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Perugia, Italy

An up to 1250 m-thick clastic succession, the upper Tortonian Terravecchia Formation (TRV), has been analysed in detail in the middle-late Miocene Scillato wedge-top Basin grown above an already deformed tectonic stack in the northern Sicilian fold-and-thrust belt. The study involved field-based sedimentological and stratigraphic analyses aimed to determine to what extent both the depositional and sequence stratigraphic evolution of the Scillato Basin have been ruled by syn-sedimentary compressional to transpressional tectonics. Widespread intraformational angular unconformities associated with sudden change of palaeocurrents pattern and successive source area shifting suggest that tectonics acted, at least during the late Tortonian, as a major controlling factor during the sedimentation and generation of the sequential architecture of the basin infill.Six main facies associations were recognized, respectively: (1) gravelly braidplain " A" , (2) alluvial plain with ephemeral ponds " B" , (3) sandy - gravelly river-dominated delta front " C" , (4) brackish prodelta clayey siltstones " D" ; (5) prograding delta slopes and delta front " E" and (6) delta top conglomerates and sandstones " F" These associations are arranged into two main successive depositional systems: (1) the entrenched valley fill system (EVF) and (2) a retrograding to prograding river-dominated delta system (RDS). Both depositional systems and facies associations are arranged laterally and vertically to create a tectonically-induced late Tortonian Transgressive-Regressive cycle developed in a time interval roughly coinciding with the III order, 3.1. eustatic cycle. The Scillato Basin Transgressive-Regressive cycle is internally modulated by a depositional sequence set consisting of four IV order sequences here named LTS1, LTS2, LTS3, LTS4, respectively, bounded by tectonically-enhanced unconformities. The data here shown from the Terravecchia Formation suggest that the Scillato Basin is a good case-study of tectonically controlled sequence stratigraphic evolution and an analogy for similar continental to shallow-marine wedge-top basin infill. © 2013 Elsevier Ltd. Source

Donatelli U.,Urbino University | Tramontana M.,Urbino University | Venturi F.,Piazza dellUniversita
Italian Journal of Geosciences

The presence of ammonites in the Bonarelli Level (uppermost Cenomanian) of the Umbria-Marche Succession is reported here for the first time. The horizon studied has been recognised near Serra S. Abbondio, on the external limb of the Mt. Catria anticline, where the upper part of the Scaglia Bianca Formation and the interbedded Bonarelli Level crop out. An ammonite, preserved as a bidimensional trace, has been found within one black shale bed which characterizes the level. The lack of diagnostic elements does not allow a precise taxonomic identification. However, based on the morphologic features, this form can be tentatively ascribed to the suborder Lytoceratina. Source

The analysis of 56 specimens of the branched, walled post-depositional trace fossil Rutichnus, sampled from 31 thin-bedded, overbank turbidites from the Verghereto Formation, Romagna Apennines, indicates high morphologic variability of this ichnotaxon in hypichnial preservation. The variability concerns the arrangement of outer and inner walls, number and shape of annulations, distribution of pustules, the (false) branching arrangement and the general external shape. Highest variability has been observed mainly in the Rutichnus rutis ichnospecies, clearly less in the R. irregularis ichnospecies that is rare. The Dino-Lite microscope camera analysis of oriented thin sections indicates that endichnial preservation exhibits many structures due to burrowing in soft substrate, destroying laminae of sand. Consequently, Rutichnus probably was produced by a worm or arthropod, inducing strong deformation in turbidite sand during the feeding activity on phytodetritus and organic matter transported by the turbidity flow. Source

Monaco P.,Piazza dellUniversita | Checconi A.,Piazza dellUniversita
Rivista Italiana di Paleontologia e Stratigrafia

Five, 3-8 cm-thick calcarenitic turbiditic beds belonging to overbank deposits in the marginal sector of Marnoso-arenacea Basin, close to the intrabasinal high of Verghereto (Romagna, Northern Apennines, Upper Miocene), exhibit a well preserved ichnofossil-lagerstätte. The lagerstätte is composed by 43 ichnotaxa: 31 of them are preserved as casts at the sole of turbidites (background hypichnia) (group a), while 12 of them occur at the top (post-turbidite epichnia) and within (endichnia) (group b). The ichnodensity reaches its maximum at the top of the turbiditic beds. Background hypichnia (group a) is represented by graphoglyptids and non-graphoglyptid resting traces (background ichnofauna), with three-dimensional networks and shafts, meander systems, radiate, plug-shaped or stellatae structures forming clusters and unbranched systems of strings. Many taphonomic features suggest a fluting induced by bottom currents; graphoglyptids should have colonised the substrate after the action of these currents being not destroyed or fluted. AU hypichnial structures are perfectly preserved by the rurbidite casting and in this phase also endichnial burrows could develop. Post-turbidite epichnia (group b) concern vagile feeding burrows that developed horizontal patterns in a post-turbiditic regime, during the suspension phase of fine material; they were probably produced by organisms transported by suspension flows. Here, the very high ichnodensity suggests a competition among burrowers under stable currents with occurrence of vagile opportunistic organisms immediately followed by others that produced radiate spreite structures. Source

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