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Quaternary geomorphological dynamics in the lowland tropics of South America can be described from the stratigraphy of hillslope colluvium and alluvial deposits. The analysis of sediments through the identification of depositional microfeatures and biomineralized microfossils, combined with their absolute dating by optically stimulated luminescence (OSL), allow the reconstruction of paleoenvironmental conditions. The objective of this work was to investigate the dynamics of depositional processes leading to colluvial deposition in the Araripe Plateau, Northeastern Brazil, from the analysis of stratigraphic sections, using phytoliths as indicators of paleovegetation and sediment micromorphology in the identification of depositional processes. The correlation of sediments ages, ranging from the OS3 to the OS2 (Last Glacial Maximum) with phytophysiognomy indices indicated the contribution and deposition of phytoliths from an arboreal/shrubby vegetation, replaced on the surface by grass vegetation. Periods of drier climates were correlated with LGM ages, with more open vegetation composed of grasses, in synchronously with less intense geomorphological events. The micromorphological analysis revealed that the characteristics of the deposits reflect more the action of depositional processes than pedogenetic ones. The correlation of phytolithic indices with micromorphology corroborated the environmental and geomorphological dynamics of the periods dated in the stratigraphic sections. [ABSTRACT FROM AUTHOR]

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]

All known Pleistocene South American fossil ursids belong to Arctotherium , an extinct genus of tremarctine bears. Its occurrence encompasses many countries in Central and South America, with findings mainly from Argentina. In Brazil, the genus is recorded in eight states, highlighting Rio Grande do Sul due to its provenance from fluvial deposits. In contrast, all other Brazilian records come from caves or fossil tanks. The Arctotherium material from Rio Grande do Sul comes from the Passo do Juquiry site, located on the banks of the Quaraí River, which marks the frontier between Brazil and Uruguay. The fossils are MCN-PV 1940/A-K, a set of postcranial bones: first to sixth lumbar vertebrae, sacrum, left scapula, left humerus, right portion of the pelvic girdle, and left femur. The anatomic description of these bones confirmed their belonging to Arctotherium sp. due to their size, the form of the vertebral processes, the presence of the entepicondylar foramen of the humerus, and the morphology of the trochlea and capitulum. Body mass estimates resulted in values mostly above 400 kg. The first absolute age from Passo do Juquiry indicated 40,000 years BP. The stratigraphic framework of the outcrop conformed to a floodplain fines facies association, a succession of mudstones with carbonate nodules on top. This facies association has lithological correlations to the Brazilian Touro Passo Formation, the Uruguayan Sopas Formation, and the Argentinean Toropí/Yupoí Formation. While having similar features, the ages of the lithologically correlated facies associations do not always line up, indicating that the evolution of the Uruguay River basin throughout the Late Pleistocene followed a pattern, but not synchronously. The presence of carbonate levels suggests that the climate during the time of deposition was drier than the present one, with the carbonate-less middle layer representing a more humid period. [ABSTRACT FROM AUTHOR]

A column experiment at a laboratory level was carried out to assess the effect of the application of nanotechnology in the decontamination of soils and alluvial deposits with high levels of potentially toxic elements (PTEs). A suspension of zero-valent iron nanoparticles (nZVI) was injected at three different concentrations in selected samples (two sediments, one soil). For most of the elements, the retention by nZVI was proportional to the concentration of the suspension and the trend was similar. Metals were immobilized by adsorption on the surface layer of the nanoparticles and/or by complexation, co-precipitation, and chemical reduction. By day 60 following injection, the nZVI lost reactivity and the retained species were desorbed and back into the soluble phase. The definition of spatial patterns for PTEs' distribution allowed for the construction of contamination risk maps using a geostatistical simulation approach. The analysis obtained from the extractable contents of five target elements (Zn, Cu, Cd, Pb, As) was cross-checked with the estimated map network to assess their retention efficiency. Data from the analysis of these elements, in the extractable phase and in the porewater of the sediments/soils, indicate the nZVI injection as a suitable technique for reducing the risk level of PTEs in contaminated Fe-rich tropical environments. [ABSTRACT FROM AUTHOR]

Smirnite is the natural equivalent of Bi 2 TeO 5 , a compound that has piezoelectrical and nonlinear optical properties. The mineral has rarely been described worldwide. Here, we describe the finding of a Bi–Te oxide, compositionally similar to the mineral smirnite, from an alluvial gold nugget. The mineral occurs within a goethite pseudomorph after arsenopyrite, forming an aggregate with the nugget gold. Electron-microprobe analyses gave an empirical stoichiometry of (Bi 1.6 ,Fe 0.2) 1.8 Te 1.1 O 5 , on the basis of five atoms of oxygen. The occurrence of smirnite in the municipality of Ouro Preto, Minas Gerais, Brazil, is noteworthy because the mineral: (i) is described in South America for the first time; (ii) represents a provenance indicator, connecting the gold nugget to auriferous quartz lodes with primary Bi–Te minerals in the Mariana anticline; (iii) indicates that Bi and Te were retained by goethite formation during oxidative weathering of gold deposits; (iv) has the critical metals Bi and Te as essential components, which should be considered in the economic evaluation of gold prospects as strategically important byproducts, in addition to the potential use of Bi and Te in the weathering zone as pathfinder elements to gold mineralisation at depth. • The first finding of smirnite, the natural equivalent of Bi 2 TeO 5 , in South America. • Bismuth and Te are retained in the weathering zone as smirnite. • The mineral can be used as a provenance indicator in alluvial deposits. [ABSTRACT FROM AUTHOR]

Mining is an activity that has had a considerable impact on the history of Brazil, whether from an economic, political, social, geographic, or demographic, artistic, and religious point of view. Its history is stamped by several phases starting in 1693 with gold discoveries in Minas Gerais, and diamond findings in 1729. This lasted almost 150 years for gold, and 140 years for diamond. With exhaustion of alluvial deposits in rivers and streams, the Portuguese expertise was over, being replaced by English and French companies who started gold extraction in veins and lodes. English presence started soon after 1824, when a decree gave them permission to work in Brazil. These operations have been constant until nowadays. During the ninteenth century, other minerals were produced, such as coal, lignite, peat, oil, and iron. In 1934, the first Mining Code was enacted during Vargas Era. The big jump in iron ore production happened only in 1942, when Companhia Vale do Rio Doce-CVRD was established as an outcome of Washington Agreements, signed by the USA, England, and Brazil. In current times, Brazil has reached the status of an intermediate economy close to G7, being an outstanding player in international minerals trade, together with other developing nations (South Africa, Chile, Peru, India, and Indonesia). [ABSTRACT FROM AUTHOR]

Detailed sedimentological studies of the university main campus of São Paulo city, Brazil, revealed a significant unconformity at the top of the Cenozoic sedimentary deposits of the São Paulo Formation. This unconformity is overlapped by Quaternary sediments which can be traced in 1:20,000 scale and are here named as the Bosque Formation. This unit is characterized by poorly sorted mud deposits and very fine-grained red sand with granuleand pebble-sized clasts of the underlying São Paulo Formation. Furthermore, it overlies topographic highs of the Precambrian basement, and is laterally interfingered with fluvial terraces; it is eroded by the modern river at the lower reaches of the outcrops. The Bosque Formation records sedimentation characterized by a widespread mudflow that overlays old alluviums sediments, and was likely deposited during the beginning of the Holocene. [ABSTRACT FROM AUTHOR]

The Aptian evaporitic transitional sequence (sag phase) of the Brazilian marginal basins records the first connection between the Central and South Atlantic oceans in the equatorial area. During this phase, lacustrine carbonate reservoirs and giant salt deposits developed in the southern basins of Santos and Campos, forming world‐class petroleum reservoirs. The sag succession is also well‐preserved in the interior rift basins of north‐eastern Brazil, where upper Aptian strata are represented by a continuous section. This contribution presents an interpretation of the evolution of a third‐order depositional sequence comprising lacustrine limestones, marine siliciclastic facies and evaporite deposits of the intracontinental Araripe Basin. The Lowstand Systems Tract is characterized by fluvial deposits filling accommodation generated during the syn‐rift phase. The overlying deposits comprise marine facies with preservation of dinoflagellates and marine ichnotaxa, evidencing marine deposition in bayhead delta settings. The transgressive surface is represented by limestones, including the Konservat–Lagerstätte laminites, onlapping the basement rocks. Above, tide‐dominated bay deposits with distinct subtidal, intertidal and supratidal portions are recorded. The Maximum Flooding Surface is a dark shale below foreshore to shoreface facies, marking the beginning of the Highstand Systems Tract, culminating with deposition of evaporites (gypsum and anhydrite). The stratigraphic architecture and palaeocurrents measured in different facies associations suggest that marine waters reached the basin from the south. The data unequivocally records late Aptian marine ingressions of an incipient South Atlantic Ocean over the interior basins of north‐eastern Brazil, while lacustrine conditions were still prevailing in the Pre‐Salt sag units of the Santos and Campos basins. [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]

