The parareptilian group Procolophonoidea has been increasingly studied in recent years, and a high survival rate during the P/Tr extinction event has been estimated tor the ciade. Procolophonoid interrelationships, however, remain poorly known. Here, descriptions of the procolophonids Anomoiodon liliensterni and Leptopleuron lacertinum, and the possible Permian Russian procolophonoids, are provided. Anomoiodon and the genus Kapes were found to be closely related but there is not enough evidence to support the synonymy of the two genera. Leptopleuron is described in great detail, making it one of the most completely knovm procolophonoids. Of the possible Permian Russian procolophonoids, Suchonosaurus minimus was found to be a member of the more inclusive Procolophonidae, whereas Microphon exiguus and Kinelia broomi fall outside of Procolophonoidea. Nyctiphruretus acudens might be the sister taxon of Procolophonoidea but an alternative hypothesis of Nyctiphruretus being more closely related to pareiasaurs and nycteroleterids also received support, A phylogenetic study. including 39 procolophonoid taxa, was conducted. The results suggest novel compositions of the procolophonid clades Leptopleuroninae and Procolopphoninae; the monophyly of the genus Kapes was questioned; the phylogenetic position of Suchonosaurus, Pintosaurus and Phaantosaurus among the other basal procolophonids remains unresolved; and the results cast doubt on Procolophonoidea being divided into the clades Owenettidae and Procolophonidae. The topology with the best stratigraphic fit indicates that only 57% of procolophonoid lineages might have survived through the P/Tr boundary. However, it is also possible that up to 80% lineages crossed the boundary but this requires a scenario that maximizes the number of ghost lineages. A stratigraphical analysis supports separate Owenettidae and Procolophonidae.

Student Number : 9902718G - MSc dissertation - School of Geosciences - Faculty of Science / The Late Permian (251.0 ± 0.4 Ma) mass extinction is universally acknowledged as the most consequential of the five major Phanerozoic mass extinctions. More than 90% of marine species, ~70% of terrestrial vertebrates, and ~90% of plant life were lost in a very short interval. The nature of the Permian-Triassic (P-Tr) boundary and the cause of the mass extinction associated with it have been the subject of extensive international debate. Possible causes for the P-Tr extinction include asteroid/comet impact, oceanic anoxia, volcanism, methane clathrate dissociation, or combinations of these causes. Geochemical studies of the P-Tr boundary have traditionally been focused on the marine realm, as the boundary in continental sections is typically difficult to pinpoint. One continental setting of the P-Tr boundary that has, however, received much attention is that in the main Karoo Basin, South Africa. The Karoo Basin is a large retro-arc foreland basin which accumulated sediment from the Carboniferous (300 Ma) through to the Early Jurassic (180 Ma) in southwestern Gondwana. Mineralogical and geochemical investigations across two palaeontologically well-constrained continental P-Tr boundary sections at Commando Drift Dam and Wapadsberg in the southern Karoo Basin of South Africa have been undertaken in order to aid in our understanding of this extinction event. The Commando Drift Dam section is also constrained palaeomagnetically. There is a change in paleosol colour across the P-Tr boundary from green-grey to red-brown, which is believed to reflect a change of oxidizing conditions at the P-Tr boundary. Quartz grains were examined for possibly impact-produced microdeformation features, but these were not found. Iridium concentrations are below the detection limit (by instrumental neutron activation analysis) and the sections could not be evaluated as to whether any significant enrichment has taken place at the P-Tr boundary. Major element chemical profiles are dominated by the signatures of carbonate nodular horizons in both sequences. Iron contents (and accompanying siderophile element abundances) increase across the palaeontologically-defined P-Tr boundary, followed by a decrease thereafter. The major element concentrations, together with the effects of weathering, largely control trace element distribution. Carbon isotopic results from the Commando Drift Dam section show a gradual decrease in values before the P-Tr boundary, with a larger negative excursion at the P-Tr boundary. Above the boundary, gradual recovery to initial ratios is observed, followed by another gradual decrease in values to the palaeomagnetically defined boundary. No evidence supporting an extraterrestrial impact extinction mechanism has been found. Rather, the carbon isotope data from this study support two gradual palaeoclimatic changes separated by a sudden change in the carbon isotopic content of the atmosphere. The size and nature of these excursions support the addition of large amounts of anoxic material into the atmosphere. This is proposed to have been caused by the multiple influx of carbon dioxide, methane and other greenhouse gases at various times and by different mechanisms. Such a release of carbon dioxide, methane and other greenhouse gases could have been caused by the coincident volcanic event (the formation of the Siberian Traps) and the episodic release of methane clathrates.

