Roberto Rettori

Bio: Roberto Rettori is an academic researcher from University of Perugia. The author has contributed to research in topics: Permian & Ladinian. The author has an hindex of 25, co-authored 93 publications receiving 1814 citations. Previous affiliations of Roberto Rettori include University of Urbino.

Extinction, survival, and recovery of lagenide foraminifers in the permian–triassic boundary interval, central taurides, turkey

Abstract: The assemblage of lagenide foraminifers in uppermost Permian rocks of the central Taurides consists of 22 species in 16 genera, including the new species Rectostipulina pentamerata, plus additional unidentified elements. Of these, only two identifiable species in “Nodosaria” and indeterminate syzraniids survived the end-Permian mass extinction. The last occurrences of most taxa fall within the upper half-meter of the Permian System, a pattern consistent with abrupt extinction when tested for the Signor-Lipps effect. Permian survivors are joined locally in the Lower Triassic and lower Middle Triassic by three additional species. Globally, lagenide species diversity remained low until latest Anisian time, and probably did not reach pre-extinction levels until Late Triassic or Early Jurassic time. The survival of the lagenide clade, in contrast to the complete elimination of fusulinoidean fusulinides, may be linked to the lagenides' comparatively greater paleoenvironmental tolerances and wider paleogeographic distribution. Evaluation of lagenide extinction and survival across the Permian–Triassic boundary in the central Taurides is complicated by a facies change from bioclastic wackestones and packstones to oolitic grainstones near the top of the Permian, and by the development of variably dolomitized and pyritic stromatolites and overlying oolites in the lowest Triassic. The stromatolitic and oolitic Lower Triassic lithologies represent a sedimentologic response to the end-Permian mass extinction and unusual Early Triassic marine environments. Stromatolites likely became established as disaster forms in an ecologically permissive period that lacked normal marine grazing and bioturbating benthos. Their calcification and preservation may have been promoted by high carbonate saturation levels. Oolites, which are found in recurring facies associations with stromatolites and other anachronistic carbonates in Lower Triassic rocks throughout the Tethyan embayment, probably also formed in response to elevated saturation levels and the absence of a skeletal sink for carbonate.

The geology of Khuff outcrop analogues in the Musandam Peninsula, United Arab Emirates and Oman

Abstract: A revision of the stratigraphy of late Paleozoic and early Mesozoic carbonates (Bih Formation) in the Musandam Mountains near Ras Al Khaimah, United Arab Emirates (UAE), clarifies the presence of deposits that are age-equivalent to the Late Permian and Early Triassic Khuff Formation. Biostratigraphic markers including benthic foraminifera and calcareous algae indicate a Permian age for the stratigraphically oldest outcrops ranging from late Wuchiapingian to late Changhsingian (K4 and K3 reservoir units in the subsurface). A late Induan – early Olenekian (Early Triassic) age is documented for the stratigraphically youngest outcrops. Sedimentological features, stacking patterns and microfacies of the Permian outcrops show strong affinity to the KS3 and KS2 Khuff sequences, dominated by high-energy bioclastic pack- and grainstone. The depositional environment of the Bih Formation is further characterised by a palynological evaluation of claystones and by XRD analysis of clay minerals. Spectral gamma-ray data from the outcrop, which indicate Uranium depletion following the extinction of Permian foraminifera, help to pinpoint the position of the Permian – Triassic boundary and to correlate the measured section with the subsurface. Some stratigraphic intervals in outcrop are affected by strong secondary dolomitisation and do not reflect the same diagenetic patterns as their subsurface counterparts. Patterns of secondary dolomitisation, however, indicate the flow of formation water and thus mimic pore-fluid flow in the subsurface reservoirs. The depositional facies show clear resemblances to the reservoir facies, and the studied outcrops most likely represent the best analogue to the Khuff reservoirs in the UAE and in the North Dome / South Pars field area offshore Qatar and Iran.

