3,804 research outputs found
Depositional architecture and sedimentology of the Tuppa Niedda molassic Late Carboniferous outcrop (Arburese, SW Sardinia)
No full textThe Late Carboniferous conglomerates of Tuppa Niedda (Arburese,
SW Sardinia, Italy) (BARCA et alii, 1995a) have been analyzed
in detail using facies analysis and depositional architecture procedures
(MIALL, 1985, 1988, 1996). So, the splendid coastal outcrop
has been minutely resolved into several architectural elements and
sub-elements, each featured by precise lithofacies associations and
linked to well-defined depositional processes. Its depositional environment
was interpreted as to be a debris-flow dominated alluvial
fan, in the following buried by stream flows produced by the distal
part of a major alluvial fan.
A comparison with similar, coeval sedimentological context has
been attempted
Stratigrafia, analisi di facies ed architettura deposizionale della successione permiana di Guardia Pisano (Sulcis, Sardegna SW)
No full textA detailed stratigraphic and facies analysis has been carried out
on the Guardia Pisano sedimentary succession (BARCA et alii, 1992;
PITTAU et alii, 2002), the most complete Permian section cropping
out in SW Sardinia. This succession has been subdivided into three
lithostratigraphic units. The lower unit (approximately 14.46 m) is
formed by laminated, grey to blackish pelites and rare fine sandstones
containing both acidic volcanic intercalations (lavas and
pyroclastics) and epiclastites deriving from the erosion of volcanic products. Here, siltitic-clayey horizons containing a rich pollen
assemblage suggesting an Asselian age (Lower Permian) has been
found (PITTAU et alii, 2002). The depositional environment of this
unit was a palustrine to alluvial plain (meandering stream) under
probably humid climatic conditions, characterized by a certain
degree of tectono-magmatic activity. The intermediate unit (approximately
59 m) is built up by reddish siltites and clayey siltites containing
subordinate intercalations of micaceous sandstones and rare
conglomerates: the high content of micas and K-feldspars of these
sandstones is probably due to the erosion of former volcanites. This
unit was laid down into a meandering stream environment under
conditions of regular rainfall. The upper unit (approximately 45.8 m)
is constituted by rapid alternations of reddish pelites and sandstones
with sheet-like and lens-shaped conglomeratic-sandstone intercalations,
deposited into a meandering environment under more pronounced
subarid conditions with irregular, catastrophic rainfall
episodes: several crevasse splays have also been recognized here.
These last two units are referable to the «New Red Sandstone»
informal unit, showing a red beds facies, and having a sub-continental
aspect in the frame of the Permian of Europe. The sedimentological
features evidenced suggest a gradual evolution from (warm?)
humid to subarid climates during the time of deposition of the succession.
The volcanism, aged 297±5 Ma (PITTAU et alii, 2002), pertinent
to the lower unit, post-orogenic in type, has been linked to the
first opening stages of this Permian basin.
Thanks to its extremely good exposure, the succession described,
especially the part pertaining to the «New Red Sandstone», has been
analysed and subdivided into channelized and overbank elements,
using the MIALL’s (1985, 1996) «Depositional Architecture» criteria,
so obtaining a clearer understanding of the palaeoenvironments and
their evolution
The Triassic and Jurassic sedimentary cycles in Central Sardinia: stratigraphy, depositional environment and relationship between tectonics and sedimentation
No full textThis field trip presents a general overview of the stratigraphical, sedimentological and paleogeographic evolution of the Middle Triassic and Middle Jurassic successions in the Central Sardinia Tacchi area (Gerrei, Sarcidano, Barbagia, Ogliastra). These successions are divided by an unconformity and are both laid down under active extensional tectonics conditions.
The Triassic Eastern Sardinia succession belongs to the Germanic Triassic Domain (Buntsandstein and Muschelkalk facies group), so showing strict affinites with the Iberian and Mid-European successions. It is featured by transgressive siliciclastic to carbonate deposits not more than few tens of meters thick: they represent the evolution from a continental, middle to low-energy environment to a restricted shallow marine one. This succession deposited along the stretching southern margin of the Paleo-European Plate under a hot-arid climate: it represents the last remain of the first Mesozoic depositional cycle in the area.
