Late Ladinian Research Articles

A Flora Dicroidium no Rio Grande do Sul: implicações bioestratigráficas

A Triassic taphoflora identified in the Central Region of the State of Rio Grande do Sul, southern Brazil, represents an important biostratigraphic stage in the paleofloristic succession of the Paraná Basin. This megafloristic association is composed of compressed leaves, fronds and seeds of a “Dicroidium Flora” and shows a predominance of the Dicroidium genus, with several species, and other important taxa like Neocalamites sp, Cladophlebis sp, Tetraptilon aff, heteromerum, Ginkgoites Antarctica, Sphenobaiera sp, Podozamites sp, Nilssonia sp, Pteruchus sp and Carpolithus sp. Taking into account the stratigraphical distribution of different species of the Dicroidium genus, a biostratigraphic framework was established. The biostratigraphical position of this Triassic flora was established by comparison with Triassic floras from Argentina, South Africa and Australasia. Considering that the recognition of this Dicroidium Flora was based on limited outcrops belonging to one lithostratiphic level (Santa Maria Formation – Passo das Tropas Facies), it was impossible to establish a formal biostratigraphic zonation. Instead, at present time, an informal floristic interval, named “Dicroidium odontopteroides Flora” is proposed (Late Anisian to Late Ladinian, Middle Triassic).

CTENOGNATHICHTHYS BELLOTTII (DE ALESSANDRI, 1910): NOMENCLATURAL PROBLEMS AND STRATIGRAPHICAL IMPORTANCE OF THIS MIDDLE TRIASSIC ACTINOPTERYGIAN FISH

The existence of one of the original specimens of Ctenognathichthys bellottii (De Alessandri 1910), figured and labelled as ‘type specimen’ by De Alessandri himself, raises a nomenclatural question as there is also a neotype designated by Burgin (1992). The International Commission of Zoological Nomenclature has been asked to rule on the validity of the neotype. As some of the requirements for the designation of a neotype were not met, the holotype should be treated as the name-bearing type. The discovery of this species in both the Besano Formation (Grenzbitumenzone Auct .) and the Perledo-Varenna Formation is very important from a stratigraphic point of view, confirming that the so called Perledo fish-fauna is composed of different assemblages. In fact, the Perledo fauna has most species in common with the Ca’ del Frate (Viggiu, Varese, Italy) fauna from the Kalkschieferzone (uppermost Meride Limestone), which is latest Ladinian in age, while a few of the Perledo species have been found also in the Grenzbitumenzone and/or in the lower Meride Limestone of Lower Ladinian age.

The mud mound nature of the Cassian Platform Margins of the Dolomites A case history: the Cipit boulders from Punta Grohmann (Sasso Piatto Massif, northern Italy)

The sedimentological features and the microbiofacies of the Cassian platforms (Late Ladinian-Carnian) of the Dolomites can be studied only on the basis of the socalled “Cipit boulders”, that are platform-derived olistoliths and clasts fed to the basin and escaped to the extensive dolomitization affecting the buildups. Our paper deals with the Cipit boulders occurring in the Punta Grohmann section (Wengen and S. Cassiano formations, Late Ladinian, Archelaus and Regoledanus Zones). The dominant microfacies are represented by boundstone, consisting of nearly 60% of micritic limestone occurring both as peloidal or aphanitic micrite, mostly organized into stromatolitic laminites of thrombolites. The skeletal organism (Tubiphytes, skeletal cyanobacteria, sphinctozoan sponges, etc.) represent only a minor component of the rock (usually less than 10%). Early cements are widespread and consist both of fan-shaped calcite (replacing former aragonite), bladed isopachous magnesian calcite and radial-fibrous calcite (neomorphic after Mg-calcite). The carbonate platforms from which the olistoliths derive were made up mainly of carbonate mud that underwent early lithification, as witnessed by the considerable amount of early cements: therefore they may be regarded to as mudmounds, and more precisely as microbial mud-mounds, due to the clearly accretionary, organic-controlled nature of most micrites. The micrites, subdivided into auto- and allomicrite on the basis of micromorphological and fabric characteristics, have been tested for epifluorescence. The results confirm the organic control on the deposition of automicrite, also in the cases in which a microbial influence is not obvious (i.e. aphanitic micrite without internal organization).