End-permian mass extinction of lagenide foraminifers in the southern alps (northern italy)

Abstract: The Permian–Triassic boundary, examined at two sections in the Southern Alps, occurs ∼1.0 to 1.5 m above the base of the Tesero Oolite Member of the Werfen Formation in a depositionally continuous sequence of inner neritic carbonates. Lagenide foraminifers from the boundary interval comprise 27 species in 15 genera plus additional unidentified taxa, most of which became extinct during the end-Permian crisis. The only survivors were “Nodosaria” elabugae and unidentified species in Geinitzina and Nodosinelloides, with representatives of the latter two genera being short-term holdovers. The end-Permian lagenide extinction level occurs a few decimeters below the biostratigraphically defined erathem boundary, just above the contact between the Bulla Member of the Bellerophon Formation and the overlying Tesero Oolite Member. Confidence intervals (>96%) for the lagenide extinction at the two sections are 0.03 and 0.04 m thick. Plots of species' stratigraphic abundance versus their last observed occurren...

Pennsylvanian to Early Triassic stratigraphy in Alborz Mountains (Iran)

Abstract: Abstract New fieldwork was carried out in the central and eastern Alborz, addressing the sedimentary succession from the Pennsylvanian to the Early Triassic. A regional synthesis is proposed, based on sedimentary analysis and a wide collection of new palaeontological data. The Moscovian Qezelqaleh Formation, deposited in a mixed coastal marine and alluvial setting, is present in a restricted area of the eastern Alborz, transgressing on the Lower Carboniferous Mobarak and Dozdehband formations. The late Gzhelian–early Sakmarian Dorud Group is instead distributed over most of the studied area, being absent only in a narrow belt to the SE. The Dorud Group is typically tripartite, with a terrigenous unit in the lower part (Toyeh Formation), a carbonate intermediate part (Emarat and Ghosnavi formations, the former particularly rich in fusulinids), and a terrigenous upper unit (Shah Zeid Formation), which however seems to be confined to the central Alborz. A major gap in sedimentation occurred before the deposition of the overlying Ruteh Limestone, a thick package of packstone–wackestone interpreted as a carbonate ramp of Middle Permian age (Wordian–Capitanian). The Ruteh Limestone is absent in the eastern part of the range, and everywhere ends with an emersion surface, that may be karstified or covered by a lateritic soil. The Late Permian transgression was directed southwards in the central Alborz, where marine facies (Nesen Formation) are more common. Time-equivalent alluvial fans with marsh intercalations and lateritic soils (Qeshlaq Formation) are present in the east. Towards the end of the Permian most of the Alborz emerged, the marine facies being restricted to a small area on the Caspian side of the central Alborz. There, the Permo-Triassic boundary interval is somewhat similar to the Abadeh–Shahreza belt in central Iran, and contains oolites, flat microbialites and domal stromatolites, forming the base of the Elikah Formation. The P–T boundary is established on the basis of conodonts, small foraminifera and stable isotope data. The development of the lower and middle part of the Elikah Formation, still Early Triassic in age, contains vermicular bioturbated mudstone/wackestone, and anachronostic-facies-like gastropod oolites and flat pebble conglomerates. Three major factors control the sedimentary evolution. The succession is in phase with global sea-level curve in the Moscovian and from the Middle Permian upwards. It is out of phase around the Carboniferous–Permian boundary, when the Dorud Group was deposited during a global lowstand of sealevel. When the global deglaciation started in the Sakmarian, sedimentation stopped in the Alborz and the area emerged. Therefore, there is a consistent geodynamic control. From the Middle Permian upwards, passive margin conditions control the sedimentary evolution of the basin, which had its depocentre(s) to the north. Climate also had a significant role, as the Alborz drifted quickly northwards with other central Iran blocks towards the Turan active margin. It passed from a southern latitude through the aridity belt in the Middle Permian, across the equatorial humid belt in the Late Permian and reached the northern arid tropical belt in the Triassic.

The Prati di Stuores Stuores Wiesen Section (Dolomites, Italy): A candidate global stratotype section and point for the base of the Carnian stage