The Middle Triassic deposits pass upward through an disconformity to the Middle Jurassic transgressive siliciclastic to carbonate succession that is some houndreds of meters thick. The represented depositional environments are all those comprised between high-energy fluvial deposits (fluvial fan) and carbonate shelf margin ones. These sediments deposited under a hot-humid climate and correspond to the second Mesozoic depositional cycle of Central Sardinia. They are directly linked to the opening of the Alpine Tethys that triggered in the Eastern Sardinia area the uplift of a wide tectonic high leading to the dismantling of the main part of the previous Mesozoic (Triassic-lowermost Jurassic) to Permian successions
Analisi di facies e stratigrafia della successione permo?-triassica di Campumari-Coremò (Iglesiente, Sardegna SW)
No full textThe Campumari-Coremò succession, at least 50 m thick, starts
with the «Rio Is Corras Formation», a lithostratigraphic unit consisting
of alternations of conglomerates and dolomites and rare sandstones
with caliches, reddish siltites and argillaceous siltites. These
deposits are transgressive and discordant over the folded Hercynian
basement, which is irregularly cut by erosion channels. The lithotypes
described show abrupt lateral facies changes. The abundance
of the carbonate sediments increases towards the south, thus suggesting
the provenance direction of the transgressive sediments. Sediment
deposition probably occurred in variable environments, ranging
alternatively from alluvial fan-delta to restricted carbonate
(lagoonal?-coastal?) lake, with frequent emersions related to fluctuations
of the base level. The consequent oscillation of the water table
may be one of the possible causes of dolomitization and calcretization
of carbonate sediments, together with variations of temperature
and salinity under a dry-hot climate with sporadic hard rainfall episodes.
In some of the calcretes, Characeae remains have been found,
testifying to the former subaqueous (brackish?) depositional environment
of the calcretized sediments. In its lower part, the Riu Is
Corras Formation is also crossed by thin veins containing barite and
sulfides. These features, together with sedimentological characters
and facies analogues, suggest an age older than previously supposed
and connected with the late-post Hercynian (Permian) hydrothermal
circulation.
The Rio Is Corras Formation shows a maximum thickness of
23-24 m at the west side of the Riu Is Corras valley: it can be dated
as Permo?-Triassic, but its age cannot yet be better defined.
Upwards, the carbonate-bearing «Campumari Fm.» follows after
an unconformity. The «Campumari Formation» begins with the «Su
Passu Malu Member», consisting initially of thin marly-clayey greenish
sediments, locally rich in plant debris and containing an Upper
Anisian (Pelsonian/Illyrian) palynomorph association. A thin horizon
of dark, fetid dolostones rich in former sulfate nodules with chickenwire
structure follows and is abruptly overlain by a succession consisting
of about 15 m of yellowish, finely stratified, marly dolostones
to dolostones, also rich in sulfate pseudomorphs with chert nodules.
The main feature of the latter deposit is the gradually increased folding
towards the top, caused probably by diagenetic deformation of
the evaporite layers. Close to the upper boundary of the laminated
dolomites, the folded structures pass to chaotic breccias, some of
which appear very similar to typical «tepee» deposits. Mud-cracks
and ripple marks have also been locally observed.
The «Su Grifoneddu de S’Acqua Member» is the last member of
the Campumari Fm. It starts with a thick collapse breccia made of
angular clasts of dark limestone embedded in a carbonate matrix,
locally containing pseudomorphs after sulfates. These breccias are
overlain by grey dolostones, at first thick but subsequently well-stratified.
Some horizons are characterized by pseudomorphs either
after either gypsum or anhydrite, while others contain unclassifiable
bioclasts and are bioturbated, this occurring mostly at the top of the
dolomitic succession.
The Campumari Fm. is transgressive over a substrate constituted
by the Is Corras Formation: at Su Grifoneddu de S’Acqua it
has a maximum thickness of 26 m. This formation was deposited
initially in an ephemeral, low-energy, reducing lagoon with local
clastic supply, that quickly evolved first to a restricted, frequently
hypersaline carbonate environment (with subordinated sabkha episodes),
and later to a carbonate platform environment fluctuating
from strongly to weakly hypersaline.
