Lower Triassic Sediments Research Articles

Vernaricum ‒ regional distribution, lithostratigraphy, tectonics and paleogeography

The Vernaricum is the highest partial unit belonging to the Hronic nappe system of the Internal Western Carpathians. The stratigraphic range of the Vernaricum sediments is from the Lower Triassic to the Lower Jurassic. The Permian rhyolites and volcaniclastics are tectonically incorporated into the Lower Triassic sediments. The Vernaricum overlies tectonic units of the Northern Veporicum, Fatricum, lower partial nappes of Hronicum and Southern Veporicum. The Gemeric, Meliatic and Silicic rock complexes are located in the tectonic overburden. The paleogeographic position of the Vernaricum is interpreted between the Veporic and Gemeric zones.

Petrography and geochemistry of siliciclastic sediments in Permo-Triassic transition from the southern Pranhita-Godavari Gondwana basin, India: Implications for paleoclimate

The Kamthi Formation, in the intracratonic Pranhita-Godavari Gondwana rift basin, bore signatures of climate change from a warm humid climate in Late Permian to hot arid during the Early Triassic. Sedimentation took place mainly under fluvial conditions. The Kamthi sediments were unaffected by burial diagenesis and the source remained the same, therefore this provides an excellent opportunity to study the climatic influence on petrogenesis in an intracratonic rift basin. Subsurface palynofacies data of Kamthi Formation from the southern part of the basin established the presence of Upper Permian rock units equivalent to the Raniganj Formation, which are overlain by Lower Triassic sediments equivalent to Panchet Formation of the Damodar valley Gondwana basins, and are separated by a gradational contact. QFL and trace element compositions reveal transitional continental to craton interior provenance with dominantly felsic source areas, along with some meta-sedimentary and mafic components. Dominance of kaolinite, coal, alteration of K-feldspar, and biotite in the Raniganj equivalent sandstones attests to a humid climate. The presence of mostly fresh K-feldspar, ferruginous matrices, Fe-carbonate nodules, cutans, and microcrystalline silica cement in the Panchet equivalent sandstones mark a shift from humid to arid/semi-arid. This climatic shift is not reflected in the uniform feldspatho-quartzose to quartzose sandstone compositions and mudstone major oxide compositions. The mudstones are depleted in mobile elements, have low K2O/Al2O3 (0.11–0.18), low ICV (0.35–0.72), high SiO2/Al2O3 (2.3–3.4), high K2O/Na2O and moderately high CIA (80.12–87.05) that collectively suggest moderately intense weathering. Despite the humid climate, the Raniganj Formation equivalent rock units did not attain the highest mineralogical maturity due to proximity to relatively high-relief source areas in a fluviolacustrine environment. This relationship resulted in a lack of short-term sediment storage that favoured rapid erosion and sedimentation.

Geoscience Poster G10: Addressing exploration uncertainties in the southern Bonaparte Basin: enhanced stratigraphic control and post drill analysis for upper Permian plays

Poster G10 The upper Permian to lower Triassic sedimentary succession in the southern Bonaparte Basin represents an extensive marginal marine depositional system that hosts several gas accumulations, including the Blacktip gas field that has been in production since 2009. Development of additional identified gas resources has been hampered by reservoir heterogeneity, as highlighted by preliminary results from a post drill analysis of wells in the study area that identify reservoir effectiveness as a key exploration risk. The sedimentary succession that extends across the Permian–Triassic stratigraphic boundary was deposited during a prolonged marine transgression and shows a transition in lithofacies from the carbonate-dominated Dombey Formation to the siliciclastic-dominated Tern and Penguin formations. Recent improvements in chronostratigraphic calibration of Australian biostratigraphic schemes, spanning the late Permian and early Triassic, inform our review of available palynological data, and re-interpretation and infill sampling of well data. The results provide a better-resolved, consistent and up-to-date stratigraphic scheme, allowing an improved understanding of the timing, duration and distribution of depositional environments of the upper Permian to lower Triassic sediments across the Petrel Sub-basin and Londonderry High. To access the poster click the link on the right. To read the full paper click here

Addressing exploration uncertainties in the southern Bonaparte Basin: enhanced stratigraphic control and post drill analysis for upper Permian plays

