1,721,115 research outputs found
Paleoecological insights on latest oligocene-early miocene planktonic foraminifera from the J-anomaly ridge (IODP hole U1406A)
Full text linkThis paper focuses on a paleoecological study conducted on planktonic foraminifera from upper Oligocene-lower Miocene deposits of the J-Anomaly Ridge (North Atlantic Ocean). Paleoclimatic studies are crucial to better comprehend how climatic changes occurred in the past and how they might influence global climate in the next few decades. Oceanic currents are the predominant vehicle for heat transport across the globe and therefore organisms living within the water mass can supply much information on paleoceanographic settings. In total, 53 samples from IODP Hole U1406A were selected in the core interval 96-24 CCSF-M to perform statistical analyses (R-mode cluster analysis, principal component analysis) to describe ecogroup distribution and a paleoclimatic curve based on shallow dwelling taxa. The species have been subdivided into three ecogroups referring to recent studies on planktonic foraminiferal paleoecology. The statistical analyses allowed a preliminary screening of the distribution of the foraminiferal assemblages in the biozonal interval of O7–M3. The ecogroup distribution curves revealed the behavior of each group along the section, highlighting the interconnection among the various habitats. Finally, the abundance of the surface taxa was used to trace a paleoclimatic curve (SDPC) describing the superficial water variations. Those results were compared with the Alkenone Sea Surface Temperature (SST) record from IODP Site U1404 and the δ18O North Atlantic stack from the literature. This comparison showed a good match among the foraminiferal and geochemical data, allowing the correlation of SDPC and SST minima with well-known glacial events of the North Atlantic Ocean. This study supports the potential of census data of planktonic foraminifera in paleoclimatic studies when geochemical data are not available
Sedimentary and ichnofacies analysis of the epiligurian Ponsano sandstone (northern Apennines, Tuscany, Italy)
No full textSeveral stratigraphic sections have bcen measured in the Rencine and Ponsano area to Define, trough sedimentary and ichnofacies analysis, the depositional paleoenvironment of the late Serravallian•early Tortonian Ponsano sandstone Formation. The section of Rencine is characterized mainly by medium•fine sandstones (Sm facies).
Few and thin layers of conglomerate are interbedded with sandstones,.No sedimentary structures have been recognized except for few remnants of planar cross- eds. In the section of Ponsano, the Ponsano Sandstone can be subdivided into two parts. The lower part is characterized by marlstones (Ms facies) at the bottom and medium-fine sandstones (Sm facies) in the middle and upper parts. The upper part is characterized by Ms at the bottom, Sm in the middle, and an alternation of pebble conglomerates (Cp), coarse conglomerates (Cb) and coarse sandstones (Sc) at the top. Fossils concentrations (f) occur throughout. The sandstone faeics are highly bioturbated, and most primary sedimentary structures are obscurcd: only remnants of even lamination, cross bedding and hummocky cross stratificationcould be recognized locally.
Trace fossils are indicative of the mixcd Cruziana-Skolithos and the Skolithos icnofacics. Sedirnentary and ichnofacics data indicate that the Ponsano Saodstone was deposited in Shallow water environment. The morlstone faeies are indicative inner shelf, the sandstone facies of shoreface. Conglomerates are referred to a fluvio- deltaic environment
Test morphology and organic layer of Discorinopsis aguayoi (Bermudez): relationship with enviromental conditions
No full textA detailed study of the morphology of Discorinopsis aguayoi (Bermúdez) is carried out by analyzing four populations collected in Recent and Neogene brackish environments of Tuscany (Italy). The finding of fossil D. aguayoi is reported in this study for the first time. The modern populations lived in a thermal pool of Montecatini (Pistoia) and in the Lagoon of Orbetello (Grosseto), two brackish environments characterized by different salinities. The fossil specimens were found in Messinian and Pliocene sediments of two quarries near Leghorn and Florence respectively. The present investigation points out the invariant and the echophenotypic characters of D. aguayoi. Modern specimens exhibit
morphological abnormalities, correlated to environmental conditions. In the modern populations, the organic layer, well preserved, has also been analyzed. SEM analysis shows “pore plugs” inside conical elevations beneath the pores. TEM investigation, points out the laminar fibrous nature of the organic layer, and microcavities in the organic thickenings and in the “pore plugs” of Montecatini individuals. The microcavities suggest that underlying structural differences between the two populations may be related to extreme conditions of the thermal pool
Geomorphological map of the Pianosa Island (Tuscan Archipelago, Italy)
