New sedimentological, stratigraphical and petrographical data were collected on the post-Variscan rocks cropping out below the Quaternary cover along the northwestern Sardinian coastline immediately south of Alghero. Four stratigraphic sections were analyzed in detail at Cala Bona and Il Cantaro Rock: they were dated and correlated using widely known and well-defined lithostratigraphic markers. An about 85 m thick succession is present, from the Permian siliciclastic deposits via the Early - Middle Triassic “Buntsandstein” up to the Middle Triassic “Muschelkalk”. The measured sections show the intra-Permian and Permian-Triassic unconformities, and the “Buntsandstein”-“Muschelkalk” gradual passage. Those latter features of the Permian-Triassic Nurra basin are described for the first time south of Alghero. The depositional characters show an evolution starting from continental environments of high-medium energy, in which deposition is interrupted during the Permian and at the Permian/ Triassic boundary by important erosive phases; those environments pass suddenly in Triassic times first to a siliciclastic tidal flat and later, gradually, to shallow carbonate environments comprised between the tidal flat and the lagoon. The petrographic data from the most complete Cala Bona section confirm a growing maturity of the siliciclastics passing from the Permian to the Triassic units probably linked to the peneplanation of the landscape. The overlying Triassic siliciclastic deposits again grow immature upwards, possibly suggesting the start of the Alpine tectonic activity. The comparisons with other well-known Permian-Triassic successions located to the north (Cala Viola-Porto Ferro, Monte Santa Giusta) indicate the Cala Bona-Il Cantaro succession were deposited on a structural high possibly representing the southern margin of the Nurra basin: in this hypothesis, a symmetrical graben structure may be suggested for the basin.
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|Titolo:||Facies analysis, stratigraphy and petrographic data from the Permian-Middle Triassic Cala Bona – Il Cantaro Rock sections (Alghero, NW Sardinia, Italy): contribution to the post-Variscan Nurra basin evolution|
|Data di pubblicazione:||2011|
|Tipologia:||1.1 Articolo in rivista|