Das Spurengas Lachgas (N₂O) trägt zur Klimaerwärmung und Zerstörung der Ozonschicht in der Atmosphäre bei. Mit einem Anteil von ca. 70% sind landwirtschaftliche Böden weltweit Hauptverursacher der hohen anthropogenenN₂O Emissionen. N₂O entsteht in Böden durch verschiedene mikrobiologische Prozesse, bei denen N₂O unter anderem aus düngerbürtigem N gebildet wird. Die Entwicklung effektiver Minderungsmaßnahmen wird erst möglich, wenn ein Verständnis der N₂O Quellprozesse und ihrer Dynamik in Böden vorhanden ist. In dieser Studie wurde die Denitrifikation als ein Quellprozess untersucht, der zusammen mit Nitrifikation und Nitrifizierer-Denitrifikation hauptsächlich für die N₂O Emissionen aus Böden verantwortlich ist. Die Denitrifikation beschreibt die Reduktion von Nitrat (NO₃^-) zu N2, wobei Nitrit (NO₂^-), Stickstoffmonoxid (NO) und N₂O Zwischenprodukte dieses Reaktionsweges sind. Lange Zeit galten heterotrophe Bakterien als alleinige Verursacher von N₂O Emissionen aus der Denitrifikation. Im Jahr 1972 wurde allerdings in Versuchen mit Pilzreinkulturen nachgewiesen, dass auch Pilze in der Lage sind, N₂O über die Denitrifikation zu bilden. Zwei Jahrzehnte später wurde gezeigt, dass den meisten Pilzen das Enzym N₂O-Reduktase fehlt. Somit ist nicht N₂, sondern N₂O das hauptsächliche Endprodukt der pilzlichen Denitrifikation. Dies lässt vermuten, dass die Bildung von N₂O durch pilzliche Denitrifikation noch unterschätzt wird, vorausgesetzt Pilze und Bakterien haben ähnliche Prozessraten. Bisher wurde jedoch nicht ausgiebig erforscht, welchen Anteil die einzelnen mikrobiellen Gemeinschaften an der N₂O Bildung tatsächlich haben. Zur Unterscheidung der N₂O Bildungsprozesse in Bezug auf die beteiligten Mikroorganismen stellt die Isotopenanalyse von N₂O eine vielversprechende Anwendung dar. Vor allem die ¹⁵N-Positionspräferenz im N₂O (SP = site preference, d.h. die Differenz zwischen den δ¹⁵N-Werten der außenständigen und zentralen N-Atome im linearen N₂O-Molekül) aus der Denitrifikation zeigte starke Unterschiede zwischen Reinkulturen einiger Bakterien (SP = -11 bis 0 ‰) und zwei untersuchten Pilzen (SP ~ 37 ‰). Jedoch wurden Bakterienreinkulturen bisher ausgiebiger untersucht als Pilzreinkulturen, auch wenn bekannt ist, dass sich die beteiligten Enzyme bei der Denitrifikation, bis auf die NO-Reduktase, zwischen Bakterien und Pilzen nicht unterscheiden. Die verschiedenen NO-Reduktasen sind vermutlich die Ursache für die unterschiedlichen SP-Werte des von Pilzen und Bakterien produzierten N₂O. Des Weiteren wurde bei Bakterien ein Austausch der Sauerstoffatome von Zwischenprodukten der Denitrifikation und dem umgebenden Wasser gefunden, der zwischen 4 und 100% beträgt. Ob es einen solchen Sauerstoffaustausch auch bei Pilzen gibt, ist bisher jedoch unerforscht. Würde der Sauerstoffaustausch bei pilzlicher Denitrifikation nicht erfolgen, ermöglichte dies neben der unterschiedlichen SP eine weitere Unterscheidung der Herkunft des N₂O. Der Sauerstoffaustausch würde signifikante Unterschiede in der O Isotopensignatur im N₂O pilzlicher bzw. bakterieller Herkunft verursachen. In der vorliegenden Studie, die Aufschluss über die pilzliche N₂O Produktion aus der Denitrifikation geben soll, wurden drei Hauptthemen