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 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

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).