Middle Anisian Research Articles

Ecological control of the Pelsonian colonisation event (Anisian, Triassic) leading to the first settlement of Tetractinella-beds (Brachiopoda) in the Iberian palaeomargins. Palaeobiogeographical and biostratigraphical significance

Marine benthic biota recovery after the Permian/Triassic extinction is still a challenging topic in several fossil clades such as brachiopods. In fact, available data from the Early-Middle Triassic are scarce worldwide and their global record derives from limited localities throughout the Tethys Ocean. This work presents the first record of the Anisian Tetractinella-beds (Brachiopoda, Athyridida) in the peri-Iberian epicontinental platforms established in the westernmost Tethys margins. Their utility as a reliable biohorizon marker is emphasised as they provide an effective tool for age calibration and correlation in the middle Anisian (Pelsonian) successions, also supported by the co-occurring fossil assemblage. In the South-Iberian Palaeomargin, Tetractinella-beds occur in an intensively-burrowed shallow-marine succession. The rich ichnological content has been exhaustively evaluated in order to assess the ecological factors controlling the development of the brachiopod fauna. Three ichnoassemblages are documented dominated by Oravaichnium, Balanoglossites and Thalassinoides, respectively. The gathered faunal, ichnological, taphonomical, and sedimentological data reveal an alternation of sea-level changes influencing the composition of the Anisian marine communities. The first stage consists of near-shore restricted environments sporadically disturbed by short-term shallow-marine interludes, characterised by the presence of Oravaichnium and its associated fauna. Subsequently, the Pelsonian transgression event is recorded (MID-2), documented by a firm-ground surface pointed out by the development of a Balanoglossites surface, followed by the highstand, when shallow epicontinental environments developed in connection with open-marine areas. This phase involved the spreading of Tetractinella and deep-water bivalves. Finally, near-shore restricted conditions were re-established typified by Oravaichnium and the last occurrences of Tetractinella, with the disappearance of the open sea-water fauna. The maximum flooding reached after the Pelsonian transgression facilitated new palaeobiogeographical migration routes, allowing for an Alpine-Germanic dispersion of taxa throughout the North-South epicontinental Tethyan seaway as well as the earliest first faunal migration event from the Sephardic Bioprovince northwards to the South-Iberian palaeomargin.

Prolonged and gradual recovery of metazoan-algal reefs following the end-Permian mass extinction

The tempo of biotic recovery following extinction reflects the time scales of evolutionary processes and the long-term consequences of degraded ecosystems, but recovery patterns are poorly resolved. In this study, we investigated the tempo of biotic recovery by evaluating metazoan-algal reef assembly following the end-Permian mass extinction. We combined satellite imagery analysis, field mapping, biostratigraphy, and quantitative petrography to assess recovery in the oldest-known and most stratigraphically extensive Lower to Middle Triassic platform-margin reef. The reef occurs in upper Spathian (upper Lower Triassic) to upper Anisian (lower Middle Triassic) strata of the Great Bank of Guizhou (GBG) isolated carbonate platform in south China. Previous work suggests that metazoan-algal reefs were absent for 8−10 m.y. following extinction but were biologically diverse from their Pelsonian (middle Anisian) initiation. This pattern implies that reefs can reassemble rapidly (<< 1 m.y.) when environmental conditions are favorable. In contrast, our analyses indicate that calcareous sponges, calcareous algae, and early scleractinian corals occurred progressively in the GBG reef and that biotic recovery metrics increased gradually. Unlike nonreef ecosystems, biodiverse metazoan-algal reefs were delayed until the late Pelsonian or early Illyrian, postdating broader marine ecosystem recovery and isotopic evidence for carbon-cycle stabilization by 2−4 m.y. Our findings suggest that reef and nonreef ecosystems differ in their recovery pattern and tempo. Reef recovery from severe environmental perturbation can require several million years, even after hospitable conditions return, highlighting the importance of modern reef conservation.

