Biotic response to mass extinction: the lowermost Triassic microbialites.

During the first step of the very rapid and large scale lowest Triassic transgression , we note in different areas (S Alps, Taurus,Turkey, S Armenia, E Elburz, Iran, Central Iran and Central Afghanistan) the growth of domal stromatolites, thrombolites and other microbial structures. At the dawn of Triassic time, the carbonate factory was dominated by non-skeletal species and by microrganisms able to precipitate carbonate

La edad del primer pulso de rifting continental asociado a la ruptura de Pangea en el suroeste ibérico: nueva evidencia palinológica

ABSTRACT: In this work, we report the first palynological age for the base strata of the Silves Sandstones of the Silves Group in the Algarve Basin, located in Southern Portugal. The group is the oldest sedimentary unit of the Algarve Basin and was deposited unconformably over late Pennsylvanian turbidites of the Mira Formation, which were folded and faulted during the Variscan Orogeny. The Silves Group comprises a detrital red bed succession, representing the earliest phase of sedimentation associated with the initial rifting of Pangaea. Macrofossils are rare, occurring predominantly in the top layers of this group, and do not accurately constrain the age of the entire group's deposition. From an outcrop exposed in the central Algarve, a grey mudstone bed positioned 2.5 m above the Variscan unconformity plane yielded palynomorphs that date the beginning of sedimentation in this basin to the early Carnian age (Late Triassic). The moderately well preserved and low-diversity palynological association comprises Aulisporites astigmosus, Enzonalasporites densus, Ovalipollis pseudoalatus, Samaropollenites speciosus, Tulesporites briscoensis and Vallasporites ignacii, among others, and is indicative of an early Carnian age.RESUMEN: Mediante datos de asociaciones palinológicas, describimos por primera vez la edad de los niveles de la base de la Formación Areniscas de Silves, del Grupo Silves, en la cuenca del Algarve, sur de Portugal. Este grupo representa la unidad sedimen taria más antigua del Mesozoico de la Cuenca del Algarve, y fue depositada discordantemente sobre las areniscas de edad Pensilvaniense superior de la Formación Mira, un registro sedimentario que fue plegado y fallado durante la Orogenia Varisca. El Grupo Silves muestra unos sedimentos detríticos rojos que representan la fase más temprana de la sedimentación y que está asociada a las primeras fases de la ruptura de Pangea. Los macrofósiles son escasos, se encuentran en los niveles superiores del grupo y no proporcionan una edad determinada. Una asociación palinológica ha sido encontrada y descrita en un nivel de lutitas grises situado a 2,5 cm por encima de la discordancia varisca, y que proporcionan una edad Carniense (Triásico Superior) para el comienzo de la sedimentación de esta unidad. Se trata de una asociación moderadamente bien conservada y con baja diversidad de elementos, que contiene Aulisporites astigmosus, Enzonalasporites densus, Ovalipollis pseudoalatus, Samaropollenites speciosus, Tulesporites briscoensis y Vallaspollites ignacii entre otros, y es indicativa de un Carniense inferior.info:eu-repo/semantics/publishedVersio

Palynostratigraphy of the Triassic-Jurassic of the Silves Group, Lusitanian Basin, Portugal [Resumo]

ABSTRACT: We studied the miospore assemblage from an Upper Triassic to Lower Jurassic succession of the Silves Group near Coimbra, Portugal. The latter consists of, from base to top, the Conraria, Penela, Castelo Viegas, and the Pereiros formations. The palynological assemblages allowed establishing an informal palynozonation and providing new biostratigraphic that helped constrain the age attribution to the Silves Group formations.N/

Depositional environment and biofacies characterisation of the Triassic (Carnian to Rhaetian) carbonate succession of Punta Bassano (Marettimo Island, Sicily)

The aims of this study are to reconstruct the geological setting of the Punta Bassano series (Marettimo Island, Egadi Archipelago, western Sicily) and its palaeogeographic evolution. The reference section for the Upper Triassic of Marettimo shows an alternation of marl and limestone beds together with brecciated levels. The limestones are both homogeneous mudstones with evaporite pseudomorphs and laminated with fenestrae. Foraminiferal, palynomorph, and ostracod associations constrain the Punta Bassano sequence to the Carnian-Rhaetian interval. The Punta Bassano succession represents a shallow inner ramp, ranging from open-marine environment with good water circulation to lagoonal and peritidal protected environments. Freshwater input from rivers or groundwater on the carbonate ramp is indicated by the ostracod microfauna. The comparison of facies and microfauna with those from other sequences of the Mediterranean Upper Triassic (Pyrenees, Corsica, Sardinia, and Tunisia) allows us to confine the Punta Bassano sedimentation to the northern margin of the Tethys, between the Corsican and the Pyrenean depositional setting. These new results indicate that Marettimo Island, which is considered a single structural element being formed by four tectonic units, is a piece of the southern margin of the European Plate, displaced over a longer distance to become part of the other Egadi Islands, when the Corso-Sarde block made its rotation and successive collision with the North African Margi

Palynology and palynofacies studies in the lowermost Jurassic of the Lusitanian Basin (Pereiros Formation of the Silves Group), Portugal: evidence of the first transgressive episode

