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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Neolithic agricultural management in the Eastern Mediterranean : new insight from a multi-isotope approach

Vaiglova, Petra January 2016 (has links)
The work presented in this dissertation explores the nature of agro-pastoral strategies developed by Neolithic farmers as a way to understand how early food production was inter-twined with environmental and socio-economic opportunities and constraints. Towards this end, a multi-isotope approach is used to address questions of scale and intensity of crop cultivation and animal management at the archaeological sites of Kouphovouno, southern Greece, Makriyalos, northern Greece, and Çatalhöyük, south-central Turkey. Measurements of stable carbon, nitrogen, oxygen and strontium isotope values of carbonized plant remains, human and animal bone collagen and animal tooth enamel are used to examine the similarities and differences in the types of treatments that individual species of plants and animals received during the agricultural cycle at the distinct locations. The results show that farmers at the three sites developed variable methods for exploiting the arable and pastoral landscape and catering to their economic and culinary needs. The discussion considers the implications of these findings to our understanding of the complexity and adaptability of early farming systems.
42

Isotopes in the landscape : carbon and nitrogen isotopes of domestic animals and their application to the archaeology of the Upper and Middle Thames Valley in the Neolithic to Roman periods

Hamilton, Julie January 2015 (has links)
This thesis deals with the development of farming landscapes in the Thames Valley from the Neolithic to the Roman period (4000 BCE - 410 CE). The focus is on the major domestic animal species, cattle, sheep and pig, and their roles in the agroecosystem, traced using carbon and nitrogen isotope ratios measured in collagen. The large dataset of faunal isotope values from a limited area, obtained from sites with extensive archaeological and environmental information, allowed a thorough characterisation of variability in isotope values, within and between species, sites, archaeological periods, and landscape regions. Isotope ratios in a flock of modern sheep showed less variability than archaeological assemblages. Linear mixed models were used to analyse variation in isotope values in 1490 archaeological samples from 23 sites. The pattern of change over time differed for cattle, sheep and pig, reflecting both wide-scale environmental change and changes in animal management. d13C values of cattle and pigs reflected the loss of primary closed-canopy woodland. Pig management changed from an emphasis on woodland resources to a closer association with settlement and consumption of anthropogenic waste. Herbivore d15N values probably reflect variations in the intensity of pasture use and association with arable farming. Climatic cooling since the post-glacial thermal maximum cannot explain these varied trajectories of change. Variation between sites in faunal isotope values was related to landscape regions. Faunal isotope values at individual sites were useful in site interpretation in the context of other evidence. The trend in pig and cattle δ13C values with time was widely found in the UK, as expected if it represents forest clearance. In the Neolithic, cattle management was similar to the UK at central and eastern European Neolithic sites, but pig management was different. Patterns of faunal isotope values and their changes over time, analysed in the context of archaeological and environmental information, can contribute to the interpretation of sites, and give a unique perspective on changes in farming practice and their effects on the landscape.
43

Variação na composição isotópica do carbono e nitrogênio da matéria orgânica e biomassa da coroa foliar de Aechmea aquilega (Salisb.) griseb bromeliaceae em caatinga, agreste e mata atlântica de Sergipe / CHANGE IN COMPOSITION OF CARBON AND NITROGEN ISOTOPE OF ORGANIC MATTER AND BIOMASS LEAF CROWN AECHMEA AQUILEGA (SALISB.) GRISEB BROMELIACEAE CAATINGA IN, THE ATLANTIC AND AGRESTE SERGIPE.