behandelt. In einem Isotopen-Tracerexperiment mit <up>18</sup>O-angereichertem Wasser wurde untersucht, ob bei sechs Pilzreinkulturen ein Sauerstoffaustausch zwischen Wasser und Zwischenprodukten der Denitrifikation stattfindet. Die Pilzreinkulturen zeigten tatsächlich durch Inkorporation von ¹⁸O aus Wasser in N₂O einen Sauerstoffaustausch. Auch Pilze können bis zu 100% des O während der Denitrifikation austauschen. Eine Unterscheidung zwischen der Denitrifikation durch Bakterien und Pilze anhand der Sauerstoffsignatur ist somit nicht möglich. Das zweite Thema sollte Auskunft darüber geben, ob hohe SP-Werte des N₂O aus der Denitrifikation bei Pilzreinkulturen allgemeingültig sind. Neben den zwei bisher untersuchten wurden vier weitere Pilzreinkulturen inkubiert. Diese Studie zeigte für die getesteten Pilzarten ebenfalls höhere SP-Werte (SP = 19.7 bis 32.6 ‰) im Vergleich zum Wertebereich von Bakterienreinkulturen. Basierend auf den Ergebnissen zum Sauerstoffaustausch aus dem Isotopen-Tracerexperiment wurde für die jeweiligen sechs Pilze, anhand der im Rahmen dieses Versuchs ermittelten natürlichen Sauerstoffisotopensignaturen, Mechanismen zur O Isotopenfraktionierung untersucht. Dafür wurden, neben den Werten des Sauerstoffaustausches und der natürlichen O Isotopensignatur der Pilzreinkulturen, Werte für Fraktionierungseffekte aus der Literatur in einem Isotopenfraktionierungsmodell angewendet, um die Beteiligung der verschiedenen Enzyme, die während der Denitrifikation an dem Sauerstoffaustausch beteiligt sind, abzuschätzen. Im Vergleich zu den NO₃^-- und NO-Reduktasen wies die N₂O^--Reduktase einen maßgeblich höheren Sauerstoffaustausch auf. Die Erkenntnisse aus den Experimenten mit den Pilzereinkulturen sollten im Rahmen des dritten Themas auf Ihre Übertragbarkeit auf die mikrobiellen Gemeinschaften in Böden untersucht werden, indem Bodeninkubationsversuche mit selektiver Hemmung der Organismengruppen (Pilze und Bakterien) durchgeführt wurden. Bei dieser Modifizierung der Methode zur Substrat-induzierten Respiration mit selektiver Hemmung (SIRIN) sollte untersucht werden, ob sich die spezifischen SP-Werte für Bakterien und Pilze nach selektiver Wachstumshemmung von Bodengemeinschaften durch spezifische Antibiotika nachweisen lassen. Die Ausprägung des Hemmungseffekts auf SP-Werte in den drei getesteten Böden entsprach nicht den Erwartungswerten, die sich aus den SP-Werten der Pilz- und Bakterienreinkulturen ergaben. Die ermittelten SP-Werte lagen in den meisten Fällen im Bereich jener bakterieller Reinkulturen und eine Hemmung der Bakterien führte in keinem Fall zu der erwarteten Veränderungen der SP-Werte. Folglich konnten die SP-Werte dieser Versuche nicht dazu dienen, die N₂O Bildung in den gehemmten Varianten den verschiedenen Organismengruppen zu zuordnen. Ungeklärt blieb, ob dies durch fehlende Eignung der modifizierten SIRIN-Methode zu erklären ist, oder ob die an Reinkulturen beobachteten SP-Unterschiede zwischen Pilzen und Bakterien nicht auf mikrobielle Gemeinschaften der Versuchsböden übertragbar sind. Im Hinblick auf nach wie vor bestehende methodische Defizite bei der Untersuchung der Pilzdenitrifikation im Boden sollte dies in weitergehenden Studien geklärt werden.

