The 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.

Opportunistic benthic foraminifera as indicators of eutrophicated environments. Actualistic study and comparison with the Santernian middle Tiber Valley (Central Italy) / Frezza, Virgilio; Bergamin, L; DI BELLA, Letizia. - In: BOLLETTINO DELLA SOCIETÀ PALEONTOLOGICA ITALIANA. - ISSN 0375-7633. - STAMPA. - 44:(2005), pp. 193-201.

Opportunistic benthic foraminifera as indicators of eutrophicated environments. Actualistic study and comparison with the Santernian middle Tiber Valley (Central Italy)

FREZZA, Virgilio;DI BELLA, Letizia
2005

Abstract

The 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.
2005
BENTHIC FORAMINIFERA; Organic flux; Actualistic model; Opportunistic species
01 Pubblicazione su rivista::01a Articolo in rivista
Opportunistic benthic foraminifera as indicators of eutrophicated environments. Actualistic study and comparison with the Santernian middle Tiber Valley (Central Italy) / Frezza, Virgilio; Bergamin, L; DI BELLA, Letizia. - In: BOLLETTINO DELLA SOCIETÀ PALEONTOLOGICA ITALIANA. - ISSN 0375-7633. - STAMPA. - 44:(2005), pp. 193-201.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/350064
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