Lithostratigraphy, lithofacies and deposition conditions of the late Olenekian-middle Anisian Alam Formation in the Nakhlak area, central Iran

The present study aims to investigate petrography characteristics and sedimental environments of upper Olenekian–middle Anisian deposits of Nakhlak group in the sedimentary-structural zone of central Iran. To this end, a section of these deposits with a thickness of 720 meters was first selected, and 190 samples were taken from this section for preparing thin sections. Also, quantitative and qualitative laboratory tests were performed and 25 samples of sandstone were selected for point counter analysis. The results indicated that the major deposits of this formation are related to siliciclastic, carbonate, and pyroclastic types, which are in the form of two facies associations. The facies association A at the bottom of the studied section with the thickness of 90 meters has a periodicity of clastic, carbonate, and pyroclastic facies. The clastic facies of this association consists of fine-grained sandstone. In addition, the carbonate facies in association A are characterized by two microfacies consisting of intraclast oolitic grainstone and oolitic grainstone. Further, tuffite is the only pyroclastic facies related to association A, which has a laminate structure, cross-bedding lamination, herringbone bedding, and upward-thinning and thickening cycles. The facies association, B which is deposited later, is more in the middle and top part of the section. The facies association B is 660 meters thick and has a periodicity of clastic and limestone facies. Clastic facies of this association includes four lithofacies such as conglomerate, pebble coarse-grained sandstone, medium-grained sandstone to thin layer siltstone and shale. The carbonate facies consists of four microfacies such as sandy intraclastic wackestone and mudstone. Furthermore, slumping structures, cross bedding, turbulence, boudinage structure, and convolute of sediments, along with the effects of erosional channels are observed in facies B. Field and laboratory studies conducted on this succession indicate the structure of facies association A was deposited in a mixed siliciclastic carbonate ramp. Finally, submarine canyons and submarine fan environments were left by increasing the depth of the facies association B in the deep part of sea and turbidity systems.

From shallow-water carbonate ramp to hemipelagic deep-marine carbonate deposition: Part 1. General characteristics, microfacies and depositional history of the Middle to Late Anisian Bulog sedimentary succession in the Inner Dinarides (SW Serbia)

The opening of the Neo?Tethys started in the Middle Anisian and is recorded in the drowning succession of the shallow?water Ravni/Steinalm Carbonate Ramp and the subsequent deposition of deep?marine limestones, e.g., the red nodular limestones of the Bulog Group and equivalents. In the Inner Dinarides of southwest Serbia the continental break?up of the Neo? Tethys Ocean is characterized by the formation of a horst?and?graben topography. The change from deposition of shallow?water carbonates formed in an epicontinental sea (graben stage of the Neo?Tethys Wilson Cycle) to red nodular deep?marine limestones (Bulog Limestone) in the late Pelsonian (Middle Anisian) is relatively abrupt due to the rapid decrease of carbonate production. The deeper?water Bulog Limestone, deposited in the early stage of the passive continental margin evolution of the western Neo?Tethys can be dated by conodonts and in rare cases also by ammonoids quite exactly, and therefore it is possible to reconstruct the Pelsonian to Illyrian sedimentological evolution precisely: 1) The late Pelsonian is characterized by the drowning of the shallow?water Ravni Carbonate Ramp and a rapid deepening of the depositional realm. Extension led to the formation of neptunian dikes in the shallow?water Ravni Formation, filled with deeper?marine red micrite, and the formation of a horst?and?graben morphology. Whereas some of the horsts uplifted and emerged in the grabens near to the newly formed escarpments thick breccia successions were deposited with a fining?upward trend during the early?middle Illyrian. On top of other horsts, the grabens, or the newly formed gentle slopes red nodular limestones were deposited. In cases layers with enriched ammonoids formed (Fossillagerst?tten). 2) The early?middle Illyrian ongoing subsidence resulted in the deposition of more and more condensed red nodular limestones with hardground formation. 3) Around the middle/late Illyrian boundary a new pulse of tectonic motions resulted in the tilting of blocks, the formation of new escarpments and again mobilization of mass transport deposits. In addition, a second generation of neptunian dikes was formed. They crosscut the late Pelsonian to middle Illyrian Bulog Limestone, the Pelsonian Ravni Formation, and the older generation of neptunian dikes in the shallow?water Ravni Formation. All formerly emerged horsts flooded and red nodular limestones were deposited on the karstified shallow?water Ravni Formation after a gap. This second pulse of tectonic motions is related to the widespread volcanism in the Dinarides as visible in the appearance of mm?sized biotite clasts in the late Illyrian Bulog Limestone. In contrast to the Outer Dinarides, where thick volcanics are intercalated in the Illyrian sedimentary succession, in the Bulog Limestone successions of the Inner Dinarides volcanics are missing. In general the Pelsonian?Illyrian sedimentary succession is characterized by a stepwise deepening of the depositional realm.

