Search results for "Breccia"
showing 10 items of 26 documents
Explosive eruptive history of Pantelleria, Italy: Repeated caldera collapse and ignimbrite emplacement at a peralkaline volcano
2018
A new, pre-Green Tuff (46 ka) volcanic stratigraphy is presented for the peralkaline Pantelleria Volcano, Italy. New 40Ar/39Ar and paleomagnetic data are combined with detailed field studies to develop a comprehensive stratigraphic reconstruction of the island.We find that the pre-46 ka succession is characterised by eight silicarich peralkaline (trachyte to pantellerite) ignimbrites,many ofwhich blanketed the entire island. The ignimbrites are typically welded to rheomorphic, and are commonly associated with lithic breccias and/or pumice deposits. They record sustained radial pyroclastic density currents fed by lowpyroclastic fountains. The onset of ignimbrite emplacement is typically prec…
Fluid storage and migration properties of sheared Neptunian dykes
2019
Abstract Neptunian dykes are widely reported along the Tethyan carbonate platforms and are commonly considered as subsurface baffles or barriers to fluid flow. However, the fluid storage and migration properties of sheared Neptunian dykes are poorly known. For this reason, we investigate the inner structure and fluid flow properties of two Neptunian dykes, which can be characterized by different architectures if involved or not in brittle shearing processes. The dykes strike ca. WNW-ESE and crosscutting the tight Jurassic limestones exposed at Maranfusa Mt., NW Sicily, Italy. The unsheared and sheared Neptunian dykes are almost sub-vertical and at high-angle with respect to the horizontal p…
The Early-Cambrian Boho volcano of the El Graara massif, Morocco: Petrology, geodynamic setting and coeval sedimentation
2006
15 pages; International audience; A major volcanic episode is recorded across the Neoproterozoic-Cambrian transition in the Moroccan Anti-Atlas. Several volcanic cones are still preserved in the El Graara massif, laterally correlatable with volcanic flows dated as Early Cambrian (U/Pb date of 534 ± 10 Ma). Volcanic ashes and flows are interbedded with the uppermost part of the Adoudou dolostones, whereas the best-preserved volcano (the Boho Jbel) is onlapped by the overlying Lie-de-vin strata. Available petro-geochemical data from the Boho volcano suggest an alkaline magmatism probably derived from low-grade melting of a garnet–lherzolite mantle source, followed by fractional crystallizatio…
A Km-scale Cretaceous slope in western Sicily (Italy)
2017
Cretaceous slopes are well known from many regions of the world, since they are among the most prone depositional systems to host hydrocarbons. As far as Italy, in spite of fully described examples as the Majella and Gargano escarpments, detailed sedimentological and biostratigraphic studies from Sicily are not available, although the presence of slope carbonates of Cretaceous age in northwestern Sicily, is mentioned in several papers dealing with regional geology or geological mapping. The Cretaceous slope carbonates from this area, i.e. the San Vito Lo Capo Peninsula, belong to several thrust sheets of the Maghrebian chain. The stratigraphic setting in these tectonic units allows to recon…
Lacustrine sedimentation in the diapir-controlled Miocene Bicorb Basin, Eastern Spain
1998
The Miocene Bicorb Basin is a small elongated basin developed by normal faulting of a thick Jurassic–Cretaceous carbonate succession and subsequent diapirism of Upper Triassic mudstones and evaporites. The basin fill comprises a sequence over 650 m thick formed by two units. The lower, alluvial unit consists of a complex alternation of conglomerates, sandstones, mudstones, and minor lacustrine limestones. The upper unit comprises marginal alluvial and lacustrine deposits in which seven lacustrine facies associations have been distinguished. The inner lacustrine deposits comprise mudstones and carbonates with minor evaporitic deposits. At the northeast and southwest basin edges, alluvial inp…
Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition …
2018
Joint International Ocean Discovery Program and International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub impact crater. We present P-wave velocity, density, and porosity measurements from Hole M0077A that reveal unusual physical properties of the peak-ring rocks. Across the boundary between post-impact sedimentary rock and suevite (impact melt-bearing breccia) we measure a sharp decrease in velocity and density, and an increase in porosity. Velocity, density, and porosity values for the suevite are 2900–3700 m/s, 2.06–2.37 g/cm3, and 20–35%, respectively. The thin (25 m) impact melt rock unit below the suevite has velocity measurements…
The Potential Geosite of the “Libeccio Antico” Quarries: a Sedimentological and Stratigraphic Characterisation of Ornamental Stone from Mt Cocuccio, …
2018
The Custonaci marble district of western Sicily is known for the production of a valuable ornamental stone that has been, and nowadays is exploited due to its suitable properties and aesthetic qualities. The “Libeccio Antico” was, among the “marbles”, the most appreciated ornamental stone during the Baroque Age (the XVII–XVIII centuries), due to its strong polychrome contrasts from ivory to yellow, green or dark red. This polychrome pattern is the result of dissolution processes that involved an Upper Triassic peritidal limestone. The varicoloured sediments in paleocavities, collapse breccias, paleosols and neptunian dykes that occur in the “Libeccio Antico” represent the peculiar character…
Age of initial oceanic magmatism in the Late Proterozoic Arabian Shield
1992
Lead isotopic data for zircons from a dacite clast in a volcanic breccia of the oldest oceanic assemblage (immature arc or oceanic plateau) of the southwestern Arabian Shield (Baish group), acquired with the single-grain evaporation technique, yielded a mean 207 Pb/ 206 Pb age of 842 ±17 Ma. Earlier published Rb-Sr data for Baish rocks yielded a three-point isochron of 1165 ±110 Ma. This age has been repeatedly cited as evidence for pre-1 Ga arc magmatism in the Arabian Shield. However, more recent Rb-Sr data and zircon ages for clastic metasedimentary rocks are in agreement with our new zircon age, suggesting that initial oceanic magmatism in the Arabian Shield did not begin until after 90…
Diverse Lithologies and Alteration Events on the Rim of Noachian‐Aged Endeavour Crater, Meridiani Planum, Mars: In Situ Compositional Evidence
2018
We report the results of geological studies by the Opportunity Mars rover on the Endeavour Crater rim. Four major units occur in the region (oldest to youngest): the Matijevic, Shoemaker, Grasberg, and Burns formations. The Matijevic formation, consisting of fine‐grained clastic sediments, is the only pre‐Endeavour‐impact unit and might be part of the Noachian etched units of Meridiani Planum. The Shoemaker formation is a heterogeneous polymict impact breccia; its lowermost member incorporates material eroded from the underlying Matijevic formation. The Shoemaker formation is a close analog to the Bunte Breccia of the Ries Crater, although the average clast sizes are substantially larger in…
Sedimentology, petrography and geochemistry of a limestone breccia (Pietra di Billiemi) from NW Sicily, Italy: implications for evolution of the Teth…
2009
In this study, the Pietra di Billiemi, a famous dimension stone, is investigated because it records the tectonic evolution of the south Tethys continental margin and preserves a record of major environmental changes occurring near the Triassic/Jurassic boundary. The Pietra di Billiemi is a grey, coarse-grained and clast-supported limestone breccia cropping out in an area of the Palermo Mountains representing a segment of the Apennine–Maghrebian chain in western Sicily. The rock consists of metre-sized to centimetre-sized angular clasts, derived from Upper Triassic sponge boundstones and rudstones, with a differently coloured, silt-grained matrix. Fitted fragments are observed commonly which…