmente le velocità di sedimentazione in acqua marina, utilizzando un tubo di decantazione. I fossili sono stati raccolti dai banchi a nummuliti di Pederiva di Grancona (forme A di N. lyelli e N. striatus, Bartoniano, Eocene Medio) e San Germano dei Berici (forme A e B di N. fabianii, Priaboniano, Eocene Superiore), entrambi nei Monti Berici (Veneto, Italia settentrionale). I dati sono stati elaborati e confrontati con le velocità di sedimentazione stimate che gli stessi esemplari potrebbero aver avuto in vita. Le densità sono state ricostruite simulando la condizione del guscio pieno d'acqua e, per tener conto degli effetti post-diagenetici, simulando condizioni di riempimento delle cavità da parte della calcite. Le simulazioni mostrano che le forme A e B della stessa specie, anche se differiscono fortemente per forma, volume e dimensioni, possiedono velocità di sedimentazione comparabili, e che ogni banco a nummuliti è caratterizzato da specifiche classi di parametri idrodinamici. Le velocità stimate per i due casi in esame permettono di ipotizzare una diversa profondità di sviluppo per il banco di Pederiva di Grancona, più profondo rispetto a quello di San Germano dei Berici. L'uso della velocità di sedimentazione come unico parametro per valutare il comportamento idrodinamico delle particelle in acqua di mare, permette la stima di condizioni paleoambientali quali profondità e substrato e consente di delineare lo scenario energetico. Nel complesso, i risultati di questo studio fanno propendere per una genesi autoctona dei banchi a nummuliti.
Bollettino della societa paleontologica italiana. Societa paleontologica italiana, 2015
Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determine... more Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determined using a settling tube. The tests were collected from the nummulite banks of Pederiva di Grancona (A forms of N. lyelli and N. striatus, Middle Eocene) and San Germano dei Berici (A and B forms of N. fabianii, Late Eocene), both in the Berici Mts. (Veneto, northern Italy). The data were compared with estimated settling velocities that the same specimens might have had in life conditions. This was done by reconstructing their densities simulating water-filled condition and, to simulate post-diagenetic effects, under calcite-filled condition. These simulations show that A and B forms, even if they greatly diverge in shape, volume and size, still possess comparable settling velocities, and that each nummulite bank is characterized by specific hydrodynamic parameters. The use of settling velocity as a parameter to quantify the hydrodynamic behaviour of particles in seawater enables estimati...
A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benth... more A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benthic foraminifera (LBF) is available. The taxonomic and stratigraphic revision of the most diverse groups of LBFs (nummulitids, alveolinids, orthophragmines) in the 1970-1980 produced the Tethyan SBZ (Shallow Benthics Zonation) zonation. Recent developments in systematics, isotopic geochemistry, structural analysis of the complex tests, biostratigraphic interpretation of shallow marine sediments, Cenozoic paleogeography and paleoclimate in particular, need to be presented in a way that everyone may easily get up to date information about the species of this particular group of microfossils. In order to obtain full appreciation of recent progress, a group of micropaleontologists (the Working group on Larger Foraminifera, WOLF) working on Paleogene larger foraminifera decided that an useful means for integrating diverse data is to produce atlases. Traditionally, atlases are considered as the most useful tool for the field geologists, regional stratigraphers and paleontologists. Through several meetings (Ankara 2009, Miskolc 2010, Croatia 2011, Austria and Slovenia 2012), guidelines for the atlases, including a time-line, have been defined. The updated taxonomy, paleoecology and biostratigraphy of the diverse Paleogene larger foraminifera (including over 1150 recorded species) will be thus presented through atlases. It is planned to overcome discrepancies in quantity and quality of data between the Central Tethys area (for which monographs exist since the late 19th century, and more recently from Turkey and the Northern Peritethys) and the Middle-, Far East Tethyan and Caribbean bioprovinces, by a) a revision of museum collections; b) inviting micropaleontologists from these regions to join in this collaborative effort. The first stage is an Atlas of Paleocene larger benthic foraminifera, where each species-rank taxon (at least 153 known) will be described with original or emended species descriptions, synonymy, biostratigraphic range information (the S B Z biozonation), paleoenvironmental interpretation, illustrated with original and new images, including the holotype, and whenever possible, with SEM and CT-Scan3D images
PALAIOS, 2017