From shallow-water carbonate ramp to hemipelagic deep-marine carbonate deposition: Part 3. Lithostratigraphy and Formations of the Middle to Late Anisian Bulog sedimentary successions (Bulog Group) in the Dinarides (Bosnia and Herzegovina, Serbia, Montenegro)

In the Middle Anisian the opening of the Neo?Tethys started and this is characterized by a significant change in deposition in the whole Western Tethys Realm. In the Dinarides the Middle to Late Anisian tectonostratigraphic and basin evolution is mirrored by their sedimentary successions. In the Middle Anisian, the evolution of the shallow?water Ravni Carbonate Ramp ended relatively abrupt in the late Pelsonian: a rapid decrease of carbonate production is accompanied by formation of a horst?and?graben topography. This change is expressed by the change in deposition from shallow?water carbonates to deepwater sedimentary rocks, i.e. the Ravni Carbonate Ramp experienced a drowning. Contemporaneously neptunian dikes were formed in the underlying Ravni Formation, filled with deep?water limestones. In the grabens, near to the newly formed escarpments mass transport deposits accumulated. During the time span late Pelsonian to middle Illyrian a general deepening trend is mirrored in the sedimentological trend and the microfacies characteristics. Fossilla ? gerst?tten (mainly cephalopods) and hardgrounds occur widespread in the deeper?water red nodular limestones formed widespread above the Ravni Carbonate Ramp. Around the middle/late Illyrian boundary a second intense pulse of tectonic motions, related to the onset of volcanic activity, resulted in a crosscut of the older horst?and?graben topo graphy. A second generation of neptunian dikes was formed, the blocks tilted, and again mass transport deposits accumulated near to escarpments. The late Illyrian is characterized by an overall deepening trend expressed also in a change in the microfacies characteristics to radiolarian?rich wacke? to packstones. In cases even radio larites or silicified limestones are characteristic sedimentary rocks in late Illyrian to Ladinian times beside silicified volcano?sedimentary rocks. This paper will define the late Middle?Late Anisian red nodular limestones and related sedimentary rocks with mass transport deposits overlying the Ravni Carbonate Ramp on base of new sedimen tological, stratigraphic and micro facies data following the international rules and standards. The palaeo geographic position together with characteristic litho? and microfacies features cause the lithostratigraphic definition of the different units. Included in the newly introduced Bulog Group are: 1) the emended and formalized Bulog Formation and 2) the newly introduced and defined Komarani Formation. The type?section of the Bulog Formation east of Sarajevo (Han Vidovic, central Bosnia and Herzegovina) is revisited. The Komarani Formation is introduced with the type?section in Komarani village (Zlatar Mt. in SW Serbia). The reference sections for the Bulog Formation in SW Serbia (Klisura quarry on Zlatibor Mt.), Bosnia and Herzegovina (Pridvorica locality at Romanija Mt.) and in Montenegro (Boljevici near Virpazar), are defined. In the reference sections some characteristic lithological and microfacies features are better preserved as in the type?section and included in the emendation and formalization of the Bulog Formation. The Bulog Formation at the type?section and all reference sections are in the Late Triassic overlain by the shallow?water carbonates of the Wetterstein and Dachstein Carbonate Platforms. Age and facies equivalent red nodular limestones deposited in the outer shelf region are part of the Middle to Late Triassic Hallstatt Limestone succession. In the type?region of the Hallstatt Limestones these late Middle to Late Anisian red nodular limestones are named Schreyeralm Limestones. The name Schreyeralm Limestone was introduced earlier as the name Bulog Limestone. It is discussed if also in the Dinarides the name Schreyeralm Limestone should be used for such Anisian red nodular limestones deposited in the outer shelf region, for priority reasons, or if they should be included into the Bulog Formation to avoid confusion, for historical reasons.

Bone abnormalities in the middle Anisian marine sauropsids from Winterswijk.

While the occurrence of skeletal pathologies in Middle Triassic marine reptiles has been poorly documented until now, massive accumulations of bone remains from the Germanic Basin provide the opportunities for documentation. Herein, we describe skeletal abnormalities in the Middle Triassic bone material from the Vossenveld Formation of Winterswijk, the Netherlands. The aim of the study is to distinguish in the studied bones pathologies resulting from malady or trauma and taphonomic alterations. Furthermore, an attempt was made to assess on how the pathologies also represent paleoecological data. Our survey led to the identification of one broken and healed bone, one case of abnormal coossification, and one case of posttraumatic fibro-osseous dysplasia. While the latter two pathologies give little insight into the ecology and function of the affected animals, the fractured dentary is attributed to Nothosaurus marchicus, a common sauropterygian macropredator. It proves that the individual survived long enough to heal, despite the injury hampering its hunting potential. One abnormally shaped humerus is interpreted as postmortem taphonomic deformation, emphasizing the necessity of utilization of detailed diagnostics to distinguish actual paleopathologies from nonbiological distortion.