The upper Permian to lower Triassic sedimentary succession in the southern Bonaparte Basin represents an extensive marginal marine depositional system that hosts several gas accumulations, including the Blacktip gas field that has been in production since 2009. Development of additional identified gas resources has been hampered by reservoir heterogeneity, as highlighted by preliminary results from a post drill analysis of wells in the study area that identify reservoir effectiveness as a key exploration risk. The sedimentary succession that extends across the Permian–Triassic stratigraphic boundary was deposited during a prolonged marine transgression and shows a transition in lithofacies from the carbonate-dominated Dombey Formation to the siliciclastic-dominated Tern and Penguin formations. Recent improvements in chronostratigraphic calibration of Australian biostratigraphic schemes, spanning the late Permian and early Triassic, inform our review of available palynological data, and re-interpretation and infill sampling of well data. The results provide a better-resolved, consistent and up-to-date stratigraphic scheme, allowing an improved understanding of the timing, duration and distribution of depositional environments of the upper Permian to lower Triassic sediments across the Petrel Sub-basin and Londonderry High.

Early Triassic paleogeography of the northern Perth Basin, and controls on the distribution of source rock facies

The facies distribution of the Lower Triassic Kockatea Shale in the northern Perth Basin is an important factor for assessing the Lower Triassic source rock potential in the basin. Seismic interpretation and well analyses demonstrate that Permian-aged faults are responsible for the morphology of the basin in the Early Triassic and created remnant topography that controls the deposition of Lower Triassic sediments. Cores from petroleum wells and their correlated wireline logs show the lithological variation and lateral distribution of facies across the base of the Kockatea Shale. Darker coloured mudstones were deposited under anoxic conditions in the deeper part of the basin, while lighter coloured mudstones and tidally influenced sediments with bioturbation were deposited under oxic conditions in a shallow marine setting. Microbial mats developed in shallower water depths on structural highs (Beagle Ridge and Turtle Dove Ridge) in the anoxic parts of the basin.The distribution of microbial mats is controlled by two factors during the period of ecological recovery from the end-Permian mass extinction: 1) the presence of topographic highs and, 2) distance from the edge of the basin. The source rock potential of both darker coloured mudstone and microbial mat facies is demonstrated by TOC values between 0.3 and 3.4% and HI values between 39 and 579 mg/gTOC. On the other hand, the lighter coloured mudstones, deposited under more aerobic tidal settings, have poor source rock quality and TOC values between 0.2 and 0.5% and HI values between 59 and 127 mg/gTOC.

Biotic response to environmental shift during the Permian-Triassic transition: Assessment from organic geochemical proxies and palynomorphs in terrestrial sediments from Raniganj Sub-basin, India

The Permian-Triassic (P/T) mass extinction qualifies as the severest biotic perturbation in the history of our planet. Biomarkers, stable isotopes and palynomorphs are excellent proxies offering glimpses into palaeobiota and past ecosystems. These were investigated from coal-bearing upper Permian (Raniganj Formation) and Lower Triassic (Panchet Formation) Gondwana sediments recovered from the Raniganj Sub-basin, eastern India. The geochemical and palaeobotanical data suggest a shift in the terrestrial vegetation during the Early Triassic. A distinct change occurs from high abundance of n-C23 and n-C25 alkanes and higher CPI values in the upper Permian sediments to predominantly n-C27 and n-C29 alkanes along with relatively lower CPI values in the Lower Triassic. A sharp decline of the diterpenoid compounds and Glossopteridales pollens with a concomitant rise in lycopsid spores in the Lower Triassic sediments reflects the waning of a gymnosperm-dominated mire and onset of a stressed environment. Unlike the Glossopteridales, the Coniferales appear to be a resilient floral group with several new genera adapting to the growing arid conditions in the Early Triassic. The microbial community also responded to the contemporaneous ecosystem shift, with higher concentration of C27 sterane relative to C29 sterane in Lower Triassic sediments indicating proliferation of algal phytoplankton. The decreasing moretane/hopane (M/H) suggests that the soil bacteria were adversely affected plausibly due to enhanced soil erosion at the early part of the Triassic. A marked shift in the bulk isotopic composition (δ13Corg) from higher values in the upper Permian sediments (˗21.0 to ˗24.1‰) to lower values in the Lower Triassic sediments (˗21.2 to ˗32.5‰) is diagnostic of a vegetation changeover as a result of environmental deterioration. This is the first integrated study using molecular organic geochemical proxies and palynology from terrestrial Gondwana sediments in the Indian subcontinent, designed to investigate the pattern of floral and microbial restructuring as a result of an environmental shift during the Permian-Triassic transition.

