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Earlier geological works showed that Codo Formation - CF (Parnaiba Basin, Brazil) has been deposited in the Aptian, and suffered the influence of various transgressive-regressive marine cycles, thus suggesting various depositional environment possibilities from saline lacustrine deltaic to shallow marine during sedimentation. Cretaceous potential source rock samples from the CF were investigated to identify diagnostic biomarkers in order to ascertain paleoenvironmental conditions of deposition and thermal evolution of organic matter. The TOC results showed low organic matter (OM) contents and Rock-Eval analysis implying low thermal evolution of organic matter. GC-MS analysis showed a great diversity of biomarkers within the five studied samples. The main features of organic matter composition were: low content of n-alkanes, Ph » Pr, presence of i-25, i-30 (squalane) and gammacerane thus suggesting saline to hypersaline depositional environment. The biomarkers fingerprint showed a full series of ββ hopanes and Δ13(18) hopenes, αααR and βααR steranes, and Δ5 and Δ8(14) sterenes, pointing out immature OM. Several C30 steranes have been detected, among them 4α(methyl)- and 4β(methyl)-24-ethylcholestane, 24-n-propylcholestane and 24-isopropylcholestane (all identified by co-injection) and dinosteranes, which some of them are indicative of a marine depositional system.

Asphaltenes (isolated by preparative TLC) from Potiguar Basin (Brazil) crude oils were submitted to mild oxidation to disrupt their structure, releasing the occluded oil. The released hydrocarbons ...

The accumulation of trace elements in sediments from highly productive continental margins may depend on the affinity of these elements for organic matter and their degrees of further incorporation into pyrite (FeS2). We tested the hypothesis that the relative contributions of these geochemical phases play a substantial role as trace element (As, Cd, Cr, Cu, Mn, Ni, and Zn) sinks in the highly bioturbated sediments from the tropical upwelling system off Cabo Frio, southeastern Brazil. Four sediment cores sampled across the Cabo Frio continental shelf were submitted to a sequential extraction procedure performed to separate three different operationally defined fractions, i.e., the geochemical phases soluble in 1 M HCl (considered as the “reactive” fraction), concentrated H2SO4 (considered as the organic matter-bound phase), and concentrated HNO3 (considered as the pyrite-bound phase). The trace metal incorporation into pyrite was assessed by estimating the degree of trace metal pyritization (DTMP), while the pyrite sulfur stable isotope signatures (δ 34SPyr) were used as proxies for sulfur redox cycling intensity. Relative contributions of trace element fixation by organic matter and pyrite were positively correlated for Mn, Cr, and Ni on one hand, and negative correlated for Cu, on the other hand. The positive correlations imply in synergistic roles of these geochemical phases in determining the trace elements sedimentary sinks, while the negative relationship found for Cu reflects differences in the predominant retention mechanisms along with sediment burial. The δ34SPyr signatures were negatively correlated with DTMP values of As, Cd, and Mn, suggesting a diminishing effect of the sulfur redox cycling on trace elements pyritization. These δ 34SPyr signatures were not correlated with DTMP values of Cr, Cu, and Ni, which were dominantly associated with the high organic matter contents found in this upwelling system. The role of pelagic organic matter scavenging of metals and later fueling of benthic microbial sulfate reduction and pyrite accumulation were evidenced as highly variable across the Cabo Frio shelf sediments. Differences in the organic matter accumulation in response to upwelling-enhanced primary productivity and in the intensity of bioturbation-driven sulfur redox cycling help to explain the spatial variability in the biogeochemical processes affecting the sedimentary trace metal sinks.

