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Carbonate deposits are numerous and have undeniable economic appeal for the oil industry. However, there are many uncertainties associated with different aspects of these lithologies. Understanding carbonate factories and their global distribution has been a subject of discussion in recent decades, especially concerning the products expected from different carbonate systems, their response to sea‐level variations and the transition between different depositional environments. Therefore, the goal of this study was to understand the role of sea‐level variations, and geodynamics in factories and the evolution of Albian depositional sequences on the south‐east continental margin of Brazil. Fifteen lithofacies consisting of seven facies associations and five third‐order sequences were identified. Sequence boundaries are unconformities formed by erosion or non‐deposition surfaces, representing either exposure periods or drowning events, and their correlative condensed sections. The first sequence, deposited in a shallow lagoon environment, recorded the onset of the T‐factory and the start‐up phase of the shelf. The second sequence represents a period of broad carbonate deposition in the basin, related to the catch‐up phase of the platform. The third sequence was established during a sea‐level rise and recorded the keep‐up phase of the platform and the transition from tropical to cool waters. The fourth sequence, was deposited in a deep marine environment and the fifth and last, recorded the shelf drowning. The succession typifies the beginning, the pinnacle and the end of carbonate deposition, spanning the initial and final highstand system tracts. The whole succession is part of a first‐order transgressive cycle that led to a factory transition and culminated with the definitive drowning of the depositional system.

The Late Cretaceous Marilia Formation located in the central-southern portion of Brazil is characterized by a succession of sandstones, conglomerates, and paleosols. The paleosols constitute more than 60% of this formation, providing significant information about pedogenetic processes as well as paleoenvironmental and paleoclimate implications. The paleosols of the Marilia Formation have been studied principally from a stratigraphical, sedimentological and paleopedological point of view; however, there are no studies addressing in detail the geochemical behavior of the paleosols. Therefore, we used a robust geochemical dataset combined with stratigraphical and macromorphological interpretations as well as clay mineralogy to conduct a paleoenvironmental and paleoclimate analysis of the Marilia Formation in the western portion of the state of Minas Gerais in Brazil. The results indicate that the paleosols of the Marilia Formation can be divided into three pedotypes and pedochemical units based on their geochemical variations and are limited at the base and top by pedochemical markers. Moreover, X-ray diffraction identified quartz and calcite as primary minerals associated with montmorillonite, smectite, illite and palygorskite, indicating wet periods combined with dry stages associated principally with dry and arid environments. The paleosol distribution and weathering index allow us to interpret the paleoenvironmental evolution of the Late Cretaceous Marilia Formation, suggesting an increase in humidity from east to west in the study area.

A geoquimica dos elementos maiores e traco tem sido usada como importante ferramenta para o estudo da proveniencia, evolucao tectonica e climatica das bacias sedimentares. A Formacao de Sao Carlos e uma unidade do Cretaceo Superior que ocorre na borda leste da Bacia Bauru. Apesar dos estudos paleontologicos e paleodeposicionais realizados nesta unidade nos ultimos anos, pouco se sabe sobre as condicoes tectonicas e climaticas que atuam nos primeiros estagios da sedimentacao, bem como, sua relacao estratigrafica com outras unidades da bacia. A hipotese deste trabalho consiste em avaliar se as formacoes Sao Carlos e Aracatuba possuem correspondencia e compreender a evolucao da margem leste da bacia. Dessa forma, realizaram-se estudos geoquimicos utilizando Fluorescencia de Raios-X em arenitos, siltitos e folhelhos da Formacao Sao Carlos. Atraves do uso do indice de intemperismo quimico, os oxidos dos elementos maiores indicam que, com valores entre 57,12 e 71,58%, os processos de intemperismo moderados, possivelmente associados ao clima arido-semiarido, afetaram a area de origem. Rochas alcalinas, granitos, gnaisses e metassedimentos foram os principais litotipos da area fonte. Os diagramas ternarios indicam que o ambiente tectonico era equivalente a margem continental passiva, coincidindo com as regioes da Serra do Mar e, em segundo lugar, Soerguimento Alto Paranaiba. Com base nos elementos maiores e tracos, suas razoes, e dados ja publicados da bacia, foi elaborado um modelo paleogeografico da borda leste da Bacia Bauru, concluindo-se que a area de origem dos sedimentos foi constituida por rochas intermediarias e felsicas, as vezes recicladas por processos sedimentares.