Mesozoic Igneous Suites in Hungary: Implications for Genesis and Tectonic Setting in the Northwestern Part of Tethys

Mesozoic igneous rocks occur in various tectonic units of the Intra-Carpathian Area of Eastern Europe. These rocks were situated several hundred km apart from one another during their formation, and subsequent large lateral displacements resulted in their present positions. They formed during a relatively wide temporal range (Middle Triassic to Late Cretaceous) through different petrogenetic processes associated with the Mesozoic evolution of the northwestern part of Tethys. In the Transdanubian subunit of the Alcapa block, Middle Triassic calc-alkaline, intermediate-to-acidic, and potassic rocks occur as pyroclastics, lava flows, and dikes in the Bakony and Buda mountains. The Gemer-Bukk subunit of the Alcapa block comprises two different igneous series: (1) slightly metamorphosed Middle Triassic volcanic rocks of the Eastern Bukk Mountains, which can be divided into an older (Anisian-Early Ladinian) calc-alkaline, intermediate-to-acidic volcanic series and a younger (Late Ladinian) alkaline basaltic ser...

Première découverte d'ostracodes triasiques dans la formation de khaneh kat, Montagne Michparvar (Ouest Iran)

Well preserved ostracodes are found in Khaneh Kat Formation (Zagros facies) in Iran. They are attributed to the Lower Carnian. They are the first ostracodes described in this part of Iran. Five species are recognized, three are new : Movschovitschia cf. interrupta Kristan-Tollman, 1983, Hungarella cf. ussuriensis ( Gramm, 1970), Metacytheropteron ? zagrosensis n. sp., Cytherella persensis n. sp., Reubenella khanehkatensis n. sp. This fauna was extracted from thin beds of limestones intercalated in a dolomitic formation. The species differ from species found in other iranian areas (Late Ladinian of Aghdarband, Rhaetian of Bagerabad).

The middle Triassic of the Brembana valley: preliminary study of the Esino platform (Bergamasc Alps)

The stratigraphy and paleogeography of the ladinian Esino Limestone outcropping in Valle Brembana-Valle Parina, have been integrated with the biostratigraphic analysis of cephalopod fauna. A complex internal structure of the upper anisian-ladinian Esino carbonate platform has been identified. Six different lithozones have been recognized, they record the stratigraphic-paleogeographic evolution of the Esino Limestone. This carbonate platform developed through three stages: 1) construction of a lower edifice (Late Anisian-? Early Ladinian) representing the first phase of carbonate piatform diffusion on structural highs, which were already the site of carbonate deposition during the Middle Anisian (peritidal dolomites of the Angolo Limestone); 2) buildup of the carbonate complex (main edifice). In this second phase (Early Ladinian-Late Ladinian p.p.) the most important one, the platform growth took place by prevalent aggradation; 3) development of the upper edifice and progradation of the piatform in the Late Ladinian. In this third phase, inner plarform facies with diagenetic caps at the top of peritidal cycles are common. The buildup developed in the second phase yields bioclastic packstones with ammonoids, gastropods, echinoderms, and bivalves clustered within lithozone 4 and in the proximity of the southern margin of the platform in Val Parina. Studies in progress of ammonoids and gastropods allowed for the recognition of different fossil assemblages which date from Early Ladinian to Late Ladinian. A few problematic ammonoid assemblage of probably Early Ladinian age, has been found in a stratigraphic level above the base of the Esino Limestone.

Triassic stratigraphy in the island of Hydra (Greece)

The Triassic sedimentary succession, cropping our in the island of Hydra, starts with a few metres of quartzarenites (Aghios Nikolaos Fm., Scythian) vertically making transition to a thick carbonate unit (Eros Lmst., Spathian-Pelsonian) subdivided into three lithozones and one member. During Pelsonian an extensional tectonic phase dissects the Eros carbonate platform. Its consequent downwarping results in the deposition of a pelagic sequence spanning the Pelsonian-Late Triassic time interval. This succession generally consists of few metres of nodular limestones (Han Bulog Lmst., Late Pelsonian-Early Ladinian) associated with green tuffs, followed by few hundred metres of cherty limestones (Adhami Lmst.). In the eastern part of the island a thick carbonate bank (Pantokrator Lmst.) develops, spanning the lllyrian to Late Triassic time interval. An overlying pelagic sequence, Jurassic in age, marks the downwarping of the Pantokrator carbonate platform. A typical passive continental margin succession is thus recorded in the Triassic of Hydra, suggesting its affinity with the Subpelagonian domain.