The end-Permian extinction at 252 Ma is widely regarded as the most severe of the Phanerozoic mass-extinctions and enabled the evolution of the modern carbon cycle and ecosystem structure. The cause of the extinction is still debated but the synergistic pressures of global climate change, such as anoxia and ocean acidification, were clearly important. The extinction occurred in two phases and is marked by a uniquely protracted recovery period of ~ 5 Myrs where diversity fails to reach pre-extinction levels until the Middle Triassic. This period is characterized by an unstable global carbon cycle, secondary extinctions, reef, chert and coal gaps, and changes in the carbonate factory from reef to microbial and abiotic dominated deposition. This thesis focuses on using geochemical data from the Arabian Margin to investigate the carbon cycle record and the links between kill mechanisms and carbon cycle dynamics. A new record of carbon cycling is presented for the Tethys in the form of a carbon isotope record for the entire Early Triassic from the Musandam Peninsula, United Arab Emirates (UAE). The Musandam carbon isotope record can be broadly correlated with global isotopic events but also resolves additional secondary excursions. These new short-lived events are probably related to the occurrence of the more widely recognized Early Triassic excursions, and may represent fluctuations in the driving mechanisms superimposed on the continued instability of the global carbon cycle in the aftermath of the end-Permian extinction. To unravel palaeo-depositional redox conditions this work utilizes geochemical proxies based on Fe systematics (Fe-speciation). To date, however, these proxies have only been calibrated in relation to modern and ancient siliciclastic marine sediments. This clearly limits the use of the Fe-speciation proxy, particularly in relation to carbonate-rich sediments and rocks. This thesis explores the use of Fe-speciation in carbonates using compiled literature and new data from modern oxic and anoxic settings. This new assessment expands the utility of Fe-based redox proxies to also incorporate carbonate-rich rocks that contain significant total Fe (>0.5 wt%), providing care is taken to assess possible impacts of diagenetic processes such as dolomitization. Based on this calibration work Fe-speciation is used to reconstruct the redox structure for the Arabian Margin mixed carbonate and clastic sediments, from the late Permian to the Middle Triassic. Fe-S-C systematics are utilized to identify the spatial and temporal dynamics of anoxia for a Neo-Tethyan shelf-to-basin transect. The unique spatial resolution afforded by this transect allows a direct link to be drawn between biodiversity, carbon cycling and anoxic events. For the first time we can directly observe a switch from deep-ocean dominated anoxia to a dynamic anoxic wedge at the end-Permian extinction. Additionally the data suggest that ferruginous conditions (anoxic non-sulphidic) were dominant in the Tethyan Ocean throughout the Early Triassic, proposing that euxinia was restricted regionally with potential implications for nutrient recycling, carbon cycle models and driving mechanisms. Redox dynamics may have had important implications for the wider carbonate cycle. These two themes are particularly inter-related with regards to oceanic alkalinity and pH. This thesis presents the first shallow water boron isotope record for the Permian Triasssic Boundary, used as a proxy for pH. The record demonstrates some unexpected results; firstly a sudden increase in pH is observed, prior to the first phase of the extinction and interpreted to reflect alkalinity supply from the development of slope anoxia. Secondly there is no evidence for an acidification event at the first phase of the extinction where pH remains stable. A rapid acidification event is, however, seen in the earliest Triassic, contemporary to the second phase of the mass extinction, but delayed compared to the main negative carbon isotope excursion that indicates the main phase of Siberian Trap volcanism. These events may be explained by dramatic changes in ocean the ocean’s buffering capacity linked to changes in alkalinity supply and the carbonate factory.