High productivity promoted exceptional fossil preservation of the early Middle Triassic Luoping biota of Yunnan Province, China

The early Middle Triassic (Anisian) Luoping biota is representative of marine ecosystems following their full recovery after the Permian-Triassic mass extinction; however, its exceptional preservation remains poorly understood. In this paper, we report multiple geochemical proxies (TOC, TN, P/Al, Cuxs, Nixs, Baxs, δ13Ccarb, and δ13Corg) from Member II of the Middle Triassic Guanling Formation at the Xiangdongpo section in Luoping County, Yunnan Province, China, to assess the relationship between primary productivity and exceptional preservation of the Luoping biota. Variations in TOC, TN, P/Al, Cuxs, and Nixs values show that exceptional preservation coincides with two intervals of high productivity. Relatively low C/N ratios and distributed Δ13Ccarb-org values indicate that primary productivity was dominated by eukaryotic algae and prokaryotic microbes. Based on geochemical analyses and regional correlations, we conclude that, following sea level rise, nutrients were supplied to the Luoping area by upwelling from the open ocean and facilitated the blooming of marine communities in an open platform setting. In the intra-platform depression, increased nutrients supply also fueled high primary productivity in surface waters and oxygen consumption in the water column, causing bottom water anoxia. The lack of oxygen in the bottom water reduced the rate of biomass degradation and bioturbation, promoting growth of microbial mats, leading to the exceptional preservation of macrofauna. This study highlights the important role of elevated primary productivity in exceptional fossil preservation by triggering anoxia of bottom waters. Our findings confirm the widespread development of anoxic conditions during the middle Anisian (Pelsonian), from the eastern Tethys to the Panthalassa, and also reveal the interactions between organisms and the environment after Permian-Triassic mass extinction.

Rediscovery of a classic Middle Triassic fossil site of the Balaton Highland (Transdanubian Range, Hungary): cephalopods, brachiopods and vertebrate remains from the Akol Hill at Barnag

Recent collecting of the classic Middle Anisian fossil site of the Akol Hill at Barnag (Nagyvázsony Plateau, Balaton Highland) yielded a plenty of new palaeontological data.The Middle Anisian platform carbonate succession (Tagyon Formation) is overlain by 1-2 metres thick reddish, nodular, crinoidal limestone (Vászoly Formation) that contains a very rich fossil assemblage with ammonoids, nautiloids and brachiopods. Some vertebrate fossils were also found. Besides fish teeth, remains of marine reptiles are also present in the fauna. Four vertebrae, a piece of a rib, as well as a tooth crown fragment have also been found.Based on the geological buildup and the new biostratigraphic data the active stage of the Barnag Platform was much shorter than that of the other two Middle Anisian platforms of the Balaton Highland (Tagyon Platform, Kádárta Platform). The ammonoid fauna of the lowermost thin limestone bed above the Tagyon Formation contains elements reworked from the Balatonicus Zone. The overlying some beds contain a very rich lower Illyrian ammonoid fauna which is more diverse than the equivalent faunas of the Tagyon Platform and the Kádárta Platform. The ammonites of the Balatonicus Zone in the basal part of the Vászoly Formation prove that the drowning of the Barnag Platform occured even during the Pelsonian, earlier than in the case of the Tagyon and the Kádárta Platforms where the oldest basin sediments are mid-Illyrian (Camunum Subzone of the Trinodosus Zone) above the drowning surface.The Akol Hill locality also provided the first known occurrence of ichthyosaurs like Cymbospondylus, predators that probably dwelled mostly open marine environments but also might have been well adapted for hunting in shallow environments like submarine highs.

Middle Anisian (Bithynian to Illyrian?, Middle Triassic) Ammonoidea from Rüdersdorf (Brandenburg, Germany) with a revision of Beneckeia Mojsisovics, 1882 and notes on migratory pathways

Middle Anisian (Bithynian to Illyrian?, Middle Triassic) Ammonoidea from Rüdersdorf (Brandenburg, Germany) with a revision of Beneckeia Mojsisovics, 1882 and notes on migratory pathways

Development and dolomitization of Anisian isolated carbonate platforms in the Transdanubian Range, Hungary

