Campos Basin Research Articles

Oil leakage induces changes in microbiomes of deep-sea sediments of Campos Basin (Brazil)

The Campos Basin (100,000 km2) is located on the continental shelf of southeastern Brazil. Despite the significant oil and gas industrial activities underway in the Campos Basin, scarce information is available regarding the hydrocarbon contents and microbial communities in the deep-sea sediments. To gain new insights on these aspects, we first obtained deep-sea sediment samples with different degrees of oil exposure. We obtained samples from a seabed fissure (N = 28), surroundings (250 m to 500 m from the fissure; N = 24), and a control area (N = 4). We used shotgun metagenomics to characterize the taxonomic and metabolic diversity and analyzed biogeochemical parameters (metal and oil concentration) of all samples. The high levels of unresolved complex mixture of hydrocarbons in the fissure indicate a potentially recent petrogenic contribution in these sediments. The fissure area was found to have a higher abundance of hydrocarbonoclastic bacterial genera and hydrocarbon degradation genes. These bacteria may be used as biosensors of sediment contamination. The effects of oil contamination, mainly around the fissure, are less clear at 250 m and 500 m, suggesting that the surroundings may not have been heavily affected by the oil leakage. Our study demonstrates that metagenomics can disclose biosensors for environmental monitoring.

Environmental Education in the licensing of oil and the public university: The case of the Macaé River Basin, Rio de Janeiro, Brazil

A escassez hídrica que afetou várias cidades entre 2014 e 2015, na Região Sudeste, evidenciou a fragilidade do modelo brasileiro de gestão dos recursos hídricos, sendo a Bacia Hidrográfica do Rio Macaé (RJ) um exemplo desse quadro. Apesar de sua importância regional, há previsões que apontam para o comprometimento do abastecimento hídrico impactando a vida humana e as atividades econômicas, incluindo a exploração de petróleo na Bacia de Campos nos próximos anos. Diante desse cenário, espera-se que a Educação Ambiental no licenciamento possa promover reflexões sobre a gestão das águas, sistematizando informações e criando canais de comunicação entre o poder público e os usuários. Este estudo discute também o papel da universidade interiorizada e a geração de subsídios para discussões sobre os recursos hídricos.

A new species of Travisia (Annelida, Travisiidae) from Campos Basin, Brazil

ABSTRACT Travisia Johnston, 1840 is the only genus of the family Travisiidae Hartmann-Schröder, 1971. Travisiid species have body relatively short, papillated, fusiform, often tapered anteriorly and posteriorly, and swollen medially. They are found mainly in deep-sea sediments. Several faunistic accounts from different locations in the Brazilian coast have included records of Travisia species that need to be reassessed. The aim of this study was to describe Travisia araciae n. sp., a new species from Campos Basin, off Rio de Janeiro, Southern Brazil. The new species differs from other similar species by having 23 pairs of branchiae from chaetiger 2, and interramal pores from chaetiger 1. An updated key to identification for all species in the genus is also included. http://www.zoobank.org/urn: lsid:zoobank.org:pub:92A10341-AA12-434C-BB58-61C70042F4B1

The use of variational mode decomposition in assisting sedimentary cyclicity analysis: A case study from an Albian carbonate reservoir, Campos Basin, southeast Brazil

The sedimentary cyclicity analysis investigates the cyclic patterns and the different hierarchical orders of cyclicity in the stratigraphic record. The detection of cyclic depositional patterns is a key element of quantitative stratigraphy. It is often based on well-log data, which can be challenging due to the presence of superimposed cycles and nongeologic artifacts. We have developed an approach to assist the detection of sedimentary cyclicity in well-log signals based on a multiscale spectral analysis method. First, we apply variational mode decomposition to decompose the gamma-ray logs into band-limited subsignals, the intrinsic mode functions (IMFs), to investigate different orders of smoothness, signal-to-noise ratio, and the cyclicity embedded in the geologic record. Conventional time-domain analysis is carried out to understand the general trends in the IMFs, which enables us to better identify long-term cycles associated with transgressive-regressive (T-R) sequences. Then, by appropriately selecting a given IMF and extracting the instantaneous frequency (IF) and its mirrored version, we build a cyclicity log that can map expressive behavior change in the time-frequency domain. Because the IF is more sensitive to the signal variations, we could highlight the short-term cycles throughout the formation in detail. The detected short-term cycles are in agreement with the T-R sequence. We apply our method to the Albian carbonate succession of Macaé Group, Campos Basin, Brazil. We understand that our method can be a valuable tool for semiautomated detection of sedimentary cycles, assisting in the characterization of different hierarchical orders of cyclicity.