The Late Permian mass extinction occurring at 252.6 ± 0.2 Ma is the most severe Phanerozoic extinction event and was preceded and followed by additional disturbances. Patterns and processes of extinction and recovery of marine vertebrates have been little studied compared to marine invertebrates. This project focuses on Chondrichthyes, which, together with other marine fish, appeared to have been relatively unaffected by the extinction, while most of their supporting ecosystem collapsed. This study explores the authenticity of extinction among chondrichthyans and possible explanations for the observed patterns, because extinction severities on the taxonomic and ecological levels may be decoupled or the quality of the fossil record may be variable. The presented analyses are based on a newly compiled database that supercedes older compilations. It is supplemented by material obtained from numerous localities globally, which includes newly described taxa. Hence, this study attempts to be the most up-to-date and comprehensive analysis of patterns and trends in chondrichthyan diversity and distribution that is currently available. The data demonstrate that, despite some variability in the Permian–Triassic chondrichthyan fossil record, the Lopingian record is shown to be of adequate completeness and, furthermore, range-through genus diversity is not significantly correlated with the number of taxonomic occurrences. Genus diversity declined from the mid-Guadalupian following an increasing extinction rate, which intensified throughout the Lopingian and thus supports a combined overall extinction as a result of the end-Guadalupian and Late Permian events. Furthermore, global distribution of chondrichthyan diversity shifted away from tropical regions and particularly the Boreal Sea gained in diversity, tracking extinction and recovery in marine benthic invertebrates in both time and space. No significant dependence of extinction on taxonomic structure or palaeoecological traits exists, which suggests proportional losses, except during the end-Smithian crisis. Also, a significant size decrease is absent among Permian/Triassic boundary-crossing taxa, suggesting selective loss of large-sized chondrichthyans rather than adaptive size decrease. Ultimately, the Hybodontiformes, Neoselachii, Xenacanthiformes and Holocephali are identified as the survivors, which possessed a varying combination of characteristics such as moderate body-size, adaptation to brackish/freshwater environments, benthic or generalist littoral (clutching) feeding behaviour, and a wide palaeogeographic range.

The aim of this study is to designate paleontologic, biostratigraphic and sequence stratigraphic characteristics of the Permian-Triassic Boundary beds of the Bolkar Dagi Unit in the Hadim region (Central Taurides). For this purpose a 48,06m thick stratigraphic section, composed of limestone, siltstone and sandstone, was measured and 116 samples were analyzed through the Permian Ta

abstract: There is a growing body of evidence that the evolving redox structure of the oceans has been an important influence on the evolutionary trajectory of animals. However, current understanding of connections between marine redox conditions and marine extinctions and recoveries is hampered by limited detailed knowledge of the timing, duration, and extent of marine redox changes. The recent development of U isotopes (δ238U) in carbonates as a global ocean redox proxy has provided new insight into this problem. Reliable application and interpretation of the δ238U paleoproxy in geological records requires a thorough understanding of the reliability of δ238U recorded by bulk carbonate sediments. In this dissertation, I evaluate the