1,721,227 research outputs found
A history of Triassic carbonate mud, from microbially influenced precipitation to pelagic biomineralization
No full textA continental/siliciclastic to shallow-marine/carbonate system in the Upper Triassic of Dolomites (Travenanzes Formation, northern Italy)
No full textLa Formazione di Travenanzes (ex Formazione di Raibl Auctorum) è una
successione mista silicoclastico/carbonatica di ambiente da continentale a
marino-marginale e di clima arido che si depositò nel Sudalpino orientale
durante il Carnico superiore (Tuvalico). La deposizione avvenne in un’area
costiera a basso gradiente, alimentata da sedimenti provenienti da rilievi
meridionali e aperta verso nord-nordest alla Tetide.
L’ambiente deposizionale della Fm. di Travenanzes è stato ricostruito in
Dolomiti ed inquadrato nell’ambito di un sistema di piana alluvionale – piana
costiera inondabile - laguna a sedimentazione carbonatica.
La porzione continentale del sistema deposizionale carnico è costituita da
un sistema fluviale di tipo “terminal fan” caratteristico di clima arido con
precipitazioni stagionali, dove l’intensa evaporazione ed infiltrazione porta alla
diminuzione della portata e delle dimensioni dei canali fluviali verso mare, fino
alla totale scomparsa della rete idrografica superficiale in corrispondenza di
una piana fangosa costiera, prima della linea di costa.
La piana costiera fangosa costituisce la zona di interazione tra sistema
continentale e marino, essendo temporaneamente inondata durante le tempeste
marine e le piene fluviali maggiori. Localmente il clima arido porta allo
sviluppo di una “sabkha” costiera con precipitazione di anidrite nodulare e
“chicken-wire”, e gesso laminato.
La porzione marina del sistema deposizionale carnico è costituita da piane
tidali e lagune poco profonde a sedimentazione carbonatica, caratterizzate da
dolomie afanitiche, cristalline, laminate e marnose, organizzate frequentemente
in cicli peritidali metrici del tutto simili a quelli della soprastante Dolomia
Principale, e subordinate intercalazioni di peliti scure.
Distinti modelli di facies possono essere applicati separatamente alla
porzione continentale e marina del sistema, ma un modello deposizionale
comprensivo dell’intero sistema non è ancora stato descritto in letteratura.
Punto chiave per la sua elaborazione è la comprensione dei processi
deposizionali che avvengono sulla piana costiera inondabile.
In conclusione, la Formazione di Travenanzes è un esempio di sistema a
sedimentazione mista di clima arido e di ambiente di transizione continentaleparalico-
marino marginale, ed il suo confronto con casi analoghi, antichi e
attuali, potrebbe essere utile alla costruzione di un modello deposizionale di
validità generale e applicabile ad altri casi di studio nella storia della Terra
Unraveling the origin of carbonate platform cyclothems in the Upper Triassic Durrenstein Formation (Dolomites, Italy)
No full textFacies analysis of the Du ̈rrenstein Formation, central-eastern
Dolomites, northern Italy, indicates that this unit was deposited on
a carbonate ramp, as evidenced by the lack of a shelf break, slope
facies, or a reef margin, together with the occurrence of a ‘‘molechfor’’
biological association. Its deposition following the accumulation of
rimmed carbonate platforms during the Ladinian and Early Carnian
marks a major shift in growth mode of the Triassic shallow marine
carbonates in the Dolomites.
The Du ̈ rrenstein Formation is characterized by a hierarchical cyclicity,
with elements strongly suggestive of an allocyclic origin, including
(a) subaerial exposure features directly above subtidal facies within
meter-scale cyclothems, (b) purely subtidal carbonate cyclothems, (c)
symmetric peritidal carbonate cyclothems, and (d) continuity of cyclothems
of different orders through facies boundaries. The Du ̈ rrenstein
cyclothems are usually defined by transgressive and regressive
successions, and so most of them probably originated from sea-level
oscillations. Their allocyclic origin allows their use for high-resolution
correlations over distances up to 30 km.
A stratigraphic section in the Tre Cime di Lavaredo area, encompassing
the upper part of the Du ̈ rrenstein Formation and the lower
part of the overlying Raibl Formation (Upper Carnian) was studied
using time–frequency analysis. A strong Milankovitch signal appeared
when interference arising from a variable sedimentation rate was estimated
and removed by tuning the short precession line in a spectrogram.
All of the principal periodicities related to the precession index
and eccentricity, calculated for 220 Ma, are present: P1 (21.9 ky); P2
(17.8 ky); E1 (400 ky), E2 (95 ky), and E3 (125 ky), along with a peak
at a frequency double that of the precession, which is a predicted feature
of orbitally forced insolation at the equator. Components possibly
related to Earth’s obliquity at ca. 35 ky and ca. 46 ky are present as
well. The recovery of Milankovitch periodicities allows reconstruction
of a high-resolution timescale that is in good agreement with published
durations of the Carnian based on radiometric ages.
