In eastern Sardinia, the first Jurassic sedimentary cycle (Bajocian-Kimmeridgian) develops in response to the opening of the Alpine Tethys Ocean. Starting during the Bajocian (Middle Jurassic), over a horst-and-graben system initially drowning to the northeast, at first siliciclastic sediments take place, related to continental to transitional environments. In time, they are gradually followed by marine carbonate, assigned to inner to outer ramp deposits. Afterwards, the latter, in their turn, become shallow; they are newly covered with an inner ramp lithofacies. The Kimmeridgian-Tithonian unconformity ends the cycle. Therefore, this sedimentary cycle as a whole can be interpreted as a transgressive-regressive megasequence linked to tectono-eustatic factors. All the pertaining stratigraphic units have been included within the 'Baunei Group', newly described. A comparison with the neighbouring areas, with particular regards to the Jurassic series of the Corsica, has been made, attempting to improve the reconstruction of this part of the Tethyan Ocean Western margin.
Late to post-Variscan sedimentary basins of Sardinia were influenced during Pennsylvanian to Permian times by two main tectono-sedimentary cycles: a Pennsylvanian to Cisuralian cycle represented mainly by dark limnic deposits, overlain by a Guadalupian to a possibly Lopingian cycle, mostly characterized by red-bed deposits. Lacustrine waterbodies developed in some sedimentary basins that were filled with siliciclastic to frequently early silicified carbonate deposits, depending on the climate and environmental conditions, landscape morphology and tectonic regime. The limnic successions of the lower tectono-sedimentary cycle were deposited in permanent, tens of metres deep lakes in deep, narrow tectonic strike-slip basins under a temperate to warm-humid climate. They started as lakes with terrigenous sedimentary input and developed minor carbonate deposits mainly at the end of their story. Conversely, the red-bed successions of the upper cycle were deposited in ephemeral, shallow playa lakes related to wider basins in an extensive alluvial plain under a hot and arid climate. Here, the siliciclastic sediments are intercalated with thin carbonate beds that are typical of a high evaporation rate. The evolution of the lake type could be related not only to a major climatic shift, but also to the changing morphotectonic conditions of the Variscan chain influencing the local microclimate. Comparisons with coeval successions in the Provence Basin, the Massif Central Aumance basin (France) and the Saar–Nahe Basin (Germany) show both similarities and differences between the basins.
In Eastern Sardinia during the early Middle Jurassic, Alpine Tethys opening triggered the rise of a temporary tectonic high. The high collapsed\ud rapidly, was fragmented into separate blocks, and subsequently covered by continental, transitional, and finally shallow marine deposits\ud forming a narrow depositional system comprising the Genna Selole Fm. Present-day exposures in the southern part of the palaeo-high allow\ud the sedimentological evolution of the transgressive cover sequence to be ascertained. Initial terrestrial deposits comprise alluvial fan deposits\ud located at the mouths of palaeovalleys. These pass into braid-deltas and in the coastal areas located between adjacent valleys mouths,\ud palustrine and coastal plain tidally-influenced environments developed. These environments interfingered laterally and passed seaward into\ud a transitional, siliciclastic to carbonate tidal environment. With the collapse of the tectonic high, the continental to transitional environments\ud were transgressed with deposition of marine carbonates. A comparison with similar coeval deposits of the W-Mediterranean domain has been\ud undertaken
The classical Middle to Upper Triassic carbonate sections at Monte Santa\ud Giusta and Punta del Lavatoio, North-west Sardinia (Italy), referred to the\ud Muschelkalk and Keuper lithofacies group, are revisited and their trace fossil\ud content is investigated for the first time. A combined ichnological and\ud sedimentological study reveals insights into the depositional environments,\ud regional context, palaeogeography and sequence stratigraphy. The results\ud indicate deposition on a homoclinal carbonate ramp with broad facies belts.\ud All recognized trace fossils are also known from time-equivalent deposits of\ud Germany and thus indicate a close affinity between the North-west Sardinian\ud Triassic and the Germanic Basin. Only a few trace fossils are particularly\ud abundant and these indicate opportunistic colonization by their producers,\ud which is probably related to restricted endobenthic conditions due to reduced\ud oxygen and/or increased salinity. The trace fossil association can be grouped\ud into a softground suite belonging to the Cruziana ichnofacies, and a firmground\ud suite of the Glossifungites ichnofacies. This discrimination enables an\ud interpretation of the northern Monte Santa Giusta section as a carbonate\ud ramp with extensive tidal flats and abundant carbonate accumulation in a\ud relatively proximal position, whereas the southern Punta del Lavatoio section\ud exhibits broad lagoonal environments with reduced sedimentation in a deeper\ud and more Tethys-influenced area. The Sardinian sections are ichnologically\ud similar to the Anisian–Ladinian succession known from the Tatra Mountains,\ud but differ from it by having a slightly higher ichnodiversity, which again can be\ud attributed to a less restricted lagoonal environment. This study demonstrates\ud the importance of integrating trace fossil analysis in sedimentological and\ud palaeontological investigations of carbonate systems