Petrofacies classification using machine learning algorithms

Carbonate reservoirs represent a large portion of the world’s oil and gas reserves, exhibiting specific characteristics that pose complex challenges to the reservoirs’ characterization, production, and management. Therefore, the evaluation of the relationships between the key parameters, such as porosity, permeability, water saturation, and pore size distribution, is a complex task considering only well-log data, due to the geologic heterogeneity. Hence, the petrophysical parameters are the key to assess the original composition and postsedimentological aspects of the carbonate reservoirs. The concept of reservoir petrofacies was proposed as a tool for the characterization and prediction of the reservoir quality as it combines primary textural analysis with laboratory measurements of porosity, permeability, capillary pressure, photomicrograph descriptions, and other techniques, which contributes to understanding the postdiagenetic events. We have adopted a workflow to petrofacies classification of a carbonate reservoir from the Campos Basin in southeastern Brazil, using the following machine learning methods: decision tree, random forest, gradient boosting, K-nearest neighbors, and naïve Bayes. The data set comprised 1477 wireline data from two wells (A3 and A10) that had petrofacies classes already assigned based on core descriptions. It was divided into two subsets, one for training and one for testing the capability of the trained models to assign petrofacies. The supervised-learning models have used labeled training data to learn the relationships between the input measurements and the petrofacies to be assigned. Additionally, we have developed a comparison of the models’ performance using the testing set according to accuracy, precision, recall, and F1-score evaluation metrics. Our approach has proved to be a valuable ally in petrofacies classification, especially for analyzing a well-logging database with no prior petrophysical information.

Application of stability solver for severe slugging considering a choking device and a tubing connected to a Wet Christmas Tree

This work is an improvement of a previous work (Andreolli et al. 2018) by including a tubing as a subsystem of the pipeline–riser system, a realistic choke valve model to predict the two-phase critical flow and pressure drop before the separator and boundary conditions between stretches of the geometry, in order to improve the determination of the stability boundary. The improved stability solver is applied for a three phase flow (gas, oil and water). Stability for operational points obtained from actual measurements are successfully predicted with the stability maps generated by the solver considering the tubing connected to the Wet Christmas Tree (WCT). A parametric analysis is made in order to evaluate a choke valve influence over stability maps. The stability maps are built by using field conditions at Santos and Campos basins (Brazil). The numerical results present a good agreement with numerical data and real operational conditions. The analysis to evaluate and verify the choke valve influence over stabilization shows a good agreement with the expected behavior.

