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

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

The Eocene Monte Cardiga Fm (Sardinia, Italy): a tidal strait towards a westward coal basin?

Paleogene deposits are scattered in S Sardinia. According to previous reconstructions, during the Paleogene an E-W transition between open to confined environments occurred, giving place to a restricted gulf in the W. In SW Sardinia the uppermost Paleocene – Lower Eocene 200 m thick Produttivo group rests unconformably over older rocks. Its base is formed by continental siliciclastics (Arenarie di Monte Margiani Fm, 0–25 thick). These siliciclastics are followed by the marine Miliolitico limestones (30–50 m), and by the Lignitifero siliciclastic to carbonate succession with lignite layers at the top (70–120 m), of coastal-deltaic (tidal?) environments. This succession represents the tectono-sedimentary transgressive – regressive Pyrenean cycle. The Middle Eocene – Lower Oligocene continental Cixerri Fm follows unconformably. The link between the SW and the SE Sardinia successions is represented by the central Sardinia 35 m thick Nuraghe Sioco Lower Eocene siliciclastic to minor carbonate fossiliferous succession. It represents an emerged(?) mudflat featured by frequent marine ingression. The exposed sections of this unit are too restricted to allow any reconstruction by now. Limited tidal influences are possible. In SE Sardinia crops out a 250 m thick Early-Middle? Eocene transgressive-regressive sedimentary cycle. It rests unconformably over all the previous units and it is represented by the 10 m thick Santa Caterina Fm, followed by the unconformable 240 m thick Monte Cardiga Fm. The Santa Caterina Fm is a palustrine-lacustrine-alluvial unit reworking the Triassic carbonate substrate and followed by thin siliciclastic deposits. The upper Monte Cardiga Fm is featured by siliciclastic deposits with carbonate-siliciclastic intercalations. Five lithofacies delimited by gradual boundaries are present. They are, from the bottom 1) continental, siliciclastic coarse lithofacies; 2) transitional sandstone-carbonate lithofacies; 3) laterally discontinuous, lens-shaped marine calcarenitic lithofacies; 4) marine to transitional carbonate-sandstone-pelitic lithofacies; 5) continental sandstone-conglomerate lithofacies. Every lithofacies represents a specific depositional environment. Following the continental environment of the lithofacies 1, the transitional lithofacies 2 is represented by sandstones whose bedforms are arranged in meanly EW fashion as meter-sized dunes with 35°-dipping foresets. The lithofacies 3 carbonate nummulite-bearing intercalations stick out as EW-elongated humpback from a plateau: they are organized as lens-shaped, slim bodies featured by fossiliferous grainstonespackstones with cross-bedding EW-oriented. The lithofacies 4 show possible tidal bundles with slack-water laminae. The lithofacies 5 marks a return to the original continental conditions. Sandstones are litharenites rich in rock fragments from the Variscan basement passing to lithic arkoses with k-feldspars deriving from the lower granitoid and so implying the unroofing of the basement itself. The features of the Monte Cardiga Fm marine part suggest deposition in tide-influenced environments with elongated tidal bars. The outcrops distribution and the former palaeogeographic reconstructions indicate that a tidal mechanism forced by a tectonics-related funneling was in effect. Ephemeral communications between the Sardinia SW and SE sectors were assured by the shallow, choked Tanca Aru strait where a thin Produttivo Group succession 7–8 m thick featured by lagoonal to palustrine-lacustrine deposits. This way the S Sardinia Eocene outcrops have a possible paleoenvironmental framework

Analisi di facies della successione triassico-giurassica di Porto Pino (Sardegna sud-occidentale)