The recognition of a Milankovitch signal in the Du ̈rrenstein and
lower Raibl formations, as well as in other Mesozoic carbonate platforms,
strongly supports a deterministic and predictable—rather than
stochastic—control on the formation of carbonate platforms. Carbonate
platforms might thus be used in the future for the construction of
an astronomical time scale for the Mesozoic
Sharp decoupling between continental/siliciclastic and shallow-marine/carbonate sedimentation in the Upper Triassic Travenanzes Fm. (Southern Alps, Italy)
No full textTriassic climates - State of the art and perspectives
No full textThe climate of the Triassic period was characterized by a non-zonal pattern, dictated by a strong global
monsoon system with effects that are most evident in the Tethys realm. This strong monsoonal regime is
related to the aggregation of the Pangaean supercontinent, which by Triassic time was already completed.
Climate oscillations existed within this framework. The harsh hot-house climatic conditions that
characterized the Late Permian, and perhaps precipitated the end-Permian mass extinction, were probably
maintained during the Early Triassic and may account for the impoverished, but distinctive, faunal and floral
Lower Triassic associations. Although metazoan reef builders were probably the most affected group,
carbonate production remained high at least in the western Tethys realm. The Middle Triassic was
characterized locally by humid episodes, although their geographical distribution has yet to be clarified. The
Carnian Pluvial Event, marks an episode of increased rainfall documented worldwide, was the most
distinctive climate change within the Triassic. Different hypotheses have been proposed for its causes:
changes of atmospheric or ocean circulation driven by plate tectonics; a peak of the global monsoon due to
maximum continent aggregation; or triggering by the eruption of a large igneous province. Subsequently, the
late Carnian and Norian seem to have been climatically stable, although minor climatic changes have
recently been described even from this time period. Finally, the end-Triassic extinction event is also
associated with climate change, specifically warming and increased rainfall, but this evidence comes mostly
from the northern parts of the Central Atlantic Magmatic Province, and the global pattern of climate change
at the Triassic/Jurassic boundary has still to be resolved. Many facets of Triassic climate are intriguing and
deserve further research. However, palaeoclimate studies on the Triassic have so far been carried out only
locally with different proxies. Those proxies will require inter-calibration, in order to depict correctly the
temporal and geographical patterns of Triassic climate
Carta geologica della provincia di Treviso . Sezioni 085010 Cappella Maggiore - 085020 Sacile Ovest
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Anatomy of an Upper Triassic continental to marginal-marine system: the mixed siliciclastic-carbonate Travenanzes Formation (Dolomites, northern Italy)
No full textThe Travenanzes Formation is a terrestrial to shallow-marine, siliciclastic–carbonate succession (200 m thick) that was deposited in the eastern Southern Alps during the Late Triassic. Sedimentary environments and depositional architecture have been reconstructed in the Dolomites, along a 60 km south–
north transect. Facies alternations in the field suggest nterfingering between alluvial-plain, flood-basin and shallow-lagoon deposits, with a transition from terrestrial to marine facies belts from south to north. The terrestrial portion of the Travenanzes Formation consists of a dryland river system, characterized by multicoloured floodplain mudstones with scattered conglomeratic fluvial channels, merging downslope into small ephemeral streams and sheet-flood sandstones, and losing their entire discharge subaerially before the shoreline.
Calcic and vertic palaeosols indicate an arid/semi-arid climate with strong seasonality and intermittent discharge. The terrestrial/marine transition shows a coastal mudflat, the flood basin, which is usually exposed, but at times is inundated by both major river floods and sea-water storm surges. Locally coastal
sabkha deposits occur. The marine portion of the Travenanzes Formation comprises carbonate tidal-flat and shallow-lagoon deposits, characterized by metre-scale shallowing-upward peritidal cycles and subordinate intercalations of dark clays from the continent. The depositional architecture of the Travenanzes Formation suggests an overall transgressive pattern organized in
three carbonate–siliciclastic cycles, corresponding to transgressive–regressive sequences with internal higher-frequency sedimentary cycles. The metre-scale sedimentary cyclicity of the Travenanzes Formation continues without a break
in sedimentation into the overlying Dolomia Principale. The onset of the Dolomia Principale epicontinental platform is marked by the exhaustion of continental sediment supply
Carta Geologica della Provincia di Treviso. Sezione 084030 – Tarzo 063150 - Passo di San Boldo, scala 1:10.000.
No full textPaleoecology of Triassic conodonts: constraints from oxygen isotopes of biogenic apatite.
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