robustness of δ238U paleoproxy by examining δ238U variations in marine carbonates across Permian-Triassic boundary (PTB) sections from different paleogeographic locations. Close agreement of δ238U profiles from coeval carbonate sections thousands of kilometers apart, in different ocean basins, and with different diagenetic histories, strongly suggests that bulk carbonate sediments can reliably preserve primary marine δ238U signals, validating the carbonate U-isotope proxy for global-ocean redox analysis. To improve understanding of the role of marine redox in shaping the evolutionary trajectory of animals, high-resolution δ238U records were generated across several key evolutionary periods, including the Ediacaran-to-Early Cambrian Explosion of complex life (635-541 Ma) and the delayed Early Triassic Earth system recovery from the PTB extinction (252-246 Ma). Based on U isotope variations in the Ediacaran-to-the Early Cambrian ocean, the initial diversification of the Ediacara biota immediately postdates an episode of pervasive ocean oxygenation across the Shuram event. The subsequent decline and extinction of the Ediacara biota is coincident with an episode of extensive anoxic conditions during the latest Ediacaran Period. These findings suggest that global marine redox changes drove the rise and fall of the Ediacara biota. Based on U isotope variations, the Early Triassic ocean was characterized by multiple episodes of extensive marine anoxia. By comparing the high-resolution δ238U record with the sub-stage ammonoid extinction rate curve, it appears that multiple oscillations in marine anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2018

La transition Permien – Trias est une période importante dans l’histoire de la Terre. L’extinction en masse de la fin du Permien est l’événement d’extinction le plus sévère de l’histoire de la vie sur Terre. Les études précédentes se sont principalement focalisées sur les événements biotiques en milieux océaniques. Récemment, de plus en plus de nouvelles recherches se sont développées sur les événements en milieu continental.Les bassins de Junggar et de Turpan en Chine du Nord, présentent une opportunité unique d’étudier la limite Permien – Trias en milieu continental grâce à de nombreux affleurements avec des séries continues.Les facies continentaux de la coupe de Dalongkou sur le flanc sud du bassin de Junggar et de la coupe de Taoshuyuan sur le flanc nord du basin de Turpan, ont été sélectionnés pour cette thèse. Les niveaux de l’intervalle de transition Permien – Trias correspondent aux formations “Wutonggou”, “Guodikeng” et “Jiucaiyuan”. D’abondants bois fossiles et empreintes de plantes ont été découverts dans ces coupes. Des logs sédimentaires détaillés ont été levés. L’approche utilisée ici est pluridisciplinaire pour reconstruire les Paléoenvironnements avec les bois fossiles et les plantes, les patrons des cernes croissance des bois et l’analyse des microfaciès sédimentaires.Cinq genres et six espèces de bois fossiles ont été découverts. Nous établissons trois nouveaux genres: Junggaropitys, Xinjiangoxylon et un nouveau genre (soumis pour publication). La courbe CSDM (Cumulative Sum of the Deviation from Mean diameter) a été utilisée pour analyser les cernes de croissance dans le but de déterminer les conditions d’intersaisonnalité et la longévité des feuilles des arbres. Nous avons déterminé que Junggaropitys dalongkouensis est une espèce à feuilles persistantes avec les feuilles à longévité de 3 à 6 ans; le XTT-C-4 gen. et sp. nov. est également à feuilles persistantes mais avec une longévité des feuilles de 3 à 15 ans.Septomedullopitys, Junggaropitys, Xinjiangoxylon et XTT-C-4 gen. nov. montrent tous un xylème secondaire