Rhizoliths are organosedimentary structures produced by plants and are an important proxy for paleoenvironmental reconstructions because the differences in the morphology of rhizoliths and their rooting depths can be used to interpret soil humidity regimes, overall biomass at the soil surface, and the behavior of the water table. With the objective of advancing knowledge on rhizoliths, a study was performed on the macromorphological and micromorphological characterizations of the rhizoliths preserved in the thirty-one paleosols of the Marilia Formation in Minas Gerais, southeastern Brazil. Based on the topological and architectural attributes of rhizoliths, and on their possible functional adaptations, such as mycorrhizal associations, three different types of rhizoliths are described in this study and represent at least three different plants: rhizohaloes, root casts and rhizocretions. Well-developed paleosols with nodular horizons contain the higher density of long root casts, indicating a seasonally dry environment, because the root casts present two meters in length. These adaptations are associated with an exploitation of a lowered water table during most times of the year. The higher density of rhizoliths indicates an area with agglomerated arboreous arbustive vegetation cover. Paleosols with chalky horizons also show a high density of root casts, indicating a landscape with high plant density that is adapted to drained soils, but with a seasonally elevated water table or the influence of ephemeral flows, given the proximity to the flow channels. The poorly drained paleosols with redoximorphic features show the lowest density of rhizoliths, thus indicating an incipient vegetation in response to near-surface water table and waterlogged soils in a distal floodplain. The rhizogenic laminar horizons have developed near fluvial channels with frequent sedimentary input, resulting in a sequence of laminar horizons composed of rhizocretions that are separated by sandy deposits or poorly developed pedogenic horizons. The micromorphological analysis on the rhizogenic laminar calcretes showed biogenic features, such as alveolar septal structures, calcified filaments, microcodium, calcified cells and pisoliths. Despite the scarce paleobotanical findings in the Marilia Formation, the results obtained indicate an ecosystem that was composed of plants varying from herbaceous to arboreous, with an environment similar to modern semiarid shrublands.

The current research was performed in the eastern portion of the Marlim oilfield to identify the hydrocarbon-generating potential of the Albian-Oligocene sequences (Macae Group, Ubatuba and Carapebus formations) in the Campos Basin, Brazil. On the basis of petroleum geochemical proxies, an integrated approach was developed using source rock characterizations to establish the distribution of source rock properties, such as organic matter content, hydrocarbon-generating potential, thermal maturity and stratigraphic thickness. The outcomes of a comprehensive petroleum geochemical characterization were integrated with cuttings and core sample descriptions, biostratigraphic controls, well log analyses and 2-D/3-D seismic interpretations. Our results reveal that for the Albian-Oligocene deposits, the key geochemical properties required to develop hydrocarbon source kitchens converge in specific locations, demonstrating a variable hydrocarbon potential ranging from poor to excellent and suggesting the existence of local generation pods in the central and principally northern portions of the research area. The accumulation and preservation of the organic matter were influenced by the paleo-topography and tectonic controls, and the lowest concentrations of organic carbon were attributed to significant siliciclastic dilution taking place mostly toward the middle and southern portions of the Eastern Marlim oilfield. Lateral variations in both the lithofacies and organic facies are the main conditions controlling the behavior of the petroleum potential in the investigated sediments. Our results indicate that the Macae Group has sufficient source-rock potential, maturation patterns, and hydrocarbon-generating potential to be considered as an active source rock in the Eastern Marlim oilfield, where the petroleum geochemical properties converge and are adequate to generate hydrocarbon compounds. In addition, the Ubatuba and Carapebus formations are also likely to generate oil and/or gas, but due to their relatively low maturity, it is difficult to establish that these rocks can be active source rocks in the study area.