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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23919号 / 工博第5006号 / 新制||工||1781(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 今堀 博, 教授 田中 庸裕, 教授 跡見 晴幸 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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La composition isotopique de l’eau (dO18 et dD) est couramment utilisée pour étudier le cycle de l’eau actuel et passé ainsi que ses variations. Alors que dans les zones polaires, cet outil géochimique représente les fondements de la reconstitution des climats polaires passés, de multiples questions demeurent quant aux facteurs pilotant la composition isotopique de l’eau dans les tropiques.Afin de répondre à ces questions, le présent travail de thèse a porté sur la réalisation de mesures en continu de la composition isotopique de la vapeur d’eau sur l’île de La Réunion (océan Indien), ainsi que sur l’évaluation du potentiel de ces mesures pour la compréhension des processus atmosphériques humides prévalant sur cette zone géographique. L’implantation d’un spectromètre laser à l’Observatoire Atmosphérique du Maïdo nous a permis d’obtenir une chronique de trois ans de mesures.Dans un premier temps, les différentes variabilités temporelles que présentent nos mesures ont été étudiées. Les enregistrements ne montrent aucune cyclicité saisonnière sur la composition isotopique de la vapeur d’eau. Elles indiquent en revanche une forte cyclicité diurne, ainsi qu’une variabilité synoptique associée à des évènements cycloniques.Dans un second temps, nous montrons que cette cyclicité diurne résulte de phénomènes de mouvement de couche limite atmosphérique, avec une vapeur marine qui atteint l’Observatoire durant la journée, alors que des masses d’air en provenance de la troposphère libre y parviennent durant la nuit. La présence de certaines nuits significativement plus appauvries en dO18 et dD reflète (1) une modification de la circulation atmosphérique régionale avec un renforcement des subsidences au niveau de La Réunion, lié à la position du Jet Subtropical durant l’hiver austral, et (2) tantôt une intensification de la subsidence au niveau de La Réunion, tantôt des processus de condensation locaux ou régionaux durant l’été austral.Enfin, l’étude des phénomènes cycloniques indique qu’au cours de ces périodes, un fort appauvrissement de la composition isotopique de la vapeur est observé. Celui-ci survient 2 à 3 jours avant et perdure jusqu’à 3 jours après le passage du système. Durant cette période, l’évolution de la composition isotopique de la vapeur d’eau présente une sous-structure. On note (1) un appauvrissement isotopique qui est fonction de la distance au centre du système, (2) un enrichissement isotopique au niveau du mur du système, et (3) des évolutions abruptes de la composition isotopique de la vapeur d’eau dans les bandes précipitantes dues à des processus de mélange, de condensation et/ou de recharge. / The isotopic composition of water vapor (dO18 and dD) is commonly used to study present and past water cycle and its varations. If this geochemical tool has been widely used to study past polar climates, many questions remain about the factors governing the isotopic composition of water in the tropics.The goal of this thesis is (1) to monitor the isotopic composition of water vapor in Reunion island (Indian Ocean), and (2) to evaluate the potential of theses measurements for understanding humid climate processes. We have set up a laser spectrometer at the Maïdo Atmospheric Observatory, allowing us to obtain a three-year chronicle of measurements.First, we analyze the temporal variability in our measurements. The isotopic composition of water vapor does not record any seasonal cyclicity. On the other hand, a strong diurnal cycle is visible, as well as a synoptic variability associated with cyclonic events.We then focus on the diurnal cycle. We show that it results from atmospheric boundary layer motions, with a marine vapor reaching the Observatory during the day, and air masses originating from the free troposphere reaching the Observatory during the night. During some nights, vapor is significantly more depleted in dO18 and dD. During the austral winter, this phenomenon is due to a modification of the regional atmospheric circulation causing a reinforcement of subsidences at Reunion Island, related to the position of the Subtropical Jet. During the austral summer, this phenomenon is sometimes due to an intensification of the subsidence at Reunion Island, and at other times to local or regional condensation processes.Finally, we focus on cyclonic events. During these periods, a strong isotopic depletion of the vapor is observed. We show that this depletion occurs 2 to 3 days before the system and continues until 3 days after. During this period, the evolution of the isotopic composition of the water vapor has a substructure. We note (1) an isotopic depletion that is a function of the distance to the center of the system, (2) an isotopic enrichment at the system wall, and (3) an abrupt evolutions of the isotopic composition of the water vapor in the rainbands due to mixing, condensation and/or recycling processes.