Investigations performed along the Middle Jurassic Alpine Tethyan unconformity surface of E Sardinia evidenced an elaborate surface that developed over older Late Paleozoic to Triassic rocks. This surface is covered by the Middle Jurassic Genna Selole Fm, which has different sedimentological and petrographical characteristics and thicknesses according to its location and the morphology and evolution of the lower substrate.An analysis of the unconformity and the rocks located above and below it revealed that a tectonic high emerged early during the Middle Jurassic from E Sardinia to Corsica in response to the extensional tectonics leading to the Alpine Tethys opening. This high was almost immediately fragmented in secondary blocks, and an irregular morphology of minor lows and highs thus formed upon it. The high was, on the whole, subjected to strong erosion. Its deposits accumulated along the rims of the high and in the lows of its surface, smoothing the landscape and preparing it for the marine transgression that followed. The tectonic high rapidly collapsed starting from its North side as show the older age of the marine deposits first investigated.A similar rise-and-collapse tectosedimentary evolution can be seen in some of the W Mediterranean domains next to the Sardinia-Corsica block. Indeed, they are all related to the Alpine Tethys opening and may mark a discontinuous high separating the Paleoeuropa from the Tethyan domain. Consequently, a comparison with all of these domains has been attempted by trying to set the Sardinia-Corsica block in this extensional margin scenario.Keywords: Alpine Tethys, Unconformity, Jurassic, Paleogeography, Sedimentology, Eastern Sardinia-Corsica Tectonic high ResumenInvestigaciones llevadas a cabo en la superficie discordante del Jurásico Medio del Tetis alpino evidencia que esta superficie está muy elaborada y se desarrolló sobre rocas que abarcan desde un registro Paleozoico Superior a Triásico. Esta superficie está cubierta por la Fm Genna Selole, de edad Jurásico Medio, que tiene diferentes características sedimentológicas y petrológicas y una potencia que depende de su localización y la morfología y evolución del substrato inferior.Un análisis de esta discordancia y de las rocas localizadas por encima y debajo de la misma revela que hubo un importante alto tectónico in etapas iniciales del Jurásico Medio que afectaba desde el E de Cerdeña a Córcega en respuesta a una tectónica extensional relacionada con la apertura del Tetis alpino. Esta área elevada fue rápidamente fragmentada en bloques desarrollándose una morfología de zonas altas y deprimidas previa a la transgresión marina que llegó seguidamente. Por los datos que muestran los primeros registros marinos se puede deducir que la fragmentación del citado alto tectónico se inició por su parte norte. Una evolución similar en zonas altas y bajas puede observarse igualmente en otras zonas del Mediterráneo occidental próximas al bloque de Córcega-Cerdeña. De hecho, todas ellas están relacionadas con la apertura de...
The Variscan orogeny occurred as a result of the Late Devonian to Late Carboniferous collision and accretion of Gondwanaderived microcontinents and continental masses with those of Laurussia. The irregular boundaries of the colliding continents caused isochronous transpressional and transtensional tectonics, accompanied by a complex pattern of intracontinental shear zones at the scale of the southern European Variscides. These shear zones and their configuration controlled the subsequent evolution of Permian to Middle Triassic paleogeography. The geographic distribution, from Morocco to the Eastern Alps, of the Late Carboniferous-Permian up to Triassic basins, most of which are considered as pull-apart basins, was related with the development of the Late Palaeozoic intracontinental shear network. Our analysis of the stratigraphic, tectonic and volcanic features of the Late Carboniferous/Permian continental basins across the Laurussia/Gondwana boundary reveals the role of the East Variscan Shear Zone during this time as a precursory lineament for the development of the Permian to Triassic rifting of Pangaea and the following opening of oceanic basins (e.g., the Neothetyan Ocean).
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