de type Protophyllocladoxylon. En accord avec l’analyse paléobiogéographique, les bois de type Protophyllocladoxylon sont principalement distribués dans une zone climatique tempérée froide dans l’hémisphère sud, dans des zones climatiques variables dans l’hémisphère nord et dans la zone équatoriale au Paléozoïque supérieurLes résultats obtenus sur les bois fossiles montrent que le climat sur la région de Junggar devait être, à la limite Permien – Trias, chaud et humide, avec des températures et une humidité restant relativement stables.Il n’existe pas de période de forte sécheresse au Trias basal. Les méga-moussons de la Paléo-Téthys n’ont pas d’influence sur la région de Junggar sur la côte est de la Pangée aux latitudes moyennes. Combiné avec les résultats précédemment obtenus, nous montrons que le climat n’a pas subit de très fortes variations entre le Permien moyen et le Trias basal.L’analyse des plantes fossiles montre que le nombre de genres et d’espèces diminue progressivement de 26 genres et 53 espèces connues dans le Wuchiapingien à 10 genres et 15 espèces dans le Changhsingien et seulement 6 genres et 7 espèces dans l’Induen. La tendance à la réduction des assemblages floristiques dans les bassins de Junggar et Turpan semble montrer que le processus d’extinction est long et graduel et a débuté bien avant la limite Permien – Trias. Durant la période de récupération post-crise des flores, les lycopsides (Annalepis) et les fougères (Neocalamites et Pecopteris) ont joué un rôle d’espèces pionnières. Trois logs stratigraphiques ont été levés pour l’analyse des facies sédimentaires. Quatre principaux environnements de dépôts ont été reconnus dans la coupe de Dalongkou. Les séries de la Formation Wutonggou se sont déposées dans un environnement de rivières en tresse et de systèmes fluviaux éphémères ou d’étangs et de plaines alluviales. / Permian-Triassic transition is an important period in the Earth’s history. The end-Permian mass extinction is the Earth's most severe known extinction event. Previous studies mainly focused on the biotic events in the ocean. Recently more and more researches on the terrestrial events during the Permian-Triassic transition attracted many attentions. The Junggar and Turpan basins of Northwest China command a unique and significant position in the study of terrestrial Permian-Triassic boundary (PTB) events as it contains well and continuously exposed PTB sections. The lithostratigraphy, biostratigraphy, and cyclostratigraphy have been well established in the two basins. The problem we are trying to solve, based on paleobotanical studies associated with sedimentological analyses, is the environmental changes during the Permian-Triassic transition in the research area.The terrestrial facies in the Dalongkou section on the south flank of Junggar Basin and the Taoshuyuan section on the north flank of Turpan Basin have been selected as the researching ones for this thesis. The Permian-Triassic transition strata have been included in the “Wutonggou”, “Guodikeng” and “Jiucaiyuan” formations. Abundant fossil woods and plant impressions have been discovered and collected in these sections. Detailed sedimentary logs of the sections were drawn. The approach that we adopt to recognize the environmental changes is the fossil wood and plant impression species, growth-ring pattern, and sedimentary facies analysis.Five genera and six species of fossil woods were discovered. We establish three new genera: Junggaropitys, Xinjiangoxylon and a new genus (submitted for publication). The CSDM (Cumulative Sum of the Deviation from Mean diameter) curve was used to analyse the growth rings to determine the intraseasonal conditions and leaf longevity patterns of