Aktuelle Klimamodelle prognostizieren, dass viele bedeutendeWaldregionen in Mitteleuropa zukünftig einer steigenden Frequenz und höheren Intensität von Dürreperioden ausgesetzt sein werden. Buchendominierte Wälder bilden einen wichtigen Bestandteil dieser Waldregionen. Der Mangel hinsichtlich der Wasserversorgung ist eine der wichtigsten limitierenden Faktoren für das Wachstum der Pflanzen sowie der damit verbundene reduzierte Zugewinn an Kohlenstoff. Ein weiterer bedeutender Stressfaktor ist die Konkurrenz zwischen sowie innerhalb Pflanzengemeinschaften. Aufgrund dieser Tatsache ist es wichtig, die pflanzenphysiologischen Mechanismen während der Trockenheit sowie interspezifische und intra-spezifische Konkurrenz in buchendominierten Waldökosystemen zu verstehen. Die vorliegende Arbeit untersucht den Zusammenhang von Kohlenstoff- und Wasserhaushalt und deren Wechselwirkungen sowie die Transportwege während der Trockenheit auf unterschiedlichen räumlichen (Blattebene bis Bestandesebene) und zeitlichen (kurzfristig bis langfristig) Skalen. Insgesamt wurden sechs Arten ausgewählt (Fagus sylvatica, Acer platanoides, Fraxinus excelsior, Impatiens noli tangere, Mercurialis annua und Allium ursinum). Alle Arten haben verschiedene Strategien entwickelt, um Konkurrenz und Trockenstress zu bewältigen, zu verhindern oder zu tolerieren. In Abhängigkeit von der Trockenstressintensität wurden geringe Effekte, in der Mesophyllleitfähigkeit (gm), intrinsische Wassernutzungseffizienz (iWUE) sowie in der Transportmenge an neuen Assimilaten beobachtet. / Current climate models predict that many important forest regions in Central Europe will experience increasing frequencies and severities of drought periods. Beech-dominated forests are an important part of these forest regions. Shortage in water supply is one of the most important limiting factors for growth of plants and thereby linked to a reduced carbon gain. Another key stressor is the competition between as well as within a plant communities. Due to this fact it is important to understand the plants physiological mechanisms during drought as well as inter-specific and intra-specific competition in beech dominated forest ecosystems. This present study documents the interrelation of carbon and water balance and the interactions of its pathways during drought on different spatial (leaf area to the stand level) and temporal scales (intra-annual to decadal). Six relevant species were selected in total (tree species: Fagus sylvatica, Acer platanoides, Fraxinus excelsior and species from the understorey of beech dominated forests: Impatiens noli tangere, Mercurialis annua and Allium ursinum). All of them have developed various strategies to cope with competition and avoid or tolerate drought stress. Depending on the drought intensity (e.g. moderate realistic drought) small effects in mesophyll conductance (gm), intrinsic water use efficiency (iWUE) and amount of new assimilates within trees occurred.