The assessing of the quality of geothermal reservoirs on the example of the Lower Triassic aquifer in the Mogilno-Łódź Trough (Polish Lowlands)

Petrographic and petrophysical investigations of the aquifers allow to estimate their productivity and infectivity, as well as allow for better recognition of the origin of the chemical composition of geothermal waters. Deep deposition of the Lower Triassic sediments in the analysed area (locally above 5000 m b.s.l.) is conducive to high temperatures (above 90°C) within the reservoir and causes deterioration of reservoir parameters. The Lower Triassic geothermal reservoir consists of fine and mixed grain- size sands and sandstones layers from 10 to 650 m thick; depending on the depth. The water within the reservoir exhibits mineralization ranging from 2 to over 100 g L-1 and its temperature ranges from 30 to 100°C. The mineralization of waters varies from 140 g/dm3 (Warsaw basin) to over 350 g/dm3 in the deep zones of the basin (axial fragments of the Mogileńsko-Łódź trough). The average permeability of reservoir layers in the Polish Lowlands is 145.5 mD.

Gondwana fragments in the Eastern Alps: A travel story from U/Pb zircon data

We compare detrital U/Pb zircon age spectra of Carboniferous and Permian / Lower Triassic sedimentary rocks from different structural positions within the Austroalpine nappe pile with published ages of magmatic and metamorphic events in the Eastern Alps and the West Carpathians. Similarities between sink and possible sources are used to derive provenance of sediments and distinct frequency peaks in sink and source age pattern are used for paleogeographic plate tectonic reconstructions. From this, travel paths of Austroalpine and West Carpathian basement units are traced from the Late Neoproterozoic to the Jurassic. We place the ancestry of basement units on the northeastern Gondwana margin, next to Anatolia and the Iranian Luth-Tabas blocks. Late Cambrian rifting by retreat of the Cadomian Arc failed and continental slivers re-attached to Gondwana during a late Cambrian / early Ordovician orogenic event. In the Upper Ordovician crustal fragments of the Galatian superterrane rifted off Gondwana through retreat of the Rheic subduction. An Eo-Variscan orogenic event at ~390 Ma in the Austroalpine developed on the northern rim of Galatia, simultaneously with a passive margin evolution to the south of it. The climax of Variscan orogeny occurred already during a Meso-Variscan phase at ~350 Ma by double-sided subduction beneath Galatia fragments. The Neo-Variscan event at ~330 Ma was mild in eastern Austroalpine units. This orogenic phase was hot enough to deliver detrital white mica into adjacent basins but too cold to create significant volumes of magmatic or metamorphic zircon. Finally, the different zircon age spectra in today's adjacent Carboniferous to Lower Triassic sediments disprove original neighbourhood of basins. We propose lateral displacement of major Austroalpine and West-Carpathian units along transform faults transecting Apulia. The intracontinental transform system was released by opening of the Penninic Ocean and simultaneous closure of the Meliata Hallstatt Ocean as part of the Tethys.

Integrated rock magnetic and mineralogical study of the Lower Triassic sedimentary rocks from Spitsbergen

A rock magnetic, mineralogical and Mössbauer spectroscopy study was undertaken on the Lower Triassic sediments from the West Spitsbergen Fold and Thrust Belt (WSFTB) in Svalbard as well as the foreland of this orogen for a thorough recognition of magnetic mineralogy, necessary for a better-constrained interpretation of paleomagnetic results. SEM and Mössbauer spectroscopy indicate the presence of magnetite and pyrrhotite, both most probably of secondary origin but altered clasts of volcanic origin and grains of ilmenite and detrital magnetite are also observed. Thermomagnetic curves of whole-rock samples exhibit paramagnetic behavior whereas ferromagnetic separates indicate the presence of magnetite. IRM component analysis shows three major contributors – magnetite, hematite, and pyrrhotite to the remanence, with ferromagnetic iron oxides the most dominant. Identified ferromagnetic minerals display a wide range of grain-size and magnetic behavior, with the domination of PSD particles. Rock magnetic characteristics of both areas are similar, but sites in the fold belt were most likely remagnetized, whereas those in the foreland carry the primary magnetization. The age of remagnetization was estimated as pre-Eurekan related to rift-controlled Mesozoic extensional phases of the Barents Sea Shelf (Clark et al., 2014) and/or Cretaceous injections of dolerites in the Svalbard Archipelago (Nejbert et al., 2011) as well as early stages of the WSFTB formation. However, Triassic remanence might persist in volcanic lithoclasts and detrital magnetite indicated along the WSFTB. The multicomponent nature of the NRM, displaying a broad range of grain size, might impede the paleomagnetic interpretation of Triassic rocks in Spitsbergen.

