Search

The sedimentary basins in the Continental Rift of Southeastern Brazil (CRSB) provide an opportunity for ichnological analyses due to its well-known facies relationships and paleoenvironmental interpretations. This study reports invertebrate trace fossils from the Neogene fluvial deposits (Floriano Formation) and applies integrated ichnological and facies analyses to reconstruct the environmental conditions recorded in this lithostratigraphic unit. Fieldworks revealed a rich ichnofauna in the Floriano Formation, whose facies associations have been interpreted as indicative of meandering river environments. Four sedimentary facies were identified, including bioturbated sandstone, horizontally stratified sandstone, laminated sandstone, and mudstone. Six ichnogenera were identified, Arenicolites, Beaconites, Camborygma, Palaeophycus, Skolithos, and Taenidium. Those ichnogenera occur as Skolithos, Taenidium, and Beaconites ichnocoenoses. The Skolithos ichnocoenosis is primarily represented within sand bar deposits, indicating arthropod colonization in abandoned channels. The Taenidium ichnocoenosis, which is observed within mudstone layers and presents Camborygma burrows, suggests transitional environments between aquatic and subaerial conditions, locally with high water table levels. The Beaconites ichnocoenosis indicates changes in substrate consistency associated with progressive desiccation and extended exposure time. Therefore, the identified ichnocoenoses, combined with the analysis of physical sedimentary structures, suggest generally humid conditions during colonization by invertebrates of the meandering river deposits of the Floriano Formation. [ABSTRACT FROM AUTHOR]

The supply of Corumbataí Formation rocks, which occur widely in the State of São Paulo, Brazil, and are used by Santa Gertrudes Ceramic Cluster, is dwindling and prospecting for new deposits is essential. The current study aimed to map and characterize new reserves of ceramic raw materials which would guarantee mineral and economic sustainability of the important concentration of ceramic-processing capability in that area, and thereby contribute to improving and diversifying the range of products manufactured and to promoting a greater presence in the international market. To achieve the proposed objectives, 16 profiles were sampled and the samples were submitted to granulometric analysis by laser diffraction, and the major elements by inductively coupled plasma-mass spectrometry, and the mineralogical compositions of clay samples were determined by X-ray diffraction and ceramic properties. Six lithofacies were identified and grouped into two facies associations: a lower shoreface association comprising massive siltstone (Sm) and laminated siltstone (Sl); lithofacies, and an upper shoreface association comprising heterolithic sandstone (Sh), lenticular sandstone (Sle), intercalated sandstone/siltstone (Si), and altered siltstone (Sa) lithofacies. The lithofacies of the lower shoreface association were more clayey, flux with a significant presence of illite and microcline, and a more uniform granulometry distribution, which made its classification possible, technologically, as stoneware and semi stoneware. The main application of this material is in the production of coatings through the wet milling process. The lithofacies of the upper shoreface association was sandier, had a refractory presence with kaolinite and montmorillonite, and had a less uniform granulometric distribution; technologically, it can be characterized as porous and semi-porous. The main application of this material is in the production of coatings by the dry milling process. The results obtained by facies analysis combined with the geochemical and ceramic properties of the Corumbataí Formation rocks revealed both vertical and lateral variations of the lithofacies, which influence their properties, behavior, and application as ceramic raw materials. [ABSTRACT FROM AUTHOR]

Carbonate reservoirs are of great economic importance due to their frequent association with high permeability and hydrocarbon storage capacity. One of the most significant discoveries of this type of reservoir in recent decades has been the Brazilian Pre-salt. This deep reservoir has unusual depositional features, consisting of a wide variety of textures with different compositions, influenced by diagenetic overprinting that modify most of its mechanical, elastic and petrophysical properties. Despite the marked heterogeneity, these carbonates are characterized by excellent reservoir quality. The objective of this study is to establish a correlation between geomechanical behavior and sedimentary facies and its implications for the definition of flow units in the Barra Velha Formation, the main reservoir of the Brazilian Pre-salt. Thus, using a database from the Buzios field composed of well logs (conventional and advanced), well tests, thin sections, and laboratory petrophysics, geomechanical facies (GMFs) were defined using dynamic geomechanical modeling and an unsupervised algorithm (K-mean clutering), followed by textural classification of sedimentary facies and definition of flow units (FUs) on the decametric scale. These classifications were compared using frequency histograms. The geomechanical model revealed that the in-situ stress state exhibits a dual regime, between normal and strike slip. In addition, it was found that the direction of the maximum horizontal stress is in the NE-SW azimuth. In this context, four geomechanical facies were defined, which showed a notorious variation in mechanical strength. The strongest GMFs consisted mainly of well-cemented Grainstones and Packstones with no apparent porosity or microcrystalline porosity and correlated with the FU with the worst production rates. On the other hand, the weaker GMFs were mainly composed of Grainstones and Spherulistones with high intergranular porosity generated by dissolution processes, with higher risk of pore collapse and correlated with the FUs with the best production rates. However, this classification also identified laminated mudstones with microporosities associated with FUs that act as flow barriers. Geomechanical facies have also been incorporated into reservoir development by evaluating wellbore stability, fault reactivation risk, and brittleness index for future CO 2 injection projects. • Stress regime duality in the Búzios field (Normal to Strike-slip failure regime). • Low to intermediate mechanical strength of Brazilian pre-salt reservoir. • The sedimentary facies show a great variety of textures, and porosities, influencing the geomechanical behavior. • Lateral and vertical variations of the geomechanical properties using K-means clustering defined by facies. • Comparison between flow units and geomechanical facies. [ABSTRACT FROM AUTHOR]

