Roberto Rettori

THE PRATI DI STUORES/STUORES WIESEN SECTION (DOLOMITES, ITALY): A CANDIDATE GLOBAL STRATOTYPE SECTION AND POINT FOR THE BASE OF THE CARNIAN STAGE

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.

Pennsylvanian-Early Triassic stratigraphy in the Alborz Mountains (Iran)

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.

Wall structures in selected Paleozoic Lagenide foraminifera

Abstract Paleozoic lagenide foraminifera are strikingly similar morphologically to Mesozoic and Cenozoic Lagenida, but because benthic foraminifers suffered a catastrophic reduction in diversity during the end-Permian mass extinction, it is unclear whether the similarities of Paleozoic lagenides and younger unquestioned Lagenida link them evolutionarily or are the product of convergence. Seven species representing five families of Paleozoic lagenide foraminifers were examined and found to possess mostly monolamellar hyaline-radial walls, as in extant nodosariid Lagenida. Exceptions are Protonodosaria rauserae Gerke, 1959, whose wall is not optically radial, and Syzrania amazonica Altiner and Savini, 1997, whose hyaline-radial wall may or may not be accompanied by a secreted inner microgranular layer. The inner microgranular layer is an element that is thought to have been inherited from the ancestral Fusulinida. Its absence in all but the earliest and morphologically simplest Paleozoic lagenides indicates more advanced wall structure than generally has been ascribed to this group. The wall in Pachyphloia spp. is secondarily thickened, suggesting plesio- or ortho-monolamellar construction, whereas other examined species exhibit atelo-monolamellar wall structure. These types of lamellarity are common among modern nodosariids. Thus, on the basis of not only morphologic similarity but also similar wall structure, we strongly suspect evolutionary continuity of lagenides across the Permian-Triassic boundary. The question is not completely resolved, however, because lagenides have not yet been recovered from lowest Triassic rocks.

ORIGIN AND EARLY EVOLUTIONARY RADIATION OF THE ORDER LAGENIDA (FORAMINIFERA)

Abstract The Order Lagenida is a monophyletic group of calcareous foraminifers that originated in Middle Pennsylvanian time via acquisition of hyaline-radial wall structure and loss of microgranular wall structure, the latter being characteristic of the close sister group and likely ancestor, the Fusulinida. Early lagenides are delineated into subgroups on the basis of presence or absence of partitioning within their tests, and among partitioned forms, on continuous versus discontinuous growth styles. Partitioned, discontinuously growing forms may be further delineated on the basis of test symmetry and on modifications to chamber shape and apertural complexity. Early lagenides underwent rapid taxonomic differentiation during late Moscovian and early Kasimovian time. Taxonomic differentiation was accompanied by rapid dispersal from the presumed center of origin in the midcontinent-Andean area to tropical and subtropical shelves worldwide. By Early Permian time certain lagenides were adapted to cool water paleoenvironments, as evidenced by their occurrences in high paleolatitudes and even in glaciomarine basins. Early Permian lagenides do not exhibit marked provincialism, but there is evidence for paleolatitudinal control on assemblages. The midcontinent-Andean and present Arctic areas contain similar, diverse faunas from low- to mid paleolatitudes along the western margin of Pangaea. These faunas share many elements in common with faunas from the tropical and subtropical eastern margin of Pangaea (Paleotethys). In contrast, the Europe-Urals, Siberian and Australian areas are characterized by a slightly different faunal association from mid- to high paleolatitudes in both hemispheres. Panthalssan faunas are less well known, but seemingly contain only cosmopolitan taxa.

Lower and Middle Triassic foraminifera from the Eros Limestone, Hydra Island, Greece

The systematics and stratigraphic ranges (constrained by conodont dating) of abundant and well preserved foraminiferal faunas from six sections in the Lower and Middle Triassic Eros Limestone of central and western Hydra (Argolis Peninsula, Greece) are described. A joint analysis of the conodonts, foraminifera and bivalves has enabled the Scythian and Anisian stages to be recognized with some certainty within the Eros Limestone carbonate platform. The foraminifera have affinities with those of many other Tethyan localities, in particular the Dinarides, Balkans, Carpathians and the Southern Alps.

Nouvelle classificationdes Foraminifères Endothyroïdes du Trias

A systematic revision of the Triassic endothyroid Foraminifera allows to describe the following taxa: Endotebidae,nov. fam., Endotriadidae, nov. fam., Endotebanella, nov. gen., type-species Endothyranella kocaeliensis Dager, 1978a, Endotriada, nov. gen., type-species Endotriada tyrrhenica, nov. gen. nov. sp., Endotriadella, nov. gen., type-species Ammobaculites wirzi Koehn-Zaninetti, 1968. The species Endoteba bithynica, nov. sp., and Endotriada tyrrhenica, nov. gen. nov. sp., are described. The genus Endoteba and various species are emended. Biostratigraphic, paleogeographic and phylogenetic values of the taxa are discussed.