The end-Permian regression in the western Tethys: sedimentological and geochemical evidence from offshore the Persian Gulf, Iran

Detailed sedimentological and geochemical records across the Permian–Triassic boundary (PTB) in five offshore wells of the central Persian Gulf served to interpret the end-Permian sea-level change in this region. A decrease in sea level at the PTB was established by petrographical and geochemical study of the boundary. Thin sections showed that Upper Permian strata are composed of dolomite with minor anhydrite, changing into limestone in Lower Triassic sediments. Brine dilution toward the boundary supports sea-level fall in the Permian–Triassic transition, reflected by a decrease in anhydrite content and a shallowing-upward trend from lagoonal to peritidal facies. Isotopic changes at the boundary are in favor of sea-level fall. Changes in both carbon (from about 4 to –1‰) and oxygen (from 2 to –5‰) stable isotopes show negative excursions. The shift in carbon isotope values is a global phenomenon and is interpreted as resulting from carbonate sediment interaction with 12C-rich waters at the end-Permian sea-level fall. However, the oxygen isotope shift is attributed to the effect of meteoric waters with negative oxygen isotope values. The increase in strontium isotope ratios is also consistent with the high rate of terrestrial input at the boundary. The effect of meteoric conditions during diagenesis is evident from vuggy and moldic porosities below the PTB. The following transgression at the base of the Triassic is evident from the presence of reworked fossils and intraclasts resulting from deposition from agitated water.

Detrital provenance, depositional environment, and palaeogeographic implications of Lower Triassic marine sediments in central Tibet

ABSTRACTWe present our new investigation into the depositional environment and provenance of the Yingshuiquan Formation in the central Qiangtang region of northern Tibet, in order to further our understanding of the environment of the Longmu Co–Shuanghu Palaeo–Tethys during the Early Triassic. The Yingshuiquan Formation is composed of oolitic limestone, calcareous sandstone, calcarenite, thin-bedded ribbon limestone, bioclastic limestone, and coarse oolite limestone that were deposited in a shallow-marine basin and contain abundant Lower Triassic conodont fossils (e.g. Hadrodontina anceps, Pachycladina sp., gen. et sp, Pachyclaina oblique, Hibbardelloides sp). We selected detrital zircons from four calcareous sandstone samples for U–Pb dating, yielding minimum age peaks of 263, 269, 275, and 280 Ma, respectively, and a minimum age of 249 Ma, based on several zircons around the same age. Analysis of the conodont biofacies and zircon LA-ICP-MS dating of calcareous sandstone indicates that the data is consistent with deposition in the Early Triassic. The Yingshuiquan Formation records Early Triassic shallow-water sediment in the Longmu Co–Shuanghu Palaeo–Tethys, and has a Southern Qiangtang and Northern Qiangtang terranes provenance. During the Early Triassic, the carbonate sediments of the Yingshuiquan Formation were deposited in an active environment around the Longmu Co–Shuanghu Palaeo–Tethys, which has became a residual sea basin.

The tectonic evolution of the Bogda region from Late Carboniferous to Triassic time: evidence from detrital zircon U–Pb geochronology and sandstone petrography

AbstractField-based mapping, sandstone petrology, palaeocurrent measurements and zircon cathodoluminescence images, as well as detrital zircon U–Pb geochronology were integrated to investigate the provenance of the Upper Carboniferous – Upper Triassic sedimentary rocks from the northern Bogda Mountains, and further to constrain their tectonic evolution. Variations in sandstone composition suggest that the Upper Carboniferous – Lower Triassic sediments displayed less sedimentary recycling than the Middle–Upper Triassic sediments. U–Pb isotopic dating using the LA-ICP-MS method on zircons from 12 sandstones exhibited similar zircon U–Pb age distribution patterns with major age groups at 360–320 Ma and 320–300 Ma, and with some grains giving ages of > 541 Ma, 541–360 Ma, 300–250 Ma and 250–200 Ma. Coupled with the compiled palaeocurrent data, the predominant sources were the Late Carboniferous volcanic rocks of the North Tianshan and Palaeozoic magmatic rocks of the Yili–Central Tianshan. There was also input from the Bogda Mountains in Middle–Late Triassic time. The comprehensive geological evidence indicates that the Upper Carboniferous – Lower Permian strata were probably deposited in an extensional context which was related to a rift or post-collision rather than arc-related setting. Conspicuously, the large range of U–Pb ages of the detrital zircons, increased sedimentary lithic fragments, fluvial deposits and contemporaneous Triassic zircon ages argue for a Middle–Late Triassic orogenic movement, which was considered to be the initial uplift of the Bogda Mountains.