In this project the photodegradation of 3,5-diamino-6-chloro-N-(2-(methylamino)ethyl)pyrazine-2-carboxamide was studied. A hypothetical degradation pattern for the compound was proposed and the aim of the project was to study the formed secondary photodegradants and to, if possible, structure elucidate some of these compounds. In order to do this, the parent compound was photodegraded in two steps, where a primary photodegradant was isolated using semi-preparative supercritical fluid chromatography (SFC) and then further degraded into the secondary photodegradants. The photodegradation was first carried out in aqueous solution, where the parent compound was irradiated in UV-A light of 300-400 nm. This resulted in a primary photodegradant with a molecular ion of m/z = 227, where the chloride in position 6 of the pyrazine group had been replaced by a hydroxyl group. During the large scale photodegradation, prior to the preparative purification, the yield of primary photodegradant was very low due to the photodegradation being dependent on both sample volume and concentration and due to the primary photodegradant also being unstable in aqueous solution at room temperature. Due to the above mentioned difficulties the parent compound was photodegraded in methanol instead of water in order to avoid the freeze-drying process where a lot of the primary photodegradant was lost. This resulted in a primary photodegradant with a molecular ion of m/z = 241, where the chloride had been replaced by a methoxy group instead of a hydroxyl group. This compound was more stable which allowed workup by rotary evaporation, instead of freeze-drying, before the preparative purification. This primary photodegradant was isolated using semi-preparative SFC on a Viridis® BEH Prep OBD TM column (250 x 30 mm, 5 µm) and a Luna HILIC column (250 x 30 mm, 5 µm) with MeOH/NH3 100/1 v/v as organic modifier. About 1.2 mg material was isolated and further photodegradation tests in ordinary water and 18O-water were conducted. Some secondary photodegradants were observed in LC-MS analyses, and their element compositions were proposed by accurate mass results. Fundamental structures for these compounds were proposed. Further structural investigational analyses are needed for confirmation in the future.

Este projeto teve como objetivo investigar a variação isotópica do oxigênio (?18O) e do hidrogênio (?D) de aqüíferos subterrâneos rasos (não confinados) em quatro regiões onde foram definidas transecções, partindo do canal principal em direção ao topo da vertente. As transecções foram estabelecidas no gradiente topográfico encontrado, em quatro sub-bacias ao longo da bacia hidrográfica do rio Piracicaba. Esta região possui uma população de aproximadamente 3,5 milhões de habitantes e uma economia baseada na agricultura e na indústria. Baseando-se em estudos anteriores sobre a variação isotópica do ?18O e ?D das águas das chuvas e dos rios (Martinelli et al. 2004), onde foi identificada uma sazonalidade nos dados e variações possivelmente associadas à utilização da água em áreas urbanas (uso industrial), os estudos foram estendidos para as fontes de águas subterrâneas (fluxo de base) para o canal principal (rio Piracicaba). A sazonalidade definida por um verão chuvoso (novembro - abril) e inverno seco (maio - outubro) foi coberta com amostragens mensais (final do período seco de 2005; período chuvoso de 2005-2006 e seco de 2006) e quinzenais (período chuvoso 2006-2007) das águas da chuva, de poços rasos, nascentes e rios que drenam as sub-bacias estudadas. Os valores do ?18O e do ?D encontrados na precipitação acumulada entre coletas nas sub-áreas apresentaram maiores variações (extremos; ?18O médio de -0,4 a -13,0? ) quando comparados aos valores das águas superficiais (?18O médio de -5,1 a -9,2? ) e subterrâneas (?18O médio de -6,9 a -7,1? ), sendo que as últimas (poços rasos e nascentes) apresentaram variações ainda menores ao longo do período estudado. A precipitação e o escoamento de base possuem composição isotópica do ?18O relativamente