1,721,055 research outputs found
Composizione e struttura delle associazioni a foraminiferi bentonici in ambienti condizionati da delta fluviali. Modello di distribuzione in un’area della piattaforma continentale tirrenica (Toscana meridionale)
No full textI fossili come memoria della Terra e della Vita – Prospettive e Problemi, Roma, 6-7 giugno 2008, Volume Abstracts
No full textDistribution of benthic foraminiferal assemblages in the Ombrone River Basin (Tuscany Continental Shelf, Tyrrhenian Sea, Italy). Relationships with fluvial run-off
No full textDistribution of recent ostracods near the Ombrone river mouth (Northern Tyrrhenian Sea, Italy)
No full textOstracod assemblages of 52 samples, collected between 15 and 50m water depth on the Southern Tuscany continental shelf (Northern Tyrrhenian Sea), were analysed. Atotal of 68 species and 39 genera was determined. Q-mode cluster analysis performed on the 22most abundant species (>5% in at least one sample) led to identification of clusters (and subclusters) corresponding to four distinct ostracod assemblages. The first assemblage is characterised by the high dominance of Cytheridea neapolitana and is probably linked to an organic matter enrichment, in silty clay bottom; the other three assemblages are more diversified and are dominated, with lower percentages, by species typical of infralittoral and circalittoral environments: C. neapolitana, Cytheropteron ruggierii and Loxoconcha subrugosa assemblage (on silty clay sediments), Pontocythere turbida assemblage (silty sand and silty clay substrates) and Loxoconcha ovulata assemblage (sandy clay and vegetated bottoms). The distribution of ostracod assemblages shows a good correlation with the benthic foraminiferal assemblages founded in the investigated area. Nevertheless, the recognised low diversity can be related to an organic matter enrichment
The distribution of Recent Benthic foraminiferal assemblages near the Ombrone River Mouth (Northern Tyrrhenian Sea, Italy)
No full textDistribution of recent foraminiferal assemblages near the Ombrone River mouth (Northern Tyrrhenian Sea, Italy)
No full textBenthic foraminiferal assemblages in 127 samples, collected at water depth, ranging between 15 and 184 m on the Southern Tuscany continental shelf off the Ombrone River were analysed. Statistical analyses (Cluster and Principal Component Analysis) performed on the 48 most abundant species (>5%) and sedimentological data led to the identification of three clusters related to the size of grain sediment (sand, silt or clay). Q-mode cluster analysis singled out six groups, corresponding to six distinct foraminiferal assemblages: a typical infralittoral assemblage (15-39 m) on sandy silt, clayey silt or silty clay, dominated by Ammonia and Elphidium species, with Eggerelloides scabrus, Rectuvigerina phlegeri and Valvulineria bradyana; a second assemblage (24-78.5 m) associated with vegetated environments or sandy bottoms (Elphidium crispum, Rosalina bradyi, Asterigerinata mamilla, Neoconorbina terquemi, and Tretomphalus concinnus); a third assemblage recognised between 30 and 90 m water depth and characterised by the dominance of the opportunistic species V. bradyana (related to silty bottoms), with Bulimina marginata, R. phlegeri, Ammonia inflata and Ammonia beccarii as other common taxa; an upper circalittoral assemblage (70-100 m) on silty clays, containing B. marginata, Cassidulina carinata and V. bradyana; a lower circalittoral assemblage (95-177 m) on clayey bottoms, with B. marginata, Textularia bocki and Uvigerina mediterranea; and finally, a second lower circalittoral assemblage (104-184 m) on clayey sediments, dominated by two Uvigerina species (U. mediterranea and Uvigerina peregrina), with Sphaeroidina bulloides and B. marginata. The typical V. bradyana assemblage, characterised by relatively low diversity and high dominance, marks the most eutrophicated area running parallel to the coast. The spatial distribution of assemblages is closely associated with sea-bottom sedimentary environments and bathymetry but it is also probably influenced by the outflow of the Ombrone River. The composition, structure and distribution of V. bradyana assemblage suggest an environmental model, useful for paleogeographic reconstruction in areas characterised by a river mouth and a closed morphological setting typical of a nutrient-trap. © 2007 Elsevier Masson SAS. All rights reserved
Halimeda dominance in the coastal wedge of Pietra di Finale (Ligurian Alps, Italy). The role of trophic conditions
No full textThe Middle to Late Miocene mixed carbonate-siliciclastic coastal wedge of the Pietra di Finale, unconformably
overlying the Ligurian Alps succession, displays a carbonate portion dominated by Halimeda and Porites
fragments that fall in the photozoan assemblages. Photozoan assemblages typically develop under tropical and
oligotrophic conditions, while hetorozoan assemblages tend to thrive in high-nutrient settings. The Pietra di
Finale Formation shows, however, that high weathering and an increase of nutrient inputs related to Alpine uplift
and humid climatic conditions promoted Halimeda over the seagrass carbonate factory in the photic zone. The
successful Halimeda proliferation was due to its efficient competition for nutrients, especially nitrogen. Thus,
the Pietra di Finale Formation represents an interesting, counter-intuitive example in which increased nutrient
concentrations promoted, instead of inhibited, a photozoan over a seagrass-related heterozoan carbonate
production
Opportunistic benthic foraminfera as indicators of eutrophicated environments. Actualistic study and comparison with the Santernian middle Tiber Valley (Central Italy).