Selected Properties and Systematic Position of Soils Developed from Red Sandstones and Clays of the Lower Triassic Buntsandstein in the Nw Part of the Holy Cross Mountains (Poland) / Niektóre właściwości i pozycja systematyczna gleb wytworzonych z czerwonych piaskowców i iłów dolnego triasu w NW obrzeżeniu Gór Świętokrzyskich

AbstractThe aim of the study was to compare the properties of soils developed from the Lower Triassic Buntsandstein sediments in the north-western part of the Holy Cross Mountains (Poland). These are deposits of continental genesis and unique features such as red beds. Two representative soil pedons - the Bartków profile (pBK) developed from clay and the Góra Czerwona profile (pGC) developed from sandstone were selected for detailed analyzes. The morphology of profiles, their micromorphological features, mineralogical composition, and physico-chemical properties were examined. Most of the properties of the soils are a consequence of the original parent rock lithology. A specific feature of the morphology of the soils are the presence of red color (about 10R by the Munsell color scale) related to the presence of hematite. As shown by the XRD data, hematite is not the product of the current soil-forming processes, but it is a lithogenic component, which was inherited from the parent rock. Under the influence of climatic factors primary rock structure has been transformed into a new pedogenic one. Soils developed from clays have a characteristic angular blocky structure. Micromorphological analysis showed that an important role in the formation of soil structure involves geogenic susceptibility of Triassic clays to specific cuboid disintegration. This is indicated by the pore system of planes as an orthogonal nets visible in thin section. The soils developed from sandstone have a weak (unstable) subangular blocky structure. The main reason is the insufficient dispersion of the clay-ferruginous fraction from the sandstone matrix. Microscopic observations indicate that fine factions occurs as loose microaggregates, which results in a feature that smaller rock fragments and individual quartz grains are not bonded into soil aggregates. The studied soils are characterized by specific physical-chemical properties. Some of them strongly depend on the mineralogical properties of the soil substrate. Strong acidity (pH 3-4) and a very low content of base cations (below 1.0 cmol(+)kg-1) are due to a lack of carbonate minerals in sandstones and weak weathering of aluminium silicate. High exchangeable Al content in clay (16.5 cmol(+)kg-1) should be related to the geochemical properties of the red bed-type rocks such as the Lower Triassic Buntsandstein deposits. Soils developed from the Lower Triassic Buntsandstein clays have a sequence of genetic horizons: Ap, Bw, Bw/C, C and fulfill the criteria assigned to dystrophic typical brown soils (BDt) in the Polish Soil Classification (PSC 2011), whereas in the WRB they were classified as Endoeutric Chromic Cambisols (Loamic). Soils developed from the Lower Triassic Buntsandstein red sandstone can be classified as dystrophic humus brown soil (BDpr) in the PSC (2011). Within the WRB classification that soil can be assigned to Epidystric Chromic Endoleptic Cambisols.

Enhanced recycling of organic matter and Os-isotopic evidence for multiple magmatic or meteoritic inputs to the Late Permian Panthalassic Ocean, Opal Creek, Canada

The geochemical record for the Permian–Triassic boundary in northern latitudes is essential to evaluation of global changes associated with the most profound extinction of life on Earth. We present inorganic and organic geochemical data, and Re–Os isotope systematics in a critical stratigraphic interval of pre- and post-extinction Upper Permian–Lower Triassic sediments from Opal Creek, western Canada (paleolatitude of ∼30°N). We document significant and long-lived changes in Panthalassa seawater chemistry that were initiated during the first of four magmatic or meteoritic inputs to Late Permian seawater, evidenced by notable decreases of Os isotopic ratios upsection.Geochemical signals indicate establishment of anoxic bottom waters shortly after regional transgression reinitiated sedimentation in the Late Permian. Euxinic signals are most prominent in the Upper Permian sediments with low organic carbon and high sulfur contents, and gradually wane in the Lower Triassic. The observed features may have been generated in a strongly euxinic ocean in which high bacterioplankton productivity sustained prolific microbial sulfate reduction in the sediment and/or water column, providing hydrogen sulfide to form pyrite. This scenario requires nearly complete anaerobic decomposition of predominantly labile marine organic matter (OM) without the necessity for a complete collapse of primary marine productivity. Similar geochemical variations could have been achieved by widespread oxidation of methane by sulfate reducers after a methanogenic burst in the Late Permian. Both scenarios could have provided similar kill mechanisms for the latest Permian mass extinction.Despite the moderate thermal maturity of the section, OM in all studied samples is dominantly terrestrial and/or continentally derived, recycled and refractory ancient OM. We argue that, as such, the quantity of the OM in the section mainly reflects changes in terrestrial vegetation and/or weathering, and not in marine productivity. At Opal Creek, a pyrite layer and <20-cm-thick siltstones that are lean in OM mark dramatic and long-lived inorganic geochemical and stable isotope changes. Initial Os isotope ratios decline markedly toward values of ∼0.35 in the pyrite interval, indicating a mantle-sourced or meteoritic trigger for the intensification and expansion of latest Permian anoxia. Subsequent and stronger magmatic or meteoritic pulses recorded by low initial Os isotopes followed the main extinction.