the trees. We recognise that Junggaropitys dalongkouensis is evergreen, and the leaf longevity may be 3–6 years; XTT-C-4 gen. et sp. nov. is evergreen too, and the leaf longevity may be 3 to 15 years. Septomedullopitys, Junggaropitys, Xinjiangoxylon and XTT-C-4 gen. nov. all show a Protophyllocladoxylon-type secondary xylem. According to palaeobiogeographic analysis, the Protophyllocladoxylon-type woods distributed mainly in the cool temperate climate zone of the southern hemisphere, various climate zones of the northern hemisphere and equatorial zone during the Late Paleozoic. The results of fossil woods analysis obtained in this research shows the climate in the Junggar terrane around the PTB was warm and humid and the temperature and precipitation remained relatively stable. It did not exist a heavy dryness in the earliest Triassic. Meanwhile, the Palaeo-Tethys megamonsoons did not influence the Junggar terrane along the east coast of mid-latitude Pangaea. Combined with the previously reported fossil woods, it shows that the climate had no prominent change from the Middle Permian to earliest Triassic.Plant fossil analysis show that the numbers of plant genera and species gradually decreased from 26 genera and 53 species in the Wuchiapingian, to 10 genera and 15 species in the Changhsingian, and only 6 genera and 7 species in the Induan. The trend in the plant assemblage reduction in the Junggar and Turpan basins appears to be indicative of a long, protracted extinction process that may have started well before the Permian-Triassic boundary. During the plant recovery period, the lycopsids (Annalepis) and ferns (Neocalamites and Pecopteris) played roles of pioneer species during the plant recovery period. / 二叠-三叠纪之交是地球历史上的关键时期。发生在二叠纪末期的大灭绝事件是最严重的生物灭绝事件。前人对此次灭绝事件的研究主要集中于海洋生物的变化，近年来越来越多的研究开始关注于这一时期陆地生态系统的变化。 位于中国西北部的准噶尔盆地和吐鲁番盆地出露了完整的陆相二叠-三叠系界线附近地层，因此在这一研究方面具有独特的优势。前期研究中在这一个地区建立了良好的岩石地层，生物地层和旋回地层格架。本文将集中解决二叠-三叠纪之交研究区的环境变化问题。我们选择了位于准噶尔盆地南缘的大龙口剖面和吐鲁番盆地北缘的桃树园剖面，两个陆相地层剖面作为论文的研究对象。在这一区域，二叠-三叠系之交地层是由梧桐沟组，锅底坑组和韭菜园组组成。我们在大龙口剖面和桃树园剖面二叠-三叠系地层中发现了大量木化石和植物印模化石，对剖面绘制了详细的地层柱状图。我们鉴定了木化石和植物印模化石种属,木化石年轮类型，分析了沉积相变化，进而用来识别研究区的环境变化。 我们对所采集到的130块木化石进行了切片，通过生物显微镜对其解剖结构进行研究，共发现了木化石5属6种，包括建立的三个新属：Junggaropitys，Xinjiangoxylon和 XTT-C-4 gen. nov.（还在审稿中）。这三个属均具有内始式的初生木质部和Protophyllocladoxylon 型次生木质部，其中Junggaropitys具有同质但异细胞的髓部；Xinjiangoxylon拥有具薄壁细胞和分泌管的髓部；XTT-C-4 gen. nov.的髓部中具有独特的板状支撑结构。我们应用CSDM曲线（平均值偏差累计曲线）分析木化石的年轮用以识别其生长季的条件和叶的寿命。CSDM曲线分析表明Junggaropitys dalongkouensis为一种常绿植物，叶的寿命为3-6年；XTT-C-4 gen. et sp. nov.也为常绿植物，叶的寿命3-15年。Septomedullopitys, Junggaropitys, Xinjiangoxylon和XTT-C-4 gen. nov.四个属的木化石均展示出Protophyllocladoxylon型次生木质部。我们对晚古生代全球发现的具有Protophyllocladoxylon型次生木质部的木化石进行了生物古地理分析，我们发现，在晚古生代，具有Protophyllocladoxylon型次生木质部植物，在南半球仅分布在冷温带地区；而在北半球和赤道地区，其分布在不同的气候带。对木化石的分析显示准噶尔地块在二叠-三叠系界线附近古气候温暖湿润，温度和降雨量相对稳定；古特提斯洋巨季风没有影响到东岸的泛大陆中纬度地区。结合前人对这一地区其他木化石研究，我们认为研究区的古气候自中二叠世至早三叠世早期没有显著的变化。植物化石分析显示，植物种属由吴家坪期的26属53种逐渐减少到长兴期的10属15种再到早三叠世印度期的6属7种。在准噶尔盆地和吐鲁番盆地，二叠-三叠系之交，植物显示了一个长时间的逐渐灭绝的过程。通过对比白垩纪-第三纪植物灭绝事件和现代恶劣环境下植物恢复的实例，我们发现石松类（脊囊属）和蕨类（新芦木属和栉羊齿属）在植物复苏阶段扮演着先驱分子的角色。我们对大龙口剖面，桃树园A和C剖面进行了沉积相分析。在大龙口剖面我们识别出4个主要的沉积相。梧桐沟组上部主要由辫状河相，短暂的河流系统或湖和冲积平原相组成。锅底坑组为湖（或池塘）相和洪泛平原相沉积。韭菜园组主要由冲积平原和湖（或池塘）相沉积组成。在桃树园地区，梧桐沟组上部至锅底坑组底部的一套地层主要是湖（或池塘）相和洪泛平原相沉积。锅底坑组下部为一套辫状河沉积。而锅底坑组上部为冲积平原和湖（或池塘）相沉积。韭菜园组主要为辫状河和洪泛平原沉积。对碎屑岩的样品岩相学分析显示跨越二叠-三叠系界线，沉积物物源一致。其中火山碎屑物来源于多个火山源。大龙口剖面和桃树园剖面在界线附近沉积物的物源保持一致，这说明，这两个剖面在二叠-三叠系之交时期处于同一个盆地，而博格达山隆起晚于这一时间。灰岩样品指示了湖泊环境的沉积。二叠纪末期的植物灭绝降低了河岸的强度，增加了坡地的沉积物的提供，进而增加了河道中沉积物的卸载。这导致了研究区在吴家坪期和长兴期界线附近和早三叠世的两次沉积相的改变。