This study aimed to understand the key surfaces and the sedimentary filling pattern of the Coreaú incised valley (CIV) system (NE Brazil) using high-resolution seismic stratigraphy. Six key surfaces (Ss) and five seismic units (SUs) were identified. The difference in the basal reflector (S1) and the paleointerfluve (modern sea floor) was verified to be up to 40 m of incision, of which only 20 m are filled. S1 (sequence boundary—SB) was associated with the acoustic basement (Tibau Formation/Barreiras Group) and presented strong control (antecedent topography) in the incision (re-incisions in the Pleistocene lowstands) and sedimentary stacking pattern. The CIV fill showed lowstand system tract, LST (chaotic facies)–transgressive system tract, TST (horizontal layers to chaotic facies)–highstand system tract, HST (chaotic facies) from the base to top. Thin fluvial deposits above SB correspond to LST. Overlapping this system tract is the first marine flooding surface—transgressive surface. Afterwards, the largest seismic unit (lateral and vertical) with sub-parallel and parallel (onlap) seismic facies, interpreted as related to a low energy system, with shallow gas, and vertical accretion (central basin of estuary) occurred. This environment is related to the drowning of the shelf from the shelf break (a decrease in gradient). A tide ravinement surface truncated the top of SU3 and favored coastal to shallow marine deposition. The transgressive system tract (TST) is thicker in the middle (mainly) and outer sectors in the fluvial troughs (depocenter). The maximum flooding surface appears near the sea floor and favored the development above of carbonate sedimentation in the HST. These seimostratigraphic stacking patterns showed a strong influence of semi-arid climate and antecedent topography/structural inheritance. Thus, it is evident that the filling of the CIV differs from other valleys on semi-arid systems and/or influenced by paleotopography (e.g., South Africa and Texas Shelf), which demonstrates the importance of local settings. The great influence of estuarine to coastal sediments in the valley infilling is also observed in the modern Coreaú coastal plain incised valley. [ABSTRACT FROM AUTHOR]

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Rivers with little to no influence of vegetation and their implications for the architecture of Early Paleozoic and Precambrian fluvial deposits are an important topic of investigation for both clastic sedimentology and Earth System evolution perspectives. Despite the long‐held concept of a dominant style of wide, shallow sheet‐braided sandy channels, growing evidence for a great variability of architectural elements in pre‐vegetation settings point to the predictable occurrence of other fluvial styles, which are possibly related to areas of low‐slope alluvial plains. The present work brings sedimentological descriptions and fluvial style interpretations of Silurian fluvial successions of the Serra Grande Group in northeastern Brazil, developed in a glaciated basin margin (therefore with little to no effect of vegetation). The comparison of the resulting channel body architectures integrated to paleocurrent data and a diffusion‐based numerical model enabled the evaluation of the controls on fluvial architecture variability in unvegetated alluvial plains. [ABSTRACT FROM AUTHOR]

This paper presents the geomorphological features of four areas of subtropical, southernmost Brazil displaying striking landforms developed upon Precambrian Camaquã Basin conglomerates in the southern Brazilian shield areas. The distinctive and unique features of the Serra do Segredo cuesta, the Rincão do Inferno canyon, the Casa de Pedra inselberg, and the Pedra da Cruz cap-shaped hills are important examples of such conglomerate geomorphology in South America and in Brazil, where few occurrences were available so far. They are the first documented conglomerate landforms in southernmost Brazil, widening the distribution of such terrains in South America and in the subtropical, southern hemisphere areas, considering recent global reviews. Besides the high scientific relevance for geomorphology as a whole, such features are important also for (1) evidencing the decisive role of lithology, structure, and water flows in the formation of such landforms; as well as (2) ecology and tourism, being distributed within and in the vicinity of the Caçapava UNESCO Global Geopark of southernmost Brazil. • Novel description of conglomerate geomorphology developed upon Ediacaran alluvial/fluvial deposits of the Camaquã Basin in subtropical, southernmost Brazil. • Different landforms developed according to bed tilting and arrangement, as well as to tectonic structures "pre-design". • Decisive role of lithology and water in shaping ranges and hills. • Contribution to a global distribution of conglomerate landforms, especially in humid, subtropical areas. • Geological heritage potential, features within and in the surroundings of the Caçapava UNESCO Global Geopark. [ABSTRACT FROM AUTHOR]

This paper presents the results of the investigations that defined the formation of the sedimentary deposits and the chronological sequence of the Foz do Chapecó archaeological area in the Volta Grande of the Upper Uruguay River, Southern Brazil. This research was undertaken to contribute to the definition of the diachronic, sedimentary and stratigraphic context of the archaeological occupations. To achieve these goals a geoarchaeological prospection by land and water was conducted, focusing on the valley bottoms, in the whole Volta Grande area. It comprehended the characterization of surface sedimentary deposits, the exposure and analysis of stratigraphic profiles, and sedimentological analysis. Four superficially exposed deposits were identified: i.e., fluvial conglomerates, fine sediments with sandy texture, clay colluviums and current and recent alluvial deposits. Six interesting points for the opening of stratigraphic profiles were identified, and subsequently resulted in the identification of sedimentary facies associated with river-bed, colluvial and colluvial-alluvial deposits. Three of these points presented a clear sequence of archaeological levels in the stratigraphic context. The results indicated that the local sediments are predominantly composed of a variable mixture of silt and clay, with sands occurring predominantly in an interdigitated form. The stratigraphic structure of the identified layers led to the establishment of 7 sedimentary facies, associated with colluvium (Cm), colluvium-alluvium (Sm) and alluvium and fluvial channels (Sm, Fl, Gms, Gt, Gp, Gh). The radiocarbon dating gives an age between 12.0 and 0.3 cal kBP, indicating that the filling of the local valley occurred during the end of the Pleistocene and throughout the Holocene by means of both fluvial and colluvial systems. Nine distinct archaeological levels, with a clear stratigraphic, chronological, and technological characterization were identified. The pre-ceramic archaeological sequence shows the following chronology: the oldest occupation occurred between 12.0 and 11.0 cal kBP (Cm facies); this was followed by an occupation between 10.5 and 9.5 cal kBP (Cm, Gt, Gp and Gh facies in three archaeological sites with eleven 14C data), then an occupation between 8.7 and 8.5 cal kBP (Cm facies), another between 5.7 and 5.5 cal kBP, one more between 4.8 and 4.6 cal kBP (Cm facies), and the last between 3.4 and 3.3 cal kBP (Cm and Sm facies). The ceramic phase seems to form a single dense component with the anthropogenic soil formation, and was dated between 0.5 and 0.3 cal kBP (Sm facies). These data present a previously unpublished chronostratigraphic sequence that is unique for the context of open-air sites in inner southern Brazil. • This research presents a unique example of a well-documented archaeological settlement in an open-air, multi-component site situated in a riverine setting in inland Southern Brazil. • It marks the first geoarchaeological study in Southern Brazil's subtropical oxidic environments, utilizing an integrated approach that includes sedimentology, stratigraphy, radiocarbon dating, and the spatial distribution of archaeological features. • The study's sedimentary sequence aids in reconstructing the paleo-environments of the Upper Uruguay River region. • The findings suggest that prehistoric cultural dynamics throughout the Holocene in Southern Brazil were more complex than previously understood. [ABSTRACT FROM AUTHOR]

We describe a globally rare example of a tetrapod burrow from the Upper Cretaceous Bauru Group (Bauru Basin) from Peirópolis, Minas Gerais State, Brazil. The sedimentary succession containing the burrow includes a rich vertebrate assemblage comprising fish, podocnemid turtles, mesoeucrocodylians, saurischian dinosaurs, among others. The burrow is composed of an oblique tunnel (~30°), oval in cross-section, with a horizontal and sub-oval terminal chamber; it is 1.3 m long from the midpoint of its inferred entrance to the midpoint of the bottom of the chamber. It occurs in the upper portion of a sandstone succession, interpreted as a braided channel deposit, and the burrow-fill comprises medium-grained sandstone with mudstone intraclasts derived from fluvial floodplain facies. it is overlain by other fluvial channel deposits. Analyses suggest that the burrow was dug after the filling of the braided channel and during the pedogenesis of its exposed upper surface. Based on burrow morphology and size, the most plausible producer of this burrow is a notosuchian mesoeucrocodylian, such as small to mid-sized notosuchians (e.g., sphagesaurids). The Bauru Group has an extensive fossil record of notosuchians with disparate morphologies, and it is noteworthy that the small-sized notosuchian Labidiosuchus amicum comes from the same unit as the burrow. Moreover, arid to semi-arid conditions have been inferred for fossil-bearing rocks of this unit, and as such the data here presented add to our palaeoecological knowledge of Cretaceous mesoeucrocodylians in Gondwana. Moreover, it constitutes a new Cretaceous record of a tetrapod burrow during a period when such ichnofossils are globally rare. • The first tetrapod burrow from the Late Cretaceous of South America is reported. • The most plausible producer of this burrow is a notosuchian mesoeucrocodylian. • Findings improve knowledge of the ecology of this group. • The burrow occurs in beds with arid palaeoclimate indicators. [ABSTRACT FROM AUTHOR]