Abstract: The Prati di Stuores/Stuores Wiesen section (Dolomites, Italy) is proposed as a candidate Global Stratotype Section and Point for the base of the Carnian Stage. In addition to being a famous, richly fossiliferous locality, it includes the type-section of the Cordevolian substage. The section is located near Pralongia, along the southern slope of the crest separating the Badia/Abtei and Cordevole valleys. Below the levels with Trachyceras aon , the section contains a rich ammonoid fauna that chacterizes the lower part of the Regoledanus Subzone and subsequently records the first appearances of the mid-high latitude genus Daxatina ( Daxatina sp., D. cf. canadensis ) and of traditional Trachyceras with species different from T. aon . Moreover, the Daxatina cf. canadensis Subzone is recognised above the Regoledanus Subzone. Very rare conodonts of the Budurovignatus group and species of Gladigondolella from the diebeli Assemblage Zone occur. Gondolella polygnatyformis, already known from the Aon Subzone, is absent. Palynomorphs, foraminifers, gastropods, bivalves, brachiopods, microcrinoids and holothurian sclerites were studied. Variations in frequency and taxonomic diversity of these faunas suggest anaerobic-disaerobic bottom conditions for the lower-middle part of the section (0-105 m), followed by a more stable oxygen content in the upper portion. Magnetostratigraphy showed four intervals with normal polarity and three intervals with reversed polarity. The Daxatina cf. canadensis Subzone falls close to the normal polarity interval S2n. The present study proposes the FAD of the cosmopolitan genus Daxatina as a marker of the base of the Carnian Stage, placing it at a lower stratigraphic level than previously indicated in the Stuores area. The Prati di Stuores section is proposed as GSSP of the Ladinian-Carnian boundary.

A Mesozoic time scale

Abstract: We present an integrated geomagnetic polarity and stratigraphic time scale for the Triassic, Jurassic, and Cretaceous periods of the Mesozoic Era, with age estimates and uncertainty limits for stage boundaries. The time scale uses a suite of 324 radiomenc dates, including high-resolution 40 Ar/ 39 Ar age estimates. This framework involves the observed ties between (1) radiometric dates, biozones, and stage boundaries, and (2) between biozones and magnetic reversals on the seafloor and in sediments. Interpolation techniques include maximum likelihood estimation, smoothing cubic spline fitting, and magnetochronology

Biogeography and Dispersal of Micro-organisms: A Review Emphasizing Protists

Abstract: This review summarizes data on the biogeography and dispersal of bacteria, microfungi and selected protists, such as dinoflagellates, chrysophytes, testate amoebae, and ciliates. Furthermore, it introduces the restricted distribution and dispersal of mosses, ferns and macrofungi as arguments into the discussion on the postulated cosmopolitism and ubiquity of protists. Estimation of diversity and distribution of micro-organisms is greatly disturbed by undersampling, the scarcity of taxonomists, and the frequency of misidentifications. Thus, probably more than 50% of the actual diversity has not yet been described in many protist groups. Notwithstanding, it has been shown that a restricted geographic distribution of micro-organisms occurs in limnetic, marine, terrestrial, and fossil ecosystems. Similar as, in cryptogams and macrofungi about, 30% of the extant suprageneric taxa, described and undescribed, might be morphological and/or genetic and/or molecular endemics. At the present state of knowledge, micro-organism endemicity can be proved/disproved mainly by flagship species, excluding sites (e.g., university ponds) prone to be contaminated by invaders. In future, genetic and molecular data will be increasingly helpful. The wide distribution of many micro-organisms has been attributed to their small size and their astronomical numbers. However, this interpretation is flawed by data from macrofungi, mosses and ferns, many of which occupy distinct areas, in spite of their minute and abundant means of dispersal (spores). Thus, I suggest historic events (split of Pangaea etc.), limited cyst viability and, especially, time as major factors for dispersal and provinciality of micro-organisms. Furthermore, the true number of species and their distribution can hardly be estimated by theories and statistics but require reliable investigations on the number of morphospecies in representative ecosystems. Generally, the doubts on Beijerinck's famous metaphor "in micro-organisms everything is everywhere" can be focussed on a simple question: If the world is teeming with cosmopolitan unicells, where is everybody?

The Student's Gibbon: The History of the Decline and Fall of the Roman Empire

Abstract: Few books of scholarship have held up so well to public attention over the last two hundred years. At a time when the materials for this history were scant, a mind as great as Gibbon's was able to absorb everything known on the subject and dominate it with his historical erudition and inimitable literary style. The first volume, highly acclaimed on publication, was quickly reprinted in spite of an ambitious first print-run of 1000 copies. Careless proofreading meant numerous errors had to be rectified in later editions. It was not until the third edition, reprinted here, that the layout was improved and the footnotes appeared at the foot of each page and chapter numbers were placed in the margins.