Acoustic remote sensing is a highly effective tool for exploring the seafloor of both deep and shallow marine settings. Indeed, the acoustic response depends on several physicochemical factors such as sediment grain size, bulk density, water content, and mineralogy. The objective of the present study is to assess the suitability of seismic peak amplitude as a predictor of total organic carbon (TOC) content in shallow marine sediments, based on data collected in the Cabo Frio mud belt in an upwelling zone off southeastern Brazil. These comprise records of P-wave velocity (V P) along 680 km of high-resolution single-channel seismic surveys, combined with analyses of grain size, wet bulk density, absolute water content and TOC content for four piston-cores. TOC contents of sediments from 13 box-cores served to validate the methodology. The results show well-defined positive correlations between TOC content and mean grain size (phi scale) as well as absolute water content, and negative correlations with V P, wet bulk density, and acoustic impedance. These relationships yield a regression equation by which TOC content can be satisfactorily predicted on the basis of acoustic impedance for this region: y = − 4.84 ln(x) + 40.04. Indeed, the derived TOC contents differ by only 5% from those determined by geochemical analysis. After appropriate calibration, acoustic impedance can thus be conveniently used as a predictor of large-scale spatial distributions of organic carbon enrichment in marine sediments. This not only contributes to optimizing scientific project objectives, but also enhances the cost-effectiveness of marine surveys by greatly reducing the ship time commonly required for grid sampling.

Microbial biodegradation of hydrocarbons in petroleum reservoirs has major consequences in the petroleum value and quality. The identification of microorganisms capable of in-situ degradation of hydrocarbons under the reservoir conditions is crucial to understand microbial roles in hydrocarbon transformation and the impact of oil exploration and production on energy resources. The aim of this study was to profile the metagenome of microbial communities in crude oils and associated formation water from two high temperature and relatively saline oil-production wells, where one has been subjected to water flooding (BA-2) and the other one is considered pristine (BA-1). The microbiome was studied in the fluids using shotgun metagenome sequencing. Distinct microbial compositions were revealed when comparing pristine and water flooded oil wells in contrast to the similar community structures observed between the aqueous and oil fluids from the same well (BA-2). The equal proportion of archaea and bacteria together with the greater anaerobic hydrocarbon degradation potential in the BA-1 pristine but degraded reservoir contrasted with the predominance of bacteria over archaea, aerobic pathways and lower frequency of anaerobic degradation genes in the BA-2 water flooded undegraded well. Our results suggest that Syntrophus, Syntrophomonas, candidatus Atribacteria and Synergistia, in association with mainly acetoclastic methanogenic archaea of the genus Methanothrix, were collectively responsible for the oil biodegradation observed in the pristine petroleum well BA-1. Conversely, the microbial composition of the water flooded oil well BA-2 was mainly dominated by the fast-growing and putatively aerobic opportunists Marinobacter and Marinobacterium. This presumable allochthonous community introduced a greater metabolic versatility, although oil biodegradation has not been detected hitherto perhaps due to in-reservoir unfavorable physicochemical conditions. These findings provide a better understanding of the petroleum reservoir microbiomes and their potential roles in biogeochemical processes occurring in environments with different geological and oil recovery histories.

A set of five oil samples from the same source rock, classified at different levels of biodegradation, was evaluated by high-resolution mass spectrometry (Orbitrap). O-containing acidic compounds from the acidic oil fractions were characterized by determining their molecular formulas. The effects of biodegradation were detected in all O classes and were consistent with the biodegradation of neutral compounds. Additionally, we found a slightly biodegraded sample that contained acidic compounds, biomarkers of a highly biodegraded sample. These results led us to propose a scale of biodegradation using acidic compounds, particularly those containing two oxygen atoms (carboxylic acids).

Modern sea surface temperatures (SSTs) were estimated from UK′37 values of ten core-top sediment samples collected under the Cabo Frio upwelling system and validated by comparison with satellite-derived SSTs. UK′37-SSTs were found to reflect annual SST means in the offshore area and seasonal means (winter/spring) in the inshore and central areas. The latter areas are mainly influenced by upwelling processes whereas the offshore area is under the influence of the thermal front of the Brazil Current (BC). SST variability during the last century was then reconstructed from three short sediment cores. The record showed a general cooling trend in the inshore and central areas, suggesting intensification of the upwelling process. The trends at the offshore area reflected oscillations of the BC thermal front, with piling up of warmer BC waters closer to the coast since ca. 1950.