Apatite is one of the most common minerals found in a wide variety of rocks. It has variations of minor and trace elements in its composition that allow the recognition of its host lithotype. In this study, apatite grains identified in rock samples and grains recovered from heavy mineral concentrates in the Angico dos Dias Carbonatite Complex region, located on the border between the State of Bahia and the south of the State of Piauí, Brazil, were analyzed using an electron probe microanalyzer. These concentrates come from alluvial sediments downstream of the carbonatitic body from drainage channels. Sampling was guided by regional geochemical analytical results for the chemical elements of apatite. Grains were detected in alluvial covers for up to 9.5 km downstream in all fraction including coarse sand (1.0 mm) in proximal samples and up to medium sand fractions (0.50 mm) in distal samples. The 96 analytical results on 48 apatite grains show that most have chemical signatures characteristic of metacarbonatitic lithotypes (SrO 0.88–1.7 wt%) and that some host lithotypes were affected by the substituition processes (Si + LREE (Ce+La+Nd) 0.15–0.59 apfu), which may be an alternative to metasomatic fenitization. Statistical analysis by principal component analysis (PCA) helped the visualization and interpretation of the data by constructing clusters of the different compositions of apatite. The apatite fields of carbonatitic and silicate source rocks were separated and associated with the results obtained for alluvial apatite grains, resulting in carbonatitic derivation. The results of using this prospecting tool were satisfactory. Thus, it was possible to classify and detect the sources of alluvial apatite grains relating them to the Angico dos Dias carbonatite body, in addition to proposing a new potential area for the occurrence of carbonatitic bodies northeast of the Angico dos Dias phosphate deposit. • Apatite is used to provide the chemical signature of the source. • Stream sediment data is useful to guide sampling of indicator heavy minerals. • PCA helps in the interpretation and visualization of mineral chemistry data. • Alluvial apatite grains found in a drainage channel. [ABSTRACT FROM AUTHOR]

The Neogene Barreiras Formation is composed of continental to shallow marine sedimentary rocks that fringe the Brazilian Atlantic coast. Due to the large outcropping extent, various open questions about the evolution of this unit are still under debate. We present new U–Pb detrital zircon age spectra of four samples from the southern Espírito Santo state (Marataízes section) and two samples from the southern Bahia state (Arraial section). In both of the studied outcrops, a basal succession composed of coarse-grained cross-bedded sandstone, conglomerate and arkose with mudstone and claystone intercalations is superposed by an upper succession composed of massive sandstone, conglomerate and wacke. The U–Pb detrital zircon age spectra of all samples are dominated by Cambrian and Neoproterozoic grains. However, while the lower portion of both sections is dominated by Ediacaran-Cambrian grains, their upper portions also present significant Cryogenian-Tonian and sparse Paleoproterozoic (mainly Rhyacian and Statherian) and Neoarchean grains. This marks an important provenance shift within the Barreiras Formation, with a simple, local provenance sourced from the G1 to G5 granite supersuites of the Brasiliano Araçuaí Orogen for the basal layers contrasting with exposure of older basement rocks and Neoproterozoic anorogenic suites during deposition of the superior layers. We interpret the lower coarse sandstone and arkose-rich succession as deposited in an alluvial setting, with mud/claystones related to local flooding plains. Tectonic movements related to the evolution of the Atlantic passive margin, as described in previous works, caused a renewed uplift of the basement areas, exposing and denuding older rocks. Then, the upper layers deposited through debris flows covering the first succession. Further geochronological data is needed to test if the erosional event responsible for exposure of older basement rocks and sourcing of the upper layers would correspond to the Tortonian Sea level fall, related to growth of the Antarctic ice sheet to its present size. In this case, deposition of the lower succession would have occurred during the early Miocene, and the upper succession during the Pliocene. Our results shed light in the complex evolution of the sedimentary rocks generally grouped under the Barreiras Formation, and suggest important tectonic and climatic shifts during the Neogene evolution of the Brazilian Atlantic coast. • Detrital zircon U–Pb analysis of two sections of the Barreiras Formation • Source areas dominated by late Neoprotezoic to Cambrian sources (G1-G5 plutons) • Archean-Paleoproterozoic basement exposed in the source areas upsection • Tectonic, climatic and sea-level changes were possible provenance shift drivers • Complex evolution of the sedimentary rocks of the Barreiras Formation [ABSTRACT FROM AUTHOR]

The Ribeira de Iguape River (Southeast Brazil) is metal contaminated by mining activities. Despite it has been cataloged as “in via of restoration” by the literature, this basin is still a sink of pollution in some segments of the fluvial system. This study aimed to assess the sediment quality in the lower part of the RIR basin. The employed approach was based on biological responses of the freshwater clam Corbicula fluminea after 7-day exposure bioassays using as the reference site the Perequê Ecological Park. Toxic responses (burial activity and lethality) and biochemical biomarkers (GST, GR, GPx, LPO, MTs, AChE and DNA damage) were evaluated and then integrated with metal bioavailability and chemical concentrations to address the sediment quality in the area through the weight-of-evidence approach. A multivariate analysis identified linkages between biological responses and contamination. Results pointed that, despite being below the benchmarks of the US Environmental Protection Agency, there is slight metal contamination in the lower part of the basin which induces oxidative stress in C. fluminea; other toxic responses were sometimes attributed to As and Cr bioaccumulation. The sediment quality values (TEL-PEL values in mg/kg) were calculated for the current study for As (0.63-1.31), Cr (3.5-11.05), Cs (1.0-1.17), Cu (6.32-7.32), Ni (6.78-7.46), Ti (42.0-215), V (1.77-8.00). By comparison with other international guidelines, the sediment quality of the lower basin of the Vale de Ribeira does not identify a significant environmental risk. [ABSTRACT FROM AUTHOR]

Karstic areas in Central Brazil show significant depositional and erosive facies placed within abandoned dry valley-systems and associated with fluviokarstic dynamics. These valleys have distinct depositional characteristics that offer sedimentary records of both past climatic events in the region and its current fluviokarstic system. The purpose of this paper is to point out and characterize such sedimentary packages, protected by dry valleys that were deposited up until the fluviokarstic transition, thus enabling the correlation of such sediments to past climatic events. The study is based on a combination of geomorphic and sedimentological analyses through the employment of multiple techniques, such as mineralogy, geochronology, stable isotopes, and granulometry, to the analysis of our case studies. These are the three dry valleys around the Ventura, Pedras and Extrema rivers, which in turn comprise the River Vermelho Basin, northeastern Goiás State. Our results suggest that the valleys contain fluvial deposits remnant from the transition of superficial fluvial flow to the underground karstic system. Records provide a general view of the depositional stages placed before and up until the period of fluvial capture in terms of their morphology, dynamics, and sediment architecture. OSL ages indicate that fluviokarstic processes had been in operation since 23 Ka, when the oldest river capture was found to have occurred. Depositions occurred in a reasonably continuous manner, mainly during the last 3.5 Ka, and concentrated around relatively dry and wet events, exhibiting typical depositional gaps in fluvial environments. Consequently, no relationship between the depositions and paleoclimatic events were observed for the analyzed fluviokarstic system. [ABSTRACT FROM AUTHOR]

Multiproxy analysis of detrital minerals is a powerful tool for unravelling the source-to-sink evolution of syn-rift sedimentary basins that represent important depositional settings during major rift events. The Cenozoic Resende half-graben in SE Brazil is a classic example of a syn-rift basin developed under oblique extension, which preserves evidence of tectonic episodes and palaeoclimatic conditions during the opening of the Atlantic. Sediment in the basin was sourced from the surrounding basement rocks, which to the faulted margin consists of older Proterozoic orthogranulites and orthogneisses, whilst to the flexural margin is characterised by Neoproterozoic passive margin paragneisses. Cretaceous intra-plate alkaline stocks crop out at the western edge and in the central-south basement of the basin and represent a distinct provenance fingerprint. This study uses new detrital zircons U–Pb ages combined with previously published elemental and Nd and Sr isotopic data to characterise the sedimentary provenance of Eocene alluvial deposits and to understand how sediment sourcing has changed throughout the evolution of the basin. U–Pb detrital zircon analyses from samples collected across the Resende Basin are presented herein. Samples yield a spread of detrital age spectra from the Archaean to the Cretaceous. Precambrian zircons range from ca. 3228 Ma to ca. 542 Ma. Cretaceous zircons yield ages between ca. 138 Ma and ca. 67 Ma. The sediment source location is interpreted by comparing the yielded detrital zircon spectra with the age spectra of zircons from the basement rocks. The dominance of detrital zircons yielding ages of ca. 1500 Ma and ca. 1000 Ma is interpreted to be sourced from the Neoproterozoic basement rocks to the flexural border of the half-graben. Cretaceous zircons from samples with whole rock εNd 40Ma > −10 are found in both the western and eastern portions of the half-graben but not in the central portions. It is interpreted that an along-axis fluvial system was responsible for a small increase in the compositional maturity of the Resende sandstones from west to east, resulting in the progressive dilution of Cretaceous alkaline igneous detritus along the basin axis. Preserved metamorphic rims in zircon grains indicate low transport abrasion, suggesting that Cretaceous zircons in the eastern depocentre could be associated with other small proximal sources. U–Pb zircon analyses and Nd and Sr isotopes provide reliable insights regarding sediment provenance and transport processes, whilst element geochemistry supplies evidence for hydraulic sorting effects. Consequently, the data represents a more robust estimation of the provenance patterns of the Resende Basin, showing chemical and geochronological differences that support the division of the basin into three depocentres (western, central, and eastern) connected by a longitudinal fluvial system sourced mostly by sediments coming from the south-western flexural border. This study highlights the usefulness of using multiple provenance proxies to unravel the complex development of rift basins, assessing multiple source terrains and the variable degrees of mixing in sedimentary basins. [Display omitted] • Unravelling syn-rift sedimentary basins' source-to-sink behaviour • U–Pb detrital zircon dating reflects proximal source areas in a continental rift basin. • Palaeogeographic reconstruction and the role of a longitudinal fluvial system [ABSTRACT FROM AUTHOR]