Towards a better definition of the Middle Triassic magnetostratigraphy and biostratigraphy in the Tethyan realm

Magnetostratigraphic and biostratigraphic data for the Middle Triassic (Anisian) were obtained from the Han-Bulog facies in the Nderlysaj section from the Albanian Alps and the Dont and Bivera formations in the Dont–Monte Rite composite section from the Dolomites region of northern Italy. The Nderlysaj section is biochronologically bracketed between the late Bithynian and early Illyrian substages (i.e., late-early and early-late Anisian), whereas the Dont–Monte Rite section comprises the late Pelsonian and the early Illyrian substages. The data from Nderlysaj and Dont–Monte Rite, in conjunction with already published data, allow us to construct a nearly complete composite geomagnetic polarity sequence tied to Tethyan ammonoid and conodont biostratigraphy from the late Olenekian (late-Early Triassic) to the late Ladinian (late-Middle Triassic). New conodont data require revision of the published age of the Vlichos section (Greece).  1998 Elsevier Science B.V. All rights reserved.

Mississippian (Lower Carboniferous) microfossils from the Chios Mélange (Chios Island, Greece)

Abstract The Chios Melange is a thick Paleozoic wildflysch sequence that crops out on the Greek island Chios. It is composed of chert, limestone and volcanic blocks floating in a siliciclastic turbiditic matrix. New data suggest that the youngest blocks within the Chios Melange are clasts of a breccia from the Kouramia–Nenitouria area that contain conodonts of late Visean or early Serpukovian age. The conodont fauna from the breccias is characterized by the genera Gnathodus and Lochriea, which favored deeper-water, open-marine facies. Elsewhere on the island, in the Papalia-Nagos area, calcareous microfossils of middle to late Visean age have been recovered from lime grainstone beds within the Chios Melange. Allochems making up the grainstones are interpreted to have been transported into deeper-water turbiditic facies, but there is no evidence of stratigraphic reworking. Age-diagnostic calcareous microfossils include the alga Koninckopora inflata and foraminifers in the genus Paraarchaediscus. In situ Mississippian microfossils indicate that the Chios Melange is older than Pennsylvanian (Upper Carboniferous) – Permian, as previously thought. The revised age suggests that the origin of the Chios Melange may be related to the development of an accretionary prism during the Hercynian Orogeny.

Stratigraphic evidence for Cimmerian events in NW Caucasus (Russia)

The Upper Permian and Triassic sequences of the NW Caucasus present a good record of the Cimmerian events, rather undisturbed by the subsequent Alpine deformations. Original field work with new fossil identifications, microfacies analysis, and sandstone petrography were carried out. During the late Permian, active strike-slip basins were filled by continental clastics successions. Marine ingressions during the latest Permian, led to the formation of sponge reefs and skeletal carbonate ramps. During the Triassic, several siliciclastic wedges were intercalated within the marine carbonate succession. Most important is a conglomerate body made up of serpentinite pebbles of Spathian age (early Triassic), recording the exhumation and erosion of schistose antigorite serpentinites. By the late Anisian a severe deformation affected the Peredovoy (= Fore) Range of the NW Caucasus. Lower Triassic to Anisian sediments deformed also in chevron folds were overlaid with angular unconformity by a siliciclastic, and also volcaniclastic, conglomeratic and arenitic body, up to several hundred meters thick. By the late Ladinian-earliest Carnian, marine sedimentation resumed locally, forming a carbonate ramp during part of the Norian. Towards the end of the Norian, the entire area emerged and was again mildly tilted. The subsequent post-Cimmerian transgression occurred largely during the Middle Jurassic. Consequently, the most important Cimmerian deformations appear to be of early and middle Triassic age.

Magnetostratigraphy and biostratigraphy of an Anisian-Ladinian (Middle Triassic) boundary section from Hydra (Greece)

On the island of Hydra, the Anisian/Ladinian boundary is exposed in a 24 m thick section of nodular reddish Han-Bulog Limestone. This paper is focused on the magnetostratigraphy and conodont biostratigraphy of this section. The Anisian/Ladinian boundary is defined by the First Appearance Datum (FAD) of the conodont species Gondolella trammeri Kozur (base of the Nevadites ammonoid zone), and occurs in a normal polarity zone. Microfacies analysis has distinguished a lower and upper lithofacies recording gradual shallowing from pelagic conditions to a platform margin paleoenvironment.