Bispo, Simone Mesquita 14 September 2011 (has links)
The bromeliads are conspicuous elements of the landscape and vegetation of Brazil, in the state of Sergipe occurs in the Atlantic forest ecosystems in the ecotone and caatinga. Bromeliads have an semiarid environment in adaptive capacity to occupy various habitats both on the ground, rocks and trees is partly attributed to its CAM photosynthetic response type obligatory and/or facultative. Isotopic studies to determine the leaf carbon isotope values show that these range from -10 to -28 of PDB standard. This study analyzed the isotopic composition of carbon and nitrogen organic matter and leaf in the crown of Aechmea aquilega at three habitats: Caatinga (white forest sclerophilous), Atlantic forest (Pirambu) and a transition area between Atlantic Forest and Caatinga, an exception area of white sand-quartizose. In each habitat were collected 4 bromeliads that live in isolated bush and four plants in the ground substrates with the objective of evaluating the hypothesis of facilitation of bromeliad-tank as accumulator of organic matter. The leaves and organic matter of the crown leaves were dried in a ventilated oven, crushed, sieved and made isotopic analysis of carbon-13, nitrogen-15, and total C:N on CENA-USP laboratories. The results of analysis of content C: N and isotope ratios showed significant variations of carbon and nitrogen in the crown of leaves, as well as the total abundance in both leaf biomass and particulate organic matter. Plants of Caatinga and Atlantic Forest obligatory assimilate carbon, while the ecotone of the bromeliads, the National Park of Serra de Itabaiana responded as much as in CAM binding to isolated bushes just as the composition of bromeliads is probably of autoctone origin-open grassy areas. The isotope ratio of the 15N is 22 times more enriched in the bromeliad leaf biomass of scrub plants in relation to the white sands and 2.6 higher than in the Atlantic forest habitat, while the particulate organic matter was enriched in all habitats, but the source this organic matter require explanation, however, the study supported the hypothesis on the functional role of facilitation in the three bromeliad habitats. According to the study, we observed that the adaptive success of higher plants associated with scrub bushes when the same was not observed in other habitats. In white sands bromeliads-tank, the substrate is sandy-quartzes hot, highly permeable, facilitating evaporation and drought in the summer suggesting that there is a condition of great stress, which these tank bromeliads are well adapted to soil and not on trees. / Estudos isotópicos para determinar os valores dos isótopos do carbono foliar mostram que estes variam -10 a -28 do padrão PDB. Este estudo analisou a composição isotópica do Carbono e Nitrogênio foliar e a matéria orgânica acumulada na coroa foliar de Aechmea aquilega de três habitats: Caatinga (Poço Verde), Mata Atlântica (Pirambu) e em um área de transição Mata Atlântica Caatinga (Areia Branca). Em cada habitat foi coletado quatro bromélias que vivem em moitas e quatro plantas isoladas em substratos do chão com o objetivo de avaliar a hipótese de facilitação da bromélia-tanque como acumuladora de matéria orgânica. As folhas e a matéria orgânica da coroa foliar foram secas em estufa ventilada, trituradas, peneiradas e as análises isotópicas do carbono, nitrogênio, teor de carbono e nitrogênio total foram realizadas no CENA-USP. Os resultados das analises de teor C:N e razões isotópicas mostraram variações significativas do carbono e nitrogênio na coroa foliar, assim como na abundância total tanto na biomassa foliar como na matéria orgânica particulada. As plantas da Caatinga e Mata Atlântica assimilam carbono facultativamente, enquanto as bromélias do ecótono, Parque Nacional da Serra de Itabaiana responderam como CAM obrigatórias tanto quando em moitas como isoladas, assim como estas bromélias tem composição de origem autóctone provavelmente de áreas abertas-graminosa. A razão isotópica do N15 é 22 vezes mais enriquecido na biomassa foliar das bromélias da Caatinga em relação às plantas das Areias Branca e 2,6 maiores que em habitat de Mata Atlântica, enquanto a matéria orgânica particulada em todos habitats foi enriquecida, porém a origem desta matéria orgânica necessita de explicações, todavia, o estudo apoiou a hipótese de facilitação no papel funcional da bromélia nos três habitats. De acordo com o estudo, foi observado que o sucesso adaptativo maior das plantas da Caatinga quando associada a moitas o mesmo não foi verificado nos outros habitats. Nas Areias Brancas, o substrato arenoso-quartizoso é quente, altamente permeável, favorecendo a evaporação e déficit hídrico no verão o que sugere que haja uma condição de grande estresse, a qual essas bromélias-tanque estão bem adaptadas no solo e não nas árvores.
44

Stable Carbon And Nitrogen Isotope Analyses Of Subfossil Rats From Liang Bua (flores, Indonesia)