Perm/Trias-Grenzprofile in den Regionen von Julfa (NW-Iran) und Abadeh (Zentral-Iran) zeigen eine Abfolge von drei charakteristischen Gesteinseinheiten, (1) den Paratirolites Limestone mit dem end-permischen Massensterbehorizont an seiner Oberkante, (2) den Boundary Clay und (3) die untertriassische Elikah-Formation mit der mit Conodonten definierten Perm/Trias-Grenze an seiner Basis. Die Karbonatmikrofazies zeigt eine Veränderung in den Profilen bei Julfa; innerhalb des Paratirolites Limestone ist eine zunehmende Anzahl von Intraklasten, Fe-Mn-Krusten und biogenen Verkrustungen erkennbar. Die Karbonatproduktion des späten Perms wurde mit der Ablagerung von mikrobiellen Karbonaten an der Basis der Elikah-Formation in Julfa erneuert. Die in den Profilen von Baghuk (Abadeh-Region) vorkommenden Mikrobialite sind vielfältig; es gibt groß-und kleinskalige, arboreszierendende Mikrobialit-Ansammlungen mit auffälliger Morphologie und innerer Struktur. In den Regionen von Julfa (NW-Iran) und Abadeh (Zentral-Iran) deutet eine deutliche und weltweit nachvollziehbare negative Kohlenstoffisotopenexkursion hin. Die rasche Exkursion der Kohlenstoffisotopenexkursion unterhalb des Aussterbehorizonts im obersten Bereich des Paratirolites Limestone wird durch eine stratigraphische Kondensation, die ein Defizit der Karbonatproduktion/Akkumulation und/oder eine schnelle geochemische Veränderung in Richtung Karbonatuntersättigung spiegelt, verstärkt. Dies deutet darauf hin, dass ein länger andauernder Mechanismus, wie die thermische Metamorphose von an organischem Material reicher Sedimente, und/oder verstärkte Verwitterung auf den Kontinenten, die negative Perm/Trias- Kohlenstoffisotopenexkursion verursacht haben könnte. Die Stickstoffisotopenwerte zeigen keinen Trend unterhalb des Aussterbehorizonts, was auf eine Kombination verschiedener Prozesse (Stickstofffixierung und ein Gleichgewichtszustand zwischen Nitratassimilation, Stickstoff-Fixierung und Denitrifikation) hinweist. / Permian-Triassic boundary sections in the Julfa (NW Iran) and Abadeh (Central Iran) regions display a succession of three characteristic rock units, (1) the Paratirolites Limestone with the end-Permian mass extinction horizon at its top, (2) the Boundary Clay, and (3) the Early Triassic Elikah Formation with the conodont Permian-Triassic boundary at its base. The carbonate microfacies reveals a change, in the sections near Julfa, within the Paratirolites Limestone with an increasing number of intraclasts, Fe-Mn crusts, and biogenic encrustation. A decline in carbonate accumulation occurs towards the top of this unit, finally resulting in a complete demise of the carbonate factory. The skeletal carbonate factory was restored with the deposition of microbial carbonates at the base of the Elikah Formation at Julfa. At Baghuk Mountain (Abadeh region) large- and small-scale, arborescent microbialite buildups with conspicuous morphology and internal structure occur. In the Julfa and Abadeh regions, a prominent and globally traceable negative carbon isotope excursion indicates major perturbations of the carbon cycle around the P-Tr boundary. The sudden carbonate carbon isotope decrease below the extinction horizon is triggered by stratigraphic condensation that mirrors a deficit of the carbonate production/accumulation and/or a rapid geochemical change towards carbonate undersaturation. The negative carbon isotope trend before extinction horizon is gradual, suggesting that a longer lasting mechanism, such as thermal metamorphism of organic-rich sediments, and/or enhanced weathering on the continents may have caused the negative Permian-Triassic stable carbon isotope excursion. The bulk nitrogen isotope values in the sections of the Julfa region do not show any trend below the extinction horizon, pointing to rather mixing of different processes (nitrogen fixation and an equilibrium state between nitrate assimilation, nitrogen fixation, and denitrification).