Abstract In the Middle Anisian, extensional tectonic movements led to the development of isolated carbonate platforms in the area of the southwestern part of the Transdanubian Range. The platforms are made up of meter-scale peritidal–lagoonal cycles bounded by subaerial exposure surfaces. One of the platform successions (Tagyon Platform) consists predominantly of limestone that contains partially and completely dolomitized intervals, whereas the other one (Kádárta Platform) is completely dolomitized. Drowning of the platforms took place in the latest Pelsonian to the early Illyrian interval when submarine highs came into existence and then condensed pelagic carbonate successions with volcanic tuff interbeds were deposited on the top of the drowned platforms from the late Illyrian up to the late Ladinian. The comparative study of dolomitization of the coeval platforms, affected by different diagenetic histories, is discussed in the current paper. Traces of probably microbially-mediated early dolomitization were preserved in the slightly dolomitized successions of the Tagyon Platform. This might also have been present in the successions of the Kádárta Platform, but was overprinted by geothermal dolomitization along the basinward platform margin and by pervasive reflux dolomitization in the internal parts of the platform. The Carnian evolution of the two submarine highs was different, and this may have significantly influenced the grade of the shallow to deeper burial dolomitization.

Sedimentary aspects of the onset of Middle Triassic continental rifting in the western end of Neotethys; inferences from the Silica and Torna Nappes, NE Hungary: a review

The initiation of continental rifting from the latest Early Triassic was reconstructed by correlation of sedimentary formations deposited in the western end of Neotethys (in the Dinaric–Alpine oceanic branch). The shallow-marine and basinal strata of the Silica Nappes and the Bódvarákó Series from the Torna Nappe (located in the southern part of the Inner Western Carpathians) were studied and compared to sedimentary successions described from the Alps, the Carpathians and the Dinarides. The depositional zonation, developed on the shelf during the Late Permian‒Early Triassic transgression, was dissected and rearranged from the latest Early Triassic. The facies pattern and the differential sedimentary evolution of the shelf domains suggest that the accelerated subsidence began in the latest Early Triassic, and was connected to the onset of continental rifting. Three stages are reconstructed in the studied time-frame. (1) Dark grey carbonates, very poor in fossils, were deposited in restricted and hypersaline intraplatform basins in many shelf domains. In the external domains, shallow-marine carbonates, depositional gaps and terrestrial deposits are typical (formations in the Southern Alps, the External Dinarides and the Serbian–Macedonian Massif). From the latest Early Triassic, this latter shelf segment formed a threshold that restricted water circulation from the intraplatform basins. (2) Shallowing-up carbonate successions mark the next stage that implies a period of tectonic quiescence on the shelf from the late Early Anisian to late Middle Anisian. A peculiar change in biota occurring in previously restricted domains was coeval in shallow-marine and deep-marine settings. The biotic change is revealed by observations that dark grey carbonates, which are very poor in fossils, are overlain by carbonate successions rich in fossils typical for normal-marine water. The biota and environmental changes indicate the opening of a passage which allowed the circulation of well-oxygenated and normal-salinity marine water towards the previously restricted depositional areas. The geodynamic setting switching from continental rifting to spreading in the southern sector of the Dinaric–Alpine oceanic branch (Hellenides and Albanides), triggered the opening of the gateway between the future continental margins, i.e., between the External Dinaridic domain (Adria) and Serbian–Macedonian Massif (Eurasia). (3) Following the biotic event in the northern sector of the shelf, subsidence accelerated and additional intraplatform basins opened from the latest Pelsonian.

Placodus (Placodontia, Sauropterygia) dentaries from Winterswijk, The Netherlands (middle Anisian) and Hünfeld, Hesse, Germany (late Anisian) with comments on ontogenetic changes

Two recently found dentaries from the Lower Muschelkalk of Winterswijk (The Netherlands) and from the Upper Muschelkalk of an outcrop in the vicinity of Hünfeld (Hesse, Germany) are studied and compared to lower jaws of placodonts. As a result, the here described specimens can be assigned to Placodus cf. gigas. However, this assignment should be regarded as preliminary due to the isolated nature of the material. More diagnostic material is necessary to validate this affiliation. A certain morphological variability in P. gigas dentaries that had been pointed out before is also obvious among the new material. Placodus gigas has a wide paleogeography and stratigraphic range and a revision of the material assigned to P. gigas with new methods is overdue but beyond the scope of the current paper. The dentary from Hünfeld is with about 4 cm preserved length the smallest so far known dentary of a Placodus. It provides interesting insights in morphological changes during ontogeny and reveals differences in trajectories when compared to dentaries of different ontogenetic stages of Cyamodus hildegardis.