The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to s... more The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to shed light on it by observing the hydrodynamic behavior of selected larger foraminifera collected from both bank and nonbank deposits. Entrainment and settling velocity of both recent and fossil larger foraminifera were measured using a flume channel and settling tube. Both velocities give information about the reaction of foraminiferal shells to different hydrodynamic conditions affecting their capability to build bank-like sedimentary structures. To assess entrainment, experiments were performed on different substrates to simulate bed load transport on smooth surfaces, fine sand, coarse sand, and bioclastic substrates. Thirty-four recent and 49 fossil shells of foraminifera were used; recent taxa used are Operculina ammonoides, Heterostegina depressa, and Palaeonummulites venosus and fossil taxa used are Nummulites perforatus, N. fabianii, and N. tavertetensis (only A forms were used in this study). Our results seem to differentiate the hydrodynamic behavior of shells collected from banks from those collected from non-bank deposits. The latter possess settling velocities significantly lower than their entrainment velocities, while for taxa collected from nummulite banks, settling velocities are always close to entrainment velocities. Therefore, the relation between hydrodynamics and shape and size may explain why modern larger foraminifera, consistently of smaller size than fossil forms, cannot produce banks and that transport as bed load in moving water was possibly the main trigger for the production of nummulite banks.
Historical Biology, 2012
In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom ... more In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom Formation were deposited on a carbonate platform which is dominated by rhodalgal associations occurring in tropical–subtropical environment. The biogenic rhodalgal association is dominated by bryozoa, coralline red algae, bivalves and echinoids together with smaller amounts of photo-dependent biota including large benthic foraminifera and corals.
A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benth... more A wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene larger benthic foraminifera (LBF) is available. The taxonomic and stratigraphic revision of the most diverse groups of LBFs (nummulitids, alveolinids, orthophragmines) in the 1970-1980 produced the Tethyan SBZ (Shallow Benthics Zonation) zonation. Recent developments in systematics, isotopic geochemistry, structural analysis of the complex tests, biostratigraphic interpretation of shallow marine sediments, Cenozoic paleogeography and paleoclimate in particular, need to be presented in a way that everyone may easily get up to date information about the species of this particular group of microfossils. In order to obtain full appreciation of recent progress, a group of micropaleontologists (the Working group on Larger Foraminifera, WOLF) working on Paleogene larger foraminifera decided that an useful means for integrating diverse data is to produce atlases. Traditionally, atlases are considered as the most useful tool for the field geologists, regional stratigraphers and paleontologists. Through several meetings (Ankara 2009, Miskolc 2010, Croatia 2011, Austria and Slovenia 2012), guidelines for the atlases, including a time-line, have been defined. The updated taxonomy, paleoecology and biostratigraphy of the diverse Paleogene larger foraminifera (including over 1150 recorded species) will be thus presented through atlases. It is planned to overcome discrepancies in quantity and quality of data between the Central Tethys area (for which monographs exist since the late 19th century, and more recently from Turkey and the Northern Peritethys) and the Middle-, Far East Tethyan and Caribbean bioprovinces, by a) a revision of museum collections; b) inviting micropaleontologists from these regions to join in this collaborative effort. The first stage is an Atlas of Paleocene larger benthic foraminifera, where each species-rank taxon (at least 153 known) will be described with original or emended species descriptions, synonymy, biostratigraphic range information (the S B Z biozonation), paleoenvironmental interpretation, illustrated with original and new images, including the holotype, and whenever possible, with SEM and CT-Scan3D images
Journal of Foraminiferal Research, 2018
Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significa... more Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significance of these peculiar sedimentary structures has been debated, especially whether they are of autochthonous or allochthonous origin. At first considered as substantially autochthonous, an alternative interpretation as allochthonous deposits was suggested in the mid-1980s to explain the observation of sedimentary features indicating displacement of the nummulite tests. In more recent literature, we found examples of non-uniform use of the nummulite bank concept; sometimes the ‘banks’ are vaguely described as nummulite-rich beds, and illustrations may not allow recognition of the features characteristic of the real banks. In an attempt to achieve a scientifically robust model explaining the genesis of the nummulite banks, our objective was to test the original definition, based upon the most fundamental and useful characteristics that can be observed in the field, even in non-optimal outcr...