Anderson, Kelly C 01 January 2011 (has links)
This research study investigated the level of bone collagen preservation of rat femora from Liang Bua cave on the island of Flores, Indonesia, as well as conducted carbon and nitrogen stable isotopic analyses on well preserved samples. Although Flores is located in a hot intermediate tropical zone and the burial environment of the bone samples within the cave is considered less than optimal for collagen preservation, significant preservation of the bone collagen was found. Collagen yields, C:N ratio and carbon and nitrogen concentrations were investigated. However, this research study argues that carbon and nitrogen concentrations are an appropriate means to determine preservation on its own. According to the carbon and nitrogen concentration data 32 samples were considered well preserved. Carbon and nitrogen stable isotopic analyses were conducted on the 32 preserved samples. According to the carbon data a significant shift in the δ13C values from a C3 signature to a C4 signature occurred prior to 2,750 years ago. This shift is indicative of the introduction of a non-endemic C4 plant, which is believed to be either foxtail millet or sugarcane. Since this shift occurs abruptly it indicates that the introduction of agriculture to Flores occurred at one time and has continued to present day
45

Reconstruction et étude de la variabilité du régime alimentaire des sociétés préhispaniques de la basse vallée de Santa, Pérou

Desrosiers, Emilie 01 1900 (has links)
Ce projet de recherche porte principalement sur la reconstruction du régime alimentaire à l’aide d’une approche paléochimique. Des analyses isotopiques du carbone de l’azote ont été réalisées sur le collagène des os sur un échantillon de trente-huit individus provenant de trois sites différents de la basse vallée de Santa, sur la côte nord du Pérou : El Castillo, Guadalupito et Huaca China. Parmi les individus sélectionnés, certains sont affiliés aux groupes des Gallinazo, des Mochica, des Tanguche ou des Chimú couvrant ainsi la Période intermédiaire ancienne, l’Horizon moyen et la Période intermédiaire récente. L’approche isotopique a été utilisée afin de caractériser dans un premier temps, le régime alimentaire de la population globale en la comparant à d’autres groupes préhispaniques de l’Aire andine. Les résultats obtenus sur trente-deux individus suggèrent une alimentation variée incluant le maïs ainsi que des ressources marines, illustrant que ces groupes agriculteurs exploitaient les deux types d’écosystèmes à leur portée. Ces résultats sont supportés par l’analyse du carbone sur l’apatite pour cinq individus. Le second but fut d’étudier la variabilité du régime alimentaire entre les différents individus de l’échantillon, en fonction de la période d’occupation, du site de provenance, de l’affiliation culturelle, de l’âge et du sexe et du statut social. La petite taille de l’échantillon a limité considérablement la discussion de ces différents paramètres. Il a toutefois été possible de remarquer un accès aux ressources riches en protéines plus avantageux pour les hommes et la présence de possibles différences dans l’alimentation chez les individus juvéniles. Finalement, la confrontation des données funéraires à la reconstruction du régime alimentaire a été faite pour cinq cas particuliers de pratiques funéraires provenant du site El Castillo, premier centre régional de la civilisation Mochica dans la basse vallée de Santa. Dans tous les cas, le régime alimentaire suggéré par les compositions isotopiques supporte les interprétations des statuts sociaux de ces individus faites à partir des contextes funéraires. / This research focuses on the reconstruction of diet using a chemical approach. Carbon and nitrogen isotopes were analyzed on a bone collagen sample of thirty-eight individuals from three different sites of the Lower Santa valley, on the north coast of Peru : El Castillo, Guadalupito and Huaca China. Among those individuals selected, some are affiliated with groups of Gallinazo, Moche, Tanguche and Chimu, dated to the Ancient Intermediate Period, Middle Horizon and Recent Intermediate Period. The isotopic approach has been used to characterize in a first step, the diet of the entire population by comparing with some other prehispanic groups from the Andean area. The results of thirty-two individuals suggest a mixed diet including maize and marines resources, showing that these agriculturist groups exploited their surrounding ecosystems. These results are supported by the carbon analysis on bone apatite for five individuals. The second aim was to study the variability of the diet between individuals in the sample, depending on the time period, site, cultural identity, age and sex and social status. The small sample size has considerably limited the discussion of these parameters. However, it was possible to note a more preferential access to high proteins resources for men and some possible differences in diet among juveniles. Finally, the comparison between dietary reconstruction and funerary patterns was made for five cases of burial pratices at El Castillo site, the first Moche regional center in the Lower Santa valley. In all cases, diet suggested by isotopic compositions is consistent with interpretations of the funerary context about the individual status.
46

USING STABLE ISOTOPES TO ASSESS LONGITUDINAL DIET PATTERNS OF BLACK BEARS (URSUS AMERICANUS) IN GREAT SMOKY MOUNTAINS NATIONAL PARK