Multi‐elemental chemostratigraphy of Triassic mudstones in eastern Svalbard: Implications for source rock formation in front of the World’s largest delta plain

AbstractThe Triassic Boreal Ocean was a shallow epicontinental basin and the sink of the World's largest delta plain known to date. Nutrient and freshwater supply from this delta have been regarded as important causes for high productivity and water mass stratification, forming Middle Triassic oil‐prone source rocks. Recent studies attribute upwelling and a productivity‐induced oxygen minimum zone as important factors. A multi‐elemental chemostratigraphic study of a Spathian–Carnian mudstone succession exposed in eastern Svalbard was performed to investigate their formation. This includes 89 samples from three localities, from which 34 elements were acquired using combustion and X‐ray fluorescence analyses. The goal is to provide a correlation framework and infer the role of productivity, redox and water mass restriction on organic matter accumulation and source rock formation. These processes had major impact on the source potential. The Spathian Vendomdalen Member suggests deposition during intermittent benthic euxinia and low productivity, corresponding with a reported deep thermocline that obstructed upwelling. The lower Anisian lower–middle Muen Member shows negligible enrichment in redox‐sensitive elements but in situ phosphate nodules, consistent with developing upwelling and moderate productivity. The middle Anisian upper Muen Member formed during high productivity and phosphogenesis and is linked with basin‐wide upwelling. Productivity, phosphate and redox proxies are all strongly enriched in the upper Anisian–Ladinian Blanknuten Member. In the south‐western Barents Sea, the pro‐deltaic environment of the emerging Triassic Boreal Ocean delta system had terminated these conditions. The upper Ladinian upper Blanknuten Member formed within intermittent euxinic bottom waters due to the shallowing sea level. The Carnian Tschermakfjellet Formation marks the dominance of the prograding delta system and the end of Triassic oil‐prone source rock formation in Svalbard.

A sedimentological description of the Middle Triassic vertebrate-bearing limestone from Velika planina, the Kamnik-Savinja Alps, Slovenia

In the Kamnik-Savinja Alps (Slovenia), the Lower Serla Dolomite laterally passes into a succession of thin- to medium-bedded bituminous limestones of the Velika planina member. The finely laminated lower part of this member contains well-preserved actinopterygian fish and sauropterygian remains. The research aimed to determine the sedimentological and palaeoenvironmental characteristics of the depositional basin on the basis of three detailed sedimentological sections logged atop the Velika planina plateau. The Velika planina member is underlain by a whitish to light grey, thick bedded to massive dolomite with oncoids, stromatolites, and lumachellas deposited under peritidal to shallow subtidal conditions. The lower part of the Velika planina member consists of thin, often platy, finely laminated beds of bituminous mudstone. The Chondrites ichnofossil is very common; however, in some beds numerous lingulid brachiopods, bivalves, and crinoids were observed. Fossil vertebrates and crustaceans are relatively rare and confined to a few levels. Ammonoids are very rare. Subordinate beds of intraclastic-peloid wackestone to packstone, intraclastic-bioclastic grainstone, and bivalve floatstone occur. Slumps are common. Upwards, bedding gradually becomes thicker and bioturbation more common. Finally, stromatolites, birdseye fenestrae, and oncoids reappear. The entire succession is confined to the early to middle Anisian by the foraminifer Citaella dinarica (KOCHANSKY-DEVIDÉ & PANTIĆ). The absence of breccias at the base of the Velika planina member, the gradual transition upwards into shallow marine carbonates, as well as the presence of sauropterygians of the order Nothosauroidea suggest deposition in a relatively shallow basin. The finely laminated facies of the lower part of the member indicates a stratified water column, with oxygenated near-surface waters and hypoxic to anoxic conditions near the sea floor.

Change from shallow to deep-water environment on an isolated carbonate platform in the Middle Triassic of the Transdanubian Range (Hungary)

The stratigraphic and paleoecologic investigations of the Middle Triassic Kádárta section of the western part of the Transdanubian Range (Hungary) let an insight to the drowning of an isolated carbonate platform and the deposition of the following pelagic successions in deep neritic and bathyal environment. The biostratigraphic and radiometric ages revealed the presence of a gap between the Pelsonian (Middle Anisian) shallow-marine carbonates and the overlying deep-water succession, since the onset of pelagic sedimentation was dated as late Illyrian (latest Anisian). This suggests that the study area was located on a relatively high paleotopographic position after the break-up of the Neotethys in the late Pelsonian. Correlation with other localities of the western Neotethys indicates that some sections were located either on rapidly subsiding blocks (e.g., Klisura – Dinarides, Schreierkogel – Northern Calcareous Alps, Baradla Cave – Aggtelek-Rudabánya Unit) or on more emerged highs (Rid – Dinarides). The integrated ammonoid and conodont biostratigraphy accompanied by UPb ages provided a good opportunity for correlations with Ladinian key sections (Bagolino, Monte San Giorgio, Rio Nigra) from the Southern Alps.