Both the absence of continuous, major barriers and the lack of
significant slump deposits, as well as the gradual passage from shallow
to deeper deposits, point to a ramp depositional model. In more
detail, the Campumari-Coremò succession can have been deposited
in a carbonate ramp environment, passing from a lagoonal substage,
with restricted episodes at the beginning, to an inner ramp and then
to shallow ramp subenvironments
Frammentazione della Pangea ed apertura della Tetide alpina nei cicli sedimentari triassico-giurassici della Sardegna centrale (area dei Tacchi)
No full textIl bacino paleogenico del Sulcis-Iglesiente (Sardegna SW): nuovi dati stratigrafico-strutturali per un modello geodinamico nell'ambito dell'orogenesi pirenaica
No full textNew stratigraphic and sedimentological investigations on the Middle Eocene–Early Miocene continental successions in southwestern Sardinia (Italy): Paleogeographic and geodynamic implications
No full textAbstract
In SW Sardinia, the continental Tertiary successions referred up to now to the Cixerri Fm. (Middle Eocene–Lower Oligocene?) have been investigated. Sedimentological analysis suggests these deposits lied down in fluvial environments and comprised between distal braided streams passing eastward to meandering streams/coastal environments (?) under sub-arid climates. The scrutinization of the Cixerri Fm. westernmost successions allowed one to split locally the upper from the lower part based on sedimentological and mineralogical features and indirect dating. Unfortunately, this separation cannot be set everywhere. The few upper outcrops plainly evidenced and well-constrained have been newly named Flumentepido Fm. and assigned to Late Oligocene–Early Miocene: they figure out alluvial fans and proximal braided rivers. This way, the SW Sardinia Tertiary continental sedimentation extends its persistence, contemporaneously changing its tectostratigraphic meaning: from a molassoid c..
The "Germanic" Triassic of Sardinia (Italy): A stratigraphic, depositional and palaeogeographic review
No full textThe collection of new lithostratigraphical and sedimentological data has allowed to re-examine the Triassic sedimentation cycle in Sardinia The most important outcrops have been revisited and their general setting reinterpreted. A detailed and homogeneous depositional, palaeoenvironmental and stratigraphic picture is proposed, pointing to the analogies with both the typical Germanic Triassic of Central Europe, and the Middle Triassic Sephardic domain of Western Europe and North Africa.
The lower, essentially siliciclastic, lithostratigraphic units, resting discordantly on the Hercynian Palaeozoic basement, resemble the "Buntsandstein" facies association. They are generally of Anisian age. Their depositional environments range from high-energy continental to transitional environments to the floodplain, where a shallow, epicontinental sea gradually transgressed.
Overlaying these are the carbonate units of the "Muschelkalk" facies association. They are generally dolomitic at the bottom passing to calcareous at the top. These deposits, generally of Ladinian age, formed in the various subenvironments of a carbonate ramp.
The few Upper Triassic successions in Sardinia point to the existence, during this period, of diverse depositional conditions in the North (Nurra) and South (Sulcis) of the island. In southern Sardinia, lagoon to shallow sea carbonate shelf deposition predominates, with minor amounts of evaporites and siliciclastics. By contrast, in Northern Sardinia mixed evaporitic-siliciclastic-carbonate facies of paralic-continental (mudflat), locally restricted lagoonal environments, were deposited. The latter are very similar to the classic Germanic "Keuper" facies. These data suggest that the Upper Triassic successions in Southern Sardinia can be set in a transitional environmental context between the open Alpine-Tethyan domain and the Germanic Triassic proper.
An attempt has been made to correlate these successions with the Middle to Late Triassic eustatic cycles
Stratigrafia ed analisi di facies dei depositi permiani del Lago Mulargia ( Sardegna sud-orientale):primi risultati
No full textIn this paper preliminary results of investigations on the stratigraphic succession of the Permian
Mulargia Lake basin are here described. This succession, from 350 to 400 m thick, has been first time subdivided
into 4 stratigraphic units, and respectively, from the bottom: a “Lower siliciclastic Unit”, a “Volcano-sedimentary
Unit”, an “Upper siliciclastic Unit”, and a “Volcanic Unit”. The depositional frame of this succession is
inferred as a network of alluvial facies of various energy degrees, comprised between the palustrine, the fluvial
and the lacustrine environments. These facies are located into a continental molassic basin, progressively spreading
out during the post-collisional extensional Variscan tectonic phase, and characterized, during its evolution,
by two different volcanic activity cycles
Compressive "Alpine" Tectonics in Western Sardinia: Geodynamic Consequences
No full textNew detailed stratigraphical and structural surveys on Mesozoic and Cenozoic outcrops, particularly
of Southwestern Sardinia, point out the presence of strong compressive (with folding and thrusting
phenomena) “Alpine” tectonics, closely connected with the development of the (Laramic)-Pyrenean
Chain. The new data allows us to hypothesize a different interpretation for the tectonesedimentary
and magmatic evolution of the Sardinian Late Mesozoic-Paleogenic basins, considered in the
evolutional Western Mediterranean context
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