The "nummulite bank" is an accumulation of nummulite tests, mainly monospecific, with b... more The "nummulite bank" is an accumulation of nummulite tests, mainly monospecific, with both microspheric and megalospheric generations of the same species. Moreover, it usually contains more tests of larger B forms as compared with the normal nummulite-bearing limestones.Previous works on nummulite banks have resulted in the proposition of two models. The first, by Arni, suggests that nummulite test accumulations form autochthonous or in-situ banks acting as an effective barrier, analogous to present-day coral reefs. On the other hand Aigner, based upon several evidences of physical transportation shown in sedimentary structure and biofabrics of Nummulites deposits, considered them as allochthonous.So far there is no quantitative data available about the taxonomic composition of nummulite banks. Here we present the preliminary results of a quantitative examination on a case-study from the Middle Eocene of Northern Italy. The samples were collected in Pederiva di Grancona (Vicenza Province, Veneto area). The Nummulites lyelli from this well-known site were described and figured by Schaub in his monograph.The present work is based upon the preliminary examination of 50 grams from a washed sample of the nummulite bank. In this fraction, 509 individuals (A forms) of Nummulites have been counted. The dominant species is N. lyelli accounting for approximately 77.1%, followed by N. striatus with 10.5%. The rest are the accessory species including N. biarritzensis (5.9%), N. discorbinus (4.9%), and N. beaumonti (1.6%). According to the dominance of N. lyelli and the stratigraphic distribution of the other Nummulites species the sample is assigned to the SBZ 17 (early Bartonian).N. lyelli A in this sample has a mean diameter of 5.75 mm, whereas that of N. striatus Ais 4.20 mm. The two most abundant species display a clear difference in size: N. lyelli mean diameter exceeds about +37% in comparison with N. striatus. Given that N. lyelli is also more inflated than N. striatus, they probably had a quite different hydrodynamic behaviour.The taxonomic composition of the bank in this case study shows that it is not strictly monospecific, as in the models from the literature: even if there is a strong dominance of N. lyelli, N. striatus cannot be discarded as negligible. Moreover, there are three more species of the same genus which are present in significant percentages, pointing to an unexpectedly rich nummulite assemblage. This in turn casts serious doubts on the allochthonous model for nummulite bank accumulations
European Geosciences Union General Assembly 2011 Vienna | Austria | 03 \u2013 08 April 201
La prima descrizione della peculiare facies oggi nota come banco a nummuliti si deve a Nemkov (19... more La prima descrizione della peculiare facies oggi nota come banco a nummuliti si deve a Nemkov (1962). Ciononostante, l'introduzione dell'espressione 'banco a nummuliti', accompagnata da una definizione chiara e dettagliata delle sue caratteristiche, \ue8 data soltanto da Arni (1965), che resta i l lavoro di riferimento per ogni successiva interpretazione. Nella sua definizione originale compaiono quali elementi distintivi del banco a nummuliti la monospecificit\ue0 (in rari casi la dominanza di due specie) e l'inusuale abbondanza delle grandi forme microsferiche (B). Questi elementi, presi insieme, consentono di individuare facilmente in affioramento un banco a nummuliti, grazie all'abbondanza ed alla monotonia dei fossili visibili ad occhio nudo. La diffusione del concetto e dell'espressione 'banco a nummuliti' a livello geologico non corrisponde per\uf2 ad una maggiore chiarezza nel distinguere ci\uf2 che \ue8 banco da ci\uf2 che non lo \ue8. Il concetto originale, pur essendo di fatto abbastanza chiaro, non \ue8 finora stato definito in modo pi\uf9 rigoroso e quantitativo, lasciando troppo spazio alla soggettivit\ue0 dell'osservatore. In particolare, mancano finora definizioni chiare di quali siano i limiti a) per considerare un'associazione fossile come 'monospecifica' e b) per poter individuare un'abbondanza