1,720,967 research outputs found
Osservazioni stratigrafiche e tettoniche nella zona del Rio di Nava (Brianzonese ligure esterno, unità di Ormea).
No full textLate Triassic-Early Jurassic Paleokarst from the Ligurian Alps and its geological significance (Siderolitico Auct., Ligurian Briançonnais domain)
No full textNel domino Brianzonese ligure, le unità carbonatiche medio triassiche, note come Formazione di Costa Losera e Dolomie di San Pietro dei Monti, sono stratigraficamente seguite da una importante lacuna che segna il passaggio ai calcari neritici di Rio di Nava del Batoniano. Nell’ambito di una classica evoluzione di un margine continentale passivo, una stasi nella subsidenza, seguita da un sollevamento portò ad una erosione della piattaforma triassica in misura progressivamente maggiore procedendo verso le unità più interne, cioè verso la Tetide ligure. Tale erosione, che verosimilmente si verificò su di un substrato tettonicamente controllato, portò alla formazione di sequenze sedimentarie assai diversificate, talora mancanti di tutti i terreni triassici o persino dell’intero tegumento permiano. Nell’area studiata (ed in limitate aree esclusivamente appartenenti alla porzione più esterna dell’unità di Ormea), la lacuna mesozoica è ben più di una semplice superficie di erosione; i depositi ad essa associati (“Siderolitico” Auct.) sono costituiti sia da un corpo di peliti rosse interposto fra le sopracitate unità formazionali, sia da una breccia di origine carsica che penetra profondamente le sottostanti dolomie ladiniche. E’ stata condotta una ricerca stratigrafica di dettaglio su questi depositi, unitamente ad un’analisi delle microfacies e petrografico-composizionale, al fine di determinare le caratteristiche dei paleosuoli e del carsismo, di raccogliere maggiori informazioni sulla loro origine e sull’età. Inoltre, è stato discusso il significato regionale e l’importanza di questi depositi grazie ad un confronto a grande scala con il dominio brianzonese classico e con altre località dell’arco alpino occidentale che mostrano una unconformity del tutto simile. Alla luce dei dati raccolti, per l’evento carsico in esame viene proposta un’età compresa fra il Triassico Superiore e il Lias (sino al Baiociano Superiore ?)
A sequence stratigraphic approach to a Middle Triassic shelf-slope complex of the Ligurian Alps (Ligurian Briançonnais, Monte Carmo-Rialto Unit, Italy)
No full textThe Mesozoic sedimentary cover belonging to the Monte Carmo-Rialto unit of the Ligurian Briançonnais domain is composed of Scythian clastics and Anisian to Carnian carbonate rocks over 300 m thick. This paper focuses on the stratigraphy of this carbonate complex, its environmental significance and its evolution in light of dynamic stratigraphy. Our facies analysis of limestones and dolomites of the Triassic complex allowed us to reconstruct an environmental model. Data support a distally steepened carbonate ramp of Anisian age evolving to a more diversified Ladinian platform with an oolitic sand-bar belt separating the lagoon from the slope. The Monte Carmo-Rialto slope facies are the only witnesses of deep sedimentation in the Triassic terrains of the Ligurian Briançonnais domain, otherwise represented by shallow-water carbonate deposits. On the basis of facies succession, we have identified nine medium-scale cycles (3rd order sequences) in the study area, comparable to those evidenced in the Briançonnais s.s. domain by the French authors. Small-scale cycles analysis evidenced mainly shallowing-upward trends in the examined sequences; although a few evidences of transgression-related deposits (deepening upward cycles) have been found at the base three sequences, they have been mostly obliterated by dolomitisation and masked by local tectonics. For this reason we can undoubtly distinguish only the part of each sequence belonging to HST, while the TST, though present, still remains a partition that cannot be precisely characterised. In the same way, LSTs are not present in the Monte Carmo-Rialto unit, due to the original relative landward position of the examined area. Sequence stratigraphy analysis indicates different long-term dynamics for the two evolutionary stages of the Triassic Ligurian platform: a general landward backstepping to moderate progradation during the Early Anisian and true progradation during the latest Anisian and Ladinian. In addition, a good fit with the sequences proposed by the SEPM chart has been found, indicating a correspondence for the 3rd order sequences of the Middle Triassic
Depositional dynamic of glaucony-rich deposits in the Lower Cretaceous of the Nice arc (Southeast France).
