51 research outputs found
Caratteristiche geomorfologiche dell’Isola di Pianosa.
No full textPianosa Island belongs to the Tuscany Archipelago; it has an extension of 10 km2, 18 km of coastal development and a max altitude of 29 m a.s.l.
The island is made up of neogenic and quaternary sediments; pelitic Miocene sediments outcrops at the base of the cliff in the south-western coast, while the bio-calcarenitic Pliocene sediments cover most part of the island. Quaternary deposits are established by biodetrital shore sediments of Tyrrhenian age and by Late Pleistocene colluvial deposits.
The island is characterized by cliffs in the western and southern sector, by plain surfaces and by a small beach in the east side.
Cliffs have been distinguished in 3 different types. In the first type is always present a developing wave notch.
When the coast is not characterized by cliff we can found erosion plains (at maximum level of approximately 4 m) formed during the Tyrrhenian high stand (Isotopic stage 5e).
These erosion planes can be suspended and sub-horizontal (when the layers of the pliocenic substrate dip towards inland), or gently tilted towards sea (when the layers of the pliocenic substrate dip towards sea).
On these various erosion planes are always present rock pools characterized by different shape and dimension, besides rare fossiliferous shore deposits (Panchina). In these sediments have been recognized, between others: Strombus bubonius, Patella ferruginea and Conus testudinarius, dating Tyrrhenian age.
On the island we can found three different order of erosion planes at 2-4 m, 8 m and 25 m a.s.l.
Karst process produced erosion epigean micro-landforms, such us dissolutional flutes, dissolutional groves and dissolutional pans (kamenitza), macro-landforms represented by E-W karst oval basin depressions, enlarged hundred meters and few meters deep. The same process left isolated rock promontory residual of the tyrrhenian cliffs coast lines.
Much diffused are hypogean karst shape such as caves and conduits that, sometimes, are opened on the cliff and are visible only by the sea. In some of these caves, characterized by speleothemes, we discovered, at a quote of 7 m a.s.l., marine deposits and litodomes holes probably of Tyrrhenian age. Frequently is the founding of breccias breeded by collapse of caves and conduits. Surface karst landforms are widening covered by high agricoltural activity developed in the last two centuries due to the presence of the agricoltural penal colony
Carbonate Deposition In Restricted Basins: A Pliocene Case Study From the Central Mediterranean (Northwestern Apennines), Italy.
No full textCarbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness, because of their significance in petroleum geology. However, spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic-dominated or mixed carbonate-siliciclastic systems. Pliocene successions of Tuscany and the Tyrrhenian shelf (Northern Apennines, Italy) record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation. This study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves. Analyses of the extension, composition, facies, and sequence stratigraphic architecture of the studied Piacenzian carbonate units are complemented by new..
L'Isola di Pianosa: perla neogenica dell'Arcipelago Toscano
No full textPianosa è l'unica fra le sette isole dell'Arcipelago Toscano, tutte bellissime,
ad essere formata esclusivamente da rocce
sedimentarie di età neogenica. Le altre sono costituite
diversamente: Gorgona da rocce metamorfiche,
Capraia da rocce vulcaniche effusive, Giglio e
Montecristo da rocce magmatiche intrusi ve, Giannutri
da rocce calcaree triassiche, mentre l'Elba è
formata da rocce di genesi ed età assai diverse.
L'ubicazione geografica, approssimativamente
equidistante' fra la costa toscana e la costa corsa
(Piana di Aleria) con i rispettivi depositi neogenici,
fanno di Pianosa un elemento chiave nella ricostruzione
delle tappe evolutive dell ' apertura del
Mare Tirreno Settentrionale
Two Volcanic tephra layers within the upper Messinian succession of Tuscany (inner northern Appennine Italy): 40Ar -39Ar dating and implications on evaporitic and postevaporitic stratigraphy
No full textTwo volcanic tephra layers have been found intercalated in the upper Messinian sediments of the Migliarino and
Pignano sections, located in the Fine and Volterra-Chiusdino neogenic-quaternary basins, respectively (inner Northern
Apennines). The Migliarino section (90 m thick), about 2 km SE of Rosignano Marittimo town, consists of 13 beds of
alabaster gypsum alternating with mudstones. Lugli et al. (2010) consider the first eleven beds as primary gypsum
deposited during the evaporitic Messinian phase. The tephra layer is intercalated to laminated clay between the 10th and
11th gypsum beds.
The Pignano section (130 m thick) is located about 7 km W of the Volterra town and consists of alternations of
conglomerates, clayey sands and clays with rare secondary gypsum. The volcanic tephra is located at about 85 m from
the base of the section and it is characterized by laminated clay covered by sand deposited in a distal delta-front
environment.