Lithostratigraphic definition of the Anisian carbonate-ramp deposit of the Annaberg Formation (Middle Triassic, Northern Calcareous Alps, Austria)

Concerning the Middle Triassic stratigraphic succession of the Northern Calcareous Alps (NCA), a modern, litho- and biostratigraphic oriented evaluation of the early- and middle Anisian Annaberg Formation is presented. Due to the fact, that Middle Triassic formations are characterized by a wide distribution within the NCA, any lithostratigraphic definitions of these formations would be of great benefit for mapping geologists, engineers and hydrogeologists. The lithostratigraphic term Annaberg Formation may substitute former designations like “Alpiner Muschelkalk”, “Anisian Limestone and Dolomite” or, partly, “Gutenstein Limestone”. It is exclusively of Anisian age and earlier then the Steinalm and Reifling Formation. Mainly based on microfacies data and lithological data, we define the Annaberg Formation (former: Annaberg Limestone) as one of the most significant Middle Triassic lithostratigraphic units within the NCA. After a detailed description of the type area, findings gained in other areas of the NCA are incorporated to obtain the largest possible overview about the lithological variability and constituents of the Annaberg Formation. As a result, we can describe the Annaberg Formation as mainly organic-rich, medium bedded wackestone, containing remnants of crinoids, little bivalves and gastropods. Typically, fossil-rich layers with accumulations of bivalves and crinoids can often be observed within the Annaberg Formation. In contrast to the Gutenstein Formation no siliceous concretions or fossils (like radiolarians) appear and the fauna is in the main shallow marine. The rock-colour varies from dark- to medium-grey and the bench thicknesses are greater than within the Gutenstein Formation sensu stricto. The fossil content is also larger than in the essentially anaerobe Gutenstein Formation. With respect to the Virgloria Formation the Annaberg Formation is rather planar bedded, not so rich in bioturbation-structures and poor in silica and clay. Hence, the depositional environment of the Annaberg Formation can be described as a restricted carbonate ramp succession, with only minor water movement and separated from the open sea by a shoal with crinoid and brachiopod meadows. Breccias may be an indication for collapse-structures and slumping. In addition, knife-cavity structures (“Messerstichkalke”) indicate an occasional hypersaline environment with precipitation of evaporite-minerals like gypsum. Fossil-rich layers with accumulations of molluscs and crinoids may indicate short-term storm affected sedimentation.

The main stage of recovery after the end-Permian mass extinction: taxonomic rediversification and ecologic reorganization of marine level-bottom communities during the Middle Triassic.

The recovery of marine life from the end-Permian mass extinction event provides a test-case for biodiversification models in general, but few studies have addressed this episode in its full length and ecological context. This study analyses the recovery of marine level-bottom communities from the end-Permian mass extinction event over a period of 15 Ma, with a main focus on the previously neglected main phase during the Middle Triassic. Our analyses are based on faunas from 37 lithological units representing different environmental settings, ranging from lagoons to inner, mid- and outer ramps. Our dataset comprises 1562 species, which belong to 13 higher taxa and 12 ecological guilds. The diversification pattern of most taxa and guilds shows an initial Early Triassic lag phase that is followed by a hyperbolic diversity increase during the Bithynian (early middle Anisian) and became damped later in the Middle Triassic. The hyperbolic diversity increase is not predicted by models that suggest environmental causes for the initial lag phase. We therefore advocate a model in which diversification is primarily driven by the intensity of biotic interactions. Accordingly, the Early Triassic lag phase represents the time when the reduced species richness in the wake of the end-Permian mass extinction was insufficient for stimulating major diversifications, whereas the Anisian main diversification event started when self-accelerating processes became effective and stopped when niche-crowding prevented further diversification. Biotic interactions that might drive this pattern include interspecific competition but also habitat construction, ecosystem engineering and new options for trophic relationships. The latter factors are discussed in the context of the resurgence of large carbonate platforms, which occurred simultaneously with the diversification of benthic communities. These did not only provide new hardground habitats for a variety of epifaunal taxa, but also new options for grazing gastropods that supposedly fed from microalgae growing on dasycladaceans and other macroalgae. Whereas we do not claim that changing environmental conditions were generally unimportant for the recovery of marine level-bottom communities, we note that their actual role can only be assessed when tested against predictions of the biotic model.