Role of Brazil’s Continental Slopes in Being Provided with Hydrocarbon Resources

Abstract—Analysis more of 80 hydrocarbon fields, mainly oil-producing, in the deepwater part of the Santos, Campos and Espirito Santo basins reveal the tendency of these large fields to lie in a productive oil-pay belt extending in the sea depth from range from 400 to 2500 m (possibly 3000 m or more) in a system of external depressions stretching along the lower part of the continental slope. This belt may continued to the north. All the fields in this belt in reserves category are estimated as large and giant. In the last 10–15 years, exploration works have been conducted in this belt already in the presalt formation: in the Santos Basin, 29 fields; in the Campos Basin, 21; and in the Espirito Santo Basin 7. It is noteworthy that 48% of the total hydrocarbon production of the country formed in presalt carbonate deposits of the Aptian Formation on the continental slope, 44% postsalt rocks on the continental slope and shelf, and only 8% is attributed to the mainland. In the world, Brazil’s deepwater presalt Aptian Formation (Barremian–Aptian in the Santos Basin) is essentially unique. In recent decades, giant hydrocarbon accumulations have been discovered, thereby doubling the country’s oil and gas reserves to total reserves of more than 3 billion t and 4.7 trillion m3, respectively. The geology of the presalt formation is narrowly related to tectonic movements that took place during the breakup of the Gondwana supercontinent into the South American and African continents. This took place 150 Ma ago in the Early Cretaceous. The salt of the Aptian Formation is an excellent caprock, the presalt reservoirs are superior in their characteristics, the oil is light and sweet, and the source rocks are enriched in organic matter. The thickness of the Aptian salt is limited, varying from basin to basin; the main width of the salt is in the Santos Basin 400 km and the thickness is 2000 m; in the north, the thickness and width decrease; in the Sergipi Alagoas Basin, it already reaches 100 m.

Bioclastic accumulation in a lake rift basin: The Early Cretaceous coquinas of the Sergipe–Alagoas Basin, Brazil

ABSTRACTCoquinas constitute widespread deposits in lacustrine, estuarine, and shallow marine settings, where they are a valuable source of information on environmental conditions. Thick coquina successions were deposited in a series of lacustrine rift basins that formed along the Brazilian Continental Margin during the early stages of the opening of the South Atlantic Ocean, in the Early Cretaceous. In the Sergipe–Alagoas Basin, the coquina sequence, equivalent to the Morro do Chaves Formation, crops out in the Atol Quarry, and is considered a relevant analog for the economically important hydrocarbon reservoirs in the Pre-salt strata (Barremian to Aptian) of the Campos Basin (Pampo, Badejo, and Linguado oil fields), which occur only in the subsurface. The aim of this study is to generate a depositional and stratigraphic model through facies and stratigraphic analyses of a well core. These analyses allowed the geological characterization of the Morro do Chaves Formation and of its transition to the adjacent stratigraphic units, the Coqueiro Seco Formation above and the Penedo Formation below, contributing to the growing knowledge of sedimentation in rift basins and exploratory models in hydrocarbon-producing reservoirs. Facies analysis consists of sedimentological, taphonomic, and stratigraphic features of the rocks. Fourteen depositional facies were recognized, stacked into low-frequency and high-frequency, deepening-upward and shallowing-upward cycles driven by the interaction between climate and tectonism. A depositional model is presented, based on the correlation between well-core and outcrop data described in previous studies, providing insights into the spatial distribution of facies. The detailed analysis of facies and stacking patterns sheds light on depositional processes, paleoenvironmental conditions, and the evolution of the system through time, so we may better understand analogous deposits in the geological record.

PETRÓLEO E EMPREGO: UMA ANÁLISE EM MUNICÍPIOS SELECIONADOS DO ESTADO DO RIO DE JANEIRO

A descoberta e exploração de petróleo nos reservatórios na camada do pré-sal ocasionou o deslocamento de investimentos da Bacia de Campos para a Bacia de Santos, e, consequentemente, provocou alterações no mercado de trabalho das regiões produtoras. Deste modo, o objetivo do presente texto é analisar o impacto do setor de petróleo no mercado de trabalho nos locais em que são desenvolvidas as atividades de Exploração e Produção (E&P), por meio da análise de um número equivalente de municípios confrontantes a ambas as bacias, durante o período compreendido entre os anos de 2000 até o presente. Foram consideradas informações referentes à população residente, aos postos de trabalho e ao nível educacional. O estudo indica que os municípios que abrigam equipamentos da indústria propriamente dita são os que apresentam os melhores indicadores quanto ao emprego e ao nível educacional. O estudo é concluído ressaltando que as transformações estruturais da geopolítica do petróleo tornam os prognósticos sobre a evolução do setor um terreno altamente movediço, embora sejam necessárias análises sobre cenários futuros.