During the Cretaceous, the Brazilian Intracratonic Sanfranciscana Basin was characterised by fluvial and aeolian deposition, whose facies, palaeosols, and stratigraphic architecture indicate significant changes in tectonics and climate. This work proposes a low-frequency sequence stratigraphic model, using the facies and palaeosols distribution as the stratigraphic proxy for identifying variations in the accommodation space, sediment supply, and their relationship with the tectonic and climatic events. The Unconformity U-0 was generated by the extensional tectonic processes during the Gondwana breakup in the Early Cretaceous and marked the initial continental sedimentation. The Lower Cretaceous Sequence SF1 overlies this unconformity, constituted by fluvial and lacustrine deposits. From south to north, the unconformity U-1 truncates the top of the Lower Cretaceous Sequence SF1 and the Precambrian basement, respectively. Overlaying Unconformity U-1 are the Upper Cretaceous volcanic rocks, fluvial, and aeolian deposits of the Sequence SF2. Because of the vertical and lateral changes, Sequence SF2 is divided into two sequences, SF2A and SF2B, separated by the regional Unconformity U-2, representing climatic and tectonic changes in the basin. During the late stage of sedimentation of Sequence SF1, the ratio between accommodation (A) and sediment supply (S) was positive in the south and negative in the basin's north. The evolution of Sequence SF2A records a negative A/S ratio, followed by an abrupt change to a positive A/S ratio in Sequence SF2B, leading to the genesis of the regional erosive surface of Unconformity U-2. Sequence SF2B also records increased humidity from arid climatic conditions, marked by the 3D regional distribution of facies and palaeosols, linked to the climatic changes detected in South America for the Late Cretaceous. • Proposes low-frequency sequence stratigraphy analysis. • The 3D regional distribution of facies and palaeosols approach. • The Brazilian Intracratonic Sanfranciscana Basin. • Variations in the accommodation space, sediment supply, and their relationship with the tectonic events. • Late Cretaceous climatic changes. [ABSTRACT FROM AUTHOR]

Distributive Fluvial Systems (DFS) are fan-shaped landforms constituted by a radial system of channels that diverge downstream from an active apex, where the drainage emerges from the confinement valley. In such landforms, elevation, distance from fluvial channels, sedimentation rates, surface stability, and plant cover control weathering processes and soil development, but these features are obliterated within geological time. Thus, the micromorphological analysis of paleosols can be helpful for paleoenvironmental reconstruction of ancient DFS, improving the knowledge of soil genesis in these depositional landforms. Here, we describe macro and micromorphological features of twenty paleosols developed under arid to semiarid climates along the proximal to the medial zone of an Upper Cretaceous DFS in the Marília Formation, Bauru Basin, Brazil. Paleosols on the proximal zone typically showed features consistent with poor drainage, namely Bg, Btg and Bss horizons, and reddish Bt horizons in higher positions. Conversely, paleosols on the medial zone commonly showed reddish colours and pronounced secondary carbonate accumulation, consistent with a predominantly arid climate. Based on this distribution, we elaborated an evolution landscape model for the proximal and medial zone of the Bauru DFS, including allogenic and authigenic controls of soil development during the Campanian to the Maastrichtian epochs of southeastern Brazil. • Macro and micromorphological analysis of paleosols. • Identify the mainly paleosol-forming processes, such as palaeohydrology and palaeotopography conditions. • Soil Paleocatena. • Allogenic control in soil development and geomorphic relationships. • Conceptual framework for recognition criteria for paleosols and geomorphic evolution in distributive fluvial systems (DFS). [ABSTRACT FROM AUTHOR]