No full textThe Island of Pianosa is located in the Tuscan Archipelago, a few kilometers south-east of Elba Island, approximately 40 km from Corsica, and 50 km from the Tuscany coast. It represents the emerged portion of a long N-S submarine ridge connecting the Island of Capraia with Scoglio d'Africa, a very small islet located west of the Island of Montecristo. Pianosa has a sub-triangular shape with a similar to 10 km(2) surface area, a coastal perimeter of approximately 18 km, and a maximum height of 29 m a.s.l. The Pianosa landscape has primarily been formed by coastal and karst processes, which have resulted in numerous related landforms. Due to the particular scientific interest of the island, the Geological Survey of Italy has promoted research on Pianosa Island aimed at the development of a 1:12,500 scale geomorphological map
Nuove osservazioni su morfologia ed ecologia di Miliammina fusca (Brady) e Discorinopsis aguayoi (Bermudez) rinvenuti in una vasca termale di Montecatini Terme (Pistoia)
No full textA systematic revision of a foraminiferal fauna, recorded by Papi and Tavani (1959) in the mineral waters of a Montecatini Terme pool (Tuscany, Italy), has been performed. The foraminiferal fauna is represented by Miliammina fusca (Brady) and Discorinopsis aguayoi (Bermudez). The specimens are small-sized and often exhibit
morphological anomalies. M. fusca is characterized by an irregular growth of the chambers of the outer whorl. D . aguayoi exhibits inflated test and a large-sized, protruding chamber in the first whorl. The specimens of D. aguayoi
also show a thin test wall and a thick organic lining. These morphological anomalies are interpreted as being due to the chemical and physical water parameters, such as temperature (13°-15°C during the day), pH (7.0) and salinity
(8.6 per mille), as measured at the time of sampling. However, these anomalies would be chiefly related to the low
value of salinity. The foraminiferal fauna of Montecatini is considered relict of the Pliocene sea
Il patrimonio archeologico e paleontologico dell’Isola di Pianosa (Li): stato della ricerca e prospettive di Tutela
No full textL’isola di Pianosa è la quinta per estensione delle sette isole dell’Arcipelago Toscano, essa è posta 13 km a sud dell’Elba e dista circa 40 km dalla Corsica e 50 dal continente, ha una superfi cie di circa 10 km2, un perimetro costiero di circa 18 km ed un’altezza massima di 29 m (34 m l’Isolotto della Scola). L’isola è una piccola porzione emersa di una dorsale sottomarina che a partire dallo Scoglio d’Africa (alcune miglia ad ovest di Montecristo) si allunga con direzione nord-sud chiudendosi poche miglia ad est dell’isola di Capraia. Questo rilievo, cui viene dato il nome di Dorsale o Altofondo di
Pianosa, divide qui il Bacino tirrenico in due parti: quella compresa fra la dorsale e la Corsica, che raggiunge gli 800 m di profondità e quella fra la dorsale e il continente, con profondità massime di 400 m. Questa particolare ubicazione geografica rende l’isola particolarmente interessante sia per la comprensione dell’evoluzione geologica neogenica del Bacino tirrenico (essa rappresenta la porzione emersa più occidentale della piattaforma toscana) che per lo studio del primo popolamento dell’Arcipelago e del litorale toscano e la ricostruzione degli insediamenti insulari in epoca romana
Sedimentary and ichnology facies analysis of the "Epiligure" Ponsano sandstone (Tuscany, Italy)
No full textFirst recovery of marine quaternary deposits from geognostic boreholes of the coastal plain of Marina di Campo (Elba Island: preliminary results)
No full textHere we describe the preliminary results deriving from the analysis of the S2 geognostic borehole, which was drilled
near the town of Marina di Campo (Elba Island). Starting from a ground level at 1.29 m above the sea level, 25 m of
Quaternary deposits have been cored. These deposits are probably related to the last glacial-eustatic cycle. In
particular, the lower part of the borehole is characterized by gravel and sandy-silt sediments typical of a fluvial
environment. They settled during a low-stand phase of the Last Glacial Maximum. These deposits are unconformably
covered by coastal marine sands, sandy-silts and biocalcarenites (between -11.90 m and -5.20 m from the ground
level) that were ascribed to the last sea level rise. The upper part of the geognostic survey is characterized by dark and
plastic organic clays (from -5.20 m to the top). The basal clays are still marine (an age of 4.36÷3.81 ky cal BP has been
obtained by radiocarbon dating), whereas those of the intermediate part are brackish (3.97÷3.45 ky cal BP). In the
upper part we found clays that settled in a freshwater environment
L'arenaria Miocenica di Ponsano (Toscana, Italia): Evoluzione Paleoambientale e Bio-Cronostratigrafia
No full textL’Arenaria miocenica di Ponsano (Toscana, Italia): Evoluzione paleoambientale e Bio-cronostratigrafia
No full textIn this work benthonic and planktonic foraminifers of the Middle-Upper Miocene sediments of the Ponsano Sandstone have been studied. The investigated outcrops of this formation are located at Ponsano (SE of Siena) and Rencine (NW of Siena) in Tuscany. Some studies on these sediments have been done in the past years to define the age and the characteristic of the abundant fauna contained into the sandstones, but no environmental analyses have been done.