The Silves Group of the Lusitanian Basin in Portugal represents the initial infill of the continental rifting basins that formed during the breakup of northern Pangaea regions. Evaporites, especially halite, mark the transition from continental to marine settings and the beginning of the deposition in passive margin basins. This work presents the results of the palynostratigraphic and palynofacies analysis of two partial sections from the Pereiros Formation at the top of the Silves Group. The two sections are composed of sandstones, mudstones and dolostones interpreted as deposited in fluvial and lacustrine settings without apparent marine influence. The palynological content is diverse and wellpreserved, dating both sections to the early Hettangian (Lower Jurassic), indicated by the presence of spores Ischyosporites variegatus, Kraeuselisporites reissingeri, Porcellispora longdonensis and the pollen grains Perinopollenites elatoides and Pinuspollenites minimus. The palynological content of one of the sections (Lamas I) is noticeable by microforaminifera linings, suggesting evidence for a hitherto marine incursion at this age in the Silves Group stratigraphy. The beds that yielded the microforaminifera linings are interpreted as having been deposited in an estuarine-type setting, created by the first and short-lived marine transgressive event in the Lusitanian Basin during the early Hettangian.PRIN 2017RX9XXXYinfo:eu-repo/semantics/publishedVersio

Palynostratigraphy of the Permian Faraghan Formation in the Zagros Basin, southern Iran

A detailed microfloristic study was conducted in the Faraghan Formation in nine boreholes drilled by the National Iranian Oil Company (NIOC) and in four outcrops in the Zagros Basin. The Faraghan Formation, widely distributed in the Zagros area, generally consists of shale intercalated with sandstone and pebble conglomerate, with thin carbonate intercalations near the top. Due to the lack of significant fossils, the age of this rock unit has been strongly debated in the Iranian literature and uncertainly attributed to the Pennsylvanian or Cisuralian. In this study, the age of the Faraghan Formation was reviewed in light of new biostratigraphic advances in the Arabian Peninsula. The assemblage is characterized by an abundance of monosaccate pollen such as Florinites? balmei, Caheniasaccites spp., Plicatipollenites spp., Potonieisporites spp. and Striomonosaccites spp., and bisaccate pollen such as Alisporites spp., Corisaccites alutas, Distriatites insolitus, Hamiapollenites spp. and Striatopodocarpites spp.. The assemblage also contains polyplicate pollen such as Vittatina spp.. Spores such as Indotriradites mundus and Thymospora opaqua are also present. The stratigraphic ranges of the taxa allow reference to the biozone schemes for Oman and assignment of the Faraghan Formation to the Guadalupian

Assessing thermal maturity through a multi-proxy approach: a case study from the Permian Faraghan Formation (Zagros Basin, Southwest Iran)

This study focuses on the thermal maturity of Permian deposits from the Zagros Basin, Southwest Iran, employing both optical methods (Thermal Alteration Index, Palynomorph Darkness Index, Vitrinite Reflectance, UV Fluorescence) and geochemical analyses of organic matter (Rock Eval Pyrolysis and MicroRaman spectroscopy) applied to the Faraghan Formation along two investigated Darreh Yas and Kuh e Faraghan surface sections. Furthermore, an integrated palynofacies and lithofacies analysis was carried out in order to integrate the few studies on the depositional environment. The Faraghan Formation, which is widely distributed in the Zagros area, generally consists of shale intercalated with sandstones and pebble conglomerates in the lower part, followed by a succession of sandstone, siltstone and shaly intercalations and with carbonate levels at the top. The integrated palynofacies and lithofacies data confirm a coastal depositional setting evolving upwards to a shallow marine carbonate environment upwards. Rock Eval Pyrolysis and Vitrinite Reflectance analysis showed that the organic matter from samples of the Darreh Yas and Kuh e Faraghan sections fall in the mature to postmature range with respect to the oil to gas generation window, restricting the thermal maturity range proposed by previous authors. Similar results were obtained with MicroRaman spectroscopy and optical analysis such as Thermal Alteration Index and UV Fluorescence. Palynomorph Darkness Index values were compared with Rock Eval Pyrolysis and vitrinite reflectance values and discussed for the first time in the late stage of oil generation.This research was funded by PRIN (2017RX9XXXY-CIRILLI), by Fondo Ricerca di Base Department of Physics and Geology, University of Perugia (SPIRICBAS2018-SPINA), by the project “Paleontological Studies and Biozonation of Paleozoic Sediments in Central Iran and Zagros Basins” (coordinator R. Rettori) and MIUR grants-SORCI to PhD School of Science and Technology for Physics and Geology (XXXIV Cycle), University of Perugia; Project “Paleontological Studies and Biozonation of Paleozoic Sediments in Central Iran and Zagros Basins” (RETTORI).info:eu-repo/semantics/publishedVersio

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 Pralongià, 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.&nbsp

PALAEOENVIRONMENTAL INTERPPRETATION OF THE LATE TRIASSIC FRAELE FORMATION (ORTLES NAPPE, AUSTROALPINE DOMAIN, LOMBARDY)

The Fraele Formation crops out in the Ortles Nappe (upper Valtellina, Northern Italy), structurally part of the Central Austroalpine Domain. It consists of fine siliciclastics alternating with carbonates, mostly limestones,rare dolostones and marls. The formation differs lithologically from the underlying Norian Dolomia del Cristallo because of different paleonvironmental evolution.The change in environmental parameters was controlled mainly by a climatic change to more humid conditions.This favoured on one hand the mobilisation and trasport by rivers of siliciclastic material from the continent to the Tethys gulf,and on the other influenced the sea-water chemistry.Freshwater influxes lowered salinity and inhibited early dolomitisation. Input of low density freshwater resulted in the astablishment of a permanent water mass stratification which influenced the benthic life. This paleoenvironmental reconstruction fits with the sudden clastic input which occurred in several palaeogeographic domains of the western Tethys realm (Austroalpine, Southalpine, Apennine, Hungary, Poland, Slovakia) during the Late Norian. &nbsp