Tectonic rejuvenation has been widely described in ancient rifting areas of intraplate settings, despite extensive active tectonics being discontinued long ago. Various models have been invoked to justify such tectonic rejuvenation, suggesting that the long-term deformation in intraplate interiors may be more complex than once supposed. Inherited weakness zones, e.g., pre-existing faults are stress concentrators. However, not all weakness zones in plate interiors show tectonic rejuvenation and recognizing intraplate fault reactivation remains puzzling. Bedrock channels play an essential role in tectonically unstable landscapes and therefore they may unveil which pre-existing structures have been rejuvenated. Here we explore the Cinzas Catchment in order to investigate the interactions between tectonic rejuvenation, bedrock inheritance and geomorphic river signatures in an important Brazilian rifting feature, the Ponta Grossa Arch. We perform a geomorphic analysis combined with fieldwork, dating techniques and existing data to evaluate whether the geomorphic responses of the major rivers show perturbations related to the bedrock inheritance and post-rift rejuvenation. We also show that the interactions between river signatures and the bedrock fault zones are responses to post-rifting rejuvenation coupled with bedrock inheritance. This post-rifting rejuvenation is consistent with a mosaic of superimposed mechanisms which have been invoked by previous studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Marília Formation is a lithostratigraphic unit positioned at the top of the Bauru Group of Maastrichtian age. The present work presents a provenance study of the Marília Formation sandstones through the combined dating of the fission‐track method (FTM) and U–Pb, in which individual zircon grains are simultaneously dated by these two methods. Thirty‐one zircons were dated in the C5 sample and 26 in the C7 sample for a total of 57 grains. The data demonstrated a wide range of U–Pb ages, presenting maximum and minimum ages, respectively: 2,905 ± 11 and 128 ± 1 Ma for the C7 sample and 2,676 ± 10 and 455 ± 5 Ma for the C5 sample. Regarding the fission‐track (FT) ages, they have been grouped into three time intervals, which are associated to geological events relatively well recognized in the published literature: ages younger than 250 Ma (Wealdenian Reactivation); between 250 and 470 Ma (Palaeozoic orogenesis—Ocloyic, Precordilleran, Chanic, and Sanrafaelic); and older than 470 (Precambrian collisions—Brasiliano I, II, and III). There is a predominance of results of Precambrian age using the U–Pb dating, mainly in the Neopalaeoproterozoic, and with FT dating corresponding to the Ocloyic, Precordilleran, Chanic, and Sanrafaelic orogeneses. From the comparison of the results between the two dating methods, the age variations suggest that the zircons originated during the main south‐western orogenesis of Gondwana and were reworked during the Palaeozoic and Mesozoic geological episodes. The ages associated to the Upper Cretaceous are related to the tectonic and magmatic activity of the Alto Paranaiba Uplift. [ABSTRACT FROM AUTHOR]

The Late Cretaceous Marília 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 Marília 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 Marília Formation in the western portion of the state of Minas Gerais in Brazil. The results indicate that the paleosols of the Marília 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 Marília Formation, suggesting an increase in humidity from east to west in the study area. • A new approach using pedochemistry analysis was used. • Three pedochemical units and geochemical markers were identified. • Seasonal variations based on weathering indexes were observed. • Paleoenvironmental and paleoclimate conditions indicate arid to semiarid climate. [ABSTRACT FROM AUTHOR]

The Upper Cretaceous Bauru Group in south‐east Brazil consists of alluvial strata whose characteristics and distribution indicate a fluvial system developed in a semi‐arid to arid climate. Sections exposed within a 90 000 km2 study area in Minas Gerais State (in south‐eastern Brazil) were evaluated using facies and palaeosol analysis to formulate depositional and pedogenic models that may account for geomorphic and climate features. From east to west, the study succession records a gradual decrease in grain size, an increase in the width/thickness ratio in channels, a decrease in the lateral and vertical connectivity of channel deposits, and an increase in overbank deposits. The fluvial architecture indicates a braided channel belt, ephemeral ribbon–channels, and an unconfined fluvial facies from east to west in the study area. The lateral and vertical distribution of facies, stratigraphic architecture and palaeocurrent data suggest proximal, medial and distal portions of a progradational distributive fluvial system. The sedimentary dynamics were marked by the building and abandonment of channels related to processes of aggradation, vegetation growth and palaeosol generation. Macromorphological and micromorphological analyses have identified pedological and mineralogical features that indicate an arid to semi‐arid climate with a provenance from the north‐eastern part of the basin (Alto Paranaiba Uplift). From the proximal to the distal portions of the distributive fluvial system, the palaeosol development is different. In the proximal portion, the palaeosols are absent or poorly developed, allowing a possible general comparison with the present soil order: Inceptisols and Aridisols. In the medial portion of the fluvial system, the palaeosols are well‐developed and characterized by Bt, Btk, C and Ck horizons (Alfisols, Aridisols, Inceptisols and Entisols). Poorly drained to well‐drained palaeosols from the base to the top in the distal plain (Aridisols and Inceptisols) are associated with geomorphic and hydromorphic changes in the fluvial system due to progradational evolution. The genetic relationship between the fluvial architecture and the palaeosols enhances the understanding that the sedimentation and pedogenesis that occurs in different portions of the distributive fluvial system are related to the tectonic and climatic evolution of the basin. [ABSTRACT FROM AUTHOR]