Teunissen Van Manen, Jennapher Lynn 01 May 2011 (has links)
Long-term diet patterns based on stable isotope analysis may be helpful to understand changes in food selection of black bears (Ursus americanus) over time and guide management programs to reduce human-bear conflicts. An enriched stable carbon isotope signature indicates an anthropogenic food source in the diet and an enriched nitrogen signature indicates a higher tropic level for a species. I examined longitudinal feeding patterns from 117 hair samples of black bears live captured in Great Smoky Mountains National Park during 1980–2001 using stable carbon and nitrogen isotope analysis from hair samples. I developed a set of a priori models to examine if sex, age class, year, weight class, total hard mast index, white oak index (Quercus spp.), red oak index (Quercus spp.), nuisance status and hog harvest (Sus scrofa) affected stable isotope signatures. I used model averaging and an estimator of the unconditional variance was used to account for model uncertainty. The δ[delta]13C signatures differed by weight class with above average weight, (ß[Beta] = 0.76‰; 95% CI = 0.28 to 1.23) and average weight (ß[Beta] = 0.42‰; CI = 0.06 to 0.78) showing enriched values compared to below average bears. Bears had enriched δ[delta]15N signatures in years with low white oak mast production (ß[beta] = -0.19, CI = -0.34 to -0.03) and depleted when white oak hard mast was abundant. Sub adult bears had enriched δ[delta]15N signatures compared to adult and older adult bears. Variation of nitrogen values was small during 1980–1991 ( = 2.57, SD = 0.28) but increased substantially during 1992–2000 ( = 2.29, SD = 0.71) when there was substantial variation in hard mast production. Bears in better physical condition appear more likely to access anthropogenic food sources. In years of low white oak acorn production, the larger bears and sub adult bears are more likely to turn to alternative food sources. The long term variation detected in this study is important in identifying which bears are potentially more likely to seek out the anthropogenic food sources when changes occur in availability of natural foods.
47

Reconstruction et étude de la variabilité du régime alimentaire des sociétés préhispaniques de la basse vallée de Santa, Pérou

Desrosiers, Emilie 01 1900 (has links)
Ce projet de recherche porte principalement sur la reconstruction du régime alimentaire à l’aide d’une approche paléochimique. Des analyses isotopiques du carbone de l’azote ont été réalisées sur le collagène des os sur un échantillon de trente-huit individus provenant de trois sites différents de la basse vallée de Santa, sur la côte nord du Pérou : El Castillo, Guadalupito et Huaca China. Parmi les individus sélectionnés, certains sont affiliés aux groupes des Gallinazo, des Mochica, des Tanguche ou des Chimú couvrant ainsi la Période intermédiaire ancienne, l’Horizon moyen et la Période intermédiaire récente. L’approche isotopique a été utilisée afin de caractériser dans un premier temps, le régime alimentaire de la population globale en la comparant à d’autres groupes préhispaniques de l’Aire andine. Les résultats obtenus sur trente-deux individus suggèrent une alimentation variée incluant le maïs ainsi que des ressources marines, illustrant que ces groupes agriculteurs exploitaient les deux types d’écosystèmes à leur portée. Ces résultats sont supportés par l’analyse du carbone sur l’apatite pour cinq individus. Le second but fut d’étudier la variabilité du régime alimentaire entre les différents individus de l’échantillon, en fonction de la période d’occupation, du site de provenance, de l’affiliation culturelle, de l’âge et du sexe et du statut social. La petite taille de l’échantillon a limité considérablement la discussion de ces différents paramètres. Il a toutefois été possible de remarquer un accès aux ressources riches en protéines plus avantageux pour les hommes et la présence de possibles différences dans l’alimentation chez les individus juvéniles. Finalement, la confrontation des données funéraires à la reconstruction du régime alimentaire a été faite pour cinq cas particuliers de pratiques funéraires provenant du site El Castillo, premier centre régional de la civilisation Mochica dans la basse vallée de Santa. Dans tous les cas, le régime alimentaire suggéré par les compositions isotopiques supporte les interprétations des statuts sociaux de ces individus faites à partir des contextes funéraires. / This research focuses on the reconstruction of diet using a chemical approach. Carbon and nitrogen isotopes were analyzed on a bone collagen sample of thirty-eight individuals from three different sites of the Lower Santa valley, on the north coast of Peru : El Castillo, Guadalupito and Huaca China. Among those individuals selected, some are affiliated with groups of Gallinazo, Moche, Tanguche and Chimu, dated to the Ancient Intermediate Period, Middle Horizon and Recent Intermediate Period. The isotopic approach has been used to characterize in a first step, the diet of the entire population by comparing with some other prehispanic groups from the Andean area. The results of thirty-two individuals suggest a mixed diet including maize and marines resources, showing that these agriculturist groups exploited their surrounding ecosystems. These results are supported by the carbon analysis on bone apatite for five individuals. The second aim was to study the variability of the diet between individuals in the sample, depending on the time period, site, cultural identity, age and sex and social status. The small sample size has considerably limited the discussion of these parameters. However, it was possible to note a more preferential access to high proteins resources for men and some possible differences in diet among juveniles. Finally, the comparison between dietary reconstruction and funerary patterns was made for five cases of burial pratices at El Castillo site, the first Moche regional center in the Lower Santa valley. In all cases, diet suggested by isotopic compositions is consistent with interpretations of the funerary context about the individual status.
48