Reconstructing landscape changes in Amazonia during the late Quaternary requires dating of fluvial sedimentary units occupying large areas. This demands dating of a large number of sediment samples. The equivalent dose (De) estimation through the commonly employed single-aliquot regenerative-dose (SAR) protocol applied to quartz may take a long measurement time, especially for estimating higher De and/or when many aliquots (tens) are necessary to get reliable De statistics. The standardized growth curve (SGC) has been proposed as an alternative approach, which speeds up the De estimation, increases the number of measured aliquots per sample, reduces OSL dating costs and allows dating of a higher number of samples. The SGC is a general dose response curve constructed with OSL signals from samples of presumed similar behavior, which dismisses the need of establishing specific dose response curves for each aliquot. OSL signals (L) corrected by the test dose signal (T) and multiplied by the test dose (Dt) (L/T x Dt) are used for constructing the SGC. Here, we use a SGC built for quartz OSL in order to determine the De of sediment samples from terraces and floodplains of the Juruá River, western Amazonia. The Juruá River has a sub-Andean sediment source and is a large tributary of the right margin of the Solimões River, which becomes the Amazon River in central Amazonia. The Upper Juruá River drains Miocene rocks (shales and sandstones) uplifted by the Fitzcarrald Arch on the southern border of Peru and Brazil. In the mid-reach, its meandering channel flows over Quaternary sediments until it meets Solimões River, where the sequence of fluvial terraces analyzed here is placed. Determining the depositional ages of Juruá River deposits is crucial in order to understand how the fluvial systems on western Amazonia evolved through time and to assess which mechanisms (e.g. climate, tectonics, etc.) played the major role in the process. Firstly, we present a SGC constructed using quartz OSL signals from previously dated samples (De range about 20 mGy to 60 Gy) from Amazonian rivers with similar sediment sources. This SGC includes the initial measurements data from SAR protocol of three Juruá River quartz samples. Then, De values from 17 Juruá quartz samples are estimated by using the SGC approach and by the SAR protocol. The SGC is validated by comparing its estimated De against the respective De obtained by the SAR protocol. Finally, OSL ages are determined to discuss the formation time of the Juruá River terraces. [ABSTRACT FROM AUTHOR]

The demise of the carbonate platform in the Brazilian Equatorial Margin has been related to the progradation of massive siliciclastic inflow from the Cratonic Amazon River during the middle Miocene. The sediment plume did not influence the eastern portion of this drainage, including the Bragantina Platform andthe Marajó Basin, the onshore Pará-Maranhão Basin. The provenance signatures of these tectonic segments have been demonstrated in siliciclastic coastal deposits of the Barreiras Formation, whose progradation caused the suppression of the Oligocene-Miocene carbonate platform. Our provenance study is based on clast morphology, quartz cathodoluminescence, and heavy minerals of mainly Barreiras alluvial-fluvial deposits, using new and published facies data. This study opens a window of opportunity to investigate, for the first time, the proximal facies combined with paleocurrents exposed only in this area of Brazil. The restricted occurrence of proximal facies indicates an exceptional potential for preservation related to subsiding regions generated by reactivated faults in the Gurupi Belt. Provenance data indicate the strong influence of metamorphic source rocks with minor volcanic and plutonic contributions from the southeastern and southern of the Bragantina Platform and eastern Marajo Basin. Respectively, two heavy minerals assemblages were found: 1) staurolite, metamorphic quartz, and angular clasts; and 2) abundant zircon, kyanite, tourmaline, mixed quartz (metamorphic, plutonic, and volcanic), and rounded clasts. The assemblages are associated with São Luís Craton, mainly crystalline rocks from Gurupi Belt. In addition, the proximal facies of the Bragantina Platform provide rich staurolite concentration and angular clasts indicating near source area; the uplifted Marajó Basin during the middle Miocene contributed with reworked sediments containing rounded clasts and ultrastable minerals related to Silurian-Cretaceous rocks. This work complements the previous paleoenvironmental reconstruction for the Barreiras deposits, including the most robust proximal facies interpretation contributing to understanding sediment dispersion during the middle Miocene, reinforcing previously defined source areas. • Alluvial fan deposits are definitively included in the middle Miocene Barreiras facies model. • The Barreiras delta spread across different geotectonic segments in eastern Amazonia. • Proterozoic, Paleozoic, and Mesozoic source rocks supplied the Barreiras fan delta.. • The Oligocene-Miocene Cratonic Amazon River never influenced the Barreiras fan delta. [ABSTRACT FROM AUTHOR]

Mineralogy and geochemistry of the total suspended sediment (TSS) from a granite-gneiss watershed in southeast Brazil brought light to geogenic and anthropogenic sources. TSS was sampled in 15 points along the Piabanha watershed in summer (February 2013) and winter (August 2013). The Piabanha watershed (2 × 103 km2) is located in the mountainous region of Rio de Janeiro, and it is an affluent of the Paraiba do Sul River, the most important river from the Brazilian southeastern coast. TSS mineralogical analyses were performed with X-ray powder diffraction. Geochemical analysis was done with energy dispersive X-ray fluorescence. Quartz, kaolinite and gibbsite were dominant in the TSS mineralogy, followed by feldspar and mica. Granite and gneiss rocks contribution in the TSS have a common mineralogical and geochemical source. But the alluvial deposits from river banks might have been responsible for the differences between summer and winter samples. The major features in TSS from geogenic sources were SiO2, Al2O3, MgO, Ga2O3, Nb2O5, Rb2O, K2O, SrO, ZrO2and TiO2. The good correlation on the Si:Al molar ratio suggested that the source area is intensely weathered. Pollution features (sewage source) were given by significant TSS concentration of Fe2O3, MnO, ZnO, CuO, As2O3, CaO, Na2O, P2O5and SO3. [ABSTRACT FROM PUBLISHER]

The diversity of structures and tectonic regimes in the Borborema Province caused the various morphostructural compartments to follow different evolutionary pathways throughout and after the fragmentation of Gondwana. In the northern Borborema Highlands, post-rift evolution occurred in a differentiated way, and the present study aims to understand how this occurred. For this, a set of morphological (geomorphological mapping, mapping of drainage anomalies, and extraction of relief lineaments) and morphometrics indexes (hypsometric curves, Basin Asymmetry Factor, Hack Index, Concavity Index, and χ Index) have been applied to drainage watersheds and low-order channels. The results obtained allowed us to propose a post-rift evolutionary model. To the north, the Highlands presents a recent divide resulting from a series of Cenozoic tectonomagmatic reactivations that promoted river rearrangement processes, such as drainage direction reversal and relief inversion—the current conditions of semiaridity and the absence of epigeny cause this drainage divide to remain stationary. The results diverge from the idea that only high relief margins were subject to greater tectonic control. Despite its modest altitudes, the transforming equatorial margin of Northeastern Brazil exhibits a significant recurrence of morphotectonic reactivation events, operating at different space-time scales. The area is also one of the sectors of the Brazilian passive margin with the highest record of modern seismicity. • The location of volcanic evidence and the current patterns of fluvial dissection are controlled by Proterozoic shear zones. • Cenozoic magmatic events promoted drainage rearrangement processes in the Borborema Highlands' northeastern sector. • The absence of epigeny along the drainage divides testifies to the recent timing of the changes in the fluvial systems. • Pleistocene fluvial deposits capping the top of drainage divides attest to the occurrence of relief inversion. [ABSTRACT FROM AUTHOR]

Soft-sediment deformation (SSD) structures preserved in sedimentary successions can record significant seismic events which occurred during or right after deposition. The integrated analysis of sedimentary facies, depositional architecture, and SSD data can determine the relative temporal relationship between deposition and deformational events, and reveal the origin and mechanisms involved in the deformation and the resulting structures. The São Paulo Formation in southeastern Brazil preserves Cenozoic alluvial deposits which characterize most of the geology of the homonymous metropolis area. This succession preserves fluvial channel and floodplain deposits, with associated debris-flow dominated alluvial fan deposits, and preserves abundant SSD structures in a wide range of dimensions and morphologies. These deformation structures include small- and large-scale folds, multi-scale vents of varied geometries, ball-and-pillow structures, and clastic dykes. Here we provide an integrated analysis of sedimentary facies, depositional architecture data, and SSD data from the São Paulo Formation, in order to discuss the deformation mechanisms and plausible triggering mechanisms responsible for the development of such structures. Our interpretation is that SSD structures in the São Paulo Formation were likely triggered by a Cenozoic meteor impact recorded by a crater near the study area. • Multi-style and multi-scale soft-sediment deformation structures can be preserved in fluvial deposits. • The São Paulo Formation records multiple soft-sediment deformation structures. • Integrated analysis of soft-sediment deformation structures, sedimentary facies, and depositional architecture. • Soft-sediment deformation in the São Paulo Formation was triggered by a Quaternary meteor impact. [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]