distintas, uma vez que a média ponderada da precipitação (-8,6? observada para o período estudado) foi diferente dos valores médios encontrados nas águas subterrâneas não confinadas (-7,0? em média). O escoamento superficial para o canal principal (rio Piracicaba) teve seu valor isotópico influenciado pela precipitação no período das chuvas (podendo apresentar variações dentro deste período), caso contrário, os sinais isotópicos das águas superficiais seriam mais semelhantes aos sinais isotópicos encontrados no fluxo de base, caracterizando a contribuição deste na manutenção das menores vazões. Contudo, observou-se que o valor médio do ?18O de todos os rios e ribeirões estudados (-5,7? ) foi cerca de 1,2? mais enriquecido do que o valor médio dos poços e nascentes (-6,9? ), no período seco. As amplitudes do ?18O encontradas nxa precipitação e água subterrânea não confinada foram utilizadas em estimativas do tempo de residência médio da água no aqüífero lívre como uma primeira aproximação. / This project had the objective to investigate the oxygen (?18O) and hydrogen (?D) isotopic variation of shallow unconfined aquifers in four regions, in transects defined from the river to the limit of the drainage area. The transects were established within a topographical gradient in four sub-catchments of the Piracicaba river hydrographic basin. The population in this basin is almost three and a half millions inhabitants and an economy based on agriculture and industry is responsible for about 10% of the total Brazilian gross production. Based on a well documented isotopic variation of rainwater and river water done previously (Martinelli et al. 2004), where data seasonality and a possible variation related to water use in urban areas were identified, the studies were extended to the groundwater (baseflow) sources to the major channel (Piracicaba river) of the basin. The seasonality defined by a wet summer (november - april) and a dry winter (may - september) was covered with monthly (end of dry season of 2005; rainy season of 2005-2006 and dry season of 2006) and every two weeks sampling (rainy season 2006-2007) of rain water, shallow wells, springs and surface water (rivers) that drain the studied sub-basins. The ?18O and ?D individual values of composite precipitation in the studied sub-areas presented higher variation (extreme values; mean ?18O from -0,4 to -13,0? ) when compared to the values found for surface water (mean ?18O from -5,1 to -9,2? ) and groundwater (wells and springs; mean ?18O from -6,9 a -7,1? ), being the values of groundwater almost constant within the studied period. Precipitation and baseflow have relative different isotopic composition of ?18O, once the weighted average of precipitation (-8,6? observed for the whole studied period) is different from the average values found for unconfined groundwater (-7,0? in average). Values of surface runoff to the main channel (Piracicaba river) were similar to those found in precipitation in the rainy season (presenting variations within this period), otherwise, the isotopic signals of surface water were rather more similar to those found in baseflow, characterizing the contribution of baseflow in the lower flows. However, average value of ?18O of all rivers and streams studied (-5,7? ) were about 1,2? more enriched than the average value of wells and springs (-6,9? ) in the dry season. The amplitudes of ?18O found in precipitation and groundwater were used as a first aproximation to estimate mean residence time of unconfined groundwater.