No full textA sedimentological and stratigraphical analysis has been applied to the Early Cretaceous glaucony-rich deposits of the southeastern margin of the Vocontian Basin. Thin sections, X-ray diffraction on random powders analyses, and data from geochemical analyses, performed on pure disaggregated glauconite grains by wavelength dispersion spectroscopy (WDS), allow the distinction of two populations of highly evolved glauconite grains. The first population is interpreted to be autochthonous (i.e., grains that have not experienced any transport from their place of origin). The second is interpreted to be parautochthonous (i.e., grains that have been removed from their place of origin and concentrated landward and seaward within nearly coeval deposits). Palaeoenvironmental information has been deduced mainly from (1) the characteristics of glauconitic grains, (2) meso- and microscopic analyses performed on the named lithozones, and (3) their lateral changes on a kilometre scale. Basin palaeogeography implies a southern area belonging to an outer platform and a northern zone with the characteristics of a distal ramp (Hauterivian). This depositional setting changed during the Barremian–Aptian owing to tectonics; fault systems led to a drowning of the western segment, but the previous environmental pattern presented again during Albian–Early Cenomanian times. Four different depositional events have been distinguished in the Early Cretaceous, and the relative sea-level changes have been reconstructed. We have traced relative sea-level fall during the Late Valanginian, the Early Barremian and the Albian (the second and third of these corresponding to the tectonic uplift outlined by Wilpshaar et al. (Cretac. Res. 18 (1997) 457)), while the general subsidence is confirmed by the transgression that led to the formation of glauconitic minerals. During the Lower Cretaceous, two second-order cycles have been recognized; although of the second order, the first sequence (Late Valanginian–Barremian) is made up like a third-order depositional sequence where different system-tracts are enhanced. The compared relative sea-level change corresponds to the curve of the second-order cycles of Haq et al. (1988, SEPM Spec. Publ. 42, 71–108)
Synrift sedimentation on the northern Tethys margin: an example from the Ligurian Alps (Upper Triassic to Lower Cretaceous, Prepiedmont domain, Italy)
No full textThe Prepiedmont domain succession of the Ligurian Alps is formed by a thick Mesozoic sedimentary cover tectonically detached from its substratum. The Arnasco-Castelbianco unit preserves the most complete record of the Ligurian Prepiedmont, although completely overturned and deformed due to Alpine tectonics. It is composed of carbonate and clastics rocks deposited during the Upper Triassic-to-Lower Cretaceous interval. This paper is focused on the stratigraphy of the Jurassic series and its relationships to the Tethyan rifting. Each term of the sedimentary record is seen as a witness of the several phases through which the rifting took place. An early-rifting phase (Late Hettangian-Early Sinemurian) brought to the formation of a normal fault system affecting the carbonate platform, and favoured the development of condensed sedimentation on pelagic highs. The rapid transition from open-platform carbonate to slope-basin cherty limestones, testifies the increased subsidence of the margin in the Late Sinemurian, during which moderate fault activity is recorded (intraformational breccia horizons). Until the Early Pliensbachian, a tectonic pause brought to the sedimentation of a succession of pelagic carbonates, occasionally interrupted by clastic flows. During the Late Pliensbachian (?)-Toarcian, it followed the rifting phase, evidenced by the large amount of clastics generated by the renewed fault activity. Clastics flowed down into the basin as fluxoturbidites at first, and then they passed to breccias during the maximum tectonic pulse. In the Late Toarcian-Aalenian?, the thermal uplift of the Briançonnais shoulder generated a basinal infill of fine clastics. The following thermal subsidence (Aalenian-Tithonian) favoured the restoration of quiet basinal conditions evidenced by the deposition of radiolarites
Lower and Middle Jurassic omission surface in the Nice arc: sedimentary features and fluid inclusions analysis. An integrated approach.
No full textNuovi dati e precisazioni sull'unità di Case Tuberto (Prepiemontese delle Alpi liguri).
No full textItinerario n° 9. L'entroterra di Toirano, tra le valli del Varatello e della Neva. La "finestra" di Castelvecchio.
No full textBasin analysis and tectonostratigraphy: An integrated approach to decipher the Ligurian Alps geodynamics
No full textTowards a chronostratigraphic definition of the paroxysmal phase of rifting in the Ligurian Alps (Case Morteo Rhyodacites).
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