Extreme euxinia just prior to the Middle Triassic biotic recovery from the latest Permian mass extinction

The greatest mass extinction on Earth occurred 252million years ago during the latest Permian. Complete biotic recovery, characterized by a return to pre-extinction diversity levels, took an extraordinarily long time (ca. 5×106yr), probably because harsh conditions developed repeatedly during the Early Triassic. Here, we show the recurrence of euxinic conditions during the Early Triassic and the development of especially severe such conditions during the late Early Triassic, just prior to full biotic recovery from the mass extinction. Dibenzothiophenes and carotenoids accumulated in upper Lower Triassic sediments from South China, located on the western margin of the Paleotethys Ocean. Among these, chlorobactane, a biomarker for green-pigmented green sulfur bacteria, and okenane, a biomarker for purple sulfur photosynthetic bacteria, were identified in upper Early Triassic samples. Both compounds were detected in limestone (micrite) and we therefore infer that planktonic green and purple sulfur bacteria were the sources of these carotenoids, and that their presence indicates photic zone euxinia at the time of deposition. Concentrations of redox sensitive elements (M, V, and U), relative to that of Al, and the U/Th ratio, progressively increased during the late Early Triassic. The euxinic conditions represented by the carotenoids and the elements were likely caused by a combination of locally shallow restricted conditions and global environmental oscillations, such as those related to global warming, during the late Early Triassic. The presence of these biomarkers, together with the increase in the abundance of redox sensitive elements relative to Al and the U/Th, suggests that euxinic conditions could be one of the causes for the delayed recovery of marine communities in the Paleotethys Ocean after the latest Permian mass extinction event.

Sedimentary evolution of the continental Early–Middle Triassic Cañizar Formation (Central Spain): Implications for life recovery after the Permian–Triassic crisis

The Permian–Triassic transition (P–T) was marked by important geochemical perturbations and the largest known life crisis. Consequences of this event, as oxygen-depleted conditions and the unusual behavior of the carbon cycle, were prolonged during the Early Triassic interval delaying the recovery of life in both terrestrial and marine ecosystems. Studies on Lower Triassic sediments of continental origin, as in the case of Western Europe, are especially problematic due to the scarcity of fossils and absence of precise dating. The Cañizar Fm. is an Early–Middle Triassic unit of continental origin of the SE Iberian Ranges, E Spain. A detailed sedimentary study of this unit allows a shedding of light on some unresolved problems of the continental deposits of this age.The top of this unit is dated as early Anisian by means of a pollen association, while the age of its base is here estimated as late Smithian or Smithian–Spathian transition. Different facies associations and architectural elements have been defined in this unit. In the western and central parts of the basin, this unit shows sedimentary characteristics of fluvial deposits with locally intercalated aeolian sediments, while in the eastern part there is an alternation of both aeolian and fluvial deposits. Sedimentary structures also indicate changes in the climate conditions, mainly from arid to semiarid. Two marked arid periods when well-preserved aeolian sediments developed during early–middle Spathian and Spathian–Anisian transition. They alternated with two semiarid but more humid periods during the late Spathian and early Anisian. These conditions basically correspond with the general arid and very arid conditions described for central–western European plate during the same period of time. The Ateca–Montalbán High, in the northern border of the study basin, must have represented an important topographic barrier in the western Tethys separating aeolian dominated areas to the N and NE from fluvial dominated areas to the south.The Cañizar Fm. has been subdivided into six members (A–F) separated by seven (1–7) major bounding surfaces (MBS). These surfaces are well recognized laterally over hundred of km and they represent 104–105My. MBS-5 is considered to be of late Spathian age and it is a clear indication of tectonic activity, represented by a mild unconformity. This event represents a change in the sedimentary characteristics (reactivation) of the unit and from here to the top of the unit are found the first signals of biotic recovery, represented by tetrapod footprints, plants, roots and bioturbation. All of these characteristics and the estimated age represented by the MBS-5 event permit this surface to be related to the coeval Hardegsen unconformity of Central–Western Europe. These first signals of biotic recovery can thus be related to an increased oxygen supply due to the new created paleogeographical corridors in the context of this tectonic activity. These biotic signals occurred 5My after the Permian–Triassic limit crisis; a similar delay as occurred in other coeval and neighboring basins.