O Bloco São Gabriel, localizado na zona central do embasamento cristalino do Rio Grande Sul, apresenta extensos registros do Neoproterozóico do Ciclo Brasiliano, contidos em complexos ígneos e metamórficos. Esses complexos também guardam registros sedimentares, com sequências carbonáticas metamorfisadas, cuja evolução tectônica é pouco conhecida. Essas sequências são observadas na Formação Passo Feio (Caçapava do Sul), no Complexo Cambaí (Vila Nova do Sul) e no Complexo Metavulcano-sedimentar Coxilha do Batovi (São Gabriel). As rochas carbonáticas da Formação Passo Feio compreendem dolomita mármores impuros. As amostras do Complexo Cambaí são classificadas como calcita mármores impuros. Os mármores do Complexo Coxilha do Batovi compreendem litotipos calcíticos e cálcio-silicáticos, cuja assembleia mineral é composta predominantemente por calcita em alguns exemplares e por grafita em outros, com percentuais de até 10% de quartzo, demonstrando contribuição siliciclástica no protólito. Idades de zircões de rochas associadas com os mármores, de trabalhos anteriores, indicam um intervalo entre 770 – 700 Ma para a deposição dos carbonatos do Bloco São Gabriel. Os carbonatos da Formação Passo Feio sofreram dolomitização durante ou logo após a deposição, enquanto os carbonatos do Complexo Cambaí não foram afetados pela dolomitização. A geoquímica dos elementos traços e terras raras indica que os mármores analisados preservaram as assinaturas originais do protólito nos diferentes graus metamórficos: Coxiha do Batovi (grau baixo), Formação Passo Feio e Complexo Cambaí (grau médio). A análise integrada dos isotópicos de Sr, 13C e 18O da Formação Passo Feio e do Complexo Cambaí revelou a preservação de assinaturas isotópicas primárias. Na Formação Passo Feio essas assinaturas são: 0,7074 (Sr87/Sr86), -0,26‰ e 2,44‰ (δ13CPDB) e -5,68‰ (δ18OPDB). Quando comparadas com a variação desses isótopos na água do mar ao longo do Neoproterozóico, verifica-se que os mármores da Formação Passo Feio e do Complexo Cambaí estão situados no intervalo entre 740 e 730 Ma. O período sugerido para a deposição das rochas carbonáticas da Formação Passo Feio é de 770 a 730 Ma, e entre 740-730 para o Complexo Cambaí. / The São Gabriel Block, located in the central zone of the crystalline basement of Rio Grande do Sul has extensive Neoproterozoic records of the Brasiliano Cycle, contained in igneous and metamorphic complexes. These complexes also keep sedimentary records with metamorphosed carbonate sequences whose tectonic evolution is poorly understood. These sequences are found in Passo Feio Formation, located in Caçapava do Sul region, in Complex Cambaí, at Vila Nova do Sul region and in Coxilha do Batovi metavolcanosedimentary Complex, in the São Gabriel region. The Passo Feio Formation carbonate rocks consist of impure dolomite marbles. The Cambaí Complex samples are classified as impure calcite marbles. Coxilha do Batovi Complex samples include calcite and calc-silicate marbles whose mineral assemblage are composed predominantly of calcite in some samples and graphite in others, with quartz rates up to 10% showing the siliciclastic contribution to the protolith. Zircon ages of associated rocks from previous works indicate an interval between 770-700 Ma for carbonate deposition in S. Gabriel Block. The carbonates from Passo Feio Formation were affected by dolomitization process during or early after its deposition, while the carbonates from Cambaí Complex were not affected by dolomitization. Trace elements and REE geochemistry of marbles indicate preservation of original signature of carbonate protoliths along different metamorphic grades; Coxilha do Batovi (low grade), Passo Feio Formation and Cambaí Complex (medium grade). The integrated analysis of Sr isotope, 13C and 18O from Passo Feio Formation and Cambaí Complex revealed the preservation of primary isotopic signatures. The Passo Feio Formation signatures are: 0,7074 (Sr87/Sr86), -0,26‰ and 2,44‰ (δ13CPDB) and -5,68 (δ18OPDB). In Cambaí Complex, the primary signatures are: 0,7069 (Sr87/Sr86), 5,75 (δ13CPDB) and -11,64 (δ18OPDB). When compared with the variation of these isotopes in seawater along the Neoproterozoic it appears that Passo Feio Formation and Cambaí Complex are situated in the range between 740 and 730 Ma. Based on these data it is suggested that the São Gabriel Block depositional event occurred between 770-700 Ma. The period suggested for the carbonate rocks depositional event of Passo Feio Formation is between 770-730 Ma, and specifically between 740-730 for Cambaí Complex.