An organic geochemical investigation combined with sequence stratigraphy was performed in the Ceara Basin, an offshore basin located in Northeastern Brazil. The information available from 30 well logs (gamma-ray, resistivity, density), besides geochemical (TOC, and pyrolysis indexes) and isotopic (δ13C) data, aided the preparation of a dataset for this study. The application of sequence-stratigraphic methods helped classify and correlate seismic and organic facies. Four key petroleum source-rock units were identified, from the oldest to the youngest: (1) Mundau Formation – top of the Rift Sequence (Berriasian-Aptian); (2) Paracuru Formation – Breakup Sequence (Aptian-Albian); (3) Itapaje Member of the Ubarana Formation – Continental Drift Sequence (Albian-Turonian), and (4) Uruburetama Member of the Ubarana Formation – Continental Drift Sequence (Turonian-Maastrichtian). The geochemical characteristics of the Mundau Formation (high total organic carbon (TOC), hydrogen index (HI), relative hydrocarbon potential (RHP = (S1 + S2)/TOC)) point to a typical transgressive sequence. Six transgressive-regressive (T-R) cycles were recognized in the entire Paracuru Formation. The best geochemical marker is related to the top of the Paracuru Formation. This stratigraphic unit can be correlated to a major anoxic event and is the best source rock of this basin. Evaporitic facies found in this top section, maximum RHP values (anoxic conditions), and maximum flooding surfaces related to transgressive events characterize this interval. Moreover, the wide spatial cover of organic-rich rocks, carbon isotopic data, and the recognition of favorable characteristics for anoxia in other basins of the Equatorial Margin are suggestive of the Aptian-Albian Oceanic Anoxic Event (OAE-1b) occurring in the Ceara Basin. The Ubarana Formation represented by the Uruburetama Member and the Itapaje Member yields the least promising source rocks. However, high TOC values suggest the occurrence of the late Cenomanian–early Turonian Oceanic Anoxic Event (OAE-2), when organic-rich strata started to deposit in deep-water regions. The predominance of a regressive interval in the Uruburetama Member points to oxic or sub-oxic conditions. Additionally, the correlations between the Brazilian Equatorial Margin and its African counterpart, and the organic geochemical characterization allied to the definition of depositional systems for these regions proved to be useful for oil exploration.

The Mundau sub-basin composes the western segment of the Ceara Basin, which is one of a series of basins of the Brazilian Equatorial Margin that resulted from the breakup of Western Gondwana. This study investigates the origin and maturation of the organic matter preserved in the rocks of the middle and outer shelf of the Mundau sub-basin, in order to assess the source-rock potential for oil and gas generation. The samples selected for this study are representative of the Mundau, Paracuru, and Ubarana formations, which correlate with the rift, transition, and drift phases of the Western Gondwana breakup. The results indicate moderate to good potential for oil generation and good potential for gas generation for the Mundau Formation. Fault activity during the rift phase favored sediment supply. Kerogen type III predominates in shallower portions and probably reflects the contribution from the continent. Good to excellent potential for oil and gas generation is indicated for the Paracuru Formation. Kerogen types I and II predominate, having the marine organic matter been deposited in reducing conditions. The most promising interval for hydrocarbon generation is limited by the top of the Trairi Member and the top of the Paracuru Formation. Moderate to good potential for oil and gas generation is suggested for the Uruburetama Member of the Ubarana Formation. The source rocks located in the middle shelf were deposited under reducing conditions in a transgressive marine environment. Kerogen varies from type II, to a mixture of types II and III, and to subordinate type III. Poor to fair potential for oil generation is indicated for the Itapaje Member of the Ubarana Formation. Kerogen type IV (inert or degraded) is typical in the middle shelf, and kerogen type IV and subordinate type III are typical on the outer shelf. The presence of inert kerogen is related to high-energy, oxidizing depositional environments. The hydrocarbon expulsion threshold estimated for the outer shelf is at 2106-m, for the middle shelf at 1635-m, and for the deep waters at 3632-m depths. Source rocks of the middle and outer shelves occur between 561 m and 4080 m, whereas those in deep waters occur between 2754 m and 5007 m of depth. The Active Source Rock Depth Limits (ASDL) estimated for the outer shelf is below 4500 m, whereas for deep waters, this limit is close to 6000 m. These organic geochemical constraints are important guidelines for oil and gas exploration in the Ceara and adjacent basins.