The Mesozoic of Porto Pino (SW Sardinia) has been investigated in detail. The presence of two carbonate successions, belonging to two different stratigraphic-structural units (“Cala Su Trigu Unit” and “Guardia sa Perda Unit”, BARCA & COSTAMAGNA, 1997a) has been confirmed. Detailed sedimentological analysis has improved the recently established stratigraphy (BARCA & COSTAMAGNA, 1997a) and defined accurately the depositional environments of the successions. The whole thickness of the “Cala Su Trigu Unit” is about 120-130 m. The Unit starts at the base by the “Dolomie di Scollieddu formation”, consisting of grey, locally pinkish, dolostones passing upwards to grey calcareous dolostones; rare marly red layers also occur. This formation is characterized by several depositional textures and structures, as ooids, peloids, bioclasts, calcitic pseudomorphs after sulphates, cross- and parallel laminations and loferitic structures are clearly visible. In the lower part of the “Dolomie di Scollieddu formation” storm layers are often wellrepresented. Fossil organism (algae, brachiopods, bivalves, corals, gasteropods) are usually concentrated in few specific horizons. The age of this formation is comprised between Middle?-Upper Triassic (Megalodontidae, Thecosmilia) at the base and Liassic (defined by foraminifera) at the top. The Medau Mereu formation follows upwards; this unit is made up by green-yellow marls passing to well-stratified grey to blue-grey marly limestones. Fossils (radiolaria?, foraminifera, sponge spicules, worm tubes and rare pelagic bivalves, brachiopoda and bryozoan fragments) and nonskeletal grains (rare, reworked ooids and peloids) occur in the whole formation. The foraminifera association gives to the Medau Mereu fm. an Aalenian age. The deposition of the “Cala Su Trigu Unit” succession marks a carbonatic depositional environment ranging from a peritidal setting of inner ramp at the base (Dolomie di Scollieddu formation) to outer ramp close to the basin at the top (Medau Mereu fm.). The “Guardia Sa Perda Unit” consists of four formations; at the base the “Punta Tonnara formation” (BARCA & COSTAMAGNA, 1997a) similar to the German “Muschelkalk” facies, is made up by well-stratified, blue-grey limestones with marly limestones and marls intercalations, usually arranged in decametric “shoaling upward” sequences. In the upper part of these sequences storm layers are very common; bioclasts (bivalves, gasteropods, echinoids spines, algal fragments, crinoids, ophiuroids, cephalopods?) such as pseudomorphs after sulphates, represent the basal lag of the tempestites. The age of this formation, about 25 m thick, can be referred to Middle-?Upper Triassic on the base of presence of Agathammina sp. (MARTINI et al, 1987). A comparison made with other similar succession of Sardinia (Punta del Lavatoio; GANDIN, 1978a; Scivu-Is Arenas, BARCA et al., 1995; Monte Maiore, COSTAMAGNA et al., 1999) allows to assign to this formation a Ladinian age. The depositional environment of this formation varies from the intertidal? - shallow subtidal conditions of inner, shallow ramp to the deep subtidal ones of outer, deep ramp. The “Monte Zari formation”, corresponding to the German “Keuper” facies, follows upwards; the transition from the “Punta Tonnara formation” is marked by a thick horizon of dissolution-collapse breccias. This formation consists of grey dolostones containing rare layers of polychrome marls. The dolostones are usually well stratified and present a large spectrum of textural arrangement (loferitic bindstones, dissolution breccias, massive dolostones with evaporite casts, oolitic, more rarely peloidal, grainstones interested by large cross lamination structures). Fossils and bioclasts, with the only exception of algal mats and their derived fragments, are totally lacking. The whole thickness is about 120-130 m. The Upper Triassic - Lower Liassic age of this formation can be deduced from the paleontological data recorded in the underlying Punta Tonnara and overlying Guardia Sa Perda formations. The depositional environment is referred to a inner, shallow carbonatic ramp subjected to subtidal, lagoonal conditions, often restricted. Rarely intertidal environments have been also recorded. The limestones of the “Guardia sa Barracca Formation” sharply overlay the “Monte Zari fm.”. They consists of bioclastic-oolitic packstones to grainstones, with a minor amount of peloids. Bioclasts (crinoids, brachiopods, foraminifera, bryozoa, bivalves, green algae) are diffuse and clearly visible; the non-skeletal grains (ooids, peloids, coated grains) are also abundant. Chert nodules occur too. Some horizons are rich of macrofossils as belemnites, brachiopods and crinoids. The age of this formation is Upper Liassic (Domerian? - Toarcian). It is gradually followed by the Aalenian “Medau Mereu formation”, here made by the same alternances of marls and limestones just described in the “Cala Su Trigu Unit”. The thickness of the Guardia Sa Barracca and Medau Mereu fms. together is about 150 m. The depositional environments of Guardia Sa Barracca and Medau Mereu fm. are strictly connected, so representing the gradual evolution from an oolitic shoal of a shallow ramp (rarely interfingering with the lagoon) environment toward the outer, deep ramp close to the basin. Comparing the typical successions of the German Triassic with the lithologies described in the succession of Porto Pino (in particular those of the “Guardia Sa Perda Unit”) the latter might be resulting by the deposition during Upper Triassic times in a transitional setting between the environments of the Germanic Realm and those of the Alpine one. In addition, setting of the Triassic part of this successions is redefined referring to classic “Muschelkalk” and “Keuper” stratigraphical units, utilized as sedimentary facies associations