• Re-interpretation of the paleoenvironmental evolution of the São Francisco Basin. • Results indicate a depositional age for the Bambui Group of > 550 Ma, significantly older than recently reported. • Six sequences record the Marinoan and Gaskiers glaciations and track oxygen fluctuations through the Ediacaran. • Loess form most of the siltstones and stimulated photosynthetic oxygen production in surface waters. The Bambui Group is a ca. 2,000 m-thick mixed biochemical-siliciclastic sedimentary succession that accumulated in the Sao Francisco Basin, central Brazil. Its age is contentious, but deposition during the Cryogenian-Ediacaran (ca. 635–550 Ma) is consistent with a new sequence stratigraphic model presented herein and previously published geochemical and structural data. Six stratigraphic sequences are recognized that record depositional evolution from an epeiric sea to foreland basin during the Marinoan snowball glaciation (ca. 635 Ma) to shortly after the Gaskiers (ca. 580 Ma) glaciation. Although this stratigraphic architecture differs from the classic lithostratigraphic and more recent chemostratigraphic and sequence stratigraphic interpretations of the Bambui Group, it is supported by correlation to other Cryogenian-Ediacaran successions globally. Collectively, these six sequences preserve a robust record of seawater redox structure leading up to the oxygenation threshold that triggered the evolution of multicellular animals in the Ediacaran. Sequence 1 is composed of Marinoan glacial deposits and an overlying cap carbonate with aragonite fan pseudomorphs and barite. Sequence 2 is composed of lime-mudstone that changes laterally into loess-rich peritidal phosphorites, suggesting oxygen stratification in shallow paleoenvironments. Sequence 3 is a carbonate succession with abundant stromatolites implying widespread oxygen production. The top of Sequence 3 is marked by a regional subaerial unconformity developed during uplift associated with the onset of the Brasiliano-Pan African Orogeny. Sequence 4 signals a return to loess derived sedimentation. Distal deposits contain abundant organic matter with framboidal pyrite reflecting bacterial sulfate reduction in low sulfate Ediacaran seawater. Sequence 5 is composed of well-developed aggradational parasequences composed of alternating deep subtidal organic-rich siltstones and shallow-water carbonate grainstones. Their well-defined cyclicity is interpreted to record extreme sea level fluctuations during the onset of the Gaskiers glaciation. Stromatolites suggest an oxygen-stratified water column. Sequence 6 marks the change from an epeiric sea to a foreland basin. Interbedded basinal glauconitic siltstone and shale loess-rich are correlative with shoreface sandstones. Authigenic glauconite requires suboxic bottom waters to precipitate and thus reflects oxygenation of distal settings. Most of the deposition ended by ca. 560–550 Ma when the entire Bambui Group was deformed during the assembly of West Gondwana. In sequences 1, 2, 3, 4, 5, and the lower portion of 6, the lateral continuity of lithofacies, predictable layer-cake stratigraphy, and lack of fluvial coarse siliciclastic deposits are characteristics of epeiric sea successions. The appearance of immature sandstone, poorly sorted conglomerate, braided fluvial deposits, and synsedimentary deformation in the upper part of Sequence 6 are interpreted as the onset of foreland basin development. Stacking relationships of redox sensitive, authigenic lithofacies in both the epeiric sea and foreland phases support recent research suggesting seawater redox conditions were in a state of flux during the apex of the purported Neoproterozoic Oxygenation Event. Organic matter and authigenic pyrite in Sequences 4 and 5 reflect increased primary productivity in surface waters fertilized by nutrients such as P and Fe adsorbed on loess particles. This mechanism could be expanded to a global scale and have contributed to the increase in atmospheric and oceanic oxygen levels. These findings redefine and highlight the significance of the Bambui Group for Neoproterozoic Earth history. [ABSTRACT FROM AUTHOR]

The Pennsylvanian Epoch was marked by a well-known glaciation period documented in several basins across the Gondwana. However, stratigraphic data from the Parnaíba Basin suggest that drier climate conditions dominated mid-paleolatitudes simultaneously to the glaciation. To investigate the possible time equivalence and the causes of aridification in mid-paleolatitudes, high-resolution stratigraphic analysis of the upper Piauí Formation were conducted in the eastern margin of the Parnaíba Basin. As a result, three stratigraphic intervals separated by key stratigraphic surfaces were identified: The first stratigraphic interval is dominantly composed of fluvial deposits progressively overlain by eolian facies; the second stratigraphic unit is essentially composed of lacustrine deposits and represent a regional flooding related to a period of lake expansion and finally, the third stratigraphic unit is characterized by three eolian genetic units and depicts cyclic expansion and contraction of a dune field. The overall vertical stratigraphic succession represents a progressive change from original fluvial sedimentation to essentially eolian accumulation and constitutes a drying upward trend that reflects an increasing aridification in the Parnaíba Basin during the Late Pennsylvanian age. The detailed analysis of the paleoclimatic conditions and the atmospheric circulation during the Late Pennsylvanian Epoch evidenced that the waning and waxing of the ice sheets controlled the development, expansion and contraction of the upper Piauí Formation dune-field. • High-latitudes glaciation contemporaneous to mid-latitudes aridification. • The Gondwana aridification registered in the Piauí Formation of the Parnaíba Basin. • Shift from fluvial to eolian deposits caused by growing arid conditions. • Eolian genetic units controlled by water-table fluctuations. • Waning and waxing of the ice sheets controlled the dune field dynamics. [ABSTRACT FROM AUTHOR]

Coprostanol (5β-cholestan-3β-ol) and other fecal steroids were used as markers to trace the input of sewage to the shelf along the coast of Sergipe and Alagoas States, in NE Brazil. Surface sediment samples in shallow regions (<50 m depth) on the shelf were collected adjacent to four fluvial systems, whose drainage basins exhibit distinct levels of human influence. Highest coprostanol concentrations were observed in the area under influence of the Sergipe River (58.6 ± 74.6 ng g − 1 ; maximum of 184.1 ng g − 1 ), whereas in the Vaza-Barris (18.9 ± 23.6 ng g − 1 ) and the Piaui/Real (12.3 ± 6.7 ng g − 1 ) rivers the levels of coprostanol were near the method’s limit of detection. Nearby the São Francisco River, the largest in the NE Brazil, coprostanol was virtually absent. The findings of the present study, supported by coprostanol-based diagnostic ratios, revealed that, when sanitation is lacking in the coastal region, even a small-sized river like the Sergipe River can effectively contribute to the export of sewage-derived organic matter to the inner continental shelf in the studied region. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the evolution of uplifted areas in NE Brazil, which have been considered as residual landforms. The study focuses on the 130km-long, 41km-wide Pereiro Massif (PM). The structural control and the age of this uplift are the problems addressed in this study. We carried out topographic analysis, geomorphological and geological mapping, detailed structural analysis, and optically stimulated luminescence (OSL) dating to address these problems. The PM is bounded and cut by a system of steeply dipping normal and strike-slip faults, which control the morphology of the massif and associated sedimentary basins. The maximum uplift rate of the PM is 34m.My−1, as constrained by the age of flat topography capped by Miocene laterite, which represents the previous peneplain subsequently uplifted by ca. 600m. The minimum uplift rate is 13m.My−1, as constrained by fission-track dating of differential crustal block movements across a nearby fault. In the Quaternary, erosion occurred mainly by fault-controlled scarp retreat under semi-arid conditions, with the formation of colluvial deposits along fault scarps and alluvial deposits in the low plains. These deposits are now dated between 46 and 0.4ka, with a peak in sediment deposition in the Pleistocene/Holocene transition. It is concluded that the PM is a system of horsts and grabens that have been active in the Cenozoic. [Copyright &y& Elsevier]

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Abstract: Supergene aggregates of platinum–palladium (Pt–Pd) intermetallic compounds from the Córrego Bom Sucesso alluvial deposit, Minas Gerais, Brazil, are coated with abundant, poorly crystalline nanoparticles of anatase (TiO2). The anatase coating is widespread, suggesting that the surface of the Pt–Pd grains catalytically destabilised Ti, which was likely dissolved by organic ligands in the ground waters. Association of TiO2 nanocrystallites with organic matter further suggests that biogenic processes could have mediated their formation. These anatase-coated Pt–Pd grains demonstrate an unexpected Ti mobility in supergene environments. [Copyright &y& Elsevier]