Paleosols are soils that were formed on an ancient landscape. They may be buried soils and/or soils incorporated into the sedimentary sequences, exhumed soils, or soils developed on ancient relief surfaces (relict soils). Exposed on the surface and influenced by later environmental changes, paleosols reveal ancient environments and contain records regarding the climate, vegetation, landforms, organisms, parent material, time, intensity of pedogenesis, and sedimentation rates in effect during their training. In the Marilia Formation, the paleosols, exhumed and buried, developed on sandstones have argic (Btk, Bt and Bss), hydromorphic (Cg) and calcic (Bk) horizons with different degrees of cementation, forming mainly calcretes. The objective of this study was to characterize the genesis of the paleosols of the Marilia Formation, addressing the dynamics of their formation factors and processes at local and regional levels in order to reconstitute the conditions of environmental evolution of the Maastrichtian of the Bauru Basin. Eleven sections (S1, S2, S3, S4, S5, S6, S7, S8, S9, S10 and S11) of the Marilia Formation were described and collected on nine sample profiles. Micromorphological, mineralogical and geochemical analyses were performed according to the specialized literature. In the Marilia Formation, sedimentation, erosion and pedogenesis are processes that occurred together, concomitantly or subsequently, in view of the fluvial paleoenvironmental dynamics. The paleosols indicate the end of depositional cycles, with differentiated rates, intensities and duration. The paleosols of the Marilia Formation comprise well-drained (Bt-horizon) and poorly drained or hydromorphic (Cg-horizon) pedotypes, of drier conditions (Bkm-horizon) and pedotypes indicative of drier periods alternated with periods of higher humidity (Bss-horizon). The profiles were classified as Luvisols (Bt and Btk horizons), Calcisols (Bk and Ck horizons), Arenosols (C-horizons) and Vertisols (Bss-horizons). Paleosols developed on the flatter and lower portions of the slopes and floodplains and were commonly influenced by the oscillation of the groundwater and the seasonality of the climate. Sandstone with allochthonous and autochthonous carbonate cementation constituted the main parent material of the paleosols. The predominant climate during the Maastrichtian was semi-arid, with seasonality and variations in precipitation patterns and a precipitation-evapotranspiration relationship that provided conditions for the formation of paleosols with Bk, Btk, Bss, Bg and Bt horizons. The time of formation of these diagnostic horizons was dependent on climatic and edaphic factors. However, the time factor lasted until approximately 200,000 years, allowing paleosols to develop with Bt-horizons and prismatic and block structures. Calcification and argilluviation were the formation processes responsible for the genesis and evolution of paleosols during the Maastrichtian of the Bauru Basin. Weathering indexes have shown that paleosols with Bt-horizons are more weathered than are those with Btk and Bk horizons. The paleosols with Bk-horizons reflect periods with more arid conditions in the general context of the semi-arid paleoclimate of the Maastrichtian of the Bauru Basin.

The influence of post-burial geological processes on preserving pedogenic properties has great importance in identifying ancient paleosols both in the field and in a laboratory. However there are not many publications that focus on characterizing paleosol diagenesis. As temperature and pressure progressively increase, evidence of pedogenesis is modified and destroyed, hindering paleoenvironment characterization and interpretation. This paper discusses diagenetic evidence and its relation to strictly pedogenic features, like structure, cements, nodules, and neoformation of clay minerals using the carbonate paleosols of the Marilia Formation in the upper unit of the Bauru Basin as a case study. Despite the long geotectonic and thermal history of the Marilia Fomation, paleosols bring us pedogenic evidence that can undergo micromorphological analyses, such as cementation, clay illuviation, bioturbation, and ped structures. The results of analyses in 25 paleopedogenic horizons indicate that the paleotopographic features were responsible for distribution of the diagenetic processes and preservation of the paleosol properties. The maturity of those paleosols controls lithification. In mature paleosols that developed in more stable portions of the landscape, characteristics such as carbonate cementation and development of pedogenic structures are the main factors that inhibit diagenesis. However diagenetic processes that influence poorly-developed paleosols are controlled by depositional characteristics and by changes in the water table, enabling more advanced diagenetic processes, compared to mature paleosols.

