This note details geological mapping of a broad area situated in northern Sardinia which encompasses the historic regions of Logudoro and Mejlogu. The whole area lies within a well characterized Miocene tectonic depression, hereafter called Logudoro basin. The Logudoro basin first developed as a NNW-trending half-graben in which the Upper Burdigalian transgression led to a shallow-water sequence that onlaps the volcanic substratum and is erosionally truncated at its upper boundary. Serravallian sandstones generally overlie the shallow-water sequence, and represent the base of a second sequence that includes deposits as young as Tortonian-Messinian. These two main sequences, first identified around Florinas (Mazzei & Oggiano, 1990), have now been documented all over northern Sardinia. The older sequence consists of shallow water limestones and sandstones at its base, followed by marls of a deep marine environment. The younger sequence consists of basal fluviatile-marine sandstones followed by inner-shelf, calcareous algae-bearing, limestones. Tectonic movements have been demonstrated between the two sequences. Tectonism generated differential uplift and, in places, led both to erosion of sediments of the first sequence and to deposition of continental to transitional siliciclastic sediments. The Logudoro basin appears essentially codirectional with respect to the more northerly Porto Torres basin (Thomas & Gennesseaux, 1986), to which it is linked, by a complex transfer zone. The structural development of the Logudoro basin, and more generally of the NNW-trending, fault-bounded troughs of northern Sardinia, is subsequent to and independent of tectonic activity that generated ENE-trending transtensive troughs with Oligocene-Aquitanian fill, such as the coastal Anglona, Ottana and Chilivani-Berchidda basins (Oggiano et alii, 1995). This independence concerns both structural directions and the whole tectono-sedimentary history. Hence the structural and stratigraphic evidences derived from our mapping of the Logudoro area indicate a Cenozoic tectono-sedimentary evolution typical of an intracratonic basin. Spatial and chronological relationships among the Logudoro basin and adjacent Oligocene-Aquitanian basins lead us to reject attribution of the volcanic and sedimentary infilling of these basins to a unique Oligo-Miocene rifting phase previously thought to have generated a N-S trending trough ("Sardinian Rift" Auct.)

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