Abstract: Soft-sediment deformation (SSD) is widely described in the literature, but there is no clear consensus regarding its origin and significance. Existing models for SSD in fluvial sediments do not clearly demonstrate a relationship between the structures, preserved facies expression, and larger-scale depositional architecture. In this study several types of SSD structures are recorded in Cambrian fluvial deposits and these occur interbedded with undeformed strata throughout the entire stratigraphic interval. The random distribution of these features in relation to primary facies types and fluvial forms indicates that they have neither a direct nor indirect relationship with any depositional processes or bedform type. We propose that the relationship of SSD at the bed-set-scale to larger-scale depositional architecture, combined with tectono-stratigraphic analysis allows the determination of both short-term fluvial hydraulic conditions in ancient stream systems, such as the nature of the flow regime responsible for depositing ancient fluvial stream successions, and the long-term subsidence rates, in the form of mean recurrence interval of the seismic events responsible for triggering the generation of SSD in tectonically active basins. [Copyright &y& Elsevier]

Abstract: Although the occurrence of Pleistocene mammals is abundant in many localities of Minas Gerais State (e.g., Lagoa Santa, Janaúba, Bambuí, Cordisburgo, Patos de Minas, Araxá), there are no references at present of Quaternary megafauna in Uberaba, Triângulo Mineiro, southeastern Brazil. This region is traditionally recognized for its taxonomically diverse fauna of the Late Cretaceous Bauru Group. In 2006, fossil material attributed to giant ground sloth Eremotherium laurillardi (Xenarthra, Megatheriidae), a typical taxon of the Brazilian Pleistocene, was discovered in the Uberaba City (Minas Gerais State). The specimen (CPP 1122) which is here described consists of several cranial and postcranial bones of a single individual. The material was confined to a small alluvial deposit, yielding in the Córrego da Saudade stream, which due its restricted area distribution it is not represented in geological maps. [Copyright &y& Elsevier]

Abstract: Palynostratigraphic and sedimentary facies analyses were made on sedimentary deposits from the left bank of the Solimões River, southwest of Manaus, State of Amazonas, Brazil. These provided the age-dating and subdivision of a post-Cretaceous stratigraphic succession in the Amazonas Basin. The Novo Remanso Formation is subdivided into upper and lower units, and delineated by discontinuous surfaces at its top and bottom. The formation consists primarily of sandstones and minor mudstones and conglomerates, reflecting fluvial channel, point bar and floodplain facies of a fluvial meandering paleosystem. Fairly well-preserved palynoflora was recovered from four palynologically productive samples collected in a local irregular concentration of gray clay deposits, rich in organic material and fossilized wood, at the top of the Novo Remanso Formation upper unit. The palynoflora is dominated by terrestrial spores and pollen grains, and is characterized by abundant angiosperm pollen grains (Tricolpites, Grimsdalea, Perisyncolporites, Tricolporites and Malvacearumpollis). Trilete spores are almost as abundant as the angiosperm pollen, and are represented mainly by the genera Deltoidospora, Verrutriletes, and Hamulatisporis. Gymnosperm pollen is scarce. The presence of the index species Grimsdalea magnaclavata Germeraad et al. (1968) indicates that these deposits belong to the Middle Miocene homonymous palynozone (Lorente, 1986; Hoorn, 1993; Jaramillo et al., 2011). Sedimentological characteristics (poorly sorted, angular to sub-angular, fine to very-coarse quartz sands facies) are typical of the Novo Remanso Formation upper part. These are associated with a paleoflow to the NE-E and SE-E, and with an entirely lowland-derived palinofloristic content with no Andean ferns and gymnosperms representatives. All together, this suggests a cratonic origin for this Middle Miocene fluvial paleosystem, which was probably born in the Purus Arch eastern flank and areas surrounding the crystalline. The palynological analysis results presented herein are the first direct and unequivocal evidence of the occurrence of Middle Miocene deposits in the central part of the Amazonas Basin. They also provide new perspectives for intra- and interbasin correlations, as well as paleogeographic and paleoenvironmental interpretations for the later deposition stages in the northern Brazilian sedimentary basins. [Copyright &y& Elsevier]

Abstract: The Dom João Stage comprises an interval with variable thickness between 100 and 1200 m, composed of fluvial, eolian and lacustrine deposits of Late Jurassic age, based mainly on the lacustrine ostracod fauna (although the top deposits may extend into the Early Cretaceous). These deposits comprise the so-called Afro-Brazilian Depression, initially characterized as containing the Brotas Group of the Recôncavo Basin (which includes the Aliança and the Sergi Formations) and subsequently extended into the Tucano, Jatobá, Camamu, Almada, Sergipe, Alagoas and Araripe Basins in northeastern Brazil, encompassing the study area of this paper. The large occurrence area of the Dom João Stage gives rise to discussions about the depositional connectivity between the basins, and the real extension of sedimentation. In the first studies of this stratigraphic interval, the Dom João Stage was strictly associated with the rift phase, as an initial stage (decades of 1960–70), but subsequent analyses considered the Dom João as an intracratonic basin or pre-rift phase – without any relation to the active mechanics of a tectonic syn-rift phase (decades of 1980–2000). The present work developed an evolutionary stratigraphic and tectonic model, based on the characterization of depositional sequences, internal flooding surfaces, depositional systems arrangement and paleoflow directions. Several outcrops on the onshore basins were used to build composite sections of each basin, comprising facies, architectural elements, depositional systems, stratigraphic and lithostratigraphic frameworks, and paleocurrents. In addition to that, over a hundred onshore and offshore exploration wells were used (only 21 of which are showed) to map the depositional sequences and generate correlation sections. These show the characteristics and relations of the Dom João Stage in each studied basin, and they were also extended to the Gabon Basin. The results indicate that there were two main phases during the Dom João Stage, in which distinctive sedimentary environments were developed, reflecting depositional system arrangements, paleoflow directions were diverse, and continuous or compartmented basins were developed. [Copyright &y& Elsevier]

We delineate an approximately 240-km-long, north-trending Au-Pd-Pt belt in Minas Gerais, Brazil, which hosts hydrothermal Pd-Pt-bearing gold mineralization in its southern part (Quadrilatero Ferrifero and Itabira district) and alluvial Pd-Pt-Au mineralization in its northern part (southern Serra do Espinhaco). The hydro-thermal Pd-Pt-bearing gold mineralization, locally known as jacutinga, occurs as late-orogenic quartz-hematite-(talc-kaolinite) veins, which truncate the Brasiliano regional tectonic foliation of the itabiritic host rocks of the Paleoproterozoic Itabira Iron Formation. The alluvial Pd-Pt-Au mineralization occurs as botryoidal Pd-Pt nuggets and delicate palladiferous gold aggregates in clastic and organic-rich valley infill on quartzite and hematitic rocks of the Paleo- to Mesoproterozoic Espinhago Supergroup. The Au-Pd-Pt belt follows the regional trend of major thrust faults related to the -0.6 Ga Brasiliano orogeny, and the hydrothermal jacutinga mineralization could be regarded as an oxidized variant of the orogenic gold deposit spectrum. Secondary botryoidal and arborescent Pt-Pd aggegates and primary (detrital) Au-Pd grains are peculiar to the alluvial pla-tiniferous deposits of the northern part of the belt in the Serra do Espinhago. We suggest that their source was jacutinga-style vein mineralization, as deduced from abundant detrital hematite and rutile, and the discovery of detrital hongshiite, a Pt-Cu alloy that forms bonanza pockets within jacutinga at Itabira. Reconnaissance laser ablation-inductively coupled plasma-mass spectrometry analyses for trace metals in the botryoidal Pt-Pd grains show that they have elevated Tl and Se contents of 0.9 to 354 and 54 to 2,700 ppm, respectively. These elements correlate positively, with a Tl/Se ratio of about 0.08, a value that contrasts with Tl/Se >1 for hongshiite from the hydrothermal jacutinga system at Itabira. The low and roughly constant Tl/Se ratios of the alluvial samples are close to the average value of 0.12 for fluvial waters. We suggest that the botryoidal Pt-Pd aggregates grew in situ by electrochemical metal accretion from dilute solutions carrying Pt and Pd from the dissolution of detrital Pt-Pd minerals from jacutinga. The connection between jacutinga and platiniferous alluvia indicates that there is a prospective trend of about 240 km for Pd-Pt-bearing gold mineralization reaching from Ouro Preto to Diamantina. The very high oxidation state required for efficient low-temperature aqueous mobilization of Pt, Pd, and Au was apparently controlled by the quartzitic and hematitic rocks in the Serra do Espinhaco, but not in the southern belt where greenstone rocks buffered fluids to moderate pH and lower oxidation states. [ABSTRACT FROM AUTHOR]

Abstract: Most existing models for the evolution of rift basins predict the development of deep-water depositional systems during the stage of greatest tectonic subsidence, when accommodation generation potentially outpaces sedimentation. Despite this, some rift basins do not present deep-water systems, instead being dominated by subaerial deposits. This paper focuses on one of these particular rift basins, the Cambrian Guaritas Rift, Southern Brazil, characterized by more than 1500 m of alluvial and aeolian strata deposited in a 50-km-wide basin. The deposits of the Guaritas Rift can be ascribed to four depositional systems: basin–border alluvial fans, bed-load-dominated ephemeral rivers, mixed-load ephemeral rivers and aeolian dune fields. These four systems are in part coeval and in part succeed each other, forming three stages of basin evolution: (i) Rift Initiation to Early Rift Climax stage, (ii) Mid to Late Rift Climax stage, and (iii) Early Post-Rift stage. The first stage comprises most of the Guaritas Group and is characterized by homogeneous bed-load-dominated river deposits, which do not clearly record the evolution of subsidence rates. The onset of sedimentation of finer-grained deposits occurred as a consequence of a reactivation event that changed the outline of the basin and the distribution of the nearby highlands. This strongly suggests that the capture of the main river system to another depression decreased the sediment supply to the basin. The study of the Guaritas Rift indicates that rift basins in which the sediment supply exceeds the accommodation generation occur as a consequence of moderate subsidence combined with the capture of a major river system to the basin during the initial stages of basin evolution. In these basins, changes in the average discharge of the river system or tectonic modification of the drainage network may be the major control on the stratigraphic architecture. [Copyright &y& Elsevier]

