Upper Pennsylvanian, Permian, and Lower? Triassic continental successions in SW Sardinia (Italy): a petro-sedimentological update of the molassoid Sulcis basin

In the SW Sardinia Sulcis-Iglesiente area, the continental late to post-Variscan upper Pennsylvanian, Permian, and Triassic successions are thin, fragmentary, restricted, and scattered (Fig.1). They are rarely superimposed on each other. So, the reconstruction of the sedimentary evolution of the basin as a whole depositional unit is difficult. More detailed stratigraphical-sedimentological analysis and investigations of historically known outcrops, and stratigraphic and thin section analysis of newly found outcrops have allowed the delineation of the history of the late to post-Variscan successions in SW Sardinia

The Middle Jurassic Alpine Tethyan Unconformity and the Eastern Sardinia - Corsica Jurassic High: A sedimentary and regional analysis

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.Investigaciones 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 del Tetis alpino y pueden marcar un alto discontinuo que separa Paleoeuropa del dominio del Tetis. Consecuentemente, una comparación de todos estos dominios ha permitido situar el bloque Córcega-Cerdeña en el escenario de este margen extensiona

Investigation methods on continental outcrops: developing an upgrade of the architectural analysis method by field tests in well-exposed Sardinian outcrops

In order to perfect the analytical procedures used to investigate the continental depositional environments, an upgrade of the architectural analysis method is here proposed in its main lines. The method has been tested in several well-exposed outcrops pertaining to continental environments related to different units of various age outcropping in different parts of Sardinia. The method appears to be promising in determining the fluvial style and the features of the corresponding fluvial network of the investigated units throughout a careful analysis of a discrete number of well-exposed outcrops

Interpreting siliciclastic sedimentation in the upper Paleozoic Mulargia-Escalaplano Basin (Sardinia, Italy): influence of tectonics on provenance

Late to post-Variscan molassic basins of Late Pennsylvanian-Permian age are exposed in Sardinia (Italy). Here, the compositional and stratigraphic evolution of the Mulargia-Escalaplano sedimentary basin (central Sardinia) has been investigated to highlight how the tectono-magmatic processes have influenced the sedimentation. Ruditic and arenitic samples were collected along well-characterized stratigraphic sections to provide a new insight into the impact of the tectono-magmatic processes on siliciclastic sedimentation. As a result, the conglomerates are mainly clast-supported, petromictic, and thus immature, with no defined maturity trend upwards. Nevertheless, pebble composition changes in times from Variscan basement pebble-rich to volcanic rock-rich, as a consequence of the basin widening and the dismantling and reworking of the coeval volcanic activity. The sandstone composition clearly changes from quartzolithic to feldspatholithic upwards, as a response to the same change of feeding and reworking of the volcanic rocks. Occasionally, interbedded quartzolithic arenites suggest exceptional floods carrying debris from the far borders of the basin. Also, the immature sandstone composition has been interpreted as being controlled by a continuous supply of fresh debris and to a rapid burial rate. In addition, the disappearance of metaradiolarite (lydite AA) Paleozoic grains in the sandstone mineral suite could represent a distinctive marker of a progressive unroofing of the Variscan chain and a clastic supply from deeper tectonic units

The Middle Jurassic Alpine Tethyan Unconformity and the Eastern Sardinia - Corsica Jurassic High: A sedimentary and regional analysis

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

A palaeoenvironmental reconstruction of the Middle Jurassic of Sardinia (Italy) based on integrated palaeobotanical, palynological and lithofacies data assessment

During the Jurassic, Sardinia was close to continental Europe. Emerged lands started from a single island forming in time a progressively sinking archipelago. This complex palaeogeographic situation gave origin to a diverse landscape with a variety of habitats. Collection- and literature-based palaeobotanical, palynological and lithofacies studies were carried out on the Genna Selole Formation for palaeoenvironmental interpretations. They evidence a generally warm and humid climate, affected occasionally by drier periods. Several distinct ecosystems can be discerned in this climate, including alluvial fans with braided streams (Laconi-Gadoni lithofacies), paralic swamps and coasts (Nurri-Escalaplano lithofacies), and lagoons and shallow marine environments (Ussassai-Perdasdefogu lithofacies). The non-marine environments were covered by extensive lowland and a reduced coastal and tidally influenced environment. Both the river and the upland/hinterland environments are of limited impact for the reconstruction. The difference between the composition of the palynological and palaeobotanical associations evidence the discrepancies obtained using only one of those proxies. The macroremains reflect the local palaeoenvironments better, although subjected to a transport bias (e.g. missing upland elements and delicate organs), whereas the palynomorphs permit to reconstruct the regional palaeoclimate. Considering that the flora of Sardinia is the southernmost of all Middle Jurassic European floras, this multidisciplinary study increases our understanding of the terrestrial environments during that period of time

The lacustrine carbonates of the post-Variscan molassic basins of Sardinia (Italy)

Investigations on the carbonates embedded in the mainly siliciclastic post-Variscan lacustrine basins of Sardinia have been undertaken. The features of the carbonates evolve in space and time according to peculiar times of deposition in lacustrine environments pertaining to different morphological, tectonic and climatic context. The lacustrine depositional environments changed in times: in Late Carboniferous-Early Permian times they were permanent lakes under humid/temperate climate; conversely in Middle-Late(?) Permian times they were ephemeral lakes (playas) under hot/ dry climate. The carbonate intercalations, from few decimeters to some tens of meters thick, represent times of scarce or none terrigenous input in sheltered or hypersaline areas of the lakes and show different facies arrangement according to the evolution of the lake itself. Here we present two of the more representative examples: the Late Carboniferous-Permian Perdasdefogu succession and the Permian Mulargia-Escalaplano succession

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

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