The aim of this study is to define the thickness of this formation, the paleo-environmental changing through time, its regressive or trasgressive trend, and to controll its age.
In Rencine area the formation lie on the bedrock represented by the Ligurian Unit and it is composed mainly by sandstones and marlstones, only in the upper part of the sequence pebble conglomerates occur. In this area the unit is referred to the Neogloboquadrina continuosa-Paragloborotalia siakensis Zone (Neogloboquadrina continuosa Subzone) and therefore it is late Serravallian in age.
In the Ponsano area the base of the formation is not outcropping. On the contrary the top below the late Tortonian lacustrine sediments (“Serie lignitifera”) is well exposed. In this area, the outcropping sediments of the units are referred to Neogloboquadrina acostaensis Zone, therefore they are arly Tortonian in age. Seven stratigraphic sections have been measured and the total thickness of the outcropping sediments is about 500 m. In this area the Ponsano Formation is characterized by two marly and two sandy levels. . Sandstones layers are grey-yellow, medium to fine grained, well cemented, rich of macro fossils and trace fossils of the Skolithos ichnofacies; in the upper sandstone conglomerates occur. Marlstone are composed by grey and massive marls and sandy marls.
Benthonic Foraminifers are present in all the lithologies. In Rencine outcrop the most frequent are: Ammonia beccarii, Nonion boueanus, Textularia sagittula, Lobatula lobatula and Elphidium crispum. This assemblage is indicative of the shallow part of the infralitoral zone. The Rencine succession may have the meaning of a trasgressive trend.
In the Ponsano area, on the base of the foraminifers assemblages, it is possible to subdivide the succession in 4 part:
A - with frequent Ammonia beccari, Nonion boueanum, Textularia sagittula, Ammonia inflata, Nonion commune and Ammomarginulina sp., and common Bigenerina nodosaria, Lagenammina atlantica and Elphidium crispum;
B - with abundant Heterolepa bellincionii, Ammonia inflata, Lenticulina calcar, Textularia abbreviata, Valvulinerina bradyana, Hopkinsina bononiensis and common Nonion commune, Spiroplectinella carinata and Haplophragmoides spp.;
C - with the same abundant taxa of B, but without Hopkinsina bononiensis (present in only one sample) and with very frequent Uvigerinidae (Hofkeruva rutila and Uvigerina hollicki) and Buliminidae (Bulimina elongata, B. costata, B. affinis) and common Fondbotia wullesdorfi, Pullenia bulloides, Sphaeroidina bulloides. The maximum values of species diversity are recorded in this assemblages;
D - with rare Ammonia beccarii, Elphidium crispum, Florilus boueanus, Quniqueloculina sp. and Textularia sagittula.
The qualitative and quantitative foraminiferal data indicate a neritic environment. The first marlstone level is referred to the circalitoral zone, while sandstones and the second marlstone levels are referred to the infralitoral. Sediments of the upper part of the succession (sandstones and conglomerates) have been interpreted as deltaic deposits. The succession of the Ponsano outcrop is a regressive trend. Sedimentation of such thick succession of marls and sandstones in a shelf environment is related to a constant tectonic subsidence, while the batimetric fluctuations (Fig. 5) could be related to eustatic changing of the sea level. In particular the boundary between the upper level of marl and sandstone is correlated with Mi7 event of the isotopic zonation. Instead the end of the sedimentation could be associated with a decrease of the subsidence rate and/or to an increase of the sedimentation rate related to the uplifting of near areas
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