Palaeosols can be used as stratigraphic proxies, palaeosurface indicators, and palaeorelief reconstitution tools, as they reflect a complex interrelationship between sedimentation, erosion, non-deposition, and pedogenesis. The objective of the article was to estimate the relative time of formation of palaeosols of the Marília Formation, to determine the periods of non-deposition and non-erosion, indicative of stabilities on the surfaces, and to interpret the profiles as markers of palaeosurfaces in distributive fluvial systems (DFS) of the Late Cretaceous of Brazil. Eleven sections of the Marília Formation (S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, and S11) were described, comprising forty-three profiles. The pedotypes classification (polygenic, compound, and cumulative) and the determination of palaeosols' relative formation time and residence time were based on the specialized literature. The reconstitution of pedosedimentary cycles considered the dynamics of sedimentation, erosion, and pedogenesis. Eight sedimentary cycles and 45 pedosedimentary cycles were interpreted. All the Maastrichtian pedosedimentary cycles of the Bauru Basin corresponded to depositional cycles interspersed with erosive and pedogenic processes. Palaeosols with argillic (Btk, Bt, Bss) and calcic (Bkm) horizons, developed from fluvial sandstones, evolved in processes predominantly after the deposits, with later erosive processes. However, although most of the profiles developed in periods between deposits and erosion, pedogenic processes also occurred concomitantly with the sedimentary cycles, favouring the formation of polygenetic profiles, which presented the longest pedogenic cycles in chronological terms. Palaeosols with argillic horizons can be important stratigraphic landmarks. They represent stopping moments in erosion and sedimentation of up to 1.374 My, thus consisting of the closing of high-frequency depositional cycles. Although palaeosols can demonstrate relief inversion and pedotypes with Bt-horizons can indicate ancient regional surfaces, the complete reconstitution of the topography becomes more possible at the local level, in a palaeoslope approach, due to the variability of pedofacies. • Palaeosols represent moments of non-deposition and non-erosion, indicative of landscape stability. • Compound and polygenetic palaeosols with Bt and Btk horizons correspond to the largest intervals of non-erosion, non-deposition, of topographical and tectonic stability in the evolution of the Maastrichtian palaeolandscape of the Bauru Basin. • The palaeosols represent relief inversion and the pedotypes with Bt-horizons indicate ancient regional surfaces, providing the reconstitution of palaeoslopes. [ABSTRACT FROM AUTHOR]

The reactivation of faults may directly modify their permeability and the integrity of the petroleum system seal. Thus, this understanding is fundamental for decision-making in the petroleum industry at different levels while developing, for example, hydraulic fracturing projects, fracture networking, Enhanced Hydrocarbon Recovery (EOR), and CO 2 storage. The identification of the stress field based on elastic properties, failure criterion, rock strength, and in-situ principal stresses allow to understand the geomechanical behavior of stratigraphic units. This process becomes complex in carbonate reservoirs because they present high geomechanical variability related to the sedimentary and diagenetic processes they undergo. In this context, the present work aims to study the potential for fault reactivation in the pre-salt Barra Velha and Itapema Formations and in the Camboriu Formation in the study area, Santos Basin, Brazil, based on geomechanical modeling. Data from 28 wells with basic geophysical well-logs and wellbore image logs, absorption and formation pressure tests, and 3D pre-stack seismic data were used. The results indicate an abnormally high fluid pore pressure (9.49 ppg) concerning hydrostatic pressure (8.34 ppg). Three structural compartments delimited by interpreted seismic horizons and faults were defined. Three fault regimes were defined based on minimum and maximum horizontal stresses gradients: a double normal-transcurrent regime for the Barra Velha and Itapema Formations; a normal regime for the Piçarras Formation; and a double transcurrent-inverse regime for the Camboriu Formation. Finally, based on the stress polygon, scenarios of fault reactivation in the structural compartments were estimated. With increases between 16% and 28.1% of the pore pressure by fluid injection, the transcurrent movement of the faults can be generated. The reverse faults of a shallower structural compartment have the highest probability of reactivation and movement. • Contrasting mechanical behaviors were observed in the pre-salt carbonate rocks and in the igneous rocks • An abnormally high behavior of Ppore with respect to Ph was identified for different saturation intervals. • The orientation of the in-situ horizontal stresses is NW-SE for S hmin and NE-SW for S HMax coinciding with the azimuth of the faults (NE-SW). • A rotation of the stress fields along some wells relative to the main trend was identified. • Due to the magnitudes of the stresses S v , S hmin and S HMax , different fault regimes were identified in the formation of interest. • Fault reactivation in the BVE100 can occur under a transcurrent stress regime. • A direct relationship between the depth of fluid injection and the increase of Ppore was identified. / OTHER HIGHLITH --> A correlation was defined between the orientation of movement of the reactivated faults and the azimuth of the faults. [ABSTRACT FROM AUTHOR]