Epigenetic-Hydrothermal Fluorite Veins in a Phosphorite Deposit from Balaton Highland (Pannonian Basin, Hungary): Signatures of a Regional Fluid Flow System in an Alpine Triassic Platform

The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins.

A Hiatus Obscures the Early Evolution of Modern Lineages of Bony Fishes

About half of all vertebrate species today are ray-finned fishes (Actinopterygii), and nearly all of them belong to the Neopterygii (modern ray-fins). The oldest unequivocal neopterygian fossils are known from the Early Triassic. They appear during a time when global fish faunas consisted of mostly cosmopolitan taxa, and contemporary bony fishes belonged mainly to non-neopterygian (“paleopterygian”) lineages. In the Middle Triassic (Pelsonian substage and later), less than 10 myrs (million years) after the Permian-Triassic boundary mass extinction event (PTBME), neopterygians were already species-rich and trophically diverse, and bony fish faunas were more regionally differentiated compared to the Early Triassic. Still little is known about the early evolution of neopterygians leading up to this first diversity peak. A major factor limiting our understanding of this “Triassic revolution” is an interval marked by a very poor fossil record, overlapping with the Spathian (late Olenekian, Early Triassic), Aegean (Early Anisian, Middle Triassic), and Bithynian (early Middle Anisian) substages. Here, I review the fossil record of Early and Middle Triassic marine bony fishes (Actinistia and Actinopterygii) at the substage-level in order to evaluate the impact of this hiatus–named herein the Spathian–Bithynian gap (SBG)–on our understanding of their diversification after the largest mass extinction event of the past. I propose three hypotheses: 1) the SSBE hypothesis, suggesting that most of the Middle Triassic diversity appeared in the aftermath of the Smithian-Spathian boundary extinction (SSBE; ∼2 myrs after the PTBME), 2) the Pelsonian explosion hypothesis, which states that most of the Middle Triassic ichthyodiversity is the result of a radiation event in the Pelsonian, and 3) the gradual replacement hypothesis, i.e. that the faunal turnover during the SBG was steady and bony fishes were not affected by extinction events subsequent to the PTBME. Based on current knowledge, hypothesis three is favored herein, but further studies are necessary to test alternative hypotheses. In light of the SBG, claims of a protracted diversification of bony fishes after the PTBME should be treated with caution.

Precursor extension to final Neo-Tethys break-up: flooding events and their significance for the correlation of shallow-water and deep-marine organisms (Anisian, Eastern Alps, Austria)

The Anisian depositional history in the Western Tethys realm provides the possibility to study the stepwise opening of the Neo-Tethys, and is well preserved in the sedimentary record of the Northern Calcareous Alps. Whereas the depositional characteristic in the Early (to early Middle) Anisian is characterized by shallow-water carbonates, formed in a semi-restricted environment, the situation changed in the Middle Anisian. A rapid increase of subsidence resulted in an abrupt deepening event with deposition of deeper-water limestones, in some cases even with chert nodules, sometimes with resedimented shallow-water debris intercalated in radiolaria-filament wackestones, or with clayey or marly intercalations. This abrupt deepening, termed the Annaberg Event, is followed by a shallow-water carbonate evolution. The deeper-water limestones can be dated by conodonts and shallow-water organisms like calcareous algae or foraminifera from the resedimented intercalations as Late Bithynian to Early Pelsonian. In contrast to the Early Anisian microbial carbonates, formed under semi-restricted conditions, the Middle Anisian (Pelsonian) shallow-water carbonates were formed under fully marine influence and a diverse fauna and flora was, therefore, able to counterbalance the rapid subsidence by increasing carbonate production. During Middle Anisian times, the newly tectonically created accommodation space became rapidly filled by shallow-water carbonates. At the end of the Middle Anisian (Late Pelsonian), the final break-up of the Neo-Tethys led to a rapid decrease of carbonate production and widespread deposition of deep-marine and condensed limestones. This drowning event (Reifling Event) was accompanied by the formation of a horst-and-graben morphology, dated by conodonts and ammonoids as late Middle Anisian from overlying condensed limestones. In contrast to the well-known drowning event in the late Middle Anisian, precursor events to the final oceanic break-up of the Neo-Tethys have not yet been described, but play an important role in the reconstruction of the opening history of the Neo-Tethys. This knowledge gap is filled by the analysis of exactly datable sedimentary successions in the central Northern Calcareous Alps.