三畳紀初期における大陸風化の減少―中央ネパール・テチスヒマラヤ，マナン地域の例―

三畳紀初期における大陸風化の減少―中央ネパール・テチスヒマラヤ，マナン地域の例―

Permian–polysulphide-siderite–barite–haematite deposit Rude in Samoborska Gora Mts., Zagorje–Transdanubian zone of the Inner Dinarides

Samoborska Gora Mts. is situated within the westernmost part of the Zagorje&ndash;Mid&ndash;Transdanubian zone of the Internal Dinarides. The Samoborska Gora Mts. predominantly consists of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralisation is hosted by Permian siliciclastic sediments, below gypsum and anhydrite strata. The central part of the deposit consists of a 1.5 km long stratabound mineralisation, grading laterally into ferruginous sandstone and protruding vertically into a gypsum&ndash;anhydrite layer. Siderite&ndash;polysulphide&ndash;barite&ndash;quartz veins are located below the stratabound mineralisation. The stratiform part ofthe deposit is situated above the stratabound and consists of haematite layer with barite concretions and veinlets. Late stage galena&ndash;barite veins overprint earlier types of mineralisation. The Rude ore deposit was generated by predominantly NaCl&plusmn;CaCl2&ndash;H2O solutions. Detrital quartz from stratiform mineralisation contains fluid inclusions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150&deg;C to 230&deg;C. Stratabound/siderite&ndash;polysulphide&ndash;barite&ndash;quartz vein type mineralisation was derived from solutions with salinities between 5 and 19 wt. % NaCl equ., homogenizing between 60&deg;C and 160&deg;C, while late stage galena&ndash;barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100&deg;C to 140 &deg;C. Fluid inclusion bulk leachate chemistry recorded Na+&gt;Mg2+&gt;K+&gt;Ca2+&gt;Li+ and Cl-&gt;SO42- ions. Sulphur isotope composition of barites and overlying gypsum stems from Permian seawater sulphate, supported by increased Br- content, which follows successively the seawater evaporation line. The sulphur isotopic composition of sulphides varies between &ndash;0.2 and +12.5 &permil;, as a result of thermal reduction of Permian marine sulphate. Ore&ndash;forming fl uids were produced by hydrothermal convective cells (reflux brine model), and were derived primarily from Permian seawater, modified by evaporation and interaction with Permian sedimentary rocks. Rude deposits in Samoborska Gora Mts. may be declared as a prototype of the Permian siderite&ndash;polysulphide&ndash;barite deposits (products of rifting along the passive Gondwana margin), in the Inner Dinarides, and their equivalents extending northeastward into the Zagorje&ndash;Mid&ndash;Transdanubian Zone and the Gemerides, and southeastward to the Hellenide&ndash;Albanides.

Multiple climatic changes around the Permian-Triassic boundary event revealed by an expanded palynological record from mid-Norway

Here, we present the palynological record from two shallow core holes (6611/09-U-01 and -02) from the Trondelag Platform offshore mid-Norway consisting of 750 m of Upper Permian and Lower Triassic sediments. The relatively homogeneous assemblages recovered from the Upper Permian deposits are dominated by gymnosperm pollen, mainly pteridosperms. At the base of the Griesbachian, numerous spore species appear in the record, leading to an increased diversity. The change at this boundary is also marked by the massive reduction of one group of pteridosperm pollen ( Vittatina ). Together with other typical Permian elements (e.g., Lueckisporites virkkiae ), this group is rare but consistently present in the lower part of the Griesbachian, and it gradually disappears in its upper part. The distribution of other groups such as taeniate and non-taeniate bisaccate gymnosperm pollen (pteridosperms and conifers) shows no significant change across the boundary, whereas spores and other gymnosperm pollen increase in diversity and abundance. These changes coincide with the formational change between the Schuchert Dal Formation (Upper Permian) and the Wordie Creek Formation (Griesbachian) equivalents. Late Permian and Griesbachian palynomorph assemblages display different patterns. The former show a homogeneous composition of low diversity, whereas the latter reflect diverse and variably composed floras. The data suggest that the arid phase of the Late Permian was followed by a humid phase at the base of the Griesbachian. In the Griesbachian section, a succession of six distinct palynological assemblages (phase II–VII) can be inferred. Comparable changes have been described from East Greenland. The variations in the palynological record are interpreted to reflect changing ecological conditions (e.g., changing humidity). Comparable variations in the distribution of δ 13 C isotope values reported from various sections from Greenland and China, showing stable values during the Late Permian and highly variable values during the Griesbachian, suggest common causes for the observed fluctuations. Multiphase volcanic activity of the Siberian traps seems to be the most likely candidate to have caused the variations in the δ 13 C isotope as well as in the palynological record. In contrast to the common claim that marine and terrestrial biota both suffered a mass extinction related to the Permian-Triassic boundary event, the studied material from the Norwegian midlatitudinal sites shows no evidence for destruction of plant ecosystems. The presence of diverse microfloras of Griesbachian age supports the idea that the climate in this area allowed most plants to survive the Permian-Triassic boundary event.