Reservoir static modelling plays a fundamental role in the evaluation phase of a petroleum field. Integrated modelling allows a better understanding of how the local geology and depositional systems are related through the distribution of facies and petrophysical properties within the reservoir. In this study, geological static models of the siliciclastic Carapebus Formation of Campos Basin were built using subsurface data. The applied methodology was divided into five phases: (1) establishment of a conceptual model, (2) building of a structural model, (3) generation of 100 realizations of lithofacies using sequential indicator simulation, (4) generation of 100 realizations of porosity and permeability using sequential Gaussian simulation, and (5) validation of models by targeting both statistical and geological consistency. The obtained models are consistent and honor the conditioning data. A lithofacies constraint is crucial to better characterize the petrophysical properties distribution of the reservoir. A Dykstra-Parsons coefficient of V=0.52 characterizes this reservoir as moderately homogeneous. [ABSTRACT FROM AUTHOR]

Despite the vast crocodyliform fossil record, little is known about the reproductive biology and nesting strategies of the extinct members of the group. Here we report a large accumulation of crocodilian fossil eggs from the type-locality of the baurusuchid Pissarrachampsa sera . Sedimentary facies and architectural elements of the site support a palaeoenvironmental model with a shallow lacustrine, playa-lake system interacting to ephemeral braided fluvial channels, with aeolian influence and development of sandy soils. The presence of pedogenic calcretes in the palaeosols indicates arid to semi-arid conditions. The crocodilian affinity of the eggs is supported by the thin eggshell which bears wedge-shaped shell units with tabular microstructures. Furthermore, taphonomic data support an autochthonous assemblage of eggs and skeletal remains, hinting at a monotypical stratigraphic horizon and suggesting P. sera as the egg-laying taxon. The repeated pattern of four (eventually five) eggs per clutch at the site demonstrates that P. sera laid fewer eggs compared to modern crocodilians, indicating that k-selected reproductive strategy pattern is pervasive in the fossil record of Notosuchia. In the crocodyliform phylogenetic framework, the k-strategy and the “egg clutch sizes” optimization of Notosuchia is opposite to the strategy with larger clutches consistently occurring in modern Crocodylia and Neosuchia, the sister clade to Notosuchia. Yet, the lack of data on more early-branching taxa renders unclear which pattern is plesiomorphic for Crocodyliformes as a whole. [ABSTRACT FROM AUTHOR]

With the breakup of the supercontinent Gondwana, the South American Plate has undergone an intense process of tectonic restructuring that led to the genesis of the interior basins that encompassed continental sedimentary sequences. The Brazilian Bauru, Sanfranciscana and Parecis basins during Late Cretaceous have had their evolution linked to this process of structuring and therefore have very similar sedimentary characteristics. The purpose of this study is to establish a detailed understanding of alluvial sedimentary processes and architecture within a stratigraphic sequence framework using the concept of the stratigraphic base level or the ratio between the accommodation space and sediment supply. The integration of the stratigraphic and facies data contributed to defining the stratigraphic architecture of the Bauru, Sanfranciscana and Parecis Basins, supporting a model for continental sequences that depicts qualitative changes in the sedimentation rate (S) and accommodation space (A) that occurred during the Cretaceous. This study discusses the origin of the unconformity surfaces (K-0, K-1 and K-1A) that separate Sequences 1, 2A and 2B and the sedimentary characteristics of the Bauru, Sanfranciscana and Parecis Basins from the Aptian to the Maastrichtian, comparing the results with other Cretaceous Brazilian basins. The lower Cretaceous Sequence 1 (Caiuá and Areado groups) is interpreted as a low-accommodation systems tract compound by fluvial and aeolian systems. The upper Cretaceous lacustrine, braided river-dominated alluvial fan and aeolian systems display characteristics of the evolution from high-to low-accommodation systems tracts (Sequences 2A and 2B). Unconformity K-0 is related to the origin of the Bauru Basin itself in the Early Cretaceous. In Sanfranciscana and Parecis basins, the unconformity K-0 marks the contact between aeolian deposits from Lower Cretaceous and Upper Cretaceous alluvial systems (Sequences 1 and 2). Unconformity K-1, which was generated in the Late Cretaceous, is related to an increase of the A/S ratio, whereas Unconformity K-1A is the result of the decrease in the A/S ratio. Unconformity K-1A bound Sequence 2A (lacustrine and fluvial systems) and Sequence 2B (alluvial deposits) in Bauru Basin whereas in the Sanfranciscana and Parecis basins this unconformity marks the transition from alluvial system to aeolian system (Sequences 2A and 2B). Changes in depositional style in both basins correspond to two distinct tectonic moments occurring within the South American plate. The first associated with post-volcanic thermal subsidence of the Early Cretaceous (Serra Geral and Tapirapuã volcanismos), and the second moment associated with the uplift occurred in the Late Cretaceous (Alto Paranaíba, Vilhena and Serra Formosa Arcs). [ABSTRACT FROM AUTHOR]