article i nfo Stable isotopic composition (δ 18 Oa ndδD of water, δ 13 CDIC) of the water column in the open ocean is related to the origin of water masses. Due to the recent increase of paleoceanographic studies on continental shelves, it is alsoimportant tounderstand theirdistribution and variabilityinthosesystems. Toexamine theinfluence of con- tinental shelves internal processes on isotopic composition of water masses, we present data of stable isotopes and phosphate content from a western boundary upwelling system located on the Southeastern Brazilian coast and compare them with offshore observations. High mixing of the main water masses (SSW, TW and SACW) was observed in the majority of the samples collected during different seasons in 2011 and 2012. A mixing trian- gle approach was used to separate the water masses contribution and characterize their isotopic composition. In addition, an isotopic three end-member model was established, proposing it as a paleoceanographic tool to re- construct relative contribution of these water masses in sediment records. Variations of δ 18 O values are linked to oceanographic dynamics, mixing, continental runoff and upwelling processes on the shelf. Differently the δ 13 CDIC variations in the middle and inner parts of the shelf are related to the productivity of the upwelling sys- tem. Seasonal variability of the δ 13 CDIC values may be also related to changes in the upwelling intensity.

The Cabo Frio region in the state of Rio de Janeiro, southeast coast of Brazil, is characterized by a local coastal upwelling system and converging littoral sediment transport systems that are deflected offshore at Cabo Frio, as a consequence of which a thick cross-shelf sediment deposit has developed over time. To investigate the evolution of this muddy deposit, geophysical, sedimentological and geochemical data from four sediment cores (3.8–4.1 m in length) recovered in water depths between 88 and 141 m were analyzed. The high-resolution seismic data show variable sediment thicknesses ranging from 1 to 20 m, comprising two sedimentary units separated by a high-impedance layer at a depth of about 10 m below the seafloor at the coring sites. According to the available age datings, the upper sedimentary unit is late Pleistocene to Holocene in age, whereas the lower unit (not dated) must, by implication, be entirely Pleistocene in age. The boomer-seismic reflection signal can be divided into three echo-types, namely transparent (inner shelf), stratified (middle shelf) and reflective (outer shelf), each type seemingly related to the local sediment composition. The upper 4 m of the upper sedimentary unit is dominated by silty sediment on the middle shelf, and by upward-fining sediments (silty sand to sandy silt) on the inner and outer shelf. The downcore trends of P-wave velocity, gamma-ray density and acoustic impedance are largely similar, but generally reversed to those of water and organic carbon contents. Total organic carbon contents increase with decreasing mean grain size, periodic fluctuations suggesting temporal changes in the regional hydrodynamics and primary productivity fuelled by the local upwelling system. The reconstruction of sedimentation rates in the course of the Holocene is based on 35 AMS age datings of organic material recovered from variable downcore depths. These range from a maximum of 13.3 cm/decade near the base of the inner shelf core (7.73–7.70 ka BP) to generally very low values (

Microorganisms have shown their ability to colonize extreme environments including deep subsurface petroleum reservoirs. Physicochemical parameters may vary greatly among petroleum reservoirs worldwide and so do the microbial communities inhabiting these different environments. The present work aimed at the characterization of the microbiota in biodegraded and non-degraded petroleum samples from three Brazilian reservoirs and the comparison of microbial community diversity across oil reservoirs at local and global scales using 16S rRNA clone libraries. The analysis of 620 16S rRNA bacterial and archaeal sequences obtained from Brazilian oil samples revealed 42 bacterial OTUs and 21 archaeal OTUs. The bacterial community from the degraded oil was more diverse than the non-degraded samples. Non-degraded oil samples were overwhelmingly dominated by gammaproteobacterial sequences with a predominance of the genera Marinobacter and Marinobacterium. Comparisons of microbial diversity among oil reservoirs worldwide suggested an apparent correlation of prokaryotic communities with reservoir temperature and depth and no influence of geographic distance among reservoirs. The detailed analysis of the phylogenetic diversity across reservoirs allowed us to define a core microbiome encompassing three bacterial classes (Gammaproteobacteria, Clostridia, and Bacteroidia) and one archaeal class (Methanomicrobia) ubiquitous in petroleum reservoirs and presumably owning the abilities to sustain life in these environments.