The Role of Biological Production in Pleistocene Atmospheric Carbon Dioxide Variations and the Nitrogen Isotope Dynamics of the Southern Ocean.

Sigman, Daniel M., January 1997 (has links)
Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering, 1997. / "September 1997." "Funding was provided by National Science Foundation Grant OCE-9201286, National Science Foundation Graduate Fellowship Program, and the JOI/USSAC Ocean Drilling Graduate Fellowship Program." Includes bibliographical references (p. 152-153).
49

Laminations sédimentaires et variabilité climatique et océanographique haute-fréquence sur la marge péruvienne / Sedimentary laminations and high-frequency climatic and oceanographic variability on the Peruvian margin

Fleury, Sophie 04 June 2015 (has links)
Le Système d’Upwelling Péruvien (PUS) et la Zone à Oxygène minimum (OMZ) qui y est associée font partie des régions les plus marquées par les variations climatiques de type El Niño Southern Oscillation (ENSO), tant à l’échelle interannuelle qu’à l’échelle décennale. Or, peu d’enregistrements de l’impact de l’ENSO sur cette zone géographique atteignent ces résolutions temporelles, malgré des conditions propices à la conservation de dépôts sédimentaires laminés.Nous avons analysé ces archives sédimentaires à l’échelle de la lamine et en utilisant des marqueurs sédimentologiques, micro paléontologiques et géochimiques afin de retracer les variations de tous les paramètres susceptibles de répondre aux changements climatiques(précipitations, productivité, dénitrification, températures océaniques de surface). Cette approche nous a permis de disposer d’un enregistrement complet des conditions environnementales dans l’OMZ du Pérou à des échelles pluri-annuelle à multidécennale, ce qui est inégalé sur des périodes au-delà du dernier millénaire. Nous avons ainsi pu mettre en évidence une forte empreinte de la circulation de Walker sur le PUS. Cet impact est modulé par les régions extra tropicales de l’hémisphère Nord, en particulier par l’Oscillation Nord-Atlantique (NAO) à l’échelle multidécennale, par la circulation thermohaline à l’échelle centennale et par l’Anticyclone Sibérien à l’échelle millénaire. / The Peruvian Upwelling System (PUS) and the corresponding Oxygen Minimum Zone (OMZ) are part of the regions where the imprint of climatic variations due to El Niño Southern Oscillation (ENSO) at the interannual and multidecadal timescales is the strongest. However,only a few records of ENSO-like climatic variability reach such short timescales in thisgeographical area, despite prevailing conditions favorable to the preservation of laminatedsediments. We analyzed these sedimentary archives at the scale of the lamination, using sedimentology, micropaleontology and geochemistry. The aim was to trace variations in all parameters responding to climatic changes (rainfall, productivity, denitrification, sea surfacetemperatures). This approach has provided a full record of environmental conditions in thePeruvian OMZ at multiannual and multidecadal timescales for the first time on time intervals exceeding the last millennium. We thus evidenced a strong imprint of the Walker circulation on the PUS. This impact is paced by the extratropical northern hemisphere, especially by the North Atlantic Oscillation (NAO) at the multidecadal timescale, by the thermohaline circulation at the centennial timescale and by the Siberian High at the millennial timescale.
50

The Permian-Triassic boundary in the NW-Iranian Transcaucasus and in Central Iran

Leda, Lucyna 19 June 2020 (has links)
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).

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