No full textOpportunistic benthic foraminifera as indicators of eutrophicated environments. Actualistic study and comparison with the Santernian middle Tiber Valley (Central Italy)
No full textThe study of extant organisms is the base of the environmental micropaleontology, since the knowledge of natural mechanisms, which regulate their distribution in present environments, is the necessary base for the reconstruction of fossil environments. Since most shallow-water taxa well tolerate a wide range of environmental conditions, the organic flux, which determines trophic levels, appears the most important factor that regulates the distribution of benthic foraminifera. On the contrary, other variables like substrate, temperature and salinity are less important for their occurrence. Since the end of the 90s, many studies have been performed on recent benthic foraminifera from a small marine basin located along the southern Tuscan shelf, characterized by the sedimentary contribution of the Ombrone River. The geographical features of this basin, named Ombrone River Basin (ORB), are unfavourable to the organic matter dispersion, determining a particularly suitable environment for the study of eutrophicated sea-bottoms. Researches evidenced the correlation between a typical assemblage, dominated by the opportunistic Valvulineria bradyana and the organic flux of fluvial origin. Particularly, the statistical multivariate analysis performed on 127 samples from the ORB helped to determine the distribution of such assemblage. In this work, the quantitative parameters describing the structure of the V. bradyana assemblage (species richness, heterogeneity,
dominance) are evidenced and discussed, defining an actualistic model for assemblages that could be used to evidence the organic paleo-flux in coastal marine areas influenced by river contributions. During the Early Pleistocene, the coast of Latium was located in eastern position with respect to the present one. In front to the coast, some structural highs emerged, forming an island lineage parallel to the coast and delimiting a narrow inner basin. In this basin, the Tiber River and other minor rivers built their delta systems. This paleogegraphic setting has been evaluated as favourable to the development of eutrophicated environments, and consequently many tens of available samples from the clayey terms of the Chiani-Tevere Formation have been considered for a comparison with the actualistic model. The foraminiferal assemblages from three sites, Civita di Bagnoregio, Orte, and Nazzano, are dominated by V. bradyana and show quantitative parameters coinciding with the recent model utilized as marker of the organic flux. These episodes of eutrophication in the inner Tyrrhenian basin may be considered coeval, because all the three successions are ascribed to the Santernian (Globigerina cariacoensis Zone). Considering the paleogeography of the region, it may be supposed that the Civita di Bagnoregio site was probably influenced by the contribution of a small river which flowed
into the Tyrrhenian Sea near this locality. In addition, the Orte and the Nazzano sites corresponded to the Nera and Farfa delta systems, respectively. These preliminary results are encouraging for the development of the research aimed to the reconstruction of the organic paleo-flux along the coast of Latium, with useful implications for a detailed paleogeographic reconstruction of the Santernian middle Tiber Valley. In addition, the good accordance between a paleogeographic reconstruction based on geological evidences and the preliminary results obtained by paleoecological proxies, validate the utility of the actualistic model considered as typical marker of the river organic flux
Distribution of Recent foraminiferal assemblages near the Ponza Island (Central Tyrrhenian Sea, Latium, Italy).
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