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 Marília 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 Marília 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 Marília Formation were described and collected on nine sample profiles. Micromorphological, mineralogical and geochemical analyses were performed according to the specialized literature. In the Marília 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 Marília 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 calcretes of the Marília Formation are of pedogenic origin. • The calcretes (paleosols) developed in situ by the weathering of sandstones. • These paleosols were formed in flatter slopes of relief, under semi-arid environment. • Calcification and argilluviation acted in the evolution of the paleosols. • Paleosols with Bt-horizon are more weathered than those with Btk and Bk horizons. [ABSTRACT FROM AUTHOR]

• A robust predictive model for bitumen assaying at multi-scale was developed. • The hydrocarbon signature at 2300 nm was found consistent and comparable among scales. • Key variables that control the spectral behavior of bituminous sands was recognized. • Multi-scale imaging spectroscopy has the capability to provide continuous grade data. In this work, oil-sand outcrops of the Anhembi deposit located in the Paraná Basin, Brazil, were investigated using multi-scale imaging spectroscopy. The study incorporated VNIR–SWIR (400–2500 nm) spectroscopic data from imaging (i.e. sisuCHEMA) and nonimaging (i.e. FieldSpec-4) instruments in the lab, an AisaFENIX hyperspectral system on the ground and from the air, and WorldView-3 multispectral instrument. The aim was to assess the usefulness of emerging remote sensing technologies in characterizing hydrocarbon-bearing targets and understand the spatial variability of oil-sands at different scales using multi-source spectroscopic data. The bitumen content of the sands, estimated to be as high as 12 wt. %, was revealed to be unevenly distributed at all scales. Its distribution was shown to be controlled mainly by the clay proportion and permo-porosity of the strata, with the sand sheet facies corresponding to the highest bitumen contents. The ubiquitous clays, identified to be dominantly montmorillonite, were found to be intimately mixed with bitumen at all studied scales. The mean bitumen content was estimated to decrease from ˜ 6 to 4.5% while moving from small-, to deposit-scale as a consequence of the pixel aggregation effect and incremental clay contribution. The study showed that bitumen determination on the ground requires an imaging system with a high signal-to-noise ratio and good illumination conditions. Spectral denoising is also a crucial prerequisite for the extraction of coherent spectral information from the data. WV-3 data was proved capable of resolving HC's feature at 1700 nm wavelength by its SWIR band-4 over targets encompassing >30% of the 7.5 m SWIR pixel; albeit it was not successful in determining the total bitumen content of the sands. This work indicated that HC signatures, particularly the one centered at 2300 nm, is consistent and comparable among scales, and upon employing properly calibrated data, could be used to confidently map the bitumen content of oil-sands at all imaging scales. A multi-scale spectroscopic approach can provide a complete picture of the variations in geologic targets and is able to fill the gap in scale differences across scales that when integrated, would add synergy and help reduce the uncertainties associated with ore grade estimation. [ABSTRACT FROM AUTHOR]