Sequence Stratigraphy of Carbonate Buildups Developed in an Active Tectonic/Volcanic Setting: Triassic (Late Ladinian and Carnian) of the Dolomites, Northern Italy

Sequence Stratigraphy of Carbonate Buildups Developed in an Active Tectonic/Volcanic Setting: Triassic (Late Ladinian and Carnian) of the Dolomites, Northern Italy

Palynostratigraphy of the late Ladinian and Carnian in the Southeastern Dolomites

In the Late Ladinian and Carnian Cassian Formation, Cassian Dolomite and Raibl Group a qualitative and quantitative palynological investigation of 50 productive samples was carried out. Sixty taxa of pollen and spores were identified, one species is described as new. Comparisons with palynofloral associations of other Middle and Late Triassic sections of Europe allow the recognition of five palynological phases of the Early Langobardian to the ?Tuvalian in the study area. Chronostratigraphic classifications enable the re-interpretation of time-stratigraphic relationships, which indicate a clear diachronism of lithologic boundaries. According to these results, both the Cassian Formation and the Raibl Group extend from the Langobardian to the ?Tuvalian and thus comprise a longer period of deposition than previously thought. These lithofacies units should be considered as migrating facies zones, which show a rapid progradation to the north.

Middle Triassic strike-slip tectonics and igneous activity of the Dolomites (Southern Alps)

Strike-slip faults and south-vergent thrusts deformed a rhomb-shaped area, measuring about 20 × 20 km, in the Dolomites during the Late Ladinian. Deformation was caused by a right stepover of a NNE-SSW trending sinistral strike-slip fault. Strike-slip displacement amounted to more than 10 km; thrusting caused a relief shortening of more than 3 km and can be demonstrated by the matching of particular Ladinian carbonate facies boundaries. These tectonic movements may account for the termination of a transgressive depositional megacycle, which had begun in Permian times. Rupture of the crust of the deformed terrain caused the emplacement of a magma chamber beneath. Its evacuation in the Latest Ladinian and Early Carnian was associated with the collapse of its roof and the extrusion of shoshonitic lavas. They filled a volcano-tectonic depression which overlaps with the deformed and eroded area. The orientation of volcanic dikes suggests the absence of tectonic strain during igneous activity, provided that they formed contemporaneously.

Strontium isotope composition of marine carbonates of Middle Triassic to Early Jurassic age, Lombardic Alps, Italy*

ABSTRACTThe 87Sr/86Sr ratios and strontium concentrations for thirty‐three samples of marine carbonate rocks of Middle Triassic to Early Jurassic age have been determined. The samples were collected from four measured sections in the areas of Val Camonica in northern Italy. The strontium concentrations vary from 40 to 7000 ppm. Most of the samples are calcitic limestones containing less than 10% of non‐carbonate residues. Dolomitic samples and those containing appreciable non‐carbonate residues have significantly diminished strontium concentrations. 87Sr/86Sr ratios of the carbonate phases of these rocks appear to be unaffected by dolomitization and by the presence of non‐carbonate minerals. The average 87Sr/86Sr ratios of the formations vary systematically in a stratigraphic sense. The ratio increased from Early Anisian to Early‐Middle Ladinian, declined during Late Ladinian and Carnian, rose again during the Norian and then declined throughout the Late Norian (Rhaetian), Hettangian, Sinemurian and Pliens‐bachian ages. The average 87Sr/86Sr ratios, relative to 0.7080 for the Eimer and Amend standard, are: Anisian: 0.70805 ± 00019; Early Ladinian: 0.7085 ± 0.00038; Late Ladinian: 0.70791 ± 0.00013; Carnian: 0.70776 ± 0.00015; Norian and Rhaetian: 0.70791 ± 0.00014; Hettangian: 0.70762 ± 0.00021; Sinemurian: 0.7070 ± 0.00038; Pliensbachian: 0.7070 ± 0.00015. These variations reflect changes in the isotopic composition of Sr entering the oceans in early Mesozoic time due to varying rates of weathering and erosion of young volcanic rocks (low 87Sr/86Sr) and old granitic rocks (high 87Sr/86Sr). The data presented in this report contribute to a growing body of information regarding the changes that have occurred in the 87Sr/86Sr ratio of the oceans in Phanerozoic time.

Conodonts and Foraminifera from the Triassic of Israel

A COLLECTION of platy limestone of either latest Ladinian or earliest Carnian age, as determined by mega-fossils from Makhtesh Ramon, southern Israel, on treatment with acetic acid for ostracode investigations1, yielded both conodonts and Foraminifera. Preliminary examination disclosed one genus each in the conodont families Polygnathidae and Coleodontidae, and representatives of the foraminiferal families Reophacidae and Nodosariidae. This is the first record of Triassic conodonts and Foraminifera in Israel.