The igneous fraction of the two tephra layers consists of crystal fragments of prevailing fresh, zoned oligoclase and
sanidine, and subordinate quartz and brown mica. This latter phase is replaced to variable extent by chloritic products
and Fe-Ti oxihydroxides. In both tephra layers the igneous crystal fragments have sharp edges. In the Migliarino tephra
layer the igneous crystals are dispersed in an argillaceous yellowish matrix plus brown iron hydroxides. The Pignano
tephra layer has a topmost part constituted by finer-grained crystal fragments and by abundant Y-shaped dark and
clear fragments, likely representing altered volcanic glass shards, in a dominant argillaceous matrix. The lower portion
is made of alternating crystal rich and argillaceous 1-5 mm-thick layers. The nature and composition of the mineral
phases occurring in the Migliarino and Pignano tephra layers point to a highly evolved nature of the original magma.
Sanidine single-crystal laser fusion 40Ar-39Ar analyses of the two volcaniclastic levels give weighted average ages of
5.52±0.01 Ma for Migliarino and 5.52±0.01 Ma for Pignano [age monitor: TCR sanidine, 28.34 (Renne
et al., 1998); decay constants of Steiger & Jäger (1977)].
The comparison of these levels with others in the Northern Apennines, impose new constraints for the chronology of
the primary evaporitic Messinian succession
Neogloboquadrina atlantica praeatlantica, new subspecies from late Middle Miocene
No full textA new subspecies of Neogloquadrina atlantica atlantica previously reported under different names, is here distinguished and named Neogloboquadrina atlantica praeatlantica. Its first occurrence into the Mediterranean dated at 11.78 Ma, is not evolutionary appearance but is related to a global climatic cooling which pushed southwards from high latitude this taxon; however, the area of its evolutionary appearance is not clearly defined; its extinction occurs within the Globigerinoides obliquus extremus Zone. N. atlantica atlantica which evolves from N. atlantica praeatlantica occurs in the Mediterranean at 11.15 Ma, just after the Mediterranean exit of Paragloborotalia siakensis (Le Roy)
Integrated micropaleontological study (ostracods and calcareous plankton) of the Langhian western Hyblean succession (Sicily, Italy)
No full textFour sections cropping out in the Hyblean Plateau (SE Sicily) were studied biostratigraphically and
palaeoecologically. The investigated succession was referred to the early^late Langhian on the basis of both the
planktonic foraminifers (lowermost part of the Praeorbulina glomerosa sicana Subzone^lowermost part of the Orbulina
universa Subzone) and the calcareous nannofossils (uppermost part of the MNN4a Zone^lowermost part of the
MNN5b Subzone). All the biozonal markers were recorded and further significant events were identified. The most
remarkable ones are two paracmes of Paragloborotalia siakensis within the P. glomerosa sicana Subzone and the
distribution of Helicosphaera waltrans, which characterises the upper part of the MNN5a Subzone. The ostracod
palaeoecological analysis indicated a progressive and gradual trend from thermospheric to psychrospheric conditions
and probably a basin deepening (from upper to lower epibathyal). The flowing of deep Atlantic waters into the basin is
documented by the entry of the psychrospheric species Agrenocythere hazelae within the upper part of the P. glomerosa
sicana Subzone. Only in the late Langhian, however, were typical psychrospheric conditions probably reached. These
data provide evidence that oceanic deep water masses reached the Central Mediterranean, passing through both the
western connections to the Atlantic Ocean and the African^Sicilian threshold, during a great part of the
Langhian. ß 2001 Elsevier Science B.V. All rights reserved
The upper Messinian post-evaporitic succession of Serredi Quarry (southern Tuscany, Italy): new stratigraphic data and geochronology of an ash layer.
No full textAn ash layer, about 1 cm thick, has been found during a reinvestigation of the upper Messinian-Zanclean succession exposed at Serredi Quarry (Fine Basin, Northern Apennines), one of the best known Neogene Tuscan sections.
The Serredi Quarry succession (about 175 m thick) has been subdivided into three intervals: the lower (18 m thick) and middle (132 m thick) ones are separated by an unconformity and are both referable to the Messinian post-evaporitic phase, whereas the upper interval (25 m thick) represents marl deposition following the Pliocene transgression. The lower interval consists of relatively deep-lacustrine, anoxic, thinly laminated mudstones with subordinate sands, whereas the middle one includes lacustrine mudstones (occasionally with pedogenic features) with sands, diagenetic gypsum-rich mudstones, limestones, gravels and selenite gypsum draped by gypsarenites. These lithofacies are typically arranged into marginal-lake, cyclical stacking patterns.
The ash layer is located in the lower interval. It is faintly laminated and composed of almost pure fine-grained glass shards and rare pumices. These characteristics suggest a primary deposition from a pyroclastic fallout. Chemical analyses were carried out on well preserved pumices and glass shards were used for fission-tracks dating, which provided an age of 5.35 + 0.32 Ma. Nevertheless, its age can be further constrained by the fact that
i) the ash layer is about 145 m below the Miocene-Pliocene boundary, and ii) the intervening deposits mainly consist of mudstones with occasional pedogenic features, which are likely to comprise sedimentary hiatuses.