The Deep-Sea Genus Coronarctus (Tardigrada, Arthrotardigrada) in Brazil, South-Western Atlantic Ocean, with the Description of Three New Species

Three new marine tardigrade species from the deep-sea genus Coronarctus are described from the South-Western Atlantic Ocean: Coronarctus dissimilis sp. nov., C. neptunus sp. nov., and C. yurupari sp. nov. These, and C. laubieri Renaud-Mornant, 1987, are the first records of deep-sea tardigrades from this marine region. Specimens of those species were collected from two localities of the Brazilian continental slope (Potiguar and Campos basins) at depths comprised between 150 and 3000 m. Specimens of the three new species have short cephalic appendages and heteromorphic claws, belonging to the, here designated, C. tenellus group of species. Each of the new species can be distinguished from all the other species of the group by their peculiar-shaped secondary clavae and claws. The most relevant morphological characters used for the taxonomy of the genus: shape of cephalic cirri, shape of secondary-clavae, size and number of accessory spines on claws, and shape of seminal receptacles, are discussed and an identification key to all ten known Coronarctus species is provided.

Reducing uncertainties of reservoir properties in an automatized process coupled with geological modeling considering scalar and spatial uncertain attributes

The current work introduces an automatized process coupled with geological modeling to reduce uncertainty in reservoir properties. The method assimilates dynamic data of wells interactively, and applies the deviations to constrain uncertainties. The methodology deals with scalar (e.g. rock compressibility) and spatial (e.g. porosity) attributes at same time, employing specialized uncertainty reduction procedures. The procedure reduces the uncertainty of scalar attributes through Iterative Discrete Latin HyperCube method (IDLHC). To reduce uncertainties of spatial attributes, we worked on an extension of a regionalized co-simulation (co-DSS) method. The main contributions regard the proposition of update, at same time, both kinds of uncertainties (spatial and scalar); the definition of sequential rules, that simplify the process execution and avoiding subjectivities on the coupling of the geological modeling on data assimilation, as well as the automation of the process. The procedure was validated under a siliciclastic black-oil benchmark field (UNISIM-I-M), established based on Namorado Field, Campos Basin, Brazil. The procedure reduced the range of uncertainty of the scalar attributes, centralizing final PDFs with the values presented in the reference model, without collapse to a particular level, as well as preserved the geological consistency throughout data assimilation, obtaining porosity responses in agreement with the reference porosity distribution. The potential of the procedure is supported by the consistent production forecast observed in the outcomes.

New discoveries for the subfamily Phtisicinae Vassilenko, 1968 (Crustacea: Senticaudata) from the Brazilian coast

Amphipod material collected from Brazil on Ilha do Arvoredo, (Santa Catarina), Campos Basin, (Rio de Janeiro) and Espírito Santo Basin (Espírito Santo) in the southwestern Atlantic Ocean yielded new taxonomic findings for the subfamily Phtisicinae Vassilenko, 1968. Hemiproto wigleyi McCain, 1968, previously recorded from the Gulf of Mexico to the Caribbean Sea, is herein redescribed and recorded for the first time from the Brazilian coast. The type material of Phtisica verae Quitete, 1979, a poorly described species recorded from Brazil and based only on its original description, was examined and considered herein as a junior synonym of P. marina Slabber, 1769, a well-known and widely distributed species from the Atlantic Ocean and the Mediterranean Sea. In this paper, Phtisica marina is redescribed, with its two morphotypes of male gnathopod two, and compared with previous descriptions. The geographic distribution of both H. wigleyi and P. marina is provided.