Evidence for anoxia in deep environments of Northeast Asia at the Permian-Triassic transition

It is well known that the Permian‐Triassic transition was marked by significant changes in the biota and sedimentation settings. Evidence for the development of anoxic environments in various world areas during events at the Permian‐Triassic transition in both shallow- and deep-water settings are reported in [1‐8 and others]. Such data have been unavailable thus far for the Russian territory. The study of Permian‐Triassic boundary deepwater sediments in Northeast Asia provided the first evidence for H 2 S contamination of bottom waters in this region. Both shallow- and deep-sea basins existed in Northeast Asia during the Permian Period [9]: Ayan-Yuryakh, Balygychan, Sugoi, and Gizhiga. They were characterized by avalanche sedimentation, which was responsible for accumulation of thick (up to 7 km) sandy‐clayey and volcanogenic (frequently, turbidite) sediments with impoverished fossil assemblages. The fossils are represented by Inoceramus-like bivalves and subordinate ctenodont bivalves and gastropods ( Straparolus ). In the terminal Permian, the system of sea basins in Northeast Asia experienced some shoaling. In deep marginal sea basins, bathyal settings recorded by the accumulation of turbidite sequences gave way to shallower conditions comparable with deep shelf settings, which differed, however, from typical shelf environments. They reflected substantial shoaling of marginal basins in response to the global regression in the terminal Permian [10]. The rocks are characterized by abundant structural distortions and traces of intense bioturbation (distinctly or vaguely patchy structures). Benthic fossils are more common as compared with the underlying strata. The sea basins became deeper during the Permian‐ Triassic transition. This is evident from the change in the sedimentation pattern in the section: the complete disappearance of distorted bedding, spotty structures, and any other signs of vital activity of benthic organisms, as well as their remains. Instead, thin horizontal and, less commonly, oblique lamination appears. The rocks become fine-grained. All these features imply intense activity of contour currents and lack of benthic life. Such a lithological change in deep-water settings is characteristic of spacious areas of Northeast Asia extending from the Verkhoyansk region to the Taigonos Peninsula. Lower Triassic sediments (up to the Tompophiceras pascoei Zone) lack benthic fossils and bioturbation. The Orotukan segment of the Balygychan basin is one of the most promising areas for the study of the Permian‐Triassic boundary sediments (Fig. 1). The upper part of the Permian section (200 m) is represented here by foliated silty argillites of the Pautovaya Formation, while the lower part of the Triassic sequence is composed of silty argillites with thin siltstone laminae of the Gerba Formation [10]. The Late Permian (late Changhsingian) age of the upper Pautovaya Formation is substantiated by a finding of an impression of the bivalve Claraioides aff. primitivus (Yin) [11]. The Early Triassic age of the Gerba Formation is confirmed by ammonoid Tompophiceras pascoei (Spath) remains found several kilometers northwest of the study section 70‐80 m above the Permian‐Triassic boundary. The rocks are characterized by an elevated C org content (0.91‐0.95% on average, up to 4.92% in some samples), which makes them similar to carbonaceous black shales [12]. Organic matter is finely dispersed. Its origination is most likely related to zoo- and phytoplankton [13]. The above-mentioned lithological features of rocks and lack of benthic fossils indicate that the sediments accumulated in anoxic settings. Kholodov and Nedumov, who studied Quaternary and Tertiary sediments of the Black Sea region [14] and Cretaceous organic-rich clayey rocks of the Atlantic [15], suggested using the Mo/Mn ratio as an indicator of anoxic environments. They established that Mo/Mn values ranging from 0.0 n to 0. n correspond to H 2 S-contaminated environments in