Accordingly, the ash layer probably emplaced in the older part of the determined age interval.
On the whole, the geochronology, geochemistry and the stratigraphic framework of the first ash layer found in the post-evaporitic deposits of Tuscany could represent valuable tools for regional stratigraphic studies on the
Lago Mare phase and long-distance correlation
Benthic foraminiferal assemblages from the St. Peter's Pool section (south eastern Malta Island)
No full textPreliminary paleoecological data on benthic foraminiferal assemblages of St. Peter's PoDI section
(south-eastern Malta Island), are presented. The upper Burdigalian- Langhian St. Peter's PoDI
section (MMi4a-MMi4b planktonic foraminiferal biozonal scheme of Di Stefano et al., 2008
emended by Iaccarino et al., 2011) that outcrops at Delimara Peninsula, belongs to the Upper
Globigerina Limestone, the youngest member of the Globigerina Limestone formation. The
sedimentary record consists of cyclic alternations of calcareous mari, marly limestone and
bioturbated hardened limestone.
Benthic assemblages are mainly represented by species typical of an upper-middle bathyal
environment. Throughout the section the most abundant species are Siphonina reticulata,
Cibicidoides dutemplei-subhaidingerii, together with Uvigerina peregrina, Bulimina costata and
Bolivina spathulata. The opposite trend of S. reticulata and U. peregrina together with the
distribution patterns of the other significant species point out three mai n intervals along the section.
The ecological/paleoecological meaning of tbe main benthic species is reported in Iiterature
(Kouwenhoven and Van der Zwaan, 2006, among others).
lnterval A (O - 6 m): increasing trend of the oxic species S. reticulataup to 20% and occurrence of
the high productivity species U. peregrina (average value 11%), B. costata (average value < 1%)
and of the dysoxic species B. spathulata (average value 4%). This interval suggests a well
oxygenated bottom environment.
Interval B (6 - 12 m): increasing trend of U. peregrina and B. costata with a peak respectively of
27% and 13% at 12 m; decreasing trend of S. l'eticI/lata with its minimum value of 2% at 12 m.
This interval reveals high productivity and high organic matter content at the sea fioor as
consequence.
lnterval C (12 - 30 m): increasing trend of S. reticulata and of the oxic species C. dutempleisubhaidingerii;
generai decreasing trend of U. peregrina, which shows a peak of 17% at 24 m, and
of B. costata. This interval allows to hypothesize a relatively well oxygenated bottom environment
with an episode of increased productivity at 24 m
Middle Miocene high-resolution calcareous plankton biostratigraphy focussed on the Burdigalian/Langhian and Langhian/Serravallian boundaries
No full textRediscovering Globigerina bollii Cita and Premoli Silva 1960
No full textGlobigerina bollii Cita and Premoli Silva was described from the historical Langhian-type section
in Langhe, Piedmont (Italy). Due to its peculiar compact morphology, it was set apart from all the other globigerinids
typical of the coeval Mediterranean fauna, and it was only reported for a short and limited stratigraphic
range. The taxon became a first-order marker for the local biostratigraphy with its own Globigerina bollii Zone
within the Langhian stage. However, the species was later synonymised with Globigerina falconensis Blow, ending
its use in biostratigraphic schemes, and it was no longer utilised by authors working in the Mediterranean area
and Paratethys. We present a reassessment of Globigerina bollii, showing for the first time a full collection of
high-quality scanning electron and optical microscope images of the type series of specimens and a comparative
study with Mediterranean individuals from the Langhian of the Cretaccio Section (Italy) and extra-Mediterranean
individuals from Ocean Drilling Program Site 747 in the Kerguelen Plateau (Indian Ocean). The stratigraphic
ranges of all the occurrences cited in the scientific literature from 1960 to the present day and all the references
including images of the taxon are compiled.We compare G. bollii to other four-chambered morphospecies
inhabiting the oceans during the Miocene, providing a detailed discussion of their morphological differences,
which allows us to retain G. bollii as a valid taxon and to disclaim its synonymy with Globigerina falconensis.
Our taxonomical observations also allow us to reassign Globigerina bollii to the genus Globoturborotalita, due
to its strong affinities with other members of that genus, such as G. eolabiacrassata Spezzaferri and Coxall,
and G. ouachitaensis (Howe and Wallace). We present a direct visual comparison with the other representatives
of middle Miocene globoturborotaliids. An additional comparison is also discussed with Globigerina bollii
lentiana Rögl, a species endemic in the Paratethys. We conclude that the presence of G. bollii in the Mediterranean
Basin during such a confined stratigraphic interval (Mediterranean Subzone MMi4c–MMi4d), might be
a palaeogeographical indicator of the intermittent opening of the eastern gateway with the Paratethys, affecting
the Mediterranean faunas during the Langhian and their migration from oceanic realms into the Paratethys and
Mediterranean
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