Oscillation mitigation in subsurface and surface couplings using PID controllers

Simulation coupling subsurface (reservoir) and surface (network) systems is a challenging problem, especially for computationally intensive multi-reservoir models and complex surface network facilities. Integration of petroleum systems can be done using different simulators (explicit coupling) or considering all individual components of the system in one simulator (implicit coupling). The explicit method is more flexible, allowing the integration of commercial-off-the-shelf simulators. However, as a drawback, it can yield oscillatory solutions. In this work, a new framework for mitigating explicit coupling numerical instabilities (oscillations) is developed by recasting the problem in a control setting. Results from this work show that explicit coupling without a mechanism to avoid numerical instabilities presents oscillations that can grow throughout the simulation. In order to mitigate the numerical oscillations we develop a framework based on a feedback control system, namely a PID (Proportional, Integral and Derivative) controller. The PID controller, with parameters (KC, τI, τD) tuned manually for a group of well settings, adjusts the traditional IPR curve generated by the reservoir simulator so that the error between the bottom-hole pressure calculated by the reservoir simulator (BHPRS) and the bottom-hole pressure defined in the operating point (BHPOP) is minimal. In this case, a qOP value representative for the entire time step (next time step) is obtained. The new methodology was tested in a synthetic numerical model (UNISIM-I-D) based on Namorado field (Campos Basin – Brazil), comprised by 20 satellite wells (7 injectors and 13 producers). The PID control reduces the rate and pressure oscillations in the case study, and results converge with base case scenario, which represents the network system of producer wells by proper pressure drop tables.

An integrated approach for carbonate reservoir characterization: a case study from the Linguado Field, Campos Basin

Abstract The main reservoirs in the Linguado Field are grainstone and packstone carbonates composed of oolites, oncolites, pelloids, and rare bioclasts, of the Quissama Formation (Albian-age) and coquinas of the Coqueiros Formation (Aptian-age). Within Quissama Formation, facies have high porosity variations and their 3D characterization is of utter importance to allow for a better location of the wells. The objective of this study was a volumetric characterization of Quissama Formation by means of an adapted classical workflow composed of well-seismic tie, seismic preconditioning, seismic interpretation, seismic inversion, petrophysical properties estimation, and porosity geostatistical modeling. Seismic inversion results allowed the interpretation of a horizon to separate the carbonate platform in an upper zone, with low acoustic impedance, from a lower zone, with high acoustic impedance. Finally, behavioral knowledge of acoustic impedance and the porosity distribution within the Albian carbonate platform helped to better characterize the distribution of carbonaceous facies allowing the confirmation that commercial wells were drilled in low acoustic impedance and high porosity regions. It was also possible to confirm that a well, declared as noncommercial, was drilled in a poor reservoir region with high acoustic impedance and low porosity and identified other locations that were not yet drilled but could represent potential targets.

Facies classification and patterns of lacustrine carbonate deposition of the Barra Velha Formation, Santos Basin, Brazilian Pre-salt

Abstract The lacustrine carbonate rocks of the giant Pre-salt oil-fields in the Santos and Campos Basins differ in a number of important aspects from classic lake deposits. Prior work has described distinctive and unusual features of deposition, early diagenesis and reservoir quality with in these rocks that defy classification using established schemes. In addition to their unusual textures, debate continues as to how to interpret the vertical stacking pattern of facies. A new facies classification scheme is proposed based on the relative abundance of three end-member components: mud (micrite and clay minerals), calcite spherulites and fascicular calcite shrubs. Although focused on the main textural and mineralogical features of the rocks as seen today, the proposed scheme takes into account the relative contribution of depositional and early diagenetic components, sediment mineralogy and the degree of dissolution. Application of this scheme offers insight into depositional conditions, whilst also linking to reservoir quality. Basic (elementary) cycles can be defined using this classification in combination with the variation in the abundance of detrital grains and the chemical composition. Three possible models are suggested to interpret the origin of the basic cycle within the Barra Velha Formation in the context of variation in climate, lake level and water chemistry. Integration of data from different sources, including petrographic, core description and chemical data for the basic cycle, offers improved process-based understanding of metre-scale facies patterns and provides a foundation for understanding larger scale vertical variations within and between unconformity-bound sequences.