The Itiquira River, Mato Grosso state (western Brazil), hosts several diamond placer deposits, mined intermittently over the last century. It runs over volcanic and sedimentary rocks of the Paraná Basin until it discharges in the northern Pantanal Basin. The bedrocks were deposited in marine, continental desertic, alluvial deltaic, and fluvial environments. The meanders of the Itiquira River are controlled by NE-SW, ENE-WSW, NNW-SSE, N–S, and NW-SE fractures and normal faults, developed in response to the evolution of the Paraná Basin and by neotectonics, linked with the development of the Pantanal Basin since the Paleogene. The Itiquira River middle valley, in which the diamondiferous placers are found, is controlled by NE-SW structures inherited from the Neoproterozoic Transbrasiliano Lineament. The landscape comprises dissected plateaus and structure-controlled valleys formed by Cretaceous, Paleogene, and Neogene planation processes. The diamonds occur in the muddy-sandy matrix of the current stream bed and older terraces gravels. In the Itiquira River, the diamond deposits are related to the following traps: point bars, cut-and-fill channels, pockets, and potholes. Sapphire, garnet (including kimberlitic), ilmenite, zircon, rutile, gold, and iron oxides are documented as heavy minerals in the gravels. Detrital zircon dating of grains extracted from the Itiquira River diamond deposits resulted in the ages of 2057, 1184, 873, 645–508, 307–207, and 144-142 Ma. The potential zircon sources are the Goiás Magmatic Arc granitoids, Paraguay Belt metavolcanics and granites, and Serra Geral Formation volcanics. The ages between 307 and 207 Ma are likely to be from an unknown (possibly kimberlitic) source. The Itiquira River tectonic, geomorphological, and sedimentological evolutions suggest potential sources for the diamond placers and paleoplacers. • In Itiquira, the only known diamond deposits are alluvial placers and paleoplacers. • The alluvia are controlled mainly by NE-SW structures, inherited from the basement. • Different traps concentrate the diamonds in the Itiquira River. • Detrital U–Pb zircon ages indicate possible Paleo to Mesozoic sources. • Perspectives for mineral exploration are presented for this area and similar regions. [ABSTRACT FROM AUTHOR]

Floodplains are areas of unconfined and episodic water flow extensively affected by the first appearance and subsequent evolution of land plants. In this respect, the scarcity of documented examples of pre-Silurian floodplain deposits contrasts with the growing interest in the variability of fluvial channel deposits of the same age. The Cambrian Varzinha Formation (Guaritas Group), of Southern Brazil records coeval floodplain and channel belt deposits, that formed before the first appearance of rooted plants. The deposits are interpreted as forming on an alluvial plain, fed by a braided channel system, bordered by broad areas of sand deposition. These formed as levees with a higher width to thickness ratio than in modern settings. A particular feature of these levee deposits are Froude Transcritical and Supercritical Structures, formed during bank-full flow over bars in the fluvial channel belt, and in regions of local high slope in the floodplain, related to flow from alluvial ridges across levees. Channel belts did not have strong avulsion rates, due to aggradational infilling of the floodbasin aided by transport of sand to the floodbasin through ribbon channels and the wide levee system. Fine grained floodbasin deposits were preserved in the distal reaches of the alluvial plain, with evidence of palaeoweathering, suggesting a well drained floodplain. This record of a coarse grained floodplain in a pre-vegetation setting brings new insight into the identification of floodplain environments in the Precambrian and Early Palaeozoic, and is in agreement with the recent recognition of a greater variety of alluvial deposits prior to the evolution of vascular plants. • Braided channel system bordered by broad sandy levees and coarse grained floodplain. • Froude Transcritical and Supercritical Structures both in channels and the floodplain. • Aggradational infilling with limited channel belt avulsion in prevegetation setting. • Efficient sand dispersal to the floodbasin through ribbon channels and wide levees. [ABSTRACT FROM AUTHOR]

Kimberlite and lamproite pipes are the only economically significant source rocks forming primary diamond deposits. Brazil, the world's seventh largest diamond producer, has all of its production from alluvial deposits. The quest for a primary deposit has continued over several decades with very few positive results. To that end, airborne magnetic data from the Serra da Canastra diamondiferous province was used to identify kimberlite signatures. Serra da Canastra is located the central portion of the Brazilian province in a low-magnetic-latitude region. The main tectonic feature of the area is northwest-southeast major crustal fracture zone that extends for more than 3000 km within the territory. The interpretation strategy was based on joint analysis of analytic signal and Euler deconvolution. A selected kimberlite target should typically have a roughly circular analytic signal anomaly coincident with a depth (0-200 m) and structural (N = 2) constrained Euler solution. The proposed approach led to recognition of previously known pipes and generation of new targets. Ground geologic, geophysical, and geochemical follow-up surveys are necessary to test these selected targets. [ABSTRACT FROM AUTHOR]

In the present work, systematic dating by luminescence methods has been done on 50 Quaternary geological samples within the study area of São Paulo State, Brazil. Bleaching experiments showed that residual TL intensity of 375°C peak, of the quartz, was obtained after 10 h of sunlight exposition. Intensities decays of the 325 and 375°C TL peaks can be fitted using second order exponential equation. Paleodose values were evaluated using regeneration methods with multiple aliquots. Samples dated indicate preliminary ages varying from 9 ± 1 to 935 ± 130 ka for colluvio-elluvial deposits, and from 17 ± 2 to 215 ± 30 ka for alluvial deposits of the study area. They cover four peneplained surfaces shaped during the Quaternary: I (1000-400 ka), II (400-120 ka), III (120-10 ka) and IV (10 ka until today), in decreasing order. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the integrated application of petrographic and Sm–Nd isotopic analyses for studying the provenance of the Neoproterozoic Maricá Formation, southern Brazil. This unit encompasses sedimentary rocks of fluvial and marine affiliations. In the lower fluvial succession, sandstones plot in the “craton interior” and “transitional continental” fields of the QFL diagram. Chemical weathering probably caused the decrease of the 147Sm/144Nd ratios to 0.0826 and 0.0960, consequently lowering originally >2.0 Ga T DM ages to 1.76 and 1.81 Ga. 143Nd/144Nd ratios are also low (0.511521 to 0.511633), corresponding to negative ε Nd present-day values (−21.8 and −19.6). In the intermediate marine succession, sandstones plot in the “dissected arc” field, reflecting the input of andesitic clasts. Siltstones and shales reveal low 143Nd/144Nd ratios (0.511429 to 0.511710), ε Nd values of −18.1 and −23.6, and T DM ages of 2.16 and 2.37 Ga. Sandstones of the upper fluvial succession have “dissected arc” and “recycled orogen” provenance. 143Nd/144Nd isotopic ratios are also relatively low, from 0.511487 to 0.511560, corresponding to ε Nd values of −22.4 and −21.0 and T DM of 2.07 Ga. A uniform granite–gneissic basement block of Paleoproterozoic age, with subordinate volcanic rocks, is suggested as the main sediment source of the Maricá Formation. [Copyright &y& Elsevier]

The transport of elements in fluvial waters within the Candiota region was evaluated by determining the elements associated with suspended particulate matter (SPM). To that end, SPM samples were collected at nine different locations five times from December 1999 to October 2000. The particle-induced X-ray emission technique was used to determine elements associated with SPM. Data interpretation was performed using factor analysis. Among the results explained by factor 1, the highest score was found to be due to the effect of local anthropogenic sources (coal mines) during the dry season. On the other hand, factor 2 was substantially heterogeneous, emphasising the sum of all anthropogenic contributions generated at the basin. Flux ratio and enrichment factor were calculated to elucidate the balance between weathering and solute transport. Results showed that Mn, Ni, Fe, Cu and Zn were carried by Candiota Stream particles, indicating that coal mining is presumably responsible for contamination of these elements in SPM. [Copyright &y& Elsevier]

The geochemical distributions of Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were investigated to provide information about the mobility and availability of these elements in polluted sediments from the Baixo Jacuí region, southern Brazil. Sediment samples were collected at eight sites in the Conde stream, near coal mining and waste disposal areas, and in the Jacuí river, downstream from industrial activities. Total extraction results showed higher metals concentration at some sites, when compared to background values, as well as indicated by the calculated enrichment factor and geoaccumulation index. However, the results were insufficient to establish the existence of anthropogenic contribution to the studied area. The contamination was better evaluated by the sequential extraction. The geochemical distribution in the sediments of the Jacuí river revealed the presence of high concentrations of Cr and Cu in the oxidizable fraction, in response to effluent discharge from coal fired power stations and a steel plant. Higher percentages of the available fraction were verified in the Conde stream for the elements Cu, Fe, Ni, Pb, and Zn, indicating the sediment contamination by coal-related activities. [ABSTRACT FROM AUTHOR]

