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 nearthe Triassic/Jurassic boundary. The Pietra di Billiemi is a grey, coarse-grainedand clast-supported limestone breccia cropping out in an area of the PalermoMountains 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 suggest an in situ origin for the bulk of the breccia. The matrix is characterized by the absence of biogenic components and by variable mineralogy and geochemistry. Petrographic features and Sr-isotope values indicate that the most important and earliest fillings of the breccia consist ofblack matrix and white matrix temporally referable to Hettangian–Sinemurian times. Clotted micrite, carbonate fluorapatite and abundant pyrite, in addition to relatively high contents of redox-sensitive elements (V, Ni, Zn and S), are consistent with deposition in anoxic conditions that favoured microbial mediation for authigenic carbonate (calcite and dolomite) precipitation in the matrix. As a whole, the Billiemi breccia can be considered a product oftectonic fragmentation of a Tethyan carbonate platform edge around the Triassic/Jurassic boundary, formed when the drowned platform edge was covered by hemipelagic mudstones recording the anoxic conditions existingduring Early Jurassic times.
|Numero di pagine||17|
|Stato di pubblicazione||Published - 2009|
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