Constrained clustering approaches to identify hydraulic flow units in petroleum reservoirs

Hydraulic flow units (HFUs) are recognized as volumetric regions that favor the flow of reservoir fluids. Their determination is made possible through correlations between data that are transferred from miscroscale to reservoir scale by upscaling. However, the strong dependence on microscale parameters inherited by commonplace analytical methods based on flow indicators is still less tractable to achieve models having uniform continuity of HFUs at reservoir scale. This paper is intended to propose a class of partitioning algorithms to deal with the problem of identifying hydraulic flow units in petroleum reservoirs. As a result, a novel viewpoint inspired on constrained clusterwise linear regression is presented to describe the identification problem. We have studied the micro-to-macroscale correspondence through a mathematical isomorphism that maps the sample domain onto the reservoir domain by using the so called flow zone indicator (FZI) as underlying parameter. Each HFU is theoretically identified by a partition of FZI points that must lie on a straight line of unitary slope in a log–log plot of two quantities: porosity and reservoir quality index (RQI). By setting up constrained clustering approaches with different must-link hard constraints, we have found multiple HFUs directly from the dataset without resorting to usual conversion formulae. Pros and cons of each approach are discussed from analyses performed over the UNISIM-I-D dataset (a reservoir model for the Namorado oilfield, Campos Basin, Brazil), as with their feasibility to devise new data-driven workflows turned to reservoir modeling and characterization, especially at the interest of exploration and production oil industry upstream. Besides, a short overall comparison by taking a correlative flow zone indicator (namely, FZI*) as underlying parameter is appended to the text. We point out that an existent tradeoff between analytical and physical requirements is a limiting factor to properly identify hydraulic flow units at reservoir scale regardless the flow indicator. In particular, it turns out that algorithms that find highly correlated partitions indicate HFUs that lack of uniform continuity and are less physically meaningful. Oppositely, algorithms that produce less correlated partitions determine HFUs with satisfactory local continuity and compactness, being more physically acceptable. Additionally, we show that a inter-clustering process is recommended when selecting data points associated to representative volumes and local spots characterizing HFUs.

E&P Notes (December 2019)

E&P Notes (December 2019)

Deep-burial hydrothermal alteration of the Pre-Salt carbonate reservoirs from northern Campos Basin, offshore Brazil: Evidence from petrography, fluid inclusions, Sr, C and O isotopes

Petrographic, mineralogical, elemental, isotopic and fluid inclusion analyses were integrated to unravel the diagenetic evolution of Brazilian Pre-Salt lacustrine carbonate reservoirs of northern Campos Basin, southeast Brazilian margin. Detailed thin section and cathodoluminescence petrography, scanning electron microscopy and electron microprobe analyses established a paragenetic evolution of diagenetic processes and products, comprising extensive dolomitization, silicification, and dissolution. A paragenesis including saddle dolomite, macrocrystalline calcite, mega-quartz, Sr-barite, celestine, fluorite, dickite, sphalerite, galena, and other metallic sulfides filling fractures and dissolution porosity, and aqueous fluid inclusions with homogenization temperatures of 92–152 °C and salinities between 13 and 26 wt % eq. NaCl characterized a hydrothermal system with some analogy to carbonate-hosted Pb–Zn Mississippi Valley (MVT) and Irish-type deposits. Petroleum inclusions and solid bitumen testify atypical oil generation and migration, associated with the hydrothermal flow. The host Pre-Salt spherulitic and fascicular carbonates present highly radiogenic 87 Sr/ 86 Sr ratios, indicating strong interaction with continental crust materials. Hydrothermal phases show δ 18 O values more negative than syngenetic and diagenetic carbonates. The δ 13 C values are interpreted as result of interaction between the hydrothermal fluids and the host rocks. The combined data set provides clear evidence of intense hydrothermal alteration of northern Campos Basin Pre-Salt reservoirs at deep-burial conditions (>2 km), possibly related to Late Cretaceous or more probably Paleogene magmatic activity. Mixed-sourced fluids bearing a basinal signature fed the hydrothermal system and promoted dissolution of the host rocks. The hydrothermal alterations had strong impact on the porosity, permeability, and heterogeneity, contributing, together with the associated fracturing, to the excellent production performance of the Pre-Salt reservoirs. • A deep-burial hydrothermal system is recognized in the Campos Basin Pre-Salt carbonates. • Hydrothermal phases show low δ 18 O values, and high Th and salinity fluid inclusions. • The geochemical and fluid inclusion signatures are similar to MVT deposits. • Hydrothermal fluids are the result of mixing between different sources. • Atypical oil generation and migration occurred associated with the hydrothermal action.