This work presents combined whole-rock element and Sm Nd and Sr isotopes of the Eocene syn -rift I alluvial sediments of the Resende Basin (SE-Brazil), aiming the assessment of sedimentary provenance. Geochemical compositions are used to evaluate the potential effects of hydrodynamic sorting and weathering in the Sm Nd and Sr isotopic compositions. Mudstone, sandstone, and conglomerate samples were collected for analysis. Chemical data indicate that the major element composition of the Resende Basin sediments is compromised by present-day weathering conditions and cannot be used for source areas weathering interpretations. Similar trace and rare earth elements composition in sandstones and mudstones imply poorly mixed sediments and provenance is associated with felsic and intermediated igneous sources with a subordinate mafic component. Mudstones are enriched in elements typically associated with heavy minerals (Ti, Zr, Hf, and Y). Weathering and mineral sorting affect mainly the major and trace element compositions of the Resende Basin sediments, while most of the isotopic composition's variations are due to differences in provenance caused by different source areas and/or degrees of source mix. Based on its conspicuous contrasting isotopic signature, the Cretaceous alkaline igneous source component can be tracked in the Resende Basin sedimentary record. Samples with εNd(t) < −10 have more than 60% of alkaline-derived provenance. The Resende Basin was compartmentalized by at least two depocenters separated by a structural high. The depocenters had very proximal sources but were connected by an axial fluvial system. The structural high acted as a barrier, retaining the sediment supply coming from the Itatiaia alkaline massif. These results are compatible with what is seen in other rift-related sedimentary environments, such as the Rio Grande and the North Sea deposits, where Nd and Sr composition of first-cycle clastic sediments reflect their parental source isotopic signature. [Display omitted] [ABSTRACT FROM AUTHOR]

In the midwestern Minas Gerais, Brazil, kimberlite intrusions, particularly kamafugite and alkaline complexes, occur along the NW-SE-oriented Alto Paranaíba structural high. Diamonds in this region were discovered in the Bagagem River and later in the alluvial deposits of the Santo Antônio do Bonito, Santo Inácio and Douradinho rivers. Diamond-bearing kimberlites observed in the region are the primary sources of diamond deposits, as in the case of the Vargem Bonita diggings-in the upper São Francisco River. However, the primary sources of the alluvial diamonds that occur in the Santo Antônio do Bonito, Santo Inácio, and Douradinho rivers have not been clarified. These diamond populations have characteristics common to all three drainage area, where large stones are frequently recovered. Diamond accumulation in the alluvium is due to the erosion and re-concentration of material from basal conglomerate of the Capacete Formation. There is evidence that the sources that fed the conglomerate are local diamond-bearing kimberlites of approximately 90–120 Ma underlying the Capacete Formation, which in an upper unit of the Mata da Corda Group. Recent fieldwork led to the location of a kimberlite intrusion in the Santo Inácio River Basin, southeast of Coromandel. The intrusion fulfills the requirements constituting a primary source of diamonds in the area. • First time identification of possible primary source of diamonds in alluvial deposits of Southeast Coramandel area, Brazil. • Fieldwork allowed to locate a diamond-bearing kimberlite fullfilling the requirements for primary source characterization. • There is evidence that the sources that fed the conglomerate are local, approximately 120 to 90 Ma old kimberlite intrusion. [ABSTRACT FROM AUTHOR]

This work aimed to investigate the ichnofossiliferous sites in Nioaque and surrounding region, Mato Grosso do Sul state, Brazil, analyzing their paleontological, stratigraphic and paleoenvironmental context, because dinosaur tracks were found in an area previously mapped as Permo–Carboniferous age. Some sedimentary facies previously assigned to the glacial Aquidauana Formation were herein reinterpreted as part of the basal section of the Botucatu Formation (Late Jurassic/Early Cretaceous) and include floodplain and residual channel deposits, possibly representing the lower half of this formation's sequence in the studied area. The ichnofossils that have been found include both isolated tracks of Theropoda and Ornithopoda, a trackway of Eubrontes isp., a vertebrate burrow and invertebrate traces (Palaeophycus) possibly related to the Entradichnus ichnofacies. Sedimentological interpretation suggests the existence of a river system just before the deposition of the typical Botucatu eolian facies in this region. This is the first documented record of fluvial deposits transitionally to the traditional eolian Botucatu Formation. Noteworthy, the dinosaur tracks have played a key role for the interpretation of these rocks as Botucatu Formation and for better understanding the whole system due to the impossible Paleozoic age (dinosaur tracks). • First occurrence of fluvial deposits related to the desertic Botucatu Formation. • Dinosaur tracks, vertebrate burrows and invertebrate ichnofossils were documented. • A significant part of Permian Aquidauana Formation is reinterpreted as Jurassic—Cretaceous Botucatu Formation. • Sedimentological interpretation suggesting a fluvial system at the basal section of the Botucatu Formation. [ABSTRACT FROM AUTHOR]

• The Carajás Basin evolved in a foreland setting in the early Paleoproterozoic. • A robust stratigraphic framework is presented for the first time. • The Azul marine and the Águas Claras fluvial deposits are younger than ca. 2.27 Ga. • The paleoenvironmental changes are directly related to the Columbia configuration. The Carajás Basin, situated in the southeastern Amazonian Craton in northern Brazil, hosts a > 6 km thick pile of volcano-sedimentary rocks deposited from the Neoarchean to the early Paleoproterozoic eras (ca. 2.75–2.06 Ga). It is claimed that this basin started as a rift configuration in which volcanic and banded iron formation strata were deposited during the Neoarchean Era. However, the tectono-sedimentary evolution of this basin through the Paleoproterozoic Era remains unexplored. Based on a sedimentological, stratigraphic, and U–Pb detrital zircon geochronological investigation of a marine to a fluvial succession of this basin, this study suggests that the Carajás Basin evolved in a foreland setting during the early Paleoproterozoic Era. Probably, the Carajás Foreland Basin was sedimented in the underfilled stage (ca. 2.5–2.3 Ga) by deep-marine strata (i.e., glaciogenic submarine fan deposits), likely from the Siderian–Rhyacian Serra Sul Formation. Subsequently, shallow-marine deposits of the Azul Formation were deposited in the filled stage (ca. 2.3–2.1 Ga), followed by deposition of the fluvial to alluvial deposits of the Águas Claras and Gorotire formations during the overfilled stage (ca. 2.1–1.9 Ga). The Azul and Águas Claras formations were supplied mainly by Meso- to Neoarchean source rocks, whereas Paleoproterozoic and Paleoarchean rocks played the role of a subordinate source of sediments. The youngest U–Pb age cluster, at ca. 2.27 Ga, is interpreted as its maximum depositional age. In terms of paleogeography, the occurrence of Rhyacian zircon grains in the Azul Formation deposits suggests, at least partially, a connection between the Carajás Protocontinent with the Bacajá Domain during that period. The integrated data corroborate the hypothesis that the foreland basin was formed in a scenario of collision between the Bacajá Domain and the Carajás Protocontinent during the Transamazonian Cycle. These dramatic upheavals are directly related to the configuration of the Columbia Supercontinent, which initially led to the emergence of the Carajás Foreland Basin, and soon after, the cratonization of proto-Amazonia [ABSTRACT FROM AUTHOR]

High-resolution sequence stratigraphy (HRSS) was applied to Cretaceous fluvial deposits of Açu Formation, the principal oil-bearing unit of the Potiguar Basin, aiming to help reservoir management. Facies associations and stratigraphic surfaces were interpreted from an integrated analysis based on rock cores, ichnological, well logs, and production data. Overbank strata envelop transgressive meandering fluvial deposits and promote vertical fluid-flow barriers between reservoirs, thus characterizing zone boundaries. Zone boundaries consist of high-frequency subaerial unconformities placed at the top of paleosol levels correlated throughout the study area. The correlation allowed identifying nine high-frequency sequences and established the reservoir zonation that replaced the former four lithostratigraphic zones. The chronostratigraphic framework supports a more detailed and predictive 3D numerical geological model that is much more representative of the meandering fluvial system and its heterogeneities. Furthermore, the high-resolution stratigraphic reservoir zonation helped revitalize production by identifying intervals with high water cut, which hinder oil production, and oil-saturated intervals that were never opened to production. This case study demonstrates that the application of HRSS methodology is fundamental to improve oil reserves, production, and the final recovery factor in the Potiguar Basin oil fields and analogous situation worldwide. • High-frequency depositional sequences were interpreted in fluvial reservoirs of Açu Formation, Potiguar Basin. • They represent a reservoir zonation and the identified heterogeneities control the fluid-flow pattern. • The new zonation improved the reservoir characterization and its representation in 3D numerical geological models. • The understanding of fluid-flow pathways reduced uncertainties in reservoir management and increased oil production. • The results are examples for the increasing of reserves and reservoir characterization of mature oil fields worldwide. [ABSTRACT FROM AUTHOR]