The early diagenesis of sulfur was assessed in four short sediment cores on the continental shelf off southeastern Brazil that were deposited under the influence of an upwelling tropical system. This tropical upwelling area allows a direct focus on the coupled roles of hydrodynamic- and bioturbation-driven influences on sulfate reduction, sulfide re-oxidation and corresponding stable sulfur isotope signal formation. Under the depositional conditions of Cabo Frio, the degree of reactive iron pyritization was limited by both dissolved sulfide availability and pyrite oxidation events. Textural analyses of pyrite framboids provide evidence of re-oxidation processes, reflecting dynamic redox conditions in the sediments. The isotope composition of pore-water sulfate remained close to the modern seawater value, but very light stable sulfur isotope ratios ( 34 S/ 32 S) of chromium reducible sulfur (essentially pyrite) are found that reflect intense bioturbation-induced sulfur re-cycling. The sulfur isotope signatures developing in these tropical upwelling sites are similar to those of modern euxinic systems, although they are caused by a superimposition of sulfate reduction and an intense oxidative sulfur cycle.

International audience; Minerals and elements are important proxies that can provide information about variations in the delivery and deposition of coastal ocean sediments associated with past climate changes. In this study, postglacial changes in the accumulation of sediments on the upper shelf of southeastern Brazil are linked to the evolution of regional paleoceanographic and continental paleoclimatic conditions during the last 14.4 kyr CAL BP. Mineralogical and major and trace element analyses of a 14C-dated sediment core identify three main lithostratigraphic units of this core that reveal a succession of changes in sediment delivery and accumulation as postglacial sea level rose and Holocene climate on land evolved. The depositional setting has transitioned in response to the large sea level rise prior to 9.9 kyr CAL BP from being a shallow water high energy environment to a deeper water one. This location has since then been a lower energy environment that has persisted into modern times. Due to the high marine productivity associated with the Cabo Frio upwelling system in an oxygenated water column, the sediments have shown a complex and dynamic redox condition, making variations in redox-sensitive trace elements indicative of changes in primary production and organic matter diagenesis at this location. After sea level stabilized ~ 9 kyr CAL BP, variations in fluxes of Al, Fe, Ca, and minerals were small, indicating that climate driven changes had only secondary controls on delivery of detrital sediment components to the Cabo Frio shelf. Modern coastal upwelling conditions and the onset of mid-shelf organic-rich sediment deposition were established after 9.9 CAL kyr BP.

The acoustic patterns variation can be used to understand the sediment distribution extrapolating the information to places where is not possible to take any sample. Many authors already use this integrated method to investigate interest areas in, both, commercial and scientific aspect. In this direction the current study initiated in 2009 in the frame of the Geochemistry Network PETROBRAS/CENPES, aims to track the quaternary evolution of a muddy bank situated at the coastal western boundary upwelling system (WBUS) off Cabo Frio (23°S) in the Atlantic Ocean. The WBUS is located at the north coast of the Rio de Janeiro State, Brazil. Here the coastline orientation differs from the default East-West direction of the Brazilian coast, concomitant with the boundary of the Campos and Santos Basins, the most important oil and gas basins of the country. The upwelling phenomenon occurs due to constant northeast winds. The same winds combined with the Northeast-Southwest coastline orientation also promote a curl confluence making the environment even more complex. Seismic data was acquired in cruises on board the RV Ocean Survey. Altogether 680 km was covered by a 3.5 KHz sub-bottom using the Geopulse Geoacustic System. Further, four piston cores were collected to be scan and described in physic parameters and sedimentological content, respectively. The scan was performed using a Geotek Multi Sensor Core Logger (MSCL), which measure and register the Vp, gamma density and porosity of the core. After the scan, the cores were sample and analyzed on sedimentological grain size distribution determined by a Cilas 1064 laser analyzer. The results were integrated in order to identify common trends. Three major echo-characters were described in seismic records. Grain size analysis presented a good relationship with these echos. Echo A) Transparent, represented by a sharp bottom reflector with no sub-bottom reflectors scatter of a transparent layer mapped in seismic records. The grain size distribution is more balanced with a slight higher content of sands (55 %) in the correspondent core. Echo B) Stratified described as a series of parallel sub-bottom horizons, its percentage of clays is the highest of the three cores (77 %). The last echo, C) Reflexive, is a prolonged echo with one or none sub-bottom reflector. This echo is related to the highest percentage of sands of the three cores (61%). The sediment analysis was extrapolated all over the echo-characters extension to understand the transport regime over the area. This criteria, allied to isopach map, made possible to recognize three distinct zones inside the muddy accumulation.