O Bloco São Gabriel, localizado na zona central do embasamento cristalino do Rio Grande Sul, apresenta extensos registros do Neoproterozóico do Ciclo Brasiliano, contidos em complexos ígneos e metamórficos. Esses complexos também guardam registros sedimentares, com sequências carbonáticas metamorfisadas, cuja evolução tectônica é pouco conhecida. Essas sequências são observadas na Formação Passo Feio (Caçapava do Sul), no Complexo Cambaí (Vila Nova do Sul) e no Complexo Metavulcano-sedimentar Coxilha do Batovi (São Gabriel). As rochas carbonáticas da Formação Passo Feio compreendem dolomita mármores impuros. As amostras do Complexo Cambaí são classificadas como calcita mármores impuros. Os mármores do Complexo Coxilha do Batovi compreendem litotipos calcíticos e cálcio-silicáticos, cuja assembleia mineral é composta predominantemente por calcita em alguns exemplares e por grafita em outros, com percentuais de até 10% de quartzo, demonstrando contribuição siliciclástica no protólito. Idades de zircões de rochas associadas com os mármores, de trabalhos anteriores, indicam um intervalo entre 770 – 700 Ma para a deposição dos carbonatos do Bloco São Gabriel. Os carbonatos da Formação Passo Feio sofreram dolomitização durante ou logo após a deposição, enquanto os carbonatos do Complexo Cambaí não foram afetados pela dolomitização. A geoquímica dos elementos traços e terras raras indica que os mármores analisados preservaram as assinaturas originais do protólito nos diferentes graus metamórficos: Coxiha do Batovi (grau baixo), Formação Passo Feio e Complexo Cambaí (grau médio). A análise integrada dos isotópicos de Sr, 13C e 18O da Formação Passo Feio e do Complexo Cambaí revelou a preservação de assinaturas isotópicas primárias. Na Formação Passo Feio essas assinaturas são: 0,7074 (Sr87/Sr86), -0,26‰ e 2,44‰ (δ13CPDB) e -5,68‰ (δ18OPDB). Quando comparadas com a variação desses isótopos na água do mar ao longo do Neoproterozóico, verifica-se que os mármores da Formação Passo Feio e do Complexo Cambaí estão situados no intervalo entre 740 e 730 Ma. O período sugerido para a deposição das rochas carbonáticas da Formação Passo Feio é de 770 a 730 Ma, e entre 740-730 para o Complexo Cambaí. / The São Gabriel Block, located in the central zone of the crystalline basement of Rio Grande do Sul has extensive Neoproterozoic records of the Brasiliano Cycle, contained in igneous and metamorphic complexes. These complexes also keep sedimentary records with metamorphosed carbonate sequences whose tectonic evolution is poorly understood. These sequences are found in Passo Feio Formation, located in Caçapava do Sul region, in Complex Cambaí, at Vila Nova do Sul region and in Coxilha do Batovi metavolcanosedimentary Complex, in the São Gabriel region. The Passo Feio Formation carbonate rocks consist of impure dolomite marbles. The Cambaí Complex samples are classified as impure calcite marbles. Coxilha do Batovi Complex samples include calcite and calc-silicate marbles whose mineral assemblage are composed predominantly of calcite in some samples and graphite in others, with quartz rates up to 10% showing the siliciclastic contribution to the protolith. Zircon ages of associated rocks from previous works indicate an interval between 770-700 Ma for carbonate deposition in S. Gabriel Block. The carbonates from Passo Feio Formation were affected by dolomitization process during or early after its deposition, while the carbonates from Cambaí Complex were not affected by dolomitization. Trace elements and REE geochemistry of marbles indicate preservation of original signature of carbonate protoliths along different metamorphic grades; Coxilha do Batovi (low grade), Passo Feio Formation and Cambaí Complex (medium grade). The integrated analysis of Sr isotope, 13C and 18O from Passo Feio Formation and Cambaí Complex revealed the preservation of primary isotopic signatures. The Passo Feio Formation signatures are: 0,7074 (Sr87/Sr86), -0,26‰ and 2,44‰ (δ13CPDB) and -5,68 (δ18OPDB). In Cambaí Complex, the primary signatures are: 0,7069 (Sr87/Sr86), 5,75 (δ13CPDB) and -11,64 (δ18OPDB). When compared with the variation of these isotopes in seawater along the Neoproterozoic it appears that Passo Feio Formation and Cambaí Complex are situated in the range between 740 and 730 Ma. Based on these data it is suggested that the São Gabriel Block depositional event occurred between 770-700 Ma. The period suggested for the carbonate rocks depositional event of Passo Feio Formation is between 770-730 Ma, and specifically between 740-730 for Cambaí Complex.