Soils are good indicators of the stability of environmental systems. In meandering river floodplains, they assess river channel morphology, incision process, groundwater level dynamics, and avulsion processes. The morphological properties and physicochemical attributes give gleysols unique characteristics about formation conditions and evolution degrees related to fluvial dynamics, thus allowing elaborate models of floodplain evolution in meandering rivers. This manuscript aimed to analyze the relationship between gleysols evolution and fluvial dynamics, in the quaternary floodplain of a meandering river, in the Mogi Guaçu River basin in the State of Minas Gerais. We described three profiles, in concave and convex margins of the river, identifying facies and considering the morphological characteristics of the gley horizons. Physicochemical analyses, determination of major and minor elements, and oxides were carried out on the samples of horizons and deposits of the profiles. For the characterization of the river channel, morphometric parameters were measured. Concentrations of silica, titanium dioxide, alumina, ferric and manganese oxides, plus the molar relations of provenance (P), leaching (L), parent material (M1 and M2), oxidation (O), hydrolysis (H), and the alteration geochemical index (CIA-K) were determined to compare the profiles pedological evolution. The three analyzed profiles were classified as typic Dystrophic Tb Haplic Gleysol (P1 and P2) and typic Alic Tb Haplic Gleysol (P3) so that the relation silt/clay demonstrated profile 3 to be the most evolved (weathered). Concentrations and behavior of oxides, associated with molar relations and conditions of the surfaces S II and S III of the flat floodplains morphological, demonstrated that the meandering process, with avulsion linked to erosion and deposition, affects gleysols evolution, suggesting genesis with compound or polygenetic profiles. Under a cyclical interpretation, the evolution of gleysol profiles, with truncation and horizon overlaying, reflects processes of avulsion, incision, and floods, as well as are proxies for interpreting the quaternary evolution of the Mogi Guaçu River meandering process. • The meandering process, with avulsion associated with erosion and deposition, influences the evolution of gleysols, providing for the genesis of compound or polygenetic profiles. • The genesis of different pedotypes of gleysols are reflections of the process of avulsion and incision of the river channel. • The Gci, Sh, Sl, Sm, and Fm facies, along with intense mottling in the horizons, demonstrate oscillations in the groundwater level and changes in the channel's energy gradient. [ABSTRACT FROM AUTHOR]

Burrowing behavior is an important adaptation of animals that live in arid and semi-arid conditions. In this paper, we describe examples of vertebrate burrows from the Upper Cretaceous (Maastrichtian) Adamantina Formation of the Bauru Basin, Brazil, most likely produced by turtles. The Adamantina Formation preserves abundant and diverse turtle body fossils such as Bauruemys elegans (Testudines: Pleurodira); however turtle burrows have not been previously documented. The newly reported burrows are preserved in fluvial sandstone facies and exposed in sections that partially preserve their three-dimensional geometry. Burrows are simple J-shaped tunnels with a cross-sectional shape that is semicircular (half-dome) with a flattened floor. Such burrows show a partially preserved entrance with an inclined ramp angle (22°), and grooves and ridges up to 1 cm in width preserved along the burrows walls and floor. The architecture and sedimentary facies of the host sandstone body, together with the occurrence of Taenidium barretti and the absence of rhizoliths, suggest that the burrow was excavated by scratch digging into an exposed point bar of a meandering river channel. Based on burrow morphology, dimensions, as well as ridges,and grooves in the walls and floor, we propose that burrows were formed by a chelonian (such as a freshwater turtle) during aestivation. We highlight that these are first examples of turtle burrows reported from the Cretaceous, and their occurrence reinforces the hypothesis that the original function of turtle shells was as an adaptation to fossorial behavior. [Display omitted] • The first freshwater turtle burrows from Cretaceous of South America. • The burrows occur in fluvial point bars of Adamantina Formation. • Evidence of fossorial and aestivation behavior in turtles during Cretaceous. • Results reinforce the hypothesis of fossorial behavior in stem turtles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Weathering pattern is mainly determined by the bimodality of aeolian deposits. • Dissolution features and booklets of kaolinite reveal monosiallitisation process. • Kaolinization processes suggest an increase in moisture between Albian and Cenomanian. The work investigated the paleoenvironmental significance of kaolinite-rich weathering fronts developed during the Cretaceous in stabilized dune fields of Sanfranciscana Basin in Brazil. To this, was conducted a multi-scale analysis from the outcrops of paleosols to mineral grains and soil pores. The macro and micromorphology of paleoweathering fronts allow recognizing weathering features and estimating the porosity and hydraulic parameters (permeability, capillary pressure, and saturated hydraulic conductivity). Scanning electron microscope analyses were conducted to investigate surface microtextures of quartz grains for weathering process characterization based on dissolution microfeatures. Energy-dispersive X-ray spectrometry was utilized to identify chemical elements of clay minerals. The major and trace elements were analyzed using a Philips X-ray fluorescence (XRF) spectrometer (PW 2440). Our results showed that weathering fronts expand through preferential water paths (pipe and finger flow) in bedding planes in response to textural and porosity contrasts related to the bimodality (i.e., the difference of grain size distribution between overlapped sedimentary structures) of aeolian deposits. The dissolution features present in quartz grains, such as etching, pitting, total dissolution of grains, iron coatings, and booklets of well-developed kaolinite, reveal an increase in humidity and the pedogenetic kaolinization process typical of a humid tropical environment. These weathering patterns coincide with cooling events between the Albian and the Cenomanian report in the literature. Our study indicates that during the Cretaceous, the Sanfransicana Basin underwent climatic amelioration and a rise in water table level, which likely enhanced dune stabilization and the formation of an extensive geomorphic surface. [ABSTRACT FROM AUTHOR]