inusuale di forme B del genere Nummulites. Una serie di osservazioni quantitative eseguite su diversi casi di presunti banchi a nummuliti, e su alcuni esempi di normali calcari a nummuliti, hanno permesso di individuare parametri numerici che permettono di decidere se ci si trova davanti un banco a nummuliti o no. Le osservazioni sono state svolte su rocce di diverse et\ue0 (Eocene inferiore, medio e superiore) e diverse aree geografiche (Spagna, Italia, Germania, Romania). I risultati permettono di proporre dei limiti numerici alla dominanza di una specie, che viene individuata in almeno il 75% degli esemplari dell'associazione fossile, ed al rapporto tra forme A e forme B . Per quanto riguarda quest'ultimo parametro, i l rapporto tradizionalmente riportato come 'normale' di 10:1 si dimostra del tutto irrealistico nei casi osservati. Infatti, per i casi di banchi a nummuliti presi in esame per il presente studio, il rapporto A/B risulta variabile da 7 a 50, mentre per i normali calcari a nummuliti esso varia da 60 a circa 350. In alcuni casi, quando i parametri siano vicini ai valori limite, si sono considerati i campioni come non-banco senza per questo ritenere che si tratti di facies 'normali'; appare chiaro infatti che devono esistere una serie di facies di transizione tra il banco propriamente detto ed i normali calcari a nummuliti. In almeno un caso \ue8 stata identificata una facies di banco nella quale la specie dominante non appartiene al genere Nummulites, ma ad Assilina. Tale facies pu\uf2 essere quindi indicata come banco ad assilina (assilina bank). Arai P. (1965). L'\ue9volution des nummulitinae en tant que facteur de modification des d\ue9p\uf2ts littoraux. M\ue9moirs du Bureau de Recherches g\ue9ologiques et Mini\ue8res, 32: 7-20. Nemkov G. (1962). Remarques sur la pal\ue9o\ue9cologic des Nummulites. Voprosy Micropaleontologii SSSR, 6: 64-72
Sedimentology, 2021
Biostromes and low‐relief bioherms, some of which are characterized by exceptionally large, flat ... more Biostromes and low‐relief bioherms, some of which are characterized by exceptionally large, flat specimens of larger benthic foraminifera, are common in Palaeogene and Miocene carbonates, most notably those deposited along the Neotethys Seaway and tropical Pacific islands. By incorporating insights from palaeoceanographic research and the biology of living larger benthic foraminifera, a scenario is proposed that can account for palaeontological and sedimentological features while augmenting previous interpretations. Sexual reproduction by gamete broadcasting is common in foraminiferal taxa, including extant Nummulitidae and Amphisteginidae. Resultant zygotes can develop into tiny, resistant, easily dispersed propagules that recruit in suitable benthic‐environmental conditions. The role of algal symbiosis in the biology of larger benthic foraminifera is well‐documented. Palaeoceanographically, such taxa proliferated during times of reduced thermal stratification of the oceans. In regions with exceptionally clear, nutrient‐depleted waters, ‘twilight‐zone’ light penetration was sufficient, at least intermittently, to support some photosynthesis. On outer‐shelf or promontory sites at depths of ca 100 to 200 m, the tiny propagules of larger benthic foraminiferal species, incorporating algal symbionts with the lowest light requirements, could have settled and recruited, growing very slowly, nourished by feeding on bacteria and the limited photosynthate produced by their algal symbionts. Under such conditions, thin microspheric individuals of one or two larger benthic foraminiferal taxa could have survived and grown slowly over several years to very large shell diameters, seldom reproducing asexually. Resulting carbonate accumulation rates would have been very slow, such that even rare disturbances by currents, major storms or internal waves could have produced evidence of winnowing and sedimentary structures. The fossil evidence of such habitats should include biostromes or possibly low‐relief bioherms of low diversity assemblages characterized by abundant, exceptionally large, flat, microspheric larger benthic foraminifera.