Basic and specialized geophysical well logs to characterize an offshore carbonate reservoir in the Campos Basin, southeast Brazil

Assessing the geometry, flow dynamics and, petrophysical properties, of a carbonate reservoir has been a key task for a long time, but the challenges presented by these highly heterogeneous rocks seem endless. Geophysical well logs have been, over this time, a very important tool in this type of evaluation. The applications of logs, in the evaluation of the geological formations, range from the estimation of lithology, porosity, permeability and mechanical properties. Commonly, logs are classified as basic or special. The basic logs, used in this work, are the gamma ray, resistivity, density, neutron and sonic. The special ones, utilized in the study, are the acoustic image and the photoelectric logs. From the analysis of the basic logs, the lithologies were identified, the reservoir was delimited and zoned, the fluids and the contact between them were identified and, petrophysical properties, as porosity and water saturation, were estimated. The total porosity was estimated using the empirical relationships from density, neutron and, sonic logs. The identification of the porosity type, such as fractures, vugs etc., although, was determined from the acoustic image borehole wall, as well as different geological structures, such as lithological contacts, inclined layers, natural and induced fractures, besides the identification of caves. The photoelectric log helped to identify the different lithologies, which were compared with those derived from the basic logs. Thus, the main objective of this work was the joint use of the basic and specialized logs, in the characterization of a carbonate reservoir in the Campos Basin, using real data from the post - salt layer. In the end, the advantages and disadvantages, in the usage of these tools, were indicated, as considerably as the applications and care with the occurrence of no geological structures. The joint use of the data and, the adopted methodology proved effective in the characterization of this reservoir.

Branched GDGTs as Proxies in Surface Sediments From the South-Eastern Brazilian Continental Margin

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced by bacteria usually ascribed to soil and peat deposits. The presence of brGDGTs in marine sediments can thus be used to track terrigenous organic matter inputs to the continental margin and to infer the local continental mean annual air temperature (MAT) and soil pH. The proxy rationale is based on the degree methylation and cyclization of the brGDGTs from terrestrial bacteria, but recently evidence was found of river and oceanic production of brGDGTs with similar configuration, indicating the necessity to better constrain the applicability of the soil brGDGTs in the marine realm. Here we considered crenarchaeol and brGDGTs obtained in 46 core-top sediments from cross-margin transects in the Campos Basin in the Southwest Atlantic, with the goal to evaluate the effectiveness of the brGDGT-associated proxies in a region in the southeastern tropical Brazilian continental margin influenced by upwelling events and low terrigenous inputs. The separation of the 5- and 6-methyl brGDGTs proved to be essential for a better evaluation of the sources of brGDGTs in the environment. Direct evidence of input of terrigenous organic matter by the medium-sized Paraiba do Sul River and other small rivers in the region were observed. More importantly, the high proportions of ring-containing brGDGTs – and the consequent increased values of the #ringstetra – in the sediments deposited between 75 and 400 m water depths (mid-shelf to upper slope) were clear evidence of marine in situ production of brGDGTs. In some stations deeper than 1900 m, an increase in the acyclic 6-methyl hexamethylated compounds can also be ascribed to in situ production. Our results revealed that the initial soil signal is lost during transport and after river discharge in the Campos Basin, which compromise the use of brGDGTs to reconstruct the soil pH and MAT of the nearby land area.