• Pedogenetic processes involved in the argillic horizon (Marília Formation) have been studied. • Argillic horizons show clay illuviation, accumulation of carbonates and gleyic properties. • Argillic horizons developed in a semi-arid environment. A study of paleosols with argillic horizons found in the Marília Formation associated with Maastrichtian in the Cretaceous is presented herein. This study aims to investigate the polygenetic processes involved in argillic horizon formation under paleoclimatic conditions from arid to semiarid in the Brazilian Cretaceous and considers morphological soil attributes, such as evidence of cementation, macromorphological data (horizons, matrix color, structure, clay coatings, nodules, and bioturbations), micromorphological data (coarse/fine patterns, b-fabric, clay coatings, infillings, and nodules), and water table oscillation. Seven representative profiles of paleosols were selected in the São Paulo state, Brazil, and soil samples of lithified paleosols were collected to determine their macromorphological–micromorphological and chemical properties. Clay illuviation, carbonate accumulation, and gleization were dominant processes in the paleosols. Clay illuviation was identified from clay coatings along grain and ped surfaces. Carbonates occurred as nodules and rhizoliths and as coatings on peds. Red mottles, gray rhizohaloes with red oxidation rims, oxidic nodules, an iron-depleted matrix, and iron oxide depletion hypocoatings confirmed gleization. The argillic horizon polygenesis in the Marília Formation is usually interpreted as evidence of high-moisture events under arid/semiarid climates or climate change toward moister conditions than arid/semiarid. Thus, argillic horizon paleosols in the sedimentary records of the Marília Formation are not necessarily reliquial characteristics of wet paleoenvironments but are associated with changes in dominant granulometry, types of macroaggregates–microaggregates, carbonate accumulation in horizons, and/or water table oscillation. Thus, the presence of Bt horizons does not necessarily imply wet conditions with changes in the depositional system, as proposed by some authors. [ABSTRACT FROM AUTHOR]

An organic geochemical investigation combined with sequence stratigraphy was performed in the Ceará 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) Mundaú Formation – top of the Rift Sequence (Berriasian-Aptian); (2) Paracuru Formation – Breakup Sequence (Aptian-Albian); (3) Itapajé 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 Mundaú 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 Ceará Basin. The Ubarana Formation represented by the Uruburetama Member and the Itapajé 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. Flowchart representing the steps of this research. A) Database components. B) Data interpretation. C) Relative hidrocarbom potential (RHP) variations revealing changes in oxic conditions at depth and correlations with gamma-ray (GR) and lithofacies (Facies) stacking patterns. D) Sections showing the results obtained from data interpretation. E) A simplified model for the Paracuru Formation. [Display omitted] • Stratigraphic evolution, organic geochemistry, and Cretaceous Anoxic Events (CAE) were investigated. • Well-log correlations, redox conditions, and modeling to investigate anoxic events occurring in the Ceará Basin. • Relative sea-level fluctuations in 3rd- and 4th-order sequence-stratigraphic contexts are presented. • Relative hydrocarbon potential (RHP) as a geochemical index that reflects oxygenation conditions. • Anoxic markers were defined in the organic-rich, transgressive systems tracts (TST) and condensed section (CS) strata. [ABSTRACT FROM AUTHOR]

We present the analysis of airborne and ground gamma-ray spectrometry signatures of the Araguainha impact structure, located in central Brazil, the largest impact structure in South America with ~ 40 km diameter. The airborne data are total gamma-ray counts per second collected along flight lines spaced 1 km apart. The ground gamma-ray data are concentrations of potassium, uranium, and thorium isotopes calculated from radiations measured in three individual channels. The objectives are to distinguish lithologies within the structure, which have naturally distinctive radiogenic signatures, and identify potential post-impact hydrothermal alteration zones, as indicated by high K concentrations. Based on results obtained by numerical modeling of the crater formation, we infer the locations of potential occurrences of target rocks that may have undergone hydrothermal alteration as a result of the impact. The deviations from the background potassium concentration show significant anomalous K values at the center and in the northwestern crater rim, where high concentrations of U are also observed. The numerical model shows that ideal temperature conditions for hydrothermal fluid circulation were attained right after pos-impact gravitational stabilization.