Journal of Foraminiferal Research, 2018
Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significa... more Since the introduction of the concept of a “nummulite bank” more than 50 years ago, the significance of these peculiar sedimentary structures has been debated, especially whether they are of autochthonous or allochthonous origin. At first considered as substantially autochthonous, an alternative interpretation as allochthonous deposits was suggested in the mid-1980s to explain the observation of sedimentary features indicating displacement of the nummulite tests. In more recent literature, we found examples of non-uniform use of the nummulite bank concept; sometimes the ‘banks’ are vaguely described as nummulite-rich beds, and illustrations may not allow recognition of the features characteristic of the real banks. In an attempt to achieve a scientifically robust model explaining the genesis of the nummulite banks, our objective was to test the original definition, based upon the most fundamental and useful characteristics that can be observed in the field, even in non-optimal outcrop conditions: the A/B ratio and the percentage composition (dominance) of the fossil assemblage. Both can be quantified using simple techniques on samples collected for this purpose.
In an extensive survey of nummulite banks and non-banks from Italy, Spain, Romania, and Germany, we determined A/B ratios and taxonomic composition of the nummulite assemblages. Recognized nummulite banks are characterized by A/B ratios <60 and dominance of one species accounting for at least 75% of the specimens of Nummulites. Non-bank samples show A/B ratios between 60–350 and dominance usually <50%. An unexpected result was the discovery of an ‘Assilina bank’, characterizing both conditions for recognition of a nummulite bank, but with Assilina cuvillieri as the dominant species representing >75% of the larger foraminiferal assemblage.
In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom ... more In the Central Iran Basin, the mixed carbonate–siliciclastic deposits of the C member of the Qom Formation were deposited on a carbonate platform which is dominated by rhodalgal associations occurring in tropical– subtropical environment. The biogenic rhodalgal association is dominated by bryozoa, coralline red algae, bivalves and echinoids together with smaller amounts of photo-dependent biota including large benthic foraminifera and corals. The abundance of heterozoan association and the bloom of suspension-feeding organisms are the result of an increase in nutrient availability which has profound controlling effect on the biotic system. The low occurrence of symbiont-bearing benthic foraminifera and coral, typical of stable, oligotrophic condition, represents their low tolerance to unstable, nutrient-rich environment. In the investigated Oligocene – Miocene shallow marine carbonate succession, 10 different microfacies were distinguished through depositional texture and biotic components. The rock sequences investigated are referred to an open shelf carbonate platform in which the depositional environments range from outer shelf to inner shelf conditions.
The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to s... more The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to shed light on it by observing the hydrodynamic behavior of selected larger foraminifera collected from both bank and non-bank deposits. Entrainment and settling velocity of both recent and fossil larger foraminifera were measured using a flume channel and settling tube. Both velocities give information about the reaction of foraminiferal shells to different hydrodynamic conditions affecting their capability to build bank-like sedimentary structures. To assess entrainment, experiments were performed on different substrates to simulate bed load transport on smooth surfaces, fine sand, coarse sand, and bioclastic substrates. Thirty-four recent and 49 fossil shells of foraminifera were used; recent taxa used are Operculina ammonoides, Heterostegina depressa, and Palaeonummulites venosus and fossil taxa used are Nummulites perforatus, N. fabianii, and N. tavertetensis (only A forms were used in this study). Our results seem to differentiate the hydrodynamic behavior of shells collected from banks from those collected from non-bank deposits. The latter possess settling velocities significantly lower than their entrainment velocities, while for taxa collected from nummulite banks, settling velocities are always close to entrainment velocities. Therefore, the relation between hydrodynamics and shape and size may explain why modern larger foraminifera, consistently of smaller size than fossil forms, cannot produce banks and that transport as bed load in moving water was possibly the main trigger for the production of nummulite banks.
Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determine... more Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determined using a settling tube. The tests were collected from the nummulite banks of Pederiva di Grancona (A forms of N. lyelli and N. striatus, Middle Eocene) and San Germano dei Berici (A and B forms of N. fabianii, Late Eocene), both in the Berici Mts. (Veneto, northern Italy). The data were compared with estimated settling velocities that the same specimens might have had in life conditions. This was done by reconstructing their densities simulating water-filled condition and, to simulate post-diagenetic effects, under calcite-filled condition. These simulations show that A and B forms, even if they greatly diverge in shape, volume and size, still possess comparable settling velocities, and that each nummulite bank is characterized by specific hydrodynamic parameters. The use of settling velocity as a parameter to quantify the hydrodynamic behaviour of particles in seawater enables estimation of palaeoenvironmental conditions such as depth, substrate and the energy scenario. Such information is useful in obtaining further insights into the genesis of nummulite banks, the autochthony or allochthony of which is still being debated. Our results point to an autochthonous interpretation. RIASSUNTO-[Nuovi risultati sul comportamento idrodinamico dei gusci fossili di Nummulites da due banchi a nummuliti del Bartoniano e Priaboniano dell'Italia settentrionale]-La genesi delle strutture bio-sedimentarie note come banchi a nummuliti è tuttora dibattuta. Sono state proposte sostanzialmente due interpretazioni: genesi autoctona, dovuta a particolari condizioni paleoecologiche e genesi alloctona, determinata da trasporto passivo ed accumulo per rideposizione. Questo studio ha lo scopo di fornire dati sulle proprietà idrodinamiche dei gusci fossili di Nummulites. Su 58 esemplari fossili ben conservati di tre diverse specie di questo genere sono state determinate sperimentalmente le velocità di sedimentazione in acqua marina, utilizzando un tubo di decantazione. I fossili sono stati raccolti dai banchi a nummuliti di Pederiva di Grancona (forme A di N. lyelli e N. striatus, Bartoniano, Eocene Medio) e San Germano dei Berici (forme A e B di N. fabianii, Priaboniano, Eocene Superiore), entrambi nei Monti Berici (Veneto, Italia settentrionale). I dati sono stati elaborati e confrontati con le velocità di sedimentazione stimate che gli stessi esemplari potrebbero aver avuto in vita. Le densità sono state ricostruite simulando la condizione del guscio pieno d'acqua e, per tener conto degli effetti post-diagenetici, simulando condizioni di riempimento delle cavità da parte della calcite. Le simulazioni mostrano che le forme A e B della stessa specie, anche se differiscono fortemente per forma, volume e dimensioni, possiedono velocità di sedimentazione comparabili, e che ogni banco a nummuliti è caratterizzato da specifiche classi di parametri idrodinamici. Le velocità stimate per i due casi in esame permettono di ipotizzare una diversa profondità di sviluppo per il banco di Pederiva di Grancona, più profondo rispetto a quello di San Germano dei Berici. L'uso della velocità di sedimentazione come unico parametro per valutare il comportamento idrodinamico delle particelle in acqua di mare, permette la stima di condizioni paleoambientali quali profondità e substrato e consente di delineare lo scenario energetico. Nel complesso, i risultati di questo studio fanno propendere per una genesi autoctona dei banchi a nummuliti.