Orientador: Alessandro Batezelli Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociências Resumo: O clima do Cretáceo foi caracterizado por condições áridas e semiáridas em todo o mundo. As variações climáticas ocorridas no início do período Cretáceo foram objeto de diversas investigações, com o objetivo de interpretar a evolução paleogeográfica da Laurasia e Gondwana. A presença de sequencias sedimentares cretáceas bem preservadas na Bacia Bauru torna interessante o desenvolvimento de reconstruções paleoambientais e paleoclimáticas no limite do Cretáceo Inferior ao Cretáceo Superior. Uma das principais características das sequencias cretáceas na Bacia Bauru é a presença de perfis de paleossolos. Os paleossolos são uma ferramenta poderosa usada nos estudos paleoclimáticos e paleoambientais e o uso da geoquímica de paleossolos é uma ótima técnica para essas interpretações. Portanto, nesta investigação usamos um robusto conjunto de dados geoquímicos, mineralogia de argilas e interpretações estratigráficas e macro/micro morfológicas para desenvolver uma evolução paleoambiental e paleoclimática da transição do Cretáceo Inferior ao Cretáceo Superior no leste da Bacia Bauru. Essa interpretação baseada em um conjunto robusto de dados geoquímicos é a primeira feita na bacia para explicar as condições paleoclimáticas e paleoambientais usando as respostas geoquímicas registradas nos paleossolos que, juntamente com outras técnicas, permitem uma abordagem detalhada e confiável das variações climáticas ocorridas no passado. Os resultados mostram que, para o Cretáceo Inferior; o clima era seco e com baixas paleoprecipitações, em contraste com o clima do Cretáceo Superior que era mais úmido e com aumento das paleoprecipitações. Os padrões geoquímicos permitem identificar que para o Cretáceo Inferior o intemperismo era incipiente a intermediário com altas taxas de calcificação e para o Cretáceo Superior o intemperismo era mais forte com baixas taxas de acumulação de carbonato de cálcio. Além disso, os minerais argilosos constituídos por rochas do Cretáceo Inferior indicam condições áridas a semi-áridas, em contraste com os minerais argilosos do Cretáceo Superior que indicam características úmidas. Igualmente, os resultados permitiram identificar três fácies principais que envolvem um sistema fluvial distributivo (fácies proximal-intermediária, fácies intermediária e fácies distal). Finalmente, os resultados permitem construir mapas de evolução paleoclimática das sequencias do Cretáceo Inferior ao Superior no leste da Bacia Bauru que contribuem para o entendimento da geologia regional da área de estudo Abstract: The Cretaceous climate was characterized by arid and semiarid conditions around the world. Climatic variations which occurred in the Early to Late Cretaceous period have been focus of several investigations aiming to interpret the paleogeographic evolution of Laurasia and Gondwana. The presence of well-preserved Cretaceous sedimentary sequences in the Bauru Basin located in Brazil turns interesting the development of paleoenvironmental and paleoclimatic reconstructions in their Lower to Upper Cretaceous boundary. One of the main characteristics of the Cretaceous sequences in the Bauru Basin is the presence of paleosol profiles. Paleosols are a powerful tool that have been used in paleoclimatic and paleoenvironmental studies, which along with the use of paleosol geochemistry are great techniques for these kinds of interpretations. Therefore, in this research a robust geochemical dataset, clay mineralogy, stratigraphic and macro/micro morphological interpretations were used to understand the paleoenvironmental and paleoclimatic evolution of the Early to Late Cretaceous transition in the eastern Bauru Basin. This interpretation was based on a robust geochemical dataset, which is the first one made in the Bauru Basin aiming to explain their paleoclimatic and paleoenvironmental conditions. Using the geochemical responses recorded in the paleosols along with other techniques, a detailed and reliable approach of the climatic variations that have been occurred in the past was developed. The results demonstrate that the Early Cretaceous climate was dry with low paleoprecipitations. On the other hand, the Late Cretaceous climate was more humid showing an increase in paleoprecipitations. The geochemical patterns allowed to identify that the Lower Cretaceous weathering was incipient to intermediate accompanying with high rates of calcification. In contrast, the Upper Cretaceous weathering was strong displaying low rates of accumulation of calcium carbonate. In addition, the clay minerals that constituted the Lower Cretaceous rocks of the Bauru Basin indicated arid to semi-arid conditions in contrast with the Upper Cretaceous were the clay minerals indicated humid characteristics. Likewise, the results allowed to identify three major facies involving a distributive fluvial system (proximal-intermediate, intermediate, and distal facies). Finally, the results allowed to elaborate maps of the paleoclimatic evolution of the Lower to Upper Cretaceous sequences in the eastern Bauru Basin that aiming to contribute towards the understanding of the Brazilian Cretaceous regional geology Doutorado Geologia e Recursos Naturais Doutora em Ciências CAPES

Orientador: Alessandro Batezelli Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências Resumo: Estudos geoquímicos e mineralógicos de arenitos e argilitos da Bacia Bauru (Cretáceo Superior), localizada na região do Triângulo Mineiro (Minas Gerais) foram realizados visando à determinação da proveniência, tectônica da rocha fonte, o papel de processos como intemperismo e reciclagem sedimentar na assinatura geoquímica da rocha fonte e à proposição de um modelo de evolução paleoambiental para a área de estudo. As amostras tem sua mineralogia principal composta por quartzo, microclínio, calcita, albita, dolomita e hematita. Illita, montmorillonita e paligorsquita são os argilominerais identificados. Elementos maiores, traços e terras raras e as razões elementares entre eles foram utilizadas para determinar a composição da rocha fonte. Valores do Índice Químico de Alteração e do Índice de Intemperismo Químico variando de 64 a 92 e de 84 a 98, respectivamente, e a ocorrência de feldspatos nas rochas sedimentares indicam intemperismo químico moderado na área fonte. Gráficos de elementos maiores e traços e valores para razões como La/Sc (1,47-4,86), (La/Yb)c (3,86-20,44) e a anomalia de Eu (Eu/Eu* = 0,62-0,92) comparados com dados da literatura sugerem que os sedimentos da Bacia Bauru na área de estudo tenham sido originados de rochas de composição quartzítica a granítico-gnáissica, derivadas de áreas continentais estáveis e depositados em ambientes de bacias intracratônica. A possível área-fonte para as rochas estudadas localiza-se a NE da Bacia Bauru, consistindo em rochas graníticas e metassedimentares do embasamento pré-cambriano. A deposição sedimentar na Bacia Bauru reflete a interação de processos aluviais e lacustres Abstract: Geochemical and mineralogical studies of sandstones and mudstones from the Late Cretaceous Bauru Basin of Triângulo Mineiro region (Minas Gerais State) were undertaken to determine the provenance, tectonic setting, the role of weathering, sorting and recycling on the source rock geochemical signature and to propose a palaeoenvironmental evolution model to the study area. The analysed samples are mainly composed by quartz, microcline, calcite, albite, dolomite and hematite. Illite, montmorillonite and palygorskite are the identified clay minerals. Major elements were used to determine the source rock composition, as well as trace and rare earth elements and the ratios among them. Chemical Index of Alteration and Chemical Index of Weathering ranging from 64.83 to 92.3 and from 84 to 98.2, respectively, along with the feldspar occurrence on sedimentary rocks indicate a moderate weathering in the source area. Plots of major and trace elements and values for the ratios such as La/Sc (1.47-4.86), (La/Yb)c (3.86-20.44) and the Eu anomaly (Eu/Eu*= 0.62-0.92), compared to data from the literature indicate source rock was located into a continental passive margin tectonic setting and sediments were derived from quartzitic to granitic-gneissic rocks of stable continental areas and deposited in an intracratonic basin. Probable source area to the studied rocks is located at NE of Bauru Basin and consists in granitic and metassedimentary rocks from the Precambrian basement. Sedimentary deposition in Bauru Basin reflects an interaction of alluvial and processes Mestrado Geologia e Recursos Naturais Mestra em Geociências